Missing matter in the vicinity of the sun

NASA Technical Reports Server (NTRS)

Bahcall, John N.

1986-01-01

The Poisson and Vlasov equations are solved numerically for realistic Galaxy models which include multiple disk components, a Population II spheroid, and an unseen massive halo. The total amount of matter in the vicinity of the sun is determined by comparing the observed distributions of tracer stars, samples of F dwarfs, and K giants with the predictions of the Galaxy models. Results are obtained for a number of different assumed distributions of the unseen disk mass. For all the observed samples, typical models imply that about half of the mass in the solar vicinity must be in the form of unobserved matter. The volume density of unobserved material near the sun is about 0.1 solar mass/cu pc; the corresponding column density is about 30 solar mass/sq pc. This so far unseen material must be in a disk with an exponential scale height of less than 0.7 kpc.

Disk Masses for Embedded Class I Protostars in the Taurus Molecular Cloud

NASA Astrophysics Data System (ADS)

Sheehan, Patrick D.; Eisner, Josh A.

2017-12-01

Class I protostars are thought to represent an early stage in the lifetime of protoplanetary disks, when they are still embedded in their natal envelope. Here we measure the disk masses of 10 Class I protostars in the Taurus Molecular Cloud to constrain the initial mass budget for forming planets in disks. We use radiative transfer modeling to produce synthetic protostar observations and fit the models to a multi-wavelength data set using a Markov Chain Monte Carlo fitting procedure. We fit these models simultaneously to our new Combined Array for Research in Millimeter-wave Astronomy 1.3 mm observations that are sensitive to the wide range of spatial scales that are expected from protostellar disks and envelopes so as to be able to distinguish each component, as well as broadband spectral energy distributions compiled from the literature. We find a median disk mass of 0.018 {M}ȯ on average, more massive than the Taurus Class II disks, which have median disk mass of ∼ 0.0025 {M}ȯ . This decrease in disk mass can be explained if dust grains have grown by a factor of 75 in grain size, indicating that by the Class II stage, at a few Myr, a significant amount of dust grain processing has occurred. However, there is evidence that significant dust processing has occurred even during the Class I stage, so it is likely that the initial mass budget is higher than the value quoted here.

The dark side of NGC 3109

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jobin, M.; Carignan, C.

1990-09-01

Optical and radio observations of the Magellanic-type spiral galaxy NGC 3109 were carried out to obtain data on the kinematics and distribution of H I. I-band photometry, performed in order to determine the distribution of the old stellar disk population, more representative of the true mass distribution of the disk, is compared with the B-band photometry. H I spectral line imaging shows that the total neutral hydrogen content is 4.9 + or - 1.0 x 10 to the 8th solar masses; the systematic velocity is 406 + or - 2 km/s. The contribution from the dark component is found tomore » dominate at nearly all radii, indicating a breakdown of the disk-halo conspiracy towards the low end of the luminosity function. 29 refs.« less

Evidence for Cluster to Cluster Variations in Low-mass Stellar Rotational Evolution

NASA Astrophysics Data System (ADS)

Coker, Carl T.; Pinsonneault, Marc; Terndrup, Donald M.

2016-12-01

The concordance model for angular momentum evolution postulates that star-forming regions and clusters are an evolutionary sequence that can be modeled with assumptions about protostar-disk coupling, angular momentum loss from magnetized winds that saturates in a mass-dependent fashion at high rotation rates, and core-envelope decoupling for solar analogs. We test this approach by combining established data with the large h Per data set from the MONITOR project and new low-mass Pleiades data. We confirm prior results that young low-mass stars can be used to test star-disk coupling and angular momentum loss independent of the treatment of internal angular momentum transport. For slow rotators, we confirm the need for star-disk interactions to evolve the ONC to older systems, using h Per (age 13 Myr) as our natural post-disk case. There is no evidence for extremely long-lived disks as an alternative to core-envelope decoupling. However, our wind models cannot evolve rapid rotators from h Per to older systems consistently, and we find that this result is robust with respect to the choice of angular momentum loss prescription. We outline two possible solutions: either there is cosmic variance in the distribution of stellar rotation rates in different clusters or there are substantially enhanced torques in low-mass rapid rotators. We favor the former explanation and discuss observational tests that could be used to distinguish them. If the distribution of initial conditions depends on environment, models that test parameters by assuming a universal underlying distribution of initial conditions will need to be re-evaluated.

Dust distributions in debris disks: effects of gravity, radiation pressure and collisions

NASA Astrophysics Data System (ADS)

Krivov, A. V.; Löhne, T.; Sremčević, M.

2006-08-01

We model a typical debris disk, treated as an idealized ensemble of dust particles, exposed to stellar gravity and direct radiation pressure and experiencing fragmenting collisions. Applying the kinetic method of statistical physics, written in orbital elements, we calculate size and spatial distibutions expected in a steady-state disk, investigate timescales needed to reach the steady state, and calculate mass loss rates. Particular numerical examples are given for the debris disk around Vega. The disk should comprise a population of larger grains in bound orbits and a population of smaller particles in hyperbolic orbits. The cross section area is dominated by the smallest grains that still can stay in bound orbits, for Vega about 10 {μ m} in radius. The size distribution is wavy, implying secondary peaks in the size distribution at larger sizes. The radial profile of the pole-on surface density or the optical depth in the steady-state disk has a power-law index between about -1 and -2. It cannot be much steeper even if dust production is confined to a narrow planetesimal belt, because collisional grinding produces smaller and smaller grains, and radiation pressure pumps up their orbital eccentricities and spreads them outward, which flattens the radial profile. The timescales to reach a steady state depend on grain sizes and distance from the star. For Vega, they are about 1 Myr for grains up to some hundred {μ m} at 100 AU. The total mass of the Vega disk needed to produce the observed amount of micron and submillimeter-sized dust does not exceed several earth masses for an upper size limit of parent bodies of about 1 km. The collisional depletion of the disk occurs on Gyr timescales.

Gas and Dust Structures of the Protoplanetary Disk around HD 142527

NASA Astrophysics Data System (ADS)

Momose, M.; Muto, T.; Hanawa, T.; Fukagawa, M.; Tsukagoshi, T.; Saigo, K.; Kataoka, A.; Nomura, H.; Takeuchi, T.; Akiyama, E.; Ohashi, N.; Fujiwara, H.; Shibai, H.; Kitamura, Y.; Inutsuka, S.; Kobayashi, H.; Honda, M.; Aso, Y.; Takahashi, S. Z.

2015-12-01

HD142527 is a Herbig Fe star accompanied by a disk with ring-like structure. We derive the distributions of dust and gas separately by model fitting and discuss the spatial variation of gas-to-dust mass ratio in the disk. The radial distribution of dust is well approximated by a Gaussian function, while the gas is roughly followed by a power-law distribution between 110 and 400 AU in radius, which is significantly more extended than dust. G/d may reach the order of unity at the northern peak.

Protoplanetary Disk Properties in the Orion Nebula Cluster: Initial Results from Deep, High-resolution ALMA Observations

NASA Astrophysics Data System (ADS)

Eisner, J. A.; Arce, H. G.; Ballering, N. P.; Bally, J.; Andrews, S. M.; Boyden, R. D.; Di Francesco, J.; Fang, M.; Johnstone, D.; Kim, J. S.; Mann, R. K.; Matthews, B.; Pascucci, I.; Ricci, L.; Sheehan, P. D.; Williams, J. P.

2018-06-01

We present Atacama Large Millimeter Array 850 μm continuum observations of the Orion Nebula Cluster that provide the highest angular resolution (∼0.″1 ≈ 40 au) and deepest sensitivity (∼0.1 mJy) of the region to date. We mosaicked a field containing ∼225 optical or near-IR-identified young stars, ∼60 of which are also optically identified “proplyds.” We detect continuum emission at 850 μm toward ∼80% of the proplyd sample, and ∼50% of the larger sample of previously identified cluster members. Detected objects have fluxes of ∼0.5–80 mJy. We remove submillimeter flux due to free–free emission in some objects, leaving a sample of sources detected in dust emission. Under standard assumptions of isothermal, optically thin disks, submillimeter fluxes correspond to dust masses of ∼0.5–80 Earth masses. We measure the distribution of disk sizes, and find that disks in this region are particularly compact. Such compact disks are likely to be significantly optically thick. The distributions of submillimeter flux and inferred disk size indicate smaller, lower-flux disks than in lower-density star-forming regions of similar age. Measured disk flux is correlated weakly with stellar mass, contrary to studies in other star-forming regions that found steeper correlations. We find a correlation between disk flux and distance from the massive star θ 1 Ori C, suggesting that disk properties in this region are influenced strongly by the rich cluster environment.

Spectral energy distributions of T Tauri stars - Disk flaring and limits on accretion

NASA Technical Reports Server (NTRS)

Kenyon, S. J.; Hartmann, L.

1987-01-01

The Adams et al. (1987) conclusion that much of the IR excess emission in the spectral energy distribution of T Tauri stars arises from reprocessing of stellar radiation by a dusty circumstellar disk is presently supported by analyses conducted in light of various models of these stars' spectra. A low mass reprocessing disk can, however, produce these spectra as well as a massive accretion disk. The detection of possible boundary layer radiation in the optical and near-UV regions poses the strongest limits on accretion rates. Disk accretion in the T Tauri phase does not significantly modify stellar evolution.

Debris disks as signposts of terrestrial planet formation. II. Dependence of exoplanet architectures on giant planet and disk properties

NASA Astrophysics Data System (ADS)

Raymond, S. N.; Armitage, P. J.; Moro-Martín, A.; Booth, M.; Wyatt, M. C.; Armstrong, J. C.; Mandell, A. M.; Selsis, F.; West, A. A.

2012-05-01

We present models for the formation of terrestrial planets, and the collisional evolution of debris disks, in planetary systems that contain multiple marginally unstable gas giants. We previously showed that in such systems, the dynamics of the giant planets introduces a correlation between the presence of terrestrial planets and cold dust, i.e., debris disks, which is particularly pronounced at λ ~ 70 μm. Here we present new simulations that show that this connection is qualitatively robust to a range of parameters: the mass distribution of the giant planets, the width and mass distribution of the outer planetesimal disk, and the presence of gas in the disk when the giant planets become unstable. We discuss how variations in these parameters affect the evolution. We find that systems with equal-mass giant planets undergo the most violent instabilities, and that these destroy both terrestrial planets and the outer planetesimal disks that produce debris disks. In contrast, systems with low-mass giant planets efficiently produce both terrestrial planets and debris disks. A large fraction of systems with low-mass (M ≲ 30 M⊕) outermost giant planets have final planetary separations that, scaled to the planets' masses, are as large or larger than the Saturn-Uranus and Uranus-Neptune separations in the solar system. We find that the gaps between these planets are not only dynamically stable to test particles, but are frequently populated by planetesimals. The possibility of planetesimal belts between outer giant planets should be taken into account when interpreting debris disk SEDs. In addition, the presence of ~ Earth-mass "seeds" in outer planetesimal disks causes the disks to radially spread to colder temperatures, and leads to a slow depletion of the outer planetesimal disk from the inside out. We argue that this may explain the very low frequency of >1 Gyr-old solar-type stars with observed 24 μm excesses. Our simulations do not sample the full range of plausible initial conditions for planetary systems. However, among the configurations explored, the best candidates for hosting terrestrial planets at ~1 AU are stars older than 0.1-1 Gyr with bright debris disks at 70 μm but with no currently-known giant planets. These systems combine evidence for the presence of ample rocky building blocks, with giant planet properties that are least likely to undergo destructive dynamical evolution. Thus, we predict two correlations that should be detected by upcoming surveys: an anti-correlation between debris disks and eccentric giant planets and a positive correlation between debris disks and terrestrial planets. Three movies associated to Figs. 1, 3, and 7 are available in electronic form at http://www.aanda.org

ALMA Survey of Class II Disks in the Young Stellar Cluster IC 348

NASA Astrophysics Data System (ADS)

Ruiz, Dary; Cieza, Lucas; Williams, Jonathan; Andrews, Sean; Principe, David

2018-01-01

We present a 1.3 mm continuum survey of the young (2-3 Myr) stellar cluster IC 348 at a distance of 270 pc, which is dominated by low-mass stars. We observed 146 Class II sources (disks that are optically thick in the infrared) at 0.8 '' (200 au) resolution with a 3σ sensitivity of 0.2 MEarth. We detect 46 of the targets and construct a disk luminosity function. We compare the disk mass distribution in IC 348 to those of younger and older regions, taking into account the dependence on stellar mass. We find a clear evolution in disk masses from 1 to 5-10 Myr. The disk masses in IC 348 are significantly lower than those in Taurus (1-2 Myr) and Lupus (1-3 Myr), similar to those of Chamaleon I, (2-3 Myr) and σ-Ori (3-5 Myr) and significantly higher than in Upper Scorpius (5-10 Myr). About 20 disks in our sample (~5% of the cluster members) have estimated masses (dust + gas) of >1 MJUP. and might be the precursors of giant planets in the cluster. Some of the most massive disks include transition objects with inner opacity holes based on their infrared SEDs. From an stacking analysis of the 90 non-detections, we find that these disks have a typical dust mass of just ≤ 0.1 MEarth, even though the vast majority of their infrared SEDs remain optically thick and show little signs of evolution. Such low-mass disks are likely to be the precursors of the small rocky planets found by Kepler around M-type stars.

VizieR Online Data Catalog: SDSS bulge, disk and total stellar mass estimates (Mendel+, 2014)

NASA Astrophysics Data System (ADS)

Mendel, J. T.; Simard, L.; Palmer, M.; Ellison, S. L.; Patton, D. R.

2014-01-01

We present a catalog of bulge, disk, and total stellar mass estimates for ~660000 galaxies in the Legacy area of the Sloan Digital Sky Survey Data (SDSS) Release 7. These masses are based on a homogeneous catalog of g- and r-band photometry described by Simard et al. (2011, Cat. J/ApJS/196/11), which we extend here with bulge+disk and Sersic profile photometric decompositions in the SDSS u, i, and z bands. We discuss the methodology used to derive stellar masses from these data via fitting to broadband spectral energy distributions (SEDs), and show that the typical statistical uncertainty on total, bulge, and disk stellar mass is ~0.15 dex. Despite relatively small formal uncertainties, we argue that SED modeling assumptions, including the choice of synthesis model, extinction law, initial mass function, and details of stellar evolution likely contribute an additional 60% systematic uncertainty in any mass estimate based on broadband SED fitting. We discuss several approaches for identifying genuine bulge+disk systems based on both their statistical likelihood and an analysis of their one-dimensional surface-brightness profiles, and include these metrics in the catalogs. Estimates of the total, bulge and disk stellar masses for both normal and dust-free models and their uncertainties are made publicly available here. (4 data files).

Stellar models simulating the disk-locking mechanism and the evolutionary history of the Orion Nebula cluster and NGC 2264

NASA Astrophysics Data System (ADS)

Landin, N. R.; Mendes, L. T. S.; Vaz, L. P. R.; Alencar, S. H. P.

2016-02-01

Context. Rotational evolution in young stars is described by pre-main sequence evolutionary tracks including non-gray boundary conditions, rotation, conservation of angular momentum, and simulations of disk-locking. Aims: By assuming that disk-locking is the regulation mechanism for the stellar angular velocity during the early stages of pre-main sequence evolution, we use our rotating models and observational data to constrain disk lifetimes (Tdisk) of a representative sample of low-mass stars in two young clusters, the Orion Nebula cluster (ONC) and NGC 2264, and to better understand their rotational evolution. Methods: The period distributions of the ONC and NGC 2264 are known to be bimodal and to depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated sets of evolutionary tracks from a fully convective configuration with low central temperatures (before D- and Li-burning). We assumed that the evolution of fast rotators can be represented by models considering conservation of angular momentum during all stages and of moderate rotators by models considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars. Results: The resulting mass distribution for the bulk of the cluster population is in the ranges of 0.2-0.4 M⊙ and 0.1-0.6 M⊙ for the ONC and NGC 2264, respectively. For the ONC, we assume that the secondary peak in the period distribution is due to high-mass objects still locked in their disks, with a locking period (Plock) of ~8 days. For NGC 2264 we make two hypotheses: (1) the stars in the secondary peak are still locked with Plock = 5 days, and (2) NGC 2264 is in a later stage in the rotational evolution. Hypothesis 2 implies in a disk-locking scenario with Plock = 8 days, a disk lifetime of 1 Myr and, after that, constant angular momentum evolution. We then simulated the period distribution of NGC 2264 when the mean age of the cluster was 1 Myr. Dichotomy and bimodality appear in the simulated distribution, presenting one peak at 2 days and another one at 5-7 days, indicating that the assumption of Plock = 8 days is plausible. Our hypotheses are compared with observational disk diagnoses available in the literature for the ONC and NGC 2264, such as near-infrared excess, Hα emission, and spectral energy distribution slope in the mid-infrared. Conclusions: Disk-locking models with Plock = 8 days and 0.2 Myr ≤ Tdisk ≤ 3 Myr are consistent with observed periods of moderate rotators of the ONC. For NGC 2264, the more promising explanation for the observed period distribution is an evolution with disk-locking (with Plock near 8 days) during the first 1 Myr, approximately, but after this, the evolution continued with constant angular momentum. Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A96

A hot compact dust disk around a massive young stellar object.

PubMed

Kraus, Stefan; Hofmann, Karl-Heinz; Menten, Karl M; Schertl, Dieter; Weigelt, Gerd; Wyrowski, Friedrich; Meilland, Anthony; Perraut, Karine; Petrov, Romain; Robbe-Dubois, Sylvie; Schilke, Peter; Testi, Leonardo

2010-07-15

Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass ( approximately 20 solar masses) young stellar object. The image shows an elongated structure with a size of approximately 13 x 19 astronomical units, consistent with a disk seen at an inclination angle of approximately 45 degrees . Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system.

Mass storage technology in networks

NASA Astrophysics Data System (ADS)

Ishii, Katsunori; Takeda, Toru; Itao, Kiyoshi; Kaneko, Reizo

1990-08-01

Trends and features of mass storage subsystems in network are surveyed and their key technologies spotlighted. Storage subsystems are becoming increasingly important in new network systems in which communications and data processing are systematically combined. These systems require a new class of high-performance mass-information storage in order to effectively utilize their processing power. The requirements of high transfer rates, high transactional rates and large storage capacities, coupled with high functionality, fault tolerance and flexibility in configuration, are major challenges in storage subsystems. Recent progress in optical disk technology has resulted in improved performance of on-line external memories to optical disk drives, which are competing with mid-range magnetic disks. Optical disks are more effective than magnetic disks in using low-traffic random-access file storing multimedia data that requires large capacity, such as in archive use and in information distribution use by ROM disks. Finally, it demonstrates image coded document file servers for local area network use that employ 130mm rewritable magneto-optical disk subsystems.

Planetesimal-driven planet migration in the presence of a gas disk

NASA Astrophysics Data System (ADS)

Capobianco, Christopher C.; Duncan, Martin; Levison, Harold F.

2011-01-01

We report here on an extension of a previous study by Kirsh et al. (Kirsh, D.R., Duncan, M., Brasser, R., Levison, H.F. [2009]. Icarus 199, 197-209) of planetesimal-driven migration using our N-body code SyMBA (Duncan, M.J., Levison, H.F., Lee, M.H. [1998]. Astron. J. 116, 2067-2077). The previous work focused on the case of a single planet of mass Mem, immersed in a planetesimal disk with a power-law surface density distribution and Rayleigh distributed eccentricities and inclinations. Typically 10 4-10 5 equal-mass planetesimals were used, where the gravitational force (and the back-reaction) on each planetesimal by the Sun and planet were included, while planetesimal-planetesimal interactions were neglected. The runs reported on here incorporate the dynamical effects of a gas disk, where the Adachi et al. (Adachi, I., Hayashi, C., Nakazawa, K. [1976]. Prog. Theor. Phys. 56, 1756-1771) prescription of aerodynamic gas drag is implemented for all bodies. In some cases the Papaloizou and Larwood (Papaloizou, J.C.B., Larwood, J.D. [2000]. Mon. Not. R. Astron. Soc. 315, 823-833) prescription of Type-I migration for the planet are implemented, as well as a mass distribution. In the gas-free cases, rapid planet migration was observed - at a rate independent of the planet's mass - provided the planet's mass was not large compared to the mass in planetesimals capable of entering its Hill sphere. In such cases, both inward and outward migrations can be self-sustaining, but there is a strong propensity for inward migration. When a gas disk is present, aerodynamic drag can substantially modify the dynamics of scattered planetesimals. For sufficiently large or small mono-dispersed planetesimals, the planet typically migrates inward. However, for a range of plausible planetesimal sizes (i.e. 0.5-5.0 km at 5.0 AU in a minimum mass Hayashi disk) outward migration is usually triggered, often accompanied by substantial planetary mass accretion. The origins of this behaviour are explained in terms of a toy model. The effects of including a size distribution and torques associated with Type-I migration are also discussed.

The Radial Distribution of Mono-metallicity Populations in the Galactic Disk as Evidence for Two-phase Disk Formation

NASA Astrophysics Data System (ADS)

Domínguez-Tenreiro, R.; Obreja, A.; Brook, C. B.; Martínez-Serrano, F. J.; Serna, A.

2017-09-01

Recent determinations of the radial distributions of mono-metallicity populations (MMPs, I.e., stars in narrow bins in [Fe/H] within wider [α/Fe] ranges) by the SDSS-III/APOGEE DR12 survey cast doubts on the classical thin- and thick-disk dichotomy. The analysis of these observations led to the non-[α /Fe] enhanced populations splitting into MMPs with different surface densities according to their [Fe/H]. By contrast, [α /Fe] enhanced (I.e., old) populations show a homogeneous behavior. We analyze these results in the wider context of disk formation within non-isolated halos embedded in the Cosmic Web, resulting in a two-phase mass assembly. By performing hydrodynamical simulations in the context of the ΛCDM model, we have found that the two phases of halo mass assembly (an early fast phase, followed by a slow phase with low mass-assembly rates) are very relevant to determine the radial structure of MMP distributions, while radial mixing only plays a secondary role, depending on the coeval dynamical and/or destabilizing events. Indeed, while the frequent dynamical violent events occuring at high redshift remove metallicity gradients and imply efficient stellar mixing, the relatively quiescent dynamics after the transition keeps [Fe/H] gaseous gradients and prevents newly formed stars from suffering strong radial mixing. By linking the two-component disk concept with the two-phase halo mass-assembly scenario, our results set halo virialization (the event marking the transition from the fast to the slow phases) as the separating event that marks periods that are characterized by different physical conditions under which thick- and thin-disk stars were born.

Young stars in ɛ Chamaleontis and their disks: disk evolution in sparse associations

NASA Astrophysics Data System (ADS)

Fang, M.; van Boekel, R.; Bouwman, J.; Henning, Th.; Lawson, W. A.; Sicilia-Aguilar, A.

2013-01-01

Context. The nearby young stellar association ɛ Cha has an estimated age of 3-5 Myr, making it an ideal laboratory to study the disk dissipation process and provide empirical constraints on the timescale of planet formation. Aims: We wish to complement existing optical and near-infrared data of the ɛ Cha association, which provide the stellar properties of its members, with mid-infrared data that probe the presence, geometry, and mineralogical composition of protoplanetary disks around individual stars. Methods: We combine the available literature data with our Spitzer/IRS spectroscopy and VLT/VISIR imaging data. We use proper motions to refine the membership of ɛ Cha. Masses and ages of individual stars are estimated by fitting model atmospheres to the optical and near-infrared photometry, followed by placement in the Hertzsprung-Russell diagram. The Spitzer/IRS spectra are analyzed using the two-layer temperature distribution spectral decomposition method. Results: Two stars previously identified as members, CXOU J120152.8 and 2MASS J12074597, have proper motions that are very different from those of the other stars. But other observations suggest that the two stars are still young and thus might still be related to ɛ Cha. HD 104237C is the lowest mass member of ɛ Cha with an estimated mass of ~13-15 Jupiter masses. The very low mass stars USNO-B120144.7 and 2MASS J12005517 show globally depleted spectral energy distributions, pointing at strong dust settling. 2MASS J12014343 may have a disk with a very specific inclination, where the central star is effectively screened by the cold outer parts of a flared disk, but the 10 μm radiation of the warm inner disk can still reach us. We find that the disks in sparse stellar associations are dissipated more slowly than those in denser (cluster) environments. We detect C2H2 rovibrational band around 13.7 μm on the IRS spectrum of USNO-B120144.7. We find strong signatures of grain growth and crystallization in all ɛ Cha members with 10 μm features detected in their IRS spectra. We combine the dust properties derived in the ɛ Cha sample with those found using identical or similar methods in the MBM 12, Coronet, η Cha associations, and in the cores-to-disks legacy program. We find that disks around low-mass young stars show a negative radial gradient in the mass-averaged grain size and mass fraction of crystalline silicates. A positive correlation exists between the mass-averaged grain sizes of amorphous silicates and the accretion rates if the latter is above ~10-9 M⊙ yr-1, possibly indicating that those disks are sufficiently turbulent to prevent grains of several microns in size to sink into the disk interior. Based on observations performed at ESO's La Silla-Paranal observatory under programme 076.C-0470.

The Mass Distribution in Disk Galaxies

NASA Astrophysics Data System (ADS)

Courteau, Stéphane; Dutton, Aaron A.

We present the relative fraction of baryons and dark matter at various radii in galaxies. For spiral galaxies, this fraction measured in a galaxy's inner parts is typically baryon-dominated (maximal) and dark-matter dominated (sub-maximal) in the outskirts. The transition from maximal to sub-maximal baryons occurs within the inner parts of low-mass disk galaxies (with V tot <= 200 km s-1) and in the outer disk for more massive systems. The mean mass fractions for late- and early-type galaxies vary significantly at the same fiducial radius and circular velocity, suggesting a range of galaxy formation mechanisms. A more detailed discussion, and resolution of the so-called ``maximal disk problem'', is presented in Courteau & Dutton, ApJL, 801, 20.

The great dichotomy of the Solar System: Small terrestrial embryos and massive giant planet cores

NASA Astrophysics Data System (ADS)

Morbidelli, A.; Lambrechts, M.; Jacobson, S.; Bitsch, B.

2015-09-01

The basic structure of the Solar System is set by the presence of low-mass terrestrial planets in its inner part and giant planets in its outer part. This is the result of the formation of a system of multiple embryos with approximately the mass of Mars in the inner disk and of a few multi-Earth-mass cores in the outer disk, within the lifetime of the gaseous component of the protoplanetary disk. What was the origin of this dichotomy in the mass distribution of embryos/cores? We show in this paper that the classic processes of runaway and oligarchic growth from a disk of planetesimals cannot explain this dichotomy, even if the original surface density of solids increased at the snowline. Instead, the accretion of drifting pebbles by embryos and cores can explain the dichotomy, provided that some assumptions hold true. We propose that the mass-flow of pebbles is two-times lower and the characteristic size of the pebbles is approximately ten times smaller within the snowline than beyond the snowline (respectively at heliocentric distance r rice , where rice is the snowline heliocentric distance), due to ice sublimation and the splitting of icy pebbles into a collection of chondrule-size silicate grains. In this case, objects of original sub-lunar mass would grow at drastically different rates in the two regions of the disk. Within the snowline these bodies would reach approximately the mass of Mars while beyond the snowline they would grow to ∼ 20 Earth masses. The results may change quantitatively with changes to the assumed parameters, but the establishment of a clear dichotomy in the mass distribution of protoplanets appears robust provided that there is enough turbulence in the disk to prevent the sedimentation of the silicate grains into a very thin layer.

THE STRUCTURE AND STELLAR CONTENT OF THE OUTER DISKS OF GALAXIES: A NEW VIEW FROM THE Pan-STARRS1 MEDIUM DEEP SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Zheng; Thilker, David A.; Heckman, Timothy M.

2015-02-20

We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r {sub 90}, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples ofmore » galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r {sub 90}. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic 'U' shape. There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk.« less

Alma Survey of Circumstellar Disks in the Young Stellar Cluster IC 348

NASA Astrophysics Data System (ADS)

Ruíz-Rodríguez, D.; Cieza, L. A.; Williams, J. P.; Andrews, S. M.; Principe, D. A.; Caceres, C.; Canovas, H.; Casassus, S.; Schreiber, M. R.; Kastner, J. H.

2018-05-01

We present a 1.3 mm continuum survey of the young (2-3 Myr) stellar cluster IC 348, which lies at a distance of 310 pc, and is dominated by low-mass stars (M⋆ ˜ 0.1-0.6 M⊙). We observed 136 Class II sources (disks that are optically thick in the infrared) at 0.8″ (200 au) resolution with a 3σ sensitivity of ˜ 0.45 mJy (Mdust ˜ 1.3 M⊕). We detect 40 of the targets and construct a mm-continuum luminosity function. We compare the disk mass distribution in IC 348 to those of younger and older regions, taking into account the dependence on stellar mass. We find a clear evolution in disk masses from 1 to 5-10 Myr. The disk masses in IC 348 are significantly lower than those in Taurus (1-3 Myr) and Lupus (1-3 Myr), similar to those of Chamaleon I, (2-3 Myr) and σ Ori (3-5 Myr) and significantly higher than in Upper Scorpius (5-10 Myr). About 20 disks in our sample (˜5% of the cluster members) have estimated masses (dust + gas) >1 MJup and hence might be the precursors of giant planets in the cluster. Some of the most massive disks include transition objects with inner opacity holes based on their infrared SEDs. From a stacking analysis of the 96 non-detections, we find that these disks have a typical dust mass of just ≲ 0.4 M⊕, even though the vast majority of their infrared SEDs remain optically thick and show little signs of evolution. Such low-mass disks may be the precursors of the small rocky planets found by Kepler around M-type stars.

EVIDENCE FOR CLUSTER TO CLUSTER VARIATIONS IN LOW-MASS STELLAR ROTATIONAL EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coker, Carl T.; Pinsonneault, Marc; Terndrup, Donald M., E-mail: coker@astronomy.ohio-state.edu, E-mail: pinsono@astronomy.ohio-state.edu, E-mail: terndrup@astronomy.ohio-state.edu

2016-12-10

The concordance model for angular momentum evolution postulates that star-forming regions and clusters are an evolutionary sequence that can be modeled with assumptions about protostar–disk coupling, angular momentum loss from magnetized winds that saturates in a mass-dependent fashion at high rotation rates, and core-envelope decoupling for solar analogs. We test this approach by combining established data with the large h Per data set from the MONITOR project and new low-mass Pleiades data. We confirm prior results that young low-mass stars can be used to test star–disk coupling and angular momentum loss independent of the treatment of internal angular momentum transport.more » For slow rotators, we confirm the need for star–disk interactions to evolve the ONC to older systems, using h Per (age 13 Myr) as our natural post-disk case. There is no evidence for extremely long-lived disks as an alternative to core-envelope decoupling. However, our wind models cannot evolve rapid rotators from h Per to older systems consistently, and we find that this result is robust with respect to the choice of angular momentum loss prescription. We outline two possible solutions: either there is cosmic variance in the distribution of stellar rotation rates in different clusters or there are substantially enhanced torques in low-mass rapid rotators. We favor the former explanation and discuss observational tests that could be used to distinguish them. If the distribution of initial conditions depends on environment, models that test parameters by assuming a universal underlying distribution of initial conditions will need to be re-evaluated.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lieman-Sifry, Jesse; Hughes, A. Meredith; Flaherty, Kevin M.

We present a CO(2-1) and 1240 μ m continuum survey of 23 debris disks with spectral types B9-G1, observed at an angular resolution of 0.″5–1″ with the Atacama Large Millimeter/Submillimeter Array (ALMA). The sample was selected for large infrared excess and age ∼10 Myr, to characterize the prevalence of molecular gas emission in young debris disks. We identify three CO-rich debris disks, plus two additional tentative (3 σ) CO detections. Twenty disks were detected in the continuum at the >3 σ level. For the 12 disks in the sample that are spatially resolved by our observations, we perform an independentmore » analysis of the interferometric continuum visibilities to constrain the basic dust disk geometry, as well as a simultaneous analysis of the visibilities and broadband spectral energy distribution to constrain the characteristic grain size and disk mass. The gas-rich debris disks exhibit preferentially larger outer radii in their dust disks, and a higher prevalence of characteristic grain sizes smaller than the blowout size. The gas-rich disks do not exhibit preferentially larger dust masses, contrary to expectations for a scenario in which a higher cometary destruction rate would be expected to result in a larger mass of both CO and dust. The three debris disks in our sample with strong CO detections are all around A stars: the conditions in disks around intermediate-mass stars appear to be the most conducive to the survival or formation of CO.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Mo; Evans II, Neal J.; Dodson-Robinson, Sarah E.

Gas in protostellar disks provides the raw material for giant planet formation and controls the dynamics of the planetesimal-building dust grains. Accurate gas mass measurements help map the observed properties of planet-forming disks onto the formation environments of known exoplanets. Rare isotopologues of carbon monoxide (CO) have been used as gas mass tracers for disks in the Lupus star-forming region, with an assumed interstellar CO/H{sub 2} abundance ratio. Unfortunately, observations of T-Tauri disks show that CO abundance is not interstellar, a finding reproduced by models that show CO abundance decreasing both with distance from the star and as a functionmore » of time. Here, we present radiative transfer simulations that assess the accuracy of CO-based disk mass measurements. We find that the combination of CO chemical depletion in the outer disk and optically thick emission from the inner disk leads observers to underestimate gas mass by more than an order of magnitude if they use the standard assumptions of interstellar CO/H{sub 2} ratio and optically thin emission. Furthermore, CO abundance changes on million-year timescales, introducing an age/mass degeneracy into observations. To reach a factor of a few accuracy for CO-based disk mass measurements, we suggest that observers and modelers adopt the following strategies: (1) select low- J transitions; (2) observe multiple CO isotopologues and use either intensity ratios or normalized line profiles to diagnose CO chemical depletion; and (3) use spatially resolved observations to measure the CO-abundance distribution.« less

Does the Presence of Planets Affect the Frequency and Properties of Extrasolar Kuiper Belts? Results from the Herschel Debris and Dunes Surveys

NASA Astrophysics Data System (ADS)

Moro-Martín, A.; Marshall, J. P.; Kennedy, G.; Sibthorpe, B.; Matthews, B. C.; Eiroa, C.; Wyatt, M. C.; Lestrade, J.-F.; Maldonado, J.; Rodriguez, D.; Greaves, J. S.; Montesinos, B.; Mora, A.; Booth, M.; Duchêne, G.; Wilner, D.; Horner, J.

2015-03-01

The study of the planet-debris disk connection can shed light on the formation and evolution of planetary systems and may help “predict” the presence of planets around stars with certain disk characteristics. In preliminary analyses of subsamples of the Herschel DEBRIS and DUNES surveys, Wyatt et al. and Marshall et al. identified a tentative correlation between debris and the presence of low-mass planets. Here we use the cleanest possible sample out of these Herschel surveys to assess the presence of such a correlation, discarding stars without known ages, with ages \\lt 1 Gyr, and with binary companions \\lt 100 AU to rule out possible correlations due to effects other than planet presence. In our resulting subsample of 204 FGK stars, we do not find evidence that debris disks are more common or more dusty around stars harboring high-mass or low-mass planets compared to a control sample without identified planets. There is no evidence either that the characteristic dust temperature of the debris disks around planet-bearing stars is any different from that in debris disks without identified planets, nor that debris disks are more or less common (or more or less dusty) around stars harboring multiple planets compared to single-planet systems. Diverse dynamical histories may account for the lack of correlations. The data show a correlation between the presence of high-mass planets and stellar metallicity, but no correlation between the presence of low-mass planets or debris and stellar metallicity. Comparing the observed cumulative distribution of fractional luminosity to those expected from a Gaussian distribution in logarithmic scale, we find that a distribution centered on the solar system’s value fits the data well, while one centered at 10 times this value can be rejected. This is of interest in the context of future terrestrial planet detection and characterization because it indicates that there are good prospects for finding a large number of debris disk systems (i.e., with evidence of harboring planetesimals, the building blocks of planets) with exozodiacal emission low enough to be appropriate targets for an ATLAST-type mission to search for biosignatures.

Torques Induced by Scattered Pebble-flow in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Benítez-Llambay, Pablo; Pessah, Martin E.

2018-03-01

Fast inward migration of planetary cores is a common problem in the current planet formation paradigm. Even though dust is ubiquitous in protoplanetary disks, its dynamical role in the migration history of planetary embryos has not been assessed. In this Letter, we show that the scattered pebble-flow induced by a low-mass planetary embryo leads to an asymmetric dust-density distribution that is able to exert a net torque. By analyzing a large suite of multifluid hydrodynamical simulations addressing the interaction between the disk and a low-mass planet on a fixed circular orbit, and neglecting dust feedback onto the gas, we identify two different regimes, gas- and gravity-dominated, where the scattered pebble-flow results in almost all cases in positive torques. We collect our measurements in a first torque map for dusty disks, which will enable the incorporation of the effect of dust dynamics on migration into population synthesis models. Depending on the dust drift speed, the dust-to-gas mass ratio/distribution, and the embryo mass, the dust-induced torque has the potential to halt inward migration or even induce fast outward migration of planetary cores. We thus anticipate that dust-driven migration could play a dominant role during the formation history of planets. Because dust torques scale with disk metallicity, we propose that dust-driven outward migration may enhance the occurrence of distant giant planets in higher-metallicity systems.

Constraints on the spin evolution of young planetary-mass companions

NASA Astrophysics Data System (ADS)

Bryan, Marta L.; Benneke, Björn; Knutson, Heather A.; Batygin, Konstantin; Bowler, Brendan P.

2018-02-01

Surveys of young star-forming regions have discovered a growing population of planetary-mass (<13 MJup) companions around young stars1. There is an ongoing debate as to whether these companions formed like planets (that is, from the circumstellar disk)2, or if they represent the low-mass tail of the star-formation process3. In this study, we utilize high-resolution spectroscopy to measure rotation rates of three young (2-300 Myr) planetary-mass companions and combine these measurements with published rotation rates for two additional companions4,5 to provide a picture of the spin distribution of these objects. We compare this distribution to complementary rotation-rate measurements for six brown dwarfs with masses <20 MJup, and show that these distributions are indistinguishable. This suggests that either these two populations formed via the same mechanism, or that processes regulating rotation rates are independent of formation mechanism. We find that rotation rates for both populations are well below their break-up velocities and do not evolve significantly during the first few hundred million years after the end of accretion. This suggests that rotation rates are set during the late stages of accretion, possibly by interactions with a circumplanetary disk. This result has important implications for our understanding of the processes regulating the angular momentum evolution of young planetary-mass objects, and of the physics of gas accretion and disk coupling in the planetary-mass regime.

Observability of characteristic binary-induced structures in circumbinary disks

NASA Astrophysics Data System (ADS)

Avramenko, R.; Wolf, S.; Illenseer, T. F.

2017-07-01

Context. A substantial fraction of protoplanetary disks form around stellar binaries. The binary system generates a time-dependent non-axisymmetric gravitational potential, inducing strong tidal forces on the circumbinary disk. This leads to a change in basic physical properties of the circumbinary disk, which should in turn result in unique structures that are potentially observable with the current generation of instruments. Aims: The goal of this study is to identify these characteristic structures, constrain the physical conditions that cause them, and evaluate the feasibility of observing them in circumbinary disks. Methods: To achieve this, first we perform 2D hydrodynamic simulations. The resulting density distributions are post-processed with a 3D radiative transfer code to generate re-emission and scattered light maps. Based on these distributions, we study the influence of various parameters, such as the mass of the stellar components, mass of the disk, and binary separation on observable features in circumbinary disks. Results: We find that the Atacama Large (sub-)Millimetre Array (ALMA) as well as the European Extremely Large Telescope (E-ELT) are capable of tracing asymmetries in the inner region of circumbinary disks, which are affected most by the binary-disk interaction. Observations at submillimetre/millimetre wavelengths allow the detection of the density waves at the inner rim of the disk and inner cavity. With the E-ELT one can partially resolve the innermost parts of the disk in the infrared wavelength range, including the disk's rim, accretion arms, and potentially the expected circumstellar disks around each of the binary components.

Transitional Disks Associated with Intermediate-Mass Stars: Results of the SEEDS YSO Survey

NASA Technical Reports Server (NTRS)

Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; McElwain, M.;

Non-LTE effects on the strength of the Lyman edge in quasar accretion disks

NASA Technical Reports Server (NTRS)

Stoerzer, H.; Hauschildt, P. H.; Allard, F.

1994-01-01

We have calculated UV/EUV (300 A which is less than or equal to lambda which is less than or equal to 1500 A) continuous energy distributions of accretion disks in the centers of active galactic nuclei (AGNs) for disk luminosities in the range 0.1 L(sub Edd) less than or equal to L(sub acc) less than 1.0 L(sub Edd) and central masses ranging from 10(exp 8) solar mass to 10(exp 9) solar mass. The vertical gas pressure structure of the disk and the disk height are obtained analytically; the temperature stratification and the resulting continuum radiation fields are calculated numerically. We have included non-Local Thermodynamic Equilibrium (LTE) effects of both the ionization equilibrium and the level populations of hydrogen and helium. We show that these non-LTE effects reduce the strength of the Lyman edge when comapred to the LTE case. In non-LTE we find that the edge can be weakly in emission or absorption for disks seen face-on, depending on the disk parameters.

Recent Observational Progress on Accretion Disks Around Compact Objects

NASA Astrophysics Data System (ADS)

Miller, Jon M.

2016-04-01

Studies of accretion disks around black holes and neutron stars over the last ten years have made remarkable progress. Our understanding of disk evolution as a function of mass accretion rate is pushing toward a consensus on thin/thick disk transitions; an apparent switching between disk-driven outflow modes has emerged; and monitoring observations have revealed complex spectral energy distributions wherein disk reprocessing must be important. Detailed studies of disk winds, in particular, have the potential to reveal the basic physical processes that mediate disk accretion, and to connect with numerical simulations. This talk will review these developments and look ahead to the potential of Astro-H.

High-Resolution Submillimeter and Near-Infrared Studies of the Transition Disk Around Sz 91

NASA Technical Reports Server (NTRS)

Tsukagoshi, Takashi; Momose, Munetake; Abe, Lyu; Akiyama, Eiji; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph; Currie, Thayne; Egner, Sebastian E.; Goto, Miwa;

SMOOTHING ROTATION CURVES AND MASS PROFILES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berrier, Joel C.; Sellwood, J. A.

2015-02-01

We show that spiral activity can erase pronounced features in disk galaxy rotation curves. We present simulations of growing disks, in which the added material has a physically motivated distribution, as well as other examples of physically less realistic accretion. In all cases, attempts to create unrealistic rotation curves were unsuccessful because spiral activity rapidly smoothed away features in the disk mass profile. The added material was redistributed radially by the spiral activity, which was itself provoked by the density feature. In the case of a ridge-like feature in the surface density profile, we show that two unstable spiral modesmore » develop, and the associated angular momentum changes in horseshoe orbits remove particles from the ridge and spread them both inward and outward. This process rapidly erases the density feature from the disk. We also find that the lack of a feature when transitioning from disk to halo dominance in the rotation curves of disk galaxies, the so called ''disk-halo conspiracy'', could also be accounted for by this mechanism. We do not create perfectly exponential mass profiles in the disk, but suggest that this mechanism contributes to their creation.« less

The Last Gasp of Gas Giant Planet Formation: A Spitzer Study of the 5 Myr Old Cluster NGC 2362

NASA Astrophysics Data System (ADS)

Currie, Thayne; Lada, Charles J.; Plavchan, Peter; Robitaille, Thomas P.; Irwin, Jonathan; Kenyon, Scott J.

2009-06-01

Expanding upon the Infrared Array Camera (IRAC) survey from Dahm & Hillenbrand, we describe Spitzer IRAC and Multiband Imaging Photometer for Spitzer observations of the populous, 5 Myr old open cluster NGC 2362. We analyze the mid-IR colors of cluster members and compared their spectral energy distributions (SEDs) to star+circumstellar disk models to constrain the disk morphologies and evolutionary states. Early/intermediate-type confirmed/candidate cluster members either have photospheric mid-IR emission or weak, optically thin IR excess emission at λ >= 24 μm consistent with debris disks. Few late-type, solar/subsolar-mass stars have primordial disks. The disk population around late-type stars is dominated by disks with inner holes (canonical "transition disks") and "homologously depleted" disks. Both types of disks represent an intermediate stage between primordial disks and debris disks. Thus, in agreement with previous results, we find that multiple paths for the primordial-to-debris disk transition exist. Because these "evolved primordial disks" greatly outnumber primordial disks, our results undermine standard arguments in favor of a lsim105 yr timescale for the transition based on data from Taurus-Auriga. Because the typical transition timescale is far longer than 105 yr, these data also appear to rule out standard ultraviolet photoevaporation scenarios as the primary mechanism to explain the transition. Combining our data with other Spitzer surveys, we investigate the evolution of debris disks around high/intermediate-mass stars and investigate timescales for giant planet formation. Consistent with Currie et al., the luminosity of 24 μm emission in debris disks due to planet formation peaks at ≈10-20 Myr. If the gas and dust in disks evolve on similar timescales, the formation timescale for gas giant planets surrounding early-type, high/intermediate-mass (gsim1.4 M sun) stars is likely 1-5 Myr. Most solar/subsolar-mass stars detected by Spitzer have SEDs that indicate their disks may be actively leaving the primordial disk phase. Thus, gas giant planet formation may also occur by ~5 Myr around solar/subsolar-mass stars as well.

Wave Excitation in Accretion Disks by Protoplanets

NASA Astrophysics Data System (ADS)

Koller, J.; Li, H.

2002-05-01

The ongoing discoveries of extrasolar planets in the recent years revealed remarkable properties and unexpected results concerning the formation process. We studied the perturbation of a protostellar accretion disk by a companion utilizing APOLLO, a fast hydro disk code well tested in the case of accretion disks without a companion (Li et al. 2001, ApJ, 551, 874). We consider limiting cases where the companion's mass is much smaller than the central protostar and resides in a circular keplerian orbit. The gravitational field of the protoplanet, embedded in a numerically thin disk, generates spiral density waves and Rossby instabilities resulting in a non-axisymmetric density distribution. We present nonlinear hydro simulations to investigate those non-axisymmetric density distribution with different disk and planet parameters in order to understand how disks respond to a fixed companion in orbit. This work has been supported by IGPP at LANL (award # 1109) and NASA (grant # NAG5-9223).

Masers in Disks due to Gravitational Instabilities

NASA Astrophysics Data System (ADS)

Mejia, A. C.; Durisen, R. H.; Pickett, B. K.; Hartquist, T. W.

2001-12-01

Evidence suggests that some masers associated with massive protostars may originate in the outer regions of large circumstellar disks, at radii of 100's to 1000's of AU from the central mass. This is particularly true for methanol (CH3OH), where linear distributions of masers are found with disk-like kinematics. In 3D hydrodynamics simulations we have made to study the effects of gravitational instabilities in the outer parts of disks around young low-mass stars, the nonlinear development of the instabilities leads to a complex of intersecting spiral shocks, clumps, and arclets within the disk and to significant time-dependent, nonaxisymmetric distortions of the disk surface. A rescaling of our disk simulations to the case of a massive protostar shows that conditions in the disturbed outer disk seem conducive to the appearance of masers if it is viewed edge-on. This work was supported by NASA Origins Program Grant NAGW5-4342, by the Alexander von Humboldt Foundation, and by NASA Planetary Geology and Geophysics Program Grant NAG5-10262.

The Carnegie-Irvine Galaxy Survey. V. Statistical Study of Bars and Buckled Bars

NASA Astrophysics Data System (ADS)

Li, Zhao-Yu; Ho, Luis C.; Barth, Aaron J.

2017-08-01

Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle (I), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high I) or as a barlens structure (at low I). We visually identify bars, boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70%-80%) in late-type disks with low stellar mass (M * < 1010.5 M ⊙) and high gas mass ratio. In contrast, the buckled bar fraction increases to 80% toward massive and early-type disks (M * > 1010.5 M ⊙), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO 506-G004) that could provide further clues to understand the timescale of the buckling process.

THE EVOLUTION OF INNER DISK GAS IN TRANSITION DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoadley, K.; France, K.; McJunkin, M.

2015-10-10

Investigating the molecular gas in the inner regions of protoplanetary disks (PPDs) provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H{sub 2}) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed Hi-Lyman α-pumped H{sub 2} disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H{sub 2} emissionmore » in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H{sub 2} FUV emission arising in primordial disk targets (full dust disk) are demonstrably different than those of transition disks (little-to-no warm dust observed). For each best-fit model, we estimate inner and outer disk emission boundaries (r{sub in} and r{sub out}), describing where the bulk of the observed H{sub 2} emission arises in each disk, and we examine correlations between these and several observational disk evolution indicators, such as n{sub 13–31}, r{sub in,} {sub CO}, and the mass accretion rate. We find strong, positive correlations between the H{sub 2} radial distributions and the slope of the dust spectral energy distribution, implying the behavior of the molecular disk atmosphere changes as the inner dust clears in evolving PPDs. Overall, we find that H{sub 2} inner radii are ∼4 times larger in transition systems, while the bulk of the H{sub 2} emission originates inside the dust gap radius for all transitional sources.« less

Measuring Protoplanetary Disk Gas Surface Density Profiles with ALMA

NASA Astrophysics Data System (ADS)

Williams, Jonathan P.; McPartland, Conor

2016-10-01

The gas and dust are spatially segregated in protoplanetary disks due to the vertical settling and radial drift of large grains. A fuller accounting of the mass content and distribution in disks therefore requires spectral line observations. We extend the modeling approach presented in Williams & Best to show that gas surface density profiles can be measured from high fidelity 13CO integrated intensity images. We demonstrate the methodology by fitting ALMA observations of the HD 163296 disk to determine a gas mass, M gas = 0.048 M ⊙, and accretion disk characteristic size R c = 213 au and gradient γ = 0.39. The same parameters match the C18O 2-1 image and indicate an abundance ratio [12CO]/[C18O] of 700 independent of radius. To test how well this methodology can be applied to future line surveys of smaller, lower mass T Tauri disks, we create a large 13CO 2-1 image library and fit simulated data. For disks with gas masses 3-10 M Jup at 150 pc, ALMA observations with a resolution of 0.″2-0.″3 and integration times of ˜20 minutes allow reliable estimates of R c to within about 10 au and γ to within about 0.2. Economic gas imaging surveys are therefore feasible and offer the opportunity to open up a new dimension for studying disk structure and its evolution toward planet formation.

The evolved circumbinary disk of AC Herculis: a radiative transfer, interferometric, and mineralogical study

NASA Astrophysics Data System (ADS)

Hillen, M.; de Vries, B. L.; Menu, J.; Van Winckel, H.; Min, M.; Mulders, G. D.

2015-06-01

Context. Many post-asymptotic giant branch (post-AGB) stars in binary systems have an infrared (IR) excess arising from a dusty circumbinary disk. The disk formation, current structure, and further evolution are, however, poorly understood. Aims: We aim to constrain the structure of the circumstellar material around the post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial distribution of the amorphous and of the crystalline dust. Methods: We present very high-quality mid-IR interferometric data that were obtained with the MIDI/VLTI instrument. We analyze the MIDI visibilities and differential phases in combination with the full spectral energy distribution, using the MCMax radiative transfer code, to find a good structure model of AC Her's circumbinary disk. We include a grain size distribution and midplane settling of dust self-consistently in our models. The spatial distribution of crystalline forsterite in the disk is investigated with the mid-IR features, the 69 μm band and the 11.3 μm signatures in the interferometric data. Results: All the data are well fitted by our best model. The inclination and position angle of the disk are precisely determined at i = 50 ± 8° and PA = 305 ± 10°. We firmly establish that the inner disk radius is about an order of magnitude larger than the dust sublimation radius. The best-fit dust grain size distribution shows that significant grain growth has occurred, with a significant amount of mm-sized grains now being settled to the midplane of the disk. A large total dust mass ≥10-3 M⊙ is needed to fit the mm fluxes. By assuming αturb = 0.01, a good fit is obtained with a small grain size power law index of 3.25, combined with a small gas/dust ratio ≤10. The resulting gas mass is compatible with recent estimates employing direct gas diagnostics. The spatial distribution of the forsterite is different from the amorphous dust, as more warm forsterite is needed in the surface layers of the inner disk. Conclusions: The disk in the AC Her system is in a very evolved state, as shown by its small gas/dust ratio and large inner hole. Mid-IR interferometry offers unique constraints, complementary to mid-IR features, for studying the mineralogy in disks. A better uv coverage is needed to constrain in detail the distribution of the crystalline forsterite in the disk of AC Her, but we find strong similarities with the protoplanetary disk HD 100546. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 075.D-0605.

Modeling collisions in circumstellar debris disks

NASA Astrophysics Data System (ADS)

Nesvold, Erika

2015-10-01

Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions. In this thesis, I present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. I show that SMACK is stable to numerical viscosity and numerical heating over 107 yr, and that it can reproduce analytic models of disk evolution. As an example of the algorithm's capabilities, I use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit and demonstrate that differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring. To demonstrate SMACK's utility in studying debris disk physics, I apply SMACK to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (alpha = 2/7). I find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index alpha of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by alpha = 0.32(t/ tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. I investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. I also find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ˜1--10MJup. I apply my model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and beta Pictoris. Finally, to show how SMACK can be used to analyze a single debris disk in detail, I present a new model of the beta Pictoris disk and planet system that, for the first time, combines simulations of the colliding planetesimals and the dynamics of the dust grains, allowing me to model features and asymmetries in both submillimeter and scattered light images of the disk. I combine a 100,000 superparticle SMACK simulation with N-body integrations of the dust produced by the simulated collisions. I find that secular perturbations of the planet's measured inclination and eccentricity can explain the observed warp and planetesimal ring, while collisions between planetesimals shape the disk by eroding close-in material. The complex 3D structure of the disk due to the perturbations from the planet creates an azimuthally asymmetric spatial distribution of collisions, which could contribute to the observed azimuthal clump of CO gas seen with ALMA. My simulations of the small dust grains produced by collisions demonstrate that the "birth ring" approximation for beta Pictoris fails to account for the ˜54% of dust mass produced outside of the planetesimal ring. I also reproduce the gross morphology of high-resolution scattered light images of the disk, including the two-disk "x"-pattern seen in scattered light, which has not been replicated by previous dust dynamics models.

Color-size Relations of Disc Galaxies with Similar Stellar Masses

NASA Astrophysics Data System (ADS)

Fu, W.; Chang, R. X.; Shen, S. Y.; Zhang, B.

2011-01-01

To investigate the correlations between colors and sizes of disc galaxies with similar stellar masses, a sample of 7959 local face-on disc galaxies is collected from the main galaxy sample of the Seventh Data Release of Sloan Digital Sky Survey (SDSS DR7). Our results show that, under the condition that the stellar masses of disc galaxies are similar, the relation between u-r and size is weak, while g-r, r-i and r-z colors decrease with disk size. This means that the color-size relations of disc galaxies with similar stellar masses do exist, i.e., the more extended disc galaxies with similar stellar masses tend to have bluer colors. An artificial sample is constructed to confirm that this correlation is not driven by the color-stellar mass relations and size-stellar mass relation of disc galaxies. Our results suggest that the mass distribution of disk galaxies may have an important influence on their stellar formation history, i.e., the galaxies with more extended mass distribution evolve more slowly.

The SW Sextantis-type star 2MASS J01074282+4845188: an unusual bright accretion disk with non-steady emission and a hot white dwarf

NASA Astrophysics Data System (ADS)

Khruzina, T.; Dimitrov, D.; Kjurkchieva, D.

2013-03-01

Context. Cataclysmic variables (CVs) present a short evolutional stage of binary systems. The nova-like stars are rare objects, especially those with eclipses (only several tens). But precisely these allow to determine the global parameters of their configurations and to learn more about the late stage of stellar evolution. Aims: The light curve solution allows one to determine the global parameters of the newly discovered nova-like eclipsing star 2MASS J01074282+4845188 and to estimate the contribution of the different light sources. Methods: We present new photometric and spectral observations of 2MASS J01074282+4845188. To obtain a light curve solution we used a model of a nova-like star whose emission sources are a white dwarf surrounded by an accretion disk, a secondary star filling its Roche lobe, a hot spot and a hot line. The obtained global parameters are compared with those of the eclipsing nova-like UX UMa. Results: 2MASS J01074282+4845188 shows the deepest permanent eclipse among the known nova-like stars. It is reproduced by covering the very bright accretion disk by the secondary component. The luminosity of the disk is much bigger than that of the rest light sources. The determined high temperature of the disk is typical for that observed during the outbursts of CVs. The primary of 2MASS J01074282+4845188 is one of the hottest white dwarfs in CVs. The temperature of 5090 K of its secondary is also quite high and more appropriate for a long-period SW Sex star. It might be explained by the intense heating from the hot white dwarf and the hot accretion disk of the target. Conclusions: The high mass accretion rate Ṁ = 8 × 10-9 M⊙ yr-1, the broad and single-peaked Hα emission profile, and the presence of an S-wave are sure signs for the SW Sex classification of 2MASS J01074282+4845188. The obtained flat temperature distribution along the disk radius as well as the deviation of the energy distribution from the black-body law are evidence of the non-steady emission of the disk. It can be attributed to the low viscosity of the disk matter due to its unusual high temperature. The close values of the disk temperature and the parameter αg of 2MASS J01074282+4845188 and those of the cataclysmic stars at eruptions might be considered as an additional argument for the permanent active state of nova-like stars. Based on data collected with telescopes at Rozhen National Astronomical Observatory.

STARS DO NOT EAT THEIR YOUNG MIGRATING PLANETS: EMPIRICAL CONSTRAINTS ON PLANET MIGRATION HALTING MECHANISMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Plavchan, Peter; Bilinski, Christopher

The discovery of ''hot Jupiters'' very close to their parent stars confirmed that Jovian planets migrate inward via several potential mechanisms. We present empirical constraints on planet migration halting mechanisms. We compute model density functions of close-in exoplanets in the orbital semi-major axis-stellar mass plane to represent planet migration that is halted via several mechanisms, including the interior 1:2 resonance with the magnetospheric disk truncation radius, the interior 1:2 resonance with the dust sublimation radius, and several scenarios for tidal halting. The models differ in the predicted power-law dependence of the exoplanet orbital semi-major axis as a function of stellarmore » mass, and thus we also include a power-law model with the exponent as a free parameter. We use a Bayesian analysis to assess the model success in reproducing empirical distributions of confirmed exoplanets and Kepler candidates that orbit interior to 0.1 AU. Our results confirm a correlation of the halting distance with stellar mass. Tidal halting provides the best fit to the empirical distribution of confirmed Jovian exoplanets at a statistically robust level, consistent with the Kozai mechanism and the spin-orbit misalignment of a substantial fraction of hot Jupiters. We can rule out migration halting at the interior 1:2 resonances with the magnetospheric disk truncation radius and the interior 1:2 resonance with the dust disk sublimation radius, a uniform random distribution, and a distribution with no dependence on stellar mass. Note that our results do not rule out Type-II migration, but rather eliminate the role of a circumstellar disk in stopping exoplanet migration. For Kepler candidates, which have a more restricted range in stellar mass compared to confirmed planets, we are unable to discern between the tidal dissipation and magnetospheric disk truncation braking mechanisms at a statistically significant level. The power-law model favors exponents in the range of 0.38-0.9. This is larger than that predicted for tidal halting (0.23-0.33), which suggests that additional physics may be missing in the tidal halting theory.« less

Evolution of the Solar Nebula. II. Thermal Structure during Nebula Formation

NASA Astrophysics Data System (ADS)

Boss, Alan P.

1993-11-01

Models of the thermal structure of protoplanetary disks are required for understanding the physics and chemistry of the earliest phases of planet formation. Numerical hydrodynamical models of the protostellar collapse phase have not been evolved far enough in time to be relevant to planet formation, i.e., to a relatively low-mass disk surrounding a protostar. One simplification is to assume a pre-existing solar-mass protostar, and calculate the structure of just the disk as it forms from the highest angular momentum vestiges of the placental cloud core. A spatially second-order accurate, axisymmetric (two-dimensional), radiative hydrodynamics code has been used to construct three sets of protoplanetary disk models under this assumption. Because compressional heating has been included, but not viscous or other heating sources, the model temperatures obtained should be considered lower bounds. The first set started from a spherically symmetric configuration appropriate for freely falling gas: ρ ∝ r-3/2, υr ∝ r-1/2, but with rotation (Ω ∝ r-1, where r is the spherical coordinate radius). These first models turned out to be unsatisfactory because in order to achieve an acceptable mass accretion rate onto the protostar (Mṡ ≤ 10-5 Msun yr-1 for low-mass star formation), the disk mass became much too small (˜ 0.0002 Msun). The second set improved on the first set by ensuring that the late-arriving, high angular momentum gas did not accrete directly onto the protosun. By starting from a disklike cloud flattened about the equatorial plane and flowing vertically toward the midplane, these models led to Mṡ → 0, as desired. However, because the initial cloud was not chosen to be close to equilibrium, the disk rapidly contracted vertically, producing an effective disk mass accretion rate Mṡd ˜ 10-2 Msun yr-1, again too high. Hence, the third (and most realistic) set started from an approximate equilibrium state for an adiabatic, self-gravitating "fat" Keplerian disk, with surface density σ ∝ r-1/2, surrounded by a much lower density "halo" infalling onto the disk. This initial condition produced Mṡs → 0 and Mṡd ˜ 10-6 to 10-5 Msun yr-1, as desired. The resulting nebula temperature distributions show that midplane temperatures of at least 1000 K inside 2.5 AU, falling to around 100 K outside 5 AU, are to be expected during the formation phase of a minimum mass nebula containing ˜0.02 Msun within 10 AU. This steady state temperature distribution appears to be consistent with cosmochemical evidence which has been interpreted as implying a phase of relatively high temperatures in the inner nebula. The temperature distribution also implies that the nebula would be cool enough outside 5 AU to allow ices to accumulate into planetesimals even at this relatively early phase of nebula evolution.

Modeling of debris disks in Single and Binary stars

NASA Astrophysics Data System (ADS)

García, L.; Gómez, M.

2016-10-01

Infrared space observatories such as Spitzer and Herschel have allowed the detection of likely analogs to the Kuiper Belt in single as well as binary systems. The aim of this work is to characterize debris disks in single and binary stars and to identify features shared by the disks in both types of systems, as well as possible differences. We compiled a sample of 25 single and 14 binary stars (ages > 100 Myr) with flux measurements at λ >100 μm and evidence of infrared excesses attributed to the presence of debris disks. Then, we constructed and modeled the observed spectral energy distributions (SEDs), and compared the parameters of the disks of both samples. Both types of disks are relatively free of dust in the inner region (< 3-5 AU) and extend beyond 100 AU. No significant differences in the mass and dust size distributions of both samples are found.

The Carnegie-Irvine Galaxy Survey. V. Statistical Study of Bars and Buckled Bars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhao-Yu; Ho, Luis C.; Barth, Aaron J., E-mail: lizy@shao.ac.cn

Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle ( i ), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high i ) or as a barlens structure (at low i ). We visually identify bars, boxy/peanut-shaped bulges, andmore » barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70%–80%) in late-type disks with low stellar mass ( M {sub *} < 10{sup 10.5} M {sub ⊙}) and high gas mass ratio. In contrast, the buckled bar fraction increases to 80% toward massive and early-type disks ( M {sub *} > 10{sup 10.5} M {sub ⊙}), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO 506−G004) that could provide further clues to understand the timescale of the buckling process.« less

Constraining the physical structure of the inner few 100 AU scales of deeply embedded low-mass protostars

NASA Astrophysics Data System (ADS)

Persson, M. V.; Harsono, D.; Tobin, J. J.; van Dishoeck, E. F.; Jørgensen, J. K.; Murillo, N.; Lai, S.-P.

2016-05-01

Context. The physical structure of deeply embedded low-mass protostars (Class 0) on scales of less than 300 AU is still poorly constrained. While molecular line observations demonstrate the presence of disks with Keplerian rotation toward a handful of sources, others show no hint of rotation. Determining the structure on small scales (a few 100 AU) is crucial for understanding the physical and chemical evolution from cores to disks. Aims: We determine the presence and characteristics of compact, disk-like structures in deeply embedded low-mass protostars. A related goal is investigating how the derived structure affects the determination of gas-phase molecular abundances on hot-core scales. Methods: Two models of the emission, a Gaussian disk intensity distribution and a parametrized power-law disk model, are fitted to subarcsecond resolution interferometric continuum observations of five Class 0 sources, including one source with a confirmed Keplerian disk. Prior to fitting the models to the de-projected real visibilities, the estimated envelope from an independent model and any companion sources are subtracted. For reference, a spherically symmetric single power-law envelope is fitted to the larger scale emission (~1000 AU) and investigated further for one of the sources on smaller scales. Results: The radii of the fitted disk-like structures range from ~90-170 AU, and the derived masses depend on the method. Using the Gaussian disk model results in masses of 54-556 × 10-3 M⊙, and using the power-law disk model gives 9-140 × 10-3 M⊙. While the disk radii agree with previous estimates the masses are different for some of the sources studied. Assuming a typical temperature distribution (r-0.5), the fractional amount of mass in the disk above 100 K varies from 7% to 30%. Conclusions: A thin disk model can approximate the emission and physical structure in the inner few 100 AU scales of the studied deeply embedded low-mass protostars and paves the way for analysis of a larger sample with ALMA. Kinematic data are needed to determine the presence of any Keplerian disk. Using previous observations of p-H218O, we estimate the relative gas phase water abundances relative to total warm H2 to be 6.2 × 10-5 (IRAS 2A), 0.33 × 10-5 (IRAS 4A-NW), 1.8 × 10-7 (IRAS 4B), and < 2 × 10-7 (IRAS 4A-SE), roughly an order of magnitude higher than previously inferred when both warm and cold H2 were used as reference. A spherically symmetric single power-law envelope model fails to simultaneously reproduce both the small- and large-scale emission. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Continuum data for the sources are available through http://dx.doi.org/10.5281/zenodo.47642 and at CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A33

Physical properties of dusty protoplanetary disks in Lupus: evidence for viscous evolution?

NASA Astrophysics Data System (ADS)

Tazzari, M.; Testi, L.; Natta, A.; Ansdell, M.; Carpenter, J.; Guidi, G.; Hogerheijde, M.; Manara, C. F.; Miotello, A.; van der Marel, N.; van Dishoeck, E. F.; Williams, J. P.

2017-10-01

Context. The formation of planets strongly depends on the total amount as well as on the spatial distribution of solids in protoplanetary disks. Thanks to the improvements in resolution and sensitivity provided by ALMA, measurements of the surface density of mm-sized grains are now possible on large samples of disks. Such measurements provide statistical constraints that can be used to inform our understanding of the initial conditions of planet formation. Aims: We aim to analyze spatially resolved observations of 36 protoplanetary disks in the Lupus star forming complex from our ALMA survey at 890 μm, aiming to determine physical properties such as the dust surface density, the disk mass and size, and to provide a constraint on the temperature profile. Methods: We fit the observations directly in the uv-plane using a two-layer disk model that computes the 890 μm emission by solving the energy balance at each disk radius. Results: For 22 out of 36 protoplanetary disks we derive robust estimates of their physical properties. The sample covers stellar masses between 0.1 and 2 M⊙, and we find no trend in the relationship between the average disk temperatures and the stellar parameters. We find, instead, a correlation between the integrated sub-mm flux (a proxy for the disk mass) and the exponential cut-off radii (a proxy of the disk size) of the Lupus disks. Comparing these results with observations at similar angular resolution of Taurus-Auriga and Ophiuchus disks found in literature and scaling them to the same distance, we observe that the Lupus disks are generally fainter and larger at a high level of statistical significance. Considering the 1-2 Myr age difference between these regions, it is possible to tentatively explain the offset in the disk mass-size relation with viscous spreading, however with the current measurements other mechanisms cannot be ruled out.

Protoplanetary Disks as (Possibly) Viscous Disks

NASA Astrophysics Data System (ADS)

Rafikov, Roman R.

2017-03-01

Protoplanetary disks are believed to evolve on megayear timescales in a diffusive (viscous) manner as a result of angular momentum transport driven by internal stresses. Here we use a sample of 26 protoplanetary disks resolved by ALMA with measured (dust-based) masses and stellar accretion rates to derive the dimensionless α-viscosity values for individual objects, with the goal of constraining the angular momentum transport mechanism. We find that the inferred values of α do not cluster around a single value, but instead have a broad distribution extending from 10-4 to 0.04. Moreover, they correlate with neither the global disk parameters (mass, size, surface density) nor the stellar characteristics (mass, luminosity, radius). However, we do find a strong linear correlation between α and the central mass accretion rate \\dot{M}. This correlation is unlikely to result from the direct physical effect of \\dot{M} on internal stress on global scales. Instead, we suggest that it is caused by the decoupling of stellar \\dot{M} from the global disk characteristics in one of the following ways: (1) The behavior (and range) of α is controlled by a yet-unidentified parameter (e.g., ionization fraction, magnetic field strength, or geometry), ultimately driving the variation of \\dot{M}. (2) The central \\dot{M} is decoupled from the global accretion rate as a result of an instability, or mass accumulation (or loss in a wind or planetary accretion) in the inner disk. (3) Perhaps the most intriguing possibility is that angular momentum in protoplanetary disks is transported nonviscously, e.g., via magnetohydrodynamic winds or spiral density waves.

THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romero, Gisela A.; Schreiber, Matthias R.; Rebassa-Mansergas, Alberto

2012-04-10

Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transitionmore » disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from {approx}<1 to 10 M{sub JUP}, and accretion rates ranging from {approx}<10{sup -11} to 10{sup -7.7} M{sub Sun} yr{sup -1}. Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole. We find the same heterogeneity of the transition disk population in Lupus III, IV, and Corona Australis as in our previous analysis of transition disks in Ophiuchus while all transition disk candidates selected in Lupus V, VI turned out to be contaminating background asymptotic giant branch stars. All transition disks classified as photoevaporating disks have small disk masses, which indicates that photoevaporation must be less efficient than predicted by most recent models. The three systems that are excellent candidates for harboring giant planets potentially represent invaluable laboratories to study planet formation with the Atacama Large Millimeter/Submillimeter Array.« less

Young Stellar Objects in Lynds 1641: Disks and Accretion

NASA Astrophysics Data System (ADS)

Fang, Min; Kim, Jinyoung Serena; van Boekel, Roy; Sicilia-Aguilar, Aurora; Henning, Thomas; Flaherty, Kevin

2013-07-01

We investigate the young stellar objects (YSOs) in the Lynds 1641 (L1641) cloud using multi-wavelength data including Spitzer, WISE, 2MASS, and XMM covering 1390 YSOs across a range of evolutionary stages. In addition, we targeted a sub-sample of YSOs for optical spectroscopy with the MMT/Hectospec and the MMT/Hectochelle. We use this data, along with archival photometric data, to derive spectral types, masses, ages and extinction values. We also use the H_alpha and H_beta lines to derive accretion rates. We calculate the disk fraction as N(II)/N(II+III), where N(II) and N(III) are numbers of Class\\ II and Class\\ III sources, respectively, and obtain a disk fraction of 50% in L1641. We find that the disk frequency is almost constant as a function of stellar mass with a slight peak at log(M_*/M_sun) -0.25. The analysis of multi-epoch data indicates that the accretion variability of YSOs cannot explain the two orders of magnitude of scatter for YSOs with similar masses in the M_acc vs. M_* plot. Forty-six new transition disk objects are confirmed in our spectroscopic survey and we find that the fraction of transition disks that are actively accreting is lower than for optically thick disks (40-45% vs. 77-79% respectively). We confirm our previous result that the accreting YSOs with transition disks have a similar median accretion rate to normal optically thick disks. Analyzing the age distributions of various populations, we find that the diskless YSOs are statistically older than the YSOs with optically-thick disks and the transition disk objects have a median age which is intermediate between the two populations.

Emission Lines from the Gas Disk Around TW Hydra and the Origin of the Inner Hole

NASA Technical Reports Server (NTRS)

Gorti, U.; Hollenbach, D.; Najita, J.; Pascucci, I.

2011-01-01

We compare line emission calculated from theoretical disk models with optical to submillimeter wavelength observational data of the gas disk surrounding TW Hya and infer the spatial distribution of mass in the gas disk. The model disk that best matches observations has a gas mass ranging from approx.10(exp -4) to 10(exp -5) M for 0.06AU < r < 3.5 AU and approx. 0.06M for 3.5AU < r < 200 AU. We find that the inner dust hole (r < 3.5 AU) in the disk must be depleted of gas by approx. 1-2 orders of magnitude compared with the extrapolated surface density distribution of the outer disk. Grain growth alone is therefore not a viable explanation for the dust hole. CO vibrational emission arises within r approx. 0.5 AU from thermal excitation of gas. [O i] 6300Å and 5577Å forbidden lines and OH mid-infrared emission are mainly due to prompt emission following UV photodissociation of OH and water at r < or approx. 0.1 AU and at r approx. 4 AU. [Ne ii] emission is consistent with an origin in X-ray heated neutral gas at r < or approx. 10 AU, and may not require the presence of a significant extreme-ultraviolet (h? > 13.6 eV) flux from TW Hya. H2 pure rotational line emission comes primarily from r approx. 1 to 30 AU. [Oi] 63microns, HCO+, and CO pure rotational lines all arise from the outer disk at r approx. 30-120 AU. We discuss planet formation and photoevaporation as causes for the decrease in surface density of gas and dust inside 4 AU. If a planet is present, our results suggest a planet mass approx. 4-7MJ situated at 3 AU. Using our photoevaporation models and the best surface density profile match to observations, we estimate a current photoevaporative mass loss rate of 4x10(exp -9M)/yr and a remaining disk lifetime of approx.5 million years.

Fall-Back Disks in Long and Short GRBS

NASA Technical Reports Server (NTRS)

Cannizo, John K.; Troja, E.; Gehrels, N.

2011-01-01

We present numerical time-dependent calculations for fall-back disks relevant for GRBs in which the disk of material surrounding the black hole (BH) powering the GRB jet modulates the mass flow, and hence the strength of the jet. Given the initial existence of a small mass appr oximately less than 10(exp -4) M(solar) near the progenitor with a circularization radius approximately 10(exp 10) - 10(exp 11) cm, an una voidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. For long GRBs, if the mass distribution in the initial fall-back disk traces the progenitor envelope, then a radius approximates 10(exp 11) cm gives a time scale app roximately 10(exp 4) s for the X-ray plateau. For late times t > 10(exp 7) s a steepening due to a cooling front in the disk may have obser vational support in GRB 060729. For short GRBs, one expects most of t he mass initially to lie at small radii < 10(exp 8) cm; however the presence of even a trace amount approximately 10(exp -9) M(solar) of hi gh angular material can give a brief plateau in the light curve.

A Survey for Circumstellar Disks around Young Substellar Objects

NASA Astrophysics Data System (ADS)

Liu, Michael C.; Najita, Joan; Tokunaga, Alan T.

2003-03-01

We have completed the first systematic survey for disks around spectroscopically identified young brown dwarfs and very low mass stars. For a sample of 38 very cool objects in IC 348 and Taurus, we have obtained L'-band (3.8 μm) imaging with sufficient sensitivity to detect objects with and without disks. The sample should be free of selection biases for our purposes. Our targets span spectral types from M6 to M9.5, corresponding to masses of ~15-100 MJup and ages of <~5 Myr, based on current models. None appear to be binaries at 0.4" resolution (55-120 AU). Using the objects' measured spectral types and extinctions, we find that most of our sample (77%+/-15%) possess intrinsic IR excesses, indicative of circum(sub)stellar disks. Because the excesses are modest, conventional analyses using only IR colors would have missed most of the sources with excesses. Such analyses inevitably underestimate the disk fraction and will be less reliable for young brown dwarfs than for T Tauri stars. The observed IR excesses are correlated with Hα emission, consistent with a common accretion disk origin. In the same star-forming regions, we find that disks around brown dwarfs and T Tauri stars are contemporaneous; assuming coevality, this demonstrates that the inner regions of substellar disks are at least as long-lived as stellar disks and evolve slowly for the first ~3 Myr. The disk frequency appears to be independent of mass. However, some objects in our sample, including the very coolest (lowest mass) ones, lack IR excesses and may be diskless. The observed excesses can be explained by disk reprocessing of starlight alone; the implied accretion rates are at least an order of magnitude below typical values for classical T Tauri stars. The observed distribution of IR excesses suggests inner disk holes with radii of >~2R*, consistent with the idea that such holes arise from disk-magnetosphere interactions. Altogether, the frequency and properties of young circumstellar disks appear to be similar from the stellar regime down to the substellar and planetary-mass regime. This provides prima facie evidence of a common origin for most stars and brown dwarfs.

A UNIVERSAL NEUTRAL GAS PROFILE FOR NEARBY DISK GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bigiel, F.; Blitz, L., E-mail: bigiel@uni-heidelberg.de

2012-09-10

Based on sensitive CO measurements from HERACLES and H I data from THINGS, we show that the azimuthally averaged radial distribution of the neutral gas surface density ({Sigma}{sub HI}+ {Sigma}{sub H2}) in 33 nearby spiral galaxies exhibits a well-constrained universal exponential distribution beyond 0.2 Multiplication-Sign r{sub 25} (inside of which the scatter is large) with less than a factor of two scatter out to two optical radii r{sub 25}. Scaling the radius to r{sub 25} and the total gas surface density to the surface density at the transition radius, i.e., where {Sigma}{sub HI} and {Sigma}{sub H2} are equal, as wellmore » as removing galaxies that are interacting with their environment, yields a tightly constrained exponential fit with average scale length 0.61 {+-} 0.06 r{sub 25}. In this case, the scatter reduces to less than 40% across the optical disks (and remains below a factor of two at larger radii). We show that the tight exponential distribution of neutral gas implies that the total neutral gas mass of nearby disk galaxies depends primarily on the size of the stellar disk (influenced to some degree by the great variability of {Sigma}{sub H2} inside 0.2 Multiplication-Sign r{sub 25}). The derived prescription predicts the total gas mass in our sub-sample of 17 non-interacting disk galaxies to within a factor of two. Given the short timescale over which star formation depletes the H{sub 2} content of these galaxies and the large range of r{sub 25} in our sample, there appears to be some mechanism leading to these largely self-similar radial gas distributions in nearby disk galaxies.« less

Asymmetric mass models of disk galaxies. I. Messier 99

NASA Astrophysics Data System (ADS)

Chemin, Laurent; Huré, Jean-Marc; Soubiran, Caroline; Zibetti, Stefano; Charlot, Stéphane; Kawata, Daisuke

2016-04-01

Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M 99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M 99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2-2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M 99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter.

Unlocking CO Depletion in Protoplanetary Disks. I. The Warm Molecular Layer

NASA Astrophysics Data System (ADS)

Schwarz, Kamber R.; Bergin, Edwin A.; Cleeves, L. Ilsedore; Zhang, Ke; Öberg, Karin I.; Blake, Geoffrey A.; Anderson, Dana

2018-03-01

CO is commonly used as a tracer of the total gas mass in both the interstellar medium and in protoplanetary disks. Recently, there has been much debate about the utility of CO as a mass tracer in disks. Observations of CO in protoplanetary disks reveal a range of CO abundances, with measurements of low CO to dust mass ratios in numerous systems. One possibility is that carbon is removed from CO via chemistry. However, the full range of physical conditions conducive to this chemical reprocessing is not well understood. We perform a systematic survey of the time dependent chemistry in protoplanetary disks for 198 models with a range of physical conditions. We vary dust grain size distribution, temperature, comic-ray and X-ray ionization rates, disk mass, and initial water abundance, detailing what physical conditions are necessary to activate the various CO depletion mechanisms in the warm molecular layer. We focus our analysis on the warm molecular layer in two regions: the outer disk (100 au) well outside the CO snowline and the inner disk (19 au) just inside the midplane CO snowline. After 1 Myr, we find that the majority of models have a CO abundance relative to H2 less than 10‑4 in the outer disk, while an abundance less than 10‑5 requires the presence of cosmic-rays. Inside the CO snowline, significant depletion of CO only occurs in models with a high cosmic-ray rate. If cosmic-rays are not present in young disks, it is difficult to chemically remove carbon from CO. Additionally, removing water prior to CO depletion impedes the chemical processing of CO. Chemical processing alone cannot explain current observations of low CO abundances. Other mechanisms must also be involved.

RESOLVED CO GAS INTERIOR TO THE DUST RINGS OF THE HD 141569 DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flaherty, Kevin M.; Hughes, A. Meredith; Zachary, Julia

2016-02-10

The disk around HD 141569 is one of a handful of systems whose weak infrared emission is consistent with a debris disk, but still has a significant reservoir of gas. Here we report spatially resolved millimeter observations of the CO(3-2) and CO(1-0) emission as seen with the Submillimeter Array and CARMA. We find that the excitation temperature for CO is lower than expected from cospatial blackbody grains, similar to previous observations of analogous systems, and derive a gas mass that lies between that of gas-rich primordial disks and gas-poor debris disks. The data also indicate a large inner hole inmore » the CO gas distribution and an outer radius that lies interior to the outer scattered light rings. This spatial distribution, with the dust rings just outside the gaseous disk, is consistent with the expected interactions between gas and dust in an optically thin disk. This indicates that gas can have a significant effect on the location of the dust within debris disks.« less

Three Radial Gaps in the Disk of TW Hydrae Imaged with SPHERE

NASA Astrophysics Data System (ADS)

van Boekel, R.; Henning, Th.; Menu, J.; de Boer, J.; Langlois, M.; Müller, A.; Avenhaus, H.; Boccaletti, A.; Schmid, H. M.; Thalmann, Ch.; Benisty, M.; Dominik, C.; Ginski, Ch.; Girard, J. H.; Gisler, D.; Lobo Gomes, A.; Menard, F.; Min, M.; Pavlov, A.; Pohl, A.; Quanz, S. P.; Rabou, P.; Roelfsema, R.; Sauvage, J.-F.; Teague, R.; Wildi, F.; Zurlo, A.

2017-03-01

We present scattered light images of the TW Hya disk performed with the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument in Polarimetric Differential Imaging mode at 0.63, 0.79, 1.24, and 1.62 μm. We also present H2/H3-band angular differential imaging (ADI) observations. Three distinct radial depressions in the polarized intensity distribution are seen, around ≈85, ≈21, and ≲6 au.21 The overall intensity distribution has a high degree of azimuthal symmetry; the disk is somewhat brighter than average toward the south and darker toward the north-west. The ADI observations yielded no signifiant detection of point sources in the disk. Our observations have a linear spatial resolution of 1-2 au, similar to that of recent ALMA dust continuum observations. The sub-micron-sized dust grains that dominate the light scattering in the disk surface are strongly coupled to the gas. We created a radiative transfer disk model with self-consistent temperature and vertical structure iteration and including grain size-dependent dust settling. This method may provide independent constraints on the gas distribution at higher spatial resolution than is feasible with ALMA gas line observations. We find that the gas surface density in the “gaps” is reduced by ≈50% to ≈80% relative to an unperturbed model. Should embedded planets be responsible for carving the gaps then their masses are at most a few 10 {{{M}}}\\oplus . The observed gaps are wider, with shallower flanks, than expected for planet-disk interaction with such low-mass planets. If forming planetary bodies have undergone collapse and are in the “detached phase,” then they may be directly observable with future facilities such as the Mid-Infrared E-ELT Imager and Spectrograph at the E-ELT.

NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications, volume 1

NASA Technical Reports Server (NTRS)

Kobler, Benjamin (Editor); Hariharan, P. C. (Editor); Blasso, L. G. (Editor)

1992-01-01

Papers and viewgraphs from the conference are presented. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include magnetic disk and tape technologies, optical disks and tape, software storage and file management systems, and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's.

Missing mass or missing light?

NASA Astrophysics Data System (ADS)

Davies, J. I.

1990-07-01

Disney et al. (1989) have argued that the observational data are consistent with disk galaxies being optically thick, particularly in their inner regions. Here, these results are used to reinterpret the radial surface-brightness distributions of spiral galaxies. It is found that the fitting of a profile with an absorbed disk plus bulge leads to both disk and bulge masses (mass in luminous material) that are larger than previously assumed. In addition, it is shown how the rotation velocity, as determined from optical data in the central regions, may systematically underestimate the true rotational velocity in an optically thick disk. If the bulges of late-type galaxies are as large as is hypothesized, then this has important implications in models of galaxy evolution and galaxy dynamics. The model greatly reduces or even eliminates the need for dark matter within the optical radius; it removes a major argument against S0 evolution from later-type galaxies; it accounts for the similarity of rotation curve forms among galaxies of different morphological types; and it leads to a further reappraisal of the observed constancy of the extrapolated central surface brightness of galactic disks.

Refining Models of L1527-IRS

NASA Astrophysics Data System (ADS)

Baker Metzler-Winslow, Elizabeth; Terebey, Susan

2018-06-01

This project examines the Class 0/Class 1 protostar L1527-IRS (hereby referred to as L1527) in the interest of creating a more accurate computational model. In a Class 0/Class I protostar like L1527, the envelope is massive, the protostar is growing in mass, and the disk is a small fraction of the protostar mass. Recent work based on ALMA data indicates that L1527, located in the constellation Taurus (about 140 parsecs from Earth), is about ~0.44 solar masses. Existing models were able to fit the spectral energy distribution of L1527 by assuming a puffed-up inner disk. However, the inclusion of the puffed-up disk results in a portion of the disk coinciding with the outflow cavities, a physically unsatisfying arrangement. This project tests models which decrease the size of the disk and increase the density of the outflow cavities (hypothesizing that some dust from the walls of the outflow cavities is swept up into the cavity itself) against existing observational data, and finds that these models fit the data relatively well.

Herschel evidence for disk flattening or gas depletion in transitional disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keane, J. T.; Pascucci, I.; Espaillat, C.

Transitional disks are protoplanetary disks characterized by reduced near- and mid-infrared emission, with respect to full disks. This characteristic spectral energy distribution indicates the presence of an optically thin inner cavity within the dust disk believed to mark the disappearance of the primordial massive disk. We present new Herschel Space Observatory PACS spectra of [O I] 63.18 μm for 21 transitional disks. Our survey complements the larger Herschel GASPS program ({sup G}as in Protoplanetary Systems{sup )} by quadrupling the number of transitional disks observed with PACS in this wavelength. [O I] 63.18 μm traces material in the outer regions ofmore » the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [O I] 63.18 μm line luminosities ∼2 times fainter than their full disk counterparts. We self-consistently determine various stellar properties (e.g., bolometric luminosity, FUV excess, etc.) and disk properties (e.g., disk dust mass, etc.) that could influence the [O I] 63.18 μm line luminosity, and we find no correlations that can explain the lower [O I] 63.18 μm line luminosities in transitional disks. Using a grid of thermo-chemical protoplanetary disk models, we conclude that either transitional disks are less flared than full disks or they possess lower gas-to-dust ratios due to a depletion of gas mass. This result suggests that transitional disks are more evolved than their full disk counterparts, possibly even at large radii.« less

THE SPITZER INFRARED SPECTROGRAPH SURVEY OF PROTOPLANETARY DISKS IN ORION A. I. DISK PROPERTIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, K. H.; Watson, Dan M.; Manoj, P.

2016-09-01

We present our investigation of 319 Class II objects in Orion A observed by Spitzer /IRS. We also present the follow-up observations of 120 of these Class II objects in Orion A from the Infrared Telescope Facility/SpeX. We measure continuum spectral indices, equivalent widths, and integrated fluxes that pertain to disk structure and dust composition from IRS spectra of Class II objects in Orion A. We estimate mass accretion rates using hydrogen recombination lines in the SpeX spectra of our targets. Utilizing these properties, we compare the distributions of the disk and dust properties of Orion A disks with thosemore » of Taurus disks with respect to position within Orion A (Orion Nebular Cluster [ONC] and L1641) and with the subgroups by the inferred radial structures, such as transitional disks (TDs) versus radially continuous full disks (FDs). Our main findings are as follows. (1) Inner disks evolve faster than the outer disks. (2) The mass accretion rates of TDs and those of radially continuous FDs are statistically significantly displaced from each other. The median mass accretion rate of radially continuous disks in the ONC and L1641 is not very different from that in Taurus. (3) Less grain processing has occurred in the disks in the ONC compared to those in Taurus, based on analysis of the shape index of the 10 μ m silicate feature ( F {sub 11.3}/ F {sub 9.8}). (4) The 20–31 μ m continuum spectral index tracks the projected distance from the most luminous Trapezium star, θ {sup 1} Ori C. A possible explanation is UV ablation of the outer parts of disks.« less

High-Resolution Submillimeter and Near-Infrared Studies of the Transition Disk around Sz 91

NASA Technical Reports Server (NTRS)

Tsukagoshi, Takashi; Momose, Munetake; Hashimoto, Jun; Kudo, Tomoyuki; Andrews, Sean; Saito, Masao; Kitamura, Yoshimi; Ohashi, Nagayoshi; Wilner, David; Kawabe, Ryohei;

Protoplanetary Disks in Multiple Star Systems

NASA Astrophysics Data System (ADS)

Harris, Robert J.

Most stars are born in multiple systems, so the presence of a stellar companion may commonly influence planet formation. Theory indicates that companions may inhibit planet formation in two ways. First, dynamical interactions can tidally truncate circumstellar disks. Truncation reduces disk lifetimes and masses, leaving less time and material for planet formation. Second, these interactions might reduce grain-coagulation efficiency, slowing planet formation in its earliest stages. I present three observational studies investigating these issues. First is a spatially resolved Submillimeter Array (SMA) census of disks in young multiple systems in the Taurus-Auriga star-forming region to study their bulk properties. With this survey, I confirmed that disk lifetimes are preferentially decreased in multiples: single stars have detectable millimeter-wave continuum emission twice as often as components of multiples. I also verified that millimeter luminosity (proportional to disk mass) declines with decreasing stellar separation. Furthermore, by measuring resolved-disk radii, I quantitatively tested tidal-truncation theories: results were mixed, with a few disks much larger than expected. I then switch focus to the grain-growth properties of disks in multiple star systems. By combining SMA, Combined Array for Research in Millimeter Astronomy (CARMA), and Jansky Very Large Array (VLA) observations of the circumbinary disk in the UZ Tau quadruple system, I detected radial variations in the grain-size distribution: large particles preferentially inhabit the inner disk. Detections of these theoretically predicted variations have been rare. I related this to models of grain coagulation in gas disks and find that our results are consistent with growth limited by radial drift. I then present a study of grain growth in the disks of the AS 205 and UX Tau multiple systems. By combining SMA, Atacama Large Millimeter/submillimeter Array (ALMA), and VLA observations, I detected radial variations of the grain-size distribution in the AS 205 A disk, but not in the UX Tau A disk. I find that some combination of radial drift and fragmentation limits growth in the AS 205 A disk. In the final chapter, I summarize my findings that, while multiplicity clearly influences bulk disk properties, it does not obviously inhibit grain growth. Other investigations are suggested.

MEASURING PROTOPLANETARY DISK GAS SURFACE DENSITY PROFILES WITH ALMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Jonathan P.; McPartland, Conor, E-mail: jpw@ifa.hawaii.edu

2016-10-10

The gas and dust are spatially segregated in protoplanetary disks due to the vertical settling and radial drift of large grains. A fuller accounting of the mass content and distribution in disks therefore requires spectral line observations. We extend the modeling approach presented in Williams and Best to show that gas surface density profiles can be measured from high fidelity {sup 13}CO integrated intensity images. We demonstrate the methodology by fitting ALMA observations of the HD 163296 disk to determine a gas mass, M {sub gas} = 0.048 M {sub ⊙}, and accretion disk characteristic size R {sub c} =more » 213 au and gradient γ = 0.39. The same parameters match the C{sup 18}O 2–1 image and indicate an abundance ratio [{sup 12}CO]/[C{sup 18}O] of 700 independent of radius. To test how well this methodology can be applied to future line surveys of smaller, lower mass T Tauri disks, we create a large {sup 13}CO 2–1 image library and fit simulated data. For disks with gas masses 3–10 M {sub Jup} at 150 pc, ALMA observations with a resolution of 0.″2–0.″3 and integration times of ∼20 minutes allow reliable estimates of R {sub c} to within about 10 au and γ to within about 0.2. Economic gas imaging surveys are therefore feasible and offer the opportunity to open up a new dimension for studying disk structure and its evolution toward planet formation.« less

MASS MEASUREMENTS IN PROTOPLANETARY DISKS FROM HYDROGEN DEUTERIDE

DOE Office of Scientific and Technical Information (OSTI.GOV)

McClure, M. K.; Bergin, E. A.; Cleeves, L. I., E-mail: mmcclure@eso.org, E-mail: ebergin@umich.edu, E-mail: ilse.cleeves@cfa.harvard.edu

2016-11-10

The total gas mass of a protoplanetary disk is a fundamental, but poorly determined, quantity. A new technique has been demonstrated to assess directly the bulk molecular gas reservoir of molecular hydrogen using the HD J = 1–0 line at 112 μ m. In this work we present a Herschel Space Observatory {sup 10} survey of six additional T Tauri disks in the HD line. Line emission is detected at >3 σ significance in two cases: DM Tau and GM Aur. For the other four disks, we establish upper limits to the line flux. Using detailed disk structure and ray-tracingmore » models, we calculate the temperature structure and dust mass from modeling the observed spectral energy distributions, and we include the effect of UV gas heating to determine the amount of gas required to fit the HD line. The ranges of gas masses are 1.0–4.7 × 10{sup -2} for DM Tau and 2.5–20.4 × 10{sup -2} for GM Aur. These values are larger than those found using CO for GM Aur, while the CO-derived gas mass for DM Tau is consistent with the lower end of our mass range. This suggests a CO chemical depletion from the gas phase of up to a factor of five for DM Tau and up to two orders of magnitude for GM Aur. We discuss how future analysis can narrow the mass ranges further.« less

Dust in circumstellar disks

NASA Astrophysics Data System (ADS)

Rodmann, Jens

2006-02-01

This thesis presents observational and theoretical studies of the size and spatial distribution of dust particles in circumstellar disks. Using millimetre interferometric observations of optically thick disks around T Tauri stars, I provide conclusive evidence for the presence of millimetre- to centimetre-sized dust aggregates. These findings demonstrate that dust grain growth to pebble-sized dust particles is completed within less than 1 Myr in the outer disks around low-mass pre-main-sequence stars. The modelling of the infrared spectral energy distributions of several solar-type main-sequence stars and their associated circumstellar debris disks reveals the ubiquity of inner gaps devoid of substantial amounts of dust among Vega-type infrared excess sources. It is argued that the absence of circumstellar material in the inner disks is most likely the result of the gravitational influence of a large planet and/or a lack of dust-producing minor bodies in the dust-free region. Finally, I describe a numerical model to simulate the dynamical evolution of dust particles in debris disks, taking into account the gravitational perturbations by planets, photon radiation pressure, and dissipative drag forces due to the Poynting-Robertson effect and stellar wind. The validity of the code it established by several tests and comparison to semi-analytic approximations. The debris disk model is applied to simulate the main structural features of a ring of circumstellar material around the main-sequence star HD 181327. The best agreement between model and observation is achieved for dust grains a few tens of microns in size locked in the 1:1 resonance with a Jupiter-mass planet (or above) on a circular orbit.

Constraining the Structure of the Transition Disk HD 135344B (SAO 206462) by Simultaneous Modeling of Multiwavelength Gas and Dust Observations

NASA Technical Reports Server (NTRS)

Carmona, A.; Pinte, C.; Thi, W. F.; Benisty, M.; Menard, F.; Grady, C.; Kamp, I.; Woitke, P.; Olofsson, J.; Roberge, A.;

Spectro-astrometry Of H2O And OH In A Protoplanetary Disk

NASA Astrophysics Data System (ADS)

Brown, Logan R.; Gibb, E. L.; Troutman, M. R.

2012-05-01

To understand how life originated on Earth, we must investigate how the necessary water and other prebiotic molecules were distributed through the protoplanetary disk from which the solar system formed. To infer this, we study analogs to the early solar system, T Tauri stars, which are surrounded by circumstellar disks. These disks generally have masses on the order of tens of Jupiter masses and extend outward to about 100 AU. These disks have a flared geometry. Of particular interest here is the chemistry of these objects. Disks have three main chemical regions: the cold midplane, warm molecular layer, and hot ionized region (Walsh et. al. 2010). The cold midplane is a cold, dense region where molecules freeze onto dust grains. In the warm molecular layer above that, molecular synthesis is stimulated by increasing temperatures and the evaporation of molecules from dust grains. Above that, stellar and cosmic radiation dissociates and ionizes molecules into constituent radicals, atoms, and ions in the hot ionized disk atmosphere. Spitzer Space Telescope observations found a rich water emission spectrum toward T Tauri star AA Tau (Salyk et al. 2008). How this water is distributed through a protoplanetary disk is of particular interest. This can be determined using a technique called spectro-astrometry that measures the spatial dependence of a spectral feature. We present high-resolution, near-infrared spectroscopic data from the T Tauri star DR Tau, obtained on 16 -18 February 2011 using NIRSPEC at the Keck II telescope. We detected both water and OH in emission and report our spectro-astrometric signals and the derived spatial extent of the gas emission in the disk. Supported by NSF 0908230. Salyk, C. et al. 2008, ApJ, 676, 49 Walsh, C., Miller, T. J., & Nomura, H. 2010 ApJ, 722, 1607

Debris Disk Dust Characterization through Spectral Types: Deep Visible-Light Imaging of Nine Systems

NASA Astrophysics Data System (ADS)

Choquet, Elodie

2017-08-01

We propose STIS coronagraphy of 9 debris disks recently seen in the near-infrared from our re-analysis of archival NICMOS data. STIS coronagraphy will provide complementary visible-light images that will let us characterize the disk colors needed to place constraints on dust grain sizes, albedos, and anisotropy of scattering of these disks. With 3 times finer angular resolution and much better sensitivity, our STIS images will dramatically surpass the NICMOS discovery images, and will more clearly reveal disk local structures, cleared inner regions, and test for large-scale asymmetries in the dust distributions possibly triggered by associated planets in these systems. The exquisite sensitivity to visible-light scattering by submicron particles uniquely offered by STIS coronagraphy will let us detect and spatially characterize the diffuse halo of dust blown out of the systems by the host star radiative pressure. Our sample includes disks around 3 low-mass stars, 3 solar-type stars, and 3 massive A stars; together with our STIS+NICMOS imaging of 6 additional disks around F and G stars, our sample covers the full range of spectral types and will let us perform a comparative study of dust distribution properties as a function of stellar mass and luminosity. Our sample makes up more than 1/3 of all debris disks imaged in scattered light to date, and will offer the first homogeneous characterization of the visible-light to near-IR properties of debris disk systems over a large range of spectral types. Our program will let us analyze how the dynamical balance is affected by initial conditions and star properties, and how it may be perturbed by gas drag or planet perturbations.

An Incipient Debris Disk in the Chamaeleon I Cloud

NASA Astrophysics Data System (ADS)

Espaillat, C. C.; Ribas, Á.; McClure, M. K.; Hernández, J.; Owen, J. E.; Avish, N.; Calvet, N.; Franco-Hernández, R.

2017-07-01

The point at which a protoplanetary disk becomes a debris disk is difficult to identify. To better understand this, here we study the ˜40 au separation binary T 54 in the Chamaeleon I cloud. We derive a K5 spectral type for T 54 A (which dominates the emission of the system) and an age of ˜2 Myr. However, the dust disk properties of T 54 are consistent with those of debris disks seen around older- and earlier-type stars. At the same time, T 54 has evidence of gas remaining in the disk, as indicated by [Ne II], [Ne III], and [O I] line detections. We model the spectral energy distribution of T 54 and estimate that ˜ 3× {10}-3 {M}\\oplus of small dust grains (<0.25 μm) are present in an optically thin circumbinary disk along with at least ˜ 3× {10}-7 {M}\\oplus of larger (>10 μm) grains within a circumprimary disk. Assuming a solar-like mixture, we use Ne line luminosities to place a minimum limit on the gas mass of the disk (˜ 3× {10}-4 {M}\\oplus ) and derive a gas-to-dust mass ratio of ˜0.1. We do not detect substantial accretion, but we do see Hα in emission in one epoch, which is suggestive that there may be intermittent dumping of small amounts of matter onto the star. Considering the low dust mass, the presence of gas, and young age of T 54, we conclude that this system is on the bridge between the protoplanetary and debris disk stages.

Toward a Deterministic Model of Planetary Formation. IV. Effects of Type I Migration

NASA Astrophysics Data System (ADS)

Ida, S.; Lin, D. N. C.

2008-01-01

In a further development of a deterministic planet formation model (Ida & Lin), we consider the effect of type I migration of protoplanetary embryos due to their tidal interaction with their nascent disks. During the early phase of protostellar disks, although embryos rapidly emerge in regions interior to the ice line, uninhibited type I migration leads to their efficient self-clearing. But embryos continue to form from residual planetesimals, repeatedly migrate inward, and provide a main channel of heavy-element accretion onto their host stars. During the advanced stages of disk evolution (a few Myr), the gas surface density declines to values comparable to or smaller than that of the minimum mass nebula model, and type I migration is no longer effective for Mars-mass embryos. Over wide ranges of initial disk surface densities and type I migration efficiencies, the surviving population of embryos interior to the ice line has a total mass of several M⊕. With this reservoir, there is an adequate inventory of residual embryos to subsequently assemble into rocky planets similar to those around the Sun. However, the onset of efficient gas accretion requires the emergence and retention of cores more massive than a few M⊕ prior to the severe depletion of the disk gas. The formation probability of gas giant planets and hence the predicted mass and semimajor axis distributions of extrasolar gas giants are sensitively determined by the strength of type I migration. We suggest that the distributions consistent with observations can be reproduced only if the actual type I migration timescale is at least an order of magnitude longer than that deduced from linear theories.

HST Observations of the Beta Pictoris Circumstellar Disk

NASA Astrophysics Data System (ADS)

Burrows, C. J.; Krist, J. E.; Stapelfeldt, K. R.; WFPC2 Investigation Definition Team

1995-12-01

The disk surrounding Beta Pictoris has been imaged with the Hubble Space Telescope Planetary Camera in the four photometric filters centered near 439, 555, 675 and 814 nm, and at a total of four different spacecraft roll angles. After masking the images to exclude the disk region, a composite PSF was constructed that enabled us to generate three statistically independent images of the disk for each filter. The images show the disk in reflected light from a radius of about 1.5 arcseconds to about 10 arcseconds. We have developed a full three dimensional simulation of the disk which reproduces the observed scattered light distribution and the known infrared photometry and direct imaging from IRAS and previous ground based investigations in a self-consistent manner. By least squares fitting all of the data we are able to derive geometric parameters of the disk and constrain the optical properties of its particles. The scattering is well described by small particles with a visible albedo of around 0.4 and a small scattering phase function variation. The inclination of the disk axis to the plane of the sky is only of order 1 degree. There is a relatively clear zone in the disk with the normal optical depth decreasing linearly within 40 AU from the star from a constant value of 0.005 between 40 and 100 AU. We find that the scale height of the disk is roughly constant within the inner 100 AU, while the outer disk has a linear scale height power law consistent with previous investigations. The disk density is not Gaussian in cross section, as might be expected for a Maxwellian distribution of similar particles, but exponential. We do not interpret this as evidence for pressure support, but rather as evidence for a particle mass spectrum. Several previously reported north-south disk asymmetries are evident in the data, but a significant new result is a rotationally symmetric warp in the inner disk. Detailed dynamical simulations based on the observed mass distribution and with an appropriate collisional viscosity show that this warp is not sustainable in the disk for more than 1 Myr, which is very small compared to the probable age of the system and its collisional timescale with other stars. We conclude that it is likely that at least one massive substellar companion in an inclined orbit to the star is responsible for maintaining the warp. This companion may also be responsible for stirring up the disk within 100 AU and generating the clearer zone within 40 AU.

The protoplanetary disk of FT Tauri: multiwavelength data analysis and modeling

NASA Astrophysics Data System (ADS)

Garufi, A.; Podio, L.; Kamp, I.; Ménard, F.; Brittain, S.; Eiroa, C.; Montesinos, B.; Alonso-Martínez, M.; Thi, W. F.; Woitke, P.

2014-07-01

Context. Investigating the evolution of protoplanetary disks is crucial for our understanding of star and planet formation. There have been several theoretical and observational studies in past decades to advance this knowledge. The launch of satellites operating at infrared wavelengths, such as the Spitzer Space Telescope and the Herschel Space Observatory, has provided important tools for investigating the properties of circumstellar disks. Aims: FT Tauri is a young star in the Taurus star forming region that was included in a number of spectroscopic and photometric surveys. We investigate the properties of the star, the circumstellar disk, and the accretion/ejection processes and propose a consistent gas and dust model also as a reference for future observational studies. Methods: We performed a multiwavelength data analysis to derive the basic stellar and disk properties, as well as mass accretion/outflow rate from TNG/DOLoRes, WHT/LIRIS, NOT/NOTCam, Keck/NIRSpec, and Herschel/PACS spectra. From the literature, we compiled a complete spectral energy distribution. We then performed detailed disk modeling using the MCFOST and ProDiMo codes. Multiwavelength spectroscopic and photometric measurements were compared with the reddened predictions of the codes in order to constrain the disk properties. Results: We have determined the stellar mass (~ 0.3 M⊙), luminosity (~ 0.35 L⊙), and age (~ 1.6 Myr), as well as the visual extinction of the system (1.8 mag). We estimate the mass accretion rate (~ 3 × 10-8 M⊙/yr) to be within the range of accreting objects in Taurus. The evolutionary state and the geometric properties of the disk are also constrained. The radial extent (0.05 to 200 AU), flaring angle (power law with exponent =1.15), and mass (0.02 M⊙) of the circumstellar disk are typical of a young primordial disk. This object can serve as a benchmark for primordial disks with significant mass accretion rate, high gas content, and typical size. Based on Herschel data. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Tables 3, 4 and Appendix A are available in electronic form at http://www.aanda.org

Dust Coagulation in Protoplanetary Accretion Disks

NASA Technical Reports Server (NTRS)

Schmitt, W.; Henning, Th.; Mucha, R.

1996-01-01

The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects is discussed. In particular, we consider the coagulation of grains due to collisional aggregation. The coagulation of the particles is calculated by solving numerically the non-linear Smoluchowski equation. The different physical processes leading to relative velocities between the grains are investigated. The relative velocities may be induced by Brownian motion, turbulence and drift motion. Starting from different regimes which can be identified during the grain growth we also discuss the evolution of dust opacities. These opacities are important for both the derivation of the circumstellar dust mass from submillimeter/millimeter continuum observations and the dynamical behavior of the disks. We present results of our numerical studies of the coagulation of dust grains in a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) alpha-model. For several periods and disk radii, mass distributions of coagulated grains have been calculated. From these mass spectra, we determined the corresponding Rosseland mean dust opacities. The influence of grain opacity changes due to dust coagulation on the dynamical evolution of a protostellar disk is considered. Significant changes in the thermal structure of the protoplanetary nebula are observed. A 'gap' in the accretion disk forms at the very frontier of the coagulation, i.e., behind the sublimation boundary in the region between 1 and 5 AU.

Imaging the disk around IRAS 20126+4104 at subarcsecond resolution

NASA Astrophysics Data System (ADS)

Cesaroni, R.; Galli, D.; Neri, R.; Walmsley, C. M.

2014-06-01

Context. The existence of disks around high-mass stars has yet to be established on a solid ground, as only few reliable candidates are known to date. The disk rotating about the ~104 L⊙ protostar IRAS 20126+4104 is probably the most convincing of these. Aims: We would like to resolve the disk structure in IRAS 20126+4104 and, if possible, investigate the relationship between the disk and the associated jet emitted along the rotation axis. Methods: We performed observations at 1.4 mm with the IRAM Plateau de Bure interferometer attaining an angular resolution of ~0.̋4 (~660 AU). We imaged the methyl cyanide J = 12 → 11 ground state and vibrationally excited transitions as well as the CH313CN isotopologue, which had proved to be disk tracers. Results: Our findings confirm the existence of a disk rotating about a ~7-10 M⊙ star in IRAS 20126+4104, with rotation velocity increasing at small radii. The dramatic improvement in sensitivity and spectral and angular resolution with respect to previous observations allows us to establish that higher excitation transitions are emitted closer to the protostar than the ground state lines, which demonstrates that the gas temperature is increasing towards the centre. We also find that the material is asymmetrically distributed in the disk and speculate on the possible origin of such a distribution. Finally, we demonstrate that the jet emitted along the disk axis is co-rotating with the disk. Conclusions: We present iron-clad evidence of the existence of a disk undergoing rotation around a B-type protostar, with rotation velocity increasing towards the centre. We also demonstrate that the disk is not axially symmetric. These results prove that B-type stars may form through disk-mediated accretion as their low-mass siblings do, but also show that the disk structure may be significantly perturbed by tidal interactions with (unseen) companions, even in a relatively poor cluster such as that associated with IRAS 20126+4104. Based on observations carried out with the Plateau de Bure interferometer.

Toward a Deterministic Model of Planetary Formation. II. The Formation and Retention of Gas Giant Planets around Stars with a Range of Metallicities

NASA Astrophysics Data System (ADS)

Ida, Shigeru; Lin, D. N. C.

2004-11-01

The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass Mp through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semimajor axis a through tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate an Mp-a distribution. Our results reproduce the observed lack of planets with intermediate mass Mp=10-100 M⊕ and a<~3 AU and with large mass Mp>~103 M⊕ and a<~0.2 AU. Based on the simulated Mp-a distributions, we also evaluate the metallicity dependence of the fraction of stars harboring planets that are detectable with current radial velocity surveys. If protostellar disks attain the same fraction of heavy elements as contained in their host stars, the detection probability around metal-rich stars would be greatly enhanced because protoplanetary cores formed in them can grow to several Earth masses prior to their depletion. These large masses are required for the cores to initiate rapid gas accretion and to transform into giant planets. The theoretically extrapolated metallicity dependence is consistent with the observations. This correlation does not arise naturally in the gravitational-instability scenario. We also suggest other metallicity dependences of the planet distributions that can be tested by ongoing observations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mittal, Tushar; Chen, Christine H.; Jang-Condell, Hannah

During the Spitzer Space Telescope cryogenic mission, astronomers obtained Infrared Spectrograph (IRS) observations of hundreds of debris disk candidates that have been compiled in the Spitzer IRS Debris Disk Catalog. We have discovered 10 and/or 20 μm silicate emission features toward 120 targets in the catalog and modeled the IRS spectra of these sources, consistent with MIPS 70 μm observations, assuming that the grains are composed of silicates (olivine, pyroxene, forsterite, and enstatite) and are located either in a continuous disk with power-law size and surface density distributions or thin rings that are well-characterized using two separate dust grain temperatures.more » For systems better fit by the continuous disk model, we find that (1) the dust size distribution power-law index is consistent with that expected from a collisional cascade, q = 3.5-4.0, with a large number of values outside this range, and (2) the minimum grain size, a {sub min}, increases with stellar luminosity, L {sub *}, but the dependence of a {sub min} on L {sub *} is weaker than expected from radiation pressure alone. In addition, we also find that (3) the crystalline fraction of dust in debris disks evolves as a function of time with a large dispersion in crystalline fractions for stars of any particular stellar age or mass, (4) the disk inner edge is correlated with host star mass, and (5) there exists substantial variation in the properties of coeval disks in Sco-Cen, indicating that the observed variation is probably due to stochasticity and diversity in planet formation.« less

Molecular Gas Clumps from the Destruction of Icy Bodies in the beta Pictoris Debris Disk

NASA Technical Reports Server (NTRS)

Dent, W. R. F.; Wyatt, M. C.; Roberge, A.; Augereau, J. -C.; Casassus, S.; Corder, S.; Greaves, J. S.; DeGregorio-Monsalvo, I.; Hales, A.; Jackson, A. P.;

A Direct Imaging Survey of Spitzer-detected Debris Disks: Occurrence of Giant Planets in Dusty Systems

NASA Astrophysics Data System (ADS)

Meshkat, Tiffany; Mawet, Dimitri; Bryan, Marta L.; Hinkley, Sasha; Bowler, Brendan P.; Stapelfeldt, Karl R.; Batygin, Konstantin; Padgett, Deborah; Morales, Farisa Y.; Serabyn, Eugene; Christiaens, Valentin; Brandt, Timothy D.; Wahhaj, Zahed

2017-12-01

We describe a joint high-contrast imaging survey for planets at the Keck and Very Large Telescope of the last large sample of debris disks identified by the Spitzer Space Telescope. No new substellar companions were discovered in our survey of 30 Spitzer-selected targets. We combine our observations with data from four published surveys to place constraints on the frequency of planets around 130 debris disk single stars, the largest sample to date. For a control sample, we assembled contrast curves from several published surveys targeting 277 stars that do not show infrared excesses. We assumed a double power-law distribution in mass and semimajor axis (SMA) of the form f(m,a)={{Cm}}α {a}β , where we adopted power-law values and logarithmically flat values for the mass and SMA of planets. We find that the frequency of giant planets with masses 5-20 M Jup and separations 10-1000 au around stars with debris disks is 6.27% (68% confidence interval 3.68%-9.76%), compared to 0.73% (68% confidence interval 0.20%-1.80%) for the control sample of stars without disks. These distributions differ at the 88% confidence level, tentatively suggesting distinctness of these samples. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Espaillat, C.; Andrews, S.; Qi, C.

Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We findmore » that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.« less

Zoom-in Simulations of Protoplanetary Disks Starting from GMC Scales

NASA Astrophysics Data System (ADS)

Kuffmeier, Michael; Haugbølle, Troels; Nordlund, Åke

2017-09-01

We investigate the formation of protoplanetary disks around nine solar-mass stars formed in the context of a (40 pc)3 Giant Molecular Cloud model, using ramses adaptive mesh refinement simulations extending over a scale range of about 4 million, from an outer scale of 40 pc down to cell sizes of 2 au. Our most important result is that the accretion process is heterogeneous in multiple ways: in time, in space, and among protostars of otherwise similar mass. Accretion is heterogeneous in time, in the sense that accretion rates vary during the evolution, with generally decreasing profiles, whose slopes vary over a wide range, and where accretion can increase again if a protostar enters a region with increased density and low speed. Accretion is heterogeneous in space, because of the mass distribution, with mass approaching the accreting star-disk system in filaments and sheets. Finally, accretion is heterogeneous among stars, since the detailed conditions and dynamics in the neighborhood of each star can vary widely. We also investigate the sensitivity of disk formation to physical conditions and test their robustness by varying numerical parameters. We find that disk formation is robust even when choosing the least favorable sink particle parameters, and that turbulence cascading from larger scales is a decisive factor in disk formation. We also investigate the transport of angular momentum, finding that the net inward mechanical transport is compensated for mainly by an outward-directed magnetic transport, with a contribution from gravitational torques usually subordinate to the magnetic transport.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, K. H.; Watson, Dan M.; Manoj, P.

We present 5-40 {mu}m Spitzer Infrared Spectrograph spectra of a collection of transitional disks, objects for which the spectral energy distribution (SED) indicates central clearings (holes) or gaps in the dust distribution, in the Chamaeleon I star-forming region. Like their counterparts in the Taurus-Auriga star-forming region that we have previously observed, the spectra of these young objects (1-3 Myr old) reveal that the central clearings or gaps are very sharp-edged, and are surrounded by optically thick dusty disks similar to those around other classical T Tauri stars in the Chamaeleon I association. Also like the Taurus transitional disks, the Chamaeleonmore » I transitional disks have extremely large depletion factors for small dust grains in their gaps, compared to the full accretion disks whose SEDs are represented by the median SED of Class II objects in the region. We find that the fraction of transitional disks in the Chamaeleon I cloud is somewhat higher than that in the Taurus-Auriga cloud, possibly indicating that the frequency of transitional disks, on average, increases with cluster age. We also find a significant correlation between the stellar mass and the radius of the outer edge of the gap. We discuss the disk structures implied by the spectra and the constraints they place on gap-formation mechanisms in protoplanetary disks.« less

Particle Size Distributions Obtained Through Unfolding 2D Sections: Towards Accurate Distributions of Nebular Solids in the Allende Meteorite

NASA Technical Reports Server (NTRS)

Christoffersen, P. A.; Simon, Justin I.; Ross, D. K.; Friedrich, J. M.; Cuzzi, J. N.

2012-01-01

Size distributions of nebular solids in chondrites suggest an efficient sorting of these early forming objects within the protoplanetary disk. The effect of this sorting has been documented by investigations of modal abundances of CAIs (e.g., [1-4]) and chondrules (e.g., [5-8]). Evidence for aerodynamic sorting in the disk is largely qualitative, and needs to be carefully assessed. It may be a way of concentrating these materials into planetesimal-mass clumps, perhaps 100 fs of ka after they formed. A key parameter is size/density distributions of particles (i.e., chondrules, CAIs, and metal grains), and in particular, whether the radius-density product (rxp) is a better metric for defining the distribution than r alone [9]. There is no consensus between r versus rxp based models. Here we report our initial tests and preliminary results, which when expanded will be used to test the accuracy of current dynamical disk models.

Disk Evolution and the Fate of Water

NASA Astrophysics Data System (ADS)

Hartmann, Lee; Ciesla, Fred; Gressel, Oliver; Alexander, Richard

2017-10-01

We review the general theoretical concepts and observational constraints on the distribution and evolution of water vapor and ice in protoplanetary disks, with a focus on the Solar System. Water is expected to freeze out at distances greater than 1-3 AU from solar-type central stars; more precise estimates are difficult to obtain due to uncertainties in the complex processes involved in disk evolution, including dust growth, settling, and radial drift, and the level of turbulence and viscous dissipation within disks. Interferometric observations are now providing constraints on the positions of CO snow lines, but extrapolation to the unresolved regions where water ice sublimates will require much better theoretical understanding of mass and angular momentum transport in disks as well as more refined comparison of observations with sophisticated disk models.

NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications, volume 2

NASA Technical Reports Server (NTRS)

Kobler, Ben (Editor); Hariharan, P. C. (Editor); Blasso, L. G. (Editor)

1992-01-01

This report contains copies of nearly all of the technical papers and viewgraphs presented at the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Application. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include the following: magnetic disk and tape technologies; optical disk and tape; software storage and file management systems; and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's.

NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications, volume 3

NASA Technical Reports Server (NTRS)

Kobler, Ben (Editor); Hariharan, P. C. (Editor); Blasso, L. G. (Editor)

1992-01-01

This report contains copies of nearly all of the technical papers and viewgraphs presented at the National Space Science Data Center (NSSDC) Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include magnetic disk and tape technologies, optical disk and tape, software storage and file management systems, and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990s.

Photoevaporation Does Not Create a Pileup of Giant Planets at 1 au

NASA Astrophysics Data System (ADS)

Wise, A. W.; Dodson-Robinson, S. E.

2018-03-01

The semimajor axis distribution of giant exoplanets appears to have a pileup near 1 au. Photoevaporation opens a gap in the inner few au of gaseous disks before dissipating them. Here, we investigate if photoevaporation can significantly affect the final distribution of giant planets by modifying gas surface density and hence Type II migration rates near the photoevaporation gap. We first use an analytic disk model to demonstrate that newly formed giant planets have a long migration epoch before photoevaporation can significantly alter their migration rates. Next, we present new 2D hydrodynamic simulations of planets migrating in photoevaporating disks, in which each are paired with a control simulation of migration in an otherwise identical disk without photoevaporation. We show that in disks with surface densities near the minimum threshold for forming giant planets, photoevaporation alters the final semimajor axis of a migrating gas giant by at most 5% over the course of 0.1 Myr of migration. Once the disk mass has become low enough for photoevaporation to carve a sharp gap, migration has almost completely stalled due to the low surface density of gas at the Lindblad resonances. We find that photoevaporation modifies migration rates so little that it is unlikely to leave a significant signature on the distribution of giant exoplanets.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pawellek, Nicole; Krivov, Alexander V.; Marshall, Jonathan P.

The radii of debris disks and the sizes of their dust grains are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Here we use a representative sample of 34 debris disks resolved in various Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) programs to constrain the disk radii and the size distribution of their dust. While we modeled disks with both warm and cold components, and identified warm inner disks around about two-thirds of the stars, we focusmore » our analysis only on the cold outer disks, i.e., Kuiper-belt analogs. We derive the disk radii from the resolved images and find a large dispersion for host stars of any spectral class, but no significant trend with the stellar luminosity. This argues against ice lines as a dominant player in setting the debris disk sizes, since the ice line location varies with the luminosity of the central star. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distribution to determine the dust temperature and the grain size distribution for each target. While the dust temperature systematically increases toward earlier spectral types, the ratio of the dust temperature to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by a clear trend of typical sizes increasing toward more luminous stars. The typical grain sizes are compared to the radiation pressure blowout limit s {sub blow} that is proportional to the stellar luminosity-to-mass ratio and thus also increases toward earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times s {sub blow} at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of s {sub blow}, appear to decrease with the luminosity, which may be suggestive of the disk's stirring level increasing toward earlier-type stars. The dust opacity index β ranges between zero and two, and the size distribution index q varies between three and five for all the disks in the sample.« less

Inferring a Gap in the Group II Disk of the Herbig Ae/Be Star HD 142666

NASA Astrophysics Data System (ADS)

Ezra Rubinstein, Adam; Macías, Enrique; Espaillat, Catherine; Calvet, Nuria; Robinson, Connor; Zhang, Ke

2018-01-01

Disks around Herbig Ae/Be (HAeBe) stars have been classified into Group I or Group II, which are thought to be flared and flat disks respectively. Most Group I disks have been shown to have large gaps, suggesting ongoing planet formation, while no large gaps have been found in Group II disks. We analyzed the Group II disk of HD 142666 using irradiated accretion disk modeling of the broad-band spectral energy distribution along with the 1.3 millimeter spatial brightness distribution traced by Atacama Large Millimeter and Submillimeter Array (ALMA) observations. Our model is able to reproduce the available data, predicting a high degree of settling in the disk, which is consistent with the Group II classification of HD 142666. Although the ALMA observations did not have enough angular resolution to fully resolve the inner parts of the disk, the observed visibilities and synthesized image can only be reproduced when including a gap between ~5 to 12 au in our disk model. In addition, we also infer that the disk has an outer radius of ~65 au, which may be evidence of radial migration of dust or an unseen, low-mass companion that is truncating the outer disk. These results may suggest that Group II disks around HAeBe stars have gaps, possibly carved by young giant planets in the disk. Further ALMA observations of HD 142666 and other Group II disks are needed to discern if gaps are common in this class of objects, as well as to reveal their possible origin.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quintana, Elisa V.; Lissauer, Jack J., E-mail: elisa.quintana@nasa.gov

Models of planet formation have shown that giant planets have a large impact on the number, masses, and orbits of terrestrial planets that form. In addition, they play an important role in delivering volatiles from material that formed exterior to the snow line (the region in the disk beyond which water ice can condense) to the inner region of the disk where terrestrial planets can maintain liquid water on their surfaces. We present simulations of the late stages of terrestrial planet formation from a disk of protoplanets around a solar-type star and we include a massive planet (from 1 Mmore » {sub ⊕} to 1 M {sub J}) in Jupiter's orbit at ∼5.2 AU in all but one set of simulations. Two initial disk models are examined with the same mass distribution and total initial water content, but with different distributions of water content. We compare the accretion rates and final water mass fraction of the planets that form. Remarkably, all of the planets that formed in our simulations without giant planets were water-rich, showing that giant planet companions are not required to deliver volatiles to terrestrial planets in the habitable zone. In contrast, an outer planet at least several times the mass of Earth may be needed to clear distant regions of debris truncating the epoch of frequent large impacts. Observations of exoplanets from radial velocity surveys suggest that outer Jupiter-like planets may be scarce, therefore, the results presented here suggest that there may be more habitable planets residing in our galaxy than previously thought.« less

ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii

NASA Astrophysics Data System (ADS)

Ansdell, M.; Williams, J. P.; Trapman, L.; van Terwisga, S. E.; Facchini, S.; Manara, C. F.; van der Marel, N.; Miotello, A.; Tazzari, M.; Hogerheijde, M.; Guidi, G.; Testi, L.; van Dishoeck, E. F.

2018-05-01

We present Atacama Large Millimeter/Sub-Millimeter Array (ALMA) Band 6 observations of a complete sample of protoplanetary disks in the young (∼1–3 Myr) Lupus star-forming region, covering the 1.33 mm continuum and the 12CO, 13CO, and C18O J = 2–1 lines. The spatial resolution is ∼0.″25 with a medium 3σ continuum sensitivity of 0.30 mJy, corresponding to M dust ∼ 0.2 M ⊕. We apply Keplerian masking to enhance the signal-to-noise ratios of our 12CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than millimeter dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission and the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, α visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 μm continuum observations, we also calculate the millimeter spectral index, α mm, for 70 Lupus disks; we find an anticorrelation between α mm and millimeter flux for low-mass disks (M dust ≲ 5), followed by a flattening as disks approach α mm ≈ 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys.

The Transitional Protoplanetary Disk Frequency as a Function of Age: Disk Evolution In the Coronet Cluster, Taurus, and Other 1-8 Myr Old Regions

NASA Astrophysics Data System (ADS)

Currie, Thayne; Sicilia-Aguilar, Aurora

2011-05-01

We present Spitzer 3.6-24 μm photometry and spectroscopy for stars in the 1-3 Myr old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters—IC 348, NGC 2362, and η Cha—to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks—those with inner holes and those that are homologously depleted. The percentage of disks in the transitional phase increases from ~15%-20% at 1-2 Myr to >=50% at 5-8 Myr the mean transitional disk lifetime is closer to ~1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. and Sicilia-Aguilar et al. In the Coronet Cluster and IC 348, transitional disks are more numerous for very low mass M3-M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral-type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically thick primordial disks is M disk ≈ 0.001-0.003 M sstarf. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full spectral energy distribution modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.

Surface geometry of protoplanetary disks inferred from near-infrared imaging polarimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takami, Michihiro; Hasegawa, Yasuhiro; Gu, Pin-Gao

2014-11-01

We present a new method of analysis for determining the surface geometry of five protoplanetary disks observed with near-infrared imaging polarimetry using Subaru-HiCIAO. Using as inputs the observed distribution of polarized intensity (PI), disk inclination, assumed properties for dust scattering, and other reasonable approximations, we calculate a differential equation to derive the surface geometry. This equation is numerically integrated along the distance from the star at a given position angle. We show that, using these approximations, the local maxima in the PI distribution of spiral arms (SAO 206462, MWC 758) and rings (2MASS J16042165-2130284, PDS 70) are associated with localmore » concave-up structures on the disk surface. We also show that the observed presence of an inner gap in scattered light still allows the possibility of a disk surface that is parallel to the light path from the star, or a disk that is shadowed by structures in the inner radii. Our analysis for rings does not show the presence of a vertical inner wall as often assumed in studies of disks with an inner gap. Finally, we summarize the implications of spiral and ring structures as potential signatures of ongoing planet formation.« less

Constraining the mass of the planet(s) sculpting a disk cavity. The intriguing case of 2MASS J16042165-2130284

NASA Astrophysics Data System (ADS)

Canovas, H.; Hardy, A.; Zurlo, A.; Wahhaj, Z.; Schreiber, M. R.; Vigan, A.; Villaver, E.; Olofsson, J.; Meeus, G.; Ménard, F.; Caceres, C.; Cieza, L. A.; Garufi, A.

2017-02-01

Context. The large cavities observed in the dust and gas distributions of transition disks may be explained by planet-disk interactions. At 145 pc, 2MASS J16042165-2130284 (J1604) is a 5-12 Myr old transitional disk with different gap sizes in the mm- and μm-sized dust distributions (outer edges at 79 and at 63 au, respectively). Its 12CO emission shows a 30 au cavity. This radial structure suggests that giant planets are sculpting this disk. Aims: We aim to constrain the masses and locations of plausible giant planets around J1604. Methods: We observed J1604 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT), in IRDIFS_EXT, pupil-stabilized mode, obtaining YJH-band images with the integral field spectrograph (IFS) and K1K2-band images with the Infra-Red Dual-beam Imager and Spectrograph (IRDIS). The dataset was processed exploiting the angular differential imaging (ADI) technique with high-contrast algorithms. Results: Our observations reach a contrast of ΔK,ΔYH 12 mag from 0".15 to 0".80 ( 22 to 115 au), but no planet candidate is detected. The disk is directly imaged in scattered light at all bands from Y to K, and it shows a red color. This indicates that the dust particles in the disk surface are mainly ≳0.3 μm-sized grains. We confirm the sharp dip/decrement in scattered light in agreement with polarized light observations. Comparing our images with a radiative transfer model we argue that the southern side of the disk is most likely the nearest. Conclusions: This work represents the deepest search yet for companions around J1604. We reach a mass sensitivity of ≳2-3 MJup from 22 to 115 au according to a hot start scenario. We propose that a brown dwarf orbiting inside of 15 au and additional Jovian planets at larger radii could account for the observed properties of J1604 while explaining our lack of detection. Based on observations made with the VLT, program 095.C-0673(A).The reduced images (FITS files) are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A43

On Estimating the Mass of Keplerian Accretion Disks in H2O Maser Galaxies

NASA Astrophysics Data System (ADS)

Kuo, C. Y.; Reid, M. J.; Braatz, J. A.; Gao, F.; Impellizzeri, C. M. V.; Chien, W. T.

2018-06-01

H2O maser disks with Keplerian rotation in active galactic nuclei offer a clean way to determine accurate black hole mass and the Hubble constant. An important assumption made in using a Keplerian H2O maser disk for measuring black hole mass and the Hubble constant is that the disk mass is negligible compared to the black hole mass. A simple and useful model of Huré et al. can be used to test this assumption. In that work, the authors apply a linear disk model to a position–dynamical mass diagram and re-analyze position–velocity data from H2O maser disks associated with active galactic nuclei. They claim that a maser disk with nearly perfect Keplerian rotation could have a disk mass comparable to the black hole mass. This would imply that ignoring the effects of disk self-gravity can lead to large systematic errors in the measurement of black hole mass and the Hubble constant. We examine their methods and find that their large estimated disk masses of Keplerian disks are likely the result of their use of projected instead of three-dimensional position and velocity information. To place better constraints on the disk masses of Keplerian maser systems, we incorporate disk self-gravity into a three-dimensional Bayesian modeling program for maser disks and also evaluate constraints based on the physical conditions for disks that support water maser emission. We find that there is little evidence that disk masses are dynamically important at the ≲1% level compared to the black holes.

The Stellar Mass of M31 as inferred by the Andromeda Optical & Infrared Disk Survey

NASA Astrophysics Data System (ADS)

Sick, Jonathan; Courteau, Stephane; Cuillandre, Jean-Charles; Dalcanton, Julianne; de Jong, Roelof; McDonald, Michael; Simard, Dana; Tully, R. Brent

2015-04-01

Our proximity and external vantage point make M31 an ideal testbed for understanding the structure of spiral galaxies. The Andromeda Optical and Infrared Disk Survey (ANDROIDS) has mapped M31's bulge and disk out to R=40 kpc in ugriJKs bands with CFHT using a careful sky calibration. We use Bayesian modelling of the optical-infrared spectral energy distribution (SED) to estimate profiles of M31's stellar populations and mass along the major axis. This analysis provides evidence for inside-out disk formation and a declining metallicity gradient. M31's i-band mass-to-light ratio (M/Li *) decreases from 0.5 dex in the bulge to ~ 0.2 dex at 40 kpc. The best-constrained stellar population models use the full ugriJKs SED but are also consistent with optical-only fits. Therefore, while NIR data can be successfully modelled with modern stellar population synthesis, NIR data do not provide additional constraints in this application. Fits to the gi-SED alone yield M/Li * that are systematically lower than the full SED fit by 0.1 dex. This is still smaller than the 0.3 dex scatter amongst different relations for M/Li via g - i colour found in the literature. We advocate a stellar mass of M *(30 kpc) = 10.3+2.3 -1.7 × 1010 M⊙ for the M31 bulge and disk.

V3885 Sagittarius: A Comparison With a Range of Standard Model Accretion Disks

NASA Technical Reports Server (NTRS)

Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion, Edward M; Szkody, Paula; Barrett, Paul E.

2009-01-01

A chi-squared analysis of standard model accretion disk synthetic spectrum fits to combined Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius, on an absolute flux basis, selects a model that accurately represents the observed spectral energy distribution. Calculation of the synthetic spectrum requires the following system parameters. The cataclysmic variable secondary star period-mass relation calibrated by Knigge in 2006 and 2007 sets the secondary component mass. A mean white dwarf (WD) mass from the same study, which is consistent with an observationally determined mass ratio, sets the adopted WD mass of 0.7M(solar mass), and the WD radius follows from standard theoretical models. The adopted inclination, i = 65 deg, is a literature consensus, and is subsequently supported by chi-squared analysis. The mass transfer rate is the remaining parameter to set the accretion disk T(sub eff) profile, and the Hipparcos parallax constrains that parameter to mas transfer = (5.0 +/- 2.0) x 10(exp -9) M(solar mass)/yr by a comparison with observed spectra. The fit to the observed spectra adopts the contribution of a 57,000 +/- 5000 K WD. The model thus provides realistic constraints on mass transfer and T(sub eff) for a large mass transfer system above the period gap.

Bringing "The Moth" to light: A planet-sculpting scenario for the HD 61005 debris disk

DOE PAGES

Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; ...

2016-09-16

Here, the HD 61005 debris disk ("The Moth") stands out from the growing collection of spatially resolved circumstellar disks by virtue of its unusual swept-back morphology, brightness asymmetries, and dust ring offset. Despite several suggestions for the physical mechanisms creating these features, no definitive answer has been found. In this work, we demonstrate the plausibility of a scenario in which the disk material is shaped dynamically by an eccentric, inclined planet. We present new Keck NIRC2 scattered-light angular differential imaging of the disk at 1.2–2.3 μm that further constrains its outer morphology (projected separations of 27–135 au). We also presentmore » complementary Gemini Planet Imager 1.6 μm total intensity and polarized light detections that probe down to projected separations less than 10 au. To test our planet-sculpting hypothesis, we employed secular perturbation theory to construct parent body and dust distributions that informed scattered-light models. We found that this method produced models with morphological and photometric features similar to those seen in the data, supporting the premise of a planet-perturbed disk. Briefly, our results indicate a disk parent body population with a semimajor axis of 40–52 au and an interior planet with an eccentricity of at least 0.2. Many permutations of planet mass and semimajor axis are allowed, ranging from an Earth mass at 35 au to a Jupiter mass at 5 au.« less

Properties of the outer regions of spiral disks: abundances, colors and ages

NASA Astrophysics Data System (ADS)

Mollá, Mercedes; Díaz, Angeles I.; Gibson, Brad K.; Cavichia, Oscar; López-Sánchez, Ángel-R.

2017-03-01

We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.

Characterizing the Evolution of Circumstellar Systems with the Hubble Space Telescope and the Gemini Planet Imager

NASA Astrophysics Data System (ADS)

Wolff, Schuyler; Schuyler G. Wolff

2018-01-01

The study of circumstellar disks at a variety of evolutionary stages is essential to understand the physical processes leading to planet formation. The recent development of high contrast instruments designed to directly image the structures surrounding nearby stars, such as the Gemini Planet Imager (GPI) and coronagraphic data from the Hubble Space Telescope (HST) have made detailed studies of circumstellar systems possible. In my thesis work I detail the observation and characterization of three systems. GPI polarization data for the transition disk, PDS 66 shows a double ring and gap structure with a temporally variable azimuthal asymmetry. This evolved morphology could indicate shadowing from some feature in the innermost regions of the disk, a gap-clearing planet, or a localized change in the dust properties of the disk. Millimeter continuum data of the DH Tau system places limits on the dust mass that is contributing to the strong accretion signature on the wide-separation planetary mass companion, DH Tau b. The lower than expected dust mass constrains the possible formation mechanism, with core accretion followed by dynamical scattering being the most likely. Finally, I present HST scattered light observations of the flared, edge-on protoplanetary disk ESO H$\\alpha$ 569. I combine these data with a spectral energy distribution to model the key structural parameters such as the geometry (disk outer radius, vertical scale height, radial flaring profile), total mass, and dust grain properties in the disk using the radiative transfer code MCFOST. In order to conduct this work, I developed a new tool set to optimize the fitting of disk parameters using the MCMC code \\texttt{emcee} to efficiently explore the high dimensional parameter space. This approach allows us to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties.

Constraints from Dust Mass and Mass Accretion Rate Measurements on Angular Momentum Transport in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Mulders, Gijs D.; Pascucci, Ilaria; Manara, Carlo F.; Testi, Leonardo; Herczeg, Gregory J.; Henning, Thomas; Mohanty, Subhanjoy; Lodato, Giuseppe

2017-09-01

In this paper, we investigate the relation between disk mass and mass accretion rate to constrain the mechanism of angular momentum transport in protoplanetary disks. We find a correlation between dust disk mass and mass accretion rate in Chamaeleon I with a slope that is close to linear, similar to the one recently identified in Lupus. We investigate the effect of stellar mass and find that the intrinsic scatter around the best-fit {M}{dust}-{M}\\star and {\\dot{M}}{acc}-{M}\\star relations is uncorrelated. We simulate synthetic observations of an ensemble of evolving disks using a Monte Carlo approach and find that disks with a constant α viscosity can fit the observed relations between dust mass, mass accretion rate, and stellar mass but overpredict the strength of the correlation between disk mass and mass accretion rate when using standard initial conditions. We find two possible solutions. In the first one, the observed scatter in {M}{dust} and {\\dot{M}}{acc} is not primordial, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likely grain growth and radial drift affect the observable dust mass, while variability on large timescales affects the mass accretion rates. In the second scenario, the observed scatter is primordial, but disks have not evolved substantially at the age of Lupus and Chamaeleon I owing to a low viscosity or a large initial disk radius. More accurate estimates of the disk mass and gas disk sizes in a large sample of protoplanetary disks, through either direct observations of the gas or spatially resolved multiwavelength observations of the dust with ALMA, are needed to discriminate between both scenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk winds.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.

Here, the HD 61005 debris disk ("The Moth") stands out from the growing collection of spatially resolved circumstellar disks by virtue of its unusual swept-back morphology, brightness asymmetries, and dust ring offset. Despite several suggestions for the physical mechanisms creating these features, no definitive answer has been found. In this work, we demonstrate the plausibility of a scenario in which the disk material is shaped dynamically by an eccentric, inclined planet. We present new Keck NIRC2 scattered-light angular differential imaging of the disk at 1.2–2.3 μm that further constrains its outer morphology (projected separations of 27–135 au). We also presentmore » complementary Gemini Planet Imager 1.6 μm total intensity and polarized light detections that probe down to projected separations less than 10 au. To test our planet-sculpting hypothesis, we employed secular perturbation theory to construct parent body and dust distributions that informed scattered-light models. We found that this method produced models with morphological and photometric features similar to those seen in the data, supporting the premise of a planet-perturbed disk. Briefly, our results indicate a disk parent body population with a semimajor axis of 40–52 au and an interior planet with an eccentricity of at least 0.2. Many permutations of planet mass and semimajor axis are allowed, ranging from an Earth mass at 35 au to a Jupiter mass at 5 au.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Currie, Thayne; Sicilia-Aguilar, Aurora

We present Spitzer 3.6-24 {mu}m photometry and spectroscopy for stars in the 1-3 Myr old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters-IC 348, NGC 2362, and {eta} Cha-to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks-those with inner holes and thosemore » that are homologously depleted. The percentage of disks in the transitional phase increases from {approx}15%-20% at 1-2 Myr to {>=}50% at 5-8 Myr; the mean transitional disk lifetime is closer to {approx}1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. and Sicilia-Aguilar et al. In the Coronet Cluster and IC 348, transitional disks are more numerous for very low mass M3-M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral-type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically thick primordial disks is M{sub disk} {approx} 0.001-0.003 M{sub *}. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full spectral energy distribution modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.« less

Galactic Spiral Shocks with Thermal Instability in Vertically Stratified Disks

NASA Astrophysics Data System (ADS)

Kim, Chang-Goo; Kim, W.; Ostriker, E. C.

2010-01-01

Galactic spiral shocks are dominant morphological features and believed to be responsible for substructure formation of spiral arms in disk galaxies. They can also provide a large amount of kinetic energy for the interstellar gas by tapping the rotational energy. We use numerical hydrodynamic simulations to investigate dynamics and structure of spiral shocks with thermal instability in vertically stratified galactic disks. We initially consider an isothermal disk in vertical hydrostatic equilibrium and let it evolve under interstellar cooling and heating. Due to cooling and heating, the disk rapidly turns to a dense slab near the midplane surrounded by rarefied gas at high-altitude regions. The imposed stellar spiral potential develops a vertically curved shock that exhibits strong flapping motions along the direction perpendicular to the arm. The flows across the spiral shock are characterized by transitions from rarefied to dense phases at the shock and from dense to rarefied phases at the postshock expansion zone. The shock flapping motions stirs the disk, supplying the gas with random kinetic energy. For a model resembling the galactic disk near the solar neighborhood, the density-weighted vertical velocity dispersions are 2 km/s for the rarefied gas and 1 km/s for the dense gas. The shock compression in this model reduces an amount of the rarefied gas from 29% to 19% by mass. Despite the flapping motions, the time-averaged profiles of surface density are similar to those of the one-dimensional counterparts, and the vertical density distribution is overall consistent with effective hydrostatic equilibrium. When self-gravity is included, the shock compression forms large gravitationally bound condensations with virial ratio of about 2 and typical masses of 0.5 to one million solar masses, comparable to the Jeans mass.

The Megamaser Cosmology Project. X. High-resolution Maps and Mass Constraints for SMBHs

NASA Astrophysics Data System (ADS)

Zhao, W.; Braatz, J. A.; Condon, J. J.; Lo, K. Y.; Reid, M. J.; Henkel, C.; Pesce, D. W.; Greene, J. E.; Gao, F.; Kuo, C. Y.; Impellizzeri, C. M. V.

2018-02-01

We present high-resolution (submas) Very Long Baseline Interferometry maps of nuclear H2O megamasers for seven galaxies. In UGC 6093, the well-aligned systemic masers and high-velocity masers originate in an edge-on, flat disk and we determine the mass of the central supermassive black holes (SMBH) to be M SMBH = 2.58 × 107 M ⊙ (±7%). For J1346+5228, the distribution of masers is consistent with a disk, but the faint high-velocity masers are only marginally detected, and we constrain the mass of the SMBH to be in the range (1.5–2.0) × 107 M ⊙. The origin of the masers in Mrk 1210 is less clear, as the systemic and high-velocity masers are misaligned and show a disorganized velocity structure. We present one possible model in which the masers originate in a tilted, warped disk, but we do not rule out the possibility of other explanations including outflow masers. In NGC 6926, we detect a set of redshifted masers, clustered within a parsec of each other, and a single blueshifted maser about 4.4 pc away, an offset that would be unusually large for a maser disk system. Nevertheless, if it is a disk system, we estimate the enclosed mass to be M SMBH < 4.8 × 107 M ⊙. For NGC 5793, we detect redshifted masers spaced about 1.4 pc from a clustered set of blueshifted features. The orientation of the structure supports a disk scenario as suggested by Hagiwara et al. We estimate the enclosed mass to be M SMBH < 1.3 × 107 M ⊙. For NGC 2824 and J0350‑0127, the masers may be associated with parsec- or subparsec-scale jets or outflows.

Modeling Protoplanetary Disks to Characterize the Evolution of their Structure

NASA Astrophysics Data System (ADS)

Allen, Magdelena; van der Marel, Nienke; Williams, Jonathan

2018-01-01

Stars form from gravitationally collapsing clouds of gas and dust. Most young stars retain a protoplanetary disk for a few million years. This disk’s dust reemits stellar flux in the infrared, producing a spectral energy distribution (SED) observable by Spitzer and other telescopes. To understand the inner clearing of dust cavities and evolution in the SED, we used the Chiang & Goldreich two-layer approximation. We first wrote a python script based on refinements by Dullemond that includes a hot, puffed inner rim, shadowed mid region, flaring outer disk, and a variable inner cavity. This was then coupled with a Markov Chain Monte Carlo procedure to fit the observed SEDs of disks in the star forming Lupus region. The fitting procedure recovers physical characteristics of the disk including temperature, size, mass, and surface density. We compare the characteristics of circumstellar disks without holes and more evolved transition disks with cleared inner regions.

The Influence of Interactions and Minor Mergers on the Structure of Galactic Disks

NASA Astrophysics Data System (ADS)

Schwarzkopf, U.

1999-07-01

A detailed statistical study is presented focused on the effects of minor mergers and tidal interactions on the radial and vertical structure of galactic disks. The fundamental disk parameters of 112 highly-inclined/edge-on galaxies are studied in optical and in near-infrared passbands. This sample consists of two subsamples of 65 non-interacting and 47 interacting/merging galaxies. Additionally, 41 of these galaxies were observed in the near-infrared. A 3-dimensional disk modelling and -fitting procedure was applied in order to analyze and to compare characteristic disk parameters of all sample galaxies. Furthermore, n-body simulations were performed in order to study the influence of minor mergers in the mass range Msat/Mdisk 0.1 on the vertical structure of disks in spiral galaxies. In particular, the dependence of vertical, tidally-triggered disk thickening on initial disk parameters is investigated. The quantitative results of both simulation and observation are compared in order to find similarities in the distribution of characteristic disk parameters.

Angular Momentum in Disk Wind Revealed in the Young Star MWC 349A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Qizhou; Claus, Brian; Watson, Linda

Disk winds are thought to play a critical role in star birth. As winds extract excess angular momentum from accretion disks, matter in the disk can be transported inward to the star to fuel mass growth. However, observational evidence of wind carrying angular momentum has been very limited. We present Submillimeter Array (SMA) observations of the young star MWC 349A in the H26 α and H30 α recombination lines. The high signal-to-noise ratios made possible by the maser emission process allow us to constrain the relative astrometry of the maser spots to milli-arcsecond precision. Previous observations of the H30 αmore » line with the SMA and the Plateau de Bure interferometer (PdBI) showed that masers are distributed in the disk and wind. Our new high-resolution observations of the H26 α line reveal differences in spatial distribution from that of the H30 α line. H26 α line masers in the disk are excited in a thin annulus with a radius of about 25 au, while the H30 α line masers are formed in a slightly larger annulus with a radius of 30 au. This is consistent with expectations for maser excitation in the presence of an electron density variation of approximately R {sup −4}. In addition, the H30 α and H26 α line masers arise from different parts in the wind. This difference is also expected from maser theory. The wind component of both masers exhibits line-of-sight velocities that closely follow a Keplerian law. This result provides strong evidence that the disk wind extracts significant angular momentum, thereby facilitating mass accretion in the young star.« less

Ultraviolet line diagnostics of accretion disk winds in cataclysmic variables

NASA Technical Reports Server (NTRS)

Vitello, Peter; Shlosman, Isaac

1993-01-01

The IUE data base is used to analyze the UV line shapes of the cataclysmic variables RW Sex, RW Tri, and V Sge. Observed lines are compared to synthetic line profiles computed using a model of rotating biconical winds from accretion disks. The wind model calculates the wind ionization structure self-consistently including photoionization from the disk and boundary layer and treats 3D line radiation transfer in the Sobolev approximation. It is found that winds from accretion disks provide a good fit for reasonable parameters to the observed UV lines which include the P Cygni profiles for low-inclination systems and pure emission at large inclination. Disk winds are preferable to spherical winds which originate on the white dwarf because they: (1) require a much lower ratio of mass-loss rate to accretion rate and are therefore more plausible energetically; (2) provide a natural source for a biconical distribution of mass outflow which produces strong scattering far above the disk leading to P Cygni profiles for low-inclination systems and pure line emission profiles at high inclination with the absence of eclipses in UV lines; and (3) produce rotation-broadened pure emission lines at high inclination.

UV line diagnostics of accretion disk winds in cataclysmic variables

NASA Technical Reports Server (NTRS)

Vitello, Peter; Shlosman, Isaac

1992-01-01

The IUE data base is used to analyze the UV line shapes of cataclysmic variables RW Sex, RW Tri, and V Sge. Observed lines are compared to synthetic line profiles computed using a model of rotating bi-conical winds from accretion disks. The wind model calculates the wind ionization structure self-consistently including photoionization from the disk and boundary layer and treats 3-D line radiation transfer in the Sobolev approximation. It is found that winds from accretion disks provide a good fit for reasonable parameters to the observed UV lines which include the P Cygni profiles for low inclination systems and pure emission at large inclination. Disk winds are preferable to spherical winds which originate on the white dwarf because they (1) require a much lower ratio of mass loss rate to accretion rate and are therefore more plausible energetically, (2) provide a natural source for a bi-conical distribution of mass outflow which produces strong scattering far above the disk leading to P Cygni profiles for low inclination systems, and pure line emission profiles at high inclination with the absence of eclipses in UV lines, and (3) produce rotation broadened pure emission lines at high inclination.

Herschel PACS Observations of 4–10 Myr Old Classical T Tauri Stars in Orion OB1

NASA Astrophysics Data System (ADS)

Maucó, Karina; Briceño, César; Calvet, Nuria; Hernández, Jesús; Ballesteros-Paredes, Javier; González, Omaira; Espaillat, Catherine C.; Li, Dan; Telesco, Charles M.; José Downes, Juan; Macías, Enrique; Qi, Chunhua; Michel, Raúl; D’Alessio, Paola; Ali, Babar

2018-05-01

We present Herschel PACS observations of eight classical T Tauri Stars in the ∼7–10 Myr old OB1a and the ∼4–5 Myr old OB1b Orion subassociations. Detailed modeling of the broadband spectral energy distributions, particularly the strong silicate emission at 10 μm, shows that these objects are (pre-)transitional disks with some amount of small optically thin dust inside their cavities, ranging from ∼4 to ∼90 au in size. We analyzed Spitzer IRS spectra for two objects in the sample: CVSO-107 and CVSO-109. The IRS spectrum of CVSO-107 indicates the presence of crystalline material inside its gap, while the silicate feature of CVSO-109 is characterized by a pristine profile produced by amorphous silicates; the mechanisms creating the optically thin dust seem to depend on disk local conditions. Using millimeter photometry, we estimated dust disk masses for CVSO-107 and CVSO-109 lower than the minimum mass of solids needed to form the planets in our solar system, which suggests that giant planet formation should be over in these disks. We speculate that the presence and maintenance of optically thick material in the inner regions of these pre-transitional disks might point to low-mass planet formation.

OT1_ipascucc_1: Understanding the Origin of Transition Disks via Disk Mass Measurements

NASA Astrophysics Data System (ADS)

Pascucci, I.

2010-07-01

Transition disks are a distinguished group of few Myr-old systems caught in the phase of dispersing their inner dust disk. Three different processes have been proposed to explain this inside-out clearing: grain growth, photoevaporation driven by the central star, and dynamical clearing by a forming giant planet. Which of these processes lead to a transition disk? Distinguishing between them requires the combined knowledge of stellar accretion rates and disk masses. We propose here to use 43.8 hours of PACS spectroscopy to detect the [OI] 63 micron emission line from a sample of 21 well-known transition disks with measured mass accretion rates. We will use this line, in combination with ancillary CO millimeter lines, to measure their gas disk mass. Because gas dominates the mass of protoplanetary disks our approach and choice of lines will enable us to trace the bulk of the disk mass that resides beyond tens of AU from young stars. Our program will quadruple the number of transition disks currently observed with Herschel in this setting and for which disk masses can be measured. We will then place the transition and the ~100 classical/non-transition disks of similar age (from the Herschel KP "Gas in Protoplanetary Systems") in the mass accretion rate-disk mass diagram with two main goals: 1) reveal which gaps have been created by grain growth, photoevaporation, or giant planet formation and 2) from the statistics, determine the main disk dispersal mechanism leading to a transition disk.

Zoom-in Simulations of Protoplanetary Disks Starting from GMC Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuffmeier, Michael; Haugbølle, Troels; Nordlund, Åke, E-mail: kueffmeier@nbi.ku.dk

2017-09-01

We investigate the formation of protoplanetary disks around nine solar-mass stars formed in the context of a (40 pc){sup 3} Giant Molecular Cloud model, using ramses adaptive mesh refinement simulations extending over a scale range of about 4 million, from an outer scale of 40 pc down to cell sizes of 2 au. Our most important result is that the accretion process is heterogeneous in multiple ways: in time, in space, and among protostars of otherwise similar mass. Accretion is heterogeneous in time, in the sense that accretion rates vary during the evolution, with generally decreasing profiles, whose slopes varymore » over a wide range, and where accretion can increase again if a protostar enters a region with increased density and low speed. Accretion is heterogeneous in space, because of the mass distribution, with mass approaching the accreting star–disk system in filaments and sheets. Finally, accretion is heterogeneous among stars, since the detailed conditions and dynamics in the neighborhood of each star can vary widely. We also investigate the sensitivity of disk formation to physical conditions and test their robustness by varying numerical parameters. We find that disk formation is robust even when choosing the least favorable sink particle parameters, and that turbulence cascading from larger scales is a decisive factor in disk formation. We also investigate the transport of angular momentum, finding that the net inward mechanical transport is compensated for mainly by an outward-directed magnetic transport, with a contribution from gravitational torques usually subordinate to the magnetic transport.« less

Massive stars, disks, and clustered star formation

NASA Astrophysics Data System (ADS)

Moeckel, Nickolas Barry

The formation of an isolated massive star is inherently more complex than the relatively well-understood collapse of an isolated, low-mass star. The dense, clustered environment where massive stars are predominantly found further complicates the picture, and suggests that interactions with other stars may play an important role in the early life of these objects. In this thesis we present the results of numerical hydrodynamic experiments investigating interactions between a massive protostar and its lower-mass cluster siblings. We explore the impact of these interactions on the orientation of disks and outflows, which are potentially observable indications of encounters during the formation of a star. We show that these encounters efficiently form eccentric binary systems, and in clusters similar to Orion they occur frequently enough to contribute to the high multiplicity of massive stars. We suggest that the massive protostar in Cepheus A is currently undergoing a series of interactions, and present simulations tailored to that system. We also apply the numerical techniques used in the massive star investigations to a much lower-mass regime, the formation of planetary systems around Solar- mass stars. We perform a small number of illustrative planet-planet scattering experiments, which have been used to explain the eccentricity distribution of extrasolar planets. We add the complication of a remnant gas disk, and show that this feature has the potential to stabilize the system against strong encounters between planets. We present preliminary simulations of Bondi-Hoyle accretion onto a protoplanetary disk, and consider the impact of the flow on the disk properties as well as the impact of the disk on the accretion flow.

Internal kinematics and dynamics of galaxies; Proceedings of the Symposium, Universitede Franche-Comte, Besancon, France, August 9-13, 1982

NASA Astrophysics Data System (ADS)

Athanassoula, E.

Various aspects of the internal kinematics and dynamics of galaxies are considered. The kinematics of the gas and the underlying mass distribution are discussed, including the systematics of H II rotation curves, H I velocity fields and rotation curves, the distribution of molecular clouds in spiral galaxies, gas at large radii, the implications for galactic mass models of vertical motion and the thickness of H I disks, and mass distribution and dark halos. The theory of spiral structure is addressed, along with conflicts and directions in spiral structure studies. Theories of warps are covered. Barred galaxies are treated, including their morphology, stellar kinematics, and dynamics, the stability of their disks, theoretical studies of their gas flows, and the formation of rings and lenses. Spheroidal systems are considered, including dynamics of early type galaxies, models of ellipticals and bulges, and interstellar matter in elliptical galaxies. Simulations and observational evidence for mergers are addressed, and the formation of galaxies and dynamics of globular cluster systems are examined. For individual items see A83-49202 to A83-49267

Modeling Dust Emission of HL Tau Disk Based on Planet-Disk Interactions

DOE PAGES

Jin, Sheng; Li, Shengtai; Isella, Andrea; ...

2016-02-09

In this paper, we use extensive global two-dimensional hydrodynamic disk gas+dust simulations with embedded planets, coupled with three-dimensional radiative transfer calculations, to model the dust ring and gap structures in the HL Tau protoplanetary disk observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We include the self-gravity of disk gas and dust components and make reasonable choices of disk parameters, assuming an already settled dust distribution and no planet migration. We can obtain quite adequate fits to the observed dust emission using three planets with masses of 0.35, 0.17, and 0.26 M Jup at 13.1, 33.0, and 68.6 AU, respectively.more » Finally, implications for the planet formation as well as the limitations of this scenario are discussed.« less

A near-infrared imaging survey of interacting galaxies - The disk-disk merger candidates subset

NASA Technical Reports Server (NTRS)

Stanford, S. A.; Bushouse, H. A.

1991-01-01

Near-infrared imaging obtained for systems believed to be advanced disk-disk mergers are presented and discussed. These systems were chosen from a sample of approximately 170 objects from the Arp Atlas of Peculiar Galaxies which have been imaged in the JHK bands as part of an investigation into the stellar component of interacting galaxies. Of the eight remnants which show optical signs of a disk-disk merger, the near-infrared surface brightness profiles are well-fitted by an r exp 1/4 law over all measured radii in four systems, and out to radii of about 3 kpc in three systems. These K band profiles indicate that most of the remnants in the sample either have finished or are in the process of relaxing into a mass distribution like that of normal elliptical galaxies.

Local heat transfer in turbine disk-cavities. I - Rotor and stator cooling with hub injection of coolant

NASA Astrophysics Data System (ADS)

Bunker, R. S.; Metzger, D. E.; Wittig, S.

1990-06-01

Detailed radial heat-transfer coefficient distributions applicable to the cooling of disk-cavity regions of gas turbines are obtained experimentally from local heat-transfer data on both the rotating and stationary surfaces of a parallel-geometry disk-cavity system. Attention is focused on the hub injection of a coolant over a wide range of parameters including disk rotational Reynolds numbers of 200,000 to 50,000, rotor/stator spacing-to-disk ratios of 0.025 to 0.15, and jet mass flow rates between 0.10 and 0.40 times the turbulent pumped flow rate of a free disk. It is shown that rotor heat transfer exhibits regions of impingement and rotational domination with a transition region between, while stator heat transfer displays flow reattachment and convection regions with an inner recirculation zone.

Properties of the Closest Young Binaries. I. DF Tau’s Unequal Circumstellar Disk Evolution

NASA Astrophysics Data System (ADS)

Allen, T. S.; Prato, L.; Wright-Garba, N.; Schaefer, G.; Biddle, L. I.; Skiff, B.; Avilez, I.; Muzzio, R.; Simon, M.

2017-08-01

We present high-resolution, spatially resolved, near-infrared spectroscopy and imaging of the two components of DF Tau, a young, low-mass, visual binary in the Taurus star-forming region. With these data, we provide a more precise orbital solution for the system, determine component spectral types, radial velocity, veiling and v\\sin I values, and construct individual spectral energy distributions. We estimate the masses of both stars to be ˜ 0.6 {M}⊙ . We find markedly different circumstellar properties for DF Tau A and B: evidence for a disk, such as near-infrared excess and accretion signatures, is clearly present for the primary, while it is absent for the secondary. Additionally, the v\\sin I and rotation period measurements show that the secondary is rotating significantly more rapidly than the primary. We interpret these results in the framework of disk-locking and argue that DF Tau A is an example of disk-modulated rotation in a young system. The DF Tau system raises fundamental questions about our assumptions of universal disk formation and evolution.

How Turbulence Can Set the Radial Distribution of Gas Giants Formed by Pebble Accretion

NASA Astrophysics Data System (ADS)

Morley Rosenthal, Mickey; Murray-Clay, Ruth

2018-04-01

I discuss how turbulence impacts the orbital separation at which the cores of gas giants can form via pebble accretion. While pebble accretion is extremely rapid for massive planets, I demonstrate that pebble accretion is inhibited at protoplanet masses, an effect which is strongly enhanced in a turbulent disk. Using these considerations I derive a “minimum” mass, past which pebble accretion proceeds on timescales less than the disk lifetime. By considering core formation where early growth to this minimum mass proceeds by gravitational focusing of planetesimals, I demonstrate that the the semi-major axes where gas giants can form are more restricted as the strength of the nebular turbulence increases — e.g. formation can only occur at distances < 30 AU for α > 10^-2. I also examine the implications of turbulence on the mass gas giants can reach before opening a substantial gap and halting growth. I find that while weak turbulence allows gas giants to form far out in the disk, the masses of these planets are substantially lower (< 1 Jupiter mass), which would preclude them from having been detected by the current generation of direct imaging surveys.

A Universal Angular Momentum Profile for Dark Matter Halos

NASA Astrophysics Data System (ADS)

Liao, Shihong; Chen, Jianxiong; Chu, M.-C.

2017-07-01

The angular momentum distribution in dark matter halos and galaxies is a key ingredient in understanding their formation. Specifically, the internal distribution of angular momenta is closely related to the formation of disk galaxies. In this article, we use halos identified from a high-resolution simulation, the Bolshoi simulation, to study the spatial distribution of specific angular momenta, j(r,θ ). We show that by stacking halos with similar masses to increase the signal-to-noise ratio, the profile can be fitted as a simple function, j{(r,θ )={j}s{\\sin }2{(θ /{θ }s)(r/{r}s)}2/(1+r/{r}s)}4, with three free parameters, {j}s,{r}s, and {θ }s. Specifically, j s correlates with the halo mass M vir as {j}s\\propto {M}{vir}2/3, r s has a weak dependence on the halo mass as {r}s\\propto {M}{vir}0.040, and {θ }s is independent of M vir. This profile agrees with that from a rigid shell model, though its origin is unclear. Our universal specific angular momentum profile j(r,θ ) is useful in modeling the angular momenta of halos. Furthermore, by using an empirical stellar mass-halo mass relation, we can infer the average angular momentum distribution of a dark matter halo. The specific angular momentum-stellar mass relation within a halo computed from our profile is shown to share a similar shape as that from the observed disk galaxies.

Water Delivery and Giant Impacts in the 'Grand Tack' Scenario

NASA Technical Reports Server (NTRS)

O'Brien, David P.; Walsh, Kevin J.; Morbidelli, Alessandro; Raymond, Sean N.; Mandell, Avi M.

2014-01-01

A new model for terrestrial planet formation has explored accretion in a truncated protoplanetary disk, and found that such a configuration is able to reproduce the distribution of mass among the planets in the Solar System, especially the Earth/Mars mass ratio, which earlier simulations have generally not been able to match. Walsh et al. tested a possible mechanism to truncate the disk-a two-stage, inward-then-outward migration of Jupiter and Saturn, as found in numerous hydrodynamical simulations of giant planet formation. In addition to truncating the disk and producing a more realistic Earth/Mars mass ratio, the migration of the giant planets also populates the asteroid belt with two distinct populations of bodies-the inner belt is filled by bodies originating inside of 3 AU, and the outer belt is filled with bodies originating from between and beyond the giant planets (which are hereafter referred to as 'primitive' bodies). One implication of the truncation mechanism proposed in Walsh et al. is the scattering of primitive planetesimals onto planet-crossing orbits during the formation of the planets. We find here that the planets will accrete on order 1-2% of their total mass from these bodies. For an assumed value of 10% for the water mass fraction of the primitive planetesimals, this model delivers a total amount of water comparable to that estimated to be on the Earth today. The radial distribution of the planetary masses and the dynamical excitation of their orbits are a good match to the observed system. However, we find that a truncated disk leads to formation timescales more rapid than suggested by radiometric chronometers. In particular, the last giant impact is typically earlier than 20 Myr, and a substantial amount of mass is accreted after that event. This is at odds with the dating of the Moon-forming impact and the estimated amount of mass accreted by Earth following that event. However, 5 of the 27 planets larger than half an Earth mass formed in all simulations do experience large late impacts and subsequent accretion consistent with those constraints.

The Angular Momentum Distribution and Baryon Content of Star-forming Galaxies at z ˜ 1-3

NASA Astrophysics Data System (ADS)

Burkert, A.; Förster Schreiber, N. M.; Genzel, R.; Lang, P.; Tacconi, L. J.; Wisnioski, E.; Wuyts, S.; Bandara, K.; Beifiori, A.; Bender, R.; Brammer, G.; Chan, J.; Davies, R.; Dekel, A.; Fabricius, M.; Fossati, M.; Kulkarni, S.; Lutz, D.; Mendel, J. T.; Momcheva, I.; Nelson, E. J.; Naab, T.; Renzini, A.; Saglia, R.; Sharples, R. M.; Sternberg, A.; Wilman, D.; Wuyts, E.

2016-08-01

We analyze the angular momenta of massive star-forming galaxies (SFGs) at the peak of the cosmic star formation epoch (z ˜ 0.8-2.6). Our sample of ˜360 log(M */M ⊙) ˜ 9.3-11.8 SFGs is mainly based on the KMOS3D and SINS/zC-SINF surveys of Hα kinematics, and collectively provides a representative subset of the massive star-forming population. The inferred halo scale angular momentum distribution is broadly consistent with that theoretically predicted for their dark matter halos, in terms of mean spin parameter < λ > ˜ 0.037 and its dispersion (σ logλ ˜ 0.2). Spin parameters correlate with the disk radial scale and with their stellar surface density, but do not depend significantly on halo mass, stellar mass, or redshift. Our data thus support the long-standing assumption that on average, even at high redshifts, the specific angular momentum of disk galaxies reflects that of their dark matter halos (j d = j DM). The lack of correlation between λ × (j d /j DM) and the nuclear stellar density Σ*(1 kpc) favors a scenario where disk-internal angular momentum redistribution leads to “compaction” inside massive high-redshift disks. For our sample, the inferred average stellar to dark matter mass ratio is ˜2%, consistent with abundance matching results. Including the molecular gas, the total baryonic disk to dark matter mass ratio is ˜5% for halos near 1012 M ⊙, which corresponds to 31% of the cosmologically available baryons, implying that high-redshift disks are strongly baryon dominated. Based on observations obtained at the Very Large Telescope of the European Southern Observatory, Paranal, Chile (ESO Programme IDs 075.A-0466, 076.A-0527, 079.A-0341, 080.A-0330, 080.A-0339, 080.A-0635, 081.B-0568, 081.A-0672, 082.A-0396, 183.A-0781, 087.A-0081, 088.A-0202, 088.A-0209, 091.A-0126, 092.A-0091, 093.A-0079, 094.A-0217, 095.A-0047, 096.A-0025).

From dust to light: a study of star formation in NGC2264

NASA Astrophysics Data System (ADS)

Teixeira, P. S.

2008-10-01

The goal of this dissertation is to characterize the star formation history of the young cluster NGC2264 using the unique observational capabilities of the Spitzer Space Telescope. The motivation to conduct this study stems from the fact that most stars are formed within clusters, so the formation and evolution of the latter will effect the stellar mass distribution in the field. Detailed observational studies of young stellar clusters are therefore crucial to provide necessary constraints for theoretical models of cloud and cluster formation and evolution. This study also addresses the evolution of circumstellar disks in NGC2264; empirical knowledge of protoplanetary disk evolution is required for the understanding of how planetary systems such as our own form. The first result obtained from this study was both completely new and unexpected. A dense region within NGC2264 was found to be teeming with bright 24 μm Class I protostars; these sources are embedded within dense submillimeter cores and are spatially distributed along dense filamentary fingers of gas and dust that radially converge on a B-type binary Class I source. This cluster of protostars was baptized the "Spokes cluster" and its analysis provided further insight into the role of thermal support during core formation, collapse and fragmentation. The nearest neighbor projected separation distribution of these Class I sources shows a characteristic spacing that is similar to the Jeans length for the region, indicating that the dusty filaments may have undergone thermal fragmentation. The submillimeter cores of the Spokes cluster were observed at 230GHz using the SubMillimeter Array (SMA) and the resulting high resolution (~1.3") continuum observations revealed a dense grouping of 7 Class 0 sources embedded within a particular core, D-MM1 (~20"x20"). The compact sources have masses ranging between 0.4M and 1.2M, and radii of ~600AU. The mean separation of the Class 0 sources within D-MM1 is considerably smaller than the characteristic spacing between the Class I sources in the larger Spokes cluster and is consistent with hierarchical thermal fragmentation of the dense molecular gas in this region. The results obtained by the study of the Spokes cluster show that the spatial substructuring of a cluster or subcluster is correlated with age, i.e., groupings of very young protostars have clearly more concentrated and substructured spatial distributions. The Spokes cluster could thus be one of several building blocks of NGC2264, and will likely expand and disperse its members through the surrounding region, adding to the rest of NGC2264's stellar population.To further explore this scenario, I identified Pre-Main Sequence (PMS) disk bearing sources in the whole region of NGC2264, as surveyed by InfraRed Array Camera (IRAC) analyzing both their spatial distributions and ages. Of the 1404 sources detected in all four IRAC bands, 116 sources were found to have anemic IRAC disks and 217 sources were found to have thick IRAC disks; the disk fraction was calculated to be 37.5%±6.3% and found to be a function of spectral type, increasing for later type sources. I identified 4 candidate sources with transition disks (disks with inner holes), as well as 6 sources with anemic inner disks and thick outer disks that could be the immediate precursors of transition disks. This is a relevant result for it suggests planet formation may be occurring in the inner disk at very early ages. I found that the spatial distribution of the disk-bearing sources was a function of both disk type and amount of reddening. This spatial analysis enabled the identification of three groups of sources, namely, (i) embedded (AV> 3 magnitudes) sources with thick disks, (ii) unembedded sources with thick disks, and (iii) sources with anemic disks. The first group was found to have a median age of 1 Myr and its spatial distribution is highly concentrated and substructured. The second group, (ii), has a median age of 2 Myr and its spatial distribution is less concentrated and substructured than group (i), but more than the group of sources with anemic disks - the spatial distribution of this third group (age ~ 2 Myr) is not substructured and is more distributed, showing no particular peak or concentration. The star formation history of NGC2264 appears to be as follows: the northern region appears to have undergone the first epoch or episode of star formation, while the second epoch is currently occurring in the center (Spokes cluster) and south (near Allen's source). Status: RO

Mapping the Asymmetric Thick Disk. II. Distance, Size, and Mass of the Hercules Thick Disk Cloud

NASA Astrophysics Data System (ADS)

Larsen, Jeffrey A.; Cabanela, Juan E.; Humphreys, Roberta M.

2011-04-01

The Hercules Thick Disk Cloud was initially discovered as an excess in the number of faint blue stars between Quadrants 1 and 4 of the Galaxy. The origin of the Cloud could be an interaction with the disk bar, a triaxial Thick Disk, or a merger remnant or stream. To better map the spatial extent of the Cloud along the line of sight, we have obtained multi-color UBVR photometry for 1.2 million stars in 63 fields each of approximately 1 deg2. Our analysis of the fields beyond the apparent boundaries of the excess has already ruled out a triaxial Thick Disk as a likely explanation. In this paper, we present our results for the star counts over all of our fields, determine the spatial extent of the overdensity across and along the line of sight, and estimate the size and mass of the Cloud. Using photometric parallaxes, the stars responsible for the excess are between 1 and 6 kpc from the Sun, 0.5-4 kpc above the Galactic plane, and extend approximately 3-4 kpc across our line of sight. The Cloud is thus a major substructure in the Galaxy. The distribution of the excess along our sight lines corresponds with the density contours of the bar in the Disk, and its most distant stars are directly over the bar. We also see through the Cloud to its far side. Over the entire 500 deg2 of the sky containing the Cloud, we estimate more than 5.6 million stars and 1.9 million solar masses of material. If the overdensity is associated with the bar, it would exceed 1.4 billion stars and more than 50 million solar masses. Finally, we argue that the Hercules-Aquila Cloud is actually the Hercules Thick Disk Cloud.

MAPPING THE ASYMMETRIC THICK DISK. II. DISTANCE, SIZE, AND MASS OF THE HERCULES THICK DISK CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larsen, Jeffrey A.; Cabanela, Juan E.; Humphreys, Roberta M., E-mail: larsen@usna.edu, E-mail: cabanela@mnstate.edu, E-mail: roberta@umn.edu

2011-04-15

The Hercules Thick Disk Cloud was initially discovered as an excess in the number of faint blue stars between Quadrants 1 and 4 of the Galaxy. The origin of the Cloud could be an interaction with the disk bar, a triaxial Thick Disk, or a merger remnant or stream. To better map the spatial extent of the Cloud along the line of sight, we have obtained multi-color UBVR photometry for 1.2 million stars in 63 fields each of approximately 1 deg{sup 2}. Our analysis of the fields beyond the apparent boundaries of the excess has already ruled out a triaxialmore » Thick Disk as a likely explanation. In this paper, we present our results for the star counts over all of our fields, determine the spatial extent of the overdensity across and along the line of sight, and estimate the size and mass of the Cloud. Using photometric parallaxes, the stars responsible for the excess are between 1 and 6 kpc from the Sun, 0.5-4 kpc above the Galactic plane, and extend approximately 3-4 kpc across our line of sight. The Cloud is thus a major substructure in the Galaxy. The distribution of the excess along our sight lines corresponds with the density contours of the bar in the Disk, and its most distant stars are directly over the bar. We also see through the Cloud to its far side. Over the entire 500 deg{sup 2} of the sky containing the Cloud, we estimate more than 5.6 million stars and 1.9 million solar masses of material. If the overdensity is associated with the bar, it would exceed 1.4 billion stars and more than 50 million solar masses. Finally, we argue that the Hercules-Aquila Cloud is actually the Hercules Thick Disk Cloud.« less

Taking Measure of the Milky Way

NASA Technical Reports Server (NTRS)

Majewski, Steven R.; Bahcall, John N.; Geisler, Douglas; Gieren, Wolfgang; Grebel, Eva; Grillmair, Carl; Irwin, Michael; Johnston, Kathryn V.; Patterson, Richard J.; Reid, Neill I.

2004-01-01

We intend to use SIM to make definitive measurements of fundamental structural and dynamical parameters of the Milky Way. The important niche in dynamical parameter space afforded by SIM can be exploited to resolve, with unprecedented precision, a number of classical problems of Galactic astronomy. In addition, we have developed new tests of the Galactic mass distribution specifically designed for data with the special properties of SIM products. Our proposed suite of experiments will utilize the SIM Astrometric Grid as well as complementary observations of star clusters and other strategically-selected, distant "test particles" for a definitive characterization of the major components (bulge, disk, halo, satellite system) of the Milky Way. Specifically, our goals will be: 1) The determination of two fundamental parameters that play a central role in virtually every problem in Galactic astronomy, namely (a) the solar distance to the center of the Milky Way, R(sub 0); (b) the solar angular velocity around the Galactic: center, omega(sub 0). 2) The measurement of fundamental dynamical properties of the Milky Way, among them (a) the pattern speed of the central bar (b) the rotation field and velocity-dispersion tensor in the disk (c) the kinematics (mean rotational velocity and velocity dispersion tensor) of the halo as a function of position 3. The definition of the mass distribution of the Galaxy, which is dominated by the presence of dark matter. We intend to measure (a) the relative contribution of the disk and halo to the gravitational potential (b) the local volume and surface mass density of the disk (c) the shape, mass and extent of the dark halo of the Milky Way out to 250 kpc.

Jefferson Lab Mass Storage and File Replication Services

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ian Bird; Ying Chen; Bryan Hess

Jefferson Lab has implemented a scalable, distributed, high performance mass storage system - JASMine. The system is entirely implemented in Java, provides access to robotic tape storage and includes disk cache and stage manager components. The disk manager subsystem may be used independently to manage stand-alone disk pools. The system includes a scheduler to provide policy-based access to the storage systems. Security is provided by pluggable authentication modules and is implemented at the network socket level. The tape and disk cache systems have well defined interfaces in order to provide integration with grid-based services. The system is in production andmore » being used to archive 1 TB per day from the experiments, and currently moves over 2 TB per day total. This paper will describe the architecture of JASMine; discuss the rationale for building the system, and present a transparent 3rd party file replication service to move data to collaborating institutes using JASMine, XM L, and servlet technology interfacing to grid-based file transfer mechanisms.« less

IONIZATION AND DUST CHARGING IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivlev, A. V.; Caselli, P.; Akimkin, V. V., E-mail: ivlev@mpe.mpg.de

2016-12-10

Ionization–recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance ofmore » the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.« less

THE STRUCTURE OF PRE-TRANSITIONAL PROTOPLANETARY DISKS. II. AZIMUTHAL ASYMMETRIES, DIFFERENT RADIAL DISTRIBUTIONS OF LARGE AND SMALL DUST GRAINS IN PDS 70 {sup ,}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hashimoto, J.; Wisniewski, J.; Tsukagoshi, T.

The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-μm size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report Submillimeter Array observations of the dust continuum atmore » 1.3 mm and {sup 12}CO J = 2 → 1 line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS 70. PDS 70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of ∼65 AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of ∼80 AU at 1.3 mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap radii of the disk around PDS 70 are potentially formed by several (unseen) accreting planets inducing dust filtration.« less

The Structure of Pre-Transitional Protoplanetary Disks. II Azimuthal Asymmetries, Different Radial Distributions of Large and Small Dust Grains in PDS 70

NASA Technical Reports Server (NTRS)

Hashimoto, J.; Tsukagoshi, T.; Brown, J. M.; Dong, R.; Muto, T.; Zhu, Z.; Wisniewski, J.; Ohashi, N.; Kudo, T.; Kusakabe, N.;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, Stefan; Espaillat, Catherine; Wilner, David J.

Pre-transitional disks are protoplanetary disks with a gapped disk structure, potentially indicating the presence of young planets in these systems. In order to explore the structure of these objects and their gap-opening mechanism, we observed the pre-transitional disk V1247 Orionis using the Very Large Telescope Interferometer, the Keck Interferometer, Keck-II, Gemini South, and IRTF. This allows us to spatially resolve the AU-scale disk structure from near- to mid-infrared wavelengths (1.5-13 {mu}m), tracing material at different temperatures and over a wide range of stellocentric radii. Our observations reveal a narrow, optically thick inner-disk component (located at 0.18 AU from the star)more » that is separated from the optically thick outer disk (radii {approx}> 46 AU), providing unambiguous evidence for the existence of a gap in this pre-transitional disk. Surprisingly, we find that the gap region is filled with significant amounts of optically thin material with a carbon-dominated dust mineralogy. The presence of this optically thin gap material cannot be deduced solely from the spectral energy distribution, yet it is the dominant contributor at mid-infrared wavelengths. Furthermore, using Keck/NIRC2 aperture masking observations in the H, K', and L' bands, we detect asymmetries in the brightness distribution on scales of {approx}15-40 AU, i.e., within the gap region. The detected asymmetries are highly significant, yet their amplitude and direction changes with wavelength, which is not consistent with a companion interpretation but indicates an inhomogeneous distribution of the gap material. We interpret this as strong evidence for the presence of complex density structures, possibly reflecting the dynamical interaction of the disk material with sub-stellar mass bodies that are responsible for the gap clearing.« less

CSI 2264: Investigating rotation and its connection with disk accretion in the young open cluster NGC 2264

NASA Astrophysics Data System (ADS)

Venuti, L.; Bouvier, J.; Cody, A. M.; Stauffer, J. R.; Micela, G.; Rebull, L. M.; Alencar, S. H. P.; Sousa, A. P.; Hillenbrand, L. A.; Flaccomio, E.

2017-03-01

Context. The low spin rates measured for solar-type stars at an age of a few Myr ( 10% of the break-up velocity) indicate that some mechanism of angular momentum regulation must be at play in the early pre-main sequence. This may be associated with magnetospheric accretion and star-disk interaction, as suggested by observations that disk-bearing objects (CTTS) are slower rotators than diskless sources (WTTS) in young star clusters. Aims: We characterize the rotation properties for members of the star-forming region NGC 2264 ( 3 Myr) as a function of mass, and investigate the accretion-rotation connection at an age where about 50% of the stars have already lost their disks. Methods: We examined a sample of 500 cluster members (40% with disks, 60% without disks), distributed in mass between 0.15 and 2 M⊙, whose photometric variations were monitored in the optical for 38 consecutive days with the CoRoT space observatory. Light curves were analyzed for periodicity using three different techniques: the Lomb-Scargle periodogram, the autocorrelation function and the string-length method. Periods were searched in the range between 0.17 days (I.e., 4 h, twice the data sampling adopted) and 19 days (half the total time span). Period detections were confirmed using a variety of statistical tools (false alarm probability, Q-statistics), as well as visual inspection of the direct and phase-folded light curves. Results: About 62% of sources in our sample were found to be periodic; the period detection rate is 70% among WTTS and 58% among CTTS. The vast majority of periodic sources exhibit rotational periods shorter than 13 d. The period distribution obtained for the cluster consists of a smooth distribution centered around P = 5.2 d with two peaks, located respectively at P = 1-2 d and at P = 3-4 d. A separate analysis of the rotation properties for CTTS and WTTS indicates that the P = 1-2 d peak is associated with the latter, while both groups contribute to the P = 3-4 d peak. The comparison between CTTS and WTTS supports the idea of a rotation-accretion connection: their respective rotational properties are statistically different, and CTTS rotate on average more slowly than WTTS. We also observe that CTTS with the strongest signatures of accretion (largest UV flux excesses) tend to exhibit slow rotation rates; a clear dearth of fast rotators with strong accretion signatures emerges from our sample. This connection between rotation properties and accretion traced via UV excess measurements is consistent with earlier findings, revealed by IR excess measurements, that fast rotators in young star clusters are typically devoid of dusty disks. On the other hand, WTTS span the whole range of rotation periods detected across the cluster. We also investigated whether the rotation properties we measure for NGC 2264 members show any dependence on stellar mass or on stellar inner structure (radiative core mass to total mass ratio). No statistically significant correlation emerged from our analysis regarding the second issue; however, we did infer some evidence of a period-mass trend, lower-mass stars spinning on average faster than higher-mass stars, although our data did not allow us to assess the statistical significance of such a trend beyond the 10% level. Conclusions: This study confirms that disks impact the rotational properties of young stars and influence their rotational evolution. The idea of disk-locking, recently tested in numerical models of the rotational evolution of young stars between 1 and 12 Myr, may be consistent with the pictures of rotation and rotation-accretion connection that we observe for the NGC 2264 cluster. However, the origin of the several substructures that we observe in the period distribution, notably the multiple peaks, deserves further investigation. Based on observations obtained with the CoRoT space telescope, and with the wide-field imager MegaCam at the Canada-France-Hawaii Telescope (CFHT).Table F.1 is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A23

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kudritzki, R. P.; Ho, I.-T.; Bresolin, F.

Low-resolution (4.5–5 Å) spectra of 58 blue supergiant stars distributed over the disk of the Magellanic spiral galaxy NGC 55 in the Sculptor group are analyzed by means of non-LTE techniques to determine stellar temperatures, gravities, and metallicities (from iron peak and α -elements). A metallicity gradient of −0.22 ± 0.06 dex/ R {sub 25} is detected. The central metallicity on a logarithmic scale relative to the Sun is [ Z ] = −0.37 ± 0.03. A chemical evolution model using the observed distribution of column densities of the stellar and interstellar medium gas mass reproduces the observed metallicity distributionmore » well and reveals a recent history of strong galactic mass accretion and wind outflows with accretion and mass-loss rates of the order of the star formation rate. There is an indication of spatial inhomogeneity in metallicity. In addition, the relatively high central metallicity of the disk confirms that two extraplanar metal-poor H ii regions detected in previous work 1.13 to 2.22 kpc above the galactic plane are ionized by massive stars formed in situ outside the disk. For a subsample of supergiants, for which Hubble Space Telescope photometry is available, the flux-weighted gravity–luminosity relationship is used to determine a distance modulus of 26.85 ± 0.10 mag.« less

The Late-Time Formation and Dynamical Signatures of Small Planets

NASA Astrophysics Data System (ADS)

Lee, Eve Jihyun

The riddle posed by super-Earths is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. In this thesis, I demonstrate that this puzzle is solved if super-Earths formed late, in the inner cavities of transitional disks. Super-puffs present the inverse problem of being too voluminous for their small masses. I show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside 1 AU, and then migrate in just after super-Earths appear. Super-Earths and Earth-sized planets around FGKM dwarfs are evenly distributed in log orbital period down to 10 days, but dwindle in number at shorter periods. I demonstrate that both the break at 10 days and the slope of the occurrence rate down to 1 day can be reproduced if planets form in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by asynchronous equilibrium tides raised on their stars. Small planets may remain ubiquitous out to large orbital distances. I demonstrate that the variety of debris disk morphologies revealed by scattered light images can be explained by viewing an eccentric disk, secularly forced by a planet of just a few Earth masses, from different observing angles. The farthest reaches of planetary systems may be perturbed by eccentric super-Earths.

DUST DYNAMICS IN PROTOPLANETARY DISK WINDS DRIVEN BY MAGNETOROTATIONAL TURBULENCE: A MECHANISM FOR FLOATING DUST GRAINS WITH CHARACTERISTIC SIZES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyake, Tomoya; Suzuki, Takeru K.; Inutsuka, Shu-ichiro, E-mail: miyake.tomoya@e.mbox.nagoya-u.ac.jp, E-mail: stakeru@nagoya-u.jp

We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. For the minimum mass solar nebula at 1 au, dust grains with sizemore » of 25–45 μm float around 4 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects.« less

High-resolution observations of IRAS 08544-4431. Detection of a disk orbiting a post-AGB star and of a slow disk wind

NASA Astrophysics Data System (ADS)

Bujarrabal, V.; Castro-Carrizo, A.; Winckel, H. Van; Alcolea, J.; Contreras, C. Sánchez; Santander-García, M.; Hillen, M.

2018-06-01

Context. Aims: In order to study the effects of rotating disks in the post-asymptotic giant branch (post-AGB) evolution, we observe a class of binary post-AGB stars that seem to be systematically surrounded by equatorial disks and slow outflows. Although the rotating dynamics had only been well identified in three cases, the study of such structures is thought to be fundamental to the understanding of the formation of disks in various phases of the late evolution of binary stars and the ejection of planetary nebulae from evolved stars. Methods: We present ALMA maps of 12CO and 13CO J = 3-2 lines in the source IRAS 08544-4431, which belongs to the above mentioned class of objects. We analyzed the data by means of nebula models, which account for the expectedly composite source and can reproduce the data. From our modeling, we estimated the main nebula parameters, including the structure and dynamics and the density and temperature distributions. We discuss the uncertainties of the derived values and, in particular, their dependence on the distance. Results: Our observations reveal the presence of an equatorial disk in rotation; a low-velocity outflow is also found, probably formed of gas expelled from the disk. The main characteristics of our observations and modeling of IRAS 08544-4431 are similar to those of better studied objects, confirming our interpretation. The disk rotation indicates a total central mass of about 1.8 M⊙, for a distance of 1100 pc. The disk is found to be relatively extended and has a typical diameter of 4 × 1016 cm. The total nebular mass is 2 × 10-2 M⊙, of which 90% corresponds to the disk. Assuming that the outflow is due to mass loss from the disk, we derive a disk lifetime of 10 000 yr. The disk angular momentum is found to be comparable to that of the binary system at present. Assuming that the disk angular momentum was transferred from the binary system, as expected, the high values of the disk angular momentum in this and other similar disks suggest that the size of the stellar orbits has significantly decreased as a consequence of disk formation.

Resolved Millimeter Observations of the HR 8799 Debris Disk

NASA Astrophysics Data System (ADS)

Wilner, David J.; MacGregor, Meredith A.; Andrews, Sean M.; Hughes, A. Meredith; Matthews, Brenda; Su, Kate

2018-03-01

We present 1.3 mm observations of the debris disk surrounding the HR 8799 multi-planet system from the Submillimeter Array to complement archival ALMA observations that spatially filtered away the bulk of the emission. The image morphology at 3.″8 (150 au) resolution indicates an optically thin circumstellar belt, which we associate with a population of dust-producing planetesimals within the debris disk. The interferometric visibilities are fit well by an axisymmetric radial power-law model characterized by a broad width, ΔR/R ≳ 1. The belt inclination and orientation parameters are consistent with the planet orbital parameters within the mutual uncertainties. The models constrain the radial location of the inner edge of the belt to {R}in}={104}-12+8 au. In a simple scenario where the chaotic zone of the outermost planet b truncates the planetesimal distribution, this inner edge location translates into a constraint on the planet b mass of {M}pl}={5.8}-3.1+7.9 M Jup. This mass estimate is consistent with infrared observations of the planet luminosity and standard hot-start evolutionary models, with the uncertainties allowing for a range of initial conditions. We also present new 9 mm observations of the debris disk from the Very Large Array and determine a millimeter spectral index of 2.41 ± 0.17. This value is typical of debris disks and indicates a power-law index of the grain size distribution q = 3.27 ± 0.10, close to predictions for a classical collisional cascade.

Period Ratio Distribution of Near-Resonant Planets Indicates Planetesimal Scattering

NASA Astrophysics Data System (ADS)

Chatterjee, Sourav; Krantzler, Seth O.; Ford, Eric B.

2016-10-01

An intriguing trend among it Kepler's multi-planet systems is an overabundance of planet pairs with period ratios just wide of mean motion resonances (MMR) and a dearth of systems just narrow of them. In a recently published paper Chatterjee & Ford (2015; henceforth CF15) has proposed that gas-disk migration traps planets in a MMR. After gas dispersal, orbits of these trapped planets are altered through interaction with a residual planetesimal disk. They found that for massive enough disks planet-planetesimal disk interactions can break resonances and naturally create moderate to large positive offsets from the initial period ratio for large ranges of planetesimal disk and planet properties. Divergence from resonance only happens if the mass of planetesimals that interact with the planets is at least a few percent of the total planet mass. This threshold, above which resonances are broken and the offset from resonances can grow, naturally explains why the asymmetric large offsets were not seen in more massive planet pairs found via past radial velocity surveys. In this article we will highlight some of the key findings of CF15. In addition, we report preliminary results from an extension of this study, that investigates the effects of planet-planetesimal disk interactions on initially non-resonant planet pairs. We find that planetesimal scattering typically increases period ratios of non-resonant planets. If the initial period ratios are below and in proximity of a resonance, under certain conditions, this increment in period ratios can create a deficit of systems with period ratios just below the exact integer corresponding to the MMR and an excess just above. From an initially uniform distribution of period ratios just below a 2:1 MMR, planetesimal interactions can create an asymmetric distribution across this MMR similar to what is observed for the kepler planet pairs.

The Mass Dependence between Protoplanetary Disks and their Stellar Hosts

NASA Astrophysics Data System (ADS)

Andrews, Sean M.; Rosenfeld, Katherine A.; Kraus, Adam L.; Wilner, David J.

2013-07-01

We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new "snapshot" λ = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L mm), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3σ depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L mm and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L mm and the disk mass, Md , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of ~25 mJy for 1 M ⊙ hosts and a power-law scaling L_mm ∝ M_{\\ast}^{1.5-2.0}. We suggest that a reasonable treatment of dust temperature in the conversion from L mm to Md favors an inherently linear Md vpropM * scaling, with a typical disk-to-star mass ratio of ~0.2%-0.6%. The measured rms dispersion around this regression curve is ±0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of ~40 on the inferred Md (or L mm) at any given host mass. We argue that this relationship between Md and M * likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the exoplanet population, and provides some basic support for the core accretion model for planet formation. Moreover, we caution that the effects of incompleteness and selection bias must be considered in comparative studies of disk evolution, and illustrate that fact with statistical comparisons of f(L mm) between the Taurus catalog presented here and incomplete subsamples in the Ophiuchus, IC 348, and Upper Sco young clusters.

Probing active galactic nuclei with H2O megamasers.

PubMed

Moran, J; Greenhill, L; Herrnstein, J; Diamond, P; Miyoshi, M; Nakai, N; Inque, M

1995-12-05

We describe the characteristics of the rapidly rotating molecular disk in the nucleus of the mildly active galaxy NGC4258. The morphology and kinematics of the disk are delineated by the point-like watervapor emission sources at 1.35-cm wavelength. High angular resolution [200 microas where as is arcsec, corresponding to 0.006 parsec (pc) at 6.4 million pc] and high spectral resolution (0.2 km.s-1 or nu/Deltanu = 1.4 x 10(6)) with the Very-Long-Baseline Array allow precise definition of the disk. The disk is very thin, but slightly warped, and is viewed nearly edge-on. The masers show that the disk is in nearly perfect Keplerian rotation within the observable range of radii of 0.13-0.26 pc. The approximately random deviations from the Keplerian rotation curve among the high-velocity masers are approximately 3.5 km.s-1 (rms). These deviations may be due to the masers lying off the midline by about +/-4 degrees or variations in the inclination of the disk by +/-4 degrees. Lack of systematic deviations indicates that the disk has a mass of <4 x 10(6) solar mass (M[symbol: see text]). The gravitational binding mass is 3.5 x 10(7) M[symbol: see text], which must lie within the inner radius of the disk and requires that the mass density be >4 x 10(9) M[symbol: see text].pc-3. If the central mass were in the form of a star cluster with a density distribution such as a Plummer model, then the central mass density would be 4 x 10(12) M[symbol: see text].pc-3. The lifetime of such a cluster would be short with respect to the age of the galaxy [Maoz, E. (1995) Astrophys. J. Lett. 447, L91-L94]. Therefore, the central mass may be a black hole. The disk as traced by the systemic velocity features is unresolved in the vertical direction, indicating that its scale height is <0.0003 pc (hence the ratio of thickness to radius, H/R, is <0.0025). For a disk in hydrostatic equilibrium the quadrature sum of the sound speed and Alfven velocity is <2.5 km.s-1, so that the temperature of the disk must be <1000 K and the toroidal magnetic field component must be <250 mG. If the molecular mass density in the disk is 10(10) cm-3, then the disk mass is approximately 10(4) M[symbol: see text], and the disk is marginally stable as defined by the Toomre stability parameter Q (Q = 6 at the inner edge and 1 at the outer edge). The inward drift velocity is predicted to be <0.007 km.s-1, for a viscosity parameter of 0.1, and the accretion rate is <7 x 10(-5) M[symbol: see text].yr-1. At this value the accretion would be sufficient to power the nuclear x-ray source of 4 x 10(40) ergs-1 (1 erg = 0.1 microJ). The volume of individual maser components may be as large as 10(46) cm3, based on the velocity gradients, which is sufficient to supply the observed luminosity. The pump power undoubtedly comes from the nucleus, perhaps in the form of x-rays. The warp may allow the pump radiation to penetrate the disk obliquely [Neufeld, D. A. & Maloney, P. R. (1995) Astrophys. J. Lett. 447, L17-L19]. A total of 15 H2O megamasers have been identified out of >250 galaxies searched. Galaxy NGC4258 may be the only case where conditions are optimal to reveal a well-defined nuclear disk. Future measurement of proper motions and accelerations for NGC4258 will yield an accurate distance and a more precise definition of the dynamics of the disk

The Inner Disk of M31 is Full of Cold Molecular Gas

NASA Astrophysics Data System (ADS)

Allen, R. J.; Lequeux, J.; Loinard, L.

1994-12-01

The Andromeda galaxy is conspicuously devoid of the classical tracers of star formation inside a radius of about 8 kpc. This ``hole'' shows up in the distribution of HI, of HII regions, and of CO. The IRAS infrared and radio continuum also show similar ``donut''-shaped distributions, although they have additional nuclear sources. The conclusion that the inner disk of M31 contains little or no interstellar gas is, however, quite incorrect. We have carried out a sensitive CO survey with the 30m IRAM millimeter radio telescope at more than two dozen randomly-chosen points in the ``hole'' of M31, and find faint CO emission characteristic of giant molecular clouds at more than half of them, often (but not always) coincident with known dust patches. The CO is more than a factor of 10 under-luminous when compared to Galactic GMC's, a consequence of its very low excitation temperature. Estimates of the mass surface density of molecular gas can be made using the virial theorem, leading to values of about 10 solar masses per square parsec averaged over the inner disk. We conclude that THE ``HOLE'' IN M31 IS FULL OF COLD MOLECULAR GAS. The implications of this for our current views of the distribution of the ISM in galaxies will be discussed.

Towards a Global Evolutionary Model of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bai, Xue-Ning

2016-04-01

A global picture of the evolution of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-UV (FUV) radiation), wind kinematics is also affected by the FUV penetration depth and disk geometry. For a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. Fractional wind mass loss increases with increasing disk lifetime. Significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation.

Tidal Barrier and the Asymptotic Mass of Proto-Gas Giant Planets

NASA Astrophysics Data System (ADS)

Dobbs-Dixon, Ian; Li, Shu Lin; Lin, D. N. C.

2007-05-01

According to the conventional sequential accretion scenario, observed extrasolar planets acquired their current masses via efficient gas accretion onto super-Earth cores with accretion timescales that rapidly increase with mass. Gas accretion in weak-line T Tauri disks may be quenched by global depletion of gas, but such a mechanism is unlikely to have stalled the growth in planetary systems that contain relatively low-mass, close-in planets together with more massive, longer period companions. Here, we suggest a potential solution for this conundrum. In general, supersonic infall of surrounding gas onto a protoplanet is only possible interior to both its Bondi and Roche radii. Above the critical mass where the Roche and Bondi radii are equal to the disk thickness, the protoplanet's tidal perturbation induces the formation of a gap. However, despite continued diffusion into the gap, the azimuthal flux across the protoplanet's Roche lobe will be quenched. Using two different schemes, we present the results of numerical simulations and analysis to show that the accretion rate increases rapidly with the ratio of the protoplanet's Roche to Bondi radii or equivalently to the disk thickness. Gas accretion is quenched, yielding relatively low protoplanetary masses, in regions with low aspect ratios. This becomes important for determining the gas giant planet's mass function, the distribution of their masses within multiple-planet systems, and for suppressing the emergence of gas giants around low-mass stars. Finally, we find that accretion rates onto protoplanets declines gradually on a characteristic timescale of a few Myr, during which the protracted accretion timescale onto circumplanetary disks may allow for the formation and retention of regular satellites.

The DiskMass Survey. VII. The distribution of luminous and dark matter in spiral galaxies

NASA Astrophysics Data System (ADS)

Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Bershady, Matthew A.; Andersen, David R.; Swaters, Rob A.

2013-09-01

We present dynamically-determined rotation-curve mass decompositions of 30 spiral galaxies, which were carried out to test the maximum-disk hypothesis and to quantify properties of their dark-matter halos. We used measured vertical velocity dispersions of the disk stars to calculate dynamical mass surface densities (Σdyn). By subtracting our observed atomic and inferred molecular gas mass surface densities from Σdyn, we derived the stellar mass surface densities (Σ∗), and thus have absolute measurements of all dominant baryonic components of the galaxies. Using K-band surface brightness profiles (IK), we calculated the K-band mass-to-light ratio of the stellar disks (Υ∗ = Σ∗/IK) and adopted the radial mean (overline{mls}) for each galaxy to extrapolate Σ∗ beyond the outermost kinematic measurement. The derived overline{mls} of individual galaxies are consistent with all galaxies in the sample having equal Υ∗. We find a sample average and scatter of mlab overline{mls}mrab = 0.31 ± 0.07. Rotation curves of the baryonic components were calculated from their deprojected mass surface densities. These were used with circular-speed measurements to derive the structural parameters of the dark-matter halos, modeled as either a pseudo-isothermal sphere (pISO) or a Navarro-Frenk-White (NFW) halo. In addition to our dynamically determined mass decompositions, we also performed alternative rotation-curve decompositions by adopting the traditional maximum-disk hypothesis. However, the galaxies in our sample are submaximal, such that at 2.2 disk scale lengths (hR) the ratios between the baryonic and total rotation curves (Fb2.2hR) are less than 0.75. We find this ratio to be nearly constant between 1-6hR within individual galaxies. We find a sample average and scatter of mlab Fb2.2hRmrab = 0.57 ± 0.07, with trends of larger Fb2.2hR for more luminous and higher-surface-brightness galaxies. To enforce these being maximal, we need to scale Υ∗ by a factor 3.6 on average. In general, the dark-matter rotation curves are marginally better fit by a pISO than by an NFW halo. For the nominal-Υ∗ (submaximal) case, we find that the derived NFW-halo parameters have values consistent with ΛCDM N-body simulations, suggesting that the baryonic matter in our sample of galaxies has only had a minor effect on the dark-matter distribution. In contrast, maximum-Υ∗ decompositions yield halo-concentration parameters that are too low compared to the ΛCDM simulations. Appendix is available in electronic form at http://www.aanda.org

The Surface Density Distribution in the Solar Nebula

NASA Technical Reports Server (NTRS)

Davis, Sanford S.

2004-01-01

The commonly used minimum mass power law representation of the pre-solar nebula is reanalyzed using a new cumulative-mass-model. This model predicts a smoother surface density approximation compared with methods based on direct computation of surface density. The density is quantified using two independent analytical formulations. First, a best-fit transcendental function is applied directly to the basic planetary data. Next a solution to the time-dependent disk evolution equation is parametrically adapted to the solar nebula data. The latter model is shown to be a good approximation to the finite-size early Solar Nebula, and by extension to other extra solar protoplanetary disks.

Morphology and kinematics of orbital components in CALIFA galaxies across the Hubble sequence

NASA Astrophysics Data System (ADS)

Zhu, Ling; van de Ven, Glenn; Méndez-Abreu, Jairo; Obreja, Aura

2018-06-01

Based on the stellar orbit distribution derived from orbit-superposition Schwarzschild models, we decompose each of 250 representative present-day galaxies into four orbital components: cold with strong rotation, warm with weak rotation, hot with dominant random motion and counter-rotating (CR). We rebuild the surface brightness (Σ) of each orbital component and we present in figures and tables a quantification of their morphologies using the Sersic index n, concentration C = log {(Σ _{0.1R_e}/Σ _{R_e})} and intrinsic flattening qRe and qRmax, with Re the half-light-radius and Rmax the CALIFA data coverage. We find that: (1) kinematic hotter components are generally more concentrated and rounder than colder components, and (2) all components become more concentrated and thicker/rounder in more massive galaxies; they change from disk-like in low mass late-type galaxies to bulge-like in high-mass early type galaxies. Our findings suggest that Sersic n is not a good discriminator between rotating bulges and non-rotating bulges. The luminosity fraction of cold orbits fcold is well correlated with the photometrically-decomposed disk fraction fdisk as f_{cold} = 0.14 + 0.23f_{disk}. Similarly, the hot orbit fraction fhot is correlated with the bulge fraction fbulge as f_{hot} = 0.19 + 0.31f_{bulge}. The warm orbits mainly contribute to disks in low-mass late-type galaxies, and to bulges in high-mass early-type galaxies. The cold, warm, and hot components generally follow the same morphology (ɛ = 1 - qRmax) versus kinematics (σ _z^2/\\overline{V_{tot}^2}) relation as the thin disk, thick disk/pseudo bulge, and classical bulge identified from cosmological simulations.

New HErschel Multi-wavelength Extragalactic Survey of Edge-on Spirals (NHEMESES)

NASA Astrophysics Data System (ADS)

Holwerda, B. W.; Bianchi, S.; Baes, M.; de Jong, R. S.; Dalcanton, J. J.; Radburn-Smith, D.; Gordon, K.; Xilouris, M.

2012-08-01

Edge-on spiral galaxies offer a unique perspective on the vertical structure of spiral disks, both stars and the iconic dark dustlanes. The thickness of these dustlanes can now be resolved for the first time with Herschel in far-infrared and sub-mm emission. We present NHEMESES, an ongoing project that targets 12 edge-on spiral galaxies with the PACS and SPIRE instruments on Herschel. These vertically resolved observations of edge-on spirals will impact on several current topics. First and foremost, these Herschel observations will settle whether or not there is a phase change in the vertical structure of the ISM with disk mass. Previously, a dramatic change in dustlane morphology was observed as in massive disks the dust collapses into a thin lane. If this is the case, the vertical balance between turbulence and gravity dictates the ISM structure and consequently star-formation and related phenomena (spiral arms, bars etc.). We specifically target lower mass nearby edge-ons to complement existing Herschel observations of high-mass edge-on spirals (the HEROES project). Secondly, the combined data-set, together with existing Spitzer observations, will drive a new generation of spiral disk Spectral Energy Distribution models. These model how dust reprocesses starlight to thermal emission but the dust geometry remains the critical unknown. And thirdly, the observations will provide an accurate and unbiased census of the cold dusty structures occasionally seen extending out of the plane of the disk, when backlit by the stellar disk. To illustrate the NHEMESES project, we present early results on NGC 4244 and NGC 891, two well studies examples of a low and high-mass edge-on spiral.

Proceedings of the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications

NASA Technical Reports Server (NTRS)

Blackwell, Kim; Blasso, Len (Editor); Lipscomb, Ann (Editor)

1991-01-01

The proceedings of the National Space Science Data Center Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications held July 23 through 25, 1991 at the NASA/Goddard Space Flight Center are presented. The program includes a keynote address, invited technical papers, and selected technical presentations to provide a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include magnetic disk and tape technologies, optical disk and tape, software storage and file management systems, and experiences with the use of a large, distributed storage system. The technical presentations describe integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's.

An ALMA Survey of CO Isotopologue Emission from Protoplanetary Disks in Chamaeleon I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long Feng; Herczeg, Gregory J.; Pascucci, Ilaria

The mass of a protoplanetary disk limits the formation and future growth of any planet. Masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey {sup 13}CO and C{sup 18}O J = 3–2 line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from in the nearby Chamaeleon I star-forming region. We detect {sup 13}CO emission from 17 sources and C{sup 18}O from only one source.more » Gas masses for disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical interstellar medium CO-to-H{sub 2} ratio of 10{sup −4}, the resulting gas masses are implausibly low, with an average gas mass of ∼0.05 M {sub Jup} as inferred from the average flux of stacked {sup 13}CO lines. The low gas masses and gas-to-dust ratios for Cha I disks are both consistent with similar results from disks in the Lupus star-forming region. The faint CO line emission may instead be explained if disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.« less

An ALMA Survey of CO Isotopologue Emission from Protoplanetary Disks in Chamaeleon I

NASA Astrophysics Data System (ADS)

Long, Feng; Herczeg, Gregory J.; Pascucci, Ilaria; Drabek-Maunder, Emily; Mohanty, Subhanjoy; Testi, Leonardo; Apai, Daniel; Hendler, Nathan; Henning, Thomas; Manara, Carlo F.; Mulders, Gijs D.

2017-08-01

The mass of a protoplanetary disk limits the formation and future growth of any planet. Masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey 13CO and C18O J = 3–2 line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from in the nearby Chamaeleon I star-forming region. We detect 13CO emission from 17 sources and C18O from only one source. Gas masses for disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical interstellar medium CO-to-H2 ratio of 10‑4, the resulting gas masses are implausibly low, with an average gas mass of ∼0.05 M Jup as inferred from the average flux of stacked 13CO lines. The low gas masses and gas-to-dust ratios for Cha I disks are both consistent with similar results from disks in the Lupus star-forming region. The faint CO line emission may instead be explained if disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.

Radio Observations of Ultra-Luminous X-Ray Sources ---Microblazars or Intermediate-Mass Black Holes?---

NASA Astrophysics Data System (ADS)

Körding, E.; Colbert, E.; Falcke, H.

In recent years Ultra-Luminous X-Ray sources (ULXs) received wide attention, however, their true nature is not yet understood. Many explanations have been suggested, including intermediate-mass black holes, super-Eddington accretion flows, anisotropic emission, and relativistic beaming of microquasars. We model the logN-logS distribution of ULXs assuming that each neutron star or black hole XRB can be described by an accretion disk plus jet model, where the jet is relativistically beamed. The distribution can be either fit by intermediate-mass black holes or by stellar mass black holes with mildly relativistic jets. Even though the jet is intrinsically weaker than the accretion disk, relativistic beaming can in the latter approach lead to the high fluxes observed. To further explore the possibility of microblazars contributing to the ULX phenomenon, we have embarked on a radio-monitoring study of ULXs in nearby galaxies with the VLA. However, up to now no radio flare has been detected. Using the radio/X-ray correlation the upper limits on the radio flux can be converted into upper limits for the black hole masses of MBH ≲ 10^3 M⊙.

Adaptive Optics Imaging of the Circumbinary Disk around the T Tauri Binary UY Aurigae: Estimates of the Binary Mass and Circumbinary Dust Grain Size Distribution

NASA Astrophysics Data System (ADS)

Close, L. M.; Dutrey, A.; Roddier, F.; Guilloteau, S.; Roddier, C.; Northcott, M.; Ménard, F.; Duvert, G.; Graves, J. E.; Potter, D.

1998-05-01

We have obtained high-resolution (FWHM = 0.15") deep images of the UY Aur binary at J, H, and K' with the University of Hawaii adaptive optics instrument. We clearly detect an R ~ 500 AU circumbinary disk discovered with millimeter interferometry, making UY Aur the second young binary with a confirmed circumbinary disk. It appears that the disk is inclined ~42° from face on. We find that the near side of the disk is brighter than the far side by factors of 2.6, 2.7, and 6.5 times at K', H, and J, respectively. The original GG Tau circumbinary disk has been reexamined and is found to have similar flux ratios of 1.5, 2.6, and 3.6 at K', H, and J, respectively. A realistic power-law distribution (p = 4.7) of spherical dust aggregates (composed of silicates, amorphous carbon, and graphite) that reproduces the observed ISM extinction curve also predicts these observed flux ratios from Mie scattering theory. We find the observed preference of forward-scattering over back-scattering is well fitted (global χ2 minimization) by Mie scattering off particles in the range amin = 0.03 μm to amax = 0.5-0.6 μm. The existence of a significant population of grain radii larger than 0.6 μm is not supported by the scattering observations. Based on the observed disk inclination we derive an orbit for UY Aur where the mass for the binary is 1.6+0.47-0.67 M⊙. Based on the observed K7 and M0 spectral types for UY Aur A and B, accretion disk models for the inner disks around the central stars were constructed. The models suggest that small (lower limit R ~ 5-10 AU) inner disks exist around B and A. It appears that B is accreting ~5 times faster than A, and that both inner disks may be exhausted in ~102-103 yr without replenishment from the outer circumbinary disk. Our images suggest that these inner disks may indeed be resupplied with material through thin streamers of material that penetrate inside the circumbinary disk. Currently it appears that such a streamer may be a close to UY Aur B. Comparison of our IR images and the millimeter images of the gas clearly show that the dust seen in our IR images traces the gas in the circumbinary disk, as was also the case with GG Tau.

High-resolution submillimeter and near-infrared studies of the transition disk around Sz 91

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsukagoshi, Takashi; Momose, Munetake; Hashimoto, Jun

2014-03-10

To reveal the structures of a transition disk around a young stellar object in Lupus, Sz 91 , we have performed aperture synthesis 345 GHz continuum and CO(3-2) observations with the Submillimeter Array (∼1''-3'' resolution) and high-resolution imaging of polarized intensity at the K{sub s} -band using the HiCIAO instrument on the Subaru Telescope (0.''25 resolution). Our observations successfully resolved the inner and outer radii of the dust disk to be 65 and 170 AU, respectively, which indicates that Sz 91 is a transition disk source with one of the largest known inner holes. The model fitting analysis of themore » spectral energy distribution reveals an H{sub 2} mass of 2.4 × 10{sup –3} M {sub ☉} in the cold (T < 30 K) outer part at 65 AU 3 × 10{sup –9} M {sub ☉}) of hot (T ∼ 180 K) dust possibly remains inside the inner hole of the disk. The structure of the hot component could be interpreted as either an unresolved self-luminous companion body (not directly detected in our observations) or a narrow ring inside the inner hole. Significant CO(3-2) emission with a velocity gradient along the major axis of the dust disk is concentrated on the Sz 91 position, suggesting a rotating gas disk with a radius of 420 AU. The Sz 91 disk is possibly a rare disk in an evolutionary stage immediately after the formation of protoplanets because of the large inner hole and the lower disk mass than other transition disks studied thus far.« less

Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective

NASA Astrophysics Data System (ADS)

Vorobyov, Eduard I.

2011-03-01

We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun, M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun, M mdn d,CI = 0.15 M sun, respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun. Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

Evidence of early disk-locking among low-mass members of the Orion Nebula Cluster

NASA Astrophysics Data System (ADS)

Biazzo, K.; Melo, C. H. F.; Pasquini, L.; Randich, S.; Bouvier, J.; Delfosse, X.

2009-12-01

Context: We present new high-resolution spectroscopic observations for 91 pre-main sequence stars in the Orion Nebular Cluster (ONC) with masses in the range 0.10-0.25~M_⊙ carried out with the multi-fiber spectrograph flames attached to the UT2 at the Paranal Observatory. Aims: Our aim is to better understand the disk-locking scenario in very low-mass stars. Methods: We have derived radial velocities, projected rotational velocities, and full width at 10% of the Hα emission peak. Using published measurements of infrared excess (Δ(I_C-K)), as disk tracer and equivalent width of the nead-infrared Ca II line λ8542, mid-infrared difference [3.6]-[8.0] μm derived by Spitzer data, and 10% Hα width as diagnostic of the level of accretion, we looked for any correlation between projected angular rotational velocity divided by the radius (v sin i/R) and presence of disk and accretion. Results: For 4 low-mass stars, the cross-correlation function is clearly double-lined, indicating that the stars are SB2 systems. The distribution of rotation periods derived from our v sin i measurements is unimodal with a peak of a few days, in agreement with previous results for M<0.25~M_⊙. The photometric periods were combined with our v sin i to derive the equatorial velocity and the distribution of rotational axes. Our < sin i> is lower than the one expected for a random distribution, as previously found. We find no evidence of a population of fast rotators close to the break-up velocity. A clear correlation between v sin i/R and Δ(I_C-K) has been found. While a spread in the rotation rates is seen for stars with no circumstellar disk (Δ(I_C-K)<0.3), stars with a circumstellar disk (Δ(I_C-K)>0.3) show an abrupt drop in their rotation rates by a factor of ~5. On the other hand, only a partial correlation between v sin i and accretion is observed when other indicators are used. The X-ray coronal activity level (log L_X/L_bol) shows no dependence on v sin i/R, suggesting that all stars are in a saturated regime limit. The critical velocity is probably below our v sin i detection limit of 9 km s-1. Conclusions: The ONC low-mass stars in our sample, close to the hydrogen burning limit, at present do not seem to be locked, but the clear correlation we find between rotation and infrared color excess suggests that they were locked once. In addition, the percentage of accretors seems to scale inversely to the stellar mass. Based on the flames Science Verification proposal 60.A-9145(A) and the flames proposal 76.C-0524(A). Table [see full textsee full textsee full textsee full text] is only available in electronic form at http://www.aanda.org

An Upper Limit on the Mass of the Circumplanetary Disk for DH Tau b

NASA Astrophysics Data System (ADS)

Wolff, Schuyler G.; Ménard, François; Caceres, Claudio; Lefèvre, Charlene; Bonnefoy, Mickael; Cánovas, Héctor; Maret, Sébastien; Pinte, Christophe; Schreiber, Matthias R.; van der Plas, Gerrit

2017-07-01

DH Tau is a young (˜1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious {{H}}α emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of 17.2+/- 1.7 {M}\\oplus , which gives a disk to star mass ratio of 0.014 (assuming the usual gas to dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42 M ⊕ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model, including heating of the circumplanetary disk by DH Tau b and DH Tau A, suggests that a mass-averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09 M ⊕ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models. This work is based on observations carried out under project D15AC with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Radial distributions of surface mass density and mass-to-luminosity ratio in spiral galaxies

NASA Astrophysics Data System (ADS)

Sofue, Yoshiaki

2018-03-01

We present radial profiles of the surface mass density (SMD) in spiral galaxies directly calculated using rotation curves of two approximations of flat-disk (SMD-F) and spherical mass distribution (SMD-S). The SMDs are combined with surface brightness using photometric data to derive radial variations of the mass-to-luminosity ratio (ML). It is found that the ML generally has a central peak or a plateau, and decreases to a local minimum at R ˜ 0.1-0.2 h, where R is the radius and h is the scale radius of optical disk. The ML, then, increases rapidly until ˜0.5 h, and is followed by gradual rise till ˜2 h, remaining at around ˜2 [M_{⊙} L^{-1}_{⊙}] in the w1 band (infrared λ3.4 μm) and ˜ 10 [M_⊙ L_⊙ ^{-1}] in the r band (λ6200-7500 Å). Beyond this radius, the ML increases steeply with approaching the observed edges at R ˜ 5 h, attaining to as high values as ˜20 in w1 and ˜ 10^2 [M_⊙ L_⊙ ^{-1}] in the r band, which are indicative of dominant dark matter. The general properties of the ML distributions will be useful for constraining cosmological formation models of spiral galaxies.

A Detached Protostellar Disk around a ˜0.2 M ⊙ Protostar in a Possible Site of a Multiple Star Formation in a Dynamical Environment in Taurus

NASA Astrophysics Data System (ADS)

Tokuda, Kazuki; Onishi, Toshikazu; Saigo, Kazuya; Hosokawa, Takashi; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro; Machida, Masahiro N.; Tomida, Kengo; Kunitomo, Masanobu; Kawamura, Akiko; Fukui, Yasuo; Tachihara, Kengo

2017-11-01

We report ALMA observations in 0.87 mm continuum and 12CO (J = 3-2) toward a very low-luminosity (<0.1 L ⊙) protostar, which is deeply embedded in one of the densest cores, MC27/L1521F, in Taurus with an indication of multiple star formation in a highly dynamical environment. The beam size corresponds to ˜20 au, and we have clearly detected blueshifted/redshifted gas in 12CO associated with the protostar. The spatial/velocity distributions of the gas show there is a rotating disk with a size scale of ˜10 au, a disk mass of ˜10-4 M ⊙, and a central stellar mass of ˜0.2 M ⊙. The observed disk seems to be detached from the surrounding dense gas, although it is still embedded at the center of the core whose density is ˜106 cm-3. The current low-outflow activity and the very low luminosity indicate that the mass accretion rate onto the protostar is extremely low in spite of a very early stage of star formation. We may be witnessing the final stage of the formation of ˜0.2 M ⊙ protostar. However, we cannot explain the observed low luminosity with the standard pre-main-sequence evolutionary track unless we assume cold accretion with an extremely small initial radius of the protostar (˜0.65 {R}⊙ ). These facts may challenge our current understanding of the low mass star formation, in particular the mass accretion process onto the protostar and the circumstellar disk.

Physical properties and evolutionary time scales of disks around solar-type and intermediate mass stars

NASA Technical Reports Server (NTRS)

Strom, Stephen E.; Edwards, Suzan

1993-01-01

Recent observations of circumstellar disks and their evolutionary timescales are reviewed. It is concluded that disks appear to be a natural outcome of the star-formation process. The disks surrounding young stars initially are massive, with optically thick structures comprised of gas and micron-sized grains. Disk masses are found to range from 0.01 to 0.2 solar masses for solar-type PMS stars, and from 0.01 to 6 solar masses for young, intermediate mass stars. Massive, optically thick accretion disks have accretion rates between 10 exp -8 and 10 exp -6 solar masses/yr for solar type PMS stars and between 10 exp -6 and 10 exp -4 solar masses/yr for intermediate stars. The results suggest that a significant fraction of the mass comprising the star may have passed through a circumstellar accretion disk.

The DiskMass Survey. II. Error Budget

NASA Astrophysics Data System (ADS)

Bershady, Matthew A.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.; Martinsson, Thomas

2010-06-01

We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio (Υ_{*}), and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find that a disk inclination range of 25°-35° is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale heights are significant, but can be estimated from radial scale lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction ({F}_bar) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error budget for the key quantities: dynamical disk mass surface density (Σdyn), disk stellar mass-to-light ratio (Υ^disk_{*}), and disk maximality ({F}_{*,max}^disk≡ V^disk_{*,max}/ V_c). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

Thermal Disk Winds in X-Ray Binaries: Realistic Heating and Cooling Rates Give Rise to Slow, but Massive, Outflows

NASA Astrophysics Data System (ADS)

Higginbottom, N.; Proga, D.; Knigge, C.; Long, K. S.

2017-02-01

A number of X-ray binaries exhibit clear evidence for the presence of disk winds in the high/soft state. A promising driving mechanism for these outflows is mass loss driven by the thermal expansion of X-ray heated material in the outer disk atmosphere. Higginbottom & Proga recently demonstrated that the properties of thermally driven winds depend critically on the shape of the thermal equilibrium curve, since this determines the thermal stability of the irradiated material. For a given spectral energy distribution, the thermal equilibrium curve depends on an exact balance between the various heating and cooling mechanisms at work. Most previous work on thermally driven disk winds relied on an analytical approximation to these rates. Here, we use the photoionization code cloudy to generate realistic heating and cooling rates which we then use in a 2.5D hydrodynamic model computed in ZEUS to simulate thermal winds in a typical black hole X-ray binary. We find that these heating and cooling rates produce a significantly more complex thermal equilibrium curve, with dramatically different stability properties. The resulting flow, calculated in the optically thin limit, is qualitatively different from flows calculated using approximate analytical rates. Specifically, our thermal disk wind is much denser and slower, with a mass-loss rate that is a factor of two higher and characteristic velocities that are a factor of three lower. The low velocity of the flow—{v}\\max ≃ 200 km s-1—may be difficult to reconcile with observations. However, the high mass-loss rate—15 × the accretion rate—is promising, since it has the potential to destabilize the disk. Thermally driven disk winds may therefore provide a mechanism for state changes.

Young Stellar Objects in Lynds 1641: Disks, Accretion, and Star Formation History

NASA Astrophysics Data System (ADS)

Fang, Min; Kim, Jinyoung Serena; van Boekel, Roy; Sicilia-Aguilar, Aurora; Henning, Thomas; Flaherty, Kevin

2013-07-01

We investigate the young stellar objects (YSOs) in the Lynds 1641 (L1641) cloud using multi-wavelength data including Spitzer, WISE, the Two Micron All Sky Survey, and XMM covering ~1390 YSOs across a range of evolutionary stages. In addition, we targeted a sub-sample of YSOs for optical spectroscopy with the MMT/Hectospec and the MMT/Hectochelle. We use these data, along with archival photometric data, to derive spectral types, extinction values, masses, ages, and accretion rates. We obtain a disk fraction of ~50% in L1641. The disk frequency is almost constant as a function of stellar mass with a slight peak at log (M */M ⊙) ≈ -0.25. The analysis of multi-epoch spectroscopic data indicates that the accretion variability of YSOs cannot explain the two orders of magnitude of scatter for YSOs with similar masses. Forty-six new transition disk (TD) objects are confirmed in this work, and we find that the fraction of accreting TDs is lower than for optically thick disks (40%-45% versus 77%-79%, respectively). We confirm our previous result that the accreting TDs have a median accretion rate similar to normal optically thick disks. We confirm that two star formation modes (isolated versus clustered) exist in L1641. We find that the diskless YSOs are statistically older than the YSOs with optically thick disks and the TD objects have a median age that is intermediate between those of the other two populations. We tentatively study the star formation history in L1641 based on the age distribution and find that star formation started to be active 2-3 Myr ago.

Circumstellar and circumplanetary disks

NASA Astrophysics Data System (ADS)

Chiang, Eugene

2000-11-01

This thesis studies disks in three astrophysical contexts: (1)protoplanetary disks; (2)the Edgeworth-Kuiper Belt; and (3)planetary rings. We derive hydrostatic, radiative equilibrium models of passive protoplanetary disks surrounding T Tauri and Herbig Ae/Be stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer is responsible for up to ~70% of the disk luminosity at wavelengths between ~5 and 60 μm. The heated disk flares and absorbs more stellar radiation at a given stellocentric distance than a flat disk would. Spectral energy distributions are computed and found to compare favorably with the observed flattish infrared excesses of several young stellar objects. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on. We present the results of a pencil-beam survey of the Kuiper Belt using the Keck 10-m telescope. Two new objects are discovered. Data from all surveys are pooled to construct the luminosity function from mR = 20 to 27. The cumulative number of objects per square degree, Σ(< mR), is such that log10Σ (< mR) = 0.52(mR - 23.5). The luminosity function is consistent with a power-law size distribution for which the smallest objects possess most of the surface area but the largest bodies contain most of the mass. To order-of-magnitude, 0.2 M⊕ and 1 × 1010 comet progenitors lie between 30 and 50 AU. The classical Kuiper Belt appears truncated at a distance of 50 AU. We propose that rigid precession of narrow eccentric planetary rings surrounding Uranus and Saturn is maintained by a balance of forces due to ring self- gravity, planetary oblateness, and interparticle collisions. Collisional impulses play an especially dramatic role near ring edges. Pressure-induced accelerations are maximal near edges because there (1)velocity dispersions are enhanced by resonant satellite perturbations, and (2)the surface density declines steeply. Remarkably, collisional forces felt by material in the last ~100 m of a ~10 km wide ring can increase equilibrium masses up to a factor of ~100. New ring surface densities are derived which accord with Voyager radio measurements.

Multiwavelength Imaging Of YSOs With Disk In South Pillars Of Eta Carina

NASA Astrophysics Data System (ADS)

Reyes, J. A.; Porras, B. A.

2013-04-01

We present multiwavelength imaginery and spectral energy distributions (SEDs) of 15 Young Stellar Objects (YSOs) with disk components lying on the South Pillars region close to Eta Carina (η Car). The SEDs include IR fluxes from 2MASS, IRAC, MSX, AKARI, and MIPS-24 μm, and 1.1 mm flux from AzTEC camera at the ASTE antenna. Millimeter fluxes help to constrain the number of fitted models, which provide the list of physical parameters for the star, the disk and the envelope. We then compare the parameters of the YSOs and their spatial location within the star forming region.

A study of circumstellar disk properties in low-mass stars and brown dwarfs

NASA Astrophysics Data System (ADS)

Riaz, Basmah

We present Spitzer Space Telescope IRAC and MIPS observations for a sample of eight M dwarfs: six dMe, one dM, and one sdMe star. All of our targets are found to have Spectral Energy Distributions (SEDs) which are fitted within the error bars by a purely photospheric spectrum out to 24m m . The estimated ages for all are >10 Myr, suggesting that enough disk dissipation has occurred within the inner several AU of the star. Scaling from Houdebine's model of the AU Mic chromosphere, we have computed the free-free infrared excesses for a range of densities. Our Spitzer 24m m data shows that the chromospheres in two of our targets are less dense than in AU Mic by a factor of 10 or more. Our models also indicate that the chromospheric contribution to the observed AU Mic emission at submillimeter wavelengths is only about 2%. We present Spitzer IRAC, MIPS and IRS observations for three sub-stellar members of the TW Hydrae Association (TWA): 2MASSW J1207334-393254 (2M1207), SSSPM J1102-3431 (SSSPM 1102), and 2MASS J1139511-315921 (2M1139). The near- to mid-infrared SEDs indicate the presence of flat optically thick disks around 2M1207 and SSSPM 1102, and a transition disk around 2M1139. 2M1207 shows absorption in the 10 m m silicate feature, with a peak near 11.3 m m due to crystalline forsterite. The absorption can be attributed to a close to edge-on disk. No silicate absorption/emission is observed towards SSSPM 1102. We have performed detailed modeling of these two brown dwarf disks. The best-fits have been obtained using a flat disk of mass 10 -4 [Special characters omitted.] , M of 10 -10 [Special characters omitted.] /yr, and an inclination angle of 75=B0 for 2M1207, whereas a disk mass of 10 -5 [Special characters omitted.] , M of 10 -11 [Special characters omitted.] /yr, and an inclination angle of 63° provides a good fit to SSSPM 1102. Modeling of the 10 m m silicate feature requires the presence of large (>50 m m ) grains in the disk midplane, which indicates substantial grain growth and dust settling in both brown dwarf disks. Our analysis of the stellar and sub-stellar members of the TWA indicates that while only 6 out of 25 stellar members show excess emission at these mid- infrared wavelengths, all of the TWA brown dwarfs that have been observed so far with Spitzer show signs of disks around them, resulting in a disk fraction of at least 60%. A comparison with younger clusters indicates that by the age of the TWA (~10 Myr), the disk fraction for brown dwarfs has not decreased, whereas it drops by a factor of ~2 for the higher mass stars. This suggests longer disk decay time scales for brown dwarfs compared to higher mass stars.

An Azimuthal Asymmetry in the LkHα 330 Disk

NASA Astrophysics Data System (ADS)

Isella, Andrea; Pérez, Laura M.; Carpenter, John M.; Ricci, Luca; Andrews, Sean; Rosenfeld, Katherine

2013-09-01

Theory predicts that giant planets and low mass stellar companions shape circumstellar disks by opening annular gaps in the gas and dust spatial distribution. For more than a decade it has been debated whether this is the dominant process that leads to the formation of transitional disks. In this paper, we present millimeter-wave interferometric observations of the transitional disk around the young intermediate mass star LkHα 330. These observations reveal a lopsided ring in the 1.3 mm dust thermal emission characterized by a radius of about 100 AU and an azimuthal intensity variation of a factor of two. By comparing the observations with a Gaussian parametric model, we find that the observed asymmetry is consistent with a circular arc, that extends azimuthally by about 90° and emits about 1/3 of the total continuum flux at 1.3 mm. Hydrodynamic simulations show that this structure is similar to the azimuthal asymmetries in the disk surface density that might be produced by the dynamical interaction with unseen low mass companions orbiting within 70 AU from the central star. We argue that such asymmetries might lead to azimuthal variations in the millimeter-wave dust opacity and in the dust temperature, which will also affect the millimeter-wave continuum emission. Alternative explanations for the observed asymmetry that do not require the presence of companions cannot be ruled out with the existing data. Further observations of both the dust and molecular gas emission are required to derive firm conclusions on the origin of the asymmetry observed in the LkHα 330 disk.

Disk mass and disk heating in the spiral galaxy NGC 3223

NASA Astrophysics Data System (ADS)

Gentile, G.; Tydtgat, C.; Baes, M.; De Geyter, G.; Koleva, M.; Angus, G. W.; de Blok, W. J. G.; Saftly, W.; Viaene, S.

2015-04-01

We present the stellar and gaseous kinematics of an Sb galaxy, NGC 3223, with the aim of determining the vertical and radial stellar velocity dispersion as a function of radius, which can help to constrain disk heating theories. Together with the observed NIR photometry, the vertical velocity dispersion is also used to determine the stellar mass-to-light (M/L) ratio, typically one of the largest uncertainties when deriving the dark matter distribution from the observed rotation curve. We find a vertical-to-radial velocity dispersion ratio of σz/σR = 1.21 ± 0.14, significantly higher than expectations from known correlations, and a weakly-constrained Ks-band stellar M/L ratio in the range 0.5-1.7, which is at the high end of (but consistent with) the predictions of stellar population synthesis models. Such a weak constraint on the stellar M/L ratio, however, does not allow us to securely determine the dark matter density distribution. To achieve this, either a statistical approach or additional data (e.g. integral-field unit) are needed. Based on observations collected at the European Southern Observatory, Chile, under proposal 68.B-0588.

Galactoseismology: From The Milky Way To XUV Disks

NASA Astrophysics Data System (ADS)

Chakrabarti, Sukanya

The variety of discrepancies between observations and simulations on galactic scales, from the anisotropic distribution of dwarf galaxies to the "too big to fail" problem (where massive satellites in simulations are too dense relative to observations), suggests that we may not yet fully understand galaxy formation. If these satellites exist, they would leave traces of their passage in extended HI disks. Extended HI disks of galaxies reach to several times the optical radius, presenting the largest possible cross-section for interaction with sub-halos at large distances (where theoretical models expect them to be). We will provide definitive constraints on the distribution of dark matter in spiral galaxies by building on our ongoing work in characterizing galactic satellites from analysis of disturbances in extended HI disks with respect to hydrodynamical simulations. Spiral galaxies in the Local Volume (from the Milky Way to the XUV disks discovered by GALEX) exhibit a wealth of unexplained morphology, but these morphological signatures have not yet been used to place constraints on the evolution of HI disks and the dark matter distribution. We are now poised to make significant progress in Galactoseismology, i.e. connect morphological disturbances with the mass distribution. By using the FIRE model for explicit star formation and feedback, we will also develop a better understanding for the star formation history of our Galaxy and XUV Disks. Our Milky Way models will be informed by the HST proper motions, and will match the observed planar disturbances, the warp, and vertical waves recently discovered by the RAVE and LAMOST surveys. We are also carrying high resolution simulations with the Gizmo code that incorporates the FIRE model to develop a comprehensive understanding of the star formation history and star formation rate (that matches Spitzer observations) of the Milky Way. These models will provide a much needed interpretative framework for JWST and WFIRST observations. By mapping to the HI image, the GALEX UV image, the multi-wavelength SED of XUV disks, as well as the masses and deprojected distances of the satellites in a statistically robust way using a Monte Carlo Markov Chain analysis, we will produce evolutionary histories of XUV disks and their satellite populations for the first time. This will enable an apples-to-apples comparison for XUV disks in the Local Volume. There is currently no study that has examined the morphological effects of satellites in cosmological simulations on the gas and stellar disk. This is a critical test of the distribution (the number, the mass, and orbits) of satellites in cosmological simulations. We will also investigate if the vast polar structure (VPOS) of dwarf galaxies around the Milky Way is a serious problem for the Lambda-CDM paradigm. Here we ask two simple questions: 1) Is the VPOS dynamically coherent? If the VPOS is a serious problem for Lambda-CDM, one expects that it should persist over a dynamical time and should not be unique to the present day. 2) Are there certain satellites that drive the appearance of the planar structure at present day? If so, it is critical to examine whether a sub-set excluding these satellites resembles cosmological simulations. Our preliminary results show that this structure is not dynamically coherent, and is driven by two satellites: Leo I and Leo II, both of which have extreme kinematic properties. We will also examine the evolution of the VPOS in non-spherical and time-dependent potentials. We will seek to obtain more accurate proper motions of Leo II in the upcoming HST cycle, as we find that Leo II particularly influences the fit to the planar structure. These results will have far-reaching impact in understanding data from many NASA missions - HST, GALEX, Spitzer, and Herschel to JWST and WFIRST missions. We will also provide a framework for understanding data from the GAIA and GALAH surveys of the Milky Way.

Photoevaporating Disks around Young Stars: Ultracompact HII Regions and Protoplanetary Disks.

NASA Astrophysics Data System (ADS)

Johnstone, Douglas Ian

1995-01-01

Newly formed stars produce sufficient Lyman continuum luminosity phi to significantly alter the structure and evolution of the accretion disk surrounding them. In the absence of a stellar wind, a nearly static, photoionized, 10^4 K, disk atmosphere, with a scale height that increases with disk radius varpi as varpi^{3/2 }, forms inside the gravitational radius varpig ~ 1014(M_*/ M_odot) cm where M _* is the mass of the central star. This ionized atmosphere is maintained by both the direct radiation from the central star and the diffuse field produced in the disk atmosphere by the significant fraction of hydrogen recombinations directly to the ground state. Beyond varpig the material evaporated from the disk is capable of escaping from the system and produces an ionized disk wind. The mass-loss due to this disk wind peaks at varpig . The inclusion of a stellar wind into the basic picture reduces the height of the inner disk atmosphere and introduces a new scale radius varpi_ {w} where the thermal pressure of the material evaporated from the disk balances the ram pressure in the wind. In this case the mass-loss due to the disk wind peaks at varpiw and is enhanced over the no-wind case. The photoevaporation of disks around newly formed stars has significance to both ultracompact HII regions and the dispersal of solar-type nebulae. High mass stars are intrinsically hot and thus yield sufficient Lyman luminosity to create, even without a stellar wind, disk mass-loss rates of order 2 times 10 ^{-5}phi_sp{49} {1/2} M_odotyr ^{-1}, where phi 49 = phi/(10 49 Lyman continuum photons s^{-1}). This wind, which will last until the disk is dispersed, ~ 10^5 yrs if the disk mass is M_ {d}~0.3M_*, yields sizes, emission measures and ages consistent with observations of ultracompact HII regions. The well-observed high mass star MWC 349 may be the best example to date of an evaporating disk around a high mass star. On the other end of the stellar scale, many newly formed low-mass stars are known to have enhanced extreme ultraviolet luminosity suggested to be due to boundary layer accretion. Assuming that most low mass stars have such an enhanced Lyman luminosity phi ~ 1041 s ^{-1}, for ~ 3 times 10^7 yrs it is possible to remove most of the gas in the outer disk. A diagnostic of this mass loss may be the low-velocity forbidden oxygen, nitrogen, and sulphur line emission observed around young stars with disks. Photoevaporating disk models yield reasonable agreement with the flux seen in these lines. The process of photoevaporation also has implications for the formation of the giant planets within the solar nebula. Within young stellar clusters a few high mass stars may overwhelm the internal Lyman continuum flux from low mass stars and externally evaporated disks may result. The Trapezium region presents the best studied example of such a cluster. Photoionization due to high energy photons from the high mass stars erode the disks around nearby low mass stars. The resulting short destruction times for these disks constrain the gestation period for creating planets.

The Cluster Population of UGC 2885

NASA Astrophysics Data System (ADS)

Holwerda, Benne

2017-08-01

UGC 2885 was discoverd to be the most extended disk galaxy [250 kpc diameter] by Vera Rubin in the 1980's. We ask for HST observations of UGC 2885 as it is close enough to resolve the GC population with HST but it is a substantially more extended disk than any studied before. LCDM galaxy assembly implies that the GC population comes from small accreted systems and the disk -and the clusters associated with it- predominantly from gas accretion (matching angular momentum to the disk). Several scaling relations between the GC population and parent galaxy have been observed but these differ for disk and spheroidal (massive) galaxies.We propose to observe this galaxy with HST in 4 point WFC3 mosaic with coordinated ACS parallels to probe both the disk and outer halo component of the GC population. GC populations have been studied extensively using HST color mosaics of local disk galaxies and these can serve as comparison samples. How UGC 2885 cluster populations relate to its stellar and halo mass, luminosity and with radius will reveal the formation history of extra-ordinary disk.Our goals are twofold: our science goal is to map the luminosity, (some) size, and color distributions of the stellar and globular clusters in and around this disk. In absolute terms, we expect to find many GC but the relative relation of the GC population to this galaxy's mass (stellar and halo) and size will shed light on its formation history; similar to a group or cluster central elliptical or to a field galaxy (albeit one with a disk 10x the Milky Way's size)? Our secondary motive is to make an HST tribute image to the late Vera Rubin.

CONNECTING ANGULAR MOMENTUM AND GALACTIC DYNAMICS: THE COMPLEX INTERPLAY BETWEEN SPIN, MASS, AND MORPHOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teklu, Adelheid F.; Remus, Rhea-Silvia; Dolag, Klaus

The evolution and distribution of the angular momentum of dark matter (DM) halos have been discussed in several studies over the past decades. In particular, the idea arose that angular momentum conservation should allow us to infer the total angular momentum of the entire DM halo from measuring the angular momentum of the baryonic component, which is populating the center of the halo, especially for disk galaxies. To test this idea and to understand the connection between the angular momentum of the DM halo and its galaxy, we use a state-of-the-art, hydrodynamical cosmological simulation taken from the set of Magneticummore » Pathfinder simulations. Thanks to the inclusion of the relevant physical processes, the improved underlying numerical methods, and high spatial resolution, we successfully produce populations of spheroidal and disk galaxies self-consistently. Thus, we are able to study the dependence of galactic properties on their morphology. We find that (1) the specific angular momentum of stars in disk and spheroidal galaxies as a function of their stellar mass compares well with observational results; (2) the specific angular momentum of the stars in disk galaxies is slightly smaller compared to the specific angular momentum of the cold gas, in good agreement with observations; (3) simulations including the baryonic component show a dichotomy in the specific stellar angular momentum distribution when splitting the galaxies according to their morphological type (this dichotomy can also be seen in the spin parameter, where disk galaxies populate halos with slightly larger spin compared to spheroidal galaxies); (4) disk galaxies preferentially populate halos in which the angular momentum vector of the DM component in the central part shows a better alignment to the angular momentum vector of the entire halo; and (5) the specific angular momentum of the cold gas in disk galaxies is approximately 40% smaller than the specific angular momentum of the total DM halo and shows a significant scatter.« less

Open star clusters and Galactic structure

NASA Astrophysics Data System (ADS)

Joshi, Yogesh C.

2018-04-01

In order to understand the Galactic structure, we perform a statistical analysis of the distribution of various cluster parameters based on an almost complete sample of Galactic open clusters yet available. The geometrical and physical characteristics of a large number of open clusters given in the MWSC catalogue are used to study the spatial distribution of clusters in the Galaxy and determine the scale height, solar offset, local mass density and distribution of reddening material in the solar neighbourhood. We also explored the mass-radius and mass-age relations in the Galactic open star clusters. We find that the estimated parameters of the Galactic disk are largely influenced by the choice of cluster sample.

TESTING THE PROPAGATING FLUCTUATIONS MODEL WITH A LONG, GLOBAL ACCRETION DISK SIMULATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hogg, J Drew; Reynolds, Christopher S.

2016-07-20

The broadband variability of many accreting systems displays characteristic structures; log-normal flux distributions, root-mean square (rms)-flux relations, and long inter-band lags. These characteristics are usually interpreted as inward propagating fluctuations of the mass accretion rate in an accretion disk driven by stochasticity of the angular momentum transport mechanism. We present the first analysis of propagating fluctuations in a long-duration, high-resolution, global three-dimensional magnetohydrodynamic (MHD) simulation of a geometrically thin ( h / r ≈ 0.1) accretion disk around a black hole. While the dynamical-timescale turbulent fluctuations in the Maxwell stresses are too rapid to drive radially coherent fluctuations in themore » accretion rate, we find that the low-frequency quasi-periodic dynamo action introduces low-frequency fluctuations in the Maxwell stresses, which then drive the propagating fluctuations. Examining both the mass accretion rate and emission proxies, we recover log-normality, linear rms-flux relations, and radial coherence that would produce inter-band lags. Hence, we successfully relate and connect the phenomenology of propagating fluctuations to modern MHD accretion disk theory.« less

Physics and chemistry of the solar nebula.

PubMed

Lunine, J I

1997-06-01

The solar system is thought to have begun in a flattened disk of gas and dust referred to traditionally as the solar nebula. Such a construct seems to be a natural product of the collapse of dense parts of giant molecular clouds, the vast star-forming regions that pepper the Milky Way and other galaxies. Gravitational, magnetic and thermal forces within the solar nebula forced a gradual evolution of mass toward the center (where the sun formed) and angular momentum (borne by a small fraction of the mass) toward the outer more distant regions of the disk. This evolution was accompanied by heating and a strong temperature contrast from the hot, inner regions to the cold, more remote parts of the disk. The resulting chemistry in the disk determined the initial distribution of organic matter in the planets; most of the reduced carbon species, in condensed form, were located beyond the asteroid belt (the 'outer' solar system). The Earth could have received much of its inventory of pre-biological material from comets and other icy fragments of the process of planetary formation in the outer solar system.

Gas Content and Kinematics in Clumpy, Turbulent Star-forming Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, Heidi A.; Abraham, Roberto G.; Fisher, David B.

2017-09-01

We present molecular gas-mass estimates for a sample of 13 local galaxies whose kinematic and star-forming properties closely resemble those observed in z ≈ 1.5 main-sequence galaxies. Plateau de Bure observations of the CO[1-0] emission line and Herschel Space Observatory observations of the dust emission both suggest molecular gas-mass fractions of ∼20%. Moreover, dust emission modeling finds T {sub dust} < 30 K, suggesting a cold dust distribution compared to their high infrared luminosity. The gas-mass estimates argue that z ∼ 0.1 DYNAMO galaxies not only share similar kinematic properties with high- z disks, but they are also similarly richmore » in molecular material. Pairing the gas-mass fractions with existing kinematics reveals a linear relationship between f {sub gas} and σ / v {sub c}, consistent with predictions from stability theory of a self-gravitating disk. It thus follows that high gas-velocity dispersions are a natural consequence of large gas fractions. We also find that the systems with the lowest t {sub dep} (∼0.5 Gyr) have the highest ratios of σ / v{sub c} and more pronounced clumps, even at the same high molecular gas fraction.« less

Millimeter observations of the disk around GW Orionis

NASA Astrophysics Data System (ADS)

Fang, M.; Sicilia-Aguilar, A.; Wilner, D.; Wang, Y.; Roccatagliata, V.; Fedele, D.; Wang, J. Z.

2017-07-01

The GW Ori system is a pre-main sequence triple system (GW Ori A/B/C) with companions (GW Ori B/C) at 1 AU and 8 AU, respectively, from the primary (GW Ori A). The primary of the system has a mass of 3.9 M⊙, but shows a spectral type of G8. Thus, GW Ori A could be a precursor of a B star, but it is still at an earlier evolutionary stage than Herbig Be stars. GW Ori provides an ideal target for experiments and observations (being a "blown-up" solar system with a very massive sun and at least two upscaled planets). We present the first spatially resolved millimeter interferometric observations of the disk around the triple pre-main sequence system GW Ori, obtained with the Submillimeter Array, both in continuum and in the 12CO J = 2-1, 13CO J = 2-1, and C18O J = 2-1 lines. These new data reveal a huge, massive, and bright disk in the GW Ori system. The dust continuum emission suggests a disk radius of around 400 AU, but the 12CO J = 2-1 emission shows a much more extended disk with a size around 1300 AU. Owing to the spatial resolution ( 1''), we cannot detect the gap in the disk that is inferred from spectral energy distribution (SED) modeling. We characterize the dust and gas properties in the disk by comparing the observations with the predictions from the disk models with various parameters calculated with a Monte Carlo radiative transfer code RADMC-3D. The disk mass is around0.12 M⊙, and the disk inclination with respect to the line of sight is around 35°. The kinematics in the disk traced by the CO line emission strongly suggest that the circumstellar material in the disk is in Keplerian rotation around GW Ori.Tentatively substantial C18O depletion in gas phase is required to explain the characteristics of the line emission from the disk.

Local heat transfer in turbine disk-cavities. II - Rotor cooling with radial location injection of coolant

NASA Astrophysics Data System (ADS)

Bunker, R. S.; Metzger, D. E.; Wittig, S.

1990-06-01

The detailed radial distributions of rotor heat-transfer coefficients for three basic disk-cavity geometries applicable to gas turbines are presented. The coefficients are obtained over a range of parameters including disk rotational Reynolds numbers of 200,000 to 50,000, rotor/stator spacing-to-disk ratios of 0.025 to 0.15, and jet mass flow rates between 0.10 and 0.40 times the turbulent pumped flow rate of a free disk. The effects of a parallel rotor are analyzed, and strong variations in local Nusselt numbers for all but the rotational speed are pointed out and compared with the associated hub-injection data from a previous study. It is demonstrated that the overall rotor heat transfer is optimized by either the hub injection or radial location injection of a coolant, dependent on the configuration.

SED Modeling of 20 Massive Young Stellar Objects

NASA Astrophysics Data System (ADS)

Tanti, Kamal Kumar

In this paper, we present the spectral energy distributions (SEDs) modeling of twenty massive young stellar objects (MYSOs) and subsequently estimated different physical and structural/geometrical parameters for each of the twenty central YSO outflow candidates, along with their associated circumstellar disks and infalling envelopes. The SEDs for each of the MYSOs been reconstructed by using 2MASS, MSX, IRAS, IRAC & MIPS, SCUBA, WISE, SPIRE and IRAM data, with the help of a SED Fitting Tool, that uses a grid of 2D radiative transfer models. Using the detailed analysis of SEDs and subsequent estimation of physical and geometrical parameters for the central YSO sources along with its circumstellar disks and envelopes, the cumulative distribution of the stellar, disk and envelope parameters can be analyzed. This leads to a better understanding of massive star formation processes in their respective star forming regions in different molecular clouds.

Accretion and Magnetic Reconnection in the Pre-Main Sequence Binary DQ Tau as Revealed through High-Cadence Optical Photometry

NASA Astrophysics Data System (ADS)

Tofflemire, Benjamin M.; Mathieu, Robert D.; Ardila, David R.; Akeson, Rachel L.; Ciardi, David R.; Herczeg, Gregory; Johns-Krull, Christopher M.; Vodniza, Alberto

2016-01-01

Protostellar disks are integral to the formation and evolution of low-mass stars and planets. A paradigm for the star-disk interaction has been extensively developed through theory and observation in the case of single stars. Most stars, however, form in binaries or higher order systems where the distribution of disk material and mass flows are more complex. Pre-main sequence (PMS) binary stars can have up to three accretion disks: two circumstellar disks and a circumbinary disk separated by a dynamically cleared gap. Theory suggests that mass may periodically flow in an accretion stream from a circumbinary disk across the gap onto circumstellar disks or stellar surfaces.The archetype for this theory is the eccentric, PMS binary DQ Tau. Moderate-cadence broadband photometry (~10 observations per orbital period) has shown pulsed brightening events near most periastron passages, just as numerical simulations would predict for a binary of similar orbital parameters. While this observed behavior supports the accretion stream theory, it is not exclusive to variable accretion rates. Magnetic reconnection events (flares) during the collision of stellar magnetospheres at periastron (when separated by 8 stellar radii) could produce the same periodic, broadband behavior when observed at a one-day cadence. Further evidence for magnetic activity comes from gyrosynchrotron, radio flares (typical of stellar flares) observed near multiple periastron passages. To reveal the physical mechanism seen in DQ Tau's moderate-cadence observations, we have obtained continuous, moderate-cadence, multi-band photometry over 10 orbital periods (LCOGT 1m network), supplemented with 32 nights of minute-cadence photometry centered on 4 separate periastron passages (WIYN 0.9m; APO ARCSAT). With detailed lightcurve morphologies we distinguish between the gradual rise and fall on multi-day time-scales predicted by the accretion stream theory and the hour time-scale, rapid-rise and exponential-decay typical of flares. While both are present, accretion dominates the observed variability providing evidence for the accretion stream theory and detailed mass accretion rates for comparison with numerical simulations.

Particle size and composition distribution analysis of automotive brake abrasion dusts for the evaluation of antimony sources of airborne particulate matter

NASA Astrophysics Data System (ADS)

Iijima, Akihiro; Sato, Keiichi; Yano, Kiyoko; Tago, Hiroshi; Kato, Masahiko; Kimura, Hirokazu; Furuta, Naoki

Abrasion dusts from three types of commercially available non-steel brake pads were generated by a brake dynamometer at disk temperatures of 200, 300 and 400 °C. The number concentration of the abrasion dusts and their aerodynamic diameters ( Dp) were measured by using an aerodynamic particle sizer (APS) spectrometer with high temporal and size resolution. Simultaneously, the abrasion dusts were also collected based on their size by using an Andersen low-volume sampler, and the concentrations of metallic elements (K, Ti, Fe, Cu, Zn, Sb and Ba) in the size-classified dusts were measured by ICP-AES and ICP-MS. The number distributions of the brake abrasion dusts had a peak at Dp values of 1 and 2 μm; this peak shifted to the coarse side with an increase in the disk temperature. The mass distributions calculated from the number distributions have peaks between Dp values of 3 and 6 μm. The shapes of the elemental mass distributions (Ti, Fe, Cu, Zn, Sb and Ba) in size-classified dusts were very similar to the total mass distributions of the brake abrasion dusts. These experimental results indicated that the properties of brake abrasion dusts were consistent with the characteristics of Sb-enriched fine airborne particulate matter. Based on these findings and statistical data, the estimation of Sb emission as airborne particulate matter from friction brakes was also discussed.

Distribution and motions of atomic hydrogen in lenticular galaxies. X - The blue S0 galaxy NGC 5102

NASA Technical Reports Server (NTRS)

Van Woerden, H.; Van Driel, W.; Braun, R.; Rots, A. H.

1993-01-01

Results of the mapping of the blue gas-rich S0 galaxy NGC 5102 in the 21-cm H I line with a spatial resolution of 34 x 37 arcsec (delta(alpha) x Delta(delta)) and a velocity resolution of 12 km/s are presented. The H I distribution has a pronounced central depression of 1.9 kpc radius, and most of the H I is concentrated in a 3.6 kpc wide ring with an average radius of 3.7 kpc, assuming a distance of 4 Mpc for NGC 5102. The maximum azimuthally averaged H I surface density in the ring is 1.4 solar mass/sq pc, comparable to that found in other S0 galaxies. The HI velocity field is quite regular, showing no evidence for large-scale deviations from circular rotation, and the H I is found to rotate in the plane of the stellar disk. Both the H I mass/blue luminosity ratio and the radial H I distribution are similar to those in early-type spirals. The H I may be an old disk or it may have been acquired through capture of a gas-rich smaller galaxy. The recent starburst in the nuclear region, which gave the galaxy its blue color, may have been caused by partial radial collapse of the gas disk, or by infall of a gas-rich dwarf galaxy.

Global survey of star clusters in the Milky Way. VI. Age distribution and cluster formation history

NASA Astrophysics Data System (ADS)

Piskunov, A. E.; Just, A.; Kharchenko, N. V.; Berczik, P.; Scholz, R.-D.; Reffert, S.; Yen, S. X.

2018-06-01

Context. The all-sky Milky Way Star Clusters (MWSC) survey provides uniform and precise ages, along with other relevant parameters, for a wide variety of clusters in the extended solar neighbourhood. Aims: In this study we aim to construct the cluster age distribution, investigate its spatial variations, and discuss constraints on cluster formation scenarios of the Galactic disk during the last 5 Gyrs. Methods: Due to the spatial extent of the MWSC, we have considered spatial variations of the age distribution along galactocentric radius RG, and along Z-axis. For the analysis of the age distribution we used 2242 clusters, which all lie within roughly 2.5 kpc of the Sun. To connect the observed age distribution to the cluster formation history we built an analytical model based on simple assumptions on the cluster initial mass function and on the cluster mass-lifetime relation, fit it to the observations, and determined the parameters of the cluster formation law. Results: Comparison with the literature shows that earlier results strongly underestimated the number of evolved clusters with ages t ≳ 100 Myr. Recent studies based on all-sky catalogues agree better with our data, but still lack the oldest clusters with ages t ≳ 1 Gyr. We do not observe a strong variation in the age distribution along RG, though we find an enhanced fraction of older clusters (t > 1 Gyr) in the inner disk. In contrast, the distribution strongly varies along Z. The high altitude distribution practically does not contain clusters with t < 1 Gyr. With simple assumptions on the cluster formation history, the cluster initial mass function and the cluster lifetime we can reproduce the observations. The cluster formation rate and the cluster lifetime are strongly degenerate, which does not allow us to disentangle different formation scenarios. In all cases the cluster formation rate is strongly declining with time, and the cluster initial mass function is very shallow at the high mass end.

Hot Molecular Gas in the Circumnuclear Disk

NASA Astrophysics Data System (ADS)

Mills, Elisabeth A. C.; Togi, Aditya; Kaufman, Michael

2017-12-01

We present an analysis of archival Infrared Space Observatory observations of H2 for three 14\\prime\\prime × 20\\prime\\prime pointings in the central 3 pc of the Galaxy: toward the southwest region and northeast region of the Galactic center circumnuclear disk (CND), and toward the supermassive black hole Sgr A*. We detect pure rotational lines from 0-0 S(0) to S(13), as well as a number of rovibrationally excited transitions. Using the pure rotational lines, we perform both fits to a discrete temperature distribution (measuring up to three temperature components with T = 500-600 K, T = 1250-1350 K, and T > 2600 K) and fits to a continuous temperature distribution, assuming a power-law distribution of temperatures. We measure power-law indices of n = 3.22 for the northeast region and n = 2.83 for the southwest region. These indices are lower than those measured for other galaxies or other Galactic center clouds, indicating a larger fraction of gas at high temperatures. We also test whether extrapolating this temperature distribution can yield a reasonable estimate of the total molecular mass, as has been recently done for H2 observations in other galaxies. Extrapolating to a cutoff temperature of 50 K in the southwest (northeast) region, we would measure 32% (140%) of the total molecular gas mass inferred from the dust emission, and 26% (125%) of the total molecular gas mass inferred from the CO emission. Ultimately, the inconsistency of the masses inferred in this way suggests that a simple application of this method cannot yield a reliable estimate of the mass of the CND.

Gravitational Instabilities in a Young Protoplanetary Disk with Embedded Objects

NASA Astrophysics Data System (ADS)

Desai, Karna M.

Gravitational Instabilities (GIs), a mechanism for angular momentum transport, are prominent during the early phases of protoplanetary disk evolution when the disk is relatively massive. In this dissertation, I analyze GIs by inserting different objects in a disk by employing 3D hydrodynamics simulations. GIs in a circumbinary disks are studied to determine how the presence of the companion affects the nature and strength of GIs in the disk. The circumbinary disk achieves a state of sustained marginal instability similar to an identical disk without the companion. A realistic evolution of the binary is detected. Planet and disk interactions play an important role in the evolution of planetary systems. To study this interaction during the early phases of planet formation, a migration study of Jovian planets in a GI-active disk is conducted. I find the migration timescales to be longer in a GI-active disk, when compared to laminar disks. The 3 MJupiter planet controls its own orbital evolution, while the migration of a 0.3 MJupiter planet is stochastic in nature. I define a 'critical mass' as the mass of an arm of the dominant two-armed spiral density wave within the planet's Hill diameter. Planets above this mass control their own destiny, and planets below this mass are scattered by the disk. This critical mass could provide a recipe for predicting the migration behavior of planets in GI-active disks. To understand the stochastic migration of low-mass planets, I perform a simulation of 240 zero-mass planet-tracers by inserting these at a range of locations in the disk. A Diffusion Coefficient is calculated to characterize the stochastic migration of low-mass objects. The eccentricity dispersion for the sample is also studied. I find that the diffusion of planets can be a slow process, resulting in the survival of small planetary cores.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Kate Y. L.; Smith, Paul S.; Rieke, George H.

HD 95086 is a young early-type star that hosts (1) a 5 M{sub J} planet at the projected distance of 56 AU revealed by direct imaging, and (2) a prominent debris disk. Here we report the detection of 69 μm crystalline olivine feature from the disk using the Spitzer/MIPS-SED data covering 55-95 μm. Due to the low resolution of the MIPS-SED mode, this feature is not spectrally resolved, but is consistent with the emission from crystalline forsterite contributing ∼5% of the total dust mass. We also present detailed analysis of the disk spectral energy distribution and re-analysis of resolved images obtained bymore » Herschel. Our results suggest that the debris structure around HD 95086 consists of a warm (∼175 K) belt, a cold (∼55 K) disk, and an extended disk halo (up to ∼800 AU), and is very similar to that of HR 8799. We compare the properties of the three debris components, and suggest that HD 95086 is a young analog of HR 8799. We further investigate and constrain single-planet, two-planet, three-planet, and four-planet architectures that can account for the observed debris structure and are compatible with dynamical stability constraints. We find that equal-mass four-planet configurations of geometrically spaced orbits, with each planet of mass ∼ 5 M{sub J} , could maintain the gap between the warm and cold debris belts, and also be just marginally stable for timescales comparable to the age of the system.« less

Near-infrared time-series photometry in the field of Cygnus OB2 association. I. Rotational scenario for candidate members

NASA Astrophysics Data System (ADS)

Roquette, J.; Bouvier, J.; Alencar, S. H. P.; Vaz, L. P. R.; Guarcello, M. G.

2017-07-01

Context. In recent decades, the picture of early pre-main sequence stellar rotational evolution has been constrained by studies targeting different regions at a variety of ages with respect to young star formation. Observational studies suggest a dependence of rotation with mass, and for some mass ranges a connection between rotation and the presence of a circumstellar disk. The role of environmental conditions on the rotational regulation, however, has still not been fully explored. Aims: We investigate the rotational properties of candidate members of the young massive association Cygnus OB2. By evaluating their rotational properties, we address questions regarding the effect of environment properties on PMS rotational evolution. Methods: We studied JHK-band variability in 5083 candidate members (24% of them are disk-bearing stars). We selected variable stars with the Stetson variability index and performed the period search with the Lomb-Scargle periodogram for periods between 0.83-45 days. Period detections were verified using false alarm probability levels, Saunders statistics, the string and rope length method, and visual verification of folded light curves. Results: We identified 1224 periodic variable stars (24% of the candidate member sample, 8% of the disk-bearing sample, and 28% of the non-disk-bearing sample). Monte Carlo simulations were performed in order to evaluate completeness and contamination of the periodic sample, out of which 894 measured periods were considered reliable. Our study was considered reasonably complete for periods between 2 and 30 days. Conclusions: The general scenario for the rotational evolution of young stars seen in other regions is confirmed by Cygnus OB2 period distributions with disc-bearing stars rotating on average more slowly than non-disk-bearing stars. A mass-rotation dependence was also verified, but as in NGC 6530, very low mass stars (M ≤ 0.4 M⊙) are rotating on average slower than higher mass stars (0.4M⊙

High-performance mass storage system for workstations

NASA Technical Reports Server (NTRS)

Chiang, T.; Tang, Y.; Gupta, L.; Cooperman, S.

1993-01-01

Reduced Instruction Set Computer (RISC) workstations and Personnel Computers (PC) are very popular tools for office automation, command and control, scientific analysis, database management, and many other applications. However, when using Input/Output (I/O) intensive applications, the RISC workstations and PC's are often overburdened with the tasks of collecting, staging, storing, and distributing data. Also, by using standard high-performance peripherals and storage devices, the I/O function can still be a common bottleneck process. Therefore, the high-performance mass storage system, developed by Loral AeroSys' Independent Research and Development (IR&D) engineers, can offload a RISC workstation of I/O related functions and provide high-performance I/O functions and external interfaces. The high-performance mass storage system has the capabilities to ingest high-speed real-time data, perform signal or image processing, and stage, archive, and distribute the data. This mass storage system uses a hierarchical storage structure, thus reducing the total data storage cost, while maintaining high-I/O performance. The high-performance mass storage system is a network of low-cost parallel processors and storage devices. The nodes in the network have special I/O functions such as: SCSI controller, Ethernet controller, gateway controller, RS232 controller, IEEE488 controller, and digital/analog converter. The nodes are interconnected through high-speed direct memory access links to form a network. The topology of the network is easily reconfigurable to maximize system throughput for various applications. This high-performance mass storage system takes advantage of a 'busless' architecture for maximum expandability. The mass storage system consists of magnetic disks, a WORM optical disk jukebox, and an 8mm helical scan tape to form a hierarchical storage structure. Commonly used files are kept in the magnetic disk for fast retrieval. The optical disks are used as archive media, and the tapes are used as backup media. The storage system is managed by the IEEE mass storage reference model-based UniTree software package. UniTree software will keep track of all files in the system, will automatically migrate the lesser used files to archive media, and will stage the files when needed by the system. The user can access the files without knowledge of their physical location. The high-performance mass storage system developed by Loral AeroSys will significantly boost the system I/O performance and reduce the overall data storage cost. This storage system provides a highly flexible and cost-effective architecture for a variety of applications (e.g., realtime data acquisition with a signal and image processing requirement, long-term data archiving and distribution, and image analysis and enhancement).

A circumstellar disk associated with a massive protostellar object.

PubMed

Jiang, Zhibo; Tamura, Motohide; Fukagawa, Misato; Hough, Jim; Lucas, Phil; Suto, Hiroshi; Ishii, Miki; Yang, Ji

2005-09-01

The formation process for stars with masses several times that of the Sun is still unclear. The two main theories are mergers of several low-mass young stellar objects, which requires a high stellar density, or mass accretion from circumstellar disks in the same way as low-mass stars are formed, accompanied by outflows during the process of gravitational infall. Although a number of disks have been discovered around low- and intermediate-mass young stellar objects, the presence of disks around massive young stellar objects is still uncertain and the mass of the disk system detected around one such object, M17, is disputed. Here we report near-infrared imaging polarimetry that reveals an outflow/disk system around the Becklin-Neugebauer protostellar object, which has a mass of at least seven solar masses (M(o)). This strongly supports the theory that stars with masses of at least 7M(o) form in the same way as lower mass stars.

The End of Protoplanetary Disk Evolution: An ALMA Survey of Upper Scorpius

NASA Astrophysics Data System (ADS)

Barenfeld, Scott A.; Carpenter, John M.; Sargent, Anneila I.; Ricci, Luca; Isella, Andrea

2017-01-01

The evolution of the mass of solids in circumstellar disks is a key factor in determining how planets form. Infrared observations have established that the dust in primordial disks vanishes around the majority of stars by an age of 5-10 Myr. However, how this disappearance proceeds is poorly constrained. Only with longer wavelength observations, where the dust emission is optically thin, is it possible to measure disk dust mass and how it varies as a function of age. To this end, we have obtained ALMA 0.88 mm observations of over 100 sources with suspected circumstellar disks in the Upper Scorpius OB Association (Upper Sco). The 5-11 Myr age of Upper Sco suggests that any such disks will be quite evolved, making this association an ideal target to compare to systems of younger disks in order to study evolution. With ALMA, we achieve an order of magnitude improvement in sensitivity over previous (sub)millimeter surveys of Upper Sco and detect 58 disks in the continuum. We calculate the total dust masses of these disks and compare their masses to those of younger disks in Taurus, Lupus, and Chamaeleon. We find strong evidence for a decline in disk dust mass between these 1-3 Myr old systems and the 5-11 Myr old Upper Sco. Our results represent the first definitive measurement of a decline in disk dust mass with age.

Host Star Dependence of Small Planet Mass–Radius Distributions

NASA Astrophysics Data System (ADS)

Neil, Andrew R.; Rogers, Leslie A.

2018-05-01

The planet formation environment around M dwarf stars is different than around G dwarf stars. The longer hot protostellar phase, activity levels and lower protoplanetary disk mass of M dwarfs all may leave imprints on the composition distribution of planets. We use hierarchical Bayesian modeling conditioned on the sample of transiting planets with radial velocity mass measurements to explore small planet mass–radius distributions that depend on host star mass. We find that the current mass–radius data set is consistent with no host star mass dependence. These models are then applied to the Kepler planet radius distribution to calculate the mass distribution of close-orbiting planets and how it varies with host star mass. We find that the average heavy element mass per star at short orbits is higher for M dwarfs compared to FGK dwarfs, in agreement with previous studies. This work will facilitate comparisons between microlensing planet surveys and Kepler, and will provide an analysis framework that can readily be updated as more M dwarf planets are discovered by ongoing and future surveys such as K2 and the Transiting Exoplanet Survey Satellite.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Christine H.; Mittal, Tushar; Kuchner, Marc

During the Spitzer Space Telescope cryogenic mission, Guaranteed Time Observers, Legacy Teams, and General Observers obtained Infrared Spectrograph (IRS) observations of hundreds of debris disk candidates. We calibrated the spectra of 571 candidates, including 64 new IRAS and Multiband Imaging Photometer for Spitzer (MIPS) debris disks candidates, modeled their stellar photospheres, and produced a catalog of excess spectra for unresolved debris disks. For 499 targets with IRS excess but without strong spectral features (and a subset of 420 targets with additional MIPS 70 μm observations), we modeled the IRS (and MIPS data) assuming that the dust thermal emission was well-describedmore » using either a one- or two-temperature blackbody model. We calculated the probability for each model and computed the average probability to select among models. We found that the spectral energy distributions for the majority of objects (∼66%) were better described using a two-temperature model with warm (T {sub gr} ∼ 100-500 K) and cold (T {sub gr} ∼ 50-150 K) dust populations analogous to zodiacal and Kuiper Belt dust, suggesting that planetary systems are common in debris disks and zodiacal dust is common around host stars with ages up to ∼1 Gyr. We found that younger stars generally have disks with larger fractional infrared luminosities and higher grain temperatures and that higher-mass stars have disks with higher grain temperatures. We show that the increasing distance of dust around debris disks is inconsistent with self-stirred disk models, expected if these systems possess planets at 30-150 AU. Finally, we illustrate how observations of debris disks may be used to constrain the radial dependence of material in the minimum mass solar nebula.« less

Two-dimensional modeling of density and thermal structure of dense circumstellar outflowing disks

NASA Astrophysics Data System (ADS)

Kurfürst, P.; Feldmeier, A.; Krtička, J.

2018-06-01

Context. Evolution of massive stars is affected by a significant loss of mass either via (nearly) spherically symmetric stellar winds or by aspherical mass-loss mechanisms, namely the outflowing equatorial disks. However, the scenario that leads to the formation of a disk or rings of gas and dust around massive stars is still under debate. It is also unclear how various forming physical mechanisms of the circumstellar environment affect its shape and density, as well as its kinematic and thermal structure. Aims: We study the hydrodynamic and thermal structure of optically thick, dense parts of outflowing circumstellar disks that may be formed around various types of critically rotating massive stars, for example, Be stars, B[e] supergiant (sgB[e]) stars or Pop III stars. We calculate self-consistent time-dependent models of temperature and density structure in the disk's inner dense region that is strongly affected by irradiation from a rotationally oblate central star and by viscous heating. Methods: Using the method of short characteristics, we specify the optical depth of the disk along the line-of-sight from stellar poles. Within the optically thick dense region with an optical depth of τ > 2/3 we calculate the vertical disk thermal structure using the diffusion approximation while for the optically thin outer layers we assume a local thermodynamic equilibrium with the impinging stellar irradiation. For time-dependent hydrodynamic modeling, we use two of our own types of hydrodynamic codes: two-dimensional operator-split numerical code based on an explicit Eulerian finite volume scheme on a staggered grid, and unsplit code based on the Roe's method, both including full second-order Navier-Stokes shear viscosity. Results: Our models show the geometric distribution and contribution of viscous heating that begins to dominate in the central part of the disk for mass-loss rates higher than Ṁ ≳ 10-10 M⊙ yr-1. In the models of dense viscous disks with Ṁ > 10-8 M⊙ yr-1, the viscosity increases the central temperature up to several tens of thousands of Kelvins, however the temperature rapidly drops with radius and with distance from the disk midplane. The high mass-loss rates and high viscosity lead to instabilities with significant waves or bumps in density and temperature in the very inner disk region. Conclusions: The two-dimensional radial-vertical models of dense outflowing disks including the full Navier-Stokes viscosity terms show very high temperatures that are however limited to only the central disk cores inside the optically thick area, while near the edge of the optically thick region the temperature may be low enough for the existence of neutral hydrogen, for example.

Quasi-periodic Behavior of Mini-disks in Binary Black Holes Approaching Merger

NASA Astrophysics Data System (ADS)

Bowen, Dennis B.; Mewes, Vassilios; Campanelli, Manuela; Noble, Scott C.; Krolik, Julian H.; Zilhão, Miguel

2018-01-01

We present the first magnetohydrodynamic simulation in which a circumbinary disk around a relativistic binary black hole feeds mass to individual accretion disks (“mini-disks”) around each black hole. Mass flow through the accretion streams linking the circumbinary disk to the mini-disks is modulated quasi-periodically by the streams’ interaction with a nonlinear m = 1 density feature, or “lump,” at the inner edge of the circumbinary disk: the stream supplying each mini-disk comes into phase with the lump at a frequency 0.74 times the binary orbital frequency. Because the binary is relativistic, the tidal truncation radii of the mini-disks are not much larger than their innermost stable circular orbits; consequently, the mini-disks’ inflow times are shorter than the conventional estimate and are comparable to the stream modulation period. As a result, the mini-disks are always in inflow disequilibrium, with their masses and spiral density wave structures responding to the stream’s quasi-periodic modulation. The fluctuations in each mini-disk’s mass are so large that as much as 75% of the total mini-disk mass can be contained within a single mini-disk. Such quasi-periodic modulation of the mini-disk structure may introduce distinctive time-dependent features in the binary’s electromagnetic emission.

Gas Mass Tracers in Protoplanetary Disks: CO is Still the Best

NASA Astrophysics Data System (ADS)

Molyarova, Tamara; Akimkin, Vitaly; Semenov, Dmitry; Henning, Thomas; Vasyunin, Anton; Wiebe, Dmitri

2017-11-01

Protoplanetary disk mass is a key parameter controlling the process of planetary system formation. CO molecular emission is often used as a tracer of gas mass in the disk. In this study, we consider the ability of CO to trace the gas mass over a wide range of disk structural parameters, and we search for chemical species that could possibly be used as alternative mass tracers to CO. Specifically, we apply detailed astrochemical modeling to a large set of models of protoplanetary disks around low-mass stars to select molecules with abundances correlated with the disk mass and being relatively insensitive to other disk properties. We do not consider sophisticated dust evolution models, restricting ourselves to the standard astrochemical assumption of 0.1 μm dust. We find that CO is indeed the best molecular tracer for total gas mass, despite the fact that it is not the main carbon carrier, provided reasonable assumptions about CO abundance in the disk are used. Typically, chemical reprocessing lowers the abundance of CO by a factor of 3, compared to the case where photodissociation and freeze-out are the only ways of CO depletion. On average, only 13% C atoms reside in gas-phase CO, albeit with variations from 2% to 30%. CO2, H2O, and H2CO can potentially serve as alternative mass tracers, with the latter two only applicable if disk structural parameters are known.

Toward a Galactic Distribution of Planets. I. Methodology and Planet Sensitivities of the 2015 High-cadence Spitzer Microlens Sample

NASA Astrophysics Data System (ADS)

Zhu, Wei; Udalski, A.; Calchi Novati, S.; Chung, S.-J.; Jung, Y. K.; Ryu, Y.-H.; Shin, I.-G.; Gould, A.; Lee, C.-U.; Albrow, M. D.; Yee, J. C.; Han, C.; Hwang, K.-H.; Cha, S.-M.; Kim, D.-J.; Kim, H.-W.; Kim, S.-L.; Kim, Y.-H.; Lee, Y.; Park, B.-G.; Pogge, R. W.; KMTNet Collaboration; Poleski, R.; Mróz, P.; Pietrukowicz, P.; Skowron, J.; Szymański, M. K.; KozLowski, S.; Ulaczyk, K.; Pawlak, M.; OGLE Collaboration; Beichman, C.; Bryden, G.; Carey, S.; Fausnaugh, M.; Gaudi, B. S.; Henderson, C. B.; Shvartzvald, Y.; Wibking, B.; Spitzer Team

2017-11-01

We analyze an ensemble of microlensing events from the 2015 Spitzer microlensing campaign, all of which were densely monitored by ground-based high-cadence survey teams. The simultaneous observations from Spitzer and the ground yield measurements of the microlensing parallax vector {{\\boldsymbol{π }}}{{E}}, from which compact constraints on the microlens properties are derived, including ≲25% uncertainties on the lens mass and distance. With the current sample, we demonstrate that the majority of microlenses are indeed in the mass range of M dwarfs. The planet sensitivities of all 41 events in the sample are calculated, from which we provide constraints on the planet distribution function. In particular, assuming a planet distribution function that is uniform in {log}q, where q is the planet-to-star mass ratio, we find a 95% upper limit on the fraction of stars that host typical microlensing planets of 49%, which is consistent with previous studies. Based on this planet-free sample, we develop the methodology to statistically study the Galactic distribution of planets using microlensing parallax measurements. Under the assumption that the planet distributions are the same in the bulge as in the disk, we predict that ∼1/3 of all planet detections from the microlensing campaigns with Spitzer should be in the bulge. This prediction will be tested with a much larger sample, and deviations from it can be used to constrain the abundance of planets in the bulge relative to the disk.

Gravitomagnetic acceleration of accretion disk matter to polar jets

NASA Astrophysics Data System (ADS)

Poirier, John; Mathews, Grant

2016-03-01

The motion of the masses of an accretion disk around a black hole creates a general relativistic, gravitomagnetic field (GEM) from the moving matter (be it charged or uncharged) of the accretion disk. This GEM field accelerates moving masses (neutral or charged) near the accretion disk vertically upward and away from the disk, and then inward toward the axis of the disk. As the accelerated material nears the axis with approximately vertical angles, a frame dragging effect contributes to the formation of narrow jets emanating from the poles. This GEM effect is numerically evaluated in the first post Newtonian (1PN) approximation from observable quantities like the mass and velocity of the disk. This GEM force is linear in the total mass of the accretion disk matter and quadratic in the velocity of matter near to the disk with approximately the same velocity. Since these masses and velocities can be quite high in astrophysical contexts, the GEM force, which in other contexts is weak, is quite significant. This GEM effect is compared to the ordinary electromagnetic effects applied to this problem in the past.

Photoionization of disk galaxies: An explanation of the sharp edges in the H I distribution

NASA Technical Reports Server (NTRS)

Dove, James B.; Shull, J. Michael

1994-01-01

We have reproduced the observed radial truncation of the H I distribution in isolated spiral galaxies with a model in which extragalactic radiation photoionizes the gaseous disk. For a galactic mass distribution model that reproduces the observed rotation curves, including dark matter in the disk and halo, the vertical structure of the gas is determined self-consistently. The ionization structure and column densities of H and He ions are computed by solving the radiation transfer equation for both continuum and lines. Our model is similar to that of Maloney, and the H I structure differs by less than 10%. The radial structure of the column density of H I is found to be more sensitive to the extragalactic radiation field than to the distribution of mass. For this reason, considerable progress can be made in determining the extragalactic flux of ionizing photons, phi(sub ex), with more 21 cm observations of isolated galaxies. However, owing to the uncertainty of the radial distribution of total hydrogen at large radii, inferring the extragalactic flux by comparing the observed edges to photoionization models is somewhat subjective. We find 1 x 10(exp 4)/sq cm/s is less than or approximately phi(sub ex) is less than or approximately 5 x 10(exp 4)/sq cm/s, corresponding to 2.1 is less than or approximately iota(sub 0) is less than or approximately 10.5 x 10(exp -23) ergs/sq cm/s/Hz/sr for a 1/nu spectrum. Although somewhat higher, our inferred range of iota(sub 0) is consistent with the large range of values obtained by Kulkarni & Fall from the 'proximity effect' toward Quasi-Stellar Objects (QSOs) at approximately 0.5.

A Comprehensive View of Circumstellar Disks in Chamaeleon I: Infrared Excess, Accretion Signatures, and Binarity

NASA Astrophysics Data System (ADS)

Damjanov, Ivana; Jayawardhana, Ray; Scholz, Alexander; Ahmic, Mirza; Nguyen, Duy C.; Brandeker, Alexis; van Kerkwijk, Marten H.

2007-12-01

We present a comprehensive study of disks around 81 young, low-mass stars and brown dwarfs in the nearby ~2 Myr old Chamaeleon I star-forming region. We use mid-infrared photometry from the Spitzer Space Telescope, supplemented by findings from ground-based high-resolution optical spectroscopy and adaptive optics imaging. We derive disk fractions of 52%+/-6% and 58+6-7% based on 8 and 24 μm color excesses, respectively, consistent with those reported for other clusters of similar age. Within the uncertainties, the disk frequency in our sample of K3-M8 objects in Cha I does not depend on stellar mass. Diskless and disk-bearing objects have similar spatial distributions. There are no obvious transition disks in our sample, implying a rapid timescale for the inner disk clearing process; however, we find two objects with weak excess at 3-8 μm and substantial excess at 24 μm, which may indicate grain growth and dust settling in the inner disk. For a subsample of 35 objects with high-resolution spectra, we investigate the connection between accretion signatures and dusty disks: in the vast majority of cases (29/35) the two are well correlated, suggesting that, on average, the timescale for gas dissipation is similar to that for clearing the inner dust disk. The exceptions are six objects for which dust disks appear to persist even though accretion has ceased or dropped below measurable levels. Adaptive optics images of 65 of our targets reveal that 17 have companions at (projected) separations of 10-80 AU. Of the five <~20 AU binaries, four lack infrared excess, possibly indicating that a close companion leads to faster disk dispersal. The closest binary with excess is separated by ~20 AU, which sets an upper limit of ~8 AU for the outer disk radius. The overall disk frequency among stars with companions (35+15-13%) is lower than (but still statistically consistent with) the value for the total sample.

The Disk Wind Model of the Broad Line Regions in Active Galactic Nuclei and Cataclysmic Variables

NASA Technical Reports Server (NTRS)

Begelman, Mitchell

2002-01-01

This is the final progress report for our Astrophysics Theory Program (NRA 97-OSS12) grant NAG5-7723. We have made considerable progress on incorporating photoionization calculations with a 2.5D hydrodynamical code to model disk winds in AGNs. Following up on our simultaneous broad band monitoring campaign of the type I Seyfert galaxy NGC 5548, we have investigated the constraints imposed on models of accretion in Seyfert galaxies by their optical, UV, and X-ray spectral energy distributions (SEDs). Using results from thermal Comptonization models that relate the physical properties of the hot inner accretion flow to the thermal reprocessing that occurs in the surrounding colder thin disk, we find that we can constrain the central black hole mass, accretion rate and size scale of the hot central flow. We have applied our model to observations of Seyfert galaxies NGC 3516, NGC 7469 and NGC 5548. Our mass and accretion rate estimates for these objects roughly agree with those found using other methods.

FALL-BACK DISKS IN LONG AND SHORT GAMMA-RAY BURSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cannizzo, J. K.; Troja, E.; Gehrels, N., E-mail: John.K.Cannizzo@nasa.gov

2011-06-10

We present time-dependent numerical calculations for fall-back disks relevant to gamma-ray bursts (GRBs) in which the disk of material surrounding the black hole powering the GRB jet modulates the mass flow and hence the strength of the jet. Given the initial existence of a small mass {approx}< 10{sup -4} M{sub sun} near the progenitor with a circularization radius {approx}10{sup 10}-10{sup 11} cm, an unavoidable consequence will be the formation of an 'external disk' whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. For long GRBs, if the mass distribution inmore » the initial fall-back disk traces the progenitor envelope, then a radius {approx}10{sup 11} cm gives a timescale {approx}10{sup 4} s for the X-ray plateau. For late times t > 10{sup 7} s a steepening due to a cooling front in the disk may have observational support in GRB 060729. For short GRBs, one expects most of the mass initially to lie at small radii <10{sup 8} cm; however, the presence of even a trace amount {approx}10{sup -9} M{sub sun} of high angular material can give a brief plateau in the light curve. By studying the plateaus in the X-ray decay of GRBs, which can last up to {approx}10{sup 4} s after the prompt emission, Dainotti et al. find an apparent inverse relation between the X-ray luminosity at the end of the plateau and the duration of the plateau. We show that this relation may simply represent the fact that one is biased against detecting faint plateaus and therefore preferentially sampling the more energetic GRBs. If, however, there were a standard reservoir in fall-back mass, our model could reproduce the inverse X-ray luminosity-duration relation. We emphasize that we do not address the very steep, initial decays immediately following the prompt emission, which have been modeled by Lindner et al. as fall back of the progenitor core, and may entail the accretion of {approx}> 1 M{sub sun}.« less

Do Disk Galaxies Have Different Central Velocity Dispersions At A Given Rotation Velocity?

NASA Astrophysics Data System (ADS)

Danilovich, Taissa; Jones, H.; Mould, J.; Taylor, E.; Tonini, C.; Webster, R.

2011-05-01

Hubble's classification of spiral galaxies was one dimensional. Actually it was 1.5 dimensional, as he distinguished barred spirals. Van den Bergh's was two dimensional: spirals had luminosity classes too. Other schemes are summarized at http://www.daviddarling.info/encyclopedia/G/galaxyclassification.html A more quantitative approach is to classify spiral galaxies by rotation velocity. Their central velocity dispersion (bulge) tends to be roughly one half of their rotation velocity (disk). There is a trend from σ/W = 0.8 to σ/W = 0.2 as one goes from W = 100 to 500 km/s, where W is twice the rotation velocity. But some fraction of spirals have a velocity dispersion up to a factor of two larger than that. In hierarchical galaxy formation models, the relative contributions of σ and W depend on the mass accretion history of the galaxy, which determines the mass distribution of the dynamical components such as disk, bulge and dark matter halo. The wide variety of histories that originate in the hierarchical mass assembly produce at any value of W a wide range of σ/W, that reaches high values in more bulge- dominated systems. In a sense the two classifiers were both right: spirals are mostly one dimensional, but σ/W (bulge to disk ratio) is often larger than average. Is this a signature of merger history?

The low-mass stellar population in the young cluster Tr 37. Disk evolution, accretion, and environment

NASA Astrophysics Data System (ADS)

Sicilia-Aguilar, Aurora; Kim, Jinyoung Serena; Sobolev, Andrej; Getman, Konstantin; Henning, Thomas; Fang, Min

2013-11-01

Aims: We present a study of accretion and protoplanetary disks around M-type stars in the 4 Myr-old cluster Tr 37. With a well-studied solar-type population, Tr 37 is a benchmark for disk evolution. Methods: We used low-resolution spectroscopy to identify and classify 141 members (78 new ones) and 64 probable members, mostly M-type stars. Hα emission provides information about accretion. Optical, 2MASS, Spitzer, and WISE data are used to trace the spectral energy distributions (SEDs) and search for disks. We construct radiative transfer models to explore the structures of full-disks, pre-transition, transition, and dust-depleted disks. Results: Including the new members and the known solar-type stars, we confirm that a substantial fraction (~2/5) of disks show signs of evolution, either as radial dust evolution (transition/pre-transition disks) or as a more global evolution (with low small-dust masses, dust settling, and weak/absent accretion signatures). Accretion is strongly dependent on the SED type. About half of the transition objects are consistent with no accretion, and dust-depleted disks have weak (or undetectable) accretion signatures, especially among M-type stars. Conclusions: The analysis of accretion and disk structure suggests a parallel evolution of dust and gas. We find several distinct classes of evolved disks, based on SED type and accretion status, pointing to different disk dispersal mechanisms and probably different evolutionary paths. Dust depletion and opening of inner holes appear to be independent processes: most transition disks are not dust-depleted, and most dust-depleted disks do not require inner holes. The differences in disk structure between M-type and solar-type stars in Tr 37 (4 Myr old) are not as remarkable as in the young, sparse, Coronet cluster (1-2 Myr old), suggesting that other factors, like the environment/interactions in each cluster, are likely to play an important role in the disk evolution and dispersal. Finally, we also find some evidence of clumpy star formation or mini-clusters within Tr 37. Observations reported here were obtained at the MMT Observatory, a jointfacility of the Smithsonian Institution and the University of Arizona.Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC).Appendices A and B are available in electronic form at http://www.aanda.orgFull Tables A.1-A.5 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/A3

Dusty Dwarfs Galaxies Occulting A Bright Background Spiral

NASA Astrophysics Data System (ADS)

Holwerda, Benne

2017-08-01

The role of dust in shaping the spectral energy distributions of low mass disk galaxies remains poorly understood. Recent results from the Herschel Space Observatory imply that dwarf galaxies contain large amounts of cool (T 20K) dust, coupled with very modest optical extinctions. These seemingly contradictory conclusions may be resolved if dwarfs harbor a variety of dust geometries, e.g., dust at larger galactocentric radii or in quiescent dark clumps. We propose HST observations of six truly occulting dwarf galaxies drawn from the Galaxy Zoo catalog of silhouetted galaxy pairs. Confirmed, true occulting dwarfs are rare as most low-mass disks in overlap are either close satellites or do not have a confirmed redshift. Dwarf occulters are the key to determining the spatial extent of dust, the small scale structure introduced by turbulence, and the prevailing dust attenuation law. The recent spectroscopic confirmation of bona-fide low mass occulting dwarfs offers an opportunity to map dust in these with HST. What is the role of dust in the SED of these dwarf disk galaxies? With shorter feedback scales, how does star-formation affect their morphology and dust composition, as revealed from their attenuation curve? The resolution of HST allows us to map the dust disks down to the fine scale structure of molecular clouds and multi-wavelength imaging maps the attenuation curve and hence dust composition in these disks. We therefore ask for 2 orbits on each of 6 dwarf galaxies in F275W, F475W, F606W, F814W and F125W to map dust from UV to NIR to constrain the attenuation curve.

2MASS J22560844+5954299: the newly discovered cataclysmic star with the deepest eclipse

NASA Astrophysics Data System (ADS)

Kjurkchieva, D.; Khruzina, T.; Dimitrov, D.; Groebel, R.; Ibryamov, S.; Nikolov, G.

2015-12-01

Context. The SW Sex stars are assumed to represent a distinguished stage in cataclysmic variable (CV) evolution, making it especially important to study them. Aims: We discovered a new cataclysmic star and carried out prolonged and precise photometric observations, as well as medium-resolution spectral observations. Modelling these data allowed us to determine the physical parameters and to establish its peculiarities. Methods: To obtain a light curve solution we used model whose emission sources are a white dwarf surrounded by an accretion disk with a hot spot, a gaseous stream near the disk's lateral side, and a secondary star filling its Roche lobe. The obtained physical parameters are compared with those of other SW Sex-subtype stars. Results: The newly discovered cataclysmic variable 2MASS J22560844+5954299 shows the deepest eclipse amongst the known nova-like stars. It was reproduced by totally covering a very luminous accretion disk by a red secondary component. The temperature distribution of the disk is flatter than that of steady-state disk. The target is unusual with the combination of a low mass ratio q ~ 1.0 (considerably below the limit q = 1.2 of stable mass transfer of CVs) and an M-star secondary. The intensity of the observed three emission lines, Hα, He 5875, and He 6678, sharply increases around phase 0.0, accompanied by a Doppler jump to the shorter wavelength. The absence of eclipses of the emission lines and their single-peaked profiles means that they originate mainly in a vertically extended hot-spot halo. The emission Hα line reveals S-wave wavelength shifts with semi-amplitude of around 210 km s-1 and phase lag of 0.03. Conclusions: The non-steady-state emission of the luminous accretion disk of 2MASS J22560844+5954299 was attributed to the low viscosity of the disk matter caused by its unusually high temperature. The star shows all spectral properties of an SW Sex variable apart from the 0.5 central absorption. Based on data collected with the telescopes at Rozhen National Astronomical Observatory.Spectra (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A40

70 DA White Dwarfs Identified in LAMOST Pilot Survey

NASA Astrophysics Data System (ADS)

Zhao, J. K.; Luo, A. L.; Oswalt, T. D.; Zhao, G.

2013-06-01

We present a spectroscopically identified catalog of 70 DA white dwarfs (WDs) from the LAMOST pilot survey. Thirty-five are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogs. The effective temperature and gravity of these WDs are estimated by Balmer lines fitting. Most of them are hot WDs. The cooling times and masses of these WDs are estimated by interpolation in theoretical evolution tracks. The peak of the mass distribution is found to be ~0.6 M ⊙, which is consistent with prior work in the literature. The distances of these WDs are estimated using the method of synthetic spectral distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation that WDs with high mass are concentrated near the plane of the Galactic disk.

70 DA WHITE DWARFS IDENTIFIED IN LAMOST PILOT SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, J. K.; Luo, A. L.; Zhao, G.

2013-06-01

We present a spectroscopically identified catalog of 70 DA white dwarfs (WDs) from the LAMOST pilot survey. Thirty-five are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogs. The effective temperature and gravity of these WDs are estimated by Balmer lines fitting. Most of them are hot WDs. The cooling times and masses of these WDs are estimated by interpolation in theoretical evolution tracks. The peak of the mass distribution is found to be {approx}0.6 M {sub Sun }, which is consistent with prior work in the literature. The distances of these WDs aremore » estimated using the method of synthetic spectral distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation that WDs with high mass are concentrated near the plane of the Galactic disk.« less

Investigating FP Tau’s protoplanetary disk structure through modeling

NASA Astrophysics Data System (ADS)

Brinjikji, Marah; Espaillat, Catherine

2017-01-01

This project presents a study aiming to understand the structure of the protoplanetary disk around FP Tau, a very young, very low mass star in the Taurus star-forming region. We have gathered existing optical, Spitzer, Herschel and submillimeter observations to construct the spectral energy distribution (SED) of FP Tau. We have used the D’Alessio et al (2006) physically self-consistent irradiated accretion disk model including dust settling to model the disk of FP Tau. Using this method, the best fit for the SED of FP Tau is a model that includes a gap located 10-20 AU away from the star. This gap is filled with optically thin dust that separates the optically thick dust in the outer disk from the optically thick dust in the inner disk. These characteristics indicate that FP Tau’s protostellar system is best classified as a pre-transitional disk. Near-infrared interferometry in the K-Band from Willson et al 2016 indicates that FP Tau has a small gap located 10-20 AU from the star, which is consistent with the model we produced, lending further support to the pre-transitional disk interpretation. The most likely explanation for the existence of a gap in the disk is a forming planet.

CN rings in full protoplanetary disks around young stars as probes of disk structure

NASA Astrophysics Data System (ADS)

Cazzoletti, P.; van Dishoeck, E. F.; Visser, R.; Facchini, S.; Bruderer, S.

2018-01-01

Aims: Bright ring-like structure emission of the CN molecule has been observed in protoplanetary disks. We investigate whether such structures are due to the morphology of the disk itself or if they are instead an intrinsic feature of CN emission. With the intention of using CN as a diagnostic, we also address to which physical and chemical parameters CN is most sensitive. Methods: A set of disk models were run for different stellar spectra, masses, and physical structures via the 2D thermochemical code DALI. An updated chemical network that accounts for the most relevant CN reactions was adopted. Results: Ring-shaped emission is found to be a common feature of all adopted models; the highest abundance is found in the upper outer regions of the disk, and the column density peaks at 30-100 AU for T Tauri stars with standard accretion rates. Higher mass disks generally show brighter CN. Higher UV fields, such as those appropriate for T Tauri stars with high accretion rates or for Herbig Ae stars or for higher disk flaring, generally result in brighter and larger rings. These trends are due to the main formation paths of CN, which all start with vibrationally excited H_2^* molecules, that are produced through far ultraviolet (FUV) pumping of H2. The model results compare well with observed disk-integrated CN fluxes and the observed location of the CN ring for the TW Hya disk. Conclusions: CN rings are produced naturally in protoplanetary disks and do not require a specific underlying disk structure such as a dust cavity or gap. The strong link between FUV flux and CN emission can provide critical information regarding the vertical structure of the disk and the distribution of dust grains which affects the UV penetration, and could help to break some degeneracies in the SED fitting. In contrast with C2H or c-C3H2, the CN flux is not very sensitive to carbon and oxygen depletion.

HIDING IN THE SHADOWS: SEARCHING FOR PLANETS IN PRE-TRANSITIONAL AND TRANSITIONAL DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dobinson, Jack; Leinhardt, Zoë M.; Dodson-Robinson, Sarah E.

Transitional and pre-transitional disks can be explained by a number of mechanisms. This work aims to find a single observationally detectable marker that would imply a planetary origin for the gap and, therefore, indirectly indicate the presence of a young planet. N-body simulations were conducted to investigate the effect of an embedded planet of one Jupiter mass on the production of instantaneous collisional dust derived from a background planetesimal disk. Our new model allows us to predict the dust distribution and resulting observable markers with greater accuracy than previous works. Dynamical influences from a planet on a circular orbit aremore » shown to enhance dust production in the disk interior and exterior to the planet orbit, while removing planetesimals from the orbit itself, creating a clearly defined gap. In the case of an eccentric planet, the gap opened by the planet is not as clear as the circular case, but there is a detectable asymmetry in the dust disk.« less

Hydrocarbon Emission Rings in Protoplanetary Disks Induced by Dust Evolution

NASA Astrophysics Data System (ADS)

Bergin, Edwin A.; Du, Fujun; Cleeves, L. Ilsedore; Blake, G. A.; Schwarz, K.; Visser, R.; Zhang, K.

2016-11-01

We report observations of resolved C2H emission rings within the gas-rich protoplanetary disks of TW Hya and DM Tau using the Atacama Large Millimeter Array. In each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. In addition, we detect a C3H2 emission ring with an identical spatial distribution to C2H in the TW Hya disk. This suggests that these are hydrocarbon rings (I.e., not limited to C2H). Using a detailed thermo-chemical model we show that reproducing the emission from C2H requires a strong UV field and C/O > 1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. This naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. This stratification causes the disk surface and outer disk to have a greater permeability to UV photons. Furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of CO, leads to an elemental C/O ratio that exceeds unity in the UV-dominated disk. Thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane.

The ages and baryonic masses of clumps in turbulent, clumpy disk galaxies

NASA Astrophysics Data System (ADS)

Fisher, David

2017-08-01

We propose to measure the stellar populations and masses of massive star forming clumps at the resolution of the Jeans' length in a sample of massive, turbulent disk galaxies. Massive star-forming clumps are a critical component of the morphogical transformation of galaxies and the build-up of bulges. If, however, clumps dissipate quickly bulges may not form through clump phase, then clumps would build thick disks. Different feedback prescriptions have drastically different effects on clumps. Some feedback models (e.g. Hopkins et al 2012, FIRE simulations) completely destroy clumps whereas other feedback models allow clumps to persist (e.g. Bournaud et al. 2014). Therefore, to build accurate models of galaxy evolution we must know how long the lives of clumps are. The problem is that both due to resolution and available wavelength coverage it is impossible to precisely measure the ages and stellar masses of individual clumps in high-z galaxies. We have discovered a sample of extremely rare galaxies at z 0.1 that are extremely gas rich, turbulent and have a clumpy distribution of ionized gas. In all ways they are identical to those of the high-redshift Universe. We propose to employ UV-optical-near IR imaging with WFC3 to measure the stellar masses and mean ages of a set of 6 clumpy galaxies, containing 80 giant star forming clumps. This data complements our ALMA CO(1-0) maps of the same targets, and we will thus make the first maps of the full baryonic mass in turbulent disk galaxies. This work builds on our previous HST Halpha imaging program, and validates massive investments of HST time on high-z surveys of galaxies.

Companions and Environments of Low-Mass Stars: From Star-Forming Regions to the Field

NASA Astrophysics Data System (ADS)

Ward-Duong, Kimberly; Patience, Jenny; De Rosa, Robert J.; Bulger, Joanna; Rajan, Abhijith; Goodwin, Simon; Parker, Richard J.; McCarthy, Donald W.; Kulesa, Craig; van der Plas, Gerrit; Menard, Francois; Pinte, Christophe; Jackson, Alan Patrick; Bryden, Geoffrey; Turner, Neal J.; Harvey, Paul M.; Hales, Antonio

2017-01-01

We present results from two studies probing the multiplicity and environmental properties of low-mass stars: (1) The MinMs (M-dwarfs in Multiples) Survey, a large, volume-limited survey of 245 field M-dwarfs within 15 pc, and (2) the TBOSS (Taurus Boundary of Stellar/Substellar) Survey, an ongoing study of disk properties for the lowest-mass members within the Taurus star-forming region. The MinMs Survey provides new measurements of the companion star fraction, separation distribution, and mass ratio distribution for the nearest K7-M6 dwarfs, utilizing a combination of high-resolution adaptive optics imaging and digitized widefield archival plates to cover an unprecedented separation range of ~1-10,000 AU. Within these data, we also identify companions below the stellar/brown dwarf boundary, enabling characterization of the substellar companion population to low-mass field stars. For the much younger population in Taurus, we present results from ALMA Band 7 continuum observations of low-mass stellar and substellar Class II objects, spanning spectral types from M4-M7.75. The sub-millimeter detections of these disks provide key estimates of the dust mass in small grains, which is then assessed within the context of region age, environment, and viability for planet formation. This young population also includes a number of interesting young binary systems. Covering both young (1-2 Myr) and old (>5 Gyr) populations of low-mass stars, the results from these studies provide benchmark measurements on the population statistics of low-mass field stars, and on the early protoplanetary environments of their younger M-star counterparts.

The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps

NASA Astrophysics Data System (ADS)

Menu, J.; van Boekel, R.; Henning, Th.; Leinert, Ch.; Waelkens, C.; Waters, L. B. F. M.

2015-09-01

Context. The disks around Herbig Ae/Be stars are commonly divided into group I and group II based on their far-infrared spectral energy distribution, and the common interpretation for that is flared and flat disks. Our understanding of the evolution of these disks is rapidly changing. Recent observations suggest that many flaring disks have gaps, whereas flat disks are thought to be gapless. Aims: The different groups of objects can be expected to have different structural signatures in high-angular-resolution data, related to gaps, dust settling, and flaring. We aim to use such data to gain new insight into disk structure and evolution. Methods: Over the past 10 years, the MIDI instrument on the Very Large Telescope Interferometer has collected observations of several tens of protoplanetary disks. We modeled the large set of observations with simple geometric models and compared the characteristic sizes among the different objects. A population of radiative-transfer models was synthesized for interpreting the mid-infrared signatures. Results: Objects with similar luminosities show very different disk sizes in the mid-infrared. This may point to an intrinsic diversity or could also hint at different evolutionary stages of the disks. Restricting this to the young objects of intermediate mass, we confirm that most group I disks are in agreement with being transitional (i.e., they have gaps). We find that several group II objects have mid-infrared sizes and colors that overlap with sources classified as group I, transition disks. This suggests that these sources have gaps, which has been demonstrated for a subset of them. This may point to an intermediate population between gapless and transition disks. Conclusions: Flat disks with gaps are most likely descendants of flat disks without gaps. Potentially related to the formation of massive bodies, gaps may therefore even develop in disks in a far stage of grain growth and settling. The evolutionary implications of this new population could be twofold. Either gapped flat disks form a separate population of evolved disks or some of them may evolve further into flaring disks with large gaps. The latter transformation may be governed by the interaction with a massive planet, carving a large gap and dynamically exciting the grain population in the disk. Appendices A and B are available in electronic form at http://www.aanda.org

In-N-Out: The Gas Cycle from Dwarfs to Spiral Galaxies

NASA Astrophysics Data System (ADS)

Christensen, Charlotte R.; Davé, Romeel; Governato, Fabio; Pontzen, Andrew; Brooks, Alyson; Munshi, Ferah; Quinn, Thomas; Wadsley, James

2016-06-01

We examine the scalings of galactic outflows with halo mass across a suite of 20 high-resolution cosmological zoom galaxy simulations covering halo masses in the range {10}9.5{--}{10}12 {M}⊙ . These simulations self-consistently generate outflows from the available supernova energy in a manner that successfully reproduces key galaxy observables, including the stellar mass-halo mass, Tully-Fisher, and mass-metallicity relations. We quantify the importance of ejective feedback to setting the stellar mass relative to the efficiency of gas accretion and star formation. Ejective feedback is increasingly important as galaxy mass decreases; we find an effective mass loading factor that scales as {v}{{circ}}-2.2, with an amplitude and shape that are invariant with redshift. These scalings are consistent with analytic models for energy-driven wind, based solely on the halo potential. Recycling is common: about half of the outflow mass across all galaxy masses is later reaccreted. The recycling timescale is typically ˜1 Gyr, virtually independent of halo mass. Recycled material is reaccreted farther out in the disk and with typically ˜2-3 times more angular momentum. These results elucidate and quantify how the baryon cycle plausibly regulates star formation and alters the angular momentum distribution of disk material across the halo mass range where most cosmic star formation occurs.

On the nature of the symbiotic binary AX Persei

NASA Technical Reports Server (NTRS)

Mikolajewska, Joanna; Kenyon, Scott J.

1992-01-01

Photometric and spectroscopic observations of the symbiotic binary AX Persei are presented. This system contains a red giant that fills its tidal lobe and transfers material into an accretion disk surrounding a low-mass main-sequence star. The stellar masses - 1 solar mass for the red giant and about 0.4 solar mass for the companion - suggest AX Per is poised to enter a common envelope phase of evolution. The disk luminosity increases from L(disk) about 100 solar luminosity in quiescence to L(disk) about 5700 solar luminosity in outburst for a distance of d = 2.5 kpc. Except for visual maximum, high ionization permitted emission lines - such as He II - imply an EUV luminosity comparable to the disk luminosity. High-energy photons emitted by a hot boundary layer between the disk and central star ionize a surrounding nebula to produce this permitted line emission. High ionization forbidden lines form in an extended, shock-excited region well out of the binary's orbital plane and may be associated with mass loss from the disk.

Galaxy dynamics and the mass density of the universe.

PubMed

Rubin, V C

1993-06-01

Dynamical evidence accumulated over the past 20 years has convinced astronomers that luminous matter in a spiral galaxy constitutes no more than 10% of the mass of a galaxy. An additional 90% is inferred by its gravitational effect on luminous material. Here I review recent observations concerning the distribution of luminous and nonluminous matter in the Milky Way, in galaxies, and in galaxy clusters. Observations of neutral hydrogen disks, some extending in radius several times the optical disk, confirm that a massive dark halo is a major component of virtually every spiral. A recent surprise has been the discovery that stellar and gas motions in ellipticals are enormously complex. To date, only for a few spheroidal galaxies do the velocities extend far enough to probe the outer mass distribution. But the diverse kinematics of inner cores, peripheral to deducing the overall mass distribution, offer additional evidence that ellipticals have acquired gas-rich systems after initial formation. Dynamical results are consistent with a low-density universe, in which the required dark matter could be baryonic. On smallest scales of galaxies [10 kiloparsec (kpc); Ho = 50 km.sec-1.megaparsec-1] the luminous matter constitutes only 1% of the closure density. On scales greater than binary galaxies (i.e., >/=100 kpc) all systems indicate a density approximately 10% of the closure density, a density consistent with the low baryon density in the universe. If large-scale motions in the universe require a higher mass density, these motions would constitute the first dynamical evidence for nonbaryonic matter in a universe of higher density.

Galaxy dynamics and the mass density of the universe.

PubMed Central

Rubin, V C

1993-01-01

Dynamical evidence accumulated over the past 20 years has convinced astronomers that luminous matter in a spiral galaxy constitutes no more than 10% of the mass of a galaxy. An additional 90% is inferred by its gravitational effect on luminous material. Here I review recent observations concerning the distribution of luminous and nonluminous matter in the Milky Way, in galaxies, and in galaxy clusters. Observations of neutral hydrogen disks, some extending in radius several times the optical disk, confirm that a massive dark halo is a major component of virtually every spiral. A recent surprise has been the discovery that stellar and gas motions in ellipticals are enormously complex. To date, only for a few spheroidal galaxies do the velocities extend far enough to probe the outer mass distribution. But the diverse kinematics of inner cores, peripheral to deducing the overall mass distribution, offer additional evidence that ellipticals have acquired gas-rich systems after initial formation. Dynamical results are consistent with a low-density universe, in which the required dark matter could be baryonic. On smallest scales of galaxies [10 kiloparsec (kpc); Ho = 50 km.sec-1.megaparsec-1] the luminous matter constitutes only 1% of the closure density. On scales greater than binary galaxies (i.e., >/=100 kpc) all systems indicate a density approximately 10% of the closure density, a density consistent with the low baryon density in the universe. If large-scale motions in the universe require a higher mass density, these motions would constitute the first dynamical evidence for nonbaryonic matter in a universe of higher density. Images Fig. 3 Fig. 5 PMID:11607393

Rotational properties of hypermassive neutron stars from binary mergers

NASA Astrophysics Data System (ADS)

Hanauske, Matthias; Takami, Kentaro; Bovard, Luke; Rezzolla, Luciano; Font, José A.; Galeazzi, Filippo; Stöcker, Horst

2017-08-01

Determining the differential-rotation law of compact stellar objects produced in binary neutron stars mergers or core-collapse supernovae is an old problem in relativistic astrophysics. Addressing this problem is important because it impacts directly on the maximum mass these objects can attain and, hence, on the threshold to black-hole formation under realistic conditions. Using the results from a large number of numerical simulations in full general relativity of binary neutron star mergers described with various equations of state and masses, we study the rotational properties of the resulting hypermassive neutron stars. We find that the angular-velocity distribution shows only a modest dependence on the equation of state, thus exhibiting the traits of "quasiuniversality" found in other aspects of compact stars, both isolated and in binary systems. The distributions are characterized by an almost uniformly rotating core and a "disk." Such a configuration is significantly different from the j -constant differential-rotation law that is commonly adopted in equilibrium models of differentially rotating stars. Furthermore, the rest-mass contained in such a disk can be quite large, ranging from ≃0.03 M⊙ in the case of high-mass binaries with stiff equations of state, up to ≃0.2 M⊙ for low-mass binaries with soft equations of state. We comment on the astrophysical implications of our findings and on the long-term evolutionary scenarios that can be conjectured on the basis of our simulations.

Accretion Disk Spectra of the Ultra-luminous X-ray Sources in Nearby Spiral Galaxies and Galactic Superluminal Jet Sources

NASA Technical Reports Server (NTRS)

White, Nicholas E. (Technical Monitor); Ebisawa, Ken; Zycki, Piotr; Kubota, Aya; Mizuno, Tsunefumi; Watarai, Ken-ya

2003-01-01

Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures which cannot be explained in the framework of the standard optically thick accretion disk in the Schwarzschild metric. On the other hand, the standard accretion disk around the Kerr black hole might explain the observed high disk temperature, as the inner radius of the Kerr disk gets smaller and the disk temperature can be consequently higher. However, we point out that the observable Kerr disk spectra becomes significantly harder than Schwarzschild disk spectra only when the disk is highly inclined. This is because the emission from the innermost part of the accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen for a face-on disk. The Galactic superluminal jet sources are known to be highly inclined systems, thus their energy spectra may be explained with the standard Kerr disk with known black hole masses. For ULXs, on the other hand, the standard Kerr disk model seems implausible, since it is highly unlikely that their accretion disks are preferentially inclined, and, if edge-on Kerr disk model is applied, the black hole mass becomes unreasonably large (greater than or approximately equal to 300 Solar Mass). Instead, the slim disk (advection dominated optically thick disk) model is likely to explain the observed super- Eddington luminosities, hard energy spectra, and spectral variations of ULXs. We suggest that ULXs are accreting black holes with a few tens of solar mass, which is not unexpected from the standard stellar evolution scenario, and their X-ray emission is from the slim disk shining at super-Eddington luminosities.

RADIATION HYDRODYNAMICS MODELS OF THE INNER RIM IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flock, M.; Turner, N. J.; Fromang, S.

2016-08-20

Many stars host planets orbiting within a few astronomical units (AU). The occurrence rate and distributions of masses and orbits vary greatly with the host star’s mass. These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric and includemore » starlight heating; silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density; and accretion stresses parameterizing the results of MHD magnetorotational turbulence models. The results compare well with radiation hydrostatic solutions and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rim’s location. A small optically thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops near the location of thermal ionization at temperatures of about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.« less

Searching for Dust around Hyper Metal Poor Stars

NASA Astrophysics Data System (ADS)

Venn, Kim A.; Puzia, Thomas H.; Divell, Mike; Côté, Stephanie; Lambert, David L.; Starkenburg, Else

2014-08-01

We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] <-5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e.g., a warm debris disk (T <= 290 K), or debris disks with inner radii <=1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 μm is detected at the 2σ level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.

The AU Microscopii Debris Disk: Multiwavelength Imaging and Modeling

NASA Astrophysics Data System (ADS)

Fitzgerald, Michael P.; Kalas, Paul G.; Duchêne, Gaspard; Pinte, Christophe; Graham, James R.

2007-11-01

Debris disks around main-sequence stars are produced by the destruction of unseen parent bodies. AU Microscopii (GJ 803) is a compelling object to study in the context of disk evolution across different spectral types, as it is an M dwarf whose nearly edge-on disk may be directly compared to that of its A5 V sibling β Pic. We resolve the disk from 8-60 AU in the near-IR JHK' bands at high resolution with the Keck II Telescope and adaptive optics, and develop a data reduction technique for the removal of the stellar point-spread function. We measure a blue color across the near-IR bands, and confirm the presence of substructure in the inner disk. Some of the structural features exhibit wavelength-dependent positions. Recent measurements of the scattered-light polarization indicate the presence of porous grains. The scattering properties of these porous grains have a strong effect on the inferred structure of the disk relative to the majority of previously modeled grain types. Complementing prior work, we use a Monte Carlo radiative transfer code to compare a relatively simple model of the distribution of porous grains to a broad data set, simultaneously fitting midplane surface brightness profiles and the spectral energy distribution. Our model confirms that the large-scale architecture of the disk is consistent with detailed models of steady state grain dynamics. A belt of parent bodies from 35-40 AU produces dust that is then swept outward by stellar wind and radiation. We infer the presence of very small grains in the region exterior to the belt, down to sizes of ~0.05 μm. These sizes are consistent with stellar mass-loss rates M˙*<<102 M˙solar

CONSTRAINTS FROM ASYMMETRIC HEATING: INVESTIGATING THE EPSILON AURIGAE DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearson, Richard L. III; Stencel, Robert E., E-mail: richard.pearson@du.edu, E-mail: robert.stencel@du.edu

2015-01-01

Epsilon Aurigae is a long-period eclipsing binary that likely contains an F0Ia star and a circumstellar disk enshrouding a hidden companion, assumed to be a main-sequence B star. High uncertainty in its parallax has kept the evolutionary status of the system in question and, hence, the true nature of each component. This unknown, as well as the absence of solid state spectral features in the infrared, requires an investigation of a wide parameter space by means of both analytic and Monte Carlo radiative transfer (MCRT) methods. The first MCRT models of epsilon Aurigae that include all three system components aremore » presented here. We seek additional system parameter constraints by melding analytic approximations with MCRT outputs (e.g., dust temperatures) on a first-order level. The MCRT models investigate the effects of various parameters on the disk-edge temperatures; these include two distances, three particle size distributions, three compositions, and two disk masses, resulting in 36 independent models. Specifically, the MCRT temperatures permit analytic calculations of effective heating and cooling curves along the disk edge. These are used to calculate representative observed fluxes and corresponding temperatures. This novel application of thermal properties provides the basis for utilization of other binary systems containing disks. We find degeneracies in the model fits for the various parameter sets. However, the results show a preference for a carbon disk with particle size distributions ≥10 μm. Additionally, a linear correlation between the MCRT noon and basal temperatures serves as a tool for effectively eliminating portions of the parameter space.« less

Formation of Planetary Populations I: Metallicity & Envelope Opacity Effects

NASA Astrophysics Data System (ADS)

Alessi, Matthew; Pudritz, Ralph E.

2018-05-01

We present a comprehensive body of simulations of the formation of exoplanetary populations that incorporate the role of planet traps in slowing planetary migration. The traps we include in our model are the water ice line, the disk heat transition, and the dead zone outer edge. We reduce our model parameter set to two physical parameters: the opacity of the accreting planetary atmospheres (κenv) and a measure of the efficiency of planetary accretion after gap opening (fmax). We perform planet population synthesis calculations based on the initial observed distributions of host star and disk properties - their disk masses, lifetimes, and stellar metallicities. We find the frequency of giant planet formation scales with disk metallicity, in agreement with the observed Jovian planet frequency-metallicity relation. We consider both X-ray and cosmic ray disk ionization models, whose differing ionization rates lead to different dead zone trap locations. In both cases, Jovian planets form in our model out to 2-3 AU, with a distribution at smaller radii dependent on the disk ionization source and the setting of envelope opacity. We find that low values of κenv (0.001-0.002 cm2 g-1) and X-ray disk ionization are necessary to obtain a separation between hot Jupiters near 0.1 AU, and warm Jupiters outside 0.6 AU, a feature present in the data. Our model also produces a large number of super Earths, but the majority are outside of 2 AU. As our model assumes a constant dust to gas ratio, we suggest that radial dust evolution must be taken into account to reproduce the observed super Earth population.

Rotation-Infall Motion around the Protostar IRAS 16293-2422 Traced by Water Maser Emission

NASA Astrophysics Data System (ADS)

Imai, Hiroshi; Iwata, Takahiro; Miyoshi, Makoto

1999-08-01

We made VLBI observations of the water maser emission associated with a protostar, IRAS 16293-2422, using the Kashima-Nobeyama Interferometer (KNIFE) and the Japanese domestic VLBI network (J-Net).\\footnote[2]. These distributions of water maser features showed the blue-shifted and red-shifted components separated in the north-south direction among three epochs spanning three years. The direction of the separation was perpendicular to the molecular outflow and parallel to the elongation of the molecular disk. These steady distributions were successfully modeled by a rotating-infalling disk with an outer radius of 100 AU around a central object with a mass of 0.3 MO . The local specific angular momentum of the disk was calculated to be 0.2-1.0times 10-3 km s-1 pc at a radius of 20-100 AU. This value is roughly equal to that of the disk of IRAS 00338+6312 in L1287 and those of the molecular disks around the protostars in the Taurus molecular cloud. The relatively large disk radius of about 100 AU traced by water maser emission suggests that impinging clumps onto the disk should be hotter than 200 K to excite the water maser emission. Mizusawa, Nobeyama, and Kagoshima stations are operated by staff members of National Astronomical Observatory of the Ministry of Education, Science, Sports and Culture. Kashima station is operated by staff members of Communications Research Laboratory of the Ministry of Posts and Telecomunications. The recent status of J-Net is seen in the WWW home page: http://www.nro.nao.ac.jp/\\ \\ miyaji/Jnet.

A Pan-Carina Young Stellar Object Catalog: Intermediate-mass Young Stellar Objects in the Carina Nebula Identified Via Mid-infrared Excess Emission

NASA Astrophysics Data System (ADS)

Povich, Matthew S.; Smith, Nathan; Majewski, Steven R.; Getman, Konstantin V.; Townsley, Leisa K.; Babler, Brian L.; Broos, Patrick S.; Indebetouw, Rémy; Meade, Marilyn R.; Robitaille, Thomas P.; Stassun, Keivan G.; Whitney, Barbara A.; Yonekura, Yoshinori; Fukui, Yasuo

2011-05-01

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M sun < m <~ 10 M sun) objects with disks, including Herbig Ae/Be stars and their less evolved progenitors. The PCYC provides a valuable complementary data set to the CCCP X-ray source catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars. Candidate protostars with X-ray detections tend to be more evolved than those without. In most cases, X-ray emission apparently originating from intermediate-mass, disk-dominated YSOs is consistent with the presence of low-mass companions, but we also find that X-ray emission correlates with cooler stellar photospheres and higher disk masses. We suggest that intermediate-mass YSOs produce X-rays during their early pre-main-sequence evolution, perhaps driven by magnetic dynamo activity during the convective atmosphere phase, but this emission dies off as the stars approach the main sequence. Extrapolating over the stellar initial mass function scaled to the PCYC population, we predict a total population of >2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M sun yr-1. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bergin, Edwin A.; Du, Fujun; Schwarz, K.

We report observations of resolved C{sub 2}H emission rings within the gas-rich protoplanetary disks of TW Hya and DM Tau using the Atacama Large Millimeter Array. In each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. In addition, we detect a C{sub 3}H{sub 2} emission ring with an identical spatial distribution to C{sub 2}H in the TW Hya disk. This suggests that these are hydrocarbon rings (i.e., not limited to C{sub 2}H). Using a detailed thermo-chemical model we show that reproducing the emission frommore » C{sub 2}H requires a strong UV field and C/O > 1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. This naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. This stratification causes the disk surface and outer disk to have a greater permeability to UV photons. Furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of CO, leads to an elemental C/O ratio that exceeds unity in the UV-dominated disk. Thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane.« less

A CONSTANT LIMITING MASS SCALE FOR FLAT EARLY-TYPE GALAXIES FROM z {approx} 1 TO z = 0: DENSITY EVOLVES BUT SHAPES DO NOT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holden, Bradford P.; Van der Wel, Arjen; Rix, Hans-Walter

2012-04-20

We measure the evolution in the intrinsic shape distribution of early-type galaxies from z {approx} 1 to z {approx} 0 by analyzing their projected axis-ratio distributions. We extract a low-redshift sample (0.04 < z < 0.08) of early-type galaxies with very low star formation rates from the Sloan Digital Sky Survey, based on a color-color selection scheme and verified through the absence of emission lines in the spectra. The inferred intrinsic shape distribution of these early-type galaxies is strongly mass dependent: the typical short-to-long intrinsic axis ratio of high-mass early-type galaxies (>10{sup 11} M{sub Sun }) is 2:3, whereas atmore » masses below 10{sup 11} M{sub Sun} this ratio narrows to 1:3, or more flattened galaxies. In an entirely analogous manner, we select a high-redshift sample (0.6 < z < 0.8) from two deep-field surveys with multi-wavelength and Hubble Space Telescope/Advanced Camera for Surveys imaging: GEMS and COSMOS. We find a seemingly universal mass of {approx}10{sup 11} M{sub Sun} for highly flattened early-type systems at all redshifts. This implies that the process that grows an early-type galaxy above this ceiling mass, irrespective of cosmic epoch, involves forming round systems. Using both parametric and non-parametric tests, we find no evolution in the projected axis-ratio distribution for galaxies with masses >3 Multiplication-Sign 10{sup 10} M{sub Sun} with redshift. At the same time, our samples imply an increase of 2-3 Multiplication-Sign in comoving number density for early-type galaxies at masses >3 Multiplication-Sign 10{sup 10} M{sub Sun }, in agreement with previous studies. Given the direct connection between the axis-ratio distribution and the underlying bulge-to-disk ratio distribution, our findings imply that the number density evolution of early-type galaxies is not exclusively driven by the emergence of either bulge- or disk-dominated galaxies, but rather by a balanced mix that depends only on the stellar mass of the galaxy. The challenge for galaxy formation models is to reproduce this overall non-evolving ratio of flattened to round early-type galaxies in the context of a continually growing population.« less

Bimodal star formation - Constraints from the solar neighborhood

NASA Technical Reports Server (NTRS)

Wyse, Rosemary F. G.; Silk, J.

1987-01-01

The chemical evolution resulting from a simple model of bimodal star formulation is investigated, using constraints from the solar neighborhood to set the parameters of the initial mass function and star formation rate. The two modes are an exclusively massive star mode, which forms stars at an exponentially declining rate, and a mode which contains stars of all masses and has a constant star formation rate. Satisfactory agreement with the age-metallicity relation for the thin disk and with the metallicity structure of the thin-disk and spheroid stars is possible only for a small range of parameter values. The preferred model offers a resolution to several of the long-standing problems of galactic chemical evolution, including explanations of the age-metallicity relation, the gas consumption time scale, and the stellar cumulative metallicity distributions.

DETECTION OF STRONG MILLIMETER EMISSION FROM THE CIRCUMSTELLAR DUST DISK AROUND V1094 SCO: COLD AND MASSIVE DISK AROUND A T TAURI STAR IN A QUIESCENT ACCRETION PHASE?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsukagoshi, Takashi; Kohno, Kotaro; Saito, Masao

2011-01-01

We present the discovery of a cold massive dust disk around the T Tauri star V1094 Sco in the Lupus molecular cloud from the 1.1 mm continuum observations with AzTEC on ASTE. A compact (r{approx}< 320 AU) continuum emission coincides with the stellar position having a flux density of 272 mJy, which is the largest among T Tauri stars in Lupus. We also present the detection of molecular gas associated with the star in the five-point observations in {sup 12}CO J = 3-2 and {sup 13}CO J = 3-2. Since our {sup 12}CO and {sup 13}CO observations did not showmore » any signature of a large-scale outflow or a massive envelope, the compact dust emission is likely to come from a disk around the star. The observed spectral energy distribution (SED) of V1094 Sco shows no distinct turnover from near-infrared to millimeter wavelengths, can be well described by a flattened disk for the dust component, and no clear dip feature around 10 {mu}m suggestive of the absence of an inner hole in the disk. We fit a simple power-law disk model to the observed SED. The estimated disk mass ranges from 0.03 M{sub sun} to {approx}>0.12 M{sub sun}, which is one or two orders of magnitude larger than the median disk mass of T Tauri stars in Taurus. The resultant temperature is lower than that of a flared disk with well-mixed dust in hydrostatic equilibrium and is probably attributed to the flattened disk geometry for the dust which the central star cannot illuminate efficiently. From these results, together with the fact that there is no signature of an inner hole in the SED, we suggest that the dust grains in the disk around V1094 Sco sank into the midplane with grain growth by coalescence and are in the evolutional stage just prior to or at the formation of planetesimals.« less

The early evolution of protostellar disks

NASA Technical Reports Server (NTRS)

Stahler, Steven W.; Korycansky, D. G.; Brothers, Maxwell J.; Touma, Jihad

1994-01-01

We consider the origin and intital growth of the disks that form around protostars during the collapse of rotating molecular cloud cores. These disks are assumed to be inviscid and pressure free, and to have masses small compared to those of their central stars. We find that there exist three distinct components-an outer disk, in which shocked gas moves with comparable azimuthal and radical velocities; and inner disk, where material follows nearly circular orbits, but spirals slowly toward the star because of the drag exerted by adjacent onfalling matter, and a turbulent ring adjoining the first two regions. Early in the evolution, i.e., soon after infalling matter begins to miss the star, only the outer disk is present, and the total mass acceration rate onto the protostar is undiminished. Once the outer disk boundary grows to more than 2.9 times the stellar radius, first the ring, and then the inner disk appear. Thereafter, the radii of all three components expand as t(exp 3). The mass of the ring increase with time and is always 13% of the total mass that has fallen from the cloud. Concurrently with the buildup of the inner disk and ring, the accretion rate onto the star falls off. However, the protostellar mass continue to rise, asymptotically as t(exp 1/4). We calculated the radiated flux from the inner and outer disk components due to the release of gravitational potential energy. The flux from the inner disk is dominant and rises steeply toward the stellar surface. We also determine the surface temperature of the inner disk as a function of radius. The total disk luminosity decreases slowly with time, while the contributions from the ring and inner disk both fall as t(exp -2).

Near-infrared structure of fast and slow-rotating disk galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schechtman-Rook, Andrew; Bershady, Matthew A., E-mail: andrew@astro.wisc.edu

We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHK {sub s}-band images and three-dimensional radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 km s{sup –1} 150 km s{sup –1}) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral galaxy, contains disks with h{sub z} ≲ 200 pc. NGC 4565, another fast-rotator, contains a prominent ring at a radius ∼5 kpc but nomore » super-thin disk. Despite these differences, all fast-rotating galaxies in our sample have inner truncations in at least one of their disks. These truncations lead to Freeman Type II profiles when projected face-on. Slow-rotating galaxies are less complex, lacking inner disk truncations and requiring fewer disk components to reproduce their light distributions. Super-thin disk components in undisturbed disks contribute ∼25% of the total K {sub s}-band light, up to that of the thin-disk contribution. The presence of super-thin disks correlates with infrared flux ratios; galaxies with super-thin disks have f{sub K{sub s}}/f{sub 60} {sub μm}≤0.12 for integrated light, consistent with super-thin disks being regions of ongoing star-formation. Attenuation-corrected vertical color gradients in (J – K {sub s}) correlate with the observed disk structure and are consistent with population gradients with young-to-intermediate ages closer to the mid-plane, indicating that disk heating—or cooling—is a ubiquitous phenomenon.« less

COAGULATION CALCULATIONS OF ICY PLANET FORMATION AT 15-150 AU: A CORRELATION BETWEEN THE MAXIMUM RADIUS AND THE SLOPE OF THE SIZE DISTRIBUTION FOR TRANS-NEPTUNIAN OBJECTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenyon, Scott J.; Bromley, Benjamin C., E-mail: skenyon@cfa.harvard.edu, E-mail: bromley@physics.utah.edu

2012-03-15

We investigate whether coagulation models of planet formation can explain the observed size distributions of trans-Neptunian objects (TNOs). Analyzing published and new calculations, we demonstrate robust relations between the size of the largest object and the slope of the size distribution for sizes 0.1 km and larger. These relations yield clear, testable predictions for TNOs and other icy objects throughout the solar system. Applying our results to existing observations, we show that a broad range of initial disk masses, planetesimal sizes, and fragmentation parameters can explain the data. Adding dynamical constraints on the initial semimajor axis of 'hot' Kuiper Beltmore » objects along with probable TNO formation times of 10-700 Myr restricts the viable models to those with a massive disk composed of relatively small (1-10 km) planetesimals.« less

Galactic disk dynamical tracers: Open clusters and the local Milky Way rotation curve and velocity field

NASA Astrophysics Data System (ADS)

Frinchaboy, Peter Michael, III

Establishing the rotation curve of the Milky Way is one of the fundamental contributions needed to understand the Galaxy and its mass distribution. We have undertaken a systematic spectroscopic survey of open star clusters which can serve as tracers of Galactic disk dynamics. We report on our initial sample of 67 clusters for which the Hydra multi-fiber spectrographs on the WIYN and Blanco telescopes have delivered ~1-2 km s -1 radial velocities (RVs) of many dozens of stars in the fields of each cluster, which are used to derive cluster membership and bulk cluster kinematics when combined with Tycho-2 proper motions. The clusters selected for study have a broad spatial distribution in order to be sensitive to the disk velocity field in all Galactic quadrants and across a Galactocentric radius range as much as 3.0 kpc from the solar circle. Through analysis of the cluster sample, we find (1) the rotation velocity of the Local Standard of Rest (LSR) is [Special characters omitted.] km s -1 , (2 ) the local rotation curve is declining with radius having a slope of -9.1 km s -1 kpc -1 , (3) we find (using R 0 = 8.5 kpc) the following Galactic parameters: A = 17.0 km s -1 kpc -1 and B = -8.9 km s -1 kpc -1 , which using a flat rotation curve and our determined values for the rotation velocity of the LSR yields a Galaxy mass within 1.5 R 0 of M = 1.4 ± 0.2 × 10 11 [Spe cial characters omitted.] and a M/L of 9 [Special characters omitted.] . We also explore the distribution of the local velocity field and find evidence for non- circular motion due to the spiral arms. Additionally, a number of outer disk ( R gc > 12 kpc) open clusters, including Be29 and Sa1, are studied that have potentially critical leverage on radial, age and metallicity gradients in the outer Galactic disk. We find that the measured kinematics of Sa1 and Be29 are consistent with being associated with the Galactic anticenter stellar structure (GASS; or Monoceros stream), which points to a possible "accretion" origin for these and possibly other outer disk open clusters, if one believes that GASS represents an accreting dwarf galaxy system.

THE DISTRIBUTION AND CHEMISTRY OF H{sub 2}CO IN THE DM TAU PROTOPLANETARY DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loomis, Ryan A.; Öberg, Karin I.; Guzman, Viviana V.

H{sub 2}CO ice on dust grains is an important precursor of complex organic molecules (COMs). H{sub 2}CO gas can be readily observed in protoplanetary disks and may be used to trace COM chemistry. However, its utility as a COM probe is currently limited by a lack of constraints on the relative contributions of two different formation pathways: on icy grain surfaces and in the gas phase. We use archival Atacama Large (sub-)Millimeter Array observations of the resolved distribution of H{sub 2}CO emission in the disk around the young low-mass star DM Tau to assess the relative importance of these formationmore » routes. The observed H{sub 2}CO emission has a centrally peaked and radially broad brightness profile (extending out to 500 AU). We compare these observations with disk chemistry models with and without grain-surface formation reactions and find that both gas and grain-surface chemistry are necessary to explain the spatial distribution of the emission. Gas-phase H{sub 2}CO production is responsible for the observed central peak, while grain-surface chemistry is required to reproduce the emission exterior to the CO snow line (where H{sub 2}CO mainly forms through the hydrogenation of CO ice before being non-thermally desorbed). These observations demonstrate that both gas and grain-surface pathways contribute to the observed H{sub 2}CO in disks and that their relative contributions depend strongly on distance from the host star.« less

Apparent Disk-mass Reduction and Planetisimal Formation in Gravitationally Unstable Disks in Class 0/I Young Stellar Objects

NASA Astrophysics Data System (ADS)

Tsukamoto, Y.; Okuzumi, S.; Kataoka, A.

2017-04-01

We investigate the dust structure of gravitationally unstable disks undergoing mass accretion from the envelope, envisioning its application to Class 0/I young stellar objects (YSOs). We find that the dust disk quickly settles into a steady state and that, compared to a disk with interstellar medium (ISM) dust-to-gas mass ratio and micron-sized dust, the dust mass in the steady state decreases by a factor of 1/2 to 1/3, and the dust thermal emission decreases by a factor of 1/3 to 1/5. The latter decrease is caused by dust depletion and opacity decrease owing to dust growth. Our results suggest that the masses of gravitationally unstable disks in Class 0/I YSOs are underestimated by a factor of 1/3 to 1/5 when calculated from the dust thermal emission assuming an ISM dust-to-gas mass ratio and micron-sized dust opacity, and that a larger fraction of disks in Class 0/I YSOs is gravitationally unstable than was previously believed. We also investigate the orbital radius {r}{{P}} within which planetesimals form via coagulation of porous dust aggregates and show that {r}{{P}} becomes ˜20 au for a gravitationally unstable disk around a solar mass star. Because {r}{{P}} increases as the gas surface density increases and a gravitationally unstable disk has maximum gas surface density, {r}{{P}}˜ 20 {au} is the theoretical maximum radius for planetesimal formation. We suggest that planetesimal formation in the Class 0/I phase is preferable to that in the Class II phase because a large amount of dust is supplied by envelope-to-disk accretion.

Far-infrared HD emission as a measure of protoplanetary disk mass

NASA Astrophysics Data System (ADS)

Trapman, L.; Miotello, A.; Kama, M.; van Dishoeck, E. F.; Bruderer, S.

2017-09-01

Context. Protoplanetary disks around young stars are the sites of planet formation. While the dust mass can be estimated using standard methods, determining the gas mass - and thus the amount of material available to form giant planets - has proven to be very difficult. Hydrogen deuteride (HD) is a promising alternative to the commonly used gas mass tracer, carbon monoxide. However, the potential of HD has not yet been investigated with models incorporating both HD and CO isotopologue-specific chemistry, and its sensitivity to uncertainties in disk parameters has not yet been quantified. Aims: We examine the robustness of HD as tracer of the disk gas mass, specifically the effect of gas mass on HD far-infrared emission and its sensitivity to the vertical structure. Also, we seek to provide requirements for future far-infrared missions such as SPICA. Methods: Deuterium chemistry reactions relevant for HD were implemented in the thermochemical code DALI and more than 160 disk models were run for a range of disk masses and vertical structures. Results: The HD J = 1-0 line intensity depends directly on the gas mass through a sublinear power law relation with a slope of 0.8. Assuming no prior knowledge about the vertical structure of a disk and using only the HD 1-0 flux, gas masses can be estimated to within a factor of two for low mass disks (Mdisk ≤ 10-3M⊙). For more massive disks, this uncertainty increases to more than an order of magnitude. Adding the HD 2-1 line or independent information about the vertical structure can reduce this uncertainty to a factor of 3 for all disk masses. For TW Hya, using the radial and vertical structure from the literature, the observations constrain the gas mass to 6 × 10-3M⊙ ≤ Mdisk ≤ 9 × 10-3M⊙. Future observations require a 5σ sensitivity of 1.8 × 10-20 W m-2 (2.5 × 10-20 W m-2) and a spectral resolving power R ≥ 300 (1000) to detect HD 1-0 (HD 2-1) for all disk masses above 10-5M⊙ with a line-to-continuum ratio ≥ 0.01. Conclusions: These results show that HD can be used as an independent gas mass tracer with a relatively low uncertainty and should be considered an important science goal for future far-infrared missions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodigas, Timothy J.; Hinz, Philip M.; Malhotra, Renu, E-mail: rodigas@as.arizona.edu

Planets can affect debris disk structure by creating gaps, sharp edges, warps, and other potentially observable signatures. However, there is currently no simple way for observers to deduce a disk-shepherding planet's properties from the observed features of the disk. Here we present a single equation that relates a shepherding planet's maximum mass to the debris ring's observed width in scattered light, along with a procedure to estimate the planet's eccentricity and minimum semimajor axis. We accomplish this by performing dynamical N-body simulations of model systems containing a star, a single planet, and an exterior disk of parent bodies and dustmore » grains to determine the resulting debris disk properties over a wide range of input parameters. We find that the relationship between planet mass and debris disk width is linear, with increasing planet mass producing broader debris rings. We apply our methods to five imaged debris rings to constrain the putative planet masses and orbits in each system. Observers can use our empirically derived equation as a guide for future direct imaging searches for planets in debris disk systems. In the fortuitous case of an imaged planet orbiting interior to an imaged disk, the planet's maximum mass can be estimated independent of atmospheric models.« less

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey. II. Disk Masses from ALMA Continuum Observations

NASA Astrophysics Data System (ADS)

Ward-Duong, K.; Patience, J.; Bulger, J.; van der Plas, G.; Ménard, F.; Pinte, C.; Jackson, A. P.; Bryden, G.; Turner, N. J.; Harvey, P.; Hales, A.; De Rosa, R. J.

2018-02-01

We report 885 μm ALMA continuum flux densities for 24 Taurus members spanning the stellar/substellar boundary with spectral types from M4 to M7.75. Of the 24 systems, 22 are detected at levels ranging from 1.0 to 55.7 mJy. The two nondetections are transition disks, though other transition disks in the sample are detected. Converting ALMA continuum measurements to masses using standard scaling laws and radiative transfer modeling yields dust mass estimates ranging from ∼0.3 to 20 M ⊕. The dust mass shows a declining trend with central object mass when combined with results from submillimeter surveys of more massive Taurus members. The substellar disks appear as part of a continuous sequence and not a distinct population. Compared to older Upper Sco members with similar masses across the substellar limit, the Taurus disks are brighter and more massive. Both Taurus and Upper Sco populations are consistent with an approximately linear relationship in M dust to M star, although derived power-law slopes depend strongly upon choices of stellar evolutionary model and dust temperature relation. The median disk around early-M stars in Taurus contains a comparable amount of mass in small solids as the average amount of heavy elements in Kepler planetary systems on short-period orbits around M-dwarf stars, with an order of magnitude spread in disk dust mass about the median value. Assuming a gas-to-dust ratio of 100:1, only a small number of low-mass stars and brown dwarfs have a total disk mass amenable to giant planet formation, consistent with the low frequency of giant planets orbiting M dwarfs.

The AU Mic Debris Disk: Far-infrared and Submillimeter Resolved Imaging

NASA Astrophysics Data System (ADS)

Matthews, Brenda C.; Kennedy, Grant; Sibthorpe, Bruce; Holland, Wayne; Booth, Mark; Kalas, Paul; MacGregor, Meredith; Wilner, David; Vandenbussche, Bart; Olofsson, Göran; Blommaert, Joris; Brandeker, Alexis; Dent, W. R. F.; de Vries, Bernard L.; Di Francesco, James; Fridlund, Malcolm; Graham, James R.; Greaves, Jane; Heras, Ana M.; Hogerheijde, Michiel; Ivison, R. J.; Pantin, Eric; Pilbratt, Göran L.

2015-10-01

We present far-infrared and submillimeter maps from the Herschel Space Observatory and the James Clerk Maxwell Telescope of the debris disk host star AU Microscopii. Disk emission is detected at 70, 160, 250, 350, 450, 500, and 850 μm. The disk is resolved at 70, 160, and 450 μm. In addition to the planetesimal belt, we detect thermal emission from AU Mic’s halo for the first time. In contrast to the scattered light images, no asymmetries are evident in the disk. The fractional luminosity of the disk is 3.9× {10}-4 and its milimeter-grain dust mass is 0.01 {M}\\oplus (±20%). We create a simple spatial model that reconciles the disk spectral energy distribution as a blackbody of 53 ± 2 K (a composite of 39 and 50 K components) and the presence of small (non-blackbody) grains which populate the extended halo. The best-fit model is consistent with the “birth ring” model explored in earlier works, i.e., an edge-on dust belt extending from 8.8 to 40 AU, but with an additional halo component with an {r}-1.5 surface density profile extending to the limits of sensitivity (140 AU). We confirm that AU Mic does not exert enough radiation force to blow out grains. For stellar mass-loss rates of 10-100 times solar, compact (zero porosity) grains can only be removed if they are very small; consistently with previous work, if the porosity is 0.9, then grains approaching 0.1 μm can be removed via corpuscular forces (i.e., the stellar wind).

On the shoulders of giants: properties of the stellar halo and the Milky Way mass distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kafle, Prajwal Raj; Sharma, Sanjib; Lewis, Geraint F.

2014-10-10

Halo stars orbit within the potential of the Milky Way, and hence their kinematics can be used to understand the underlying mass distribution. However, the inferred mass distribution depends sensitively on assumptions made on the density and the velocity anisotropy profiles of the tracer population. Also, there is a degeneracy between the parameters of the halo and those of the disk or bulge. Most previous attempts that use halo stars have made arbitrary assumptions about these. In this paper, we decompose the Galaxy into three major components—a bulge, a Miyamoto-Nagai disk, and a Navarro-Frenk-White dark matter halo - and thenmore » model the kinematic data of the halo blue horizontal branch and K-giant stars from the Sloan Extension for Galactic Understanding and Exploration. Additionally, we use the gas terminal velocity curve and the Sgr A* proper motion. With the distance of the Sun from the center of the Galaxy R {sub ☉} = 8.5 kpc, our kinematic analysis reveals that the density of the stellar halo has a break at 17.2{sub −1.0}{sup +1.1} kpc and an exponential cutoff in the outer parts starting at 97.7{sub −15.8}{sup +15.6} kpc. Also, we find that the tracer velocity anisotropy is radially biased with β {sub s} = 0.4 ± 0.2 in the outer halo. We measure halo virial mass M {sub vir} to be 0.80{sub −0.16}{sup +0.31}×10{sup 12} M{sub ⊙}, concentration c to be 21.1{sub −8.3}{sup +14.8}, disk mass to be 0.95{sub −0.30}{sup +0.24}×10{sup 11} M{sub ⊙}, disk scale length to be 4.9{sub −0.4}{sup +0.4} kpc, and bulge mass to be 0.91{sub −0.38}{sup +0.31}×10{sup 10} M{sub ⊙}. The halo mass is found to be small, and this has important consequences. The giant stars reveal that the outermost halo stars have low velocity dispersion, but interestingly this suggests a truncation of the stellar halo density rather than a small overall mass of the Galaxy. Our estimates of local escape velocity v{sub esc}=550.9{sub −22.1}{sup +32.4} km s{sup −1} and dark matter density ρ{sub ⊙}{sup DM}=0.0088{sub −0.0018}{sup +0.0024} M{sub ⊙} pc{sup −3} (0.35{sub −0.07}{sup +0.08} GeV cm{sup –3}) are in good agreement with recent estimates. Some of the above estimates, in particular M {sub vir}, are dependent on the adopted value of R {sub ☉} and also on the choice of the outer power-law index of the tracer number density.« less

Spitzer observations of NGC 2264: the nature of the disk population

NASA Astrophysics Data System (ADS)

Teixeira, P. S.; Lada, C. J.; Marengo, M.; Lada, E. A.

2012-04-01

Aims: NGC 2264 is a young cluster with a rich circumstellar disk population which makes it an ideal target for studying the evolution of stellar clusters. Our goal is to study the star formation history of NGC 2264 and to analyse the primordial disk evolution of its members. Methods: The study presented is based on data obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope, combined with deep near-infrared (NIR) ground-based FLAMINGOS imaging and previously published optical data. Results: We build NIR dust extinction maps of the molecular cloud associated with the cluster, and determine it to have a mass of 2.1 × 103 M⊙ above an AV of 7 mag. Using a differential Ks-band luminosity function (KLF) of the cluster, we estimate the size of the population of NGC 2264, within the area observed by FLAMINGOS, to be 1436 ± 242 members. The star formation efficiency is ≥ ~25%. We identify the disk population and divide it into 3 groups based on their spectral energy distribution slopes from 3.6 μm to 8 μm and on the 24 μm excess emission: (i) optically thick inner disks, (ii) anaemic inner disks, and (iii) disks with inner holes, or transition disks. We analyse the spatial distribution of these sources and find that sources with thick disks segregate into sub-clusterings, whereas sources with anaemic disks do not. Furthermore, sources with anaemic disks are found to be unembedded (i.e., with AV < 3 mag), whereas the clustered sources with thick disks are still embedded within the parental cloud. Conclusions: NGC 2264 has undergone more than one star-forming event, where the anaemic and extincted thick disk population appear to have formed in separate episodes: the sources with anaemic disks are more evolved and have had time to disperse and populate a halo of the cluster. We also find tentative evidence of triggered star-formation in the Fox Fur Nebula. In terms of disk evolution, our findings support the emerging disk evolution paradigm of two distinct evolutionary paths for primordial optically thick disks: a homologous one where the disk emission decreases uniformly at NIR and mid-infrared (MIR) wavelengths, and a radially differential one where the emission from the inner region of the disk decreases more rapidly than from the outer region (forming transition disks).

The correlation between HCN/H2O flux ratios and disk mass: evidence for protoplanet formation

NASA Astrophysics Data System (ADS)

Rose, Caitlin; Salyk, Colette

2017-01-01

We analyze hydrogen cyanide (HCN) and water vapor flux ratios in protoplanetary disks as a way to trace planet formation. Analyzing only disks in the Taurus molecular cloud, Najita et al. (2013) found a tentative correlation between protoplanetary disk mass and the HCN/H2O line flux ratio in Spitzer-IRS emission spectra. They interpret this correlation to be a consequence of more massive disks forming planetesimals more efficiently than smaller disks, as the formation of large planetesimals may lock up water ice in the cool outer disk region and prevent it from migrating, drying out the inner disk. The sequestering of water (and therefore oxygen) in the outer disk may also increase the carbon-to- oxygen ratio in the inner disk, leading to enhanced organic molecule (e.g. HCN) emission. To confirm this trend, we expand the Najita et al. sample by calculating HCN/H2O line flux ratios for 8 more sources with known disk masses from clusters besides Taurus. We find agreement with the Najita et al. trend, suggesting that this is a widespread phenomenon. In addition, we find HCN/H2O line flux ratios for 17 more sources that await disk mass measurements, which should become commonplace in the ALMA era. Finally, we investigate linear fits and outliers to this trend, and discuss possible causes.

THE CIRCUMSTELLAR DISK OF THE Be STAR o AQUARII AS CONSTRAINED BY SIMULTANEOUS SPECTROSCOPY AND OPTICAL INTERFEROMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sigut, T. A. A.; Tycner, C.; Jansen, B.

Omicron Aquarii is a late-type, Be shell star with a stable and nearly symmetric Hα emission line. We combine Hα interferometric observations obtained with the Navy Precision Optical Interferometer covering 2007 through 2014 with Hα spectroscopic observations over the same period and a 2008 observation of the system's near-infrared spectral energy distribution to constrain the properties of o Aqr's circumstellar disk. All observations are consistent with a circumstellar disk seen at an inclination of 75° ±  3° with a position angle on the sky of 110° ±  8° measured East from North. From the best-fit disk density model, we find that 90% ofmore » the Hα emission arises from within 9.5 stellar radii, and the mass associated with this Hα disk is ∼1.8 × 10{sup −10} of the stellar mass, and that the associated angular momentum, assuming Keplerian rotation for the disk, is ∼1.6 × 10{sup −8} of the total stellar angular momentum. The occurrence of a central quasi-emission feature in Mg ii λ4481 is also predicted by this best-fit disk model and the computed profile compares successfully with observations from 1999. To obtain consistency between the Hα line profile modeling and the other constraints, it was necessary in the profile fitting to weight the line core (emission peaks and central depression) more heavily than the line wings, which were not well reproduced by our models. This may reflect the limitation of assuming a single power law for the disk's variation in equatorial density. The best-fit disk density model for o Aqr predicts that Hα is near its maximum strength as a function of disk density, and hence the Hα equivalent width and line profile change only weakly in response to large (factor of ∼5) changes in the disk density. This may in part explain the remarkable observed stability of o Aqr's Hα emission line profile.« less

Protoplanetary disks in Taurus: Probing the role of multiplicity with ALMA observations

NASA Astrophysics Data System (ADS)

Laos, Stefan; Akeson, Rachel L.; Jensen, Eric L. N.

2017-01-01

We present results from an ALMA survey of single and multiple young systems in Taurus designed to probe how protoplanetary disk mass depends on both stellar mass and multiplicity. In observations taken in Cycles 0 and 2, we detect over 25 new disks. These detections include disks around stars in both single and multiple systems and are predominantly around lower mass stars with spectral types from M0 to M6. Combined with previous detections, these observations reveal a wide range of disk mass around both primary and companion stars, and allow us to test if the relation previously seen between disk and stellar mass continues at lower stellar masses. We find that within multiple systems the ratio of primary to secondary stellar mass is not correlated with the ratio of primary to secondary disk mass. In some cases, the secondary star hosts the more massive disk, contrary to theoretical predictions. We will discuss the implications of these results for the process of planet formation in multiple systems.This work makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00150.S. and ADS/JAO.ALMA#2013.1.00105.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Gas Heating, Chemistry and Photoevaporation in Protostellar Disks

NASA Technical Reports Server (NTRS)

Hollenbach, David

2004-01-01

We model the thermal balance, the chemistry, and the radiative transfer in dusty disks orbiting young, low mass stars. These models are motivated by observations of infrared and ultraviolet transitions of H2 from protoplanetary disks, as well as millimeter and submillimeter observations of other molecules such as CO, and infrared continuum observations of the dust. The dust grains are heated primarily by the stellar radiation and the infrared radiation field produced by the dust itself. The gas is heated by collisions with warmer dust grains, X-rays from the region close to the stellar surface, UV pumping of hydrogen molecules, and the grain photoelectric heating mechanism initiated by UV photons from the central star. We treat cases where the gas to dust ratio is high, because the dust has settled to the midplane and coagulated into relatively large objects. We discuss situations in which the infrared emission from H2 can be detected, and how the comparison of the observations with our models can deduce physical parameters such as the mass and the density and temperature distribution of the gas.

Nebular and Stellar Dust Extinction Across the Disk of Emission-line Galaxies on Kiloparsec Scales

NASA Astrophysics Data System (ADS)

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam; Nayyeri, Hooshang; Sobral, David; Miller, Sarah

2015-11-01

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study.

CHARACTERIZING THE BROWN DWARF FORMATION CHANNELS FROM THE INITIAL MASS FUNCTION AND BINARY-STAR DYNAMICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thies, Ingo; Pflamm-Altenburg, Jan; Kroupa, Pavel

2015-02-10

The stellar initial mass function (IMF) is a key property of stellar populations. There is growing evidence that the classical star-formation mechanism by the direct cloud fragmentation process has difficulties reproducing the observed abundance and binary properties of brown dwarfs and very-low-mass stars. In particular, recent analytical derivations of the stellar IMF exhibit a deficit of brown dwarfs compared to observational data. Here we derive the residual mass function of brown dwarfs as an empirical measure of the brown dwarf deficiency in recent star-formation models with respect to observations and show that it is compatible with the substellar part ofmore » the Thies-Kroupa IMF and the mass function obtained by numerical simulations. We conclude that the existing models may be further improved by including a substellar correction term that accounts for additional formation channels like disk or filament fragmentation. The term ''peripheral fragmentation'' is introduced here for such additional formation channels. In addition, we present an updated analytical model of stellar and substellar binarity. The resulting binary fraction and the dynamically evolved companion mass-ratio distribution are in good agreement with observational data on stellar and very-low-mass binaries in the Galactic field, in clusters, and in dynamically unprocessed groups of stars if all stars form as binaries with stellar companions. Cautionary notes are given on the proper analysis of mass functions and the companion mass-ratio distribution and the interpretation of the results. The existence of accretion disks around young brown dwarfs does not imply that these form just like stars in direct fragmentation.« less

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks. IV. Simulations with Envelope Irradiation

NASA Astrophysics Data System (ADS)

Cai, Kai; Durisen, Richard H.; Boley, Aaron C.; Pickett, Megan K.; Mejía, Annie C.

2008-02-01

It is generally thought that protoplanetary disks embedded in envelopes are more massive and thus more susceptible to gravitational instabilities (GIs) than exposed disks. We present three-dimensional radiative hydrodynamic simulations of protoplanetary disks with the presence of envelope irradiation. For a disk with a radius of 40 AU and a mass of 0.07 M⊙ around a young star of 0.5 M⊙, envelope irradiation tends to weaken and even suppress GIs as the irradiating flux is increased. The global mass transport induced by GIs is dominated by lower order modes, and irradiation preferentially suppresses higher order modes. As a result, gravitational torques and mass inflow rates are actually increased by mild irradiation. None of the simulations produce dense clumps or rapid cooling by convection, arguing against direct formation of giant planets by disk instability, at least in irradiated disks. However, dense gas rings and radial mass concentrations are produced, and these might be conducive to accelerated planetary core formation. Preliminary results from a simulation of a massive embedded disk with physical characteristics similar to one of the disks in the embedded source L1551 IRS 5 indicate a long radiative cooling time and no fragmentation. The GIs in this disk are dominated by global two- and three-armed modes.

Probing circumplanetary disks with MagAO and ALMA

NASA Astrophysics Data System (ADS)

Wu, Ya-Lin

2018-01-01

The dedication of the Magellan Adaptive Optics (MagAO) on the 6.5 m Clay Telescope has opened a new era in high-contrast imaging. Its unique diffraction-limited wavelengths of 0.6 to 1 micron helps to probe circumplanetary disks by measuring the amount of dust reddening as well as by searching for the strongest gas accretion indicator H-alpha (0.65 micron). Using MagAO, I found that two wide-orbit planetary-mass companions CT Cha B and 1RXS 1609 B have a significant dust extinction of Av ~ 3 to 5 mag likely from their disks. For GQ Lup B, I found that it is actively accreting material from its disk and emitting strong H-alpha emission. My research with MagAO demonstrates that circumplanetary disks could be ubiquitous among young giant planets. I later carried out a survey using ALMA to image accretion disks around several wide planet-mass companions at 1.3 mm continuum and CO (2-1). This is the first systematic study aiming to measure the size, mass, and structure of planetary disks. However, except for FW Tau C (which was shown to actually be a low-mass star from the dynamical mass measurement) no disks around the companions were found in my ALMA survey. This surprising null result implies that circumplanetary disks are much more compact and denser than expected, so they are faint and optically thick in the radio wavelengths. Therefore, mid- to far-infrared may be more favorable to characterize disk properties. The MIRI camera on the JWST can test this compact optically-thick disk hypothesis by probing disk thermal emission between 10 and 25 micron.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dodson-Robinson, Sarah E.; Salyk, Colette, E-mail: sdr@astro.as.utexas.edu

Although there has yet been no undisputed discovery of a still-forming planet embedded in a gaseous protoplanetary disk, the cleared inner holes of transitional disks may be signposts of young planets. Here, we show that the subset of accreting transitional disks with wide, optically thin inner holes of 15 AU or more can only be sculpted by multiple planets orbiting inside each hole. Multiplanet systems provide two key ingredients for explaining the origins of transitional disks. First, multiple planets can clear wide inner holes where single planets open only narrow gaps. Second, the confined, non-axisymmetric accretion flows produced by multiplemore » planets provide a way for an arbitrary amount of mass transfer to occur through an apparently optically thin hole without overproducing infrared excess flux. Rather than assuming that the gas and dust in the hole are evenly and axisymmetrically distributed, one can construct an inner hole with apparently optically thin infrared fluxes by covering a macroscopic fraction of the hole's surface area with locally optically thick tidal tails. We also establish that other clearing mechanisms, such as photoevaporation, cannot explain our subset of accreting transitional disks with wide holes. Transitional disks are therefore high-value targets for observational searches for young planetary systems.« less

Gas Cavities inside Dust Cavities in Disks Inferred from ALMA Observations

NASA Astrophysics Data System (ADS)

van der Marel, Nienke; van Dishoeck, Ewine F.; Bruderer, Simon; Pinilla, Paola; van Kempen, Tim; Perez, Laura; Isella, Andrea

2016-01-01

Protoplanetary disks with cavities in their dust distribution, also named transitional disks, are expected to be in the middle of active evolution and possibly planet formation. In recent years, millimeter-dust rings observed by ALMA have been suggested to have their origin in dust traps, caused by pressure bumps. One of the ways to generate these is by the presence of planets, which lower the gas density along their orbit and create pressure bumps at the edge. We present spatially resolved ALMA Cycle 0 and Cycle 1 observations of CO and CO isotopologues of several famous transitional disks. Gas is found to be present inside the dust cavities, but at a reduced level compared with the gas surface density profile of the outer disk. The dust and gas emission are quantified using the physical-chemical modeling code DALI. In the majority of these disks we find clear evidence for a drop in gas density of at least a factor of 10 inside the cavity, whereas the dust density drops by at least a factor 1000. The CO isotopologue observations reveal that the gas cavities are significantly smaller than the dust cavities. These gas structures suggest clearing by one or more planetary-mass companions.

MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry

Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign,more » trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R{sub g}, where R{sub g} = 2GM/c{sup 2} is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.« less

Characterizing Protoplanetary Disks in a Young Binary in Orion

NASA Astrophysics Data System (ADS)

Powell, Jonas; Hughes, A. Meredith; Mann, Rita; Flaherty, Kevin; Di Francesco, James; Williams, Jonathan

2018-01-01

Planetary systems form in circumstellar disks of gas and dust surrounding young stars. One open question in the study of planet formation involves understanding how different environments affect the properties of the disks and planets they generate. Understanding the properties of disks in high-mass star forming regions (SFRs) is critical since most stars - probably including our Sun - form in those regions. By comparing the disks in high-mass SFRs to those in better-studied low-mass SFRs we can learn about the role environment plays in planet formation. Here we present 0.5" resolution observations of the young two-disk binary system V2434 Ori in the Orion Nebula from the Atacama Large Millimeter/submillimeter Array (ALMA) in molecular line tracers of CO(3-2), HCN(4-3), HCO+(4-3) and CS(7-6). We model each disk’s mass, radius, temperature structure, and molecular abundances, by creating synthetic images using an LTE ray-tracing code and comparing simulated observations with the ALMA data in the visibility domain. We then compare our results to a previous study of molecular line emission from a single Orion proplyd, modeled using similar methods, and to previously characterized disks in low-mass SFRs to investigate the role of environment in disk chemistry and planetary system formation.

A black hole nova obscured by an inner disk torus.

PubMed

Corral-Santana, J M; Casares, J; Muñoz-Darias, T; Rodríguez-Gil, P; Shahbaz, T; Torres, M A P; Zurita, C; Tyndall, A A

2013-03-01

Stellar-mass black holes (BHs) are mostly found in x-ray transients, a subclass of x-ray binaries that exhibit violent outbursts. None of the 50 galactic BHs known show eclipses, which is surprising for a random distribution of inclinations. Swift J1357.2-093313 is a very faint x-ray transient detected in 2011. On the basis of spectroscopic evidence, we show that it contains a BH in a 2.8-hour orbital period. Further, high-time-resolution optical light curves display profound dips without x-ray counterparts. The observed properties are best explained by the presence of an obscuring toroidal structure moving outward in the inner disk, seen at very high inclination. This observational feature should play a key role in models of inner accretion flows and jet collimation mechanisms in stellar-mass BHs.

Heating during solar nebula formation and Mg isotopic fractionation in precursor grains of CAIs and chondrules

NASA Technical Reports Server (NTRS)

Sasaki, S.; Nagahara, H.; Kitagami, K.; Nakagawa, Y.

1994-01-01

In some Ca-Al-rich inclusion (CAI) grains, mass-dependent isotopic fractionations of Mg, Si, and O are observed and large Mg isotopic fractionation is interpreted to have been produced by cosmochemical processes such as evaporation and condensation. Mass-dependent Mg isotopic fractionation was found in olivine chondrules of Allende meteorites. Presented is an approximate formula for the temperature of the solar nebula that depends on heliocentric distance and the initial gas distribution. Shock heating during solar nebula formation can cause evaporative fractionation within interstellar grains involved in a gas at the inner zone (a less than 3 AU) of the disk. Alternatively collision of late-accreting gas blobs might cause similar heating if Sigma(sub s) and Sigma are large enough. Since the grain size is small, the solid/gas mass ratio is low and solar (low P(sub O2)), and the ambient gas pressure is low, this heating event could not produce chondrules themselves. Chondrule formation should proceed around the disk midplane after dust grains would grow and sediment to increase the solid/gas ratio there. The heating source there is uncertain, but transient rapid accretion through the disk could release a large amount of heat, which would be observed as FU Orionis events.

Small Scale Chemical Segregation Within Keplerian Disk Candidate G35.20-0.74N

NASA Astrophysics Data System (ADS)

Allen, Veronica; van der Tak, Floris; Sánchez-Monge, Álvaro; Cesaroni, Riccardo; Beltrán, Maria T.

2016-06-01

In the study of high-mass star formation, hot cores are empirically defined stages where chemically rich emission is detected toward a massive protostar. It is unknown whether the physical origin of this emission is a disk, inner envelope, or outflow cavity wall and whether the hot core stage is common to all massive stars. With the advent of the highly sensitive sub-millimeter interferometer, ALMA, the ability to chemically characterize high mass star forming regions other than Orion has become possible. In the up-and-coming field of observational astrochemistry, these sensitive high resolution observations have opened up opportunities to find small scale variations in young protostellar sources.We have done an in depth analysis of high spatial resolution (~1000 AU) Cycle 0 ALMA observations of the high mass star forming region G35.20-0.74N, where Sánchez-Monge et al (2013) found evidence for Keplerian rotation. After further chemical analysis, numerous complex organic species have been identified in this region and we notice an interesting asymmetry in the distribution of the Nitrogen-bearing species within this source. In my talk, I will briefly outline the case for the disk and the consequences for this hypothesis following the chemical segregation we have seen.

The detection and study of pre-planetary disks

NASA Technical Reports Server (NTRS)

Sargent, A. I.; Beckwith, S. V. W.

1994-01-01

A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that surrounded the Sun before the formation of the planets. The properties of these disks may bear strongly on the way in which planetary systems form and evolve. As a result of major instrumental developments over the last decade, it is now possible to detect and study the circumstellar environments of the very young, solar-type stars in some detail, and to compare the results with theoretical models of the early solar system. For example, millimeter-wave aperture synthesis imaging provides a direct means of studying in detail the morphology, temperature and density distributions, velocity field and chemical constituents in the outer disks, while high resolution, near infrared spectroscopy probes the inner, warmer parts; the emergence of gaps in the disks, possibly reflecting the formation of planets, may be reflected in the variation of their dust continuum emission with wavelength. We review progress to date and discuss likely directions for future research.

Near-IR Polarized Scattered Light Imagery of the DoAr 28 Transitional Disk

NASA Technical Reports Server (NTRS)

Rich, Evan A.; Wisiniewski, John P.; Mayama, Satoshi; Brandt, Timothy D.; Hashimoto, Jun; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Espaillat, Catherine; Serabyn, Eugene; Grady, Carol A.;

Millimeter Studies of Nearby Debris Disks

NASA Astrophysics Data System (ADS)

MacGregor, Meredith Ann

2017-03-01

At least 20% of nearby main sequence stars are known to be surrounded by disks of dusty material resulting from the collisional erosion of planetesimals, similar to asteroids and comets in our own Solar System. The material in these ‘debris disks’ is directly linked to the larger bodies, like planets, in the system through collisions and gravitational perturbations. Observations at millimeter wavelengths are especially critical to our understanding of these systems, since the large grains that dominate emission at these long wavelengths reliably trace the underlying planetesimal distribution. In this thesis, I have used state-of-the-art observations at millimeter wavelengths to address three related questions concerning debris disks and planetary system evolution: 1) How are wide-separation, substellar companions formed? 2) What is the physical nature of the collisional process in debris disks? And, 3) Can the structure and morphology of debris disks provide probes of planet formation and subsequent dynamical evolution? Using ALMA observations of GQ Lup, a pre-main sequence system with a wide-separation, substellar companion, I have placed constraints on the mass of a circumplanetary disk around the companion, informing formation scenarios for this and other similar systems (Chapter 2). I obtained observations of a sample of fifteen debris disks with both the VLA and ATCA at centimeter wavelengths, and robustly determined the millimeter spectral index of each disk and thus the slope of the grain size distribution, providing the first observational test of collision models of debris disks (Chapter 3). By applying an MCMC modeling framework to resolved millimeter observations with ALMA and SMA, I have placed the first constraints on the position, width, surface density gradient, and any asymmetric structure of the AU Mic, HD 15115, Epsilon Eridani, Tau Ceti, and Fomalhaut debris disks (Chapters 4–8). These observations of individual systems hint at trends in disk structure and dynamics, which can be explored further with a comparative study of a sample of the eight brightest debris disks around Sun-like stars within 20 pc (Chapter 9). This body of work has yielded the first resolved images of notable debris disks at millimeter wavelengths, and complements other ground- and space-based observations by providing constraints on these systems with uniquely high angular resolution and wavelength coverage. Together these results provide a foundation to investigate the dynamical evolution of planetary systems through multi-wavelength observations of debris disks.

PEERING INTO THE GIANT-PLANET-FORMING REGION OF THE TW HYDRAE DISK WITH THE GEMINI PLANET IMAGER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rapson, Valerie A.; Kastner, Joel H.; Millar-Blanchaer, Maxwell A.

2015-12-20

We present Gemini Planet Imager (GPI) adaptive optics near-infrared images of the giant-planet-forming regions of the protoplanetary disk orbiting the nearby (D = 54 pc), pre-main-sequence (classical T Tauri) star TW Hydrae. The GPI images, which were obtained in coronagraphic/polarimetric mode, exploit starlight scattered off small dust grains to elucidate the surface density structure of the TW Hya disk from ∼80 AU to within ∼10 AU of the star at ∼1.5 AU resolution. The GPI polarized intensity images unambiguously confirm the presence of a gap in the radial surface brightness distribution of the inner disk. The gap is centered near ∼23 AU,more » with a width of ∼5 AU and a depth of ∼50%. In the context of recent simulations of giant-planet formation in gaseous, dusty disks orbiting pre-main-sequence stars, these results indicate that at least one young planet with a mass ∼0.2 M{sub J} could be present in the TW Hya disk at an orbital semimajor axis similar to that of Uranus. If this (proto)planet is actively accreting gas from the disk, it may be readily detectable by GPI or a similarly sensitive, high-resolution infrared imaging system.« less

MAGELLAN AO SYSTEM z ′, Y{sub S}, AND L ′ OBSERVATIONS OF THE VERY WIDE 650 AU HD 106906 PLANETARY SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ya-Lin; Close, Laird M.; Males, Jared R.

2016-05-20

We analyze archival data from Bailey and co-workers from the Magellan adaptive optics system and present the first 0.9 μ m detection ( z ′ = 20.3 ± 0.4 mag; Δ z ′ = 13.0 ± 0.4 mag) of the 11 M {sub Jup} circumbinary planet HD 106906AB b, as well as 1 and 3.8 μ m detections of the debris disk around the binary. The disk has an east–west asymmetry in length and surface brightness, especially at 3.8 μ m where the disk appears to be one-sided. The spectral energy distribution of b, when scaled to the K{sub S}more » -band photometry, is consistent with 1800 K atmospheric models without significant dust reddening, unlike some young, very red, low-mass companions such as CT Cha B and 1RXS 1609 B. Therefore, the suggested circumplanetary disk of Kalas and co-workers might not contain much material, or might be closer to face-on. Finally, we suggest that the widest ( a ≳ 100 AU) low mass ratio ( M {sub p}/ M {sub ⋆} ≡ q ≲ 0.01) companions may have formed inside protoplanetary disks but were later scattered by binary/planet interactions. Such a scattering event may have occurred for HD 106906AB b with its central binary star, but definitive proof at this time is elusive.« less

Probing the Cold Dust Emission in the AB Aur Disk: A Dust Trap in a Decaying Vortex?

PubMed

Fuente, Asunción; Baruteau, Clément; Neri, Roberto; Carmona, Andrés; Agúndez, Marcelino; Goicoechea, Javier R; Bachiller, Rafael; Cernicharo, José; Berné, Olivier

2017-09-01

One serious challenge for planet formation is the rapid inward drift of pebble-sized dust particles in protoplanetary disks. Dust trapping at local maxima in the disk gas pressure has received much theoretical attention but still lacks observational support. The cold dust emission in the AB Aur disk forms an asymmetric ring at a radius of about 120 au, which is suggestive of dust trapping in a gas vortex. We present high spatial resolution (0".58×0".78 ≈ 80×110 au) NOEMA observations of the 1.12 mm and 2.22 mm dust continuum emission from the AB Aur disk. Significant azimuthal variations of the flux ratio at both wavelengths indicate a size segregation of the large dust particles along the ring. Our continuum images also show that the intensity variations along the ring are smaller at 2.22 mm than at 1.12 mm, contrary to what dust trapping models with a gas vortex have predicted. Our two-fluid (gas+dust) hydrodynamical simulations demonstrate that this feature is well explained if the gas vortex has started to decay due to turbulent diffusion, and dust particles are thus losing the azimuthal trapping on different timescales depending on their size. The comparison between our observations and simulations allows us to constrain the size distribution and the total mass of solid particles in the ring, which we find to be of the order of 30 Earth masses, enough to form future rocky planets.

The gaseous component of the disk around Beta Pictoris

NASA Technical Reports Server (NTRS)

Hobbs, L. M.; Vidal-Madjar, A.; Ferlet, R.; Albert, C. E.; Gry, C.

1985-01-01

Optical spectra of alpha Lyr, alpha PsA, and beta Pic have been obtained at a velocity resolution of 3 km/s. No circumstellar absorption lines of Ca II or Na I are detected toward alpha Lyr or alpha PsA at sensitive limits. In the favorable case of beta Pic, where the circumstellar disk imaged by Smith and Terrile (1984) is seen nearly edge-on, a strong, narrow, circumstellar Ca II K absorption line previously reported by Slettebak (1982) and weaker, still narrower circumstellar Na I D lines are detected. Negative results of high sensitivity also are obtained for the Ca I 4226 A and CH(+) 4232 A lines, along with upper limits on the Zn II 2026, 2062 A doublet from archival IUE spectra. Under assumptions which agree with other well-established observations of the gaseous abundances of calcium and zinc, the total gaseous column density of hydrogen along a radius of the circumstellar disk is between 10 to the 18th and 4 x 10 to the 20th/sq cm. Within the boundaries of the dust disk detected by Smith and Terrile (1984) the total gaseous mass then is less than about 2, or less than 1 percent of the mass of the planetary system. A simplified model of the density distribution in the gaseous disk yields a characteristic total density n(H) of about 100,000/cu cm, which exceeds that of all interplanetary gas at earth's position by a factor of about 10,000.

Magellan AO System z‧, Y S , and L‧ Observations of the Very Wide 650 AU HD 106906 Planetary System

NASA Astrophysics Data System (ADS)

Wu, Ya-Lin; Close, Laird M.; Bailey, Vanessa P.; Rodigas, Timothy J.; Males, Jared R.; Morzinski, Katie M.; Follette, Katherine B.; Hinz, Philip M.; Puglisi, Alfio; Briguglio, Runa; Xompero, Marco

2016-05-01

We analyze archival data from Bailey and co-workers from the Magellan adaptive optics system and present the first 0.9 μm detection (z‧ = 20.3 ± 0.4 mag; Δz‧ = 13.0 ± 0.4 mag) of the 11 M Jup circumbinary planet HD 106906AB b, as well as 1 and 3.8 μm detections of the debris disk around the binary. The disk has an east-west asymmetry in length and surface brightness, especially at 3.8 μm where the disk appears to be one-sided. The spectral energy distribution of b, when scaled to the K S -band photometry, is consistent with 1800 K atmospheric models without significant dust reddening, unlike some young, very red, low-mass companions such as CT Cha B and 1RXS 1609 B. Therefore, the suggested circumplanetary disk of Kalas and co-workers might not contain much material, or might be closer to face-on. Finally, we suggest that the widest (a ≳ 100 AU) low mass ratio (M p/M ⋆ ≡ q ≲ 0.01) companions may have formed inside protoplanetary disks but were later scattered by binary/planet interactions. Such a scattering event may have occurred for HD 106906AB b with its central binary star, but definitive proof at this time is elusive. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

THE IMPACT OF STELLAR FEEDBACK ON THE STRUCTURE, SIZE, AND MORPHOLOGY OF GALAXIES IN MILKY-WAY-SIZED DARK MATTER HALOS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agertz, Oscar; Kravtsov, Andrey V., E-mail: o.agertz@surrey.ac.uk

We use cosmological zoom-in simulations of galaxy formation in a Milky-Way-sized halo started from identical initial conditions to investigate the evolution of galaxy sizes, baryon fractions, morphologies, and angular momenta in runs with different parameters of the star formation–feedback cycle. Our fiducial model with a high local star formation efficiency, which results in efficient feedback, produces a realistic late-type galaxy that matches the evolution of basic properties of late-type galaxies: stellar mass, disk size, morphology dominated by a kinematically cold disk, stellar and gas surface density profiles, and specific angular momentum. We argue that feedback’s role in this success ismore » twofold: (1) removal of low angular momentum gas, and (2) maintaining a low disk-to-halo mass fraction, which suppresses disk instabilities that lead to angular momentum redistribution and a central concentration of baryons. However, our model with a low local star formation efficiency, but large energy input per supernova, chosen to produce a galaxy with a similar star formation history as our fiducial model, leads to a highly irregular galaxy with no kinematically cold component, overly extended stellar distribution, and low angular momentum. This indicates that only when feedback is allowed to become vigorous via locally efficient star formation in dense cold gas do resulting galaxy sizes, gas/stellar surface density profiles, and stellar disk angular momenta agree with observed z = 0 galaxies.« less

THE NATURE AND NURTURE OF BARS AND DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mendez-Abreu, J.; Aguerri, J. A. L.; Zarattini, S.

The effects that interactions produce on galaxy disks and how they modify the subsequent formation of bars need to be distinguished to fully understand the relationship between bars and environment. To this aim we derive the bar fraction in three different environments ranging from the field to Virgo and Coma Clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of galaxy luminosity (and mass) in the field and Comamore » Cluster is statistically significant, with Virgo being an intermediate case. The fraction of barred galaxies shows a maximum of about 50% at M{sub r} {approx_equal} - 20.5 in clusters, whereas the peak is shifted to M{sub r} {approx_equal} - 19 in the field. We interpret this result as a variation of the effect of environment on bar formation depending on galaxy luminosity. We speculate that brighter disk galaxies are stable enough against interactions to keep their cold structure, thus, the interactions are able to trigger bar formation. For fainter galaxies, the interactions become strong enough to heat up the disks inhibiting bar formation and even destroying the disks. Finally, we point out that the controversy regarding whether the bar fraction depends on environment could be resolved by taking into account the different luminosity ranges probed by the galaxy samples studied so far.« less

The AGORA High-resolution Galaxy Simulations Comparison Project II: Isolated disk test

DOE PAGES

Kim, Ji-hoon; Agertz, Oscar; Teyssier, Romain; ...

2016-12-20

Using an isolated Milky Way-mass galaxy simulation, we compare results from 9 state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, wemore » find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly-formed stellar clump mass functions show more significant variation (difference by up to a factor of ~3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low density region, and between more diffusive and less diffusive schemes in the high density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Lastly, our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.« less

The AGORA High-resolution Galaxy Simulations Comparison Project II: Isolated disk test

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Ji-hoon; Agertz, Oscar; Teyssier, Romain

Using an isolated Milky Way-mass galaxy simulation, we compare results from 9 state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, wemore » find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly-formed stellar clump mass functions show more significant variation (difference by up to a factor of ~3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low density region, and between more diffusive and less diffusive schemes in the high density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Lastly, our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.« less

THE AGORA HIGH-RESOLUTION GALAXY SIMULATIONS COMPARISON PROJECT. II. ISOLATED DISK TEST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Ji-hoon; Agertz, Oscar; Teyssier, Romain

Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, wemore » find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt–Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of ∼3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.« less

The Dragonfly Nearby Galaxies Survey. IV. A Giant Stellar Disk in NGC 2841

NASA Astrophysics Data System (ADS)

Zhang, Jielai; Abraham, Roberto; van Dokkum, Pieter; Merritt, Allison; Janssens, Steven

2018-03-01

Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of the fact that deep H I observations typically probe to a lower-mass surface density than visible wavelength data. This paper presents low-surface-brightness, optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of ∼70 kpc (5 R 25 or 23 inner disk scale lengths). The structure in the stellar disk traces the morphology of H I emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than ∼20 kpc, the ratio of the stellar mass to gas mass surface density is a constant 3:1. Beyond ∼30 kpc, the low-surface-brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion, and in situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy.

Parameterizing the Dust Around Herbig Ae/Be Stars: Multiwavelength Imaging, Radiative Transfer Modeling, and Near-Infrared Instrumentation

NASA Astrophysics Data System (ADS)

Doering, Ryan L.

2009-01-01

Determining Herbig Ae/Be star dust parameters provides constraints for planet formation theory, and yields information about the matter around intermediate-mass stars as they approach the main sequence. In this dissertation talk, I present the results of a multiwavelength imaging and radiative transfer modeling study of Herbig Ae/Be stars, and a near-infrared instrumentation project, with the aim of parameterizing the dust in these systems. The Hubble Space Telescope was used to search for optical light scattered by dust in a sample of young stars. This survey provided the first scattered-light image of the circumstellar environment around the Herbig Ae/Be star HD 97048. Structure is observed in the dust distribution similar to that seen in other Herbig Ae/Be systems. A ground-based near-infrared imaging study of Herbig Ae/Be candidates was also carried out. Photometry was collected for spectral energy distribution construction, and binary candidates were resolved. Detailed dust modeling of HD 97048 and HD 100546 was carried out with a two-component geometry consisting of a flared disk and an extended envelope. The models achieve a reasonable global fit to the spectral energy distributions, and produce images with the desired geometry. The disk midplane densities are found to go as r-0.5 and r-1.8, giving disk dust masses of 3.0 x 10-4 and 5.9 x 10-5 Msun for HD 97048 and HD 100546, respectively. A gas-to-dust mass ratio lower limit of 3.2 was calculated for HD 97048. Furthermore, I have participated in the development of the WIYN High Resolution Infrared Camera. The instrument operates in the near-infrared ( 0.8 - 2.5 microns), includes 13 filters, and has a pixel size of 0.1 arcsec, resulting in a field of view of 3 arcmin x 3 arcmin. An angular resolution of 0.25 arcsec is anticipated. I provide an overview of the instrument and report performance results.

SUSTAINING STAR FORMATION RATES IN SPIRAL GALAXIES: SUPERNOVA-DRIVEN TURBULENT ACCRETION DISK MODELS APPLIED TO THINGS GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vollmer, Bernd; Leroy, Adam K., E-mail: bvollmer@astro.u-strasbg.fr

2011-01-15

Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproducedmore » by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}< 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.« less

Sustaining Star Formation Rates in Spiral Galaxies Supernova-driven Turbulent Accretion Disk Models Applied to THINGS Galaxies

NASA Astrophysics Data System (ADS)

Vollmer, Bernd; Leroy, Adam K.

2011-01-01

Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M ⊙) <~ 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

EVOLUTION OF TRANSIENT LOW-MASS X-RAY BINARIES TO REDBACK MILLISECOND PULSARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Kun; Li, Xiang-Dong, E-mail: lixd@nju.edu.cn

2015-11-20

Redback millisecond pulsars (MSPs; hereafter redbacks) are a subpopulation of eclipsing MSPs in close binaries. The formation processes of these systems are not clear. The three pulsars showing transitions between rotation- and accretion-powered states belong to both redbacks and transient low-mass X-ray binaries (LMXBs), suggesting a possible evolutionary link between them. Through binary evolution calculations, we show that the accretion disks in almost all LMXBs are subject to the thermal-viscous instability during certain evolutionary stages, and the parameter space for the disk instability covers the distribution of known redbacks in the orbital period—companion mass plane. We accordingly suggest that themore » abrupt reduction of the mass accretion rate during quiescence of transient LMXBs provides a plausible way to switch on the pulsar activity, leading to the formation of redbacks, if the neutron star has been spun up to be an energetic MSP. We investigate the evolution of redbacks, taking into account the evaporation feedback, and discuss its possible influence on the formation of black widow MSPs.« less

Mass perturbation techniques for tuning and decoupling of a Disk Resonator Gyroscope

NASA Astrophysics Data System (ADS)

Schwartz, David

Axisymmetric microelectromechanical (MEM) vibratory rate gyroscopes are designed so that the two Coriolis-coupled modes exploited for rate sensing possess equal modal frequencies and so that the central post which attaches the resonator to the sensor case is a nodal point of the these two modes. The former quality maximizes the signal-to-noise ratio of the sensor, while the latter quality eliminates any coupling of linear acceleration to the modes of interest, which, if present, creates spurious rate signals in response to linear vibration of the sensor case. When the gyro resonators are fabricated, however, small mass and stiffness asymmetries cause the frequencies of the two modes to deviate from each other and couple these modes to linear acceleration. In a resonator post-fabrication step, these effects can be reduced by altering the mass distribution of the resonator. In this dissertation, a scale model of the axisymmetric resonator of the Disk Resonator Gyroscope (DRG) is used to develop and test methods that successfully reduce frequency detuning (Part I) and linear acceleration coupling (Part II) through guided mass perturbations.

On the Star Formation Rate, Initial Mass Function, and Hubble Type of Disk Galaxies and the Age of the Universe

NASA Astrophysics Data System (ADS)

Sommer-Larsen, Jesper

1996-01-01

Evolutionary models for the disks of large disk galaxies, including effects of star formation, non-instantaneous gas recycling from stars, and infall of low-metallicity gas from the halo, have been calculated and compared with data for nearby, generally large disk galaxies on present disk star-formation rates (based on integrated Hα luminosities) as a function of disk gas fractions. The data were extracted from the work by Kennicutt, Tamblyn, & Congdon. The result of the comparison suggests that for disk galaxies the Hubble sequence is a disk age sequence, with early-type disks being the oldest and late types the youngest. Under the assumption of a minimum age of the Galactic disk of 10 Gyr, the mean age of Sa/Sab galaxies, and hence the age of the universe, is found to be at least 17±2 Gyr. It is furthermore found that the disk star-formation timescale is approximately independent of disk-galaxy type. Finally, it is found that the global initial mass function (IMF) in galactic disks is 2-3 times more weighted toward high-mass stars than the Scalo "best-fitting" model for the solar-neighborhood IMF. The more top-heavy model of Kennicutt provides a good fit to observation.

A Circumbinary Disk Model for the Rapid Orbital Shrinkage in Black Hole Low-mass X-Ray Binaries

NASA Astrophysics Data System (ADS)

Xu, Xiao-Tian; Li, Xiang-Dong

2018-05-01

Several black hole low-mass X-ray binaries (BHLMXBs) show very fast orbital shrinkage, which is difficult to understand in the standard picture of the LMXB evolution. Based on the possible detection of a circumbinary (CB) disk in A0620-00 and XTE J1118+480, we investigate the influence of the interaction between a CB disk and the inner binary and calculate the evolution of the binary using the Modules for Experiments in Stellar Astrophysics. We consider two cases for the CB disk formation in which it is fed by mass loss during single outburst or successive outbursts in the LMXB. We show that when taking reasonable values of the initial mass and the dissipating time of the disk, it is possible to explain the fast orbital shrinkage in the BHLMXBs without invoking a high-mass transfer rate.

High-mass X-ray binary populations. 1: Galactic modeling

NASA Technical Reports Server (NTRS)

Dalton, William W.; Sarazin, Craig L.

1995-01-01

Modern stellar evolutionary tracks are used to calculate the evolution of a very large number of massive binary star systems (M(sub tot) greater than or = 15 solar mass) which cover a wide range of total masses, mass ratios, and starting separations. Each binary is evolved accounting for mass and angular momentum loss through the supernova of the primary to the X-ray binary phase. Using the observed rate of star formation in our Galaxy and the properties of massive binaries, we calculate the expected high-mass X-ray binary (HMXRB) population in the Galaxy. We test various massive binary evolutionary scenarios by comparing the resulting HMXRB predictions with the X-ray observations. A major goal of this study is the determination of the fraction of matter lost from the system during the Roche lobe overflow phase. Curiously, we find that the total numbers of observable HMXRBs are nearly independent of this assumed mass-loss fraction, with any of the values tested here giving acceptable agreement between predicted and observed numbers. However, comparison of the period distribution of our HMXRB models with the observed period distribution does reveal a distinction among the various models. As a result of this comparison, we conclude that approximately 70% of the overflow matter is lost from a massive binary system during mass transfer in the Roche lobe overflow phase. We compare models constructed assuming that all X-ray emission is due to accretion onto the compact object from the donor star's wind with models that incorporate a simplified disk accretion scheme. By comparing the results of these models with observations, we conclude that the formation of disks in HMXRBs must be relatively common. We also calculate the rate of formation of double degenerate binaries, high velocity detached compact objects, and Thorne-Zytkow objects.

Individual Dynamical Masses of Ultracool Dwarfs

NASA Astrophysics Data System (ADS)

Dupuy, Trent J.; Liu, Michael C.

2017-08-01

We present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types M7-T5. Joint analysis of resolved imaging from Keck Observatory and Hubble Space Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. As a result, we measure 38 precise individual masses spanning 30-115 {M}{Jup}. We determine a model-independent substellar boundary that is ≈70 {M}{Jup} in mass (≈L4 in spectral type), and we validate Baraffe et al. evolutionary model predictions for the lithium-depletion boundary (60 {M}{Jup} at field ages). Assuming each binary is coeval, we test models of the substellar mass-luminosity relation and find that in the L/T transition, only the Saumon & Marley “hybrid” models accounting for cloud clearing match our data. We derive a precise, mass-calibrated spectral type-effective temperature relation covering 1100-2800 K. Our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning L4-T5 and 30-70 {M}{Jup}. We determine a median age of 1.3 Gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the Galactic disk. We discover two triple-brown-dwarf systems, the first with directly measured masses and eccentricities. We examine the eccentricity distribution, carefully considering biases and completeness, and find that low-eccentricity orbits are significantly more common among ultracool binaries than solar-type binaries, possibly indicating the early influence of long-lived dissipative gas disks. Overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs.

Evaporation of planetary atmospheres due to XUV illumination by quasars

NASA Astrophysics Data System (ADS)

Forbes, John C.; Loeb, Abraham

2018-06-01

Planetary atmospheres are subject to mass loss through a variety of mechanisms including irradiation by XUV photons from their host star. Here we explore the consequences of XUV irradiation by supermassive black holes as they grow by the accretion of gas in galactic nuclei. Based on the mass distribution of stars in galactic bulges and disks and the luminosity history of individual black holes, we estimate the probability distribution function of XUV fluences as a function of galaxy halo mass, redshift, and stellar component. We find that about 50% of all planets in the universe may lose a mass of hydrogen of ˜2.5 × 1019 g (the total mass of the Martian atmosphere), 10% may lose ˜5.1 × 1021 g (the total mass of Earth's atmosphere), and 0.2% may lose ˜1.4 × 1024 g (the total mass of Earth's oceans). The fractions are appreciably higher in the spheroidal components of galaxies, and depend strongly on galaxy mass, but only weakly on redshift.

Post-merger evolution of a neutron star-black hole binary with neutrino transport

NASA Astrophysics Data System (ADS)

Foucart, Francois; O'Connor, Evan; Roberts, Luke; Duez, Matthew D.; Haas, Roland; Kidder, Lawrence E.; Ott, Christian D.; Pfeiffer, Harald P.; Scheel, Mark A.; Szilagyi, Bela

2015-06-01

We present a first simulation of the post-merger evolution of a black hole-neutron star binary in full general relativity using an energy-integrated general-relativistic truncated moment formalism for neutrino transport. We describe our implementation of the moment formalism and important tests of our code, before studying the formation phase of an accretion disk after a black hole-neutron star merger. We use as initial data an existing general-relativistic simulation of the merger of a neutron star of mass 1.4 M⊙ with a black hole of mass 7 M⊙ and dimensionless spin χBH=0.8 . Comparing with a simpler leakage scheme for the treatment of the neutrinos, we find noticeable differences in the neutron-to-proton ratio in and around the disk, and in the neutrino luminosity. We find that the electron neutrino luminosity is much lower in the transport simulations, and that both the disk and the disk outflows are less neutron rich. The spatial distribution of the neutrinos is significantly affected by relativistic effects, due to large velocities and curvature in the regions of strongest emission. Over the short time scale evolved, we do not observe purely neutrino-driven outflows. However, a small amount of material (3 ×10-4M⊙ ) is ejected in the polar region during the circularization of the disk. Most of that material is ejected early in the formation of the disk, and is fairly neutron rich (electron fraction Ye˜0.15 - 0.25 ). Through r-process nucleosynthesis, that material should produce high-opacity lanthanides in the polar region, and could thus affect the light curve of radioactively powered electromagnetic transients. We also show that by the end of the simulation, while the bulk of the disk remains neutron rich (Ye˜0.15 - 0.2 and decreasing), its outer layers have a higher electron fraction: 10% of the remaining mass has Ye>0.3 . As that material would be the first to be unbound by disk outflows on longer time scales, and as composition evolution is slower at later times, the changes in Ye experienced during the formation phase of the disk could have an impact on nucleosynthesis outputs from neutrino-driven and viscously driven outflows. Finally, we find that the effective viscosity due to momentum transport by neutrinos is unlikely to have a strong effect on the growth of the magnetorotational instability in the post-merger accretion disk.

Magnetospheric Truncation, Tidal Inspiral, and the Creation of Short-period and Ultra-short-period Planets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Eve J.; Chiang, Eugene, E-mail: evelee@berkeley.edu

Sub-Neptunes around FGKM dwarfs are evenly distributed in log orbital period down to ∼10 days, but dwindle in number at shorter periods. Both the break at ∼10 days and the slope of the occurrence rate down to ∼1 day can be attributed to the truncation of protoplanetary disks by their host star magnetospheres at corotation. We demonstrate this by deriving planet occurrence rate profiles from empirical distributions of pre-main-sequence stellar rotation periods. Observed profiles are better reproduced when planets are distributed randomly in disks—as might be expected if planets formed in situ—rather than piled up near disk edges, as wouldmore » be the case if they migrated in by disk torques. Planets can be brought from disk edges to ultra-short (<1 day) periods by asynchronous equilibrium tides raised on their stars. Tidal migration can account for how ultra-short-period planets are more widely spaced than their longer-period counterparts. Our picture provides a starting point for understanding why the sub-Neptune population drops at ∼10 days regardless of whether the host star is of type FGK or early M. We predict planet occurrence rates around A stars to also break at short periods, but at ∼1 day instead of ∼10 days because A stars rotate faster than stars with lower masses (this prediction presumes that the planetesimal building blocks of planets can drift inside the dust sublimation radius).« less

TESTING THE HYPOTHESIS THAT METHANOL MASER RINGS TRACE CIRCUMSTELLAR DISKS: HIGH-RESOLUTION NEAR-INFRARED AND MID-INFRARED IMAGING

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Buizer, James M.; Bartkiewicz, Anna; Szymczak, Marian, E-mail: jdebuizer@sofia.usra.edu

2012-08-01

Milliarcsecond very long baseline interferometry maps of regions containing 6.7 GHz methanol maser emission have lead to the recent discovery of ring-like distributions of maser spots and the plausible hypothesis that they may be tracing circumstellar disks around forming high-mass stars. We aimed to test this hypothesis by imaging these regions in the near- and mid-infrared at high spatial resolution and compare the observed emission to the expected infrared morphologies as inferred from the geometries of the maser rings. In the near-infrared we used the Gemini North adaptive optics system of ALTAIR/NIRI, while in the mid-infrared we used the combinationmore » of the Gemini South instrument T-ReCS and super-resolution techniques. Resultant images had a resolution of {approx}150 mas in both the near-infrared and mid-infrared. We discuss the expected distribution of circumstellar material around young and massive accreting (proto)stars and what infrared emission geometries would be expected for the different maser ring orientations under the assumption that the masers are coming from within circumstellar disks. Based upon the observed infrared emission geometries for the four targets in our sample and the results of spectral energy distribution modeling of the massive young stellar objects associated with the maser rings, we do not find compelling evidence in support of the hypothesis that methanol masers rings reside in circumstellar disks.« less

Externally Induced Evaporation of Young Stellar Disks in Orion

NASA Technical Reports Server (NTRS)

Johnstone, D.; Hollenbach, D.; Shu, F.

1996-01-01

In this paper we propose a model for the evaporation of disks around young low-mass stars by external sources of high energy photons. Two evaporation techniques are possible. Lyman continuum radiation can ionize hydrogen at the disk surface powering a steady thermal ionized disk-wind, or FUV radiation can heat the disk through photo-electric grain processes powering a slower thermal neutral disk-wind. Applying these two models to the evaporating objects in the Trapezium produces a satisfactory solution to both the mass-loss rate and size of the ionized envelopes.

An Explanation of the Very Low Radio Flux of Young Planet-mass Companions

NASA Astrophysics Data System (ADS)

Wu, Ya-Lin; Close, Laird M.; Eisner, Josh A.; Sheehan, Patrick D.

2017-12-01

We report Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum upper limits for five planetary-mass companions DH Tau B, CT Cha B, GSC 6214-210 B, 1RXS 1609 B, and GQ Lup B. Our survey, together with other ALMA studies, have yielded null results for disks around young planet-mass companions and placed stringent dust mass upper limits, typically less than 0.1 M ⊕, when assuming dust continuum is optically thin. Such low-mass gas/dust content can lead to a disk lifetime estimate (from accretion rates) much shorter than the age of the system. To alleviate this timescale discrepancy, we suggest that disks around wide companions might be very compact and optically thick in order to sustain a few Myr of accretion, yet have very weak (sub)millimeter flux so as to still be elusive to ALMA. Our order-of-magnitude estimate shows that compact optically thick disks might be smaller than 1000 R Jup and only emit ∼μJy of flux in the (sub)millimeter, but their average temperature can be higher than that of circumstellar disks. The high disk temperature could impede satellite formation, but it also suggests that mid- to far-infrared might be more favorable than radio wavelengths to characterize disk properties. Finally, the compact disk size might imply that dynamical encounters between the companion and the star, or any other scatterers in the system, play a role in the formation of planetary-mass companions.

Constrained Evolution of a Radially Magnetized Protoplanetary Disk: Implications for Planetary Migration

NASA Astrophysics Data System (ADS)

Russo, Matthew; Thompson, Christopher

2015-12-01

We consider the inner ˜1 AU of a protoplanetary disk (PPD) at a stage where angular momentum transport is driven by the mixing of a radial magnetic field into the disk from a T Tauri wind. Because the radial profile of the imposed magnetic field is well constrained, a constrained calculation of the disk mass flow becomes possible. The vertical disk profiles obtained in Paper I imply a stronger magnetization in the inner disk, faster accretion, and a secular depletion of the disk material. Inward transport of solids allows the disk to maintain a broad optical absorption layer even when the grain abundance becomes too small to suppress its ionization. Thus, a PPD may show a strong mid- to near-infrared spectral excess even while its mass profile departs radically from the minimum-mass solar nebula. The disk surface density is buffered at ˜30 g cm-2 below this, X-rays trigger magnetorotational turbulence at the midplane strong enough to loft millimeter- to centimeter-sized particles high in the disk, followed by catastrophic fragmentation. A sharp density gradient bounds the inner depleted disk and propagates outward to ˜1-2 AU over a few megayears. Earth-mass planets migrate through the inner disk over a similar timescale, whereas the migration of Jupiters is limited by the supply of gas. Gas-mediated migration must stall outside 0.04 AU, where silicates are sublimated and the disk shifts to a much lower column. A transition disk emerges when the dust/gas ratio in the MRI-active layer falls below Xd ˜ 10-6 (ad/μm), where ad is the grain size.

A Triple Protostar System in L1448 IRS3B Formed via Fragmentation of a Gravitationally Unstable Disk

NASA Astrophysics Data System (ADS)

Tobin, John J.; Kratter, Kaitlin M.; Persson, Magnus; Looney, Leslie; Dunham, Michael; Segura-Cox, Dominique; Li, Zhi-Yun; Chandler, Claire J.; Sadavoy, Sarah; Harris, Robert J.; Melis, Carl; Perez, Laura M.

2017-01-01

Binary and multiple star systems are a frequent outcome of the star formation process; most stars form as part of a binary/multiple protostar system. A possible pathway to the formation of close (< 500 AU) binary/multiple star systems is fragmentation of a massive protostellar disk due to gravitational instability. We observed the triple protostar system L1448 IRS3B with ALMA at 1.3 mm in dust continuum and molecular lines to determine if this triple protostar system, where all companions are separated by < 200 AU, is likely to have formed via disk fragmentation. From the dust continuum emission, we find a massive, 0.39 solar mass disk surrounding the three protostars with spiral structure. The disk is centered on two protostars that are separated by 61 AU and the third protostar is located in the outer disk at 183 AU. The tertiary companion is coincident with a spiral arm, and it is the brightest source of emission in the disk, surrounded by ~0.09 solar masses of disk material. Molecular line observations from 13CO and C18O confirm that the kinematic center of mass is coincident with the two central protostars and that the disk is consistent with being in Keplerian rotation; the combined mass of the two close protostars is ~1 solar mass. We demonstrate that the disk around L1448 IRS3B remains marginally unstable at radii between 150~AU and 320~AU, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability, spawning the companion stars.

Abundances of sulfur in the Milky Way Disk from Peimbert Type II planetary nebulae

NASA Astrophysics Data System (ADS)

Milingo, Jacquelynne Brenda

2000-08-01

Sulfur abundance gradients and heavy element ratios for the Milky Way Disk are constructed based upon newly acquired spectrophotometry of Type II planetary nebulae (PN). These spectra extend from 3600-9600 angstroms allowing us to use the [SIII] 9069 and 9532 angstrom lines to improve upon earlier sulfur abundance estimates. Considering a significant portion of sulfur in PN exists in the S(+2) ionization stage (and higher) this method should allow us to extrapolate more reliable total element abundance from ionic abundances. Given the progenitor mass and location of Type II PN (close to the Galactic disk), this sample of objects is free of nucleosynthetic self-contamination and thus their S abundances in particular are expected to reflect levels of these elements in the interstellar medium at the time of PN progenitor formation. These sulfur abundances provide constraints for studying various aspects of GCE such as massive star yields and the distribution of S across the Milky Way disk.

Modulated mass-transfer model for superhumps in SU Ursae Majoris stars

NASA Technical Reports Server (NTRS)

Mineshige, Shin

1988-01-01

The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the superhump peaks. The elliptical accretion-disk model with extended vertical disk structure can account for the observed characteristics of superhumps in these stars.

Theory of active galactic nuclei

NASA Technical Reports Server (NTRS)

Shields, G. A.

1986-01-01

The involvement of accretion disks around supermassive black holes in the theory of active galactic nuclei (AGN) is discussed. The physics of thin and thick accretion disks is discussed and the partition between thermal and nonthermal energy production in supermassive disks is seen as uncertain. The thermal limit cycle may operate in supermassive disks (Shields, 1985), with accumulation of gas in the disk for periods of 10 to the 4th to 10 to the 7th years, punctuated by briefer outbursts during which the mass is rapidly transferred to smaller radii. An extended X-ray source in AGN is consistent with observations (Tennant and Mushotsky, 1983), and a large wind mass loss rate exceeding the central accretion rate means that only a fraction of the mass entering the disk will reach the central object; the rest being lost to the wind. Controversy in the relationship between the broad lines and the disk is also discussed.

Lupus Disks with Faint CO Isotopologues: Low Gas/Dust or High Carbon Depletion?

NASA Astrophysics Data System (ADS)

Miotello, Anna

2017-11-01

With the advent of ALMA, complete surveys of gas and dust in protoplanetary disks are being carried out in different star forming regions. In particular, continuum emission is used to trace the large (mm-sized) dust grains and CO isotopologues are observed in order to trace the bulk of the gas. The attempt is to simultaneously constrain the gas and dust disk mass as well as the gas/dust mass ratio. In this presentation I will present the Lupus disk survey observations, analyzed with thermo-chemical disk models, including radiative transfer, CO isotope-selective processes and freeze-out. The main result is that CO-based gas masses are very low, often smaller than Jupiter Mass. Moreover, gas/dust mass ratios are much lower than value of 100 found in the ISM, being mainly between 1 and 10. This result can be interpreted either as rapid loss of gas, or as a chemical effect removing carbon from CO and locking it into more complex molecules or in larger bodies. Previous data cannot distinguish between the two scenarios (except for sources with detected HD lines), but new Cycle 4 observations of hydrocarbon lines will be presented and they can help to calibrate CO-based gas masses and to constrain disk gas masses.

Hubble Space Telescope Observations of the Disk and Jet of HH 30

NASA Astrophysics Data System (ADS)

Burrows, Christopher J.; Stapelfeldt, Karl R.; Watson, Alan M.; Krist, John E.; Ballester, Gilda E.; Clarke, John T.; Crisp, David; Gallagher, John S., III; Griffiths, Richard E.; Hester, J. Jeff; Hoessel, John G.; Holtzman, Jon A.; Mould, Jeremy R.; Scowen, Paul A.; Trauger, John T.; Westphal, James A.

1996-12-01

HH 30 in Taurus has been imaged with the Hubble Space Telescope WFPC2. The images show in reflected light a flared disk with a radius of about 250 AU that obscures the protostar. The disk resembles detailed accretion disk models that constrain its density distribution and show that its inclination is less than 100. There are bipolar emission-line jets perpendicular to the disk, a very clear demonstration of the standard paradigm for accretion disk and jet systems. However, asymmetries in the light distribution show that the disk has not completely settled into a quasi-equilibrium accretion state, or that some of the observed scattering is from an asymmetric envelope. The emission-line jet itself is resolved into a number of knots with typical lengths and separations of 0".4, much smaller and more numerous than indicated by lower resolution ground-based studies. There are indications of still finer structures in the jet all the way to the resolution limit of 0".1. The knots have proper motions ranging from 100 to 300 km s-1 and are therefore generated at the surprisingly high rate of about 0.4 knots per jet per year. The jet appears to be collimated within a cone of opening angle 3° and can be seen to within 30 AU of the star. Both single- and multiple-scattering disk models have a range of possible solutions, but by requiring pressure support and temperature equilibrium, a self-consistent model emerges. There is evidence for pressure support because the disk appears to have a Gaussian height profile. The temperature at each point in the disk is determined by the disk geometry, which in turn fixes the temperature in a self- consistent manner. The extinction to the protostar is unknown but constrained to be greater than 24 mag. The optical properties of the scattering grains in the disk are determined and found to imply a large scattering asymmetry, but they seem to follow the interstellar reddening law. The absolute magnitude and colors of the unseen protostar, which has a brightness in the I bandpass of about 0.16 times solar and is very red, are obtained. The disk mass is about 0.006 times solar and has an expected lifetime of about 105 yr.

THICK DISKS OF EDGE-ON GALAXIES SEEN THROUGH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G): LAIR OF MISSING BARYONS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comeron, Sebastien; Elmegreen, Bruce G.; Knapen, Johan H.

Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T = 3 to T = 8. We fitted one-dimensional luminosity profiles with physically motivated functions-the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium-which are likely to yield more accurate results than other functions used inmore » previous studies. The images used for the fits come from the Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G). We found that thick disks are on average more massive than previously reported, mostly due to the selected fitting function. Typically, the thin and thick disks have similar masses. We also found that thick disks do not flare significantly within the observed range in galactocentric radii and that the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types. Our results tend to favor an in situ origin for most of the stars in the thick disk. In addition, the thick disk may contain a significant amount of stars coming from satellites accreted after the initial buildup of the galaxy and an extra fraction of stars coming from the secular heating of the thin disk by its own overdensities. Assigning thick disk light to the thin disk component may lead to an underestimate of the overall stellar mass in galaxies because of different mass-to-light ratios in the two disk components. On the basis of our new results, we estimate that disk stellar masses are between 10% and 50% higher than previously thought and we suggest that thick disks are a reservoir of 'local missing baryons'.« less

DUSTY OB STARS IN THE SMALL MAGELLANIC CLOUD. II. EXTRAGALACTIC DISKS OR EXAMPLES OF THE PLEIADES PHENOMENON?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Joshua J.; Simon, Joshua D.; Bolatto, Alberto D.

2013-07-10

We use mid-infrared Spitzer spectroscopy and far-infrared Herschel photometry for a sample of 20 main sequence O9-B2 stars in the Small Magellanic Cloud (SMC) with strong 24 {mu}m excesses to investigate the origin of the mid-IR emission. Either debris disks around the stars or illuminated patches of dense interstellar medium (ISM) can cause such mid-IR emission. In a companion paper, Paper I, we use optical spectroscopy to show that it is unlikely for any of these sources to be classical Be stars or Herbig Ae/Be stars. We focus our analysis on debris disks and cirrus hot spots. The local, prototypemore » objects for these models are the debris disk around Vega and the heated dust cloud surrounding the stars in the Pleiades, also known as a cirrus hot spot. These two cases predict different dust masses, radii, origins, and structures, but the cleanest classification tools are lost by the poor physical resolution at the distance of the SMC. We also consider transition disks, which would have observable properties similar to debris disks. We begin classification by measuring angular extent in the highest resolution mid-IR images available. We find 3 out of 20 stars to be significantly extended, establishing them as cirrus hot spots. We then fit the IR spectral energy distributions to determine dust temperatures and masses. Analysis yields minimum grain sizes, thermal equilibrium distances, and the resultant dust mass estimates. We find the dust masses in the SMC stars to be larger than for any known debris disks. The difference in inferred properties is driven by the SMC stars being hotter and more luminous than known debris disk hosts and not in any directly observed dust properties, so this evidence against the debris disk hypothesis is circumstantial. Finally, we created a local comparison sample of bright mid-IR OB stars in the Milky Way (MW) by cross-matching the Wide-field Infrared Survey Explorer (WISE) and Hipparcos catalogs. We find that of the thousands of nearby ({<=}1 kpc) hot stars in the MW that show a mid-IR excess, only a small fraction (few percent) match the high mid-IR luminosities of the SMC stars. All such local stars in the appropriate luminosity range that can be unambiguously classified are young stars with optical emission lines or are spatially resolved by WISE with sizes too large to be plausible debris disk candidates. We conclude that the very strong mid-IR flux excesses are most likely explained as cirrus hot spots, although we cannot rigorously rule out that a small fraction of the sample is made up of debris disks or transition disks. We present suggestive evidence that bow-shock heating around runaway stars may be a contributing mechanism to the interstellar emission. These sources, interpreted as cirrus hot spots, offer a new localized probe of diffuse interstellar dust in a low metallicity environment.« less

Course 6: Star Formation

NASA Astrophysics Data System (ADS)

Natta, A.

Contents 1 Introduction 2 Collapse of molecular cores 2.1 Giant molecular clouds and cores 2.2 Conditions for collapse 2.3 Free-fall collapse 2.4 Collapse of an isothermal sphere of gas 2.5 Collapse of a slowly rotating core 3 Observable properties of protostars 3.1 Evidence of infall from molecular line profiles 3.2 SEDs of protostars 3.3 The line spectrumof a protostar 4 Protostellar and pre-main-sequence evolution 4.1 The protostellar phase 4.2 Pre-main-sequence evolution 4.3 The birthline 5 Circumstellar disks 5.1 Accretion disks 5.2 Properties of steady accretion disks 5.3 Reprocessing disks 5.4 Disk-star interaction 6 SEDs of disks 6.1 Power-law disks 6.2 Long-wavelength flux and disk mass 6.3 Comparison with TTS observations: Heating mechanism 7 Disk properties from observations 7.1 Mass accretion rate 7.2 Inner radius 7.3 Masses 7.4 Sizes 8 Disk lifetimes 8.1 Ground-based near and mid-infrared surveys 8.2 Mid-infrared ISOCAMsurveys 8.3 ISOPHOT 60 microm survey 8.4 Surveys at millimeter wavelengths 9 Disk evolution 9.1 Can we observe the early planet formation phase? 9.2 Evidence for grain growth 9.3 Evidence of planetesimals 9.4 Where is the diskmass? 10 Secondary or debris disks 11 Summary

The Scylla Multi-Code Comparison Project

NASA Astrophysics Data System (ADS)

Maller, Ariyeh; Stewart, Kyle; Bullock, James; Oñorbe, Jose; Scylla Team

2016-01-01

Cosmological hydrodynamical simulations are one of the main techniques used to understand galaxy formation and evolution. However, it is far from clear to what extent different numerical techniques and different implementations of feedback yield different results. The Scylla Multi-Code Comparison Project seeks to address this issue by running idenitical initial condition simulations with different popular hydrodynamic galaxy formation codes. Here we compare simulations of a Milky Way mass halo using the codes enzo, ramses, art, arepo and gizmo-psph. The different runs produce galaxies with a variety of properties. There are many differences, but also many similarities. For example we find that in all runs cold flow disks exist; extended gas structures, far beyond the galactic disk, that show signs of rotation. Also, the angular momentum of warm gas in the halo is much larger than the angular momentum of the dark matter. We also find notable differences between runs. The temperature and density distribution of hot gas can differ by over an order of magnitude between codes and the stellar mass to halo mass relation also varies widely. These results suggest that observations of galaxy gas halos and the stellar mass to halo mass relation can be used to constarin the correct model of feedback.

Accretion tori and cones of ionizing radiation in Seyfert galaxies

NASA Technical Reports Server (NTRS)

Acosta-Pulido, Jose A.; Perez-Fournon, Ismael; Calvani, Massimo; Wilson, Andrew S.

1990-01-01

The photoionization of extended narrow-line regions in Seyfert galaxies by the radiation produced in a thick accretion disk is studied. The emission-line spectrum is calculated for a range of black hole masses, varying the values of the ionization parameter and the disk size. It is found that models with a million solar masses fit observations of very large accretion disk sizes, while models with 10 million solar masses fit them better with smaller disks. The latter models are preferable since they have lower super-Eddington accretion rates.

Dust clouds around red giant stars - Evidence of sublimating comet disks?

NASA Technical Reports Server (NTRS)

Matese, John J.; Whitmire, Daniel P.; Reynolds, Ray T.

1989-01-01

The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

Diversidad de Sistemas Planetarios en Discos de Baja Masa

NASA Astrophysics Data System (ADS)

Ronco, M. P.; de Elía, G. C.

The accretion process that allows the formation of terrestrial planets is strongly dependent on the mass distribution in the system and the presence of gas giant planets. Several studies suggest that planetary systems formed only by terrestrial planets are the most common in the Universe. In this work we study the diversity of planetary systems that could form around solar-type stars in low mass disks in absence of gas giants planets and search wich ones are targets of particular interest. FULL TEXT IN SPANISH

The impact of galaxy geometry and mass evolution on the survival of star clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Madrid, Juan P.; Hurley, Jarrod R.; Martig, Marie

2014-04-01

Direct N-body simulations of globular clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6 to determine the impact of the host galaxy disk mass and geometry on the survival of star clusters. A relation between disk mass and star-cluster dissolution timescale is derived. These N-body models show that doubling the mass of the disk from 5 × 10{sup 10} M {sub ☉} to 10 × 10{sup 10} M {sub ☉} halves the dissolution time of a satellite star cluster orbiting the host galaxy at 6 kpc from the galactic center. Different geometries in a disk ofmore » identical mass can determine either the survival or dissolution of a star cluster orbiting within the inner 6 kpc of the galactic center. Furthermore, disk geometry has measurable effects on the mass loss of star clusters up to 15 kpc from the galactic center. N-body simulations performed with a fine output time step show that at each disk crossing the outer layers of star clusters experiences an increase in velocity dispersion of ∼5% of the average velocity dispersion in the outer section of star clusters. This leads to an enhancement of mass loss—a clearly discernable effect of disk shocking. By running models with different inclinations, we determine that star clusters with an orbit that is perpendicular to the Galactic plane have larger mass loss rates than do clusters that evolve in the Galactic plane or in an inclined orbit.« less

The Surface Density Profile of the Galactic Disk from the Terminal Velocity Curve

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.

2016-01-01

The mass distribution of the Galactic disk is constructed from the terminal velocity curve and the mass discrepancy-acceleration relation. Mass models numerically quantifying the detailed surface density profiles are tabulated. For R0 = 8 kpc, the models have stellar mass 5 < M* < 6 × 1010 {M}⊙ , scale length 2.0 ≤ Rd ≤ 2.9 kpc, LSR circular velocity 222 ≤ Θ0 ≤ 233 {km} {{{s}}}-1, and solar circle stellar surface density 34 ≤ Σd(R0) ≤ 61 {M}⊙ {{pc}}-2. The present interarm location of the solar neighborhood may have a somewhat lower stellar surface density than average for the solar circle. The Milky Way appears to be a normal spiral galaxy that obeys scaling relations like the Tully-Fisher relation, the size-mass relation, and the disk maximality-surface brightness relation. The stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles in the terminal velocity curve correspond to known spiral features (e.g., the Centaurus arm is a ˜50% overdensity). The rotation curve switches between positive and negative over scales of hundreds of parsecs. The rms amplitude {< {| {dV}/{dR}| }2> }1/2≈ 14 {km} {{{s}}}-1 {{kpc}}-1, implying that commonly neglected terms in the Jeans equations may be nonnegligible. The spherically averaged local dark matter density is ρ0,DM ≈ 0.009 {M}⊙ {{pc}}-3 (0.34 {GeV} {{cm}}-3). Adiabatic compression of the dark matter halo may help reconcile the Milky Way with the c-V200 relation expected in ΛCDM while also helping to mitigate the too-big-to-fail problem, but it remains difficult to reconcile the inner bulge/bar-dominated region with a cuspy halo. We note that NGC 3521 is a near twin to the Milky Way, having a similar luminosity, scale length, and rotation curve.

Impacts of planet migration models on planetary populations. Effects of saturation, cooling and stellar irradiation

NASA Astrophysics Data System (ADS)

Dittkrist, K.-M.; Mordasini, C.; Klahr, H.; Alibert, Y.; Henning, T.

2014-07-01

Context. Several recent studies have found that planet migration in adiabatic disks differs significantly from migration in isothermal disks. Depending on the thermodynamic conditions, that is, the effectiveness of radiative cooling, and on the radial surface density profile, planets migrate inward or outward. Clearly, this will influence the semimajor-axis-to-mass distribution of planets predicted by population-synthesis simulations. Aims: Our goal is to study the global effects of radiative cooling, viscous torque desaturation, gap opening, and stellar irradiation on the tidal migration of a synthetic planet population. Methods: We combined results from several analytical studies and 3D hydrodynamic simulations in a new semi-analytical migration model for the application in our planet population synthesis calculations. Results: We find a good agreement of our model with torques obtained in 3D radiative hydrodynamic simulations. A typical disk has three convergence zones to which migrating planets move from the in- and outside. This strongly affects the migration behavior of low-mass planets. Interestingly, this leads to a slow type II like migration behavior for low-mass planets captured in these zones even without an ad hoc migration rate reduction factor or a yet-to-be-defined halting mechanism. This means that the new prescription of migration that includes nonisothermal effects makes the previously widely used artificial migration rate reduction factor obsolete. Conclusions: Outward migration in parts of a disk helps some planets to survive long enough to become massive. The convergence zones lead to potentially observable accumulations of low-mass planets at certain semimajor axes. Our results indicate that more studies of the mass at which the corotation torque saturates are needed since its value has a main impact on the properties of planet populations. Appendices A and B are available in electronic form at http://www.aanda.org

Fomalhaut's Debris Disk and Planet: Constraining the Mass of Formalhaut B from Disk Morphology

NASA Technical Reports Server (NTRS)

Chiang, E.; Kite, E.; Kalas, P.; Graham, J. R.; Clampin, M.

2008-01-01

Following the optical imaging of exoplanet candidate Fomalhaut b (Fom b), we present a numerical model of how Fomalhaut's debris disk is gravitationally shaped by a single interior planet. The model is simple, adaptable to other debris disks, and can be extended to accommodate multiple planets. If Fom b is the dominant perturber of the belt, then to produce the observed disk morphology it must have a mass M(sub pl) < 3M(sub J), an orbital semimajor axis a(sub pl) > 101.5AU, and an orbital eccentricity e(sub pl) = 0.11 - 0.13. These conclusions are independent of Fom b's photometry. To not disrupt the disk, a greater mass for Fom b demands a smaller orbit farther removed from the disk; thus, future astrometric measurement of Fom b's orbit, combined with our model of planet-disk interaction, can be used to determine the mass more precisely. The inner edge of the debris disk at a approximately equals 133AU lies at the periphery of Fom b's chaotic zone, and the mean disk eccentricity of e approximately equals 0.11 is secularly forced by the planet, supporting predictions made prior to the discovery of Fom b. However, previous mass constraints based on disk morphology rely on several oversimplifications. We explain why our constraint is more reliable. It is based on a global model of the disk that is not restricted to the planet's chaotic zone boundary. Moreover, we screen disk parent bodies for dynamical stability over the system age of approximately 100 Myr, and model them separately from their dust grain progeny; the latter's orbits are strongly affected by radiation pressure and their lifetimes are limited to approximately 0.1 Myr by destructive grain-grain collisions. The single planet model predicts that planet and disk orbits be apsidally aligned. Fomalhaut b's nominal space velocity does not bear this out, but the astrometric uncertainties are difficult to quantify. Even if the apsidal misalignment proves real, our calculated upper mass limit of 3 M(sub J) still holds. Parent bodies are evacuated from mean-motion resonances with Fom b; these empty resonances are akin to the Kirkwood gaps opened by Jupiter. The belt contains at least 3M(sub Earth) of solids that are grinding down to dust, their velocity dispersions stirred so strongly by Fom b that collisions are destructive. Such a large mass in solids is consistent with Fom b having formed in situ.

Protoplanetary Disk Masses from Stars to Brown Dwarfs

NASA Astrophysics Data System (ADS)

Mohanty, Subhanjoy; Greaves, Jane; Mortlock, Daniel; Pascucci, Ilaria; Scholz, Aleks; Thompson, Mark; Apai, Daniel; Lodato, Giuseppe; Looper, Dagny

2013-08-01

We present SCUBA-2 850 μm observations of seven very low mass stars (VLMS) and brown dwarfs (BDs). Three are in Taurus and four in the TW Hydrae Association (TWA), and all are classical T Tauri (cTT) analogs. We detect two of the three Taurus disks (one only marginally), but none of the TWA ones. For standard grains in cTT disks, our 3σ limits correspond to a dust mass of 1.2 M ⊕ in Taurus and a mere 0.2 M ⊕ in the TWA (3-10× deeper than previous work). We combine our data with other submillimeter/millimeter (sub-mm/mm) surveys of Taurus, ρ Oph, and the TWA to investigate the trends in disk mass and grain growth during the cTT phase. Assuming a gas-to-dust mass ratio of 100:1 and fiducial surface density and temperature profiles guided by current data, we find the following. (1) The minimum disk outer radius required to explain the upper envelope of sub-mm/mm fluxes is ~100 AU for intermediate-mass stars, solar types, and VLMS, and ~20 AU for BDs. (2) While the upper envelope of apparent disk masses increases with M * from BDs to VLMS to solar-type stars, no such increase is observed from solar-type to intermediate-mass stars. We propose this is due to enhanced photoevaporation around intermediate stellar masses. (3) Many of the disks around Taurus and ρ Oph intermediate-mass and solar-type stars evince an opacity index of β ~ 0-1, indicating significant grain growth. Of the only four VLMS/BDs in these regions with multi-wavelength measurements, three are consistent with considerable grain growth, though optically thick disks are not ruled out. (4) For the TWA VLMS (TWA 30A and B), combining our 850 μm fluxes with the known accretion rates and ages suggests substantial grain growth by 10 Myr, comparable to that in the previously studied TWA cTTs Hen 3-600A and TW Hya. The degree of grain growth in the TWA BDs (2M1207A and SSPM1102) remains largely unknown. (5) A Bayesian analysis shows that the apparent disk-to-stellar mass ratio has a roughly constant mean of log10[M disk/M *] ≈ -2.4 all the way from intermediate-mass stars to VLMS/BDs, supporting previous qualitative suggestions that the ratio is ~1% throughout the stellar/BD domain. (6) Similar analysis shows that the disk mass in close solar-type Taurus binaries (sep <100 AU) is significantly lower than in singles (by a factor of 10), while that in wide solar-type Taurus binaries (>=100 AU) is closer to that in singles (lower by a factor of three). (7) We discuss the implications of these results for planet formation around VLMS/BDs, and for the observed dependence of accretion rate on stellar mass.

Galactic Stellar and Substellar Initial Mass Function

NASA Astrophysics Data System (ADS)

Chabrier, Gilles

2003-07-01

We review recent determinations of the present-day mass function (PDMF) and initial mass function (IMF) in various components of the Galaxy-disk, spheroid, young, and globular clusters-and in conditions characteristic of early star formation. As a general feature, the IMF is found to depend weakly on the environment and to be well described by a power-law form for m>~1 Msolar and a lognormal form below, except possibly for early star formation conditions. The disk IMF for single objects has a characteristic mass around mc~0.08 Msolar and a variance in logarithmic mass σ~0.7, whereas the IMF for multiple systems has mc~0.2 Msolar and σ~0.6. The extension of the single MF into the brown dwarf regime is in good agreement with present estimates of L- and T-dwarf densities and yields a disk brown dwarf number density comparable to the stellar one, nBD~n*~0.1 pc-3. The IMF of young clusters is found to be consistent with the disk field IMF, providing the same correction for unresolved binaries, confirming the fact that young star clusters and disk field stars represent the same stellar population. Dynamical effects, yielding depletion of the lowest mass objects, are found to become consequential for ages >~130 Myr. The spheroid IMF relies on much less robust grounds. The large metallicity spread in the local subdwarf photometric sample, in particular, remains puzzling. Recent observations suggest that there is a continuous kinematic shear between the thick-disk population, present in local samples, and the genuine spheroid one. This enables us to derive only an upper limit for the spheroid mass density and IMF. Within all the uncertainties, the latter is found to be similar to the one derived for globular clusters and is well represented also by a lognormal form with a characteristic mass slightly larger than for the disk, mc~0.2-0.3 Msolar, excluding a significant population of brown dwarfs in globular clusters and in the spheroid. The IMF characteristic of early star formation at large redshift remains undetermined, but different observational constraints suggest that it does not extend below ~1 Msolar. These results suggest a characteristic mass for star formation that decreases with time, from conditions prevailing at large redshift to conditions characteristic of the spheroid (or thick disk) to present-day conditions. These conclusions, however, remain speculative, given the large uncertainties in the spheroid and early star IMF determinations. These IMFs allow a reasonably robust determination of the Galactic present-day and initial stellar and brown dwarf contents. They also have important galactic implications beyond the Milky Way in yielding more accurate mass-to-light ratio determinations. The mass-to-light ratios obtained with the disk and the spheroid IMF yield values 1.8-1.4 times smaller than for a Salpeter IMF, respectively, in agreement with various recent dynamical determinations. This general IMF determination is examined in the context of star formation theory. None of the theories based on a Jeans-type mechanism, where fragmentation is due only to gravity, can fulfill all the observational constraints on star formation and predict a large number of substellar objects. On the other hand, recent numerical simulations of compressible turbulence, in particular in super-Alfvénic conditions, seem to reproduce both qualitatively and quantitatively the stellar and substellar IMF and thus provide an appealing theoretical foundation. In this picture, star formation is induced by the dissipation of large-scale turbulence to smaller scales through radiative MHD shocks, producing filamentary structures. These shocks produce local nonequilibrium structures with large density contrasts, which collapse eventually in gravitationally bound objects under the combined influence of turbulence and gravity. The concept of a single Jeans mass is replaced by a distribution of local Jeans masses, representative of the lognormal probability density function of the turbulent gas. Objects below the mean thermal Jeans mass still have a possibility to collapse, although with a decreasing probability. The page charges for this Review were partially covered by a generous gift from a PASP supporter.

How Bright are Planet-induced Spiral Arms in Scattered Light?

NASA Astrophysics Data System (ADS)

Dong, Ruobing; Fung, Jeffrey

2017-01-01

Recently, high angular resolution imaging instruments such as SPHERE and GPI have discovered many spiral-arm-like features in near-infrared scattered-light images of protoplanetary disks. Theory and simulations have suggested that these arms are most likely excited by planets forming in the disks; however, a quantitative relation between the arm-to-disk brightness contrast and planet mass is still missing. Using 3D hydrodynamics and radiative transfer simulations, we examine the morphology and contrast of planet-induced arms in disks. We find a power-law relation for the face-on arm contrast (δmax) as a function of planet mass ({M}{{p}}) and disk aspect ratio (h/r): {δ }\\max ≈ {({({M}{{p}}/{M}{{J}})/(h/r)}1.38)}0.22. With current observational capabilities, at a 30 au separation, the minimum planet mass for driving detectable arms in a disk around a 1 Myr, 1 {M}ȯ star at 140 pc at low inclinations is around Saturn mass. For planets more massive than Neptune masses, they typically drive multiple arms. Therefore, in observed disks with spirals, it is unlikely that each spiral arm originates from a different planet. We also find that only massive perturbers with at least multi-Jupiter masses are capable of driving bright arms with {δ }\\max ≳ 2 as found in SAO 206462, MWC 758, and LkHα 330, and these arms do not follow linear wave propagation theory. Additionally, we find that the morphology and contrast of the primary and secondary arms are largely unaffected by a modest level of viscosity with α ≲ 0.01. Finally, the contrast of the arms in the SAO 206462 disk suggests that the perturber SAO 206462 b at ∼100 au is about 5{--}10 {M}{{J}} in mass.

Gravitational Instabilities in a Young Protoplanetary Disk with Embedded Objects

NASA Astrophysics Data System (ADS)

Desai, Karna M.; Steiman-Cameron, Thomas Y.; Durisen, Richard H.

2018-01-01

Gravitational Instabilities (GIs), a mechanism for angular momentum transport, are more prominent during the early phases of protoplanetary disk evolution when the disk is relatively massive. In my dissertation work, I performed radiative 3D hydrodynamics simulations (by employing the code, CHYMERA) and extensively studied GIs by inserting different objects in the ‘control disk’ (a 0.14 M⊙ protoplanetary disk around a 1 M⊙ star).Studying planetary migration helps us better constrain planet formation models. To study the migration of Jovian planets, in 9 separate simulations, each of the 0.3 MJ, 1 MJ, and 3 MJ planets was inserted near the Inner and Outer Lindblad Resonances and the Corotation Radius (CR) of the dominant GI-induced two-armed spiral density wave in the disk. I found the migration timescales to be longer in a GI-active disk when compared to laminar disks. The 3 MJ planet controls its own orbital evolution, while the migration of a 0.3 MJ planet is stochastic in nature. I defined a ‘critical mass’ as the mass of an arm of the dominant two-armed spiral density wave within the planet’s Hill diameter. Planets above this mass control their own destiny, and planets below this mass are scattered by the disk. This critical mass could provide a recipe for predicting the migration behavior of planets in GI-active disks.To understand the stochastic migration of low-mass planets, I performed a simulation of 240 zero-mass planet-tracers (hereafter, planets) by inserting these at a range of locations in the control disk (an equivalent of 240 simulations of Saturn-mass or lower-mass objects). I calculated a Diffusion Coefficient (3.6 AU2/ 1000 yr) to characterize the stochastic migration of planets. I analyzed the increase in the eccentricity dispersion and compared it with the observed exoplanet eccentricities. The diffusion of planets can be a slow process, resulting in the survival of small planetary cores. Stochastic migration of planets is dynamically similar to the radial migration of stars in the Milky Way (MW). In MW, the CR of transient spiral arms can cause radial migration of stars.Also, to determine the effects of a companion, I studied GIs in a circumbinary disk with a 0.2 M⊙ brown dwarf companion.

ALMA Imaging of HCN, CS, and Dust in Arp 220 and NGC 6240

NASA Astrophysics Data System (ADS)

Scoville, Nick; Sheth, Kartik; Walter, Fabian; Manohar, Swarnima; Zschaechner, Laura; Yun, Min; Koda, Jin; Sanders, David; Murchikova, Lena; Thompson, Todd; Robertson, Brant; Genzel, Reinhard; Hernquist, Lars; Tacconi, Linda; Brown, Robert; Narayanan, Desika; Hayward, Christopher C.; Barnes, Joshua; Kartaltepe, Jeyhan; Davies, Richard; van der Werf, Paul; Fomalont, Edward

2015-02-01

We report ALMA Band 7 (350 GHz) imaging at 0.''4-0.''6 resolution and Band 9 (696 GHz) at ~0.''25 resolution of the luminous IR galaxies Arp 220 and NGC 6240. The long wavelength dust continuum is used to estimate interstellar medium masses for Arp 220 east and west and NGC 6240 of 1.9, 4.2, and 1.6 × 109 M ⊙within radii of 69, 65, and 190 pc. The HCN emission was modeled to derive the emissivity distribution as a function of radius and the kinematics of each nuclear disk, yielding dynamical masses consistent with the masses and sizes derived from the dust emission. In Arp 220, the major dust and gas concentrations are at radii less than 50 pc in both counter-rotating nuclear disks. The thickness of the disks in Arp 220 estimated from the velocity dispersion and rotation velocities are 10-20 pc and the mean gas densities are nH_2 ˜ 10^5 cm-3 at R <50 pc. We develop an analytic treatment for the molecular excitation (including photon trapping), yielding volume densities for both the HCN and CS emission with n H2 ~ 2 × 105 cm-3. The agreement of the mean density from the total mass and size with that required for excitation suggests that the volume is essentially filled with dense gas, i.e., it is not cloudy or like swiss cheese.

Hydrodynamic Simulations of the Central Molecular Zone with a Realistic Galactic Potential

NASA Astrophysics Data System (ADS)

Shin, Jihye; Kim, Sungsoo S.; Baba, Junichi; Saitoh, Takayuki R.; Hwang, Jeong-Sun; Chun, Kyungwon; Hozumi, Shunsuke

2017-06-01

We present hydrodynamic simulations of gas clouds inflowing from the disk to a few hundred parsec region of the Milky Way. A gravitational potential is generated to include realistic Galactic structures by using thousands of multipole expansions (MEs) that describe 6.4 million stellar particles of a self-consistent Galaxy simulation. We find that a hybrid ME model, with two different basis sets and a thick-disk correction, accurately reproduces the overall structures of the Milky Way. Through non-axisymmetric Galactic structures of an elongated bar and spiral arms, gas clouds in the disk inflow to the nuclear region and form a central molecular zone-like nuclear ring. We find that the size of the nuclear ring evolves into ˜ 240 {pc} at T˜ 1500 {Myr}, regardless of the initial size. For most simulation runs, the rate of gas inflow to the nuclear region is equilibrated to ˜ 0.02 {M}⊙ {{yr}}-1. The nuclear ring is off-centered, relative to the Galactic center, by the lopsided central mass distribution of the Galaxy model, and thus an asymmetric mass distribution of the nuclear ring arises accordingly. The vertical asymmetry of the Galaxy model also causes the nuclear ring to be tilted along the Galactic plane. During the first ˜100 Myr, the vertical frequency of the gas motion is twice that of the orbital frequency, thus the projected nuclear ring shows a twisted, ∞ -like shape.

Evolution of Spin and Superorbital Modulation in 4U 0114+650

NASA Astrophysics Data System (ADS)

Hu, Chin-Ping; Ng, Chi-Yung; Chou, Yi

2016-09-01

We report on a systematic analysis of the spin and superorbital modulations of the high-mass X-ray binary 4U 0114+650, which consists of the slowest spinning neutron star known. Utilizing dynamic power spectra, we found that the spin period varied dramatically during the RXTE ASM and Swift BAT observations. This variation consists of a long-term spin-up trend, and two ~1,000 day and one ~600 day random walk epochs previously, MJD 51,000, ~MJD 51,400-52,000, and ~MJD 55,100-56,100. We further found that the events appear together with depressions of superorbital modulation amplitude. This provides evidence of the existence of an accretion disk, although the physical mechanism of superorbital modulation remains unclear. Furthermore, the decrease of the superorbital modulation amplitude may be associated with the decrease of mass accretion rate from the disk, and may distribute the accretion torque of the neutron star randomly in time.

Global Evolution of Solid Matter in Turbulent Protoplanetry Disks. Part 1; Aerodynamics of Solid Particles

NASA Technical Reports Server (NTRS)

Stepinski, T. F.; Valageas, P.

1996-01-01

The problem of planetary system formation and its subsequent character can only be addressed by studying the global evolution of solid material entrained in gaseous protoplanetary disks. We start to investigate this problem by considering the space-time development of aerodynamic forces that cause solid particles to decouple from the gas. The aim of this work is to demonstrate that only the smallest particles are attached to the gas, or that the radial distribution of the solid matter has no momentary relation to the radial distribution of the gas. We present the illustrative example wherein a gaseous disk of 0.245 solar mass and angular momentum of 5.6 x 10(exp 52) g/sq cm/s is allowed to evolve due to turbulent viscosity characterized by either alpha = 10(exp -2) or alpha = 10(exp -3). The motion of solid particles suspended in a viscously evolving gaseous disk is calculated numerically for particles of different sizes. In addition we calculate the global evolution of single-sized, noncoagulating particles. We find that particles smaller than 0.1 cm move with the gas; larger particles have significant radial velocities relative to the gas. Particles larger than 0.1 cm but smaller than 10(exp 3) cm have inward radial velocities much larger than the gas, whereas particles larger than 10(exp 4) cm have inward velocities much smaller than the gas. A significant difference in the form of the radial distribution of solids and the gas develops with time. It is the radial distribution of solids, rather than the gas, that determines the character of an emerging planetary system.

TOWARD A DETERMINISTIC MODEL OF PLANETARY FORMATION. VII. ECCENTRICITY DISTRIBUTION OF GAS GIANTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ida, S.; Lin, D. N. C.; Nagasawa, M., E-mail: ida@geo.titech.ac.jp, E-mail: lin@ucolick.org, E-mail: nagasawa.m.ad@m.titech.ac.jp

2013-09-20

The ubiquity of planets and diversity of planetary systems reveal that planet formation encompasses many complex and competing processes. In this series of papers, we develop and upgrade a population synthesis model as a tool to identify the dominant physical effects and to calibrate the range of physical conditions. Recent planet searches have led to the discovery of many multiple-planet systems. Any theoretical models of their origins must take into account dynamical interactions between emerging protoplanets. Here, we introduce a prescription to approximate the close encounters between multiple planets. We apply this method to simulate the growth, migration, and dynamicalmore » interaction of planetary systems. Our models show that in relatively massive disks, several gas giants and rocky/icy planets emerge, migrate, and undergo dynamical instability. Secular perturbation between planets leads to orbital crossings, eccentricity excitation, and planetary ejection. In disks with modest masses, two or less gas giants form with multiple super-Earths. Orbital stability in these systems is generally maintained and they retain the kinematic structure after gas in their natal disks is depleted. These results reproduce the observed planetary mass-eccentricity and semimajor axis-eccentricity correlations. They also suggest that emerging gas giants can scatter residual cores to the outer disk regions. Subsequent in situ gas accretion onto these cores can lead to the formation of distant (∼> 30 AU) gas giants with nearly circular orbits.« less

Rotating-disk sorptive extraction: effect of the rotation mode of the extraction device on mass transfer efficiency.

PubMed

Jachero, Lourdes; Ahumada, Inés; Richter, Pablo

2014-05-01

The extraction device used in rotating-disk sorptive extraction consists of a Teflon disk in which a sorptive phase is fixed on one of its surfaces. Depending on the configuration, the rotation axis of the disk device can be either perpendicular or parallel to its radius, giving rise to two different mass transfer patterns when rotating-disk sorptive extraction is applied in liquid samples. In the perpendicular case (configuration 1), which is the typical configuration, the disk contains an embedded miniature stir bar that allows the disk rotation to be driven using a common laboratory magnetic stirrer. In the parallel case (configuration 2), the disk is driven by a rotary rod connected to an electric stirrer. In this study, triclosan and its degradation product methyl triclosan were used as analyte models to demonstrate the significant effect of the rotation configuration of the disk on the efficiency of analyte mass transfer from water to a sorptive phase of polydimethylsiloxane. Under the same experimental conditions and at a rotation velocity of 1,250 rpm, extraction equilibrium was reached at 80 min when the disk was rotated in configuration 1 and at 30 min when the disk was rotated in configuration 2. The extraction equilibration time decreased to 14 min when the rotation velocity was increased to 2,000 rpm in configuration 2. Because the rotation pattern affects the mass transfer efficiency, each rotation configuration was characterized through the Reynolds number; Re values of 6,875 and 16,361 were achieved with configurations 1 and 2, respectively, at 1,250 rpm.

The Minimum-Mass Surface Density of the Solar Nebula using the Disk Evolution Equation

NASA Technical Reports Server (NTRS)

Davis, Sanford S.

2005-01-01

The Hayashi minimum-mass power law representation of the pre-solar nebula (Hayashi 1981, Prog. Theo. Phys.70,35) is revisited using analytic solutions of the disk evolution equation. A new cumulative-planetary-mass-model (an integrated form of the surface density) is shown to predict a smoother surface density compared with methods based on direct estimates of surface density from planetary data. First, a best-fit transcendental function is applied directly to the cumulative planetary mass data with the surface density obtained by direct differentiation. Next a solution to the time-dependent disk evolution equation is parametrically adapted to the planetary data. The latter model indicates a decay rate of r -1/2 in the inner disk followed by a rapid decay which results in a sharper outer boundary than predicted by the minimum mass model. The model is shown to be a good approximation to the finite-size early Solar Nebula and by extension to extra solar protoplanetary disks.

A Steeper than Linear Disk Mass-Stellar Mass Scaling Relation

NASA Astrophysics Data System (ADS)

Pascucci, Ilaria; SLICK, EOS

2017-01-01

The disk mass is among the most important input parameter of planet formation models as it determines the number and masses of the planets that can form. I will present an ALMA 887 micron survey of the disk population around objects from 2 to 0.03Msun in the nearby 2 Myr-old Chamaeleon I star-forming region. Assuming isothermal and optically thin emission, we convert the 887 micron flux densities into dust disk masses (Mdust) and show that the Mdust-Mstar scaling relation is steeper than linear. By re-analyzing all millimeter data available for nearby regions in a self-consistent way, we find that the 1-3 Myr-old regions of Taurus, Lupus, and Chamaeleon I share the same Mdust-Mstar relation, while the 10 Myr-old Upper Sco association has an even steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.

Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters

NASA Astrophysics Data System (ADS)

Richert, A. J. W.; Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Broos, P. S.; Povich, M. S.; Bate, M. R.; Garmire, G. P.

2018-04-01

Photometric detections of dust circumstellar disks around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disk longevity, starting with Haisch, Lada & Lada (2001), use star samples from PMS clusters but do not consider datasets with homogeneous photometric sensitivities and/or ages placed on a uniform timescale. Here we conduct the largest study to date of the longevity of inner dust disks using X-ray and 1-8 {μ m} infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disk-free objects, we impose similar stellar mass sensitivity limits for disk-bearing and disk-free YSOs while extending the analysis to stellar masses as low as M ˜ 0.1 M⊙. We find that the disk longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disk fraction of 100% at zero age, the inferred disk half-life changes significantly, from t1/2 ˜ 1.3 - 2 Myr to t1/2 ˜ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disk fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disk fraction and star-forming environment are also explored.

Exploring Structures and Variability in the Pre-transitional Disk in HD 169142

NASA Astrophysics Data System (ADS)

Wagner, Kevin Robert; Sitko, Michael L.; Grady, Carol A.; Whitney, Barbara; Swearingen, Jeremy R.; Champney, Elizabeth H.; Johnson, Alexa N.; Warren, Chelsea C.; Russell, Ray W.; Schneider, Glenn; Momose, Muntake; Muto, Takayuki; Inoue, Akio K.; Lauroesch, James Thomas; Hornbeck, Jeremy; Brown, Alexander; Fukagawa, Misato; Currie, Thayne M.; Wisniewski, John P.; Woodgate, Bruce E.

2015-01-01

We present a theoretical modelling analysis of of the structures in the pre-transisitonal disk in HD 169142 using 3D Monte-Carlo radiative transfer simulation. The multi-epoch broadband spectral energy distribution (SED) exhibits clear evidence of changes to the inner (sub-AU) regions of the disk over a maximum timescale of 10 years with the additional constraint that the shadowing of the outer (>25 AU) disk is non-time-dependent. We find that changes to the inner dust rim (0.2 AU) cannot account for this behavior. Instead, we find that if the inner disk posses an optically thin body of small grains then changes to the outer edge of these structures may successfully reproduce the two states in the SED (analogous to what may be occurring due to accretion onto the central star or dynamical clearing by planets). Furthermore, we explore the density distributions of the outer disk structures as they are constrained by the SED and imaged surface brightness profiles, with the conclusion that a mid-plane density power law profile of r^{-2} and r^{-1} for the 35-70 AU and 70-250 AU regions, respectively, may reproduce the observations to the limit of our available complexity of structures within our modelling software. Finally, we find that a 0.3x density scaling of the 35-70 AU region reproduces the second gap imaged in the near-infrared and at 7 mm, strengthening the link to this structure being cleared by one or more planetary mass bodies.This work was supported by NASA ADAP grant NNX09AC73G, Hubble Space Telescope grant HST-GO-13032, the IR&D program at The Aerospace Corporation, and the University of Cincinnati Honors Program.

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago

NASA Astrophysics Data System (ADS)

Genzel, R.; Schreiber, N. M. Förster; Übler, H.; Lang, P.; Naab, T.; Bender, R.; Tacconi, L. J.; Wisnioski, E.; Wuyts, S.; Alexander, T.; Beifiori, A.; Belli, S.; Brammer, G.; Burkert, A.; Carollo, C. M.; Chan, J.; Davies, R.; Fossati, M.; Galametz, A.; Genel, S.; Gerhard, O.; Lutz, D.; Mendel, J. T.; Momcheva, I.; Nelson, E. J.; Renzini, A.; Saglia, R.; Sternberg, A.; Tacchella, S.; Tadaki, K.; Wilman, D.

2017-03-01

In the cold dark matter cosmology, the baryonic components of galaxies—stars and gas—are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius—a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

PubMed

Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

2017-03-15

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

Migration of Gas Giant Planets in a Gravitationally Unstable Disk

NASA Astrophysics Data System (ADS)

Desai, Karna Mahadev; Steiman-Cameron, Thomas Y.; Michael, Scott; Durisen, Richard H.

2017-01-01

Understanding the migration of giant planets in gravitationally unstable protoplanetary disks is important for understanding planetary system architecture, especially the existence of planets orbiting close to and at large distances from their stars. Migration rates can determine the efficiency of planet formation and survival rates of planets. We present results from simulations of 0.3, 1, and 3 Jupiter-mass planets in a 0.14 M⊙ protoplanetary disk around a 1 M⊙ star, where the disk is marginally unstable to gravitational instabilities (GIs). Each planet is simulated separately. We use CHYMERA, a radiative 3D hydrodynamics code developed by the Indiana University Hydrodynamics Group. The simulations include radiative cooling governed by realistic dust opacities. The planets are inserted into the disk, once the disk has settled into its quasi-steady GI-active phase. We simulate each of the 0.3, 1, and 3 Jupiter-mass planets by inserting it at three different locations in the disk, at the corotation radius and at the inner and outer Lindblad resonances. No matter where placed, the 3 Jupiter-mass planets tend to drift inexorably inward but with a rate that slows after many orbital periods. The 1 Jupiter-mass planets migrate mostly inward, but their motion can be delayed or reversed near the corotation of the two-armed wave. The 0.3 Jupiter-mass planets are much less predictable and frequently migrate outward. We analyze how the density of matter and waves in the disk at different azimuthal locations affect the migration.

Probing the Cold Dust Emission in the AB Aur Disk: A Dust Trap in a Decaying Vortex?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fuente, Asunción; Bachiller, Rafael; Baruteau, Clément

One serious challenge for planet formation is the rapid inward drift of pebble-sized dust particles in protoplanetary disks. Dust trapping at local maxima in the disk gas pressure has received much theoretical attention but still lacks observational support. The cold dust emission in the AB Aur disk forms an asymmetric ring at a radius of about 120 au, which is suggestive of dust trapping in a gas vortex. We present high spatial resolution (0.″58 × 0.″78 ≈ 80 × 110 au) NOEMA observations of the 1.12 mm and 2.22 mm dust continuum emission from the AB Aur disk. Significant azimuthalmore » variations of the flux ratio at both wavelengths indicate a size segregation of the large dust particles along the ring. Our continuum images also show that the intensity variations along the ring are smaller at 2.22 mm than at 1.12 mm, contrary to what dust trapping models with a gas vortex have predicted. Our two-fluid (gas+dust) hydrodynamical simulations demonstrate that this feature is well explained if the gas vortex has started to decay due to turbulent diffusion, and dust particles are thus losing the azimuthal trapping on different timescales depending on their size. The comparison between our observations and simulations allows us to constrain the size distribution and the total mass of solid particles in the ring, which we find to be of the order of 30 Earth masses, enough to form future rocky planets.« less

Lubricant distribution and its effect on slider air bearing performance over bit patterned media disk of disk drives

NASA Astrophysics Data System (ADS)

Wu, Lin

2011-04-01

The distribution dynamics of a thin lubricant film on a bit-patterned media disk and its effect on the performance of the ultralow flying air bearing slider of disk drives are studied by direct numerical simulations. Our analysis shows that the physics governing lubricant distribution dynamics changes when deep enough sub-100-nm nanostructures are patterned on the disk surface. Air shearing under the slider that dominates lubricant flow on a flat disk may become negligible on a bit-patterned media disk. Surface tension and disjoining pressure become dominant factors instead. Our results show that disks with nanoscale patterns/roughness may no longer be treated as flat, and the air bearing load may strongly depend not only on the geometric detail of disk patterns but also on how lubricants are distributed on the patterns when slider-disk clearance is reduced to sub-10-nm. Air bearing load and consequently the slider's flying attitude are affected by disk pattern geometry, average lubricant thickness, and material properties of lubricant such as the surface tension coefficient and Hamaker constant. The significantly expanded parameter space, upon which ultralow flying slider's dynamics depends, has to be seriously considered in evaluating the head/disk interface tribology performance of next generation patterned media magnetic recording systems.

C II forbidden-line 158 micron mapping in Sagittarius A Rotation curve and mass distribution in the galactic center

NASA Technical Reports Server (NTRS)

Lugten, J. B.; Genzel, R.; Crawford, M. K.; Townes, C. H.

1986-01-01

Based on data obtained with the NASA Kuiper Airborne Observatory 91.4 cm telescope, the 158-micron fine structure line emission of C(+) is mapped near the galactic center. The strongest emission comes from a 10-pc FWHM diameter disk centered on Sgr A West whose dominant motion is rotation. Extended C(+) emission is also found from the +50 km/s galactic center molecular cloud, and a second cloud at v(LSR) of about -35 km/s. The rotation curve and mass distribution within 10 pc of the galactic center are derived, and the C(+) profiles show a drop-off of rotation velocity between 2 and 10 pc. A mass model is suggested with 2-4 million solar masses in a central point mass, and a M/L ratio of the central stellar cluster of 0.5 solar masses/solar luminosities, suggesting a large abundance of giants and relatively recent star formation in the center.

An Accretion Model for the Growth of Black Hole in Quasars

NASA Technical Reports Server (NTRS)

Lu, Ye; Cheng, K. S.; Zhang, S. N.

2003-01-01

A possible accretion model associated with the ionization instability of quasar disks is proposed to address the growth of the central black hole harbored in the host galaxy. The evolution of quasars in cosmic time is assumed to change from a highly active state to a quiescent state triggered by the S-shaped ionization instability of the quasar accretion disk. For a given external mass transfer rate ionization instability can modify accretion rate in the disk and separates the accretion flows of the disk into three different phases like a S-shape. We suggest that the bright quasars observed today are those quasars with disks in the upper branch of S-shaped instability and the dormant quasars are the system in the lower branch. The disk is assumed to evolve as ADIOS configuration in the lower branch. The mass ratio between black hole and its host galactic bulge is a nature consequence of ADIOS. Our model also demonstrates that a seed black hole 2 x 10(exp 6) solar masses similar to those found in spiral galaxies today is needed to produce a black hole with a final mass 2 x 10(exp 8) solar masses.

Locating the Accretion Footprint on a Herbig Ae Star: MWC 480

NASA Technical Reports Server (NTRS)

Grady, C. A.; Hamaguchi, K.; Schneider, G.; Stecklum, B.; Woodgate, B. E.; McCleary, J. E.; Williger, G. M.; Sitko, M. L.; Menard, F.; Henning, Th.;

Three-dimensional modeling of radiative disks in binaries

NASA Astrophysics Data System (ADS)

Picogna, G.; Marzari, F.

2013-08-01

Context. Circumstellar disks in binaries are perturbed by the companion gravity causing significant alterations of the disk morphology. Spiral waves due to the companion tidal force also develop in the vertical direction and affect the disk temperature profile. These effects may significantly influence the process of planet formation. Aims: We perform 3D numerical simulations of disks in binaries with different initial dynamical configurations and physical parameters. Our goal is to investigate their evolution and their propensity to grow planets. Methods: We use an improved version of the SPH code VINE modified to better account for momentum and energy conservation via variable smoothing and softening length. The energy equation includes a flux-limited radiative transfer algorithm. The disk cooling is obtained with the use of "boundary particles" populating the outer surfaces of the disk and radiating to infinity. We model a system made of star/disk + star/disk where the secondary star (and relative disk) is less massive than the primary. Results: The numerical simulations performed for different values of binary separation and disk density show that trailing spiral shock waves develop when the stars approach their pericenter. Strong hydraulic jumps occur at the shock front, in particular for small separation binaries, creating breaking waves, and a consistent mass stream between the two disks. Both shock waves and mass transfer cause significant heating of the disk. At apocenter these perturbations are reduced and the disks are cooled down and less eccentric. Conclusions: The disk morphology is substantially affected by the companion perturbations, in particular in the vertical direction. The hydraulic jumps may slow down or even halt the dust coagulation process. The disk is significantly heated up by spiral waves and mass transfer, and the high gas temperature may prevent the ice condensation by moving the "snow line" outward. The disordered motion triggered by the spiral waves may, on the other hand, favor direct formation of large planetesimals from pebbles. The strength of the hydraulic jumps, disk heating, and mass exchange depends on the binary separation, and for larger semi-major axes, the tidal spiral pattern is substantially reduced. The environment then appears less hostile to planet formation.

NASA Langley Research Center's distributed mass storage system

NASA Technical Reports Server (NTRS)

Pao, Juliet Z.; Humes, D. Creig

1993-01-01

There is a trend in institutions with high performance computing and data management requirements to explore mass storage systems with peripherals directly attached to a high speed network. The Distributed Mass Storage System (DMSS) Project at NASA LaRC is building such a system and expects to put it into production use by the end of 1993. This paper presents the design of the DMSS, some experiences in its development and use, and a performance analysis of its capabilities. The special features of this system are: (1) workstation class file servers running UniTree software; (2) third party I/O; (3) HIPPI network; (4) HIPPI/IPI3 disk array systems; (5) Storage Technology Corporation (STK) ACS 4400 automatic cartridge system; (6) CRAY Research Incorporated (CRI) CRAY Y-MP and CRAY-2 clients; (7) file server redundancy provision; and (8) a transition mechanism from the existent mass storage system to the DMSS.

Accretion Disks and the Formation of Stellar Systems

NASA Astrophysics Data System (ADS)

Kratter, Kaitlin Michelle

2011-02-01

In this thesis, we examine the role of accretion disks in the formation of stellar systems, focusing on young massive disks which regulate the flow of material from the parent molecular core down to the star. We study the evolution of disks with high infall rates that develop strong gravitational instabilities. We begin in chapter 1 with a review of the observations and theory which underpin models for the earliest phases of star formation and provide a brief review of basic accretion disk physics, and the numerical methods that we employ. In chapter 2 we outline the current models of binary and multiple star formation, and review their successes and shortcomings from a theoretical and observational perspective. In chapter 3 we begin with a relatively simple analytic model for disks around young, high mass stars, showing that instability in these disks may be responsible for the higher multiplicity fraction of massive stars, and perhaps the upper mass to which they grow. We extend these models in chapter 4 to explore the properties of disks and the formation of binary companions across a broad range of stellar masses. In particular, we model the role of global and local mechanisms for angular momentum transport in regulating the relative masses of disks and stars. We follow the evolution of these disks throughout the main accretion phase of the system, and predict the trajectory of disks through parameter space. We follow up on the predictions made in our analytic models with a series of high resolution, global numerical experiments in chapter 5. Here we propose and test a new parameterization for describing rapidly accreting, gravitationally unstable disks. We find that disk properties and system multiplicity can be mapped out well in this parameter space. Finally, in chapter 6, we address whether our studies of unstable disks are relevant to recently detected massive planets on wide orbits around their central stars.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duffell, Paul C.; MacFadyen, Andrew I.; Farris, Brian D.

Most standard descriptions of Type II migration state that massive, gap-opening planets must migrate at the viscous drift rate. This is based on the idea that the disk is separated into an inner and outer region and gas is considered unable to cross the gap. In fact, gas easily crosses the gap on horseshoe orbits, nullifying this necessary premise which would set the migration rate. In this work, it is demonstrated using highly accurate numerical calculations that the actual migration rate is dependent on disk and planet parameters, and can be significantly larger or smaller than the viscous drift rate. Inmore » the limiting case of a disk much more massive than the secondary, the migration rate saturates to a constant that is sensitive to disk parameters and is not necessarily of the order of the viscous rate. In the opposite limit of a low-mass disk, the migration rate decreases linearly with disk mass. Steady-state solutions in the low disk mass limit show no pile-up outside the secondary's orbit, and no corresponding drainage of the inner disk.« less

How robust are our views of Milky Way stellar populations before Gaia?

NASA Astrophysics Data System (ADS)

Haywood, M.

2014-07-01

One year before the first release of the first data from Gaia, how robust are our views of the Milky Way stellar populations? Recent results have shown that limits, differences and/or continuities between populations are not where we thought they were just a few years ago. The outer disk (> 10kpc) has properties essentially different from the inner (thin+thick) disk, while the bulge is best explained in terms of disk populations, with a negligible or inexistent classical bulge, suggesting that the Milky Way is a pure disk galaxy. Much less contingent than previously envisaged, the thick disk is probably the main phase of stellar mass creation in the MW, and the parent population of the thin disk. These results lead to fundamental changes in our views on the stellar mass growth of the Galaxy, secular mass redistribution in the disk, and imply a change of paradigm of the chemical evolution. I review these different advances, and discuss some of the key questions.

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks. III. Simulations with Radiative Cooling and Realistic Opacities

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Mejía, Annie C.; Durisen, Richard H.; Cai, Kai; Pickett, Megan K.; D'Alessio, Paola

2006-11-01

This paper presents a fully three-dimensional radiative hydrodymanics simulation with realistic opacities for a gravitationally unstable 0.07 Msolar disk around a 0.5 Msolar star. We address the following aspects of disk evolution: the strength of gravitational instabilities under realistic cooling, mass transport in the disk that arises from GIs, comparisons between the gravitational and Reynolds stresses measured in the disk and those expected in an α-disk, and comparisons between the SED derived for the disk and SEDs derived from observationally determined parameters. The mass transport in this disk is dominated by global modes, and the cooling times are too long to permit fragmentation for all radii. Moreover, our results suggest a plausible explanation for the FU Ori outburst phenomenon.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carrasco-González, Carlos; Rodríguez, Luis F.; Galván-Madrid, Roberto

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau, these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk–planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surfacemore » density profiles and grain-size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength, the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of (1–3) × 10{sup −3} M {sub ⊙}, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.« less

Featured Image: H I Gas in the Triangulum Galaxy

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-08-01

These spectacular images are of M33, otherwise known as the Triangulum Galaxy a spiral galaxy roughly 3 million light-years away. The views on the left and in the center are different Wide-field Infrared Survey Explorer (WISE) filters, and the view on the right is a full-resolution look at the H I gas distribution in M33s inner disk, made with data from the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope and Arecibo. In a new study, a team of authors led by Zacharie Sie Kam (University of Ouagadougou, Burkina Faso; University of Montreal, Canada) uses the H I gas observations to explore how the mass is distributed throughout M33 and how the gas moves as the galaxys disk rotates. To read more about what they learned, check out the paper below.CitationS. Z. Kam et al 2017 AJ 154 41. doi:10.3847/1538-3881/aa79f3

The galaxy NGC 1566 - Distribution and kinematics of the ionized gas

NASA Astrophysics Data System (ADS)

Comte, G.; Duquennoy, A.

1982-10-01

H-alpha narrowband observations are the basis of a study of ionized hydrogen in the large spiral galaxy NGC 1566 which has yielded a catalog of 418 H II regions covering the main body of the galaxy, supplemented by 59 positions and estimated H-alpha luminosities for regions located in the pseudo-outer ring where no H-alpha plate is available. A discussion of luminosity function, diameter distribution and spiral structure notes evidence for a double two-armed spiral pattern. The plane of the galaxy appears warped, and the efficiency of the two different spiral patterns in star formation is different. A preliminary radial velocity field is determined from three interferograms in H-alpha light, and is found to be acceptably fitted by a simple bulge-plus-disk dynamical model in which the apparent disk mass-to-light ratio sharply increases from center to edge.

Marangoni convection in Casson liquid flow due to an infinite disk with exponential space dependent heat source and cross-diffusion effects

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.; Shashikumar, N. S.; Hayat, T.; Alsaedi, A.

2018-06-01

Present work aims to investigate the features of the exponential space dependent heat source (ESHS) and cross-diffusion effects in Marangoni convective heat mass transfer flow due to an infinite disk. Flow analysis is comprised with magnetohydrodynamics (MHD). The effects of Joule heating, viscous dissipation and solar radiation are also utilized. The thermal and solute field on the disk surface varies in a quadratic manner. The ordinary differential equations have been obtained by utilizing Von Kármán transformations. The resulting problem under consideration is solved numerically via Runge-Kutta-Fehlberg based shooting scheme. The effects of involved pertinent flow parameters are explored by graphical illustrations. Results point out that the ESHS effect dominates thermal dependent heat source effect on thermal boundary layer growth. The concentration and temperature distributions and their associated layer thicknesses are enhanced by Marangoni effect.

Hydrodynamic Studies of Turbulent AGN Tori

NASA Astrophysics Data System (ADS)

Schartmann, M.; Meisenheimer, K.; Klahr, H.; Camenzind, M.; Wolf, S.; Henning, Th.; Burkert, A.; Krause, M.

Recently, the MID-infrared Interferometric instrument (MIDI) at the VLTI has shown that dust tori in the two nearby Seyfert galaxies NGC 1068 and the Circinus galaxy are geometrically thick and can be well described by a thin, warm central disk, surrounded by a colder and fluffy torus component. By carrying out hydrodynamical simulations with the help of the TRAMP code (Klahr et al. 1999), we follow the evolution of a young nuclear star cluster in terms of discrete mass-loss and energy injection from stellar processes. This naturally leads to a filamentary large scale torus component, where cold gas is able to flow radially inwards. The filaments join into a dense and very turbulent disk structure. In a post-processing step, we calculate spectral energy distributions and images with the 3D radiative transfer code MC3D Wolf (2003) and compare them to observations. Turbulence in the dense disk component is investigated in a separate project.

Investigation of the new cataclysmic variable 1RXS J180834.7+101041

NASA Astrophysics Data System (ADS)

Yakin, D. G.; Suleimanov, V. F.; Borisov, N. V.; Shimanskii, V. V.; Bikmaev, I. F.

2011-12-01

We present the results of our photometric and spectroscopic studies of the new eclipsing cataclysmic variable star 1RXS J180834.7+101041. Its spectrum exhibits double-peaked hydrogen and helium emission lines. The Doppler maps constructed from hydrogen lines show a nonuniform distribution of emission in the disk similar to that observed in IP Peg. This suggests that the object can be a cataclysmic variable with tidal density waves in the disk. We have determined the component masses ( M WD = 0.8 ± 0.22 M ⊙ and M RD = 0.14 ± 0.02 M ⊙) and the binary inclination ( i = 78° ± 1.5°) based on well-known relations between parameters for cataclysmic variable stars. We have modeled the binary light curves and showed that the model of a disk with two spots is capable of explaining the main observed features of the light curves.

DEAD, UNDEAD, AND ZOMBIE ZONES IN PROTOSTELLAR DISKS AS A FUNCTION OF STELLAR MASS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhanjoy; Ercolano, Barbara; Turner, Neal J., E-mail: s.mohanty@imperial.ac.uk, E-mail: ercolano@usm.lmu.de, E-mail: neal.turner@jpl.nasa.gov

We investigate the viability of the magnetorotational instability (MRI) in X-ray ionized viscous accretion disks around both solar-type stars and very low mass stars. In particular, we determine the disk regions where the MRI can be shut off either by Ohmic resistivity (the so-called dead and undead zones) or by ambipolar diffusion (a region we term the zombie zone). We consider two stellar masses: M {sub *} = 0.7 M {sub Sun} and 0.1 M {sub Sun }. In each case, we assume that: the disk surface density profile is that of a scaled Minimum Mass Solar Nebula, with Mmore » {sub disk}/M {sub *} = 0.01 as suggested by current data; disk ionization is driven primarily by stellar X-rays, complemented by cosmic rays and radionuclides; and the stellar X-ray luminosity scales with bolometric luminosity as L{sub X} /L {sub *} Almost-Equal-To 10{sup -3.5}, as observed. Ionization rates are calculated with the MOCCASIN Monte Carlo X-ray transport code, and ionization balance determined using a simplified chemical network, including well-mixed 0.1 {mu}m grains at various levels of depletion. We find that (1) ambipolar diffusion is the primary factor controlling MRI activity in disks around both solar-type and very low mass classical T Tauri stars. Assuming that the MRI yields the maximum possible field strength at each radius, we further find that: (2) the MRI-active layer constitutes only {approx}5%-10% of the total disk mass; (3) the accretion rate ( M-dot ) varies radially in both magnitude and sign (inward or outward), implying time-variable accretion as well as the creation of disk gaps and overdensities, with consequences for planet formation and migration; (4) achieving the empirical accretion rates in solar-type and very low mass stars requires a depletion of well-mixed small grains (via grain growth and/or settling) by a factor of 10-1000 relative to the standard dust-to-gas mass ratio of 10{sup -2}; and (5) the current non-detection of polarized emission from field-aligned grains in the outer disk regions is consistent with active MRI at those radii.« less

Possible Rapid Gas Giant Planet Formation in the Solar Nebula and Other Protoplanetary Disks.

PubMed

Boss

2000-06-20

Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary disk like the solar nebula. Disk instability, on the other hand, can form a gas giant protoplanet in a few hundred years. However, disk instability has previously been thought to be important only in relatively massive disks. New three-dimensional, "locally isothermal," hydrodynamical models without velocity damping show that a disk instability can form Jupiter-mass clumps, even in a disk with a mass (0.091 M middle dot in circle within 20 AU) low enough to be in the range inferred for the solar nebula. The clumps form with initially eccentric orbits, and their survival will depend on their ability to contract to higher densities before they can be tidally disrupted at successive periastrons. Because the disk mass in these models is comparable to that apparently required for the core accretion mechanism to operate, the models imply that disk instability could obviate the core accretion mechanism in the solar nebula and elsewhere.

Parameterizing the dust around Herbig Ae/Be stars: Multiwavelength imaging radiative transfer modeling, and near-infrared instrumentation

NASA Astrophysics Data System (ADS)

Doering, Ryan Lee

Herbig Ae/Be stars are considered the intermediate-mass analogs of the low-mass pre-main sequence T Tauri stars. Observations reveal that they are surrounded by dusty matter that may provide the solid-state material for building planets. Determining the dust parameters provides constraints for planet formation theory, and yields information about the matter around intermediate-mass stars as they approach the main sequence. In this dissertation, I present the results of a multiwavelength imaging and radiative transfer modeling study of Herbig Ae/Be stars, and a near-infrared instrumentation project, with the aim of parameterizing the dust in these systems. The Hubble Space Telescope was used to search for optical light scattered by dust in a sample of young stars. This survey provided the first scattered-light image of the circumstellar environment around the Herbig Ae/Be star HD 97048. Structure is observed in the dust distribution similar to that seen in other Herbig Ae/Be systems. A ground-based near-infrared imaging study of Herbig Ae/ Be candidates was also carried out. Photometry was collected for spectral energy distribution construction, and binary candidates were resolved. A mid- infrared image of the low-mass debris system, AU Microscopii, is presented, being relevant to the study of Herbig Ae/Be stars. Detailed dust modeling of HD 97048 and HD 100546 was carried out with a two- component geometry consisting of a flared disk and an extended envelope. The models achieve a reasonable global fit to the spectral energy distributions, and produce images with the desired geometry. The disk midplane densities are found to go as r -0.5 and r -1.8 , giving disk dust masses of 3.0 × 10^-4 and 5.9 × 10 ^5 [Special characters omitted.] for HD 97048 and HD 100546, respectively. A gas-to-dust mass ratio lower limit of 3.2 was calculated for HD 97048. In order to advance the imaging capabilities available for observations of Herbig Ae/Be stars, I have participated in the development of the WIYN High Resolution Infrared Camera. The instrument operates in the near-infrared (~0.8 - 2.5 mm), includes 13 filters, and has a pixel size of ~0.1 inches, resulting in a field of view of ~3' × 3'. An angular resolution of ~0.25 inches is anticipated. I provide an overview of the instrument, and report performance results with an emphasis on detector characterization.

[Expression and distribution of xenoantigen alpha-Gal in intervertebral disk of Chinese banna minipig inbred line].

PubMed

Shou, Jian-guo; Mi, Jian-hong; Ying, Da-jun

2002-09-01

To investigate the expression and distribution of xenoantigen in intervertebral disk of Chinese banna minipig inbred line, and to study the availability of xenograft transplantation of intervertebral disk. Samples of intervertebral disk were collected from six Banna pigs of 8 to 11-month-old. The fixation, embedment and slice were performed. alpha-Gal specific binding lection (BSI-B4) were used as affinity reagents and affinity-immunohistochemistry assays (SABC methods and DAB stain) were conducted to detect the expression and distribution of xenoantigen (alpha-Gal). alpha-Gal was found in chondrocyte cell and chondrocyte-like cell in intervertebral disk which have the positive yellow-stained particulate aggradation. There was no stain in the matrix, elastic fiber and collagen fiber. The distribution of xenoantigen is locally in the tissue of intervertebral disk and its expression is weak. This suggests that the intervertebral disk of Banna pig may be alternative donor for xenotransplantation.

High-Contrast Near-Infrared Imaging Polarimetry of the Protoplanetary Disk around RY Tau

NASA Technical Reports Server (NTRS)

Takami, Michihiro; Karr, Jennifer L.; Hashimoto, Jun; Kim, Hyosun; Wisenewski, John; Henning, Thomas; Grady, Carol; Kandori, Ryo; Hodapp, Klaus W.; Kudo, Tomoyuki;

Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni

NASA Astrophysics Data System (ADS)

Muñoz-Darias, T.; Casares, J.; Mata Sánchez, D.; Fender, R. P.; Armas Padilla, M.; Linares, M.; Ponti, G.; Charles, P. A.; Mooley, K. P.; Rodriguez, J.

2016-06-01

Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black-hole transients have outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole V404 Cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk. Here we report observations of a sustained outer accretion disk wind in V404 Cyg, which is unlike any seen hitherto. We find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. The large expelled mass (>10-8 solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. The luminous, but brief, accretion phases shown by transients with large accretion disks imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes.

Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni.

PubMed

Muñoz-Darias, T; Casares, J; Mata Sánchez, D; Fender, R P; Armas Padilla, M; Linares, M; Ponti, G; Charles, P A; Mooley, K P; Rodriguez, J

2016-06-02

Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black-hole transients have outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole V404 Cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk. Here we report observations of a sustained outer accretion disk wind in V404 Cyg, which is unlike any seen hitherto. We find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. The large expelled mass (>10(-8) solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. The luminous, but brief, accretion phases shown by transients with large accretion disks imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes.

Bulge Growth and Quenching since z = 2.5 in CANDELS/3D-HST

NASA Astrophysics Data System (ADS)

Lang, Philipp; Wuyts, Stijn; Somerville, Rachel S.; Förster Schreiber, Natascha M.; Genzel, Reinhard; Bell, Eric F.; Brammer, Gabe; Dekel, Avishai; Faber, Sandra M.; Ferguson, Henry C.; Grogin, Norman A.; Kocevski, Dale D.; Koekemoer, Anton M.; Lutz, Dieter; McGrath, Elizabeth J.; Momcheva, Ivelina; Nelson, Erica J.; Primack, Joel R.; Rosario, David J.; Skelton, Rosalind E.; Tacconi, Linda J.; van Dokkum, Pieter G.; Whitaker, Katherine E.

2014-06-01

Exploiting the deep high-resolution imaging of all five CANDELS fields, and accurate redshift information provided by 3D-HST, we investigate the relation between structure and stellar populations for a mass-selected sample of 6764 galaxies above 1010 M ⊙, spanning the redshift range 0.5 < z < 2.5. For the first time, we fit two-dimensional models comprising a single Sérsic fit and two-component (i.e., bulge + disk) decompositions not only to the H-band light distributions, but also to the stellar mass maps reconstructed from resolved stellar population modeling. We confirm that the increased bulge prominence among quiescent galaxies, as reported previously based on rest-optical observations, remains in place when considering the distributions of stellar mass. Moreover, we observe an increase of the typical Sérsic index and bulge-to-total ratio (with median B/T reaching 40%-50%) among star-forming galaxies above 1011 M ⊙. Given that quenching for these most massive systems is likely to be imminent, our findings suggest that significant bulge growth precedes a departure from the star-forming main sequence. We demonstrate that the bulge mass (and ideally knowledge of the bulge and total mass) is a more reliable predictor of the star-forming versus quiescent state of a galaxy than the total stellar mass. The same trends are predicted by the state-of-the-art, semi-analytic model by Somerville et al. In this model, bulges and black holes grow hand in hand through merging and/or disk instabilities, and feedback from active galactic nuclei shuts off star formation. Further observations will be required to pin down star formation quenching mechanisms, but our results imply that they must be internal to the galaxies and closely associated with bulge growth.

Long-lived Dust Asymmetries at Dead Zone Edges in Protoplanetary Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miranda, Ryan; Li, Hui; Li, Shengtai

A number of transition disks exhibit significant azimuthal asymmetries in thermal dust emission. One possible origin for these asymmetries is dust trapping in vortices formed at the edges of dead zones. We carry out high-resolution, two-dimensional hydrodynamic simulations of this scenario, including the effects of dust feedback. We find that, although feedback weakens the vortices and slows down the process of dust accumulation, the dust distribution in the disk can nonetheless remain asymmetric for many thousands of orbits. We show that even after 10{sup 4} orbits, or 2.5 Myr when scaled to the parameters of Oph IRS 48 (a significantmore » fraction of its age), the dust is not dispersed into an axisymmetric ring, in contrast to the case of a vortex formed by a planet. This is because accumulation of mass at the dead zone edge constantly replenishes the vortex, preventing it from being fully destroyed. We produce synthetic dust emission images using our simulation results. We find that multiple small clumps of dust may be distributed azimuthally. These clumps, if not resolved from one another, appear as a single large feature. A defining characteristic of a disk with a dead zone edge is that an asymmetric feature is accompanied by a ring of dust located about twice as far from the central star.« less

Rotationally-supported disks around Class I sources in Taurus: disk formation constraints

NASA Astrophysics Data System (ADS)

Harsono, D.; Jørgensen, J. K.; van Dishoeck, E. F.; Hogerheijde, M. R.; Bruderer, S.; Persson, M. V.; Mottram, J. C.

2014-02-01

Context. Disks are observed around pre-main sequence stars, but how and when they form is still heavily debated. While disks around young stellar objects have been identified through thermal dust emission, spatially and spectrally resolved molecular line observations are needed to determine their nature. Only a handful of embedded rotationally supported disks have been identified to date. Aims: We identify and characterize rotationally supported disks near the end of the main accretion phase of low-mass protostars by comparing their gas and dust structures. Methods: Subarcsecond observations of dust and gas toward four Class I low-mass young stellar objects in Taurus are presented at significantly higher sensitivity than previous studies. The 13CO and C18O J = 2-1 transitions at 220 GHz were observed with the Plateau de Bure Interferometer at a spatial resolution of ≤0.8″ (56 AU radius at 140 pc) and analyzed using uv-space position velocity diagrams to determine the nature of their observed velocity gradient. Results: Rotationally supported disks (RSDs) are detected around 3 of the 4 Class I sources studied. The derived masses identify them as Stage I objects; i.e., their stellar mass is higher than their envelope and disk masses. The outer radii of the Keplerian disks toward our sample of Class I sources are ≤100 AU. The lack of on-source C18O emission for TMR1 puts an upper limit of 50 AU on its size. Flattened structures at radii >100 AU around these sources are dominated by infalling motion (υ ∝ r-1). A large-scale envelope model is required to estimate the basic parameters of the flattened structure from spatially resolved continuum data. Similarities and differences between the gas and dust disk are discussed. Combined with literature data, the sizes of the RSDs around Class I objects are best described with evolutionary models with an initial rotation of Ω = 10-14 Hz and slow sound speeds. Based on the comparison of gas and dust disk masses, little CO is frozen out within 100 AU in these disks. Conclusions: Rotationally supported disks with radii up to 100 AU are present around Class I embedded objects. Larger surveys of both Class 0 and I objects are needed to determine whether most disks form late or early in the embedded phase. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNBRS (France), MPG (Germany) and IGN (Spain).Appendices are available in electronic form at http://www.aanda.org

BREAKS IN THIN AND THICK DISKS OF EDGE-ON GALAXIES IMAGED IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comeron, Sebastien; Salo, Heikki; Laurikainen, Eija

2012-11-10

Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms-one of dynamical origin affecting both disks simultaneously andmore » another one only affecting the thin disk-or a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artifact caused by the superposition of a thin disk and a thick disk, with the latter having a longer scale length. We estimate the real thin disk antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disk mass is roughly constant (0.2 < M{sub T} /M{sub t} < 0.7) for circular velocities v{sub c} > 120 km s{sup -1}, but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin disks to be younger and less massive than in higher-mass galaxies.« less

Stellar mass distribution of S4G disk galaxies and signatures of bar-induced secular evolution

NASA Astrophysics Data System (ADS)

Díaz-García, S.; Salo, H.; Laurikainen, E.

2016-12-01

Context. Models of galaxy formation in a cosmological framework need to be tested against observational constraints, such as the average stellar density profiles (and their dispersion) as a function of fundamental galaxy properties (e.g. the total stellar mass). Simulation models predict that the torques produced by stellar bars efficiently redistribute the stellar and gaseous material inside the disk, pushing it outwards or inwards depending on whether it is beyond or inside the bar corotation resonance radius. Bars themselves are expected to evolve, getting longer and narrower as they trap particles from the disk and slow down their rotation speed. Aims: We use 3.6 μm photometry from the Spitzer Survey of Stellar Structure in Galaxies (S4G) to trace the stellar distribution in nearby disk galaxies (z ≈ 0) with total stellar masses 108.5 ≲ M∗/M⊙ ≲ 1011 and mid-IR Hubble types - 3 ≤ T ≤ 10. We characterize the stellar density profiles (Σ∗), the stellar contribution to the rotation curves (V3.6 μm), and the m = 2 Fourier amplitudes (A2) as a function of M∗ and T. We also describe the typical shapes and strengths of stellar bars in the S4G sample and link their properties to the total stellar mass and morphology of their host galaxy. Methods: For 1154 S4G galaxies with disk inclinations lower than 65°, we perform a Fourier decomposition and rescale their images to a common frame determined by the size in physical units, by their disk scalelength, and for 748 barred galaxies by both the length and orientation of their bars. We stack the resized density profiles and images to obtain statistically representative average stellar disks and bars in bins of M∗ and T. Based on the radial force profiles of individual galaxies we calculate the mean stellar contribution to the circular velocity. We also calculate average A2 profiles, where the radius is normalized to R25.5. Furthermore, we infer the gravitational potentials from the synthetic bars to obtain the tangential-to-radial force ratio (QT) and A2 profiles in the different bins. We also apply ellipse fitting to quantitatively characterize the shape of the bar stacks. Results: For M∗ ≥ 109M⊙, we find a significant difference in the stellar density profiles of barred and non-barred systems: (I) disks in barred galaxies show larger scalelengths (hR) and fainter extrapolated central surface brightnesses (Σ°); (II) the mean surface brightness profiles (Σ∗) of barred and non-barred galaxies intersect each other slightly beyond the mean bar length, most likely at the bar corotation; and (III) the central mass concentration of barred galaxies is higher (by almost a factor 2 when T ≤ 5) than in their non-barred counterparts. The averaged Σ∗ profiles follow an exponential slope down to at least 10 M⊙ pc-2, which is the typical depth beyond which the sample coverage in the radial direction starts to drop. Central mass concentrations in massive systems (≥1010M⊙) are substantially larger than in fainter galaxies, and their prominence scales with T. This segregation also manifests in the inner slope of the mean stellar component of the circular velocity: lenticular (S0) galaxies present the most sharply rising V3.6 μm. Based on the analysis of bar stacks, we show that early- and intermediate-type spirals (0 ≤ T< 5) have intrinsically narrower bars than later types and S0s, whose bars are oval-shaped. We show a clear agreement between galaxy family and quantitative estimates of bar strength. In early- and intermediate-type spirals, A2 is larger within and beyond the typical bar region among barred galaxies than in the non-barred subsample. Strongly barred systems also tend to have larger A2 amplitudes at all radii than their weakly barred counterparts. Conclusions: Using near-IR wavelengths (S4G 3.6 μm), we provide observational constraints that galaxy formation models can be checked against. In particular, we calculate the mean stellar density profiles, and the disk(+bulge) component of the rotation curve (and their dispersion) in bins of M∗ and T. We find evidence for bar-induced secular evolution of disk galaxies in terms of disk spreading and enhanced central mass concentration. We also obtain average bars (2D), and we show that bars hosted by early-type galaxies are more centrally concentrated and have larger density amplitudes than their late-type counterparts. The FITS files of the synthetic images and the tabulated radial profiles of the mean (and dispersion of) stellar mass density, 3.6 μm surface brightness, Fourier amplitudes, gravitational force, and the stellar contribution to the circular velocity are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/596/A84

Making the cold Kuiper belt in a planetary instability migration model

NASA Astrophysics Data System (ADS)

Gomes, Rodney S.

2017-06-01

Numerical integrations of the equations of motion of Jupiter, Saturn, three ice cores and a disk of planetesimals are undertaken. Two of the ice planets stand for Uranus and Neptune and a third one is expected to be ejected from the solar system. The planets start in compact cold orbits and each one is in mean motion resonance with its neighbor(s). The disk of planetesimals is placed just outside the outermost planet and is extended to 45 au. Five hundred integrations are done for each of four masses assigned to the disk, which are 25, 30, 35 and 40 Earth masses. The integrations are extended to 100 My. After that, I choose the successful runs in which there are four planets left in closed orbits around the Sun and I separate the good runs among the successful ones, defined by semi-major axes ranges around and not too far from the real ones. Among these good runs, I further choose by visual inspection those that yield an orbital distribution of planetesimals at the Kuiper belt region that resembles the real cold Kuiper belt. I extend these runs to 1 Gy and, after that, to 4.5 Gy. These last integrations for 3.5 Gy are done after replacing the orbits of the planets in the end of the 1 Gy integrations by their current orbits, changing the semi-major axes of the planetesimals so as to keep the same mean motion ratio with Neptune and assigning null masses for the planetesimals. Orbital distributions of the cold Kuiper belt obtained in some of the runs at 4.5 Gy are quite similar to that of the real cold Kuiper belt. The mass in the Kuiper belt region can be dynamically eroded to up to 90% of the original mass. The main conclusion is that the cold Kuiper belt is compatible with a past planetary instability phase even though in some of these runs Neptune's semi-major axis and eccentricity attained values simultaneously larger than 20 au and 0.2 for over 1 My.

Circumstellar Disks and Outflows in Turbulent Molecular Cloud Cores: Possible Formation Mechanism for Misaligned Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumoto, Tomoaki; Machida, Masahiro N.; Inutsuka, Shu-ichiro, E-mail: matsu@hosei.ac.jp

2017-04-10

We investigate the formation of circumstellar disks and outflows subsequent to the collapse of molecular cloud cores with the magnetic field and turbulence. Numerical simulations are performed by using an adaptive mesh refinement to follow the evolution up to ∼1000 years after the formation of a protostar. In the simulations, circumstellar disks are formed around the protostars; those in magnetized models are considerably smaller than those in nonmagnetized models, but their size increases with time. The models with stronger magnetic fields tend to produce smaller disks. During evolution in the magnetized models, the mass ratios of a disk to amore » protostar is approximately constant at ∼1%–10%. The circumstellar disks are aligned according to their angular momentum, and the outflows accelerate along the magnetic field on the 10–100 au scale; this produces a disk that is misaligned with the outflow. The outflows are classified into two types: a magnetocentrifugal wind and a spiral flow. In the latter, because of the geometry, the axis of rotation is misaligned with the magnetic field. The magnetic field has an internal structure in the cloud cores, which also causes misalignment between the outflows and the magnetic field on the scale of the cloud core. The distribution of the angular momentum vectors in a core also has a non-monotonic internal structure. This should create a time-dependent accretion of angular momenta onto the circumstellar disk. Therefore, the circumstellar disks are expected to change their orientation as well as their sizes in the long-term evolutions.« less

Studies of Circumstellar Disk Evolution

NASA Technical Reports Server (NTRS)

Hartmann, Lee W.

2004-01-01

Spitzer Space Telescope infrared data for our program on disk evolution has been taken (the main IRAC - 3-8 micron exposures; the 24 and 70 micron MIPS data are to come later). We now have deep maps in the four IRAC bands of the 3-Myr-old cluster Trumpler 37, and the 10-Myr-old cluster NGC 7160. Analysis of these data has now begun. We will be combining these data with our ground-based photometric and spectroscopic data to obtain a complete picture of disk frequency as a function of mass through this important age range, which spans the likely epoch of (giant) planet formation in most systems. Analysis of the SIRTF data, and follow-on ground-based spectroscopy on the converted MMT telescope using the wide-field, fiber-fed, multiobject spectrographs, Hectospec and Hectochelle, will be the major activity during the next year.Work was also performed on the following: protoplanetary disk mass accretion rates in very low-mass stars; the inner edge of T Tauri disks; accretion in intermediate-mass T Tauri stars (IMPS); and the near-infrared spectra of the rapidly-accreting protostellar disks FU Ori and V1057 Cyg.

Planet-driven Spiral Arms in Protoplanetary Disks. II. Implications

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Zhu, Zhaohuan

2018-06-01

We examine whether various characteristics of planet-driven spiral arms can be used to constrain the masses of unseen planets and their positions within their disks. By carrying out two-dimensional hydrodynamic simulations varying planet mass and disk gas temperature, we find that a larger number of spiral arms form with a smaller planet mass and a lower disk temperature. A planet excites two or more spiral arms interior to its orbit for a range of disk temperatures characterized by the disk aspect ratio 0.04≤slant {(h/r)}p≤slant 0.15, whereas exterior to a planet’s orbit multiple spiral arms can form only in cold disks with {(h/r)}p≲ 0.06. Constraining the planet mass with the pitch angle of spiral arms requires accurate disk temperature measurements that might be challenging even with ALMA. However, the property that the pitch angle of planet-driven spiral arms decreases away from the planet can be a powerful diagnostic to determine whether the planet is located interior or exterior to the observed spirals. The arm-to-arm separations increase as a function of planet mass, consistent with previous studies; however, the exact slope depends on disk temperature as well as the radial location where the arm-to-arm separations are measured. We apply these diagnostics to the spiral arms seen in MWC 758 and Elias 2–27. As shown in Bae et al., planet-driven spiral arms can create concentric rings and gaps, which can produce a more dominant observable signature than spiral arms under certain circumstances. We discuss the observability of planet-driven spiral arms versus rings and gaps.

EFFECT OF ENVIRONMENT ON GALAXIES' MASS-SIZE DISTRIBUTION: UNVEILING THE TRANSITION FROM OUTSIDE-IN TO INSIDE-OUT EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cappellari, Michele

2013-11-20

The distribution of galaxies on the mass-size plane as a function of redshift or environment is a powerful test for galaxy formation models. Here we use integral-field stellar kinematics to interpret the variation of the mass-size distribution in two galaxy samples spanning extreme environmental densities. The samples are both identically and nearly mass-selected (stellar mass M {sub *} ≳ 6 × 10{sup 9} M {sub ☉}) and volume-limited. The first consists of nearby field galaxies from the ATLAS{sup 3D} parent sample. The second consists of galaxies in the Coma Cluster (Abell 1656), one of the densest environments for which good, resolvedmore » spectroscopy can be obtained. The mass-size distribution in the dense environment differs from the field one in two ways: (1) spiral galaxies are replaced by bulge-dominated disk-like fast-rotator early-type galaxies (ETGs), which follow the same mass-size relation and have the same mass distribution as in the field sample; (2) the slow-rotator ETGs are segregated in mass from the fast rotators, with their size increasing proportionally to their mass. A transition between the two processes appears around the stellar mass M {sub crit} ≈ 2 × 10{sup 11} M {sub ☉}. We interpret this as evidence for bulge growth (outside-in evolution) and bulge-related environmental quenching dominating at low masses, with little influence from merging. In contrast, significant dry mergers (inside-out evolution) and halo-related quenching drives the mass and size growth at the high-mass end. The existence of these two processes naturally explains the diverse size evolution of galaxies of different masses and the separability of mass and environmental quenching.« less

POWERFUL RADIO EMISSION FROM LOW-MASS SUPERMASSIVE BLACK HOLES FAVORS DISK-LIKE BULGES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, J.; Xu, Y.; Xu, D. W.

The origin of spin of low-mass supermassive black holes (SMBHs) is still a puzzle at present. We report here a study on the host galaxies of a sample of radio-selected nearby ( z < 0.05) Seyfert 2 galaxies with a BH mass of 10{sup 6–7} M{sub ⊙}. By modeling the SDSS r -band images of these galaxies through a two-dimensional bulge+disk decomposition, we identify a new dependence of SMBH's radio power on host bulge surface brightness profiles, in which more powerful radio emission comes from an SMBH associated with a more disk-like bulge. This result means low-mass and high-mass SMBHsmore » are spun up by two entirely different modes that correspond to two different evolutionary paths. A low-mass SMBH is spun up by a gas accretion with significant disk-like rotational dynamics of the host galaxy in the secular evolution, while a high-mass one by a BH–BH merger in the merger evolution.« less

The Andromeda Optical and Infrared Disk Survey

NASA Astrophysics Data System (ADS)

Sick, Jonathan

The spectral energy distributions of galaxies inform us about a galaxy's stellar populations and interstellar medium, revealing stories of galaxy formation and evolution. How we interpret this light depends in part on our proximity to the galaxy. For nearby galaxies, detailed star formation histories can be extracted from the resolved stellar populations, while more distant galaxies feature the contributions of entire stellar populations within their integrated spectral energy distribution (SED). This thesis aims to resolve whether the techniques used to investigate stellar populations in distant galaxies are consistent with those available for nearby galaxies. As the nearest spiral galaxy, the Andromeda Galaxy (M31) is the ideal testbed for the joint study of resolved stellar populations and panchromatic SEDs. We present the Andromeda Optical and Infrared Disk Survey (ANDROIDS), which adds new near-UV to near-IR (u*g'r'i'JKs) imaging using the MegaCam and WIRCam cameras at the Canada-France-Hawaii telescope to the available M31 panchromatic dataset. To accurately subtract photometric background from our extremely wide-field (14 square degree) mosaics, we present observing and data reduction techniques with sky-target nodding, optimization of image-to-image surface brightness, and a novel hierarchical Bayesian model to trace the background signal while modelling the astrophysical SED. We model the spectral energy distributions of M31 pixels with MAGPHYS (da Cunha et al. 2008) and compare those results to resolved stellar population models of the same pixels from the Panchromatic Hubble Andromeda Treasury (PHAT) survey (Williams et al. 2017). We find substantial (0.3 dex) differences in stellar mass estimates despite a common use of the Chabrier (2003) initial mass function. Stellar mass estimated from the resolved stellar population is larger than any mass estimate from SED models or colour-M/L relations (CMLRs). There is also considerable diversity among CMLR estimators, largely driven by differences in the star formation history prior distribution. We find broad consistency between the star formation history estimated by integrated spectral energy distributions and resolved stars. Generally, spectral energy distribution models yield a stronger inside-out radial metallicity gradient and bias towards younger mean ages than resolved stellar population models.

How to Detect Inclined Water Maser Disks (and Possibly Measure Black Hole Masses)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Darling, Jeremy, E-mail: jdarling@colorado.edu

We describe a method for identifying inclined water maser disks orbiting massive black holes and for potentially using them to measure black hole masses. Owing to the geometry of maser amplification pathways, the minority of water maser disks are observable: only those viewed nearly edge-on have been identified, suggesting that an order of magnitude additional maser disks exist. We suggest that inward-propagating masers are gravitationally deflected by the central black hole, thereby scattering water maser emission out of the disk plane and enabling detection. The signature of an inclined water maser disk would be narrow masers near the systemic velocitymore » that appear to emit from the black hole position, as identified by the radio continuum core. To explore this possibility, we present high-resolution (0.″07–0.″17) Very Large Array line and continuum observations of 13 galaxies with narrow water maser emission and show that three are good inclined-disk candidates (five remain ambiguous). For the best case, CGCG 120−039, we show that the maser and continuum emission are coincident to within 3.5 ± 1.4 pc (6.7 ± 2.7 mas). Subsequent very long baseline interferometric maps can confirm candidate inclined disks and have the potential to show maser rings or arcs that provide a direct measurement of black hole mass, although the mass precision will rely on knowledge of the size of the maser disk.« less

Magneto-thermal Disk Winds from Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bai, Xue-Ning; Ye, Jiani; Goodman, Jeremy; Yuan, Feng

2016-02-01

The global evolution and dispersal of protoplanetary disks (PPDs) are governed by disk angular-momentum transport and mass-loss processes. Recent numerical studies suggest that angular-momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal Alfvén speed vAp, (2) the sound speed cs near the wind base, and (3) how rapidly poloidal field lines diverge (achieve {R}-2 scaling). When {v}{Ap}\\gg {c}{{s}}, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. In both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. For typical PPD accretion-rate and wind-launching conditions, we expect vAp to be comparable to cs at the wind base. The resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. Implications for modeling global disk evolution and planet formation are also discussed.

NEBULAR AND STELLAR DUST EXTINCTION ACROSS THE DISK OF EMISSION-LINE GALAXIES ON KILOPARSEC SCALES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolutionmore » spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study.« less

Young stellar population and star formation history ofW4 HII region/Cluster Complex

NASA Astrophysics Data System (ADS)

Panwar, Neelam

2018-04-01

The HII region/cluster complex has been a subject of numerous investigations to study the feedback effect of massive stars on their surroundings. Massive stars not only alter the morphology of the parental molecular clouds, but also influence star formation, circumstellar disks and the mass function of low-mass stars in their vicinity. However, most of the studies of low-mass stellar content of the HII regions are limited only to the nearby regions. We study the star formation in the W4 HII region using deep optical observations obtained with the archival data from Canada - France - Hawaii Telescope, Two-Micron All Sky Survey, Spitzer, Herschel and Chandra. We investigate the spatial distribution of young stellar objects in the region, their association with the remnant molecular clouds, and search for the clustering to establish the sites of recent star formation. Our analysis suggests that the influence of massive stars on circumstellar disks is significant only to thei! r immediate neighborhood. The spatial correlation of the young stars with the distribution of gas and dust of the complex indicate that the clusters would have formed in a large filamentary cloud. The observing facilities at the 3.6-m Devasthal Optical Telescope (DOT), providing high-resolution spectral and imaging capabilities, will fulfill the major objectives in the study of HII regions.

Planetary system formation: Effects of planet-disk tidal interaction

NASA Astrophysics Data System (ADS)

Bryden, Geoffrey

The standard theory of planet formation begins with the coagulation of solid planetesimals (Safronov 1969, Wetherill & Stewart 1989) followed by the accretion of disk gas once the solid core reaches a critical mass >~10M⊕ (Perri & Cameron 1974, Mizuno 1980, Bodenheimer & Pollack 1986). The classic picture of planet formation, in which each planet's position in the nebula remain fixed, is challenged by the observed distribution of extra-solar planets (e.g. Mayor & Queloz 1995, Butler et al. 1999). The majority of these planets are on short-period orbits ( P<~10 days) very close to their central stars ( ap<~0.1 AU), suggesting that orbital migration plays an important role in the formation of planetary systems. The intent of this thesis is to explore the inclusion of protoplanetary tidal forces into the classical theory of planetary system formation. Protoplanetary interaction with the surrounding gaseous nebulae directly determines giant planets' semi-major axes, masses, gas/solid ratio, and relative spacing. In essence, the process of gap formation determines the primary observational characteristics of both individual planets and their composite systems. Detailed simulations of gap formation produce a range of planetary masses consistent with the observed distribution. Fully self-interacting models of planetary system formation can be used to create a wide variety of planetary systems, ranging from the solar system to Upsilon Andromeda (Butler et al. 1999).

Gas distribution in the central region of the galaxy. I. Atomic hydrogen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burton, W.B.; Liszt, H.S.

A simple model of the distribution and kinematics of gas within 1.5 pc of the galactic center is described, the model refers to all such gas, whether at apparently permitted or anomalous velocities. The inner-Galaxy material is confined in a layer of scale height 0.1 kpc to a disk of 3 kpc diameter, tilted 22/sup 0/ with respect to the plane b = 0/sup 0/ and 78/sup 0/ with respect to the plane of the sky. Within this disk the kinematics involve rotation and expansion of approx. 170 km s/sup -1/. Detailed specification of the model parameters arises from comparisonmore » of synthetic 21-cm emission profiles with a new set of high-sensitivity H I data. The resultant model accounts in a coherent way for many observed spectral features which were previously studied separately and variously identified with bars, spiral arms, or isolated ejecta. In particular, the model subsumes the individual features E, J2, J4, J5, VII, X, and XII, which were previously considered as evidence of recurring, collimated ejections from the galactic nucleus. The model accounts for the rotating nuclear disk feature, the principal source of the inner-Galaxy gravitational field, and subsumes several other extended spectral features (such as III, the connecting arm) at velocities which are permitted by pure rotation. The H I mass of the disk is 1 x 10/sup 7/ M sub solar, and the expansion flux across its outer boundary is 4 M sub solar yr/sup -1/. No evidence is seen of important density enhancements or kinematic perturbations associated with particular observed spectral features, nor of anisotropic ejection from the nucleus. The complete axial symmetry shared by all parameters of the synthesis suggests that a steady state prevails. The large-scale consequences of the fundamental inner-Galaxy distribution depend on the total mass. With no dynamical foundation, the principal use of the phenomenological model is the constraint of other interpretations of the inner-Galaxy gas. 11 figures, 2 tables.« less

The near-infrared properties of compact binary systems

NASA Astrophysics Data System (ADS)

Froning, Cynthia Suzanne

I present H- and K-band light curves of the dwarf nova cataclysmic variable (CV), IP Peg, and the novalike CV, RW Tri, and an H-band light curve of the novalike CV, SW Sex. All three systems showed contributions from the late-type secondary star and the accretion disk, including a primary eclipse of the accretion disk by the secondary star and a secondary eclipse of the star by the disk. The ellipsoidal variations of the secondary star in IP Peg were modeled and subtracted from the data. The subtracted light curves show a pronounced double-hump variation, resembling those seen in the dwarf novae WZ Sge and AL Com. The primary eclipse was modeled using maximum entropy disk mapping techniques. The accretion disk has a flat intensity distribution and a low brightness temperature (Tbr ~= 3000-4000 K). Superimposed on the face of the disk is the bright spot, where the mass accretion stream impacts the disk; the position of the bright spot is different from the range of positions seen at visible wavelengths. The near-infrared accretion disk flux is dominated by optically thin emission. The eclipse depth is too shallow to be caused by a fully opaque accretion disk. The NIR light curves in RW Tri show a deep primary eclipse of the accretion disk, ellipsoidal variations from the secondary star, a secondary eclipse, and strong flickering in the disk flux. The depth of the secondary eclipse indicates that the accretion disk is opaque. The light curve also has a hump extending from φ = 0.1-0.9 which was successfully modeled as flux from the inner face of the secondary star when heated by a ~0.2 L Lsolar source. The radial brightness temperature profile of the outer disk is consistent with models of a disk in steady-state for a mass transfer rate of M~=5×10- 10 Msolaryr- 1 . At small disk radii, however, the brightness temperature profile is flatter than the steady-state model. The H-band light curve of SW Sex is dominated by emission from the accretion disk. As in RW Tri, the light curve has a hump outside of primary eclipse which was modeled as flux from the secondary star when irradiated by a 0.2-0.3 Lsolar source. The light curve has a dip at φ = 0.5 which is consistent with an eclipse of the irradiated face of the secondary star by an opaque accretion disk. The accretion disk has a brightness temperature profile much flatter than the theoretical profile of a steady- state disk. The disk is asymmetric, with the front of the disk (the side facing the secondary star at mid-eclipse) hotter than the back. The bright spot, which appears in visible disk maps of SW Sex, is not seen in the NIR light curve. I also present H-band light curves of the X-ray binary system, A0620-00, and NIR spectra of two X-ray binaries, CI Cam, and the relativistic jet source, SS 433. (Abstract shortened by UMI.)

The Next Generation Virgo Cluster Survey. XXVIII. Characterization of the Galactic White Dwarf Population

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fantin, Nicholas J.; Côté, Patrick; Gwyn, S. D. J.

We use three different techniques to identify hundreds of white dwarf (WD) candidates in the Next Generation Virgo Cluster Survey (NGVS) based on photometry from the NGVS and GUViCS, and proper motions derived from the NGVS and the Sloan Digital Sky Survey (SDSS). Photometric distances for these candidates are calculated using theoretical color–absolute magnitude relations, while effective temperatures are measured by fitting their spectral energy distributions. Disk and halo WD candidates are separated using a tangential velocity cut of 200 km s{sup −1} in a reduced proper motion diagram, which leads to a sample of six halo WD candidates. Coolingmore » ages, calculated for an assumed WD mass of 0.6 M {sub ⊙}, range between 60 Myr and 6 Gyr, although these estimates depend sensitively on the adopted mass. Luminosity functions for the disk and halo subsamples are constructed and compared to previous results from the SDSS and SuperCOSMOS survey. We compute a number density of (2.81 ± 0.52) × 10{sup −3} pc{sup −3} for the disk WD population—consistent with previous measurements. We find (7.85 ± 4.55) × 10{sup −6} pc{sup −3} for the halo, or 0.3% of the disk. Observed stellar counts are also compared to predictions made by the TRILEGAL and Besançon stellar population synthesis models. The comparison suggests that the TRILEGAL model overpredicts the total number of WDs. The WD counts predicted by the Besançon model agree with the observations, although a discrepancy arises when comparing the predicted and observed halo WD populations; the difference is likely due to the WD masses in the adopted model halo.« less

An UXor among FUors: Extinction-related Brightness Variations of the Young Eruptive Star V582 Aur

NASA Astrophysics Data System (ADS)

Ábrahám, P.; Kóspál, Á.; Kun, M.; Fehér, O.; Zsidi, G.; Acosta-Pulido, J. A.; Carnerero, M. I.; García-Álvarez, D.; Moór, A.; Cseh, B.; Hajdu, G.; Hanyecz, O.; Kelemen, J.; Kriskovics, L.; Marton, G.; Mező, Gy.; Molnár, L.; Ordasi, A.; Rodríguez-Coira, G.; Sárneczky, K.; Sódor, Á.; Szakáts, R.; Szegedi-Elek, E.; Szing, A.; Farkas-Takács, A.; Vida, K.; Vinkó, J.

2018-01-01

V582 Aur is an FU Ori-type young eruptive star in outburst since ∼1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04 M ⊙. The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Hα profile. The color variations strongly indicate that both the ∼1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A V = 4.5 to 12.5 mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses.

A gaseous metal disk around a white dwarf.

PubMed

Gänsicke, B T; Marsh, T R; Southworth, J; Rebassa-Mansergas, A

2006-12-22

The destiny of planetary systems through the late evolution of their host stars is very uncertain. We report a metal-rich gas disk around a moderately hot and young white dwarf. A dynamical model of the double-peaked emission lines constrains the outer disk radius to just 1.2 solar radii. The likely origin of the disk is a tidally disrupted asteroid, which has been destabilized from its initial orbit at a distance of more than 1000 solar radii by the interaction with a relatively massive planetesimal object or a planet. The white dwarf mass of 0.77 solar mass implies that planetary systems may form around high-mass stars.

Flat spectrum T Tauri stars: The case for infall

NASA Technical Reports Server (NTRS)

Calvet, Nuria; Hartmann, Lee; Kenyon, S. J.; Whitney, B. A.

1994-01-01

We show that the mid- to far-infrared fluxes of 'flat spectrum' T Tauri stars can be explained by radiative equilibrium emission from infalling dusty envelopes. Infall eliminates the need for accretion disks with non-standard temperature distributions. The simplicity and power of this explanantion indicates that models employing 'active' disks, in which the temperature distribution is a parameterized power law, should be invoked with caution. Infall also naturally explains the scattered light nebulae detected around many flat spectrum sources. To match the observed spectra, material must fall onto a disk rather than the central star, as expected for collapse of a rotating molecular cloud. It may be necessary to invoke cavities in the envelopes to explain the strength of optical and near-infrared emission; these cavities could be produced by the powerful bipolar outflows commonly observed from young stars. If viewed along the cavity, a source may be lightly extincted at visual wavelengths, while still accreting substantial amounts of material from the envelope. Infall may also be needed to explain the infrared-bright companions of many optical T Tauri stars. This picture suggests that many of the flat spectrum sources are 'protostars'-young stellar objects surrounded by dust infalling envelopes of substantial mass.

An Extension of the EDGES Survey: Stellar Populations in Dark Matter Halos

NASA Astrophysics Data System (ADS)

van Zee, Liese

The formation and evolution of galactic disks is one of the key questions in extragalactic astronomy today. We plan to use archival data from GALEX, Spitzer, and WISE to investigate the growth and evolution of the stellar component in a statistical sample of nearby galaxies. Data covering a broad wavelength range are critical for measurement of current star formation activity, stellar populations, and stellar distributions in nearby galaxies. In order to investigate the timescales associated with the growth of galactic disks, we will (1) investigate the structure of the underlying stellar distribution, (2) measure the ratio of current-to-past star formation activity as a function of radius, and (3) investigate the growth of the stellar disk as a function of baryon fraction and total dynamical mass. The proposed projects leverage the existing deep wide field-of-view near infrared imaging observations obtained with the Spitzer Space Telescope as part of the EDGES Survey, a Cycle 8 Exploration Science Program. The proposed analysis of multiwavelength imaging observations of a well-defined statistical sample will place strong constraints on hierarchical models of galaxy formation and evolution and will further our understanding of the stellar component of nearby galaxies.

The formation of protostellar disks. 2: Disks around intermediate-mass stars

NASA Technical Reports Server (NTRS)

Yorke, Harold W.; Bodenheimer, Peter; Laughlin, G.

1995-01-01

Hydrodynamical calculations of the evolution of a collapsing, rotating axisymmetric 10 solar masses molecular clump, including the effects of radiative acceleration but without magnetic fields, are represented. The initial cloud is assumed to be uniformly rotating, centrally condensed sphere with rho is proportional to r(exp -2). Several cases are considered, in which both the overall clump size and the total amount of angular momentum are varied. The calculations show how a warm, quasi-hydrostatic disk surrounding a central unresolved core of only a few solar masses forms and grows in size and mass. The disk is encased in two distinct accretion shock fronts, both of which are several scale heights above the equatorial plane. At the end of the calculation of our standard case, the central unresolved region is found to have a mass of 2.7 solar masses and a ratio of rotational to gravitational energy of approximately 0.45, sufficiently large to be unstable to nonaxisymmetric perturbations. In addition, the inner portions of the disk containing most of the mass are unstable according to the local Toomre criterion, implying that also in this region nonaxisymmetric perturbations will lead to rapid evolution. Under the assumption that gravitational torques would transport angular momentum out of this region, a central core of less than or approximately 8 solar masses with a stable disk of greater than or approximately = 2 solar masses should result. Frequency-dependent radiative transfer calculations of the standard case at selected ages show how the continuum spectrum of the structure depends on the disk's orientation and age and how the observed isophotal contours vary with wavelength. Because of the strong dependence on viewing angle, continuum spectra alone should not be used to estimate the evolutionary stage of development of these objects. Comparable results were obtained for the other cases considered.

On the Formation of Multiple Concentric Rings and Gaps in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Zhu, Zhaohuan; Hartmann, Lee

2017-12-01

As spiral waves driven by a planet in a gaseous disk steepen into a shock, they deposit angular momentum, opening a gap in the disk. This has been well studied using both linear theory and numerical simulations, but so far only for the primary spiral arm: the one directly attached to the planet. Using 2D hydrodynamic simulations, we show that the secondary and tertiary arms driven by a planet can also open gaps as they steepen into shocks. The depths of the secondary/tertiary gaps in surface density grow with time in a low-viscosity disk (α =5× {10}-5), so even low-mass planets (e.g., super-Earth or mini-Neptune-mass) embedded in the disk can open multiple observable gaps, provided that sufficient time has passed. Applying our results to the HL Tau disk, we show that a single 30 Earth-mass planet embedded in the ring at 68.8 au (B5) can reasonably well reproduce the positions of the two major gaps at 13.2 and 32.3 au (D1 and D2), and roughly reproduce two other major gaps at 64.2 and 74.7 au (D5 and D6) seen in the mm continuum. The positions of secondary/tertiary gaps are found to be sensitive to the planetary mass and the disk temperature profile, so with accurate observational measurements of the temperature structure, the positions of multiple gaps can be used to constrain the mass of the planet. We also comment on the gaps seen in the TW Hya and HD 163296 disk.

Wind-Driven Global Evolution of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bai, Xue-Ning

It has been realized in the recent years that magnetized disk winds disk- likely play a decisive role in the global evolution of protoplanetary disks protoplanetary evolution (PPDs). Motivated by recent local simulations local , we first describe a global magnetized disk wind model, from which wind-driven accretion rate -rate wind-driven and wind mass loss rate can be reliably estimated. Both rates are shown to strongly depend on the amount of magnetic flux magnetic threading the disk. Wind kinematics is also affected by thermodynamics in the wind zone (particularly far UV heating/ionization), and the mass loss process loss- can be better termed as "magneto-photoevaporation." We then construct a framework of PPD global evolution global that incorporates wind-driven and viscously driven accretion viscously-driven as well as wind mass loss. For typical PPD accretion rates, the required field strength would lead to wind mass loss rate at least comparable to disk accretion rate, and mass loss is most significant in the outer disk (beyond ˜ 10 AU). Finally, we discuss the transport of magnetic flux in PPDs, which largely governs the long-term evolution long-term of PPDs.

Using Open Clusters to Trace the Local Milky Way Rotation Curve and Velocity Field

NASA Astrophysics Data System (ADS)

Frinchaboy, Peter M.; Majewski, S. R.

2006-12-01

Establishing the rotation curve of the Milky Way is one of the fundamental contributions needed to understand the Galaxy and its mass distribution. We have undertaken a systematic spectroscopic survey of open star clusters which can serve as tracers of Galactic disk dynamics. We report on our initial sample of 67 clusters for which the Hydra multi-fiber spectrographs on the WIYN and Blanco telescopes have delivered 1-2 km/s radial velocities (RVs) of many dozens of stars in the fields of each cluster, which are used to derive cluster membership and bulk cluster kinematics when combined with Tycho-2 proper motions. The clusters selected for study have a broad spatial distribution in order to be sensitive to the disk velocity field in all Galactic quadrants and across a Galactocentric radius range as much as 3.0 kpc from the solar circle. Through analysis of the cluster sample, we find (1) the rotation velocity of the LSR is 221 (+2,-4) km/s, (2) the local rotation curve is declining with radius having a slope of -9.0 km/s/kpc, (3) we find (using R_0 = 8.5 kpc) the following Galactic parameters: A = 17.0 km/s/kpc and B = -8.9 km/s/kpc, which yields a Galaxy mass within of 1.5 R_0 of M = 0.9 ± 0.2 x 10^11 solar masses and a M/L of 5.9 in solar units. We also explore the distribution of the local velocity field and find evidence for non-circular motion due to the sprial arms.

The Long-Lived Disks in the η Chamaeleontis Cluster

NASA Astrophysics Data System (ADS)

Sicilia-Aguilar, Aurora; Bouwman, Jeroen; Juhász, Attila; Henning, Thomas; Roccatagliata, Veronica; Lawson, Warrick A.; Acke, Bram; Feigelson, Eric D.; Tielens, A. G. G. M.; Decin, Leen; Meeus, Gwendolyn

2009-08-01

We present Infrared Spectrograph spectra and revised Multiband Imaging Photometer photometry for the 18 members of the η Chamaeleontis cluster. Aged 8 Myr, the η Cha cluster is one of the few nearby regions within the 5-10 Myr age range, during which the disk fraction decreases dramatically and giant planet formation must come to an end. For the 15 low-mass members, we measure a disk fraction ~50%, high for their 8 Myr age, and four of the eight disks lack near-IR excesses, consistent with the empirical definition of "transition" disks. Most of the disks are comparable to geometrically flat disks. The comparison with regions of different ages suggests that at least some of the "transition" disks may represent the normal type of disk around low-mass stars. Therefore, their flattened structure and inner holes may be related to other factors (initial masses of the disk and the star, environment, binarity), rather than to pure time evolution. We analyze the silicate dust in the disk atmosphere, finding moderate crystalline fractions (~10%-30%) and typical grain sizes ~1-3 μm, without any characteristic trend in the composition. These results are common to other regions of different ages, suggesting that the initial grain processing occurs very early in the disk lifetime (<1 Myr). Large grain sizes in the disk atmosphere cannot be used as a proxy for age, but are likely related to higher disk turbulence. The dust mineralogy varies between the 8-12 μm and the 20-30 μm features, suggesting high temperature dust processing and little radial mixing. Finally, the analysis of IR and optical data on the B9 star η Cha reveals that it is probably surrounded by a young debris disk with a large inner hole, instead of being a classical Be star.

Effect of Photodesorption on the Snow Lines at the Surface of Optically Thick Circumstellar Disks around Herbig Ae/Be Stars

NASA Astrophysics Data System (ADS)

Oka, Akinori; Inoue, Akio K.; Nakamoto, Taishi; Honda, Mitsuhiko

2012-03-01

We investigate the effect of photodesorption on the snow line position at the surface of a protoplanetary disk around a Herbig Ae/Be star, motivated by the detection of water ice particles at the surface of the disk around HD142527 by Honda et al. For this aim, we obtain the density and temperature structure in the disk with a 1+1D radiative transfer and determine the distribution of water ice particles in the disk by the balance between condensation, sublimation, and photodesorption. We find that photodesorption induced by far-ultraviolet radiation from the central star depresses the ice-condensation front toward the mid-plane and pushes the surface snow line significantly outward when the stellar effective temperature exceeds a certain critical value. This critical effective temperature depends on the stellar luminosity and mass, the water abundance in the disk, and the yield of photodesorption. We present an approximate analytic formula for the critical temperature. We separate Herbig Ae/Be stars into two groups on the HR diagram according to the critical temperature: one is the disks where photodesorption is effective and from which we may not find ice particles at the surface, and the other is the disks where photodesorption is not effective. We estimate the snow line position at the surface of the disk around HD142527 to be 100-300 AU, which is consistent with the water ice detection at >140 AU in the disk. All the results depend on the dust grain size in a complex way, and this point requires more work in the future.

Observations of Disks around Brown Dwarfs in the TW Hydra Association with the Spitzer Infrared Spectrograph

NASA Astrophysics Data System (ADS)

Morrow, A. L.; Luhman, K. L.; Espaillat, C.; D'Alessio, P.; Adame, L.; Calvet, N.; Forrest, W. J.; Sargent, B.; Hartmann, L.; Watson, D. M.; Bohac, C. J.

2008-04-01

Using SpeX at the NASA Infrared Telescope Facility and the Spitzer Infrared Spectrograph, we have obtained infrared spectra from 0.7 to 40 μm for three young brown dwarfs in the TW Hydra association (τ ~ 10 Myr), 2MASSW J1207334-393254, 2MASSW J1139511-315921, and SSSPM J1102-3431. The spectral energy distribution for 2MASSW J1139511-315921 is consistent with a stellar photosphere for the entire wavelength range of our data, whereas the other two objects exhibit significant excess emission at λ > 5μm. We are able to reproduce the excess emission from each brown dwarf using our models of irradiated accretion disks. According to our model fits, both disks have experienced a high degree of dust settling. We also find that silicate emission at 10 and 20 μm is absent from the spectra of these disks, indicating that grains in the upper disk layers have grown to sizes larger than ~5 μm. Both of these characteristics are consistent with previous observations of decreasing silicate emission with lower stellar masses and older ages. These trends suggest that either (1) the growth of dust grains, and perhaps planetesimal formation, occurs faster in disks around brown dwarfs than in disks around stars or (2) the radii of the mid-IR-emitting regions of disks are smaller for brown dwarfs than for stars, and grains grow faster at smaller disk radii. Finally, we note the possible detection of an unexplained emission feature near 14 μm in the spectra of both of the disk-bearing brown dwarfs. Based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory at the California Institute of Technology under NASA contract 1407.

Externally Induced Evaporation of Young Stellar Disks: The Case for HST 10 in Orion's Trapezium.

NASA Astrophysics Data System (ADS)

Johnstone, D.; Hollenbach, D.; Storzer, H.; Bally, J.; Sutherland, R.

1996-12-01

The Trapezium region in Orion is composed of a few high-mass stars, responsible for the ionization of the surrounding gas, and a plethora of low-mass stars with disks. Observations at infrared, optical, and radio wavelengths have led to the discovery of extended ionized envelopes around many of the young low-mass stars requiring evaporation rates dot M ~ 10(-7) Modot/yr. In this poster we explain these observations through a model for the evaporation of disks around young low-mass stars by an external source of high energy photons. In particular, the externally produced ultraviolet continuum longward of the Lyman limit is used to heat the disk surface and produce a warm neutral flow. The model results in an offset ionization front, where the neutral flow encounters Lyman continuum radiation, and a mass-loss rate which is fixed due to the self-regulating nature of FUV heating. Applying this model to the Trapezium region evaporating objects, particularly HST 10, produces a satisfactory solution to both the mass-loss rate and the size of the ionized envelopes. The resulting short destruction times for these disks constrain the gestation period for planet embryos around stars in dense clusters.

The Mass and Absorption Columns of Galactic Gaseous Halos

NASA Astrophysics Data System (ADS)

Qu, Zhijie; Bregman, Joel N.

2018-03-01

The galactic gaseous halo is a gas reservoir for the interstellar medium in the galaxy disk, supplying materials for star formation. We developed a gaseous halo model connecting the galaxy disk and the gaseous halo by assuming that the star formation rate on the disk is balanced by the radiative cooling rate of the gaseous halo, including stellar feedback. In addition to a single-temperature gaseous halo in collisional ionization equilibrium, we also consider the photoionization effect and a steady-state cooling model. Photoionization is important for modifying the ion distribution in low-mass galaxies and in the outskirts of massive galaxies due to the low densities. The multiphase cooling model dominates the region within the cooling radius, where t cooling = t Hubble. Our model reproduces most of the observed high ionization state ions for a wide range of galaxy masses (i.e., O VI, O VII, Ne VIII, Mg X, and O VIII). We find that the O VI column density has a narrow range around ≈1014 cm‑2 for halo masses from M ⋆ ≈ 3 × 1010 M ⊙ to 6 × 1012 M ⊙, which is consistent with some but not all observational studies. For galaxies with halo masses ≲3 × 1011 M ⊙, photoionization produces most of the O VI, while for more massive galaxies, the O VI is from the medium that is cooling from higher temperatures. Fitting the Galactic (Milky-Way) O VII and O VIII suggests a gaseous halo model where the metallicity is ≈0.55 Z ⊙ and the gaseous halo has a maximum temperature of ≈1.9 × 106 K. This gaseous halo model does not close the census of baryonic material within R 200.

Reverberation Mapping of AGN Accretion Disks

NASA Astrophysics Data System (ADS)

Fausnaugh, Michael; AGN STORM Collaboration

2017-01-01

I will discuss new reverberation mapping results that allow us to investigate the temperature structure of AGN accretion disks. By measuring time-delays between broad-band continuum light curves, we can determine the size of the disk as a function of wavelength. I will discuss the detection of continuum lags in NGC 5548 reported by the AGN STORM project and implications for the accretion disk. I will also present evidence for continuum lags in two other AGN for which we recently measured black hole masses from continuum-Hbeta reverberations. The mass measurements allow us to compare the continuum lags to predictions from standard thin disk theory, and our results indicate that the accretion disks are larger than the simplest expectations.

Optimization of the dissolution of molybdenum disks. FY-16 results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tkac, Peter; Rotsch, David A.; Chemerisov, Sergey D.

2016-09-01

Argonne National Laboratory is providing technical development assistance to NorthStar Medical Technologies LLC in its pursuit of two pathways for production of molybdenum-99: the 98Mo(n,γ) 99Mo reaction and the photonuclear reaction, 100Mo(γ,n) 99Mo. Processing of irradiated targets, from either production mode, requires dissolution of the target material in H 2O 2 followed by a concentration step, addition of ferric ion to precipitate impurities, and conversion of the final solution to 5M potassium hydroxide solution of potassium molybdate. Currently, NorthStar is using pressed and sintered Mo disks as targets. Several options are being considered for the design of Mo targets formore » the production of 99Mo using the (γ,n) reaction. In the current design, the target holder contains a series of sintered Mo disks lined up perpendicular to two incident electron beams, one entering from each side of the target stack. In this configuration, the front-most disks absorb most of the heat from the electron beam and need to be thinner to allow for better cooling, while the middle of the target can be thicker. Distribution of the total mass of Mo allows for larger masses of Mo material and thus larger production batches of 99Mo. A limitation of the sintering approach is the production of very thin disks. Recent advances in 3D printing allow for much thinner target components can be achieved than when the traditional press-and-sinter approach is used. We have demonstrated that several factors can play important roles in dissolution behavior: particle size of Mo metal used for production of targets, sintering conditions, degree of open porosity, and thickness of the sintered Mo targets. Here we report experimental results from studies of small-scale dissolution of sintered Mo disks fabricated from various recycled and commercial Mo materials, and dissolution of 3D-printed Mo disks that were fabricated by Oak Ridge National Laboratory (ORNL). We also report on large-scale dissolution studies with 600 g batches of sintered Mo disks.« less

The Dynamics and Implications of Gap Clearing via Planets in Planetesimal (Debris) Disks

NASA Astrophysics Data System (ADS)

Morrison, Sarah Jane

Exoplanets and debris disks are examples of solar systems other than our own. As the dusty reservoirs of colliding planetesimals, debris disks provide indicators of planetary system evolution on orbital distance scales beyond those probed by the most prolific exoplanet detection methods, and on timescales 10 r to 10 Gyr. The Solar System possesses both planets and small bodies, and through studying the gravitational interactions between both, we gain insight into the Solar System's past. As we enter the era of resolved observations of debris disks residing around other stars, I add to our theoretical understanding of the dynamical interactions between debris, planets, and combinations thereof. I quantify how single planets clear material in their vicinity and how long this process takes for the entire planetary mass regime. I use these relationships to assess the lowest mass planet that could clear a gap in observed debris disks over the system's lifetime. In the distant outer reaches of gaps in young debris systems, this minimum planet mass can exceed Neptune's. To complement the discoveries of wide-orbit, massive, exoplanets by direct imaging surveys, I assess the dynamical stability of high mass multi-planet systems to estimate how many high mass planets could be packed into young, gapped debris disks. I compare these expectations to the planet detection rates of direct imaging surveys and find that high mass planets are not the primary culprits for forming gaps in young debris disk systems. As an alternative model for forming gaps in planetesimal disks with planets, I assess the efficacy of creating gaps with divergently migrating pairs of planets. I find that migrating planets could produce observed gaps and elude detection. Moreover, the inferred planet masses when neglecting migration for such gaps could be expected to be observable by direct imaging surveys for young, nearby systems. Wide gaps in young systems would likely still require more than two planets even with plantesimal-driven migration. These efforts begin to probe the types of potential planets carving gaps in disks of different evolutionary stages and at wide orbit separations on scales similar to our outer Solar System.

Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

NASA Astrophysics Data System (ADS)

Koda, Jin

2012-01-01

"The GALEX UV satellite discovered tantalizing evidence of star formation (SF) far beyond the optical edge of galactic disks (i.e. extended UV disk, or XUV disk). This discovery provides a new opportunity for studying SF in the exceedingly low-density environment (˜1/10 of typical SF density), spurring intense debate on the universality of the initial mass function (IMF) in such exceptional environments. Our pilot S-Cam study of M83’s XUV disk led to support for the universal IMF at least in M83 (Koda et al. 2012). We propose an expansion of the pilot study, observing 6 XUV disks in NA656(Hα), B, I, and R-band with S-Cam. In conjunction with GALEX UV bands, these images will reveal the presence of O stars (Hα; NA656-R) and O&B stars (UV) in stellar clusters -thus, constraining the high-mass end of the IMF. The multi-broadband images will enable us to determine the masses of the clusters with much improved accuracy (previously, relied only on R). The proposed observations will not only increase the statistical significance of our previous result, but also enable us to analyze the stochastic effect of IMF sampling in very low-mass clusters (10^{2+3} M_sun) - the regime about which there is much ongoing debate."

X-rays from Young Low-Mass Stars: Inhospitable Habitable Zones?

NASA Astrophysics Data System (ADS)

Kastner, Joel

2016-09-01

The irradiation of protoplanetary disks by high-energy radiation from magnetic and accretion activity at low-mass, pre-MS stars likely plays an essential role in regulating exoplanet formation around such stars. To provide the X-ray data necessary to address the problem of the dissipation of protoplanetary disks around the lowest-mass stars, we propose a survey of a sample of previously established and newly-discovered mid- to late-type M type members of the nearby TW Hya Association (age 8 Myr), most of which were the subjects of our recent ALMA survey to detect dusty disks. The combined Chandra and ALMA survey of the TWA will provide a unique resource with which to investigate X-ray-induced photoevaporation of disks orbiting very low-mass stars and massive brown dwarfs.

Establishing a relation between the mass and the spin of stellar-mass black holes.

PubMed

Banerjee, Indrani; Mukhopadhyay, Banibrata

2013-08-09

Stellar mass black holes (SMBHs), forming by the core collapse of very massive, rapidly rotating stars, are expected to exhibit a high density accretion disk around them developed from the spinning mantle of the collapsing star. A wide class of such disks, due to their high density and temperature, are effective emitters of neutrinos and hence called neutrino cooled disks. Tracking the physics relating the observed (neutrino) luminosity to the mass, spin of black holes (BHs) and the accretion rate (M) of such disks, here we establish a correlation between the spin and mass of SMBHs at their formation stage. Our work shows that spinning BHs are more massive than nonspinning BHs for a given M. However, slowly spinning BHs can turn out to be more massive than spinning BHs if M at their formation stage was higher compared to faster spinning BHs.

Spread of the dust temperature distribution in circumstellar disks

NASA Astrophysics Data System (ADS)

Heese, S.; Wolf, S.; Dutrey, A.; Guilloteau, S.

2017-07-01

Context. Accurate temperature calculations for circumstellar disks are particularly important for their chemical evolution. Their temperature distribution is determined by the optical properties of the dust grains, which, among other parameters, depend on their radius. However, in most disk studies, only average optical properties and thus an average temperature is assumed to account for an ensemble of grains with different radii. Aims: We investigate the impact of subdividing the grain radius distribution into multiple sub-intervals on the resulting dust temperature distribution and spectral energy distribution (SED). Methods: The temperature distribution, the relative grain surface below a certain temperature, the freeze-out radius, and the SED were computed for two different scenarios: (1) Radius distribution represented by 16 logarithmically distributed radius intervals, and (2) radius distribution represented by a single grain species with averaged optical properties (reference). Results: Within the considered parameter range, I.e., of grain radii between 5 nm and 1 mm and an optically thin and thick disk with a parameterized density distribution, we obtain the following results: in optically thin disk regions, the temperature spread can be as large as 63% and the relative grain surface below a certain temperature is lower than in the reference disk. With increasing optical depth, the difference in the midplane temperature and the relative grain surface below a certain temperature decreases. Furthermore, below 20 K, this fraction is higher for the reference disk than for the case of multiple grain radii, while it shows the opposite behavior for temperatures above this threshold. The thermal emission in the case of multiple grain radii at short wavelengths is stronger than for the reference disk. The freeze-out radius (snowline) is a function of grain radius, spanning a radial range between the coldest and warmest grain species of 30 AU.

ALMA IMAGING OF HCN, CS, AND DUST IN ARP 220 AND NGC 6240

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scoville, Nick; Manohar, Swarnima; Murchikova, Lena

We report ALMA Band 7 (350 GHz) imaging at 0.''4-0.''6 resolution and Band 9 (696 GHz) at ∼0.''25 resolution of the luminous IR galaxies Arp 220 and NGC 6240. The long wavelength dust continuum is used to estimate interstellar medium masses for Arp 220 east and west and NGC 6240 of 1.9, 4.2, and 1.6 × 10{sup 9} M {sub ☉}within radii of 69, 65, and 190 pc. The HCN emission was modeled to derive the emissivity distribution as a function of radius and the kinematics of each nuclear disk, yielding dynamical masses consistent with the masses and sizes derived from the dustmore » emission. In Arp 220, the major dust and gas concentrations are at radii less than 50 pc in both counter-rotating nuclear disks. The thickness of the disks in Arp 220 estimated from the velocity dispersion and rotation velocities are 10-20 pc and the mean gas densities are n{sub H{sub 2}}∼10{sup 5} cm{sup –3} at R <50 pc. We develop an analytic treatment for the molecular excitation (including photon trapping), yielding volume densities for both the HCN and CS emission with n {sub H2} ∼ 2 × 10{sup 5} cm{sup –3}. The agreement of the mean density from the total mass and size with that required for excitation suggests that the volume is essentially filled with dense gas, i.e., it is not cloudy or like swiss cheese.« less

The Scattering Outcomes of Kepler Circumbinary Planets: Planet Mass Ratio

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Yan-Xiang; Ji, Jianghui, E-mail: yxgong@pmo.ac.cn, E-mail: jijh@pmo.ac.cn

Recent studies reveal that the free eccentricities of Kepler-34b and Kepler-413b are much larger than their forced eccentricities, implying that scattering events may take place in their formation. The observed orbital configuration of Kepler-34b cannot be well reproduced in disk-driven migration models, whereas a two-planet scattering scenario can play a significant role of shaping the planetary configuration. These studies indicate that circumbinary planets discovered by Kepler may have experienced scattering process. In this work, we extensively investigate the scattering outcomes of circumbinary planets focusing on the effects of planet mass ratio . We find that the planetary mass ratio andmore » the the initial relative locations of planets act as two important parameters that affect the eccentricity distribution of the surviving planets. As an application of our model, we discuss the observed orbital configurations of Kepler-34b and Kepler-413b. We first adopt the results from the disk-driven models as the initial conditions, then simulate the scattering process that occurs in the late evolution stage of circumbinary planets. We show that the present orbital configurations of Kepler-34b and Kepler-413b can be well reproduced when considering a two unequal-mass planet ejection model. Our work further suggests that some of the currently discovered circumbinary single-planet systems may be survivors of original multiple-planet systems. The disk-driven migration and scattering events occurring in the late stage both play an irreplaceable role in sculpting the final systems.« less

Anatomy of a flaring proto-planetary disk around a young intermediate-mass star.

PubMed

Lagage, Pierre-Olivier; Doucet, Coralie; Pantin, Eric; Habart, Emilie; Duchêne, Gaspard; Ménard, François; Pinte, Christophe; Charnoz, Sébastien; Pel, Jan-Willem

2006-10-27

Although planets are being discovered around stars more massive than the Sun, information about the proto-planetary disks where such planets have built up is sparse. We have imaged mid-infrared emission from polycyclic aromatic hydrocarbons at the surface of the disk surrounding the young intermediate-mass star HD 97048 and characterized the disk. The disk is in an early stage of evolution, as indicated by its large content of dust and its hydrostatic flared geometry, indicative of the presence of a large amount of gas that is well mixed with dust and gravitationally stable. The disk is a precursor of debris disks found around more-evolved A stars such as beta-Pictoris and provides the rare opportunity to witness the conditions prevailing before (or during) planet formation.

Software Engineering Principles 3-14 August 1981,

DTIC Science & Technology

1981-08-01

small disk used (but rot that of the extended mass storage or large disk option); it is very fast (about 1/5 the speed of the primary memory, where the...extended mass storage or large disk option); it is very fast (about 1/5 the speed of the primary memory, where the disk was 1/10000 for access); and...programed and tested - must be correct and fast D. Choice of right synchronization operations: Design problem 1. Several mentioned in literature 9-22

The low-mass star and disk populations in NGC 6611

NASA Astrophysics Data System (ADS)

Oliveira, Joana

2005-07-01

The aim of our observational program is to find empirical answers to two major questions. Do regions of high-mass star formation also produce lots of solar- and low-mass stars, i.e. is the low-mass IMF unaffected by high-mass siblings? Can low-mass stars in hostile environments retain circumstellar disks? We present results of our survey of NGC 6611, a massive cluster with an age of approximately 2 Myr which is currently ionizing the Eagle nebula. This cluster contains a dozen O-stars that emit 10 times more ionizing radiation than the Trapezium, providing a challenging environment for their lower-mass siblings. Our dataset consists of wide field optical and near infrared imaging, intermediate resolution spectroscopy (ESO-VLT) and deep L-band photometry. We have photometrically selected solar- and low-mass stars, placed them on the HR diagram and determined the IMF over an area sufficient to deal with mass segregation. We show that the IMF in NGC6611 is similar to that of the Orion Nebula Cluster down to 0.5Msun. Using K-L indices we search for colour excesses that betray the presence of circumstellar material and study what fraction of solar-mass stars still possess disks as a function of age and proximity to the massive stars. By comparing the disk frequency in NGC6611 with similarly aged but quieter regions, we find no evidence that the harsher environment of NGC6611 significantly hastens disk dissipation. Apparently the massive stars in NGC6611 have no global effect on the probability of low-mass star formation or disk retention. We have an approved HST program that will allows us to investigate the very low-mass and brown dwarf populations in NGC6611. And we complement our IR imaging with Spitzer/ORAC data, extending the area of our ground-based survey.

LUNAR ACCRETION FROM A ROCHE-INTERIOR FLUID DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salmon, Julien; Canup, Robin M., E-mail: julien@boulder.swri.edu, E-mail: robin@boulder.swri.edu

2012-11-20

We use a hybrid numerical approach to simulate the formation of the Moon from an impact-generated disk, consisting of a fluid model for the disk inside the Roche limit and an N-body code to describe accretion outside the Roche limit. As the inner disk spreads due to a thermally regulated viscosity, material is delivered across the Roche limit and accretes into moonlets that are added to the N-body simulation. Contrary to an accretion timescale of a few months obtained with prior pure N-body codes, here the final stage of the Moon's growth is controlled by the slow spreading of themore » inner disk, resulting in a total lunar accretion timescale of {approx}10{sup 2} years. It has been proposed that the inner disk may compositionally equilibrate with the Earth through diffusive mixing, which offers a potential explanation for the identical oxygen isotope compositions of the Earth and Moon. However, the mass fraction of the final Moon that is derived from the inner disk is limited by resonant torques between the disk and exterior growing moons. For initial disks containing <2.5 lunar masses (M{sub Last-Quarter-Moon }), we find that a final Moon with mass > 0.8 M{sub Last-Quarter-Moon} contains {<=}60% material derived from the inner disk, with this material preferentially delivered to the Moon at the end of its accretion.« less

Disk Evolution in Cep OB2: Results from the Spitzer Space Telescope

NASA Technical Reports Server (NTRS)

Sicilia-Aguilar Aurora; Hartmann, Lee W.; Calvet Nuria; Megeath, S. T.; Muzerolle, James; Allen, Lori; D'Alessio, Paola; Merin, Bruno; Stauffer, John; Lada, Charles;

Musculoskeletal Modeling of the Lumbar Spine to Explore Functional Interactions between Back Muscle Loads and Intervertebral Disk Multiphysics

PubMed Central

Toumanidou, Themis; Noailly, Jérôme

2015-01-01

During daily activities, complex biomechanical interactions influence the biophysical regulation of intervertebral disks (IVDs), and transfers of mechanical loads are largely controlled by the stabilizing action of spine muscles. Muscle and other internal forces cannot be easily measured directly in the lumbar spine. Hence, biomechanical models are important tools for the evaluation of the loads in those tissues involved in low-back disorders. Muscle force estimations in most musculoskeletal models mainly rely, however, on inverse calculations and static optimizations that limit the predictive power of the numerical calculations. In order to contribute to the development of predictive systems, we coupled a predictive muscle model with the passive resistance of the spine tissues, in a L3–S1 musculoskeletal finite element model with osmo-poromechanical IVD descriptions. The model included 46 fascicles of the major back muscles that act on the lower spine. The muscle model interacted with activity-related loads imposed to the osteoligamentous structure, as standing position and night rest were simulated through distributed upper body mass and free IVD swelling, respectively. Calculations led to intradiscal pressure values within ranges of values measured in vivo. Disk swelling led to muscle activation and muscle force distributions that seemed particularly appropriate to counterbalance the anterior body mass effect in standing. Our simulations pointed out a likely existence of a functional balance between stretch-induced muscle activation and IVD multiphysics toward improved mechanical stability of the lumbar spine understanding. This balance suggests that proper night rest contributes to mechanically strengthen the spine during day activity. PMID:26301218

Planning for optical disk technology with digital cartography.

USGS Publications Warehouse

Light, D.L.

1986-01-01

A major shortfall that still exists in digital systems is the need for very large mass storage capacity. The decade of the 1980s has introduced laser optical disk storage technology, which may be the breakthrough needed for mass storage. This paper addresses system concepts for digital cartography during the transition period. Emphasis will be placed on determining USGS mass storage requirements and introducing laser optical disk technology for handling storage problems for digital data in this decade.-from Author

Hydrodynamic Models of Line-Driven Accretion Disk Winds III: Local Ionization Equilibrium

NASA Technical Reports Server (NTRS)

Pereyra, Nicolas Antonio; Kallman, Timothy R.; White, Nicholas E. (Technical Monitor)

2002-01-01

We present time-dependent numerical hydrodynamic models of line-driven accretion disk winds in cataclysmic variable systems and calculate wind mass-loss rates and terminal velocities. The models are 2.5-dimensional, include an energy balance condition with radiative heating and cooling processes, and includes local ionization equilibrium introducing time dependence and spatial dependence on the line radiation force parameters. The radiation field is assumed to originate in an optically thick accretion disk. Wind ion populations are calculated under the assumption that local ionization equilibrium is determined by photoionization and radiative recombination, similar to a photoionized nebula. We find a steady wind flowing from the accretion disk. Radiative heating tends to maintain the temperature in the higher density wind regions near the disk surface, rather than cooling adiabatically. For a disk luminosity L (sub disk) = solar luminosity, white dwarf mass M(sub wd) = 0.6 solar mass, and white dwarf radii R(sub wd) = 0.01 solar radius, we obtain a wind mass-loss rate of M(sub wind) = 4 x 10(exp -12) solar mass yr(exp -1) and a terminal velocity of approximately 3000 km per second. These results confirm the general velocity and density structures found in our earlier constant ionization equilibrium adiabatic CV wind models. Further we establish here 2.5D numerical models that can be extended to QSO/AGN winds where the local ionization equilibrium will play a crucial role in the overall dynamics.

Orbital migration and the period distribution of exoplanets

NASA Astrophysics Data System (ADS)

Del Popolo, A.; Ercan, N.; Yeşilyurt, I. S.

2005-06-01

We use the model for the migration of planets introduced in Del Popolo et al. (2003, MNRAS, 339, 556) to calculate the observed mass and semimajor axis distribution of extra-solar planets. The assumption that the surface density in planetesimals is proportional to that of gas is relaxed, and in order to describe disc evolution we use a method which, using a series of simplifying assumptions, is able to simultaneously follow the evolution of gas and solid particles for up to 107 ~yr. The distribution of planetesimals obtained after 107 ~yr is used to study the migration rate of a giant planet through the model described in the present paper. The disk and migration models are used to calculate the distribution of planets as function of mass and semimajor axis. The results show that the model can give a reasonable prediction of planets' semi-major axes and mass distribution. In particular there is a pile-up of planets at a ≃ 0.05 AU, a minimum near 0.3 AU, indicating a paucity of planets at that distance, and a rise for semi-major axes larger than 0.3 AU, out to 3 AU. The semi-major axis distribution shows that the more massive planets (typically, masses larger than 4~ M_J) form preferentially in the outer regions and do not migrate much. Intermediate-mass objects migrate more easily whatever the distance at which they form, and that the lighter planets (masses from sub-Saturnian to Jovian) migrate easily.

Clumps in the outer disk by disk instability: Why they are initially gas giants and the legacy of disruption

NASA Astrophysics Data System (ADS)

Boley, Aaron C.; Hayfield, Tristen; Mayer, Lucio; Durisen, Richard H.

2010-06-01

We explore the initial conditions for fragments in the extended regions (r≳50AU) of gravitationally unstable disks. We combine analytic estimates for the fragmentation of spiral arms with 3D SPH simulations to show that initial fragment masses are in the gas giant regime. These initial fragments will have substantial angular momentum, and should form disks with radii of a few AU. We show that clumps will survive for multiple orbits before they undergo a second, rapid collapse due to H 2 dissociation and that it is possible to destroy bound clumps by transporting them into the inner disk. The consequences of disrupted clumps for planet formation, dust processing, and disk evolution are discussed. We argue that it is possible to produce Earth-mass cores in the outer disk during the earliest phases of disk evolution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikuchi, Akihiro; Higuchi, Arika; Ida, Shigeru, E-mail: kikuchi.a@geo.titech.ac.jp, E-mail: higuchia@geo.titech.ac.jp, E-mail: ida@elsi.jp

Recently, gas giant planets in nearly circular orbits with large semimajor axes (a ∼ 30-1000 AU) have been detected by direct imaging. We have investigated orbital evolution in a formation scenario for such planets, based on a core accretion model. (1) Icy cores accrete from planetesimals at ≲ 30 AU, (2) they are scattered outward by an emerging nearby gas giant to acquire highly eccentric orbits, and (3) their orbits are circularized through the accretion of disk gas in outer regions, where they spend most of their time. We analytically derived equations to describe the orbital circularization through gas accretion.more » Numerical integrations of these equations show that the eccentricity decreases by a factor of more than 5 while the planetary mass increases by a factor of 10. Because runaway gas accretion increases planetary mass by ∼10-300, the orbits are sufficiently circularized. On the other hand, a is reduced at most only by a factor of two, leaving the planets in the outer regions. If the relative velocity damping by shock is considered, the circularization slows down, but is still efficient enough. Therefore, this scenario potentially accounts for the formation of observed distant jupiters in nearly circular orbits. If the apocenter distances of the scattered cores are larger than the disk sizes, their a shrink to a quarter of the disk sizes; the a-distribution of distant giants could reflect the outer edges of the disks in a similar way that those of hot jupiters may reflect inner edges.« less

Disk irradiation and light curves of x ray novae

NASA Technical Reports Server (NTRS)

Kim, S.-W.; Wheeler, J. C.; Mineshige, S.

1994-01-01

We study the disk instability and the effect of irradiation on outbursts in the black hole X-ray nova system. In both the optical and soft X-rays, the light curves of several X-ray novae, A0620-00, GH 2000+25, Nova Muscae 1991 (GS 1124-68), and GRO J0422+32, show a main peak, a phase of exponential decline, a secondary maximum or reflare, and a final bump in the late decay followed by a rapid decline. Basic disk thermal limit cycle instabilities can account for the rapid rise and overall decline, but not the reflare and final bump. The rise time of the reflare, about 10 days, is too short to represent a viscous time, so this event is unlikely to be due to increased mass flow from the companion star. We explore the possibility that irradiation by X-rays produced in the inner disk can produce these secondary effects by enhancing the mass flow rate within the disk. Two plausible mechanisms of irradiation of the disk are considered: direct irradiation from the inner hot disk and reflected radiation from a corona or other structure above the disk. Both of these processes will be time dependent in the context of the disk instability model and result in more complex time-dependent behavior of the disk structure. We test both disk instability and mass transfer burst models for the secondary flares in the presence of irradiation.

On Noble Gas Processing in the Solar Accretion Disk

NASA Astrophysics Data System (ADS)

Pepin, R. O.

2003-04-01

Two fractionation models are applied to the problem of generating the widely distributed “Q-component” noble gases in meteorites from the solar-like isotopic and elemental compositions that presumably characterized the early solar accretion disk. Noble gas fractionation by mass-dependent dissipation of the solar nebula, as suggested by Ozima et al. (1998), is examined in the context of a model developed by Johnstone et al. (1998) for accretion disk photoevaporation driven by intense UV radiation from a neighboring giant star. Hydrodynamic escape of heavier species entrained in hydrogen outflow from the UV-heated outer regions of the disk can generate substantial noble gas fractionations, but they do not match the observed Q-component isotopic pattern and moreover require the physically unrealistic assumption that the fractionated gases are confined to the heated disk boundary zone, without mixing with the interior nebula, for long periods of time. It seems more likely that hydrodynamic outflow is actually established below this zone, in the body of the disk. In this case fractionations are governed by Rayleigh distillation of the entire remaining nebula, and are negligible at the time when disk erosion is halted by the gravitational potential of the young sun embedded in the disk. A “local” model of noble gas fractionation by hydrodynamic blowoff of transient, methane-rich atmospheres outgassed from the interiors of large primitive planetesimals (Pepin, 1991) is updated and assessed against current data. Degassed atmospheres are assumed to contain isotopically solar noble gases except for an additional nucleogenic Xe component that contributes primarily to the two heaviest isotopes; there is evidence that this same component is present at varying levels in other solar-system volatile reservoirs, possibly reflecting a compositional change with time in the solar nebula. Single fixed values for the two free parameters in the blowoff modeling equations can generate fractionated Xe, Kr, Ar and Ne compositions in the residual atmosphere that closely match observed meteoritic isotopic distributions, and Q-gas elemental ratios are approximated by adsorption of fractionated gases on planetesimal surface grains using plausible values of relative Henry Law constants. Additional requirements for adsorption of sufficient absolute amounts of Q-gases on carrier grains, and their subsequent ejection to space, mixing in the nebula, and dispersal into meteorite bodies, are examined in the context of current models for body sizes and dynamical evolution in an early mass-rich asteroid belt (Chambers and Wetherill, 2001). Despite its ability to replicate isotopic compositions, uncertainties about the environments in which the blowoff model can successfully operate suggest that there is, as yet, no entirely satisfactory understanding of how the Q-component noble gases might have evolved from solar-like precursor compositions.

How to form planetesimals from mm-sized chondrules and chondrule aggregates

NASA Astrophysics Data System (ADS)

Carrera, Daniel; Johansen, Anders; Davies, Melvyn B.

2015-07-01

The size distribution of asteroids and Kuiper belt objects in the solar system is difficult to reconcile with a bottom-up formation scenario due to the observed scarcity of objects smaller than ~100 km in size. Instead, planetesimals appear to form top-down, with large 100-1000 km bodies forming from the rapid gravitational collapse of dense clumps of small solid particles. In this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. We used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. We found that particles down to millimeter sizes can form dense particle clouds through the run-away convergence of radial drift known as the streaming instability. We made a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) that are prone to producing dense particle clumps. Finally, we estimate the distribution of collision speeds between mm-sized particles. We calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ~105 years. This means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (~106-107 years). Our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. We speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. This clumping, in turn, reduces collision speeds and enhances coagulation. Future simulations should model coagulation and the streaming instability together to explore this feedback loop further. Appendices are available in electronic form at http://www.aanda.org

Radial Distribution of Stars, Gas, and Dust in SINGS Galaxies. III. Modeling the Evolution of the Stellar Component in Galaxy Disks

NASA Astrophysics Data System (ADS)

Muñoz-Mateos, J. C.; Boissier, S.; Gil de Paz, A.; Zamorano, J.; Kennicutt, R. C., Jr.; Moustakas, J.; Prantzos, N.; Gallego, J.

2011-04-01

We analyze the evolution of 42 spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey. We make use of ultraviolet (UV), optical, and near-infrared radial profiles, corrected for internal extinction using the total-infrared to UV ratio, to probe the emission of stellar populations of different ages as a function of galactocentric distance. We fit these radial profiles with models that describe the chemical and spectro-photometric evolution of spiral disks within a self-consistent framework. These backward evolutionary models successfully reproduce the multi-wavelength profiles of our galaxies, except for the UV profiles of some early-type disks for which the models seem to retain too much gas. From the model fitting we infer the maximum circular velocity of the rotation curve V C and the dimensionless spin parameter λ. The values of V C are in good agreement with the velocities measured in H I rotation curves. Even though our sample is not volume limited, the resulting distribution of λ is close to the lognormal function obtained in cosmological N-body simulations, peaking at λ ~ 0.03 regardless of the total halo mass. We do not find any evident trend between λ and Hubble type, besides an increase in the scatter for the latest types. According to the model, galaxies evolve along a roughly constant mass-size relation, increasing their scale lengths as they become more massive. The radial scale length of most disks in our sample seems to have increased at a rate of 0.05-0.06 kpc Gyr-1, although the same cannot be said of a volume-limited sample. In relative terms, the scale length has grown by 20%-25% since z = 1 and, unlike the former figure, we argue that this relative growth rate can be indeed representative of a complete galaxy sample.

Studies of Young, Star-forming Circumstellar Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan

2017-08-01

Disks of gas and dust around forming stars - circumstellar disks - last only a few million years. This is a very small fraction of the entire lifetime of Sun-like stars, several billion years. Nevertheless, by the time circumstellar disks dissipate stars complete building up their masses, giant planets finish accreting gas, and terrestrial bodies are nearly fully grown and ready for their final assembly to become planets. Understanding the evolution of circumstellar disks are thus crucial in many contexts. Using numerical simulations as the primary tool, my thesis has focused on the studies of various physical processes that can occur throughout the lifetime of circumstellar disks, from their formation to dispersal. Chapters 2, 3, and 4 emphasize the importance of early evolution, during which time a forming star-disk system obtains mass from its natal cloud: the infall phase. In Chapter 2 and 3, I have modeled episodic outbursts of accretion in protostellar systems resulting from disk instabilities - gravitational instability and magnetorotational instability. I showed that outbursts occur preferentially during the infall phase, because the mass addition provides more favorable conditions for gravitational instability to initiate the outburst cycle, and that forming stars build up a significant fraction of their masses through repeated short-lived, episodic outbursts. The infall phase can also be important for the formation of planets. Recent ALMA observations revealed sets of bright and dark rings in circumstellar disks of young, forming stars, potentially indicating early formation of planets. In Chapter 4, I showed that infall streams can create radial pressure bumps near the outer edge of the mass landing on the disk, from which vortices can form, collecting solid particles very efficiently to make initial seeds of planets. The next three chapters highlight the role of planets in setting the observational appearance and the evolution of circumstellar disks. When a planet forms in a disk, the gravitational interaction between the planet and disk can create structures, such as spiral arms and gaps. In Chapter 5, I compared the disk structures formed by planetary companions in numerical simulations with the observed structures in the disk surrounding an 8 Myr-old Herbig Ae star SAO 206462. Based on the experiments, I made predictions for the mass and position of a currently unrevealed planet, which can help guide future observations to search for more conclusive evidence for the existence of a planetary companion in the system. In Chapter 6, I showed for the first time in global simulation domains that spiral waves, driven for instance by planets or gravitational instability, can be unstable due to resonant interactions with inertial modes, breaking into turbulence. In Chapter 7, I showed that the spiral wave instability operates on the waves launched by planets and that the resulting turbulence can significantly stir up solid particles from the disk midplane. The stirring of solid particles can have influences on the observation appearance of the parent disk and on the subsequent assembly of planetary bodies in the disk. Finally, in Chapter 8, I investigated the dispersal of circumstellar disks via photoevaporative winds, finding that the photoevaporative loss alone, coupled with a range of initial angular momenta of protostellar clouds, can explain the observed decline of the disk frequency with increasing age. The findings and future possibilities are summarized in Chapter 9.

Exploring Disks Around Planets

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and masses on the properties of the disks. Szulgyi specifically examines a range of planetary temperatures between 10,000 K and 1,000 K for the 1 MJ planet. Since the planet cools as it radiates away its formation heat, the different temperatures represent an evolutionary sequence over time.Predicted CharacteristicsSzulgyis work produced a number of intriguing observations, including the following:For the 1 MJ planet, a spherical circumplanetary envelope forms at high temperatures, flattening into a disk as the planet cools. Higher-mass planets form disks even at high temperatures.The disk has a steep temperature profile from inside to outside, and the whole disk is too hot for water to remain frozen. This suggests that satellites couldnt form in the disk earlier than 1 Myr after the planet birth. The outskirts of the disk cool first as the planet cools, indicating that satellites may eventually form in these outer parts and then migrate inward.The planets open gaps in the circumstellar disk as they orbit. As a planet radiates away its formation heat, the gap it opens becomes deeper and wider (though this is a small effect). For high-mass planets (5 MJ), the gap eccentricity increases, which creates a hostile environment for satellite formation.Szulgyi discusses a number of features of these disks that we can plan to search for in the future with our increasing telescope power including signatures in direct imaging and observations of their kinematics. The results from these simulations will help us both to detect these circumplanetary disks and to understand our observations when we do. These future observations will then allow us to learn about late-stage giant-planet formation as well as the formation of their satellites.CitationJ. Szulgyi 2017 ApJ 842 103. doi:10.3847/1538-4357/aa7515

THE OBSERVED M-{sigma} RELATIONS IMPLY THAT SUPER-MASSIVE BLACK HOLES GROW BY COLD CHAOTIC ACCRETION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nayakshin, Sergei; King, Andrew R.; Power, Chris

We argue that current observations of M-{sigma} relations for galaxies can be used to constrain theories of super-massive black holes (SMBHs) feeding. In particular, assuming that SMBH mass is limited only by the feedback on the gas that feeds it, we show that SMBHs fed via a planar galaxy-scale gas flow, such as a disk or a bar, should be much more massive than their counterparts fed by quasi-spherical inflows. This follows from the relative inefficiency of active galactic nucleus feedback on a flattened inflow. We find that even under the most optimistic conditions for SMBH feedback on flattened inflows,more » the mass at which the SMBH expels the gas disk and terminates its own growth is a factor of several higher than the one established for quasi-spherical inflows. Any beaming of feedback away from the disk and any disk self-shadowing strengthen this result further. Contrary to this theoretical expectation, recent observations have shown that SMBHs in pseudobulge galaxies (which are associated with barred galaxies) are typically under- rather than overmassive when compared with their classical bulge counterparts at a fixed value of {sigma}. We conclude from this that SMBHs are not fed by large (100 pc to many kpc) scale gas disks or bars, most likely because such planar flows are turned into stars too efficiently to allow any SMBH growth. Based on this and other related observational evidence, we argue that most SMBHs grow by chaotic accretion of gas clouds with a small and nearly randomly distributed direction of angular momentum.« less

Near-ultraviolet Excess in Slowly Accreting T Tauri Stars: Limits Imposed by Chromospheric Emission

NASA Astrophysics Data System (ADS)

Ingleby, Laura; Calvet, Nuria; Bergin, Edwin; Herczeg, Gregory; Brown, Alexander; Alexander, Richard; Edwards, Suzan; Espaillat, Catherine; France, Kevin; Gregory, Scott G.; Hillenbrand, Lynne; Roueff, Evelyne; Valenti, Jeff; Walter, Frederick; Johns-Krull, Christopher; Brown, Joanna; Linsky, Jeffrey; McClure, Melissa; Ardila, David; Abgrall, Hervé; Bethell, Thomas; Hussain, Gaitee; Yang, Hao

2011-12-01

Young stars surrounded by disks with very low mass accretion rates are likely in the final stages of inner disk evolution and therefore particularly interesting to study. We present ultraviolet (UV) observations of the ~5-9 Myr old stars RECX-1 and RECX-11, obtained with the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph on the Hubble Space Telescope, as well as optical and near-infrared spectroscopic observations. The two stars have similar levels of near-UV emission, although spectroscopic evidence indicates that RECX-11 is accreting and RECX-1 is not. The line profiles of Hα and He I λ10830 in RECX-11 show both broad and narrow redshifted absorption components that vary with time, revealing the complexity of the accretion flows. We show that accretion indicators commonly used to measure mass accretion rates, e.g., U-band excess luminosity or the Ca II triplet line luminosity, are unreliable for low accretors, at least in the middle K spectral range. Using RECX-1 as a template for the intrinsic level of photospheric and chromospheric emission, we determine an upper limit of 3 × 10-10 M ⊙ yr-1 for RECX-11. At this low accretion rate, recent photoevaporation models predict that an inner hole should have developed in the disk. However, the spectral energy distribution of RECX-11 shows fluxes comparable to the median of Taurus in the near-infrared, indicating that substantial dust remains. Fluorescent H2 emission lines formed in the innermost disk are observed in RECX-11, showing that gas is present in the inner disk, along with the dust. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

The Gaseous Disks of Young Stellar Objects

NASA Technical Reports Server (NTRS)

Glassgold, A. E.

2006-01-01

Disks represent a crucial stage in the formation of stars and planets. They are novel astrophysical systems with attributes intermediate between the interstellar medium and stars. Their physical properties are inhomogeneous and are affected by hard stellar radiation and by dynamical evolution. Observing disk structure is difficult because of the small sizes, ranging from as little as 0.05 AU at the inner edge to 100-1000 AU at large radial distances. Nonetheless, substantial progress has been made by observing the radiation emitted by the dust from near infrared to mm wavelengths, i.e., the spectral energy distribution of an unresolved disk. Many fewer results are available for the gas, which is the main mass component of disks over much of their lifetime. The inner disk gas of young stellar objects (henceforth YSOs) have been studied using the near infrared rovibrational transitions of CO and a few other molecules, while the outer regions have been explored with the mm and sub-mm lines of CO and other species. Further progress can be expected in understanding the physical properties of disks from observations with sub-mm arrays like SMA, CARMA and ALMA, with mid infrared measurements using Spitzer, and near infrared spectroscopy with large ground-based telescopes. Intense efforts are also being made to model the observations using complex thermal-chemical models. After a brief review of the existing observations and modeling results, some of the weaknesses of the models will be discussed, including the absence of good laboratory and theoretical calculations for essential microscopic processes.

On the Outer Edges of Protoplanetary Dust Disks

NASA Astrophysics Data System (ADS)

Birnstiel, Tilman; Andrews, Sean M.

2014-01-01

The expectation that aerodynamic drag will force the solids in a gas-rich protoplanetary disk to spiral in toward the host star on short timescales is one of the fundamental problems in planet formation theory. The nominal efficiency of this radial drift process is in conflict with observations, suggesting that an empirical calibration of solid transport mechanisms in a disk is highly desirable. However, the fact that both radial drift and grain growth produce a similar particle size segregation in a disk (such that larger particles are preferentially concentrated closer to the star) makes it difficult to disentangle a clear signature of drift alone. We highlight a new approach, by showing that radial drift leaves a distinctive "fingerprint" in the dust surface density profile that is directly accessible to current observational facilities. Using an analytical framework for dust evolution, we demonstrate that the combined effects of drift and (viscous) gas drag naturally produce a sharp outer edge in the dust distribution (or, equivalently, a sharp decrease in the dust-to-gas mass ratio). This edge feature forms during the earliest phase in the evolution of disk solids, before grain growth in the outer disk has made much progress, and is preserved over longer timescales when both growth and transport effects are more substantial. The key features of these analytical models are reproduced in detailed numerical simulations, and are qualitatively consistent with recent millimeter-wave observations that find gas/dust size discrepancies and steep declines in dust continuum emission in the outer regions of protoplanetary disks.

The applicability of the viscous α-parameterization of gravitational instability in circumstellar disks

NASA Astrophysics Data System (ADS)

Vorobyov, E. I.

2010-01-01

We study numerically the applicability of the effective-viscosity approach for simulating the effect of gravitational instability (GI) in disks of young stellar objects with different disk-to-star mass ratios ξ . We adopt two α-parameterizations for the effective viscosity based on Lin and Pringle [Lin, D.N.C., Pringle, J.E., 1990. ApJ 358, 515] and Kratter et al. [Kratter, K.M., Matzner, Ch.D., Krumholz, M.R., 2008. ApJ 681, 375] and compare the resultant disk structure, disk and stellar masses, and mass accretion rates with those obtained directly from numerical simulations of self-gravitating disks around low-mass (M∗ ∼ 1.0M⊙) protostars. We find that the effective viscosity can, in principle, simulate the effect of GI in stellar systems with ξ≲ 0.2- 0.3 , thus corroborating a similar conclusion by Lodato and Rice [Lodato, G., Rice, W.K.M., 2004. MNRAS 351, 630] that was based on a different α-parameterization. In particular, the Kratter et al.'s α-parameterization has proven superior to that of Lin and Pringle's, because the success of the latter depends crucially on the proper choice of the α-parameter. However, the α-parameterization generally fails in stellar systems with ξ≳ 0.3 , particularly in the Classes 0 and I phases of stellar evolution, yielding too small stellar masses and too large disk-to-star mass ratios. In addition, the time-averaged mass accretion rates onto the star are underestimated in the early disk evolution and greatly overestimated in the late evolution. The failure of the α-parameterization in the case of large ξ is caused by a growing strength of low-order spiral modes in massive disks. Only in the late Class II phase, when the magnitude of spiral modes diminishes and the mode-to-mode interaction ensues, may the effective viscosity be used to simulate the effect of GI in stellar systems with ξ≳ 0.3 . A simple modification of the effective viscosity that takes into account disk fragmentation can somewhat improve the performance of α-models in the case of large ξ and even approximately reproduce the mass accretion burst phenomenon, the latter being a signature of the early gravitationally unstable stage of stellar evolution [Vorobyov, E.I., Basu, S., 2006. ApJ 650, 956]. However, further numerical experiments are needed to explore this issue.

Chemical Evolution and Star Formation History of the Disks of Spirals in Local Group

NASA Astrophysics Data System (ADS)

Yin, J.

2011-05-01

Milky Way (MW), M31 and M33 are the only three spiral galaxies in our Local group. MW and M31 have similar mass, luminosity and morphology, while M33 is only about one tenth of MW in terms of its baryonic mass. Detailed theoretical researches on these three spirals will help us to understand the formation and evolution history of both spiral galaxies and Local group. Referring to the phenomenological chemical evolution model adopted in MW disk, a similar model is established to investigate the star formation and chemical enrichment history of these three local spirals. Firstly, the properties of M31 disk are studied by building a similar chemical evolution model which is able to successfully describe the MW disk. It is expected that a simple unified phenomenological chemical evolution model could successfully describe the radial and global properties of both disks. Comparing with the former work, we adopt an extensive data set as model constraints, including the star formation profile of M31 disk derived from the recent UV data of GALEX. The comparison among the observed properties of these two disks displays very interesting similarities in their radial profiles when the distance from the galactic center is expressed in terms of the corresponding scale length. This implies some common processes in their formation and evolution history. Based on the observed data of the gas mass surface density and SFR surface density, the SFR radial profile of MW can be well described by Kennicutt-Schmidt star formation law (K-S law) or modified K-S law (SFR is inversely proportional to the distance from the galactic center), but this is not applicable to the M31 disk. Detailed calculations show that our unified model describes fairly well all the main properties of the MW disk and most properties of M31 disk, provided that the star formation efficiency of M31 disk is adjusted to be twice as large as that of MW disk (as anticipated from the lower gas fraction of M31). However, the model fails to match the present SFR in M31 disk by predicting too much SFR in the outer disk. We attribute this disagreement to the fact that M31 has been perturbed recently by a violent encounter. The observed SFR profile of M31 caused by this encounter does not seem to follow any form of the K-S law. On the other hand, the stellar metallicity distribution functions (MDFs) measured along the disk of M31 indicate the integrated star formation during the whole disk history and should not be affected by recent events. Our model reproduces rather well those distributions from 6 kpc to 21 kpc (except the region at 16 kpc). Basically, the disks of MW and M31 are formed "inside-out" with similar infall timescale. If M31 is closer to a typical disk galaxy, it would be the best that the researches on the models of this disk galaxy are carried out within the cosmological framework. Simple models, like the one adopted in this thesis, could be used to describe the quiescent galaxy, like the MW. Secondly, the similar model is applied to investigate the formation history of M33 disk. We calculate the radial profiles of gas surface density and SFR surface density, gas fraction, abundances, the surface brightness of FUV and K bands, FUV-K color gradient and so on. All those properties are compared with observations if available. Two different infall histories, namely collapse model and accretion model, are adopted respectively. The effects of free parameters (infall timescale, infall delay time and efficiency of outflow) on the model results are discussed in detail. It is found that the disk of M33 can not be formed by fast collapse process. Observations show that M33 is much smaller and less massive than MW, but has larger gas fraction and lower metallicity. This implies that it should be formed by slow accretion process and is consistent with the slow accretion model. We study the abundance gradients of different elements in M33 disk and find that outflow should play an important role in the evolution of abundance gradients. The present abundances will be much higher than the observation if without outflow. When the disk undergoes an outflow with a similar strength to the local SFR, the abundance within the radius of 6 kpc will be reduced dramatically, but no noticeable change occurs in outer regions, resulting in a flatter abundance gradient. This is consistent with the observed features. Our model predicts a slightly flatter FUV-K color gradient when the long infall timescale and proper outflow are adopted. Considering the uncertainty of the extinction correction, the results are acceptable.

Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk Around PDS 70: Observations of the Disk

NASA Technical Reports Server (NTRS)

Hashimoto, J.; Dong, R.; Kudo, T.; Honda, M.; McClure, M. K.; Zhu, Z.; Muto, T.; Wisniewski, J.; Abe, L.; Brandner, W.;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong Ruobing; Rafikov, Roman; Zhu Zhaohuan

Through detailed radiative transfer modeling, we present a disk+cavity model to simultaneously explain both the spectral energy distribution (SED) and Subaru H-band polarized light imaging for the pre-transitional protoplanetary disk PDS 70. In particular, we are able to match not only the radial dependence but also the absolute scale of the surface brightness of the scattered light. Our disk model has a cavity 65 AU in radius, which is heavily depleted of sub-micron-sized dust grains, and a small residual inner disk that produces a weak but still optically thick near-IR excess in the SED. To explain the contrast of themore » cavity's edge in the Subaru image, a factor of {approx}1000 depletion for the sub-micron-sized dust inside the cavity is required. The total dust mass of the disk may be on the order of 10{sup -4} M {sub Sun }, only weakly constrained due to the lack of long-wavelength observations and the uncertainties in the dust model. The scale height of the sub-micron-sized dust is {approx}6 AU at the cavity edge, and the cavity wall is optically thick in the vertical direction at H-band. PDS 70 is not a member of the class of (pre-)transitional disks identified by Dong et al., whose members only show evidence of the cavity in the millimeter-size dust but not the sub-micron-sized dust in resolved images. The two classes of (pre-)transitional disks may form through different mechanisms, or they may simply be at different evolution stages in the disk-clearing process.« less

A Multi-Wavelength View of Planet Forming Regions: Unleashing the Full Power of ALMA

NASA Astrophysics Data System (ADS)

Tazzari, Marco

2017-11-01

Observations at sub-mm/mm wavelengths allow us to probe the solids in the interior of protoplanetary disks, where the bulk of the dust is located and planet formation is expected to occur. However, the actual size of dust grains is still largely unknown due to the limited angular resolution and sensitivity of past observations. The upgraded VLA and, especially, the ALMA observatories provide now powerful tools to resolve grain growth in disks, making the time ripe for developing a multi-wavelength analysis of sub-mm/mm observations of disks. In my contribution I will present a novel analysis method for multi-wavelength ALMA/VLA observations which, based on the self-consistent modelling of the sub-mm/mm disk continuum emission, allows us to constrain simultaneously the size distribution of dust grains and the disk's physical structure (Tazzari et al. 2016, A&A 588 A53). I will also present the recent analysis of spatially resolved ALMA Band 7 observations of a large sample of disks in the Lupus star forming region, from which we obtained a tentative evidence of a disk size-disk mass correlation (Tazzari et al. 2017, arXiv:1707.01499). Finally, I will introduce galario, a GPU Accelerated Library for the Analysis of Radio Interferometry Observations. Fitting the observed visibilities in the uv-plane is computationally demanding: with galario we solve this problem for the current as well as for the full-science ALMA capabilities by leveraging on the computing power of GPUs, providing the computational breakthrough needed to fully exploit the new wealth of information delivered by ALMA.

Photophoretic Levitation and Trapping of Dust in the Inner Regions of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

McNally, Colin P.; McClure, Melissa K.

2017-01-01

In protoplanetary disks, the differential gravity-driven settling of dust grains with respect to gas and with respect to grains of varying sizes determines the observability of grains, and sets the conditions for grain growth and eventually planet formation. In this work, we explore the effect of photophoresis on the settling of large dust grains in the inner regions of actively accreting protoplanetary disks. Photophoretic forces on dust grains result from the collision of gas molecules with differentially heated grains. We undertake one-dimensional dust settling calculations to determine the equilibrium vertical distribution of dust grains in each column of the disk. In the process we introduce a new treatment of the photophoresis force which is consistent at all optical depths with the representation of the radiative intensity field in a two-stream radiative transfer approximation. The levitation of large dust grains creates a photophoretic dust trap several scale heights above the mid-plane in the inner regions of the disk where the dissipation of accretion energy is significant. We find that differential settling of dust grains is radically altered in these regions of the disk, with large dust grains trapped in a layer below the stellar irradiation surface, where the dust to gas mass ratio can be enhanced by a factor of a hundred for the relevant particles. The photophoretic trapping effect has a strong dependence on particle size and porosity.

A MODEL FOR (QUASI-)PERIODIC MULTIWAVELENGTH PHOTOMETRIC VARIABILITY IN YOUNG STELLAR OBJECTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kesseli, Aurora Y.; Petkova, Maya A.; Wood, Kenneth

We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at opticalmore » and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.« less

Launching of Jets and the Vertical Structure of Accretion Disks

NASA Astrophysics Data System (ADS)

Ogilvie, Gordon I.; Livio, Mario

2001-05-01

The launching of magnetohydrodynamic outflows from accretion disks is considered. We formulate a model for the local vertical structure of a thin disk threaded by a poloidal magnetic field of dipolar symmetry. The model consists of an optically thick disk matched to an isothermal atmosphere. The disk is supposed to be turbulent and possesses an effective viscosity and an effective magnetic diffusivity. In the atmosphere, if the magnetic field lines are inclined sufficiently to the vertical, a magnetocentrifugal outflow is driven and passes through a slow magnetosonic point close to the surface. We determine how the rate of mass loss varies with the strength and inclination of the magnetic field. In particular, we find that for disks in which the mean poloidal field is sufficiently strong to stabilize the disk against the magnetorotational instability, the mass-loss rate decreases extremely rapidly with increasing field strength and is maximal at an inclination angle of 40°-50°. For turbulent disks with weaker mean fields, the mass-loss rate increases monotonically with increasing strength and inclination of the field, but the solution branch terminates before achieving excessive mass-loss rates. Our results suggest that efficient jet launching occurs for a limited range of field strengths and a limited range of inclination angles in excess of 30°. In addition, we determine the direction and rate of radial migration of the poloidal magnetic flux and discuss whether configurations suitable for jet launching can be maintained against dissipation.

Formation of wide binaries by turbulent fragmentation

NASA Astrophysics Data System (ADS)

Lee, Jeong-Eun; Lee, Seokho; Dunham, Michael M.; Tatematsu, Ken'ichi; Choi, Minho; Bergin, Edwin A.; Evans, Neal J.

2017-08-01

Understanding the formation of wide-binary systems of very low-mass stars (M ≤ 0.1 solar masses, M⊙) is challenging 1,2,3 . The most obvious route is through widely separated low-mass collapsing fragments produced by turbulent fragmentation of a molecular core4,5. However, close binaries or multiples from disk fragmentation can also evolve to wide binaries over a few initial crossing times of the stellar cluster through tidal evolution6. Finding an isolated low-mass wide-binary system in the earliest stage of formation, before tidal evolution could occur, would prove that turbulent fragmentation is a viable mechanism for (very) low-mass wide binaries. Here we report high-resolution ALMA observations of a known wide-separation protostellar binary, showing that each component has a circumstellar disk. The system is too young7 to have evolved from a close binary, and the disk axes are misaligned, providing strong support for the turbulent fragmentation model. Masses of both stars are derived from the Keplerian rotation of the disks; both are very low-mass stars.

Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity

NASA Astrophysics Data System (ADS)

Orlando, Salvatore; Reale, Fabio; Peres, Giovanni; Mignone, Andrea

2014-11-01

According to the magnetospheric accretion scenario, young low-mass stars are surrounded by circumstellar disks which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn have a signicant role in removing the excess angular momentum from the star-disk system. Although the process of mass accretion is a critical aspect of star formation, some of its mechanisms are still to be fully understood. On the other hand, strong flaring activity is a common feature of young stellar objects (YSOs). In the Sun, such events give rise to perturbations of the interplanetary medium. Similar but more energetic phenomena occur in YSOs and may influence the circumstellar environment. In fact, a recent study has shown that an intense flaring activity close to the disk may strongly perturb the stability of circumstellar disks, thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the main results obtained in the field and the future perspectives.

Understanding EROS2 observations toward the spiral arms within a classical Galactic model framework

NASA Astrophysics Data System (ADS)

Moniez, M.; Sajadian, S.; Karami, M.; Rahvar, S.; Ansari, R.

2017-08-01

Aims: EROS (Expérience de Recherche d'Objets Sombres) has searched for microlensing toward four directions in the Galactic plane away from the Galactic center. The interpretation of the catalog optical depth is complicated by the spread of the source distance distribution. We compare the EROS microlensing observations with Galactic models (including the Besançon model), tuned to fit the EROS source catalogs, and take into account all observational data such as the microlensing optical depth, the Einstein crossing durations, and the color and magnitude distributions of the catalogued stars. Methods: We simulated EROS-like source catalogs using the HIgh-Precision PARallax COllecting Satellite (Hipparcos) database, the Galactic mass distribution, and an interstellar extinction table. Taking into account the EROS star detection efficiency, we were able to produce simulated color-magnitude diagrams that fit the observed diagrams. This allows us to estimate average microlensing optical depths and event durations that are directly comparable with the measured values. Results: Both the Besançon model and our Galactic model allow us to fully understand the EROS color-magnitude data. The average optical depths and mean event durations calculated from these models are in reasonable agreement with the observations. Varying the Galactic structure parameters through simulation, we were also able to deduce contraints on the kinematics of the disk, the disk stellar mass function (at a few kpc distance from the Sun), and the maximum contribution of a thick disk of compact objects in the Galactic plane (Mthick< 5 - 7 × 1010M⊙ at 95%, depending on the model). We also show that the microlensing data toward one of our monitored directions are significantly sensitive to the Galactic bar parameters, although much larger statistics are needed to provide competitive constraints. Conclusions: Our simulation gives a better understanding of the lens and source spatial distributions in the microlensing events. The goodness of a global fit taking into account all the observables (from the color-magnitude diagrams and microlensing observations) shows the validity of the Galactic models. Our tests with the parameters excursions show the unique sensitivity of the microlensing data to the kinematical parameters and stellar initial mass function. http://www.lal.in2p3.fr/recherche/eros

FORMATION OF CLOSE IN SUPER-EARTHS AND MINI-NEPTUNES: REQUIRED DISK MASSES AND THEIR IMPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlichting, Hilke E., E-mail: hilke@mit.edu

Recent observations by the Kepler space telescope have led to the discovery of more than 4000 exoplanet candidates consisting of many systems with Earth- to Neptune-sized objects that reside well inside the orbit of Mercury around their respective host stars. How and where these close-in planets formed is one of the major unanswered questions in planet formation. Here, we calculate the required disk masses for in situ formation of the Kepler planets. We find that if close-in planets formed as isolation masses, then standard gas-to-dust ratios yield corresponding gas disks that are gravitationally unstable for a significant fraction of systems,more » ruling out such a scenario. We show that the maximum width of a planet's accretion region in the absence of any migration is 2v {sub esc}/Ω, where v {sub esc} is the escape velocity of the planet and Ω is the Keplerian frequency, and we use it to calculate the required disk masses for in situ formation with giant impacts. Even with giant impacts, formation without migration requires disk surface densities in solids at semi-major axes of less than 0.1 AU of 10{sup 3}-10{sup 5} g cm{sup –2}, implying typical enhancements above the minimum-mass solar nebular (MMSN) by at least a factor of 20. Corresponding gas disks are below but not far from the gravitational stability limit. In contrast, formation beyond a few AU is consistent with MMSN disk masses. This suggests that the migration of either solids or fully assembled planets is likely to have played a major role in the formation of close-in super-Earths and mini-Neptunes.« less

Rotation and Mass Loss

NASA Astrophysics Data System (ADS)

Owocki, S.

2008-06-01

Stellar rotation can play an important role in structuring and enhancing the mass loss from massive stars. Initial 1D models focussed on the expected centrifugal enhancement of the line-driven mass flux from the equator of a rotating star, but the review here emphasizes that the loss of centrifugal support away from the stellar surface actually limits the steady mass flux to just the point-star CAK value, with models near critical rotation characterized by a slow, subcritical acceleration. Recent suggestions that such slow outflows might have high enough density to explain disks in Be or B[e] stars are examined in the context of 2D simulations of the ``Wind Compressed Disk'' (WCD) paradigm, together with a review of the tendency for poleward components of the line-driving force to inhibit WCD formation. When one accounts for equatorial gravity darkening, the net tendency is in fact for the relatively bright regions at higher latitude to drive a faster, denser ``bipolar'' outflow. I discuss the potential relevance for the bipolar form of nebulae from LBV stars like η Carinae, but emphasize that, since the large mass loss associated with the eruption of eta Carinae's Homunculus would heavily saturate line-driving, explaining its bipolar form requires development of analogous models for continuum-driven mass loss. I conclude with a discussion of how radiation seems inherently ill-suited to supporting or driving a geometrically thin, but optically thick disk or disk outflow. The disks inferred in Be and B[e] stars may instead be centrifugally ejected, with radiation inducing an ablation flow from the disk surface, and thus perhaps playing a greater role in destroying (rather than creating) an orbiting, circumstellar disk.

Formation of Close in Super-Earths and Mini-Neptunes: Required Disk Masses and their Implications

NASA Astrophysics Data System (ADS)

Schlichting, Hilke E.

2014-11-01

Recent observations by the Kepler space telescope have led to the discovery of more than 4000 exoplanet candidates consisting of many systems with Earth- to Neptune-sized objects that reside well inside the orbit of Mercury around their respective host stars. How and where these close-in planets formed is one of the major unanswered questions in planet formation. Here, we calculate the required disk masses for in situ formation of the Kepler planets. We find that if close-in planets formed as isolation masses, then standard gas-to-dust ratios yield corresponding gas disks that are gravitationally unstable for a significant fraction of systems, ruling out such a scenario. We show that the maximum width of a planet's accretion region in the absence of any migration is 2v esc/Ω, where v esc is the escape velocity of the planet and Ω is the Keplerian frequency, and we use it to calculate the required disk masses for in situ formation with giant impacts. Even with giant impacts, formation without migration requires disk surface densities in solids at semi-major axes of less than 0.1 AU of 103-105 g cm-2, implying typical enhancements above the minimum-mass solar nebular (MMSN) by at least a factor of 20. Corresponding gas disks are below but not far from the gravitational stability limit. In contrast, formation beyond a few AU is consistent with MMSN disk masses. This suggests that the migration of either solids or fully assembled planets is likely to have played a major role in the formation of close-in super-Earths and mini-Neptunes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagen, Lea M. Z.; Hagen, Alex; Seibert, Mark

We provide evidence that UGC 1382, long believed to be a passive elliptical galaxy, is actually a giant low surface brightness (GLSB) galaxy that rivals the archetypical GLSB Malin 1 in size. Like other GLSB galaxies, it has two components: a high surface brightness disk galaxy surrounded by an extended low surface brightness (LSB) disk. For UGC 1382, the central component is a lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk has an effective radius of ∼38 kpc and an extrapolated central surface brightness of ∼26 mag arcsec{sup 2}. Both components have a combinedmore » stellar mass of ∼8 × 10{sup 10} M {sub ⊙}, and are embedded in a massive (10{sup 10} M {sub ⊙}) low-density (<3 M {sub ⊙} pc{sup 2}) HI disk with a radius of 110 kpc, making this one of the largest isolated disk galaxies known. The system resides in a massive dark matter halo of at least 2 × 10{sup 12} M {sub ⊙}. Although possibly part of a small group, its low-density environment likely plays a role in the formation and retention of the giant LSB and HI disks. We model the spectral energy distributions and find that the LSB disk is likely older than the lenticular component. UGC 1382 has UV–optical colors typical of galaxies transitioning through the green valley. Within the LSB disk are spiral arms forming stars at extremely low efficiencies. The gas depletion timescale of ∼10{sup 11} years suggests that UGC 1382 may be a very-long-term resident of the green valley. We find that the formation and evolution of the LSB disk in UGC 1382 is best explained by the accretion of gas-rich LSB dwarf galaxies.« less

Formation and Atmosphere of Complex Organic Molecules of the HH 212 Protostellar Disk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Chin-Fei; Ho, Paul T. P.; Hirano, Naomi

HH 212 is a nearby (400 pc) Class 0 protostellar system recently found to host a “hamburger”-shaped dusty disk with a radius of ∼60 au, deeply embedded in an infalling-rotating flattened envelope. We have spatially resolved this envelope-disk system with the Atacama Large Millimeter/submillimeter Array at up to ∼16 au (0.″04) resolution. The envelope is detected in HCO{sup +} J = 4–3 down to the dusty disk. Complex organic molecules (COMs) and doubly deuterated formaldehyde (D{sub 2}CO) are detected above and below the dusty disk within ∼40 au of the central protostar. The COMs are methanol (CH{sub 3}OH), deuterated methanolmore » (CH{sub 2}DOH), methyl mercaptan (CH{sub 3}SH), and formamide (NH{sub 2}CHO, a prebiotic precursor). We have modeled the gas kinematics in HCO{sup +} and COMs and found a centrifugal barrier (CB) at a radius of ∼44 au, within which a Keplerian rotating disk is formed. This indicates that HCO{sup +} traces the infalling-rotating envelope down to the CB and COMs trace the atmosphere of a Keplerian rotating disk within the CB. The COMs are spatially resolved for the first time, both radially and vertically, in the atmosphere of a disk in the earliest, Class 0 phase of star formation. Our spatially resolved observations of COMs favor their formation in the disk rather than a rapidly infalling (warm) inner envelope. The abundances and spatial distributions of the COMs provide strong constraints on models of their formation and transport in low-mass star formation.« less

Forming Planets in the Hostile Carina Nebula

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-07-01

Can protoplanetary disks form and be maintained around low-mass stars in the harsh environment of a highly active, star-forming nebula? A recent study examines the Carina nebula to answer this question.Crowded ClustersStars are often born in clusters that contain both massive and low-mass stars. The most massive stars in these clusters emit far-ultraviolet and extreme-ultraviolet light that irradiates the region around them, turning the surrounding area into a hostile environment for potential planet formation.Planet formation from protoplanetary disks typically requires timescales of at least 12 million years. Could the harsh radiation from massive stars destroy the protoplanetary disks around low-mass stars by photoevaporation before planets even have a chance to form?Artists impression of a protoplanetary disk. Such disks can be photoevaporated by harsh ultraviolet light from nearby massive stars, causing the disk to be destroyed before planets have a chance to form within them. [ESO/L. Calada]Turning ALMA Toward CarinaA perfect case study for exploring hostile environments is the Carina nebula, located about 7500 lightyears away and home to nearly 100 O-type stars as well as tens of thousands of lower-mass young stars. The Carina population is ~14 Myr old: old enough to form planets within protoplanetary disks, but also old enough that photoevaporation could already have wreaked havoc on those disks.Due to the dense stellar populations in Carinas clusters, this is a difficult region to explore, but the Atacama Large Millimeter-submillimeter Array (ALMA) is up to the task. In a recent study, a team of scientists led by Adal Mesa-Delgado (Pontifical Catholic University of Chile) made use of ALMAs high spatial resolution to image four regions spaced throughout Carina, searching for protoplanetary disks.Detections and Non-DetectionsTwo evaporating gas globules in the Carina nebula, 104-593 and 105-600, that each contain a protoplanetary disk. The top panels are Hubble images of the globules; the bottom panels are ALMA images of the disks detected within them. [Mesa-Delgado et al. 2016]In searching regions outside of the densest, most luminous clusters, the team succeeded in detecting two protoplanetary disks. This region in Carina now marks the most distant massive cluster in which disks have ever been imaged! The discovered disks have radii of roughly 60 AU and masses of 30 and 50 Jupiter masses and given their ages, its entirely plausible that planets are actively forming in these disks.Equally important: Mesa-Delgado and collaborators failed to detect any indication of disks in the core of Trumpler 14, a cluster in Carina that is home to some of the most massive and luminous stars in the Galaxy. This non-detection suggests that the particularly harsh environment of Trumpler 14 is too brutal for disks within it to survive.These observations provide new clues as to where we should be looking to study planet formation: less dense regions in star-forming nebulae seem to be locations that can support giant-planet-forming disks, whereas the harsh radiation fields of especially dense subclusters seem to cause the rapid destruction of such disks.CitationA. Mesa-Delgado et al 2016 ApJ 825 L16. doi:10.3847/2041-8205/825/1/L16

ANALYSIS OF TERRESTRIAL PLANET FORMATION BY THE GRAND TACK MODEL: SYSTEM ARCHITECTURE AND TACK LOCATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brasser, R.; Ida, S.; Matsumura, S.

2016-04-20

The Grand Tack model of terrestrial planet formation has emerged in recent years as the premier scenario used to account for several observed features of the inner solar system. It relies on the early migration of the giant planets to gravitationally sculpt and mix the planetesimal disk down to ∼1 au, after which the terrestrial planets accrete from material remaining in a narrow circumsolar annulus. Here, we investigate how the model fares under a range of initial conditions and migration course-change (“tack”) locations. We run a large number of N-body simulations with tack locations of 1.5 and 2 au andmore » test initial conditions using equal-mass planetary embryos and a semi-analytical approach to oligarchic growth. We make use of a recent model of the protosolar disk that takes into account viscous heating, includes the full effect of type 1 migration, and employs a realistic mass–radius relation for the growing terrestrial planets. Our results show that the canonical tack location of Jupiter at 1.5 au is inconsistent with the most massive planet residing at 1 au at greater than 95% confidence. This favors a tack farther out at 2 au for the disk model and parameters employed. Of the different initial conditions, we find that the oligarchic case is capable of statistically reproducing the orbital architecture and mass distribution of the terrestrial planets, while the equal-mass embryo case is not.« less

VARIABILITY OF DISK EMISSION IN PRE-MAIN SEQUENCE AND RELATED STARS. III. EXPLORING STRUCTURAL CHANGES IN THE PRE-TRANSITIONAL DISK IN HD 169142

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, Kevin R.; Sitko, Michael L.; Swearingen, Jeremy R.

We present near-IR (NIR) and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between ∼1.5-10 μm over a maximum timescale of 10 yr. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the ≲1 AU region of the disk. Through analysis of the Pa β and Brmore » γ lines in our data we derive a mass accretion rate in 2013 May of M-dot ≈ (1.5-2.7) × 10{sup –9} M {sub ☉} yr{sup –1}. We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 yr of observations. We find that shifting the outer edge (r ≈ 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ∼40-70 AU dark ring imaged in the NIR by Quanz et al. and Momose et al. and at 7 mm by Osorio et al. may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.« less

Can accretion disk properties observationally distinguish black holes from naked singularities?

NASA Astrophysics Data System (ADS)

Kovács, Z.; Harko, T.

2010-12-01

Naked singularities are hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon. Penrose has proposed a conjecture, according to which there exists a cosmic censor who forbids the occurrence of naked singularities. Distinguishing between astrophysical black holes and naked singularities is a major challenge for present day observational astronomy. In the context of stationary and axially symmetrical geometries, a possibility of differentiating naked singularities from black holes is through the comparative study of thin accretion disks properties around rotating naked singularities and Kerr-type black holes, respectively. In the present paper, we consider accretion disks around axially-symmetric rotating naked singularities, obtained as solutions of the field equations in the Einstein-massless scalar field theory. A first major difference between rotating naked singularities and Kerr black holes is in the frame dragging effect, the angular velocity of a rotating naked singularity being inversely proportional to its spin parameter. Because of the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures that could discriminate between black holes and naked singularities. For specific values of the spin parameter and of the scalar charge, the energy flux from the disk around a rotating naked singularity can exceed by several orders of magnitude the flux from the disk of a Kerr black hole. In addition to this, it is also shown that the conversion efficiency of the accreting mass into radiation by rotating naked singularities is always higher than the conversion efficiency for black holes, i.e., naked singularities provide a much more efficient mechanism for converting mass into radiation than black holes. Thus, these observational signatures may provide the necessary tools from clearly distinguishing rotating naked singularities from Kerr-type black holes.

Liners and Low Luminosity AGN in the ROSAT Database

NASA Technical Reports Server (NTRS)

Elvis, Martin; West, Donald K. (Technical Monitor)

2003-01-01

This program has led to a series of papers being written and published in the Astrophysical Journal. Together these papers try to explain major parts of the LINER and low luminosity AGN puzzle. One paper ('Accretion Disk Instabilities, Cold Dark Matter Models, and Their Role in Quasar Evolution', Hatziminaoglou E., Siemiginowska A., & Elvis M., 2001, ApJ, 547, 90) describes an analytical model for the evolution of the quasar luminosity function. By combining the Press-Schechter formalism for the masses of initial structures with the luminosity distribution for a population of single mass black holes given by an unstable accretion disk an almost complete end-to-end physics-based model of quasar evolution is produced. In this model black holes spend 75% of their time in a low accretion state (at L(Edd)). This low state population of black holes is likely to be observed as the LINER and low luminosity AGNs in the local universe. Another paper ('Broad Emission Line Regions in AGN: the Link with the Accretion Power', Nicastro F., 2000, ApJ Letters, 530, L65) gives a physical basis for why low state black holes appear as LINERS. By linking the Lightman-Eardley instability in an accretion disk to the ori.gin of a wind that contains the broad emission line cloud material this model explains the large widths seen in these lines as being the Keplerian velocity of the disk at the instability radius. For LINERS the key is that below an accretion rate of 10(exp -3)M(sub Edd)the Lightman-Eardley instability falls within the innermost stable orbit of the disk, and so leaves the entire disk stable. No wind occurs, and so no broad emission lines are seen. Most LINERS are likely to be black holes in this low state. Tests of this model are being considered.

On the formation and expansion of H II regions

NASA Technical Reports Server (NTRS)

Franco, Jose; Tenorio-Tagle, Guillermo; Bodenheimer, Peter

1990-01-01

The evolution of H II regions in spherical clouds with small, constant-density cores and power-law density distributions r exp -w outside the core is described analytically. It is found that there is a critical exponent above which the cloud becomes completely ionized. Its value in the formation phase depends on the initial conditions, but it has a well-defined value w(crit) = 3/2 during the expansion phase. For w less than w(crit), the radius of the H II region grows at a given rate, while neutral mass accumulates in the interphase between the ionization and shock fronts. For w = w(crit), the fronts move together without mass accumulation. Cases with w greater than w(crit) lead to the champagne phase: once the cloud is fully ionized, the expansion becomes supersonic. For self-gravitating disks without magnetic fields, the main features include a new 'variable-size' stage. The initial shape of the H II region has a critical point beyond which the disk becomes completely ionized.

Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

NASA Astrophysics Data System (ADS)

Koda, Jin

2013-01-01

"The GALEX UV satellite discovered tantalizing evidence of star formation (SF) far beyond the optical edge of galactic disks (i.e. extended UV disk, or XUV disk). This discovery provides a new opportunity for studying SF in the exceedingly low-density environment (˜1/10 of typical SF density), spurring intense debate on the universality of the initial mass function (IMF) in such exceptional environments. Our pilot S-Cam study of M83’s XUV disk led to support for the universal IMF at least in M83 (Koda et al. 2012). We propose an expansion of the pilot study by an order of magnitude, by observing additional 6 XUV disks in NA656(Hα), B, I, and R-band with S-Cam in S13A. In conjunction with GALEX UV bands, these images will reveal the presence of O stars (Hα; NA656-R) and O&B stars (UV) in stellar clusters -thus, constraining the high-mass end of the IMF. These multi-broadband images will enable us to determine the masses of the clusters with much improved accuracy (previously, relied only on R). The proposed observations will not only increase the statistical significance of our previous result, but also enable us to analyze the stochastic effect of IMF sampling in very low-mass - clusters (10^(2+3) M_sun) - the regime about which there is much ongoing debate."

Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

NASA Astrophysics Data System (ADS)

Koda, Jin

2013-01-01

"The GALEX UV satellite discovered tantalizing evidence of star formation (SF) far beyond the optical edge of galactic disks (i.e. extended UV disk, or XUV disk). This discovery provides a new opportunity for studying SF in the exceedingly low-density environment (˜1/10 of typical SF density), spurring intense debate on the universality of the initial mass function (IMF) in such exceptional environments. Our pilot S-Cam study of M83’s XUV disk led to support for the universal IMF at least in M83 (Koda et al. 2012). We propose an expansion of the pilot study by about an order of magnitude, by observing 6 XUV disks in NA656(Hα), B, I, and R-band with S-Cam in S13B. In conjunction with GALEX UV bands, these images will reveal the presence of O stars (Hα) and O&B stars (UV) in stellar clusters -thus, constraining the high-mass end of the IMF. These multi-broadband images will enable us to determine the masses of the clusters with much improved accuracy (previously, relied only on R). The proposed observations will not only increase the statistical significance of our previous result, but also enable us to analyze the stochastic effect of IMF sampling in very low-mass - clusters (10^{2+3} M_sun) - the regime of ongoing debate. Previously allocated 1+2 nights were cancelled (telescope failures)."

Probing the Initial Mass Function in Extended Ultraviolet (XUV) Disks

NASA Astrophysics Data System (ADS)

Koda, Jin

2014-01-01

The GALEX UV satellite discovered tantalizing evidence of star formation (SF) far beyond the optical edge of galactic disks (i.e. XUV disk). This discovery provides a new opportunity for studying SF in the exceedingly low-density environment (~1/10 of typical SF density), spurring intense debate on the universality of the initial mass function (IMF) in such exceptional environments. Our pilot study led to support for the universal IMF at least in M83’s XUV disk (Koda et al. 2012). We propose an expansion of the pilot study by about an order of magnitude, by observing total ~ 10 XUV disks (6 disks in S14A) in NA656(Halpha), B, I, and R-band with S-Cam. In conjunction with GALEX UV bands, these images will reveal the presence of O stars (Halpha) and O&B stars (UV) in stellar clusters -thus, constraining the high-mass end of the IMF. These multi-broadband images will enable us to determine the masses of the clusters with much improved accuracy (previously, relied only on R). This project will not only increase the statistical significance of our previous result, but also enable us to analyze the stochastic effect of IMF sampling in very low-mass clusters (102-3 Msun) - the regime of ongoing debate. This proposal will complete this on-going project with S-Cam.

Accretion Disks Around Binary Black Holes of Unequal Mass: GRMHD Simulations Near Decoupling

NASA Technical Reports Server (NTRS)

Gold, Roman; Paschalidis, Vasileios; Etienne, Zachariah B.; Shapiro, Stuart L.; Pfeiffer, Harald, P.

2013-01-01

We report on simulations in general relativity of magnetized disks onto black hole binaries. We vary the binary mass ratio from 1:1 to 1:10 and evolve the systems when they orbit near the binary disk decoupling radius. We compare (surface) density profiles, accretion rates (relative to a single, non-spinning black hole), variability, effective alpha-stress levels and luminosities as functions of the mass ratio. We treat the disks in two limiting regimes: rapid radiative cooling and no radiative cooling. The magnetic field lines clearly reveal jets emerging from both black hole horizons and merging into one common jet at large distances. The magnetic fields give rise to much stronger shock heating than the pure hydrodynamic flows, completely alter the disk structure, and boost accretion rates and luminosities. Accretion streams near the horizons are among the densest structures; in fact, the 1:10 no-cooling evolution results in a refilling of the cavity. The typical effective temperature in the bulk of the disk is approx. 10(exp5) (M / 10(exp 8)M solar mass (exp -1/4(L/L(sub edd) (exp 1/4K) yielding characteristic thermal frequencies approx. 10 (exp 15) (M /10(exp 8)M solar mass) (exp -1/4(L/L (sub edd) (1+z) (exp -1)Hz. These systems are thus promising targets for many extragalactic optical surveys, such as LSST, WFIRST, and PanSTARRS.

An ALMA Survey of Protoplanetary Disks in the σ Orionis Cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ansdell, M.; Williams, J. P.; Marel, N. van der

2017-05-01

The σ  Orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age (∼3–5 Myr) is comparable to the median disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around σ  Orionis members with M {sub *} ≳ 0.1  M {sub ⊙}. Our observations cover the 1.33 mm continuum and several CO J  = 2–1 lines: out of 92 sources, we detect 37 in the millimeter continuum and 6 in {sup 12}CO, 3 in {sup 13}CO, and none in C{sup 18}O. Using the continuum emission to estimate dust mass, we find only 11more » disks with M {sub dust} ≳ 10  M {sub ⊕}, indicating that after only a few Myr of evolution most disks lack sufficient dust to form giant planet cores. Stacking the individually undetected continuum sources limits their average dust mass to 5×  lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. Comparing the protoplanetary disk population in σ  Orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the M {sub dust}– M {sub *} relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. External photoevaporation from the central O9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of CO detections exist at projected separations of >1.5 pc. Collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few Myr of age.« less

Numerical Simulations of Wind Accretion in Symbiotic Binaries

NASA Astrophysics Data System (ADS)

de Val-Borro, M.; Karovska, M.; Sasselov, D.

2009-08-01

About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the mass transfer and formation of accretion disks around the secondary in detached systems consisting of an asymptotic giant branch (AGB) mass-losing star and an accreting companion. The presence of mass outflows is studied as a function of mass-loss rate, wind temperature, and binary orbital parameters. A two-dimensional hydrodynamical model is used to study the stability of mass transfer in wind accreting symbiotic binary systems. In our simulations we use an adiabatic equation of state and a modified version of the isothermal approximation, where the temperature depends on the distance from the mass losing star and its companion. The code uses a block-structured adaptive mesh refinement method that allows us to have high resolution at the position of the secondary and resolve the formation of bow shocks and accretion disks. We explore the accretion flow between the components and formation of accretion disks for a range of orbital separations and wind parameters. Our results show the formation of stream flow between the stars and accretion disks of various sizes for certain orbital configurations. For a typical slow and massive wind from an AGB star the flow pattern is similar to a Roche lobe overflow with accretion rates of 10% of the mass loss from the primary. Stable disks with exponentially decreasing density profiles and masses of the order 10-4 solar masses are formed when wind acceleration occurs at several stellar radii. The disks are geometrically thin with eccentric streamlines and close to Keplerian velocity profiles. The formation of tidal streams and accretion disks is found to be weakly dependent on the mass loss from the AGB star. Our simulations of gravitationally focused wind accretion in symbiotic binaries show the formation of stream flows and enhanced accretion rates onto the compact component. We conclude that mass transfer through a focused wind is an important mechanism in wind accreting interacting binaries and can have a significant impact on the evolution of the binary itself and the individual components.

ECO and RESOLVE: Galaxy Disk Growth in Environmental Context

NASA Astrophysics Data System (ADS)

Moffett, Amanda J.; Kannappan, Sheila J.; Berlind, Andreas A.; Eckert, Kathleen D.; Stark, David V.; Hendel, David; Norris, Mark A.; Grogin, Norman A.

2015-10-01

We study the relationships between galaxy environments and galaxy properties related to disk (re)growth, considering two highly complete samples that are approximately baryonic mass limited into the high-mass dwarf galaxy regime, the Environmental COntext catalog (data release herein) and the B-semester region of the REsolved Spectroscopy Of a Local VolumE survey. We quantify galaxy environments using both group identification and smoothed galaxy density field methods. We use by-eye and quantitative morphological classifications plus atomic gas content measurements and estimates. We find that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright disk host galaxies all become distinctly more common below group halo mass ˜ {10}11.5 {M}⊙ , implying that this low group halo mass regime may be a preferred regime for significant disk growth activity. We also find that blue early-type and blue late-type galaxies inhabit environments of similar group halo mass at fixed baryonic mass, consistent with a scenario in which blue early-types can regrow late-type disks. In fact, we find that the only significant difference in the typical group halo mass inhabited by different galaxy classes is for satellite galaxies with different colors, where at fixed baryonic mass red early- and late-types have higher typical group halo masses than blue early- and late-types. More generally, we argue that the traditional morphology-environment relation (i.e., that denser environments tend to have more early-types) can be largely attributed to the morphology-galaxy mass relation for centrals and the color-environment relation for satellites.

Black holes, disks, and jets following binary mergers and stellar collapse: The narrow range of electromagnetic luminosities and accretion rates.

PubMed

Shapiro, Stuart L

2017-05-15

We have performed magnetohydrodynamic simulations in general relativity of binary neutron star and binary black hole-neutron star mergers, as well as the magnetorotational collapse of supermassive stars. In many cases the outcome is a spinnng black hole (BH) immersed in a magnetized disk, with a jet emanating from the poles of the BH. While their formation scenarios differ and their BH masses, as well as their disk masses, densities, and magnetic field strengths, vary by orders of magnitude, these features conspire to generate jet Poynting luminosities that all lie in the same, narrow range of ~10 52±1 erg s -1 . A similar result applies to their BH accretion rates upon jet launch, which is ~0.1-10 M ⊙ s -1 . We provide a simple model that explains these unanticipated findings. Interestingly, these luminosities reside in the same narrow range characterizing the observed luminosity distributions of over 400 short and long GRBs with distances inferred from spectroscopic redshifts or host galaxies. This result, together with the GRB lifetimes predicted by the model, supports the belief that a compact binary merger is the progenitor of an SGRB, while a massive, stellar magnetorotational collapse is the progenitor of an LGRB.

Black holes, disks, and jets following binary mergers and stellar collapse: The narrow range of electromagnetic luminosities and accretion rates

PubMed Central

Shapiro, Stuart L.

2018-01-01

We have performed magnetohydrodynamic simulations in general relativity of binary neutron star and binary black hole-neutron star mergers, as well as the magnetorotational collapse of supermassive stars. In many cases the outcome is a spinnng black hole (BH) immersed in a magnetized disk, with a jet emanating from the poles of the BH. While their formation scenarios differ and their BH masses, as well as their disk masses, densities, and magnetic field strengths, vary by orders of magnitude, these features conspire to generate jet Poynting luminosities that all lie in the same, narrow range of ~1052±1 erg s−1. A similar result applies to their BH accretion rates upon jet launch, which is ~0.1–10 M⊙ s−1. We provide a simple model that explains these unanticipated findings. Interestingly, these luminosities reside in the same narrow range characterizing the observed luminosity distributions of over 400 short and long GRBs with distances inferred from spectroscopic redshifts or host galaxies. This result, together with the GRB lifetimes predicted by the model, supports the belief that a compact binary merger is the progenitor of an SGRB, while a massive, stellar magnetorotational collapse is the progenitor of an LGRB. PMID:29881790

Interaction of the stream from L 1 with the outer edge of the accretion disk in a cataclysmic variable

NASA Astrophysics Data System (ADS)

Kaigorodov, P. V.; Bisikalo, D. V.; Kurbatov, E. P.

2017-08-01

Vertical oscillations of the gas at the outer edge of the accretion disk in a semi-detached binary due to interaction with the stream of matter from the inner Lagrangian point L 1 are considered. Mixing of the matter from the stream from L 1 with matter of the disk halo results in the formation of a system of two diverging shocks and a contact discontinuity, or so-called "hot line". The passage of matter through the region of the hot line leads to an increase in its vertical velocity and a thickening of the disk at phases 0.7-0.8. Subsequently, the matter moving along the outer edge of the disk also experiences vertical oscillations, forming secondary maxima at phases 0.2-0.4. It is shown that, for systems with component mass ratios of 0.6, these oscillations will be amplified with each passage of the matter through the hotline zone, while the observations will be quenched in systems with component mass ratios 0.07 and 7. The most favorable conditions for the flow of matter from the stream through the edge of the disk arise for component mass ratios 0.62. A theoretical relation between the phases of disk thickenings and the component mass ratio of the system is derived.

REMOVING BIASES IN RESOLVED STELLAR MASS MAPS OF GALAXY DISKS THROUGH SUCCESSIVE BAYESIAN MARGINALIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-García, Eric E.; González-Lópezlira, Rosa A.; Bruzual A, Gustavo

2017-01-20

Stellar masses of galaxies are frequently obtained by fitting stellar population synthesis models to galaxy photometry or spectra. The state of the art method resolves spatial structures within a galaxy to assess the total stellar mass content. In comparison to unresolved studies, resolved methods yield, on average, higher fractions of stellar mass for galaxies. In this work we improve the current method in order to mitigate a bias related to the resolved spatial distribution derived for the mass. The bias consists in an apparent filamentary mass distribution and a spatial coincidence between mass structures and dust lanes near spiral arms.more » The improved method is based on iterative Bayesian marginalization, through a new algorithm we have named Bayesian Successive Priors (BSP). We have applied BSP to M51 and to a pilot sample of 90 spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. By quantitatively comparing both methods, we find that the average fraction of stellar mass missed by unresolved studies is only half what previously thought. In contrast with the previous method, the output BSP mass maps bear a better resemblance to near-infrared images.« less

Narrowband HST images of M87: Evidence for a disk of ionized gas around a massive black hole

NASA Technical Reports Server (NTRS)

Ford, Holland C.; Harms, Richard J.; Tsvetanov, Zlatan I.; Hartig, George F.; Dressel, Linda L.; Kriss, Gerard A.; Bohlin, Ralph C.; Davidsen, Arthur F.; Margon, Bruce; Kochhar, Ajay K.

1994-01-01

We present Hubble Space Telescope Wide Field/Planetary Camera-2 (HST WFPC2) narrowband H-alpha + (N II) images of M87 which show a small disk of ionized gas with apparent spiral structure surrounding the nucleus of M87. The jet projects approximately 19.5 deg from the minor axis of the disk, which suggests that the jet is approximately normal to the disk. In a companion Letter, Harms et al. measure the radial velocities at r = +/- 0.25 sec along a line perpendicular to the jet, showing that one side of the disk is approaching at 500 +/- 50 km/s and the other side of the disk is receding at 500 +/- 50 km/s. Absorption associated with the disk and the sense of rotation imply that the apparent spiral arms trail the rotation. The observed radial velocites corrected for a 42 deg inclination of the disk imply rotation at +/- 750 km/s. Analysis of velocity measurements at four positions near the nucleus gives a total mass of approximately 2.4 +/- 0.7 x 10(exp 9) solar mass within 18 pc of the nucleus, and a mass-to-light ratio (M/L)(sub I) = 170. We conclude that there is a disk of ionized gas feeding a massive black hole in the center of M87.

ROTATIONAL EVOLUTION OF MAGNETARS IN THE PRESENCE OF A FALLBACK DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tong, H.; Wang, W.; Liu, X. W.

2016-12-20

Magnetars may have a strong surface dipole field. Observationally, two magnetars may have passive fallback disks. In the presence of a fallback disk, the rotational evolution of magnetars may be changed. In the self-similar fallback disk model, it is found that (1) when the disk mass is significantly lower than 10{sup −6}  M {sub ⊙}, the magnetar is unaffected by the fallback disk and it will be a normal magnetar. (2) When the disk mass is high but the surface dipole field of the magnetar is about or below 10{sup 14} G, the magnetar will also be a normal magnetar.more » A magnetar plus a passive fallback disk system is expected. This may correspond to the observations of magnetars 4U 0142+61 and 1E 2259+586. (3) When the disk mass is high and the surface dipole field of the magnetar is as high as 4 × 10{sup 15} G, the magnetar will evolve from the ejector phase to the propeller phase, and then enter rotational equilibrium. The magnetar will be slowed down quickly in the propeller phase. The final rotational period can be as high 2 × 10{sup 4} s. This may correspond to the super-slow magnetar in the supernova remnant RCW 103. Therefore, the three types of magnetars can be understood in a unified way.« less

A New Determination of the Luminosity Function of the Galactic Halo.

NASA Astrophysics Data System (ADS)

Dawson, Peter Charles

The luminosity function of the galactic halo is determined by subtracting from the observed numbers of proper motion stars in the LHS Catalogue the expected numbers of main-sequence, degenerate, and giant stars of the disk population. Selection effects are accounted for by Monte Carlo simulations based upon realistic colour-luminosity relations and kinematic models. The catalogue is shown to be highly complete, and a calibration of the magnitude estimates therein is presented. It is found that, locally, the ratio of disk to halo material is close to 950, and that the mass density in main sequence and subgiant halo stars with 3 < M(,v) < 14 is about 2 x 10('-5) M(,o) pc('-3). With due allowance for white dwarfs and binaries, and taking into account the possibility of a moderate rate of halo rotation, it is argued that the total density does not much exceed 5 x 10('-5) M(,o) pc('-3), in which case the total mass interior to the sun is of the order of 5 x 10('8) M(,o) for a density distribution which projects to a de Vaucouleurs r(' 1/4) law. It is demonstrated that if the Wielen luminosity function is a faithful representation of the stellar distribution in the solar neighbourhood, then the observed numbers of large proper motion stars are inconsistent with the presence of an intermediate popula- tion at the level, and with the kinematics advocated recently by Gilmore and Reid. The initial mass function (IMF) of the halo is considered, and weak evidence is presented that its slope is at least not shallower than that of the disk population IMF. A crude estimate of the halo's age, based on a comparison of the main sequence turnoff in the reduced proper motion diagram with theoretical models is obtained; a tentative lower limit is 15 Gyr with a best estimate of between 15 and 18 Gyr. Finally, the luminosity function obtained here is compared with those determined in other investigations.

The evidence for clumpy accretion in the Herbig Ae star HR 5999

NASA Technical Reports Server (NTRS)

Perez, M. R.; Grady, C. A.; The, P. S.

1993-01-01

Analysis of IUE high- and low-dispersion spectra of the young Herbig Ae star HR 5999 (HD 144668) covering 1978-1992 revealed dramatic changes in the Mg II h and k (2795.5, 2802.7 A) emission profiles, changes in the column density and distribution in radial velocity of accreting gas, and flux in the Ly(alpha), O I, and C IV emission lines, which are correlated with the UV excess luminosity. Variability in the spectral type inferred from the UV spectral energy distribution, ranging from A5 IV-III in high state to A7 III in the low state, was also observed. The trend of earlier inferred spectral type with decreasing wavelength and with increasing UV continuum flux has previously been noted as a signature of accretion disks in lower mass pre-main sequence stars (PMS) and in systems undergoing FU Orionis-type outbursts. Our data represent the first detection of similar phenomena in an intermediate mass (M greater than or equal to 2 solar mass) PMS star. Recent IUE spectra show gas accreting toward the star with velocities as high as plus 300 km/s, much as is seen toward beta Pic, and suggest that we also view this system through the debris disk. The absence of UV lines with the rotational broadening expected given the optical data (A7 IV, V sini=180 plus or minus 20 km/s for this system) also suggests that most of the UV light originates in the disk, even in the low continuum state. The dramatic variability in the column density of accreting gas, is consistent with clumpy accretion, such as has been observed toward beta Pic, is a hallmark of accretion onto young stars, and is not restricted to the clearing phase, since detectable amounts of accretion are present for stars with 0.5 Myr less than t(sub age) less than 2.8 Myr. The implications for models of beta Pic and similar systems are briefly discussed.

The Growth of Stellar Mass Black Hole Binaries Trapped in the Accretion Disks of Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Yi, Shu-Xu; Cheng, K. S.; Taam, Ronald E.

2018-06-01

Among the four black hole (BH) binary merger events detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO), six progenitor BHs have masses greater than 20 M ⊙. The existence of such massive BHs suggests that extreme metal-poor stars are the progenitors. An alternative possibility, that a pair of stellar mass BHs each with mass ∼7 M ⊙ increases to >20 M ⊙ via accretion from a disk surrounding a supermassive BH (SMBH) in an active galactic nucleus (AGN), is considered. The growth of mass of the binary and the transfer of orbital angular momentum to the disk accelerates the merger. Based on the recent numerical work of Tang et al., it is found that, in the disk of a low-mass AGN with mass ∼106 M ⊙ and Eddington ratio >0.01, the mass of an individual BH in the binary can grow to >20 M ⊙ before coalescence, provided that accretion takes place at a rate more than 10 times the Eddington value. This mechanism predicts a new class of gravitational wave (GW) sources involving the merger of two extreme Kerr black holes associated with AGNs and a possible electromagnetic wave counterpart.

MASS TRANSPORT AND TURBULENCE IN GRAVITATIONALLY UNSTABLE DISK GALAXIES. II. THE EFFECTS OF STAR FORMATION FEEDBACK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldbaum, Nathan J.; Krumholz, Mark R.; Forbes, John C., E-mail: ngoldbau@illinois.edu

2016-08-10

Self-gravity and stellar feedback are capable of driving turbulence and transporting mass and angular momentum in disk galaxies, but the balance between them is not well understood. In the previous paper in this series, we showed that gravity alone can drive turbulence in galactic disks, regulate their Toomre Q parameters to ∼1, and transport mass inwards at a rate sufficient to fuel star formation in the centers of present-day galaxies. In this paper we extend our models to include the effects of star formation feedback. We show that feedback suppresses galaxies’ star formation rates by a factor of ∼5 andmore » leads to the formation of a multi-phase atomic and molecular interstellar medium. Both the star formation rate and the phase balance produced in our simulations agree well with observations of nearby spirals. After our galaxies reach steady state, we find that the inclusion of feedback actually lowers the gas velocity dispersion slightly compared to the case of pure self-gravity, and also slightly reduces the rate of inward mass transport. Nevertheless, we find that, even with feedback included, our galactic disks self-regulate to Q ∼ 1, and transport mass inwards at a rate sufficient to supply a substantial fraction of the inner disk star formation. We argue that gravitational instability is therefore likely to be the dominant source of turbulence and transport in galactic disks, and that it is responsible for fueling star formation in the inner parts of galactic disks over cosmological times.« less

On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

NASA Astrophysics Data System (ADS)

Windhorst, Rogier A.; Timmes, F. X.; Wyithe, J. Stuart B.; Alpaslan, Mehmet; Andrews, Stephen K.; Coe, Daniel; Diego, Jose M.; Dijkstra, Mark; Driver, Simon P.; Kelly, Patrick L.; Kim, Duho

2018-02-01

We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z ≃ 7–17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z≳ 7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be μ ≃ {10}4{--}{10}5, with rise times of hours and decline times of ≲ 1 year for cluster transverse velocities of {v}T≲ 1000 km s‑1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3–30 lensing clusters to {AB}≲ 29 mag over a decade.

PLANETARY SYSTEM FORMATION IN THE PROTOPLANETARY DISK AROUND HL TAURI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akiyama, Eiji; Hasegawa, Yasuhiro; Hayashi, Masahiko

2016-02-20

We reprocess the Atacama Large Millimeter/Submillimeter Array (ALMA) long-baseline science verification data taken toward HL Tauri. Assuming the observed gaps are opened up by currently forming, unseen bodies, we estimate the mass of such hypothetical bodies based on the following two approaches: the Hill radius analysis and a more elaborate approach developed from the angular momentum transfer analysis in gas disks. For the former, the measured gap widths are used for estimating the mass of the bodies, while for the latter, the measured gap depths are utilized. We show that their masses are comparable to or less than the mass of Jovian planets.more » By evaluating Toomre’s gravitational instability (GI) condition and cooling effect, we find that the GI might be a mechanism to form the bodies in the outer region of the disk. As the disk might be gravitationally unstable only in the outer region of the disk, inward planetary migration would be needed to construct the current architecture of the observed disk. We estimate the gap-opening mass and show that type II migration might be able to play such a role. Combining GIs with inward migration, we conjecture that all of the observed gaps may be a consequence of bodies that might have originally formed at the outer part of the disk, and have subsequently migrated to the current locations. While ALMA’s unprecedented high spatial resolution observations can revolutionize our picture of planet formation, more dedicated observational and theoretical studies are needed to fully understand the HL Tauri images.« less

A multi-wavelength interferometric study of the massive young stellar object IRAS 13481-6124

NASA Astrophysics Data System (ADS)

Boley, Paul A.; Kraus, Stefan; de Wit, Willem-Jan; Linz, Hendrik; van Boekel, Roy; Henning, Thomas; Lacour, Sylvestre; Monnier, John D.; Stecklum, Bringfried; Tuthill, Peter G.

2016-02-01

We present new mid-infrared interferometric observations of the massive young stellar object IRAS 13481-6124, using VLTI/MIDI for spectrally-resolved, long-baseline measurements (projected baselines up to ~120 m) and GSO/T-ReCS for aperture-masking interferometry in five narrow-band filters (projected baselines of ~1.8-6.4 m) in the wavelength range of 7.5-13μm. We combine these measurements with previously-published interferometric observations in the K and N bands in order to assemble the largest collection of infrared interferometric observations for a massive YSO to date. Using a combination of geometric and radiative-transfer models, we confirm the detection at mid-infrared wavelengths of the disk previously inferred from near-infrared observations. We show that the outflow cavity is also detected at both near- and mid-infrared wavelengths, and in fact dominates the mid-infrared emission in terms of total flux. For the disk, we derive the inner radius (~1.8 mas or ~6.5 AU at 3.6 kpc), temperature at the inner rim (~1760 K), inclination (~48°) and position angle (~107°). We determine that the mass of the disk cannot be constrained without high-resolution observations in the (sub-)millimeter regime or observations of the disk kinematics, and could be anywhere from ~10-3 to 20M⊙. Finally, we discuss the prospects of interpreting the spectral energy distributions of deeply-embedded massive YSOs, and warn against attempting to infer disk properties from the spectral energy distribution. Based in part on observations with the Very Large Telescope Interferometer of the European Southern Observatory, under program IDs 384.C-0625, 086.C-0543, 091.C-0357.

GASP. IV. A Muse View of Extreme Ram-pressure-stripping in the Plane of the Sky: The Case of Jellyfish Galaxy JO204

NASA Astrophysics Data System (ADS)

Gullieuszik, Marco; Poggianti, Bianca M.; Moretti, Alessia; Fritz, Jacopo; Jaffé, Yara L.; Hau, George; Bischko, Jan C.; Bellhouse, Callum; Bettoni, Daniela; Fasano, Giovanni; Vulcani, Benedetta; D’Onofrio, Mauro; Biviano, Andrea

2017-09-01

In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP) survey, we present the characterization of JO204, a jellyfish galaxy in A957, a relatively low-mass cluster with M=4.4× {10}14 {M}ȯ . This galaxy shows a tail of ionized gas that extends up to 30 kpc from the main body in the opposite direction of the cluster center. No gas emission is detected in the galaxy outer disk, suggesting that gas-stripping is proceeding outside-in. The stellar component is distributed as a regular disk galaxy; the stellar kinematics shows a symmetric rotation curve with a maximum radial velocity of 200 km s‑1 out to 20 kpc from the galaxy center. The radial velocity of the gas component in the central part of the disk follows the distribution of the stellar component; the gas kinematics in the tail retains the rotation of the galaxy disk, indicating that JO204 is moving at high speed in the intracluster medium. Both the emission and radial-velocity maps of the gas and stellar components indicate ram-pressure as the most likely primary mechanism for gas-stripping, as expected given that JO204 is close to the cluster center and it is likely at the first infall in the cluster. The spatially resolved star formation history of JO204 provides evidence that the onset of ram-pressure-stripping occurred in the last 500 Myr, quenching the star formation activity in the outer disk, where the gas has been already completely stripped. Our conclusions are supported by a set of hydrodynamic simulations.

ALMA Resolves the Nuclear Disks of Arp 220

NASA Astrophysics Data System (ADS)

Scoville, Nick; Murchikova, Lena; Walter, Fabian; Vlahakis, Catherine; Koda, Jin; Vanden Bout, Paul; Barnes, Joshua; Hernquist, Lars; Sheth, Kartik; Yun, Min; Sanders, David; Armus, Lee; Cox, Pierre; Thompson, Todd; Robertson, Brant; Zschaechner, Laura; Tacconi, Linda; Torrey, Paul; Hayward, Christopher C.; Genzel, Reinhard; Hopkins, Phil; van der Werf, Paul; Decarli, Roberto

2017-02-01

We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at λ =2.6 {mm}. The internal gas distribution and kinematics of both galactic nuclei are well resolved for the first time. In the west nucleus, the major gas and dust emission extends out to 0.″2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor of 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick ({τ }2.6{mm}˜ 1) at λ =2.6 {mm} with a dust brightness temperature of ˜147 K. The column of interstellar matter at this nucleus is {N}{{H}2}≥slant 2× {10}26 cm-2, corresponding to ˜900 gr cm-2. The east nucleus is more elongated with radial extent 0.″3 or ˜111 pc. The derived kinematics of the nuclear disks provide a good fit to the line profiles, yielding the emissivity distributions, the rotation curves, and velocity dispersions. In the west nucleus, there is evidence of a central Keplerian component requiring a central mass of 8 × 108 {M}⊙ . The intrinsic widths of the emission lines are {{Δ }}v({FWHM})=250 (west) and 120 (east) km s-1. Given the very short dissipation timescales for turbulence (≲105 years), we suggest that the line widths may be due to semicoherent motions within the nuclear disks. The symmetry of the nuclear disk structures is impressive, implying the merger timescale is significantly longer than the rotation period of the disks.

PROTOPLANETARY DISK HEATING AND EVOLUTION DRIVEN BY SPIRAL DENSITY WAVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rafikov, Roman R., E-mail: rrr@ias.edu

2016-11-10

Scattered light imaging of protoplanetary disks often reveals prominent spiral arms, likely excited by massive planets or stellar companions. Assuming that these arms are density waves, evolving into spiral shocks, we assess their effect on the thermodynamics, accretion, and global evolution of the disk. We derive analytical expressions for the direct (irreversible) heating, angular momentum transport, and mass accretion rate induced by disk shocks of arbitrary amplitude. These processes are very sensitive to the shock strength. We show that waves of moderate strength (density jump at the shock ΔΣ/Σ ∼ 1) result in negligible disk heating (contributing at the ∼1%more » level to the energy budget) in passive, irradiated protoplanetary disks on ∼100 au scales, but become important within several au. However, shock heating is a significant (or even dominant) energy source in disks of cataclysmic variables, stellar X-ray binaries, and supermassive black hole binaries, heated mainly by viscous dissipation. Mass accretion induced by the spiral shocks is comparable to (or exceeds) the mass inflow due to viscous stresses. Protoplanetary disks featuring prominent global spirals must be evolving rapidly, in ≲0.5 Myr at ∼100 au. A direct upper limit on the evolution timescale can be established by measuring the gravitational torque due to the spiral arms from the imaging data. We find that, regardless of their origin, global spiral waves must be important agents of the protoplanetary disk evolution. They may serve as an effective mechanism of disk dispersal and could be related to the phenomenon of transitional disks.« less

ECO and RESOLVE: Morphology and Disk Growth in Environmental Context

NASA Astrophysics Data System (ADS)

Moffett, Amanda J.; Kannappan, Sheila; Berlind, Andreas A.; Eckert, Kathleen D.; Stark, David; Hendel, David; Norris, Mark A.; Grogin, Norman A.; RESOLVE Team

2016-01-01

We present the first data release of the Environmental COntext (ECO) catalog, which was designed to surround and complement the RESOLVE survey with matched photometry, gas and stellar mass estimates, and environment metrics for ~13,000 galaxies in a >500,000 cubic Mpc volume. In the first results from ECO, we study the phenomenon of galaxy disk growth by considering by-eye and quantitative morphological classifications as well as galaxy environments quantified using group identifications and halo abundance matching (on integrated r-band luminosity) as well as smoothed galaxy density fields. Additionally, we derive HI gas masses and upper limits from ALFALFA data and HI mass estimates from the photometric gas fraction technique. We find that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright disk host galaxies all become distinctly more common below group halo mass ˜10^11.5 Msun, implying that this low group halo mass regime may be a preferred regime for significant disk growth activity. We also find that blue early-type and blue late-type galaxies inhabit environments of similar group halo mass at fixed baryonic mass, consistent with a scenario in which blue early types can regrow late-type disks. More generally, we argue that the traditional morphology-environment relation (i.e., that denser environments have more early types) can be largely attributed to the morphology-galaxy mass relation for centrals and the color-environment relation for satellites. This work has been supported through NSF grant AST-0955368.

Numerical simulation of heat and mass transfer in unsteady nanofluid between two orthogonally moving porous coaxial disks

NASA Astrophysics Data System (ADS)

Ali, Kashif; Akbar, Muhammad Zubair; Iqbal, Muhammad Farooq; Ashraf, Muhammad

2014-10-01

The paper deals with the study of heat and mass transfer in an unsteady viscous incompressible water-based nanofluid (containing Titanium dioxide nanoparticles) between two orthogonally moving porous coaxial disks with suction. A combination of iterative (successive over relaxation) and a direct method is employed for solving the sparse systems of linear algebraic equations arising from the FD discretization of the linearized self similar ODEs. It has been noticed that the rate of mass transfer at the disks decreases with the permeability Reynolds number whether the disks are approaching or receding. The findings of the present investigation may be beneficial for the electronic industry in maintaining the electronic components under effective and safe operational conditions.

Herschel-PACS observation of the 10 Myr old T Tauri disk TW Hya. Constraining the disk gas mass

NASA Astrophysics Data System (ADS)

Thi, W.-F.; Mathews, G.; Ménard, F.; Woitke, P.; Meeus, G.; Riviere-Marichalar, P.; Pinte, C.; Howard, C. D.; Roberge, A.; Sandell, G.; Pascucci, I.; Riaz, B.; Grady, C. A.; Dent, W. R. F.; Kamp, I.; Duchêne, G.; Augereau, J.-C.; Pantin, E.; Vandenbussche, B.; Tilling, I.; Williams, J. P.; Eiroa, C.; Barrado, D.; Alacid, J. M.; Andrews, S.; Ardila, D. R.; Aresu, G.; Brittain, S.; Ciardi, D. R.; Danchi, W.; Fedele, D.; de Gregorio-Monsalvo, I.; Heras, A.; Huelamo, N.; Krivov, A.; Lebreton, J.; Liseau, R.; Martin-Zaidi, C.; Mendigutía, I.; Montesinos, B.; Mora, A.; Morales-Calderon, M.; Nomura, H.; Phillips, N.; Podio, L.; Poelman, D. R.; Ramsay, S.; Rice, K.; Solano, E.; Walker, H.; White, G. J.; Wright, G.

2010-07-01

Planets are formed in disks around young stars. With an age of ~10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TW Hya disk, making TW Hya the perfect test case in a large survey of disks with Herschel-PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [O i] and [C ii] as part of the open-time large program GASPS. We complement this with continuum data and ground-based 12 CO 3-2 and 13CO 3-2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [O i] line at 63 μm. The other lines that were observed, [O i] at 145 μm and [C ii] at 157 μm, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [ 12CO] /[ 13CO] = 69 suggests a dust mass for grains with radius <1 mm of ~1.9 × 10-4 M⊙ (total solid mass of 3 × 10-3 M⊙) and a gas mass of (0.5-5) × 10-3 M⊙. The gas-to-dust mass may be lower than the standard interstellar value of 100. Herschel is an ESA space observatory with science instruments provided by Principal Investigator consortia. It is open for proposals for observing time from the worldwide astronomical community.Appendix is only available in electronic form at http://www.aanda.org

A 3D Numerical Study of Gravitational Instabilities in Young Circumbinary Disks

NASA Astrophysics Data System (ADS)

Cai, Kai; Michael, Scott; Durisen, Richard

2013-07-01

Gravitational instabilities (GIs) in protoplanetary disks have been suggested as one of the major formation mechanisms of giant planets. Theoretical and computational studies have indicated that certain family of GIs can be excited in a circumbinary disk, which could lead to enhanced protoplanet formation (e.g., Sellwood & Lin 1989, Boss 2006). We have carried out a 3D simulation of a gravitationally unstable circumbinary disk around a young Sun-like star and a 0.02-Msun companion, both inside the central hole of the disk. Here we present a preliminary comparison between this simulation and a similarly simulated circumstellar disk around a solar-mass star but without the low-mass companion. The GIs stimulated by the binary and those that arise spontaneously are quite different in structure and strength. However, no fragmentation is observed, even after many orbital periods as measured in the outer disk.

A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biller, Beth; Benisty, Myriam; Chauvin, Gael

2012-07-10

With the uniquely high contrast within 0.''1 ({Delta}mag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 {+-} 5 mas (12.8 {+-} 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 {+-} 0.007, 0.012 {+-} 0.008, and 0.0086 {+-} 0.0011, respectively (3{sigma} errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion withmore » an estimated mass of {approx}0.1-0.4 M{sub Sun }. HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.« less

Astrophysical Model Selection in Gravitational Wave Astronomy

NASA Technical Reports Server (NTRS)

Adams, Matthew R.; Cornish, Neil J.; Littenberg, Tyson B.

2012-01-01

Theoretical studies in gravitational wave astronomy have mostly focused on the information that can be extracted from individual detections, such as the mass of a binary system and its location in space. Here we consider how the information from multiple detections can be used to constrain astrophysical population models. This seemingly simple problem is made challenging by the high dimensionality and high degree of correlation in the parameter spaces that describe the signals, and by the complexity of the astrophysical models, which can also depend on a large number of parameters, some of which might not be directly constrained by the observations. We present a method for constraining population models using a hierarchical Bayesian modeling approach which simultaneously infers the source parameters and population model and provides the joint probability distributions for both. We illustrate this approach by considering the constraints that can be placed on population models for galactic white dwarf binaries using a future space-based gravitational wave detector. We find that a mission that is able to resolve approximately 5000 of the shortest period binaries will be able to constrain the population model parameters, including the chirp mass distribution and a characteristic galaxy disk radius to within a few percent. This compares favorably to existing bounds, where electromagnetic observations of stars in the galaxy constrain disk radii to within 20%.

DDA Computations of Porous Aggregates with Forsterite Crystals: Effects of Crystal Shape and Crystal Mass Fraction

NASA Technical Reports Server (NTRS)

Wooden, Diane H.; Lindsay, Sean S.; Harker, David; Woodward, Charles; Kelley, Michael S.; Kolokolova, Ludmilla

2015-01-01

Porous aggregate grains are commonly found in cometary dust samples and are needed to model cometary IR spectral energy distributions (SEDs). Models for thermal emissions from comets require two forms of silicates: amorphous and crystalline. The dominant crystal resonances observed in comet SEDs are from Forsterite (Mg2SiO4). The mass fractions that are crystalline span a large range from 0.0 < or = fcrystal < or = 0.74. Radial transport models that predict the enrichment of the outer disk (>25 AU at 1E6 yr) by inner disk materials (crystals) are challenged to yield the highend-range of cometary crystal mass fractions. However, in current thermal models, Forsterite crystals are not incorporated into larger aggregate grains but instead only are considered as discrete crystals. A complicating factor is that Forsterite crystals with rectangular shapes better fit the observed spectral resonances in wavelength (11.0-11.15 microns, 16, 19, 23.5, 27, and 33 microns), feature asymmetry and relative height (Lindley et al. 2013) than spherically or elliptically shaped crystals. We present DDA-DDSCAT computations of IR absorptivities (Qabs) of 3 micron-radii porous aggregates with 0.13 < or = fcrystal < or = 0.35 and with polyhedral-shaped Forsterite crystals. We can produce crystal resonances with similar appearance to the observed resonances of comet Hale- Bopp. Also, a lower mass fraction of crystals in aggregates can produce the same spectral contrast as a higher mass fraction of discrete crystals; the 11micron and 23 micron crystalline resonances appear amplified when crystals are incorporated into aggregates composed otherwise of spherically shaped amorphous Fe-Mg olivines and pyroxenes. We show that the optical properties of a porous aggregate is not linear combination of its monomers, so aggregates need to be computed. We discuss the consequence of lowering comet crystal mass fractions by modeling IR SEDs with aggregates with crystals, and the implications for radial transport models of our protoplanetary disk.

The structure of the distant Kuiper belt in a Nice model scenario

NASA Astrophysics Data System (ADS)

Pike, Rosemary E.; Lawler, Samantha; Brasser, Ramon; Shankman, Cory; Alexandersen, Mike; Kavelaars, J. J.

2016-10-01

By utilizing a well-sampled migration model and characterized survey detections, we demonstrate that the Nice-model scenario results in consistent populations of scattering trans-Neptunian objects (TNOs) and several resonant TNO populations, but fails to reproduce the large population of 5:1 resonators discovered in surveys. We examine in detail the TNO populations implanted by the Nice model simulation from Brasser and Morbidelli (2013, B&M). This analysis focuses on the region from 25-155 AU, probing the classical, scattering, detached, and major resonant populations. Additional integrations were necessary to classify the test particles and determine population sizes and characteristics. The classified simulation objects are compared to the real TNOs from the Canada-France Ecliptic Plane Survey (CFEPS), CFEPS high latitude fields, and the Alexandersen (2016) survey. These surveys all include a detailed characterization of survey depth, pointing, and tracking efficiency, which allows detailed testing of this independently produced model of TNO populations. In the B&M model, the regions of the outer Solar System populated via capture of scattering objects are consistent with survey constraints. The scattering TNOs and most n:1 resonant populations have consistent orbital distributions and population sizes with the real detections, as well as a starting disk mass consistent with expectations. The B&M 5:1 resonators have a consistent orbital distribution with the real detections and previous models. However, the B&M 5:1 Neptune resonance is underpopulated by a factor of ~100 and would require a starting proto-planetesimal disk with a mass of ~100 Earth masses. The large population in the 5:1 Neptune resonance is unexplained by scattering capture in a Nice-model scenario, however this model accurately produces the TNO subpopulations that result from scattering object capture and provides additional insight into sub-population orbital distributions.

On the role of disks in the formation of stellar systems: A numerical parameter study of rapid accretion

DOE PAGES

Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; ...

2009-12-23

We study rapidly accreting, gravitationally unstable disks with a series of idealized global, numerical experiments using the code ORION. Our numerical parameter study focuses on protostellar disks, showing that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the infall rate to the disk sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infallmore » rate and governed by gravitational torques generated by low-m spiral modes. Furthermore, we also confirm the existence of a maximum stable disk mass: disks that exceed ~50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.« less

Atlas of low-mass young stellar object disks from mid-infrared interferometry

NASA Astrophysics Data System (ADS)

Varga, J.; Ábrahám, P.; Ratzka, Th.; Menu, J.; Gabányi, K.; Kóspál, Á.; van Boekel, R.; Mosoni, L.; Henning, Th.

We present our approach of visibility modeling of disks around low-mass (< 2 M ⊙) young stellar objects (YSOs). We compiled an atlas based on mid-infrared interferometric observations from the MIDI instrument at the VLTI. We use three different models to fit the data. These models allow us to determine overall sizes (and the extent of the inner gaps) of the modeled circumstellar disks.

Migration and growth of protoplanetary embryos. I. Convergence of embryos in protoplanetary disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaojia; Lin, Douglas N. C.; Liu, Beibei

2014-12-10

According to the core accretion scenario, planets form in protostellar disks through the condensation of dust, coagulation of planetesimals, and emergence of protoplanetary embryos. At a few AU in a minimum mass nebula, embryos' growth is quenched by dynamical isolation due to the depletion of planetesimals in their feeding zone. However, embryos with masses (M{sub p} ) in the range of a few Earth masses (M {sub ⊕}) migrate toward a transition radius between the inner viscously heated and outer irradiated regions of their natal disk. Their limiting isolation mass increases with the planetesimals surface density. When M{sub p} >more » 10 M {sub ⊕}, embryos efficiently accrete gas and evolve into cores of gas giants. We use a numerical simulation to show that despite stream line interference, convergent embryos essentially retain the strength of non-interacting embryos' Lindblad and corotation torques by their natal disks. In disks with modest surface density (or equivalently accretion rates), embryos capture each other in their mutual mean motion resonances and form a convoy of super-Earths. In more massive disks, they could overcome these resonant barriers to undergo repeated close encounters, including cohesive collisions that enable the formation of massive cores.« less

Numerical Study on Outflows in Seyfert Galaxies I: Narrow Line Region Outflows in NGC 4151

NASA Astrophysics Data System (ADS)

Mou, Guobin; Wang, Tinggui; Yang, Chenwei

2017-07-01

The origin of narrow line region (NLR) outflows remains unknown. In this paper, we explore the scenario in which these outflows are circumnuclear clouds driven by energetic accretion disk winds. We choose the well-studied nearby Seyfert galaxy NGC 4151 as an example. By performing 3D hydrodynamical simulations, we are able to reproduce the radial distributions of velocity, mass outflow rate, and kinetic luminosity of NLR outflows in the inner 100 pc deduced from spatial resolved spectroscopic observations. The demanded kinetic luminosity of disk winds is about two orders of magnitude higher than that inferred from the NLR outflows, but is close to the ultrafast outflows (UFO) detected in the X-ray spectrum and a few times lower than the bolometric luminosity of the Seyfert. Our simulations imply that the scenario is viable for NGC 4151. The existence of the underlying disk winds can be confirmed by their impacts on higher density ISM, e.g., shock excitation signs, and the pressure in NLR.

UV spectroscopy of Z Chamaeleontis. I - Time dependent dips in superoutburst

NASA Technical Reports Server (NTRS)

Harlaftis, E. T.; Hassall, B. J. M.; Naylor, T.; Charles, P. A.; Sonneborn, G.

1992-01-01

Extensive IUE observations of the dwarf nova Z Cha during the 1987 April superoutburst and IUE-Exosat observations during the 1985 July superoutburst are presented. The UV light curve shows two dips when folded on the orbital period. One dip, at orbital phase 0.8 becomes shallower as the superoutburst progresses and can be associated with decreasing mass transfer rate from the secondary star. The other dip, at orbital phase 0.15, appears after the development of the superhump and some days after the occurrence of the largest dip at phase 0.8. The continuum flux distribution during superoutbursts is fainter and redder than in low-inclination dwarf novae during superoutbursts. This is interpreted in terms of the extended vertical disk structure which occults the hot inner parts of the disk with the development of a 'cool' bulge on the edge of the disk at orbital phase 0.75. Details of the behaviour of the UV emission lines during eclipse and away from eclipse are discussed.

TERRESTRIAL PLANET FORMATION AROUND THE CIRCUMBINARY HABITABLE ZONE: INWARD MIGRATION IN THE PLANETESIMAL SWARM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong Yanxiang; Zhou Jilin; Xie Jiwei, E-mail: yxgong@nju.edu.cn, E-mail: zhoujl@nju.edu.cn

2013-01-20

According to the core accretion theory, circumbinary embryos can form only beyond a critical semimajor axis (CSMA). However, due to the relatively high density of solid materials in the inner disk, a significant amount of small planetesimals must exist in the inner zone when embryos form outside this CSMA. Thus, embryo migration induced by the planetesimal swarm is possible after gas disk depletion. Through numerical simulations, we found that (1) the scattering-driven inward migration of embryos is robust and planets can form in the habitable zone if we adopt a mass distribution of an MMSN-like disk; (2) the total massmore » of the planetesimals in the inner region and continuous embryo-embryo scattering are two key factors that cause significant embryo migrations; and (3) the scattering-driven migration of embryos is a natural water-delivery mechanism. We propose that planet detections should focus on the close binary with its habitable zone near CSMA.« less

Planet-driven Spiral Arms in Protoplanetary Disks. I. Formation Mechanism

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Zhu, Zhaohuan

2018-06-01

Protoplanetary disk simulations show that a single planet can excite more than one spiral arm, possibly explaining the recent observations of multiple spiral arms in some systems. In this paper, we explain the mechanism by which a planet excites multiple spiral arms in a protoplanetary disk. Contrary to previous speculations, the formation of both primary and additional arms can be understood as a linear process when the planet mass is sufficiently small. A planet resonantly interacts with epicyclic oscillations in the disk, launching spiral wave modes around the Lindblad resonances. When a set of wave modes is in phase, they can constructively interfere with each other and create a spiral arm. More than one spiral arm can form because such constructive interference can occur for different sets of wave modes, with the exact number and launching position of the spiral arms being dependent on the planet mass as well as the disk temperature profile. Nonlinear effects become increasingly important as the planet mass increases, resulting in spiral arms with stronger shocks and thus larger pitch angles. This is found to be common for both primary and additional arms. When a planet has a sufficiently large mass (≳3 thermal masses for (h/r) p = 0.1), only two spiral arms form interior to its orbit. The wave modes that would form a tertiary arm for smaller mass planets merge with the primary arm. Improvements in our understanding of the formation of spiral arms can provide crucial insights into the origin of observed spiral arms in protoplanetary disks.

Kinematic Downsizing at z ˜ 2

NASA Astrophysics Data System (ADS)

Simons, Raymond C.; Kassin, Susan A.; Trump, Jonathan R.; Weiner, Benjamin J.; Heckman, Timothy M.; Barro, Guillermo; Koo, David C.; Guo, Yicheng; Pacifici, Camilla; Koekemoer, Anton; Stephens, Andrew W.

2016-10-01

We present results from a survey of the internal kinematics of 49 star-forming galaxies at z˜ 2 in the CANDELS fields with the Keck/MOSFIRE spectrograph, Survey in the near-Infrared of Galaxies with Multiple position Angles (SIGMA). Kinematics (rotation velocity V rot and gas velocity dispersion {σ }g) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by z˜ 2, massive star-forming galaxies ({log} {M}* /{M}⊙ ≳ 10.2) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of {V}{rot}/{σ }g that are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low-mass galaxies ({log} {M}* /{M}⊙ ≲ 10.2) at this epoch are still in the early stages of disk assembly: their kinematics are often dominated by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of V rot. This “kinematic downsizing” implies that the process(es) responsible for disrupting disks at z˜ 2 have a stronger effect and/or are more active in low-mass systems. In conclusion, we find that the period of rapid stellar mass growth at z˜ 2 is coincident with the nascent assembly of low-mass disks and the assembly and settling of high-mass disks.

A Modern Picture of Barred Galaxy Dynamics

NASA Astrophysics Data System (ADS)

Petersen, Michael; Weinberg, Martin; Katz, Neal

2018-01-01

Observations of disk galaxies suggest that bars are responsible for altering global galaxy parameters (e.g. structures, gas fraction, star formation rate). The canonical understanding of the mechanisms underpinning bar-driven secular dynamics in disk galaxies has been largely built upon the analysis of linear theory, despite galactic bars being clearly demonstrated to be nonlinear phenomena in n-body simulations. We present simulations of barred Milky Way-like galaxy models designed to elucidate nonlinear barred galaxy dynamics. We have developed two new methodologies for analyzing n-body simulations that give the best of both powerful analytic linear theory and brute force simulation analysis: orbit family identification and multicomponent torque analysis. The software will be offered publicly to the community for their own simulation analysis.The orbit classifier reveals that the details of kinematic components in galactic disks (e.g. the bar, bulge, thin disk, and thick disk components) are powerful discriminators of evolutionary paradigms (i.e. violent instabilities and secular evolution) as well as the basic parameters of the dark matter halo (mass distribution, angular momentum distribution). Multicomponent torque analysis provides a thorough accounting of the transfer of angular momentum between orbits, global patterns, and distinct components in order to better explain the underlying physics which govern the secular evolution of barred disk galaxies.Using these methodologies, we are able to identify the successes and failures of linear theory and traditional n-body simulations en route to a detailed understanding of the control bars exhibit over secular evolution in galaxies. We present explanations for observed physical and velocity structures in observations of barred galaxies alongside predictions for how structures will vary with dynamical properties from galaxy to galaxy as well as over the lifetime of a galaxy, finding that the transfer of angular momentum through previously unidentified channels can more fully explain the observed dynamics.

Numerical Simulations of Multiphase Winds and Fountains from Star-forming Galactic Disks. I. Solar Neighborhood TIGRESS Model

NASA Astrophysics Data System (ADS)

Kim, Chang-Goo; Ostriker, Eve C.

2018-02-01

Gas blown away from galactic disks by supernova (SN) feedback plays a key role in galaxy evolution. We investigate outflows utilizing the solar neighborhood model of our high-resolution, local galactic disk simulation suite, TIGRESS. In our numerical implementation, star formation and SN feedback are self-consistently treated and well resolved in the multiphase, turbulent, magnetized interstellar medium. Bursts of star formation produce spatially and temporally correlated SNe that drive strong outflows, consisting of hot (T> 5× {10}5 {{K}}) winds and warm (5050 {{K}}< T< 2× {10}4 {{K}}) fountains. The hot gas at distance d> 1 {kpc} from the midplane has mass and energy fluxes nearly constant with d. The hot flow escapes our local Cartesian box barely affected by gravity, and is expected to accelerate up to terminal velocity of {v}{wind}∼ 350{--}500 {km} {{{s}}}-1. The mean mass and energy loading factors of the hot wind are 0.1 and 0.02, respectively. For warm gas, the mean outward mass flux through d=1 {kpc} is comparable to the mean star formation rate, but only a small fraction of this gas is at velocity > 50 {km} {{{s}}}-1. Thus, the warm outflows eventually fall back as inflows. The warm fountain flows are created by expanding hot superbubbles at d< 1 {kpc}; at larger d neither ram pressure acceleration nor cooling transfers significant momentum or energy flux from the hot wind to the warm outflow. The velocity distribution at launching near d∼ 1 {kpc} is a better representation of warm outflows than a single mass loading factor, potentially enabling development of subgrid models for warm galactic winds in arbitrary large-scale galactic potentials.

VLTI + MIDI Study of the High Mass Protostellar Candidate NGC 3603 IRS 9A

NASA Astrophysics Data System (ADS)

Nürnberger, D. E. A.; Vehoff, S.; Hummel, C. A.; Duschl, W. J.

2010-02-01

The formation and early evolution of high mass stars is among the hottest topics in astrophysics. Interferometric studies of these young stars and their circumstellar environments (envelopes, disks and jets) at near and mid infrared wavelengths are still rare and in terms of data analysis/interpretation very challenging. We here report on observations of the high mass protostellar candidate NGC 3603 IRS 9A which we undertook with VLTI + MIDI in 2005, complemented by near and mid infrared imaging and spectroscopic data. We discuss our results obtained from dedicated modeling efforts, employing both DUSTY and MC3D radiative transfer codes for a selected number of source geometries and surface brightness distributions.

Dynamical Upheaval in Ice Giant Formation: A Solution to the Fine-tuning Problem in the Formation Story

NASA Astrophysics Data System (ADS)

Frelikh, Renata; Murray-Clay, Ruth

2018-04-01

We report on our recent theoretical work, where we suggest that a protoplanetary disk dynamical instability may have played a crucial role in determining the atmospheric size of the solar system’s ice giants. In contrast to the gas giants, the intermediate-size ice giants never underwent runaway gas accretion in a full gas disk. However, as their substantial core masses are comparable to those of the gas giants, they would have gone runaway, given enough time. In the standard scenario, the ice giants stay at roughly their current size for most of the disk lifetime, undergoing period of slow gas accretion onto ~full-sized cores that formed early-on. The gas disk dissipates before the ice giants accumulate too much gas, but we believe this is fine tuned. A considerable amount of solids is observed in outer disks in mm-to-cm sized particles (pebbles). Assisted by gas drag, these pebbles rapidly accrete onto cores. This would cause the growing ice giants to exceed their current core masses, and quickly turn into gas giants. To resolve this problem, we propose that Uranus and Neptune stayed small for the bulk of the disk lifetime. They only finished their core and atmospheric growth in a short timeframe just as the disk gas dissipated, accreting most of their gas from a disk depleted to ~1% of its original mass. The ice giants have atmospheric mass fractions comparable to the disk gas-to-solid ratio of this depleted disk. This coincides with a disk dynamical upheaval onset by the depletion of gas. We propose that the cores started growing closer-in, where they were kept small by proximity to Jupiter and Saturn. As the gas cleared, the cores were kicked out by the gas giants. Then, they finished their core growth and accreted their atmospheres from the remaining, sparse gas at their current locations. We predict that the gas giants may play a key role in forming intermediate-size atmospheres in the outer disk.

MOLECULAR GAS DISK STRUCTURES AROUND ACTIVE GALACTIC NUCLEI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wada, Keiichi; Papadopoulos, Padeli P.; Spaans, Marco

We present new high-resolution numerical simulations of the interstellar medium (ISM) in a central R {<=} 32 parsecs region around a supermassive black hole (1.3 x 10{sup 7} M{sub sun}) at a galactic center. Three-dimensional hydrodynamic modeling of the ISM (Wada and Norman 2002) with the nuclear starburst now includes tracking of the formation of molecular hydrogen (H{sub 2}) out of the neutral hydrogen phase as a function of the evolving ambient ISM conditions with a finer spatial resolution (0.125 pc). In a quasi-equilibrium state, mass fraction of H{sub 2} is about 0.4 (total H{sub 2} mass is {approx_equal}1.5 xmore » 10{sup 6} M{sub sun}) of the total gas mass for the uniform far ultra-violet (FUV) with G {sub 0} = 10 in Habing unit. As shown in the previous model, the gas forms an inhomogeneous disk, whose scale height becomes larger in the outer region. H{sub 2} forms a thin nuclear disk in the inner {approx_equal}5 pc, which is surrounded by molecular clouds swelled up toward h {approx}< 10 pc. The velocity field of the disk is highly turbulent in the torus region, whose velocity dispersion is {approx_equal}20 km s{sup -1} on average. Average supernova (SN) rate of {approx_equal}5 x 10{sup -5} yr{sup -1} is large enough to energize these structures. Gas column densities toward the nucleus larger than 10{sup 22} cm{sup -2} are observed if the viewing angle is smaller than {theta} {sub v} {approx_equal} 50 deg. from the edge-on. However, the column densities are distributed over almost two orders of magnitude around the average for any given viewing angle due to the clumpy nature of the torus. For a stronger FUV (G {sub 0} = 100), the total H{sub 2} mass in an equilibrium is only slightly smaller ({approx_equal}0.35), a testimony to the strong self-shielding nature of H{sub 2}, and the molecular gas is somewhat more concentrated in a midplane. Other properties of the ISM are not very sensitive either to the FUV intensity or the SN rate. Finally, the morphology and kinematics of the circum nuclear molecular gas disks emerging from our models are similar to that revealed by recent near infrared observations using VLTI/Keck.« less

Planet Formation in Stellar Binaries: How Disk Gravity Can Lower theFragmentation Barrier

NASA Astrophysics Data System (ADS)

Silsbee, Kedron; Rafikov, Roman R.

2014-11-01

Binary star systems present a challenge to current theories of planet formation. Perturbations from the companion star dynamically excite the protoplanetary disk, which can lead to destructive collisions between planetesimals, and prevent growth from 1 km to 100 km sized planetesimals. Despite this apparent barrier to coagulation, planets have been discovered within several small-separation (<20 AU), eccentric (eb 0.4) binaries, such as alpha Cen and gamma Cep. We address this problem by analytically exploring planetesimal dynamics under the simultaneous action of (1) binary perturbation, (2) gas drag (which tends to align planetesimal orbits), and (3), the gravity of an eccentric protoplanetary disk. We then use our dynamical solutions to assess the outcomes of planetesimal collisions (growth, destruction, erosion) for a variety of disk models. We find that planets in small-separation binaries can form at their present locations if the primordial protoplanetary disks were massive (>0.01M⊙) and not very eccentric (eccentricity of order several per cent at the location of planet). This constraint on the disk mass is compatible with the high masses of the giant planets in known gamma Cep-like binaries, which require a large mass reservoir for their formation. We show that for these massive disks, disk gravity is dominant over the gravity of the binary companion at the location of the observed planets. Therefore, planetesimal growth is highly sensitive to disk properties. The requirement of low disk eccentricity is in line with the recent hydrodynamic simulations that tend to show gaseous disks in eccentric binaries developing very low eccentricity, at the level of a few percent. A massive purely axisymmetric disk makes for a friendlier environment for planetesimal growth by driving rapid apsidal precession of planetesimals, and averaging out the eccentricity excitation from the binary companion. When the protoplanetary disk is eccentric we find that the most favorable conditions for planetesimal growth emerge when the disk is non-precessing and is apsidally aligned with the orbit of the binary.