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Sample records for protostellar disks predictions

  1. Planet Forming Protostellar Disks

    NASA Technical Reports Server (NTRS)

    Lubow, Stephen

    1998-01-01

    The project achieved many of its objectives. The main area of investigation was the interaction of young binary stars with surrounding protostellar disks. A secondary objective was the interaction of young planets with their central stars and surrounding disks. The grant funds were used to support visits by coinvestigators and visitors: Pawel Artymowicz, James Pringle, and Gordon Ogilvie. Funds were also used to support travel to meetings by Lubow and to provide partial salary support.

  2. Encounters with Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Heller, Clayton H.

    1992-12-01

    A numerical study of encounters between stars with circumstellar disks has bee completed. Cross sections and rates for disk tilt, disk disruption, and binary formation are estimated using a large data base of encounter simulations. The consequences of these results for star-forming regions and our solar system are discussed. A numerical code is developed which is capable of evolving a mixture of stars and gas in three dimensions. The algorithm is based on the method of smoothed-particle hydrodynamics combined with the heirarchical tree method of computing gravitational forces. The code is tested by simulating the collision between two sheets of gas and the radial pulsations of a polytropic gas sphere. A protostellar-disk model is developed based on simple assumptions. Test encounters are performed to determine the sensitivity of measured quantities on algorithm parameters, such as the gravitational tolerance and viscosity. It is shown that the solar system could have had an encounter shortly after its formation of sufficient strength to generate the observed obliquity yet retain enough mass and radial extent to form the planetary system. For the Orion B clusters as a whole, it is estimated that during a one-million-year period of time a few percent of the stars will experience an enoucnter that results in a disk tilt of 7 degrees or greater. For the central regions of NGC 2024 and the Trapezium cluster values of 24% and 39% are obtained, respectively. Encounters between equal-mass stars with periastra of 0.5, 1.0, 1.5, and 2.0 disk radii will retain on average about 15%, 40%, 55%, and 75% of the disk mass, respectively. For encounters that do not penetrate the disk a minimum of 15% of the mass is retained. Even in dense environments the characteristic lifetime of a disk due to disruptive encounters can be many millions of years. On average, an encounter that penetrates the disk will dissipate an amount of orbital energy equal to approximately 50% of the initial

  3. Molecular Line Emission from Massive Protostellar Disks: Predictions for ALMA and the EVLA

    SciTech Connect

    Krumholz, M R; Klein, R I; McKee, C F

    2007-05-07

    We compute the molecular line emission of massive protostellar disks by solving the equation of radiative transfer through the cores and disks produced by the recent radiation-hydrodynamic simulations of Krumholz, Klein, & McKee. We find that in several representative lines the disks show brightness temperatures of hundreds of Kelvin over velocity channels {approx} 10 km s{sup -1} wide, extending over regions hundreds of AU in size. We process the computed intensities to model the performance of next-generation radio and submillimeter telescopes. Our calculations show that observations using facilities such as the EVLA and ALMA should be able to detect massive protostellar disks and measure their rotation curves, at least in the nearest massive star-forming regions. They should also detect significant sub-structure and non-axisymmetry in the disks, and in some cases may be able to detect star-disk velocity offsets of a few km s{sup -1}, both of which are the result of strong gravitational instability in massive disks. We use our simulations to explore the strengths and weaknesses of different observational techniques, and we also discuss how observations of massive protostellar disks may be used to distinguish between alternative models of massive star formation.

  4. Observations of Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Ménard, F.

    2004-12-01

    Accretion disks are pivotal elements in the formation and early evolution of solar-like stars. On top of supplying the raw material, their internal conditions also regulate the formation of planets. Their study therefore holds the key to solve the mystery of the formation of our Solar System. This chapter focuses on observational studies of circumstellar disks associated with pre-main sequence solar-like stars. The direct measurement of disk parameters poses an obvious challenge: at the distance of typical star forming regions (e.g., ˜140pc for Taurus), a planetary system like ours (with diameter ≃ 50AU out to Pluto, but excluding the Kuiper belt) subtends only 0.35". Yet its surface brightness is low in comparison to the bright central star and high angular and high contrast imaging techniques are required if one hopes to resolve and measure these protoplanetary disks. Fortunately, capable instruments providing 0.1" resolution or better and high contrast have been available for just about 10 years now. They are covering a large part of the electromagnetic spectrum, from the UV/Optical with HST and the near-infrared from ground-based adaptive optics systems, to the millimetric range with long-baseline radio interferometers. It is therefore not surprising that our knowledge of the structure of the disks surrounding low-mass stars has made a gigantic leap forward in the last decade. In the following pages I will attempt to give an overview of the structural and physical parameters of protoplanetary disks that can be estimated today from direct observations.

  5. Molecule survival in magnetized protostellar disk winds. II. Predicted H2O line profiles versus Herschel/HIFI observations

    NASA Astrophysics Data System (ADS)

    Yvart, W.; Cabrit, S.; Pineau des Forêts, G.; Ferreira, J.

    2016-01-01

    Context. The origin of molecular protostellar jets and their role in extracting angular momentum from the accreting system are important open questions in star formation research. In the first paper of this series we showed that a dusty magneto-hydrodynamic (MHD) disk wind appeared promising to explain the pattern of H2 temperature and collimation in the youngest jets. Aims: We wish to see whether the high-quality H2O emission profiles of low-mass protostars, observed for the first time by the HIFI spectrograph on board the Herschel satellite, remain consistent with the MHD disk wind hypothesis, and which constraints they would set on the underlying disk properties. Methods: We present synthetic H2O line profiles predictions for a typical MHD disk wind solution with various values of disk accretion rate, stellar mass, extension of the launching area, and view angle. We compare them in terms of line shapes and intensities with the HIFI profiles observed by the WISH key program towards a sample of 29 low-mass Class 0 and Class 1 protostars. Results: A dusty MHD disk wind launched from 0.2-0.6 AU AU to 3-25 AU can reproduce to a remarkable degree the observed shapes and intensities of the broad H2O component observed in low-mass protostars, both in the fundamental 557 GHz line and in more excited lines. Such a model also readily reproduces the observed correlation of 557 GHz line luminosity with envelope density, if the infall rate at 1000 AU is 1-3 times the disk accretion rate in the wind ejection region. It is also compatible with the typical disk size and bolometric luminosity in the observed targets. However, the narrower line profiles in Class 1 sources suggest that MHD disk winds in these sources, if present, would have to be slower and/or less water rich than in Class 0 sources. Conclusions: MHD disk winds appear as a valid (though not unique) option to consider for the origin of the broad H2O component in low-mass protostars. ALMA appears ideally suited to

  6. HEATING AND COOLING PROTOSTELLAR DISKS

    SciTech Connect

    Hirose, S.; Turner, N. J. E-mail: neal.turner@jpl.nasa.gov

    2011-05-10

    We examine heating and cooling in protostellar disks using three-dimensional radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well coupled to magnetic fields, and sustains a turbulent accretion flow driven by magnetorotational instability, while the interior is resistive and magnetically dead. The turbulent layers are heated by absorbing the light from the central star and by dissipating the magnetic fields. They are optically thin to their own radiation and cool inefficiently. The optically thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations in the fields move the starlight-absorbing surface up and down. The height ranges between 13% and 24% of the radius over timescales of several orbits, with implications for infrared variability. The fields are buoyant, so the accretion heating occurs higher in the atmosphere than the stresses. The heating is localized around current sheets, caused by magnetorotational instability at lower elevations and by Parker instability at higher elevations. Gas in the sheets is heated above the stellar irradiation temperature, even though accretion is much less than irradiation power when volume averaged. The hot optically thin current sheets might be detectable through their line emission.

  7. Protostellar Disk Formation Traced by Chemistry

    NASA Astrophysics Data System (ADS)

    Sakai, N.

    2015-12-01

    Recent ALMA observations are revealing formation processes of a disk structure around a young protostars at an unprecedented spatial resolution. A few recent highlights in this area are reviewed with particular emphasis on chemistry. Our discovery of centrifugal barrier of an infalling rotating envelope gas and associated drastic chemical change are presented as an example. Chemical compositions can be used to explore not only the chemical evolution from protostellar cores to protoplanetary disks but also the physical formation process of rotationally supported disks in protostellar sources.

  8. Modeling of Radiative Transfer in Protostellar Disks

    NASA Technical Reports Server (NTRS)

    VonAllmen, Paul; Turner, Neal

    2007-01-01

    This program implements a spectral line, radiative transfer tool for interpreting Spitzer Space Telescope observations by matching them with models of protostellar disks for improved understanding of planet and star formation. The Spitzer Space Telescope detects gas phase molecules in the infrared spectra of protostellar disks, with spectral lines carrying information on the chemical composition of the material from which planets form. Input to the software includes chemical models developed at JPL. The products are synthetic images and spectra for comparison with Spitzer measurements. Radiative transfer in a protostellar disk is primarily affected by absorption and emission processes in the dust and in molecular gases such as H2, CO, and HCO. The magnitude of the optical absorption and emission is determined by the population of the electronic, vibrational, and rotational energy levels. The population of the molecular level is in turn determined by the intensity of the radiation field. Therefore, the intensity of the radiation field and the population of the molecular levels are inter-dependent quantities. To meet the computational challenges of solving for the coupled radiation field and electronic level populations in disks having wide ranges of optical depths and spatial scales, the tool runs in parallel on the JPL Dell Cluster supercomputer with C++ and Fortran compiler with a Message Passing Interface. Because this software has been developed on a distributed computing platform, the modeling of systems previously beyond the reach of available computational resources is possible.

  9. Theory of Protostellar Disk Fromation

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Yun

    2015-08-01

    Disk formation, once thought to be a simple consequence of the conservation of angular momentum during the hydrodynamic core collapse, is far more subtle in magnetized gas. In this case, the rotation can be strongly magnetically braked. Indeed, both analytic arguments and numerical simulations have shown that disk formation is suppressed in strict ideal MHD for the observed level of core magnetization. I will discuss the physical reason for this so-called "magnetic braking catastrophe," and review possible resolutions to this problem that have been proposed so far, including non-ideal MHD effects, misalignment between the magnetic field and rotation axis, and especially turbulence.

  10. Dead Zone Accretion Flows in Protostellar Disks

    NASA Technical Reports Server (NTRS)

    Turner, Neal; Sano, T.

    2008-01-01

    Planets form inside protostellar disks in a dead zone where the electrical resistivity of the gas is too high for magnetic forces to drive turbulence. We show that much of the dead zone nevertheless is active and flows toward the star while smooth, large-scale magnetic fields transfer the orbital angular momentum radially outward. Stellar X-ray and radionuclide ionization sustain a weak coupling of the dead zone gas to the magnetic fields, despite the rapid recombination of free charges on dust grains. Net radial magnetic fields are generated in the magnetorotational turbulence in the electrically conducting top and bottom surface layers of the disk, and reach the midplane by ohmic diffusion. A toroidal component to the fields is produced near the midplane by the orbital shear. The process is similar to the magnetization of the solar tachocline. The result is a laminar, magnetically driven accretion flow in the region where the planets form.

  11. Magnetic Fields in Early Protostellar Disk Formation

    NASA Astrophysics Data System (ADS)

    González-Casanova, Diego F.; Lazarian, Alexander; Santos-Lima, Reinaldo

    2016-03-01

    We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian & Vishniac model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called “magnetic braking catastrophe.” In particular, we provide a detailed study of the dynamics of a 0.5 M⊙ protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, “reconnection diffusion,” removes the magnetic flux from the disk; the other involves the change of the magnetic field's topology, but does not change the absolute value of the magnetic flux through the disk. We demonstrate that for the first mechanism, turbulence causes a magnetic flux transport outward from the inner disk to the ambient medium, thus decreasing the coupling of the disk to the ambient material. A similar effect is achieved through the change of the magnetic field's topology from a split monopole configuration to a dipole configuration. We explore how both mechanisms prevent the catastrophic loss of disk angular momentum and compare both above turbulent reconnection mechanisms with alternative mechanisms from the literature.

  12. Detection of Methanol in a Class 0 Protostellar Disk

    NASA Technical Reports Server (NTRS)

    Langer, W.; Velusamy, T.; Goldsmith, P.

    1999-01-01

    We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, class 0 protostellar object.

  13. Keplerian Circumbinary Disk and Accretion Streams around the Protostellar Binary System L1551 NE

    NASA Astrophysics Data System (ADS)

    Takakuwa, S.; Saito, M.; Lim, J.; Saigo, K.; Hanawa, T.; Matsumoto, T.

    2013-10-01

    We show our recent observational results of L1551 NE, an archetypal binary protostellar system, in the 0.9-mm dust continuum emission and the C18O (J=3-2) emission with the SubMillimeter Array (SMA). The SMA results show firm evidence for a Keplerian circumbinary disk, circumstellar disks, and an inner clearing in the circumbinary disk, in L1551 NE. We demonstrate that future observations of L1551 NE with Atacama Large Millimeter and submillimeter Array (ALMA) have the potential to unveil the theoretically-predicted “accretion streams” that channel material from the circumbinary disk to the individual circumstellar disks.

  14. Ejection of gaseous clumps from gravitationally unstable protostellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, E. I.

    2016-05-01

    Aims: We investigate the dynamics of gaseous clumps formed via gravitational fragmentation in young protostellar disks, focusing on the fragments that are ejected from the disk via many-body gravitational interaction. Methods: Numerical hydrodynamics simulations were employed to study the evolution of young protostellar disks that were formed from the collapse of rotating pre-stellar cores. Results: The protostellar disks that formed in our models undergo gravitational fragmentation driven by continuing mass-loading from parental collapsing cores. Several fragments can be ejected from the disk during the early evolution, but the low-mass fragments (<15 MJup) disperse, which creates spectacular bow-type structures while passing through the disk and collapsing core. The least massive fragment that survived the ejection (21 MJup) straddles the planetary-mass limit, while the most massive ejected fragments (145 MJup) can break up into several pieces, leading to the ejection of wide separation binary clumps in the brown-dwarf mass range. About half of the ejected fragments are gravitationally bound, the majority are supported by rotation against gravity, and all fragments have the specific angular momentum that is much higher than that expected for brown dwarfs. We found that the internal structure of the ejected fragments is distinct from what would be expected for gravitationally contracting clumps formed via molecular cloud fragmentation, which can help in differentiating their origin. Conclusions: The ejection of fragments is an important process, which is inherent to massive protostellar disks, and which produces freely floating pre-brown dwarf cores, regulates the disk and stellar masses and, potentially, enriches the intracluster medium with processed dust and complex organics.

  15. PROTOSTELLAR DISK FORMATION ENABLED BY WEAK, MISALIGNED MAGNETIC FIELDS

    SciTech Connect

    Krumholz, Mark R.; Crutcher, Richard M.; Hull, Charles L. H.

    2013-04-10

    The gas from which stars form is magnetized, and strong magnetic fields can efficiently transport angular momentum. Most theoretical models of this phenomenon find that it should prevent formation of large (>100 AU), rotationally supported disks around most protostars, even when non-ideal magnetohydrodynamic (MHD) effects that allow the field and gas to decouple are taken into account. Using recent observations of magnetic field strengths and orientations in protostellar cores, we show that this conclusion is incorrect. The distribution of magnetic field strengths is very broad, and alignments between fields and angular momentum vectors within protostellar cores are essentially random. By combining the field strength and misalignment data with MHD simulations showing that disk formation is expected for both weak and misaligned fields, we show that these observations imply that we should expect disk fractions of {approx}10%-50% even when protostars are still deeply embedded in their parent cores, and even if the gas is governed by ideal MHD.

  16. First Detection of Methanol in a Class O Protostellar Disk

    NASA Technical Reports Server (NTRS)

    Velusamy, T.; Langer, William D.; Goldsmith, Paul F.

    2000-01-01

    We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, Class O protostellar object. In addition, we identify a spectral feature in the outflow corresponding to an ethanol transition. Using the Caltech Owens Valley Millimeter Array with a synthesized beam size of 2", we detect spatially unresolved methanol in the 2(sub k) - 1(sub k) transitions at 3mm, which is coincident in position with the peak of the continuum emission. The gas phase methanol could be located in the central region (< 100 AU radius) of a flat disk, or in an extended heated surface layer (approx. 200 AU radius) of a flared disk. The fractional abundance of methanol X(CH3OH) is approx. 2 x l0(exp -8) in the flat disk model, and 3 x l0(exp -7) for the flared disk. The fractional abundance is small in the disk as a whole, but considerably larger in the warm portions. This difference indicates that substantial chemical processing probably takes place in the disk via depletion and desorption. The methanol desorbed from the grains in the warm surface layers returns to the icy grain mantles in the cooler interior of the disk, where it is available to become part of the composition of solar system-like bodies, such as comets, formed in the outer circumstellar region. This first millimeter-wavelength detection of a complex organic molecule in a young protostellar disk has implications for disk structure and chemical evolution and for potential use as a temperature probe. The research of TV and WL was conducted at the Jet Propulsion Laboratory, California Institute of Technology with support from the National Aeronautics and Space Administration.

  17. Further studies of gravitationally unstable protostellar disks

    NASA Technical Reports Server (NTRS)

    Tomley, Leslie; Steiman-Cameron, Thomas Y.; Cassen, Patrick

    1994-01-01

    Models of the solar nebula reveal that it might have been gravitationally unstable, both early and later in its evolution. Such instabilities produce density waves and associated gravitational torques, which are potent agents of angular momentum transport. In previous work, we conducted a series of numerical simulations designed to quantify the effects of gravitational instabilities in a generalizable way (Tomley, Cassen, & Steiman-Cameron 1991). Here we present a second series of simulations in which we examine disks of greater size, increased star/disk mass ratio, and flatter surface density distribution than those in our initial study. The purpose is to represent disks at a later stage of evolution than those already studied, to test the quantitative relations derived in our earlier work and to explore the effects of mass ratio on the results. The new results indicate that the tendencies for unstable, uncooled disks to heat to stability and for dynamical evolution rates to be proportional to cooling rates are general characteristics of the behavior of gravitationally unstable disks. Nevertheless, there are quantitative, and (for strong cooling) even qualitative differences that are revealed in the new simulations, particularly with regard to the cooling rates at which clumping tends to occur.

  18. On the tidal interaction between protostellar disks and companions

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Papaloizou, J. C. B.

    1993-01-01

    Formation of protoplanets and binary stars in a protostellar disk modifies the structure of the disk. Through tidal interactions, energy and angular momentum are transferred between the disk and protostellar or protoplanetary companion. We summarize recent progress in theoretical investigations of the disk-companion tidal interaction. We show that low-mass protoplanets excite density waves at their Lindblad resonances and that these waves are likely to be dissipated locally. When a protoplanet acquires sufficient mass, its tidal torque induces the formation of a gap in the vicinity of its orbit. Gap formation leads to the termination of protoplanetary growth by accretion. For proto-Jupiter to attain its present mass, we require that (1) the primordial solar nebula is heated by viscous dissipation; (2) the viscous evolution time scale of the nebula is comparable to the age of typical T Tauri stars with circumstellar disks; and (3) the mass distribution in the nebula is comparable to that estimated from a minimum-mass nebula model.

  19. Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit

    NASA Astrophysics Data System (ADS)

    Mellon, Richard R.; Li, Zhi-Yun

    2008-07-01

    Magnetic fields are usually considered dynamically important in star formation when the dimensionless mass-to-flux ratio is close to, or less than, unity (λ lesssim 1). We show that, in disk formation, the requirement is far less stringent. This conclusion is drawn from a set of 2D (axisymmetric) simulations of the collapse of rotating, singular isothermal cores magnetized to different degrees. We find that a weak field corresponding to λ ~ 100 can begin to disrupt the rotationally supported disk through magnetic braking, by creating regions of rapid, supersonic collapse in the disk. These regions are separated by one or more centrifugal barriers, where the rapid infall is temporarily halted. The number of centrifugal barriers increases with the mass-to-flux ratio λ. When λ gtrsim 100, they merge together to form a more or less contiguous, rotationally supported disk. Even though the magnetic field in such a case is extremely weak on the scale of dense cores, it is amplified by collapse and differential rotation, to the extent that its pressure dominates the thermal pressure in both the disk and its surrounding region. For relatively strongly magnetized cores with λ lesssim 10, the disk formation is suppressed completely, as found previously. A new feature is that the mass accretion is highly episodic, due to reconnection of the magnetic field lines accumulated near the center. For rotationally supported disks to appear during the protostellar mass accretion phase of star formation in dense cores with realistic field strengths, the powerful magnetic brake must be weakened, perhaps through nonideal MHD effects. Another possibility is to remove, through protostellar winds, the material that acts to brake the disk rotation. We discuss the possibility of observing a generic product of the magnetic braking, an extended circumstellar region that is supported by a combination of toroidal magnetic field and rotation—a "magnetogyrosphere"—interferometrically.

  20. Signatures of Gravitational Instability in Resolved Images of Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Dong, Ruobing; Vorobyov, Eduard; Pavlyuchenkov, Yaroslav; Chiang, Eugene; Liu, Hauyu Baobab

    2016-06-01

    Protostellar (class 0/I) disks, which have masses comparable to those of their nascent host stars and are fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and millimeter-wave interferometry, we explore the observational signatures of GI in disks using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and millimeter dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of astronomical units, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane; therefore, arms scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. In contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes; such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At millimeter wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one hour integration times at ∼0.″1 resolution. Collapsed fragments having masses ≳1 M J can be detected by ALMA within ∼10 minutes.

  1. The formation of protostellar disks. I - 1 M(solar)

    NASA Technical Reports Server (NTRS)

    Yorke, Harold W.; Bodenheimer, Peter; Laughlin, Gregory

    1993-01-01

    Hydrodynamical calculations of the collapse of an axisymmetric, rotating one solar mass protostellar cloud, including the effects of radiative transfer and radiative acceleration but without magnetic fields, are presented. The results include calculations of infrared protostellar spectra as a function of time and viewing angle. A numerical algorithm involving explicit nested grids is used to resolve the region of initial disk formation and at the same time to include the outer regions in the calculation. The central part of the protostar is modeled approximately. Initial conditions are systematically varied to investigate their influence on the evolution and final configuration of central star plus circumstellar disk. The initial state for the standard case is a centrally condensed molecular cloud core of one solar mass with a mean density of 8 x 10 exp -18 g/cu cm and a specific angular momentum at the outer edge of 7 x 10 exp 20 sq cm/s. The collapse is followed for 8 x 10 exp 4 yr, at which point 0.45 solar mass is contained in a rapidly rotating central object and most of the remainder in a surrounding equilibrium disk. The stability of this final structure is qualitatively analyzed.

  2. MAGNETIZED ACCRETION AND DEAD ZONES IN PROTOSTELLAR DISKS

    SciTech Connect

    Dzyurkevich, Natalia; Henning, Thomas; Turner, Neal J.; Kley, Wilhelm

    2013-03-10

    The edges of magnetically dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 M{sub Sun }, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freezeout line.

  3. The physical and chemical evolution of protostellar disks. The growth of protostellar disks: Progress to date

    NASA Technical Reports Server (NTRS)

    Stahler, Steven W.

    1993-01-01

    This study constitutes one part of our multi-disciplinary approach to the evolution of planet-forming disks. The goal is to establish the disks' thermal and mechanical properties as they grow by the infall of their parent interstellar clouds. Thus far, significant advances toward establishing the evolving surface density of such disks was made.

  4. RAPID MID-INFRARED VARIABILITY IN PROTOSTELLAR DISKS

    SciTech Connect

    Ke, T. T.; Huang, H.; Lin, D. N. C.

    2012-01-20

    Spectral energy distribution (SED) in protostellar disks is determined by the disks' internal dissipation and reprocessing of irradiation from their host stars. Around T Tauri stars, most mid-infrared (MIR) radiation (in a wavelength range from a few to a few tens of {mu}m) emerges from regions around a fraction to a few AU. This region is interesting because it contains both the habitable zone and the snow line. Recent observations reveal SED variations in the MIR wavelength range. These variations are puzzling because they occur on a timescale (a few days) which is much shorter than the dynamical (months to years) timescale from 1 AU to a few AU. They are probably caused by shadows cast by inner onto outer disk regions. Interaction between disks and their misaligned magnetized host stars can lead to warped structure and periodic SED modulations. Rapid aperiodic SED variations may also be induced by observed X-ray flares from T Tauri stars. These flares can significantly modulate the ionization fraction of the gas and the net charge carried by the grains near the surface of the inner disk. The newly charged grains may be accelerated by the stellar or disk magnetic field and adjust their distances from the midplane. Shadows cast by these grains attenuate the flux of stellar photons irradiated onto regions at several AU from the central stars. We use this model to account for the observed rapid aperiodic SED variabilities. We suggest that regular monitoring of SED variations will not only provide valuable information on the distribution of the disk aspect ratio near the habitable zone but also provide a probe of the interaction between the inner regions of the disk with the magnetosphere of their host stars.

  5. DUST TRANSPORT IN PROTOSTELLAR DISKS THROUGH TURBULENCE AND SETTLING

    SciTech Connect

    Turner, N. J.; Carballido, A.; Sano, T.

    2010-01-01

    We apply ionization balance and magnetohydrodynamical (MHD) calculations to investigate whether magnetic activity moderated by recombination on dust grains can account for the mass accretion rates and the mid-infrared spectra and variability of protostellar disks. The MHD calculations use the stratified shearing-box approach and include grain settling and the feedback from the changing dust abundance on the resistivity of the gas. The two-decade spread in accretion rates among solar-mass T Tauri stars is too large to result solely from variations in the grain size and stellar X-ray luminosity, but can plausibly be produced by varying these parameters together with the disk magnetic flux. The diverse shapes and strengths of the mid-infrared silicate bands can come from the coupling of grain settling to the distribution of the magnetorotational turbulence, through the following three effects. First, recombination on grains 1 mum or smaller yields a magnetically inactive dead zone extending more than two scale heights from the midplane, while turbulent motions in the magnetically active disk atmosphere overshoot the dead zone boundary by only about one scale height. Second, grains deep in the dead zone oscillate vertically in wave motions driven by the turbulent layer above, but on average settle at the rates found in laminar flow, so that the interior of the dead zone is a particle sink and the disk atmosphere will become dust-depleted unless resupplied from elsewhere. Third, with sufficient depletion, the dead zone is thinner and mixing dredges grains off the midplane. The last of these processes enables evolutionary signatures such as the degree of settling to sometimes decrease with age. The MHD results also show that the magnetic activity intermittently lifts clouds of small grains into the atmosphere. Consequently the photosphere height changes by up to one-third over timescales of a few orbits, while the extinction along lines of sight grazing the disk surface

  6. Long-term Evolution of Protostellar and Protoplanetary Disks. II. Layered Accretion with Infall

    NASA Astrophysics Data System (ADS)

    Zhu, Zhaohuan; Hartmann, Lee; Gammie, Charles

    2010-04-01

    We use one-dimensional two-zone time-dependent accretion disk models to study the long-term evolution of protostellar disks subject to mass addition from the collapse of a rotating cloud core. Our model consists of a constant surface density magnetically coupled active layer, with transport and dissipation in inactive regions only via gravitational instability. We start our simulations after a central protostar has formed, containing ~10% of the mass of the protostellar cloud. Subsequent evolution depends on the angular momentum of the accreting envelope. We find that disk accretion matches the infall rate early in the disk evolution because much of the inner disk is hot enough to couple to the magnetic field. Later infall reaches the disk beyond ~10 AU, and the disk undergoes outbursts of accretion in FU Ori-like events as described by Zhu et al. If the initial cloud core is moderately rotating, most of the central star's mass is built up by these outburst events. Our results suggest that the protostellar "luminosity problem" is eased by accretion during these FU Ori-like outbursts. After infall stops, the disk enters the T Tauri phase. An outer, viscously evolving disk has a structure that is in reasonable agreement with recent submillimeter studies and its surface density evolves from Σ vprop R -1 to R -1.5. An inner, massive belt of material—the "dead zone"—would not have been observed yet but should be seen in future high angular resolution observations by EVLA and ALMA. This high surface density belt is a generic consequence of low angular momentum transport efficiency at radii where the disk is magnetically decoupled, and would strongly affect planet formation and migration.

  7. Occurrence of instability through the protostellar accretion disks by landing of low-mass condensations

    NASA Astrophysics Data System (ADS)

    Elyasi, Mahjubeh; Nejad-Asghar, Mohsen

    2016-06-01

    Low-mass condensations (LMCs) are observed inside the envelope of the collapsing molecular cloud cores. In this research, we investigate the effects of landing LMCs for occurrence of instability through the protostellar accretion disks. We consider some regions of the disk where duration of infalling and landing of the LMCs are shorter than the orbital period. In this way, we can consider the landing LMCs as density bumps and grooves in the azimuthal direction of an initial thin axisymmetric steady state self-gravitating protostellar accretion disk (nearly Keplerian). Using the linear effects of the bump quantities, we obtain a characteristic equation for growth/decay rate of bumps; we numerically solve it to find occurrence of instability. We also evaluate the minimum-growth-time-scale (MGTS) and the enhanced mass accretion rate. The results show that infalling and landing of the LMCs in the inner regions of the protostellar accretion disks can cause faster unstable modes and less enhanced accretion rates relative to the outer regions. Also, more fragmentation of landed LMCs in the azimuthal direction have less chance for instability, and then can produce more values of enhanced mass accretion rate.

  8. Nonlinear evolution of protostellar disks and light modulations in young stellar objects

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Bell, K. R.

    1990-01-01

    An evolutionary model of dynamical processes in protostellar disks is described and illustrated with graphs of typical results. The effective transport mechanisms are discussed, including thermal convection, nonaxisymmetric gravitational instabilities in the outer regions of disks, and wave propagation. Consideration is then given to the stages of dynamical evolution, FU Ori outburst phenomena, unsteady accretion-disk flows, and nonlinear feedback as a mechanism to modulate mass transfer. The simulations show that mass redistribution is determined by angular-momentum transfer, which in turn is regulated by the effective viscosity generated by convectively driven turbulence. Significant mass transfer occurs as a result of mixing of infalling material with disk gas and is affected by the tidal torque associated with the growth of nonaxisymmetric disturbances in the outer disk. The time scale for disk evolution is found to be about 1 Myr.

  9. Radiation Magnetohydrodynamic Simulations of Protostellar Collapse: Nonideal Magnetohydrodynamic Effects and Early Formation of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Tomida, Kengo; Okuzumi, Satoshi; Machida, Masahiro N.

    2015-03-01

    The transport of angular momentum by magnetic fields is a crucial physical process in the formation and evolution of stars and disks. Because the ionization degree in star-forming clouds is extremely low, nonideal magnetohydrodynamic (MHD) effects such as ambipolar diffusion and ohmic dissipation work strongly during protostellar collapse. These effects have significant impacts in the early phase of star formation as they redistribute magnetic flux and suppress angular momentum transport by magnetic fields. We perform three-dimensional nested-grid radiation magnetohydrodynamic simulations including ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields transport angular momentum so efficiently that no rotationally supported disk is formed even after the second collapse. Ohmic dissipation works only in a relatively high density region within the first core and suppresses angular momentum transport, enabling formation of a very small rotationally supported disk after the second collapse. With both ohmic dissipation and ambipolar diffusion, these effects work effectively in almost the entire region within the first core and significant magnetic flux loss occurs. As a result, a rotationally supported disk is formed even before a protostellar core forms. The size of the disk is still small, about 5 AU at the end of the first core phase, but this disk will grow later as gas accretion continues. Thus, the nonideal MHD effects can resolve the so-called magnetic braking catastrophe while keeping the disk size small in the early phase, which is implied from recent interferometric observations.

  10. 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.

  11. A numerical model for the formation and long-term evolution of protostars and protostellar disks

    NASA Astrophysics Data System (ADS)

    Fateeva, A. M.; Zhilkin, A. G.; Pavlyuchenkov, Ya. N.; Vorobyov, E. I.

    2016-02-01

    We present a physical and numerical model for studying the formation and evolution of protostellar objects with solar and sub-solar masses. The model covers several evolutionary phases of these objects starting from the gravitational collapse of an initially unstable pre-stellar cloud, proceeding through the formation and collapse of the first hydrostatic core, and ending with the complete dissipation of the initial cloud and formation of a protostar and protostellar disk. The model is described by a system of MHD equations that includes Ohmic dissipation and ambipolar diffusion, and also a scheme for calculating the thermal and ionization structure of the cloud. We employ the multicomponent approach for computing the thermal structure of collapsing protostellar cloud, in which the dust and gas temperatures are treated separately, allowing us to accurately describe the initial stages of the cloud's gravitational contraction and collapse. We present the first results showing the structure of an initially quasi-equilibrium protostellar cloud during the first stages of gravitational collapse and subsequent evolution.

  12. Resonantly driven nonlinear density waves in protostellar disks

    NASA Technical Reports Server (NTRS)

    Yuan, Chi; Cassen, Pat

    1994-01-01

    Recent observations of binary, pre-main-sequence, solar-type stars provide evidence that such systems may coexist with circumstellar disks. The binary disk systems, besides being of general interest for the study of star formation, potentially provide useful tests of companion-disk interaction theories prominent in current hypotheses of planet formation. In this paper, we apply an asymptotic analysis of the nonlinear, resonant interaction of a stellar companion with a disk to understand the dependence of such interactions on the properties of the system: the binary mass ratio, the physical properties of the disk, and the effective dissipation (treated herein as viscosity). The method is based on a WKBJ approximation and exploits the conditions that the disk is thin and much less massive than the primary, but does not require that the companion-induced disturbance be small. Both isothermal and adiabatic responses are treated. Only circular orbit resonances are considered in this paper. It is demonstrated that the temperature of the disk as well as the relative mass of the companion affects the degree of nonlinearity, and that nonlinearity promotes high wave compression ratios, long wavelengths, and increased propagation distances. Nevertheless, the total torque exerted between the companion and the disk is well represented by linear theory. The amplitudes of density disturbances are reduced by viscosity and nonisothermality. Because resonant interactions are generally strong and capable of driving rapid evolution, one might expect observations of systems undergoing strong, resonant-driven evolution to be rare. In this connection, it is pointed out that the m = 1 resonance is distinguished by being anomalously weaker than the others and is therefore of observational interest. It is speculated that, in conditions of intrinsically small dissipation, the propagation of resonant-driven density waves is limited by the tendency of their wavelength to diminish with distance

  13. ENERGETIC PROTONS, RADIONUCLIDES, AND MAGNETIC ACTIVITY IN PROTOSTELLAR DISKS

    SciTech Connect

    Turner, N. J.; Drake, J. F.

    2009-10-01

    We calculate the location of the magnetically inactive dead zone in the minimum-mass protosolar disk, under ionization scenarios including stellar X-rays, long- or short-lived radionuclide decay, and energetic protons arriving from the general interstellar medium, from a nearby supernova explosion, from the disk corona, or from the corona of the young star. The disk contains a dead zone in all scenarios except those with small dust grains removed and a fraction of the short-lived radionuclides remaining in the gas. All the cases without exception have an 'undead zone' where intermediate resistivities prevent magneto-rotational turbulence while allowing shear-generated large-scale magnetic fields. The mass column in the undead zone is typically greater than the column in the turbulent surface layers. The results support the idea that the dead and undead zones are robust consequences of cold, dusty gas with mass columns exceeding 1000 g cm{sup -2}.

  14. Angular momentum exchange by gravitational torques and infall in the circumbinary disk of the protostellar system L1551 NE

    SciTech Connect

    Takakuwa, Shigehisa; Ho, Paul T. P.; Saito, Masao; Saigo, Kazuya; Matsumoto, Tomoaki; Lim, Jeremy; Hanawa, Tomoyuki

    2014-11-20

    We report an ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, C{sup 18}O (3-2), and {sup 13}CO (3-2) lines at a ∼1.6 times higher resolution and a ∼6 times higher sensitivity than those of our previous SubMillimeter Array (SMA) observations, which revealed a r ∼ 300 AU scale circumbinary disk in Keplerian rotation. The 0.9 mm continuum shows two opposing U-shaped brightenings in the circumbinary disk and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.

  15. Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE

    NASA Astrophysics Data System (ADS)

    Takakuwa, Shigehisa; Saito, Masao; Saigo, Kazuya; Matsumoto, Tomoaki; Lim, Jeremy; Hanawa, Tomoyuki; Ho, Paul T. P.

    2014-11-01

    We report an ALMA observation of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6 times higher resolution and a ~6 times higher sensitivity than those of our previous SubMillimeter Array (SMA) observations, which revealed a r ~ 300 AU scale circumbinary disk in Keplerian rotation. The 0.9 mm continuum shows two opposing U-shaped brightenings in the circumbinary disk and exhibits a depression between the circumbinary disk and the circumstellar disk of the primary protostar. The molecular lines trace non-axisymmetric deviations from Keplerian rotation in the circumbinary disk at higher velocities relative to the systemic velocity, where our previous SMA observations could not detect the lines. In addition, we detect inward motion along the minor axis of the circumbinary disk. To explain the newly observed features, we performed a numerical simulation of gas orbits in a Roche potential tailored to the inferred properties of L1551 NE. The observed U-shaped dust features coincide with locations where gravitational torques from the central binary system are predicted to impart angular momentum to the circumbinary disk, producing shocks and hence density enhancements seen as a pair of spiral arms. The observed inward gas motion coincides with locations where angular momentum is predicted to be lowered by the gravitational torques. The good agreement between our observation and model indicates that gravitational torques from the binary stars constitute the primary driver for exchanging angular momentum so as to permit infall through the circumbinary disk of L1551 NE.

  16. Protostellar Multiplicity in Perseus Characterized by the VLA Nascent Disk and Multiplicity (VANDAM) Survey

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The formation of multiple star systems is thought to begin early in the star formation process. However, there have not been sufficient numbers of young protostars observed with high enough resolution to determine when and where most multiple systems form. To significantly improve our knowledge of protostellar multiplicity, we have carried out the VLA Nascent Disk and Multiplicity (VANDAM) survey, a 264 hour Jansky VLA program at wavelengths of 8 mm, 1 cm, 4 cm, and 6 cm toward all known Perseus protostars (N ~ 80) down to 15 AU (0.065") resolution. The unbiased nature of the survey has enabled us to conduct the most complete characterization of protostellar multiplicity to date, finding evidence for a bi-modal distribution of multiple protostar system separations. The bi-modal distribution may be evidence for multiple processes contributing to the formation of multiple systems. The inner peak at ~75 AU could be produced from disk fragmentation, while the outer peak at ~3000 AU could be produced by turbulent and/or rotational fragmentation Moreover, three systems are found to reside within larger, disk-like structures suggesting that they may be the product of disk fragmentation via gravitational instability. The results of this survey demonstrate the power and utility of unbiased surveys toward young stars.

  17. 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.

  18. On the role of pseudodisk warping and reconnection in protostellar disk formation in turbulent magnetized cores

    SciTech Connect

    Li, Zhi-Yun; Zhao, Bo; Krasnopolsky, Ruben; Shang, Hsien

    2014-10-01

    The formation of rotationally supported protostellar disks is suppressed in ideal MHD in non-turbulent cores with aligned magnetic fields and rotation axes. A promising way to resolve this so-called 'magnetic braking catastrophe' is through turbulence. The reason for the turbulence-enabled disk formation is usually attributed to the turbulence-induced magnetic reconnection, which is thought to reduce the magnetic flux accumulated in the disk-forming region. We advance an alternative interpretation, based on magnetic decoupling-triggered reconnection of severely pinched field lines close to the central protostar and turbulence-induced warping of the pseudodisk of Galli and Shu. Such reconnection weakens the central split magnetic monopole that lies at the heart of the magnetic braking catastrophe under flux freezing. We show, through idealized numerical experiments, that the pseudodisk can be strongly warped, but not completely destroyed, by a subsonic or sonic turbulence. The warping decreases the rates of angular momentum removal from the pseudodisk by both magnetic torque and outflow, making it easier to form a rotationally supported disk. More importantly, the warping of the pseudodisk out of the disk-forming, equatorial plane greatly reduces the amount of magnetic flux threading the circumstellar, disk-forming region, further promoting disk formation. The beneficial effects of pseudodisk warping can also be achieved by a misalignment between the magnetic field and rotation axis. These two mechanisms of disk formation, enabled by turbulence and field-rotation misalignment respectively, are thus unified. We find that the disks formed in turbulent magnetized cores are rather thick and significantly magnetized. Implications of these findings, particularly for the thick young disk inferred in L1527, are briefly discussed.

  19. On the Role of Pseudodisk Warping and Reconnection in Protostellar Disk Formation in Turbulent Magnetized Cores

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Yun; Krasnopolsky, Ruben; Shang, Hsien; Zhao, Bo

    2014-10-01

    The formation of rotationally supported protostellar disks is suppressed in ideal MHD in non-turbulent cores with aligned magnetic fields and rotation axes. A promising way to resolve this so-called "magnetic braking catastrophe" is through turbulence. The reason for the turbulence-enabled disk formation is usually attributed to the turbulence-induced magnetic reconnection, which is thought to reduce the magnetic flux accumulated in the disk-forming region. We advance an alternative interpretation, based on magnetic decoupling-triggered reconnection of severely pinched field lines close to the central protostar and turbulence-induced warping of the pseudodisk of Galli and Shu. Such reconnection weakens the central split magnetic monopole that lies at the heart of the magnetic braking catastrophe under flux freezing. We show, through idealized numerical experiments, that the pseudodisk can be strongly warped, but not completely destroyed, by a subsonic or sonic turbulence. The warping decreases the rates of angular momentum removal from the pseudodisk by both magnetic torque and outflow, making it easier to form a rotationally supported disk. More importantly, the warping of the pseudodisk out of the disk-forming, equatorial plane greatly reduces the amount of magnetic flux threading the circumstellar, disk-forming region, further promoting disk formation. The beneficial effects of pseudodisk warping can also be achieved by a misalignment between the magnetic field and rotation axis. These two mechanisms of disk formation, enabled by turbulence and field-rotation misalignment respectively, are thus unified. We find that the disks formed in turbulent magnetized cores are rather thick and significantly magnetized. Implications of these findings, particularly for the thick young disk inferred in L1527, are briefly discussed.

  20. Eccentricity Evolution of Extrasolar Multiple Planetary Systems Due to the Depletion of Nascent Protostellar Disks

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

    Most extrasolar planets are observed to have eccentricities much larger than those in the solar system. Some of these planets have sibling planets, with comparable masses, orbiting around the same host stars. In these multiple planetary systems, eccentricity is modulated by the planets' mutual secular interaction as a consequence of angular momentum exchange between them. For mature planets, the eigenfrequencies of this modulation are determined by their mass and semimajor axis ratios. However, prior to the disk depletion, self-gravity of the planets' nascent disks dominates the precession eigenfrequencies. We examine here the initial evolution of young planets' eccentricity due to the apsidal libration or circulation induced by both the secular interaction between them and the self-gravity of their nascent disks. We show that as the latter effect declines adiabatically with disk depletion, the modulation amplitude of the planets' relative phase of periapsis is approximately invariant despite the time-asymmetrical exchange of angular momentum between planets. However, as the young planets' orbits pass through a state of secular resonance, their mean eccentricities undergo systematic quantitative changes. For applications, we analyze the eccentricity evolution of planets around υ Andromedae and HD 168443 during the epoch of protostellar disk depletion. We find that the disk depletion can change the planets' eccentricity ratio. However, the relatively large amplitude of the planets' eccentricity cannot be excited if all the planets had small initial eccentricities.

  1. IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

    NASA Technical Reports Server (NTRS)

    Remijan, Anthony J.; Hollis, J. M.

    2005-01-01

    We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH3CH2CN)) methyl formate (CH3OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emission has a spatial scale of approx. 20" and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of approx. 6" and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2" that map approx. 2" northeast of the A and B symmetry axis. The redshifted SiO is approx. 2" northwest of blueshifted SiO along a position angle of approx. 135deg which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive approx. 1.4 Solar Mass, interior to the SiO emission. In the same vicinity, Mundy et al. (1986) also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous CO-13 emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and CO-13 data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array CO-12C data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counter-rotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed.

  2. Using FU Orionis outbursts to constrain self-regulated protostellar disk models

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Lin, D. N. C.

    1994-01-01

    One-dimensional, convective, vertical structure models and one dimensional time-dependent, radial diffusion models are combined to create a self-consistent picture in which FU Orionis outbursts occur in young stellar objects (YSOs) as the result of a large-scale, self-regulated, thermal ionization instability in the surrounding protostellar accretion disk. Although active accretion disks have long been postulated to be ubiqitous among low-mass YSOs, few constraints have until now been imposed on physical conditions in these disks. By fitting the results of time-dependent disk models to observed timescales of FU Orionis events, we estimate the magnitude of the effective viscous stress in the inner disk (r approximately less than 1 AU) to be, in accordance with an ad hoc 'alpha' prescription, the product of the local sound speed, pressure scale height, and an efficiency factor alpha of 10(exp -4) where hydrogen is neutral and 10(exp 3) where hydrogen is ionized. We hypothesize that all YSOs receive infall onto their outer disks which is steady (or slowly declining with time) and that FU Orionis outbursts are self-regulated, disk outbursts which occur only in systems which transport matter inward at a rate sufficiently high to cause hydrogen to be ionized in the inner disk. We estimate a critical mass flux of dm(sub crit)/dt = 5 x 10(exp 7) solar mass/yr independent of the magnitude of alpha for systems with one solar mass, three solar radius central objects. Infall accretion rates in the range of dm(sub in)/dt = 1-10) x 10(exp -6) solar mass/yr produce observed FU Orionis timescales consistent with estimates of spherical molecular cloud core collapse rates. Modeled ionization fronts are typically initiated near the inner edge of the disk and propogate out to a distance of several tens of stellar radii. Beyond this region, the disk transports mass steadily inward at the supplied constant infall rate. Mass flowing through the innermost disk annulus is equal to dm

  3. A CHEMICAL VIEW OF PROTOSTELLAR-DISK FORMATION IN L1527

    SciTech Connect

    Sakai, Nami; Oya, Yoko; Watanabe, Yoshimasa; Yamamoto, Satoshi; Sakai, Takeshi; Hirota, Tomoya; Ceccarelli, Cecilia; Kahane, Claudine; Lopez-Sepulcre, Ana; Lefloch, Bertrand; Vastel, Charlotte; Bottinelli, Sandrine; Caux, Emmanuel; Coutens, Audrey; Aikawa, Yuri; Takakuwa, Shigehisa; Yen, Hsi-Wei; Ohashi, Nagayoshi

    2014-08-20

    Subarcsecond images of the rotational line emissions of CCH, CS, H{sub 2}CO, and CH{sub 3}OH have been obtained toward the low-mass protostar IRAS 04368+2557 in L1527 as one of the early science projects of the Atacama Large Millimeter/submillimeter Array. The intensity distributions of CCH and CS show a double-peaked structure along the edge-on envelope with a dip toward the protostar position, whereas those of H{sub 2}CO and CH{sub 3}OH are centrally peaked. By analyzing the position-velocity diagrams along the envelope, CCH and CS are found to reside mainly in the envelope, where the gas is infalling with conservation of its angular momentum. They are almost absent inward of the centrifugal barrier (a half of the centrifugal radius). Although H{sub 2}CO exists in the infalling rotating envelope, it also resides in the disk component inside the centrifugal barrier to some extent. On the other hand, CH{sub 3}OH seems to exist around the centrifugal barrier and in the disk component. Hence, the drastic chemical change occurs at the centrifugal barrier. A discontinuous infalling motion as well as the gas-grain interaction would be responsible for the chemical change. This result will put an important constraint on initial chemical compositions for chemical evolution of protostellar disks.

  4. THE CIRCUMBINARY OUTFLOW: A PROTOSTELLAR OUTFLOW DRIVEN BY A CIRCUMBINARY DISK

    SciTech Connect

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki E-mail: inutsuka@nagoya-u.j

    2009-10-10

    Protostellar outflow is a star's first cry at the moment of birth. The outflows have an indispensable role in the formation of single stars because they carry off the excess angular momentum from the center of the shrinking gas cloud, and permit further collapse to form a star. On the other hand, a significant fraction of stars is supposedly born as binaries with circumbinary disks that are frequently observed. Here, we investigate the evolution of a magnetized rotating cloud using a three-dimensional resistive MHD nested-grid code, and show that the outflow is driven by the circumbinary disk and has an important role even in the binary formation. After the adiabatic core formation in the collapsing cloud core, the magnetic flux is significantly removed from the center of the cloud by the Ohmic dissipation. Since this removal makes the magnetic braking ineffective, the adiabatic core continuously acquires the angular momentum to induce fragmentation and subsequent binary formation. The magnetic field accumulates in the circumbinary disk where the removal and accretion of magnetic field are balanced, and finally drives the circumbinary outflow. This result explains the spectacular morphology of some specific young stellar objects such as L1551 IRS5. We can infer that most of the bipolar molecular outflows observed by low density tracers (i.e., CO) would correspond to circumbinary or circum-multiple outflows found in this Letter, since most of the young stellar objects are supposed to be binaries or multiples.

  5. Revolutionizing our View of Protostellar Multiplicity and Disks: The VLA Nascent Disk and Multiplicity (VANDAM) Survey of the Perseus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Tobin, J. J.; Looney, L. W.; Li, Z.-Y.; Chandler, C. J.; Dunham, M. M.; Segura-Cox, D.; Cox, E. G.; Harris, R. J.; Melis, C.; Sadavoy, S. I.; Pérez, L.; Kratter, K.

    2016-05-01

    There is substantial evidence for disk formation taking place during the early stages of star formation and for most stars being born in multiple systems; however, protostellar multiplicity and disk searches have been hampered by low resolution, sample bias, and variable sensitivity. We have conducted an unbiased, high-sensitivity Karl G. Jansky Very Large Array (VLA) survey toward all known protostars (n = 94) in the Perseus molecular cloud (d ˜ 230 pc), with a resolution of ˜ 15 AU (0.06'') at λ = 8 mm. We have detected candidate protostellar disks toward 17 sources (with 12 of those in the Class 0 stage) and we have found substructure on < 50 AU scales for three Class 0 disk candidates, possibly evidence for disk fragmentation. We have discovered 16 new multiple systems (or new components) in this survey; the new systems have separations < 500 AU and 3 by < 30 AU. We also found a bi-modal distribution of separations, with peaks at ˜ 75 AU and ˜ 3000 AU, suggestive of formation through two distinct mechanisms: disk and turbulent fragmentation. The results from this survey demonstrate the necessity and utility of uniform, unbiased surveys of protostellar systems at millimeter and centimeter wavelengths.

  6. PROTOSTELLAR DISK EVOLUTION OVER MILLION-YEAR TIMESCALES WITH A PRESCRIPTION FOR MAGNETIZED TURBULENCE

    SciTech Connect

    Landry, Russell; Dodson-Robinson, Sarah E.; Turner, Neal J.

    2013-07-10

    Magnetorotational instability (MRI) is the most promising mechanism behind accretion in low-mass protostellar disks. Here we present the first analysis of the global structure and evolution of non-ideal MRI-driven T-Tauri disks on million-year timescales. We accomplish this in a 1+1D simulation by calculating magnetic diffusivities and utilizing turbulence activity criteria to determine thermal structure and accretion rate without resorting to a three-dimensional magnetohydrodynamical (MHD) simulation. Our major findings are as follows. First, even for modest surface densities of just a few times the minimum-mass solar nebula, the dead zone encompasses the giant planet-forming region, preserving any compositional gradients. Second, the surface density of the active layer is nearly constant in time at roughly 10 g cm{sup -2}, which we use to derive a simple prescription for viscous heating in MRI-active disks for those who wish to avoid detailed MHD computations. Furthermore, unlike a standard disk with constant-{alpha} viscosity, the disk midplane does not cool off over time, though the surface cools as the star evolves along the Hayashi track. Instead, the MRI may pile material in the dead zone, causing it to heat up over time. The ice line is firmly in the terrestrial planet-forming region throughout disk evolution and can move either inward or outward with time, depending on whether pileups form near the star. Finally, steady-state mass transport is an extremely poor description of flow through an MRI-active disk, as we see both the turnaround in the accretion flow required by conservation of angular momentum and peaks in M-dot (R) bracketing each side of the dead zone. We caution that MRI activity is sensitive to many parameters, including stellar X-ray flux, grain size, gas/small grain mass ratio and magnetic field strength, and we have not performed an exhaustive parameter study here. Our 1+1D model also does not include azimuthal information, which prevents

  7. The ALMA view of the protostellar system HH212. The wind, the cavity, and the disk

    NASA Astrophysics Data System (ADS)

    Codella, C.; Cabrit, S.; Gueth, F.; Podio, L.; Leurini, S.; Bachiller, R.; Gusdorf, A.; Lefloch, B.; Nisini, B.; Tafalla, M.; Yvart, W.

    2014-08-01

    Context. Because it is viewed simply edge-on, the HH212 protostellar system is an ideal laboratory for studying the interplay of infall, outflow, and rotation in the earliest stages of low-mass star formation. Aims: We wish to exploit the unmatched combination of high angular resolution, high sensitivity, high-imaging fidelity, and spectral coverage provided by ALMA to shed light on the complex kinematics of the innermost central regions of HH212. Methods: We mapped the inner 10″ (4500 AU) of the HH212 system at ≃0.5″ resolution in several molecular tracers and in the 850 μm dust continuum using the ALMA interferometer in band 7 in the extended configuration of the Early Science Cycle 0 operations. Results: Within a single ALMA spectral set-up, we simultaneously identify all the crucial ingredients known to be involved in the star formation recipe: (i) the fast, collimated bipolar SiO jet driven by the protostar; (ii) the large-scale swept-up CO outflow; (iii) the flattened rotating and infalling envelope, with bipolar cavities carved by the outflow (in C17O(3-2)); and (iv) a rotating wide-angle flow that fills the cavities and surrounds the axial jet (in C34S(7-6)). In addition, the compact high-velocity C17O emission (±1.9-3.5 km s-1 from systemic) shows a velocity gradient along the equatorial plane consistent with a rotating disk of ≃0farcs2 = 90 AU around a ≃0.3 ± 0.1 M⊙ source. The rotating disk is possibly Keplerian. Conclusions: HH212 is the third Class 0 protostar with possible signatures of a Keplerian disk of radius ≥30 AU. The warped geometry in our CS data suggests that this large Keplerian disk might result from misaligned magnetic and rotation axes during the collapse phase. The wide-angle CS flow suggests that disk winds may be present in this source. Appendix A is available in electronic form at http://www.aanda.orgFinal reduced ALMA cubes (FITS) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp

  8. Angular Momentum Loss in the Envelope–Disk Transition Region of the HH 111 Protostellar System: Evidence for Magnetic Braking?

    NASA Astrophysics Data System (ADS)

    Lee, Chin-Fei; Hwang, Hsiang-Chih; Li, Zhi-Yun

    2016-08-01

    HH 111 is a Class I protostellar system at a distance of ˜400 pc, with the central source VLA 1 associated with a rotating disk deeply embedded in a flattened envelope. Here we present the observations of this system at ˜0.″6 (240 au) resolution in C18O (J = 2 — 1) and a 230 GHz continuum obtained with the Atacama Large Millimeter/Submillimeter Array, and in SO ({N}J = {5}6-{4}5) obtained with the Submillimeter Array. The observations show for the first time how a Keplerian rotating disk can be formed inside a flattened envelope. The flattened envelope is detected in C18O, extending out to ≳2400 au from the VLA 1 source. It has a differential rotation, with the outer part (≳2000 au) better described by a rotation that has constant specific angular momentum, and the innermost part (≲160 au) by a Keplerian rotation. The rotationally supported disk is therefore relatively compact in this system, which is consistent with the dust continuum observations. Most interestingly, if the flow is in steady state, there is a substantial drop in specific angular momentum in the envelope–disk transition region from 2000 to 160 au, by a factor of ˜3. Such a decrease is not expected outside a disk formed from simple hydrodynamic core collapse, but can happen naturally if the core is significantly magnetized, because magnetic fields can be trapped in the transition region outside the disk by the ram pressure of the protostellar accretion flow, which can lead to efficient magnetic braking. In addition, SO shock emission is detected around the outer radius of the disk and could trace an accretion shock around the disk.

  9. The structure of protostellar accretion disks and the origin of bipolar flows

    NASA Technical Reports Server (NTRS)

    Wardle, Mark; Koenigl, Arieh

    1993-01-01

    Equations are obtained which govern the disk-wind structure and identify the physical parameters relevant to circumstellar disks. The system of equations is analyzed in the thin-disk approximation, and it is shown that the system can be consistently reduced to a set of ordinary differential equations in z. Representative solutions are presented, and it is shown that the apparent paradox discussed by Shu (1991) is resolved when the finite thickness of the disk is taken into account. Implications of the results for the origin of bipolar flows in young stellar objects and possible application to active galactic nuclei are discussed.

  10. THE MAGNETIC FIELD IN THE CLASS 0 PROTOSTELLAR DISK OF L1527

    SciTech Connect

    Segura-Cox, Dominique M.; Looney, Leslie W.; Stephens, Ian W.; Fernández-López, Manuel; Crutcher, Richard; Kwon, Woojin; Tobin, John J.; Li, Zhi-Yun

    2015-01-01

    We present subarcsecond (∼0.''35) resolved observations of the 1.3 mm dust polarization from the edge-on circumstellar disk around the Class 0 protostar L1527. The inferred magnetic field is consistent with a dominantly toroidal morphology; there is no significantly detected vertical poloidal component to which observations of an edge-on disk are most sensitive. This suggests that angular momentum transport in Class 0 protostars (when large amounts of material are fed down to the disk from the envelope and accreted onto the protostar) is driven mainly by magnetorotational instability rather than magnetocentrifugal winds at 50 AU scales. In addition, with the data to date there is an early, tentative trend that R > 30 AU disks have so far been found in Class 0 systems with average magnetic fields on the 1000 AU scale strongly misaligned with the rotation axis. The absence of such a disk in the aligned case could be due to efficient magnetic braking that disrupts disk formation. If this is the case, this implies that candidate Class 0 disk systems could be identified by the average magnetic field direction at ∼1000 AU spatial scales.

  11. The formation of substellar objects induced by the collision of protostellar disks

    PubMed

    Lin; Laughlin; Bodenheimer; Rozyczka

    1998-09-25

    Simulations of a close encounter between two protostars, each surrounded by a relatively massive disk, resulted in the ejection of some of the disk material into a tidal tail. A portion of the tail condensed into an object with a mass in the range of 5 to 10 jovian masses. This mechanism may explain the existence of the single objects of substellar mass that have recently been discovered. PMID:9748161

  12. The effect of external environment on the evolution of protostellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Lin, D. N. C.; Guedel, Manuel

    2015-01-01

    Aims: Using numerical hydrodynamics simulations, we studied the gravitational collapse of prestellar cores of subsolar mass embedded into a low-density external environment. Methods: Four models with different magnitude and direction of rotation of the external environment with respect to the central core were studied and compared with an isolated model. Results: We found that the infall of matter from the external environment can significantly alter the disk properties as compared to those seen in the isolated model. Depending on the magnitude and direction of rotation of the external environment, a variety of disks can form including compact (≤200 AU) ones shrinking in size owing to infall of external matter with low angular momentum, as well as extended disks forming from infall of external matter with high angular momentum. The former are usually stable against gravitational fragmentation, while the latter are prone to fragmentation and formation of stellar systems with substellar/very-low-mass companions. In the case of a counter-rotating external environment, very compact (<5 AU) and short-lived (≲ a few 105 yr) disks can form when infalling material has low angular momentum. The most interesting case is found for the infall of counter-rotating external material with high angular momentum, leading to the formation of counter-rotating inner and outer disks separated by a deep gap at a few tens AU. The gap migrates inward owing to accretion of the inner disk onto the protostar, turns into a central hole, and finally disappears, giving way to the outer strongly gravitationally unstable disk. This model may lead to the emergence of a transient stellar system with planetary/substellar components counter-rotating with respect to that of the star.

  13. Dead, Undead, and Zombie Zones in Protostellar Disks as a Function of Stellar Mass

    NASA Astrophysics Data System (ADS)

    Mohanty, Subhanjoy; Ercolano, Barbara; Turner, Neal J.

    2013-02-01

    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 * = 0.7 M ⊙ and 0.1 M ⊙. In each case, we assume that: the disk surface density profile is that of a scaled Minimum Mass Solar Nebula, with M disk/M * = 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 LX /L * ≈ 10-3.5, 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 μm 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 ~5%-10% of the total disk mass; (3) the accretion rate (\\dot{M}) 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 10-2 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.

  14. DEAD, UNDEAD, AND ZOMBIE ZONES IN PROTOSTELLAR DISKS AS A FUNCTION OF STELLAR MASS

    SciTech Connect

    Mohanty, Subhanjoy; Ercolano, Barbara; Turner, Neal J. E-mail: ercolano@usm.lmu.de

    2013-02-10

    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 M {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

  15. THE SPINDLE: AN IRRADIATED DISK AND BENT PROTOSTELLAR JET IN ORION

    SciTech Connect

    Bally, John; Youngblood, Allison; Ginsburg, Adam E-mail: Allison.Youngblood@colorado.edu

    2012-09-10

    We present Hubble Space Telescope observations of a bent, pulsed Herbig-Haro jet, HH 1064, emerging from the young star Parenago 2042 embedded in the H II region NGC 1977 located about 30' north of the Orion Nebula. This outflow contains eight bow shocks in the redshifted western lobe and five bow shocks in the blueshifted eastern lobe. Shocks within a few thousand AU of the source star exhibit proper motions of {approx}160 km s{sup -1} but motions decrease with increasing distance. Parenago 2042 is embedded in a proplyd-a photoevaporating protoplanetary disk. A remarkable set of H{alpha} arcs resembling a spindle surround the redshifted (western) jet. The largest arc with a radius of 500 AU may trace the ionized edge of a circumstellar disk inclined by {approx}30 Degree-Sign . The spindle may be the photoionized edge of either a {approx}3 km s{sup -1} FUV-driven wind from the outer disk or a faster MHD-powered flow from an inner disk. The HH 1064 jet appears to be deflected north by photoablation of the south-facing side of a mostly neutral jet beam. V2412 Ori, located 1' west of Parenago 2042 drives a second bent flow, HH 1065. Both HH 1064 and 1065 are surrounded by LL Ori-type bows marking the boundary between the outflow cavity and the surrounding nebula.

  16. Herbig stars' near-infrared excess: An origin in the protostellar disk's magnetically supported atmosphere

    SciTech Connect

    Turner, N. J.; Benisty, M.; Dullemond, C. P.; Hirose, S.

    2014-01-01

    Young stars with masses 2-8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders and Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim.

  17. Chemical Evolution of Protostellar Matter

    NASA Technical Reports Server (NTRS)

    Langer, William D.; vanDishoeck, Ewine F.; Bergin, Edwin A.; Blake, Geoffrey A.; Tielens, Alexander G. G. M.; Velusamy, Thangasamy; Whittet, Douglas C. B.

    2000-01-01

    We review the chemical processes that are important in the evolution from a molecular cloud core to a protostellar disk. These cover both gas phase and gas grain interactions. The current observational and theoretical state of this field are discussed.

  18. RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION

    SciTech Connect

    Tomida, Kengo; Tomisaka, Kohji; Matsumoto, Tomoaki; Hori, Yasunori; Saigo, Kazuya; Okuzumi, Satoshi; Machida, Masahiro N. E-mail: tomisaka@th.nao.ac.jp E-mail: saigo.kazuya@nao.ac.jp E-mail: okuzumi@nagoya-u.jp

    2013-01-20

    We report the first three-dimensional radiation magnetohydrodynamic (RMHD) simulations of protostellar collapse with and without Ohmic dissipation. We take into account many physical processes required to study star formation processes, including a realistic equation of state. We follow the evolution from molecular cloud cores until protostellar cores are formed with sufficiently high resolutions without introducing a sink particle. The physical processes involved in the simulations and adopted numerical methods are described in detail. We can calculate only about one year after the formation of the protostellar cores with our direct three-dimensional RMHD simulations because of the extremely short timescale in the deep interior of the formed protostellar cores, but successfully describe the early phase of star formation processes. The thermal evolution and the structure of the first and second (protostellar) cores are consistent with previous one-dimensional simulations using full radiation transfer, but differ considerably from preceding multi-dimensional studies with the barotropic approximation. The protostellar cores evolve virtually spherically symmetric in the ideal MHD models because of efficient angular momentum transport by magnetic fields, but Ohmic dissipation enables the formation of the circumstellar disks in the vicinity of the protostellar cores as in previous MHD studies with the barotropic approximation. The formed disks are still small (less than 0.35 AU) because we simulate only the earliest evolution. We also confirm that two different types of outflows are naturally launched by magnetic fields from the first cores and protostellar cores in the resistive MHD models.

  19. KECK ADAPTIVE OPTICS OBSERVATIONS OF THE PROTOSTELLAR DISK AROUND RADIO SOURCE I IN THE ORION KLEINMANN-LOW NEBULA

    SciTech Connect

    Sitarski, Breann N.; Morris, Mark R.; Becklin, E. E.; Ghez, Andrea M.; Lu, Jessica R.; Duchene, Gaspard; Stolte, Andrea; Zinnecker, Hans

    2013-06-20

    We have made the first detection of a near-infrared counterpart associated with the disk around Radio Source ''I'', a massive protostar in the Kleinmann-Low nebula in Orion, using imaging with laser guide star adaptive optics on the Keck II telescope. The infrared emission is evident in images acquired using L' (3.8 {mu}m) and Ms (4.7 {mu}m) filters and is not detectable at K' (2.1 {mu}m). The observed morphology strongly suggests that we are seeing some combination of scattered and thermal light emanating from the disk. The disk is also manifest in the L'/Ms flux ratio image. We interpret the near-infrared emission as the illuminated surface of a nearly edge-on disk, oriented so that only the northern face is visible; the opposite surface remains hidden by the disk. We do not see infrared radiation associated directly with the star proposed to be associated with Source ''I''. The data also suggest that there is a cavity above and below the disk that is oriented perpendicular to the disk and is sculpted by the known, strong outflow from the inner disk of Source I. We compare our data to models of a protostar with a surrounding disk, envelope, and wind-blown cavity in order to elucidate the nature of the disk around Radio Source I.

  20. ALMA results of the pseudodisk, rotating disk, and jet in the continuum and HCO{sup +} in the protostellar system HH 212

    SciTech Connect

    Lee, Chin-Fei; Hirano, Naomi; Shang, Hsien; Ho, Paul T. P.; Krasnopolsky, Ruben; Zhang, Qizhou

    2014-05-10

    HH 212 is a nearby (400 pc) Class 0 protostellar system showing several components that can be compared with theoretical models of core collapse. We have mapped it in the 350 GHz continuum and HCO{sup +} J = 4-3 emission with ALMA at up to ∼0.''4 resolution. A flattened envelope and a compact disk are seen in the continuum around the central source, as seen before. The HCO{sup +} kinematics shows that the flattened envelope is infalling with small rotation (i.e., spiraling) into the central source, and thus can be identified as a pseudodisk in the models of magnetized core collapse. Also, the HCO{sup +} kinematics shows that the disk is rotating and can be rotationally supported. In addition, to account for the missing HCO{sup +} emission at low-redshifted velocity, an extended infalling envelope is required, with its material flowing roughly parallel to the jet axis toward the pseudodisk. This is expected if it is magnetized with an hourglass B-field morphology. We have modeled the continuum and HCO{sup +} emission of the flattened envelope and disk simultaneously. We find that a jump in density is required across the interface between the pseudodisk and the disk. A jet is seen in HCO{sup +} extending out to ∼500 AU away from the central source, with the peaks upstream of those seen before in SiO. The broad velocity range and high HCO{sup +} abundance indicate that the HCO{sup +} emission traces internal shocks in the jet.

  1. TURBULENT LINEWIDTHS IN PROTOPLANETARY DISKS: PREDICTIONS FROM NUMERICAL SIMULATIONS

    SciTech Connect

    Simon, Jacob B.; Beckwith, Kris; Armitage, Philip J.

    2011-12-10

    Submillimeter observations of protoplanetary disks now approach the acuity needed to measure the turbulent broadening of molecular lines. These measurements constrain disk angular momentum transport, and furnish evidence of the turbulent environment within which planetesimal formation takes place. We use local magnetohydrodynamic (MHD) simulations of the magnetorotational instability (MRI) to predict the distribution of turbulent velocities in low-mass protoplanetary disks, as a function of radius and height above the mid-plane. We model both ideal MHD disks and disks in which Ohmic dissipation results in a dead zone of suppressed turbulence near the mid-plane. Under ideal conditions, the disk mid-plane is characterized by a velocity distribution that peaks near v {approx_equal} 0.1c{sub s} (where c{sub s} is the local sound speed), while supersonic velocities are reached at z > 3H (where H is the vertical pressure scale height). Residual velocities of v Almost-Equal-To 10{sup -2} c{sub s} persist near the mid-plane in dead zones, while the surface layers remain active. Anisotropic variation of the linewidth with disk inclination is modest. We compare our MHD results to hydrodynamic simulations in which large-scale forcing is used to initiate similar turbulent velocities. We show that the qualitative trend of increasing v with height, seen in the MHD case, persists for forced turbulence and is likely a generic property of disk turbulence. Percentage level determinations of v at different heights within the disk, or spatially resolved observations that probe the inner disk containing the dead zone region, are therefore needed to test whether the MRI is responsible for protoplanetary disk turbulence.

  2. (abstract) The Circumstellar Environment of the Extremely Young Protostellar Source L1448IRS3

    NASA Technical Reports Server (NTRS)

    Tereby, S.; Padgett, Deborah L.

    1994-01-01

    The class 0 sources form an interesting new category of protostellar objects. Many have strong millimeter continuum emission and exhibit jetlike outflows. There are suggestions that these objects are systematically younger than typical embedded (class I) sources. We are investigating the properties of class 0 sources to determine whether they are indeed very young or perhaps represent extreme physical conditions, such as rapid rotation. We present millimeter interferometric data for the class 0 object known as L1448 IRS3. This young low-mass star has extremely strong millimeter continuum emission. The interferometer data show the emission is resolved on a scale of a few arcseconds (1000 AU) This suggests the bulk of the dust continuum emission originates in an 'infall' envelope rather than a protostar disk. In addition, the C180 line data display a strong velocity gradiant which indicates the dense core is rapidly rotating. We compare our data with the predictions of protostellar collapse models.

  3. Molecular emission in chemically active protostellar outflows

    NASA Astrophysics Data System (ADS)

    Lefloch, B.

    2011-12-01

    Protostellar outflows play an important role in the dynamical and chemical evolution of cloud through shocks. The Herschel Space Observatory (HSO) brings new insight both on the molecular content and the physical conditions in protostellar shocks through high spectral and angular resolution studies of the emission of major gas cooling agents and hydrides. The Herschel/CHESS key-program is carrying out an in depth study of the prototypical shock region L1157-B1. Analysis of the line profiles detected allows to constrain the formation/destruction route of various molecular species, in relation with the predictions of MHD shock models. The Herschel/WISH key-program investigates the properties and origin of water emission in a broad sample of protostellar outflows and envelopes. Implications of the first results for future studies on mass-loss phenomena are discussed.

  4. From Prestellar to Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Aikawa, Yuri; Wakelam, Valentine; Hersant, Franck; Garrod, Robin; Herbst, Eric

    2012-07-01

    We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from dense cloud cores to protostellar cores. We solve a gas-grain reaction network, which is extended to include multi-deuterated species, using a 1-D radiative hydrodynamic model with infalling fluid parcels to derive molecular distribution in assorted evolutionary stages. We find that the abundances of large organic species in the central region increase with time. The duration of the warm-up phase, in which large organic species are efficiently formed, is longer in infalling fluid parcels at later stages. Formation of unsaturated carbon chains in the CH4 sublimation zone (warm carbon chain chemistry) is more effective in later stage. The carbon ion, which reacts with CH4 to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are both heavily deuterated, mainly because their mother molecules have high D/H ratios, which are set in the cold phase. The observed CH2DOH/CH3OH ratio towards protostars is reproduced if we assume that the grain-surface exchange and abstraction reactions of CH3OH + D occurs efficiently. In our 1-D collapse model, the fluid parcels directly fall into the protostar, and the warm-up phase in the fluid parcels is rather short. But, in reality, a circumstellar disk is formed, and fluid parcels will stay there for a longer timescale than a free-fall time. We investigate the molecular evolution in such a disk by assuming that a fluid parcel stays at a constant temperature (i.e. a fixed disk radius) after the infall. The species CH3OCH3 and HCOOCH3 become more abundant in the disk than in the envelope. Both have high D/H abundance ratios as well.

  5. Tracing Protostellar Envelope Evolution with HOPS, the Herschel Orion Protostar Survey

    NASA Astrophysics Data System (ADS)

    Fischer, Will; Megeath, Tom; Furlan, Elise; Ali, Babar; Stutz, Amy; Booker, Joseph; Tobin, John; Stanke, Thomas; Osorio, Mayra

    2013-07-01

    HOPS, the Herschel Orion Protostar Survey, is an unprecedented program of large surveys with the Herschel, Spitzer, Hubble, and APEX observatories, as well as near-IR observations from the IRTF and other telescopes. Together these are providing a comprehensive observational assessment of protostellar evolution, from the earliest phases (see poster by A. Stutz) through the dissipation of the protostellar envelope. The BLT (bolometric luminosity and temperature) diagram for the ˜300 HOPS protostars resembles those constructed for other nearby star-forming regions. We fit the 1-870 um SEDs of the protostars with our grid of radiative transfer models to determine their luminosities, envelope densities, cavity angles, and inclinations (see poster by E. Furlan). High-resolution HST images of the scattered light nebulae provide additional constraints on envelope density, disk geometry, cavity geometry, and inclination angle (see poster by J. Booker). Finally, near-IR atomic hydrogen lines provide independent estimates of reddening and accretion luminosity in the less embedded sources. This multi-pronged modeling approach provides a more reliable assessment of envelope evolution than raw observational diagnostics like the bolometric temperature. We will compare the distributions of envelope densities and protostellar luminosities to the predictions of star-formation models.

  6. Heating and Cooling Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Turner, Neal

    Many of the disks of gas and dust orbiting young Sun-like stars produce mid-infrared emission from water and other oxygen- and carbon-bearing molecules, as discovered in the last few years using the Spitzer Space Telescope. The emission reveals the temperatures, columns and chemical composition of the gas in the disk atmosphere within 2 AU of the star, directly overlying the region where the planets form. Better understanding of the processes governing the line emission is vital for converting this new class of measurements into information about the planets' raw ingredients. We propose to combine MHD models of the turbulence driving the disk accretion flows, with a thermal-chemical model of the disk atmospheres, to predict emergent spectra that will capture the dynamics, heating, and chemical composition. By comparing the predicted and observed spectra we can determine the strength of the turbulence that heats and mixes the gas, and test ideas about the conditions in the disk interior. We will investigate the coupling of the turbulence to the thermal and chemical evolution, seek to locate the line emission's power source, gauge the rate at which the atmosphere and interior exchange material, and obtain new independent measures of the disk mass accretion rates. These efforts will help infrared spectroscopy of protostellar disks reach its full potential as a diagnostic of the environments in which planets form.

  7. MAGNETIC FIELD STRUCTURE IN THE FLATTENED ENVELOPE AND JET IN THE YOUNG PROTOSTELLAR SYSTEM HH 211

    SciTech Connect

    Lee, Chin-Fei; Rao, Ramprasad; Hirano, Naomi; Ho, Paul T. P.; Hwang, Hsiang-Chih; Ching, Tao-Chung; Lai, Shih-Ping

    2014-12-10

    HH 211 is a young Class 0 protostellar system with a flattened envelope, a possible rotating disk, and a collimated jet. We have mapped it with the Submillimeter Array in the 341.6 GHz continuum and SiO J = 8-7 at ∼0.''6 resolution. The continuum traces the thermal dust emission in the flattened envelope and the possible disk. Linear polarization is detected in the continuum in the flattened envelope. The field lines implied from the polarization have different orientations, but they are not incompatible with current gravitational collapse models, which predict a different orientation depending on the region/distance. Also, we might have detected for the first time polarized SiO line emission in the jet due to the Goldreich-Kylafis effect. Observations at higher sensitivity are needed to determine the field morphology in the jet.

  8. Observed & Predicted Debris Disks Structures Beyond the Reach of Kepler

    NASA Astrophysics Data System (ADS)

    Stark, Christopher C.

    2014-06-01

    Over the last several years our theoretical understanding of debris disks has evolved significantly. A number of new computational advances, in the realms of disk modeling and data analysis, have deepened our knowledge of structures in debris disks. More than ever, we are acutely aware of the many sources of structures--be they gravitational perturbations by planets, other external perturbations, or more subtle non-perturbative sources. At the same time, new observatories, instruments, and observation strategies have provided a rich data set for debris disk theorists to test and constrain their models. I will discuss our current understanding of structures in debris disks. I will show the wide array of structures that planets can dynamically sculpt and comment on how imaging of these structures with future missions may constrain the underlying planetary system. I will also present a cautionary tale of interpreting debris disk structures as planetary perturbations, show how our appreciation of alternative sources of structures has grown, and present new methods for disentangling true density structures from projection and scattering effects.

  9. PROTOSTELLAR OUTFLOWS AND RADIATIVE FEEDBACK FROM MASSIVE STARS

    SciTech Connect

    Kuiper, Rolf; Yorke, Harold W.; Turner, Neal J. E-mail: Harold.W.Yorke@jpl.nasa.gov

    2015-02-20

    We carry out radiation hydrodynamical simulations of the formation of massive stars in the super-Eddington regime including both their radiative feedback and protostellar outflows. The calculations start from a prestellar core of dusty gas and continue until the star stops growing. The accretion ends when the remnants of the core are ejected, mostly by the force of the direct stellar radiation in the polar direction and elsewhere by the reradiated thermal infrared radiation. How long the accretion persists depends on whether the protostellar outflows are present. We set the mass outflow rate to 1% of the stellar sink particle's accretion rate. The outflows open a bipolar cavity extending to the core's outer edge, through which the thermal radiation readily escapes. The radiative flux is funneled into the polar directions while the core's collapse proceeds near the equator. The outflow thus extends the ''flashlight effect'', or anisotropic radiation field, found in previous studies from the few hundred AU scale of the circumstellar disk up to the 0.1 parsec scale of the core. The core's flashlight effect allows core gas to accrete on the disk for longer, in the same way that the disk's flashlight effect allows disk gas to accrete on the star for longer. Thus although the protostellar outflows remove material near the core's poles, causing slower stellar growth over the first few free-fall times, they also enable accretion to go on longer in our calculations. The outflows ultimately lead to stars of somewhat higher mass.

  10. STEADY STATE DUST DISTRIBUTIONS IN DISK VORTICES: OBSERVATIONAL PREDICTIONS AND APPLICATIONS TO TRANSITIONAL DISKS

    SciTech Connect

    Lyra, Wladimir; Lin, Min-Kai E-mail: mklin924@cita.utoronto.ca

    2013-09-20

    The Atacama Large Millimeter Array has returned images of transitional disks in which large asymmetries are seen in the distribution of millimeter sized dust in the outer disk. The explanation in vogue borrows from the vortex literature and suggests that these asymmetries are the result of dust trapping in giant vortices, excited via Rossby wave instabilities at planetary gap edges. Due to the drag force, dust trapped in vortices will accumulate in the center and diffusion is needed to maintain a steady state over the lifetime of the disk. While previous work derived semi-analytical models of the process, in this paper we provide analytical steady-steady solutions. Exact solutions exist for certain vortex models. The solution is determined by the vortex rotation profile, the gas scale height, the vortex aspect ratio, and the ratio of dust diffusion to gas-dust friction. In principle, all of these quantities can be derived from observations, which would validate the model and also provide constrains on the strength of the turbulence inside the vortex core. Based on our solution, we derive quantities such as the gas-dust contrast, the trapped dust mass, and the dust contrast at the same orbital location. We apply our model to the recently imaged Oph IRS 48 system, finding values within the range of the observational uncertainties.

  11. VARIABLE ACCRETION OUTBURSTS IN PROTOSTELLAR EVOLUTION

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Gammie, Charles E-mail: lhartm@umich.edu E-mail: gammie@illinois.edu

    2013-02-20

    We extend the one-dimensional, two-zone models of long-term protostellar disk evolution with infall of Zhu et al. to consider the potential effects of a finite viscosity in regions where the ionization is too low for the magnetorotational instability (MRI) to operate (the {sup d}ead zone{sup )}. We find that the presence of a small but finite dead zone viscosity, as suggested by simulations of stratified disks with MRI-active outer layers, can trigger inside-out bursts of accretion, starting at or near the inner edge of the disk, instead of the previously found outside-in bursts with zero dead zone viscosity, which originate at a few AU in radius. These inside-out bursts of accretion bear a qualitative resemblance to the outburst behavior of one FU Ori object, V1515 Cyg, in contrast to the outside-in burst models, which more closely resemble the accretion events in FU Ori and V1057 Cyg. Our results suggest that the type and frequency of outbursts are potentially a probe of transport efficiency in the dead zone. Simulations must treat the inner disk regions, R {approx}< 0.5 AU, to show the detailed time evolution of accretion outbursts in general and to observe the inside-out bursts in particular.

  12. Variable Accretion Outbursts in Protostellar Evolution

    NASA Astrophysics Data System (ADS)

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Gammie, Charles

    2013-02-01

    We extend the one-dimensional, two-zone models of long-term protostellar disk evolution with infall of Zhu et al. to consider the potential effects of a finite viscosity in regions where the ionization is too low for the magnetorotational instability (MRI) to operate (the "dead zone"). We find that the presence of a small but finite dead zone viscosity, as suggested by simulations of stratified disks with MRI-active outer layers, can trigger inside-out bursts of accretion, starting at or near the inner edge of the disk, instead of the previously found outside-in bursts with zero dead zone viscosity, which originate at a few AU in radius. These inside-out bursts of accretion bear a qualitative resemblance to the outburst behavior of one FU Ori object, V1515 Cyg, in contrast to the outside-in burst models, which more closely resemble the accretion events in FU Ori and V1057 Cyg. Our results suggest that the type and frequency of outbursts are potentially a probe of transport efficiency in the dead zone. Simulations must treat the inner disk regions, R <~ 0.5 AU, to show the detailed time evolution of accretion outbursts in general and to observe the inside-out bursts in particular.

  13. ON THE ROLE OF DISKS IN THE FORMATION OF STELLAR SYSTEMS: A NUMERICAL PARAMETER STUDY OF RAPID ACCRETION

    SciTech Connect

    Kratter, Kaitlin M.; Matzner, Christopher D.; Krumholz, Mark R.; Klein, Richard I.

    2010-01-10

    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 infall rate and governed by gravitational torques generated by low-m spiral modes. We also confirm the existence of a maximum stable disk mass: disks that exceed approx50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.

  14. revealing H{sub 2}D{sup +} depletion and compact structure in starless and protostellar cores with ALMA

    SciTech Connect

    Friesen, R. K.; Di Francesco, J.; Bourke, T. L.; Caselli, P.; Jørgensen, J. K.; Pineda, J. E.; Wong, M.

    2014-12-10

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the submillimeter dust continuum and H{sub 2}D{sup +} 1{sub 10}-1{sub 11} emission toward two evolved, potentially protostellar cores within the Ophiuchus molecular cloud, Oph A SM1 and SM1N. The data reveal small-scale condensations within both cores, with mass upper limits of M ≲ 0.02 M {sub ☉} (∼20 M {sub Jup}). The SM1 condensation is consistent with a nearly symmetric Gaussian source with a width of only 37 AU. The SM1N condensation is elongated and extends 500 AU along its major axis. No evidence for substructure is seen in either source. A Jeans analysis indicates that these sources are unlikely to fragment, suggesting that both will form single stars. H{sub 2}D{sup +} is only detected toward SM1N, offset from the continuum peak by ∼150-200 AU. This offset may be due to either heating from an undetected, young, low-luminosity protostellar source or first hydrostatic core, or HD (and consequently H{sub 2}D{sup +}) depletion in the cold center of the condensation. We propose that SM1 is protostellar and that the condensation detected by ALMA is a warm (T ∼ 30-50 K) accretion disk. The less concentrated emission of the SM1N condensation suggests that it is still starless, but we cannot rule out the presence of a low-luminosity source, perhaps surrounded by a pseudodisk. These data observationally reveal the earliest stages of the formation of circumstellar accretion regions and agree with theoretical predictions that disk formation can occur very early in the star formation process, coeval with or just after the formation of a first hydrostatic core or protostar.

  15. X-rays from protostellar jets: emission from continuous flows

    NASA Astrophysics Data System (ADS)

    Bonito, R.; Orlando, S.; Peres, G.; Favata, F.; Rosner, R.

    2007-02-01

    Context: Recently X-ray emission from protostellar jets has been detected with both XMM-Newton and Chandra satellites, but the physical mechanism which can give rise to this emission is still unclear. Aims: We performed an extensive exploration of the parameter space for the main parameters influencing the jet/ambient medium interaction. Aims include: 1) to constrain the jet/ambient medium interaction regimes leading to the X-ray emission observed in Herbig-Haro objects in terms of the emission by a shock forming at the interaction front between a continuous supersonic jet and the surrounding medium; 2) to derive detailed predictions to be compared with optical and X-ray observations of protostellar jets; 3) to get insight into the protostellar jet's physical conditions. Methods: We performed a set of two-dimensional hydrodynamic numerical simulations, in cylindrical coordinates, modeling supersonic jets ramming into a uniform ambient medium. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. Results: Our model explains the observed X-ray emission from protostellar jets in a natural way. In particular, we find that a protostellar jet that is less dense than the ambient medium well reproduces the observations of the nearest Herbig-Haro object, HH 154, and allows us to make detailed predictions of a possible X-ray source proper motion (v_sh ≈500 km s-1) detectable with Chandra. Furthermore, our results suggest that the simulated protostellar jets which best reproduce the X-rays observations cannot drive molecular outflows.

  16. The flow of a thin liquid film on a stationary and rotating disk. II - Theoretical prediction

    NASA Technical Reports Server (NTRS)

    Rahman, M. M.; Faghri, A.; Hankey, W. L.

    1990-01-01

    The existing theoretical models are improved and a systematic procedure to compute the free surface flow of a thin liquid film is suggested. The solutions for axisymmetric radial flow on a stationary horizontal disk and for the disk rotating around its axis are presented. The theoretical predictions are compared with the experimental data presented in Part I of this report. The analysis shows results for both supercritical and subcritical flows and the flow structure in the vicinity of a hydraulic jump which isolates these two flow types. The detailed flow structure in a hydraulic jump was computed and shown to contain regions of separation including a 'surface roller'. The effects of surface tension are found to be important near the outer edge of the disk where the fluid experiences a free fall. At other locations, the surface tension is negligible. For a rotating disk, the frictional resistance in the angular direction is found to be as important as that in the radial direction.

  17. SIMULATING PROTOSTELLAR JETS SIMULTANEOUSLY AT LAUNCHING AND OBSERVATIONAL SCALES

    SciTech Connect

    Ramsey, Jon P.; Clarke, David A.

    2011-02-10

    We present the first 2.5-dimensional magnetohydrodynamic (MHD) simulations of protostellar jets that include both the region in which the jet is launched magnetocentrifugally at scale lengths <0.1 AU and where the propagating jet is observed at scale lengths >10{sup 3} AU. These simulations, performed with the new adaptive mesh refinement MHD code AZEuS, reveal interesting relationships between conditions at the disk surface, such as the magnetic field strength, and direct observables such as proper motion, jet rotation, jet radius, and mass flux. By comparing these quantities with observed values, we present direct numerical evidence that the magnetocentrifugal launching mechanism is capable, by itself, of launching realistic protostellar jets.

  18. Predicting Secchi disk depth from average beam attenuation in a deep, ultra-clear lake

    USGS Publications Warehouse

    Larson, G.L.; Hoffman, R.L.; Hargreaves, B.R.; Collier, R.W.

    2007-01-01

    We addressed potential sources of error in estimating the water clarity of mountain lakes by investigating the use of beam transmissometer measurements to estimate Secchi disk depth. The optical properties Secchi disk depth (SD) and beam transmissometer attenuation (BA) were measured in Crater Lake (Crater Lake National Park, Oregon, USA) at a designated sampling station near the maximum depth of the lake. A standard 20 cm black and white disk was used to measure SD. The transmissometer light source had a nearly monochromatic wavelength of 660 nm and a path length of 25 cm. We created a SD prediction model by regression of the inverse SD of 13 measurements recorded on days when environmental conditions were acceptable for disk deployment with BA averaged over the same depth range as the measured SD. The relationship between inverse SD and averaged BA was significant and the average 95% confidence interval for predicted SD relative to the measured SD was ??1.6 m (range = -4.6 to 5.5 m) or ??5.0%. Eleven additional sample dates tested the accuracy of the predictive model. The average 95% confidence interval for these sample dates was ??0.7 m (range = -3.5 to 3.8 m) or ??2.2%. The 1996-2000 time-series means for measured and predicted SD varied by 0.1 m, and the medians varied by 0.5 m. The time-series mean annual measured and predicted SD's also varied little, with intra-annual differences between measured and predicted mean annual SD ranging from -2.1 to 0.1 m. The results demonstrated that this prediction model reliably estimated Secchi disk depths and can be used to significantly expand optical observations in an environment where the conditions for standardized SD deployments are limited. ?? 2007 Springer Science+Business Media B.V.

  19. Signatures of MRI-driven Turbulence in Protoplanetary Disks: Predictions for ALMA Observations

    NASA Astrophysics Data System (ADS)

    Simon, Jacob B.; Hughes, A. Meredith; Flaherty, Kevin M.; Bai, Xue-Ning; Armitage, Philip J.

    2015-08-01

    Spatially resolved observations of molecular line emission have the potential to yield unique constraints on the nature of turbulence within protoplanetary disks. Using a combination of local non-ideal magnetohydrodynamics (MHD) simulations and radiative transfer calculations, tailored to properties of the disk around HD 163296, we assess the ability of ALMA to detect turbulence driven by the magnetorotational instability (MRI). Our local simulations show that the MRI produces small-scale turbulent velocity fluctuations that increase in strength with height above the mid-plane. For a set of simulations at different disk radii, we fit a Maxwell-Boltzmann distribution to the turbulent velocity and construct a turbulent broadening parameter as a function of radius and height. We input this broadening into radiative transfer calculations to quantify observational signatures of MRI-driven disk turbulence. We find that the ratio of the peak line flux to the flux at line center is a robust diagnostic of turbulence that is only mildly degenerate with systematic uncertainties in disk temperature. For the CO(3-2) line, which we expect to probe the most magnetically active slice of the disk column, variations in the predicted peak-to-trough ratio between our most and least turbulent models span a range of approximately 15%. Additional independent constraints can be derived from the morphology of spatially resolved line profiles, and we estimate the resolution required to detect turbulence on different spatial scales. We discuss the role of lower optical depth molecular tracers, which trace regions closer to the disk mid-plane where velocities in MRI-driven models are systematically lower.

  20. Protostellar Collapse with a Shock

    NASA Technical Reports Server (NTRS)

    Tsai, John C.; Hsu, Juliana J. L.

    1995-01-01

    ' problem of protostellar cores since the predicted central accretion rates are significantly reduced relative to that of the expansion wave solution. Furthermore, our calculations indicate that star-forming cloud cores are not very tightly bound and that modest disturbances can easily result in both termination of infall and dispersal of unaccreted material.

  1. Protostellar Collapse with a Shock

    NASA Technical Reports Server (NTRS)

    Tsai, John C.; Hsu, Juliana J.

    1995-01-01

    ' problem of protostellar cores since the predicted central accretion rates are significantly reduced relative to that of the expansion wave solution. Furthermore, our calculations indicate that star-forming cloud cores are not very tightly bound and that modest disturbances can easily result in both termination of infall and dispersal of unaccreted material.

  2. Numerical simulations of protostellar jets

    NASA Astrophysics Data System (ADS)

    Suttner, Gerhard; Smith, Michael D.; Yorke, Harold W.; Zinnecker, Hans

    Molecular jets announce the successful birth of a protostar. We develop here a model for the jets and their environments, adapting a multi-dimensional hydrocode to follow the molecular-atomic transitions of hydrogen. We examine powerful outflows into dense gas. The cocoon which forms around a jet is a very low density cavity of atomic gas. These atoms originate from strong shocks which dissociate the molecules. The rest of the molecules are either within the jet or swept up into very thin layers. Pulsed jets produce wider cavities and molecular layers which can grow onto resolvable jet knots. Three-dimensional simulations produce shocked molecular knots, distorted and multiple bow shocks and arclike structures. Spectroscopic and excitation properties of the hydrogen molecules are calculated. In the infrared, strong emission is seen from shocks within the jet (when pulsed) as well as from discrete regions along the cavity walls. Excitation, as measured by line ratios, is not generally constant. Broad double-peaked, shifted emission lines are predicted. The jet model for protostellar outflows is confronted with the constraints imposed by CO spectroscopic observations. From the three dimensional simulations we calculate line profiles and construct position-velocity diagrams for the (low-J) CO transitions. We find (1) the profiles imply power law variation of integrated brightness with velocity over a wide range of velocities, (2) the velocity field resembles a `Hubble Law' and (3) a hollow-shell structure at low velocities becomes an elongated lobe at high velocities. Deviations from the simple power law dependence of integrated brightness versus velocity occur at high velocities in our simulations. The curve first dips to a shallow minimum and then rises rapidly and peaks sharply. Reanalysis of the NGC 2264G and Cepheus E data confirm these predictions. We identify these two features with a jet-ambient shear layer and the jet itself. A deeper analysis reveals that

  3. Infrared spectra of protostellar collapse

    NASA Technical Reports Server (NTRS)

    Hollenbach, David J.; Ceccarelli, Cecilia; Neufeld, David A.; Tielens, Alexander G. G. M.

    1995-01-01

    Theoretical models of the formation of low mass stars by cloud collapse predict that OI(63 micrometers) and IR rotational lines of CO and H2O dominate the cooling in the freefalling region 10-1000 AU from the protostar. The freefalling gas supersonically hits the protoplanetary disk orbiting the protostar, forming an accretion shock with strong IR emission in rotational lines of H2O and OH, and OI(63 microns). The accretion shock spectra and line profiles depend on the mass flux through the shock and the typical distance r-bar at which the freefalling gas strikes the disk. The line widths are of order the Keplerian speed, or approx. 10(r-bar/10AU)(exp -0.5) km/s, for the accretion shock lines, and less for the lines from the infalling gas. Measurements of the IR line fluxes and profiles from the freefalling gas and the accretion shock diagnoses how a protostar and disk are formed and requires high sensitivity and high spectral and spatial resolving power. SOFIA will be the optimum observatory for many of these lines, although ISO will contribute and the KAO may make a few pioneering detections.

  4. PROTOSTELLAR ACCRETION FLOWS DESTABILIZED BY MAGNETIC FLUX REDISTRIBUTION

    SciTech Connect

    Krasnopolsky, Ruben; Shang, Hsien; Li Zhiyun; Zhao Bo

    2012-09-20

    Magnetic flux redistribution lies at the heart of the problem of star formation in dense cores of molecular clouds that are magnetized to a realistic level. If all of the magnetic flux of a typical core were to be dragged into the central star, the stellar field strength would be orders of magnitude higher than the observed values. This well-known magnetic flux problem can in principle be resolved through non-ideal MHD effects. Two-dimensional (axisymmetric) calculations have shown that ambipolar diffusion, in particular, can transport magnetic flux outward relative to matter, allowing material to enter the central object without dragging the field lines along. We show through simulations that such axisymmetric protostellar accretion flows are unstable in three dimensions to magnetic interchange instability in the azimuthal direction. The instability is driven by the magnetic flux redistributed from the matter that enters the central object. It typically starts to develop during the transition from the prestellar phase of star formation to the protostellar mass accretion phase. In the latter phase, the magnetic flux is transported outward mainly through advection by strongly magnetized low-density regions that expand against the collapsing inflow. The tussle between the gravity-driven infall and magnetically driven expansion leads to a highly filamentary inner accretion flow that is more disordered than previously envisioned. The efficient outward transport of magnetic flux by advection lowers the field strength at small radii, making the magnetic braking less efficient and the formation of rotationally supported disks easier in principle. However, we find no evidence for such disks in any of our rotating collapse simulations. We conclude that the inner protostellar accretion flow is shaped to a large extent by the flux redistribution-driven magnetic interchange instability. How disks form in such an environment is unclear.

  5. Protostellar Accretion Flows Destabilized by Magnetic Flux Redistribution

    NASA Astrophysics Data System (ADS)

    Krasnopolsky, Ruben; Li, Zhi-Yun; Shang, Hsien; Zhao, Bo

    2012-09-01

    Magnetic flux redistribution lies at the heart of the problem of star formation in dense cores of molecular clouds that are magnetized to a realistic level. If all of the magnetic flux of a typical core were to be dragged into the central star, the stellar field strength would be orders of magnitude higher than the observed values. This well-known magnetic flux problem can in principle be resolved through non-ideal MHD effects. Two-dimensional (axisymmetric) calculations have shown that ambipolar diffusion, in particular, can transport magnetic flux outward relative to matter, allowing material to enter the central object without dragging the field lines along. We show through simulations that such axisymmetric protostellar accretion flows are unstable in three dimensions to magnetic interchange instability in the azimuthal direction. The instability is driven by the magnetic flux redistributed from the matter that enters the central object. It typically starts to develop during the transition from the prestellar phase of star formation to the protostellar mass accretion phase. In the latter phase, the magnetic flux is transported outward mainly through advection by strongly magnetized low-density regions that expand against the collapsing inflow. The tussle between the gravity-driven infall and magnetically driven expansion leads to a highly filamentary inner accretion flow that is more disordered than previously envisioned. The efficient outward transport of magnetic flux by advection lowers the field strength at small radii, making the magnetic braking less efficient and the formation of rotationally supported disks easier in principle. However, we find no evidence for such disks in any of our rotating collapse simulations. We conclude that the inner protostellar accretion flow is shaped to a large extent by the flux redistribution-driven magnetic interchange instability. How disks form in such an environment is unclear.

  6. Predicting the flying performance of thermal flying-height control sliders in hard disk drives

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Zheng, Jinglin; Bogy, David B.

    2010-07-01

    Thermal flying-height control (TFC) sliders have been recently used in commercial hard disk drives (HDDs) to increase the HDDs' capacity. The design of this new class of sliders depends on the numerical prediction of their flying performance, which requires a model for heat flux on the surface of the slider facing the disk. The currently widely used heat flux model is based on a first order slip theory and is believed to lack sufficient accuracy due to its limitation of applicability. This paper implements an improved heat flux model and compares numerical predictions of a TFC slider's flying performance based on these two models with experiments. It is found that the numerical prediction based on the currently used model has a relative error less than 10% for a state-of-the-art TFC slider. It is suggested that the currently used model might cause large errors for the sliders which do not have a pressure peak near the transducer.

  7. Protostellar collapse in a self-gravitating sheet

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee; Boss, Alan; Calvet, Nuria; Whitney, Barbara

    1994-01-01

    We present preliminary calculations of protostellar cloud collapse starting from an isothermal, self-gravitating gaseous layer in hydrostatic equilibrium. This gravitationally unstable layer collapses into a flattened or toroidal density distribution, even in the absence of rotation or magnetic fields. We suggest that the flat infalling envelope recently observed in HL Tau by Hayashi et al.is the result of collapse from an initially nonspherical layer. We also speculate that the later evolution of such a flattened, collapsing envelope can produce a structure similar to the 'flared disk' invoked by Kenyon and Hartmann to explain the infrared excesses of many T Tauri stars.

  8. Rotationally driven Fragmentation in the Formation of the Binary Protostellar System L1551 IRS 5

    NASA Astrophysics Data System (ADS)

    Lim, Jeremy; Yeung, Paul K. H.; Hanawa, Tomoyuki; Takakuwa, Shigehisa; Matsumoto, Tomoaki; Saigo, Kazuya

    2016-08-01

    Both bulk rotation and local turbulence have been widely suggested to drive the fragmentation in collapsing cores that produces multiple star systems. Even when the two mechanisms predict different alignments for stellar spins and orbits, subsequent internal or external interactions can drive multiple systems toward or away from alignment, thus masking their formation processes. Here, we demonstrate that the geometrical and dynamical relationship between a binary system and its surrounding bulk envelope provide the crucial distinction between fragmentation models. We find that the circumstellar disks of the binary protostellar system L1551 IRS 5 are closely parallel, not just with each other but also with their surrounding flattened envelope. Measurements of the relative proper motion of the binary components spanning nearly 30 years indicate an orbital motion related to that of the envelope rotation. Eliminating orbital solutions whereby the circumstellar disks would be tidally truncated to sizes smaller than observed, the remaining solutions favor a circular or low-eccentricity orbit tilted by up to ∼25° from the circumstellar disks. Turbulence-driven fragmentation can generate local angular momentum to produce a coplanar binary system, but this would have no particular relationship to the system’s surrounding envelope. Instead, the observed properties conform with predictions for rotationally driven fragmentation. If the fragments were produced at different heights or on opposite sides of the mid-plane in the flattened central region of a rotating core, the resulting protostars would then exhibit circumstellar disks parallel with the surrounding envelope but tilted from the orbital plane, as is observed.

  9. Gravitoturbulence in magnetized protostellar discs

    NASA Astrophysics Data System (ADS)

    Riols, A.; Latter, H.

    2016-08-01

    Gravitational instability (GI) features in several aspects of protostellar disc evolution, most notably in angular momentum transport, fragmentation, and the outbursts exemplified by FU Ori and EX Lupi systems. The outer regions of protostellar discs may also be coupled to magnetic fields, which could then modify the development of GI. To understand the basic elements of their interaction, we perform local 2D ideal and resistive magnetohydrodynamics simulations with an imposed toroidal field. In the regime of moderate plasma beta, we find that the system supports a hot gravitoturbulent state, characterized by considerable magnetic energy and stress and a surprisingly large Toomre parameter Q ≳ 10. This result has potential implications for disc structure, vertical thickness, ionization, etc. Our simulations also reveal the existence of long-lived and dense `magnetic islands' or plasmoids. Lastly, we find that the presence of a magnetic field has little impact on the fragmentation criterion of the disc. Though our focus is on protostellar discs, some of our results may be relevant for the outer radii of AGN.

  10. PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS. II. PREDICTIONS FOR OUTER EXTRASOLAR PLANETARY SYSTEMS

    SciTech Connect

    Raymond, Sean N.; Armitage, Philip J.; Gorelick, Noel

    2010-03-10

    We develop an idealized dynamical model to predict the typical properties of outer extrasolar planetary systems, at radii comparable to the Jupiter-to-Neptune region of the solar system. The model is based upon the hypothesis that dynamical evolution in outer planetary systems is controlled by a combination of planet-planet scattering and planetary interactions with an exterior disk of small bodies ('planetesimals'). Our results are based on 5000 long duration N-body simulations that follow the evolution of three planets from a few to 10 AU, together with a planetesimal disk containing 50 M{sub +} from 10 to 20 AU. For large planet masses (M {approx}> M{sub Sat}), the model recovers the observed eccentricity distribution of extrasolar planets. For lower-mass planets, the range of outcomes in models with disks is far greater than that which is seen in isolated planet-planet scattering. Common outcomes include strong scattering among massive planets, sudden jumps in eccentricity due to resonance crossings driven by divergent migration, and re-circularization of scattered low-mass planets in the outer disk. We present the distributions of the eccentricity and inclination that result, and discuss how they vary with planet mass and initial system architecture. In agreement with other studies, we find that the currently observed eccentricity distribution (derived primarily from planets at a {approx}< 3 AU) is consistent with isolated planet-planet scattering. We explain the observed mass dependence-which is in the opposite sense from that predicted by the simplest scattering models-as a consequence of strong correlations between planet masses in the same system. At somewhat larger radii, initial planetary mass correlations and disk effects can yield similar modest changes to the eccentricity distribution. Nonetheless, strong damping of eccentricity for low-mass planets at large radii appears to be a secure signature of the dynamical influence of disks. Radial velocity

  11. An alternative model for the origin of gaps in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.; Regaly, Zsolt; Guedel, Manuel; Lin, Doug N. C.

    2016-03-01

    Aims: Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. Methods: We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment and numerical hydrodynamics simulations of isolated disks hosting giant planets to derive the properties of the gaps that form in both cases. Results: Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates both disks has a substantial depletion factor, can be located at a distance from ten to over a hundred AU from the star, and can propagate inward with velocity ranging from 1 AU Myr-1 to >100 AU Myr-1. Unlike our previous conclusion, the gap can therefore be a long-lived phenomenon that is, in some case, comparable to the lifetime of the disk itself. For a proper choice of the planetary mass, the viscous α-parameter and disk mass, the planet-bearing gaps and gaps in counter-rotating disks may show a remarkable similarity in the gas density profile and depletion factor, which may complicate their observational differentiation.

  12. MISALIGNMENT OF MAGNETIC FIELDS AND OUTFLOWS IN PROTOSTELLAR CORES

    SciTech Connect

    Hull, Charles L. H.; Plambeck, Richard L.; Bower, Geoffrey C.; Heiles, Carl; Meredith Hughes, A.; Bolatto, Alberto D.; Jameson, Katherine; Mundy, Lee; Pound, Marc W.; Carpenter, John M.; Lamb, James W.; Pillai, Thushara; Crutcher, Richard M.; Hakobian, Nicholas S.; Kwon, Woojin; Looney, Leslie W.; Fiege, Jason D.; Franzmann, Erica; Houde, Martin; Matthews, Brenda C.; and others

    2013-05-10

    We present results of {lambda}1.3 mm dust-polarization observations toward 16 nearby, low-mass protostars, mapped with {approx}2.''5 resolution at CARMA. The results show that magnetic fields in protostellar cores on scales of {approx}1000 AU are not tightly aligned with outflows from the protostars. Rather, the data are consistent with scenarios where outflows and magnetic fields are preferentially misaligned (perpendicular), or where they are randomly aligned. If one assumes that outflows emerge along the rotation axes of circumstellar disks, and that the outflows have not disrupted the fields in the surrounding material, then our results imply that the disks are not aligned with the fields in the cores from which they formed.

  13. Pericenter precession induced by a circumstellar disk on the orbit of massive bodies: comparison between analytical predictions and numerical results

    NASA Astrophysics Data System (ADS)

    Fontana, A.; Marzari, F.

    2016-05-01

    Context. Planetesimals and planets embedded in a circumstellar disk are dynamically perturbed by the disk gravity. It causes an apsidal line precession at a rate that depends on the disk density profile and on the distance of the massive body from the star. Aims: Different analytical models are exploited to compute the precession rate of the perihelion ϖ˙. We compare them to verify their equivalence, in particular after analytical manipulations performed to derive handy formulas, and test their predictions against numerical models in some selected cases. Methods: The theoretical precession rates were computed with analytical algorithms found in the literature using the Mathematica symbolic code, while the numerical simulations were performed with the hydrodynamical code FARGO. Results: For low-mass bodies (planetesimals) the analytical approaches described in Binney & Tremaine (2008, Galactic Dynamics, p. 96), Ward (1981, Icarus, 47, 234), and Silsbee & Rafikov (2015a, ApJ, 798, 71) are equivalent under the same initial conditions for the disk in terms of mass, density profile, and inner and outer borders. They also match the numerical values computed with FARGO away from the outer border of the disk reasonably well. On the other hand, the predictions of the classical Mestel disk (Mestel 1963, MNRAS, 126, 553) for disks with p = 1 significantly depart from the numerical solution for radial distances beyond one-third of the disk extension because of the underlying assumption of the Mestel disk is that the outer disk border is equal to infinity. For massive bodies such as terrestrial and giant planets, the agreement of the analytical approaches is progressively poorer because of the changes in the disk structure that are induced by the planet gravity. For giant planets the precession rate changes sign and is higher than the modulus of the theoretical value by a factor ranging from 1.5 to 1.8. In this case, the correction of the formula proposed by Ward (1981) to

  14. Protostellar accretion traced with chemistry. Comparing synthetic C18O maps of embedded protostars to real observations

    NASA Astrophysics Data System (ADS)

    Frimann, S.; Jørgensen, J. K.; Padoan, P.; Haugbølle, T.

    2016-02-01

    Context. Understanding how protostars accrete their mass is a central question of star formation. One aspect of this is trying to understand whether the time evolution of accretion rates in deeply embedded objects is best characterised by a smooth decline from early to late stages or by intermittent bursts of high accretion. Aims: We create synthetic observations of deeply embedded protostars in a large numerical simulation of a molecular cloud, which are compared directly to real observations. The goal is to compare episodic accretion events in the simulation to observations and to test the methodology used for analysing the observations. Methods: Simple freeze-out and sublimation chemistry is added to the simulation, and synthetic C18O line cubes are created for a large number of simulated protostars. The spatial extent of C18O is measured for the simulated protostars and compared directly to a sample of 16 deeply embedded protostars observed with the Submillimeter Array. If CO is distributed over a larger area than predicted based on the protostellar luminosity, it may indicate that the luminosity has been higher in the past and that CO is still in the process of refreezing. Results: Approximately 1% of the protostars in the simulation show extended C18O emission, as opposed to approximately 50% in the observations, indicating that the magnitude and frequency of episodic accretion events in the simulation is too low relative to observations. The protostellar accretion rates in the simulation are primarily modulated by infall from the larger scales of the molecular cloud, and do not include any disk physics. The discrepancy between simulation and observations is taken as support for the necessity of disks, even in deeply embedded objects, to produce episodic accretion events of sufficient frequency and amplitude.

  15. Predicting the flow & noise of a rotor in a turbulent boundary layer using an actuator disk -- RANS approach

    NASA Astrophysics Data System (ADS)

    Buono, Armand C.

    The numerical method presented in this study attempts to predict the mean, non-uniform flow field upstream of a propeller partially immersed in a thick turbulent boundary layer with an actuator disk using CFD based on RANS in ANSYS FLUENT. Three different configurations, involving an infinitely thin actuator disk in the freestream (Configuration 1), an actuator disk near a wall with a turbulent boundary layer (Configuration 2), and an actuator disk with a hub near a wall with a turbulent boundary layer (Configuration 3), were analyzed for a variety of advance ratios ranging from J = 0.48 to J =1.44. CFD results are shown to be in agreement with previous works and validated with experimental data of reverse flow occurring within the boundary layer above the flat plate upstream of a rotor in the Virginia Tech's Stability Wind Tunnel facility. Results from Configuration 3 will be used in future aero-acoustic computations.

  16. The Infrared Reflection Nebula Around the Protostellar System in S140

    NASA Technical Reports Server (NTRS)

    Harker, D.; Bregman, J.; Tielens, A. G. G. M.; Temi, P.; Rank, D.; Morrison, David (Technical Monitor)

    1994-01-01

    We have studied the protostellar system in S140 at 2.2, 3.1 and 3.45 microns using a 128x128 InSb array at the Lick Observatory 3m telescope. Besides the protostellar sources, the data reveal a bright infrared reflection nebula. We have developed a simple model of this region and derived the physical conditions. IRSI is surrounded by a dense dusty disk viewed almost edge-on. Photons leaking out through the poles illuminate almost directly north and south the inner edge of a surrounding shell of molecular gas, Analysis of the observed colors and intensities of the NIR light, using Mie scattering theory, reveal that the dust grains in the molecular cloud are somewhat larger than in the general diffuse interstellar medium. Moreover, the incident light has a "cool" color temperature, approximately equals 800K, and likely originates from a dust photosphere close to the protostar. Finally, we find little H2O ice associated with the dusty disk around IRSI. Most of the 3.1 micron ice extinction arises instead from cool intervening molecular cloud material. We have compared our infrared dust observations with millimeter and radio observations of molecular gas associated with this region. The large scale structure observable in the molecular gas is indicative of the interaction between the protostellar wind and the surrounding molecular cloud rather than the geometry of the protostellar disk. We conclude that S140 is a young blister formed by this outflow on the side of a molecular cloud and viewed edge-on.

  17. Chemistry in low-mass protostellar and protoplanetary regions.

    PubMed

    van Dishoeck, Ewine F

    2006-08-15

    When interstellar clouds collapse to form new stars and planets, the surrounding gas and dust become part of the infalling envelopes and rotating disks, thus providing the basic material from which new solar systems are formed. Instrumentation to probe the chemistry in low-mass star-forming regions has only recently become available. The results of a systematic program to study the abundances in solar-mass protostellar and protoplanetary regions are presented. Surveys at submillimeter and infrared wavelengths reveal a rich chemistry, including simple and complex (organic) gases, ices, polycyclic aromatic hydrocarbons, and silicates. Each of these species traces different aspects of the physical and chemical state of the objects as they evolve from deeply embedded protostars to pre-main sequence stars with planet-forming disks. Quantitative information on temperatures, densities, and abundances is obtained through molecular excitation and radiative transfer models as well as from analysis of solid-state line profiles. The chemical characteristics are dominated by freeze-out in the coldest regions and ice evaporation in the warmer zones. In the surface layers of disks, UV radiation controls the chemistry. The importance of complementary laboratory experiments and calculations to obtain basic molecular data is emphasized. PMID:16894165

  18. Chemistry in low-mass protostellar and protoplanetary regions

    PubMed Central

    van Dishoeck, Ewine F.

    2006-01-01

    When interstellar clouds collapse to form new stars and planets, the surrounding gas and dust become part of the infalling envelopes and rotating disks, thus providing the basic material from which new solar systems are formed. Instrumentation to probe the chemistry in low-mass star-forming regions has only recently become available. The results of a systematic program to study the abundances in solar-mass protostellar and protoplanetary regions are presented. Surveys at submillimeter and infrared wavelengths reveal a rich chemistry, including simple and complex (organic) gases, ices, polycyclic aromatic hydrocarbons, and silicates. Each of these species traces different aspects of the physical and chemical state of the objects as they evolve from deeply embedded protostars to pre-main sequence stars with planet-forming disks. Quantitative information on temperatures, densities, and abundances is obtained through molecular excitation and radiative transfer models as well as from analysis of solid-state line profiles. The chemical characteristics are dominated by freeze-out in the coldest regions and ice evaporation in the warmer zones. In the surface layers of disks, UV radiation controls the chemistry. The importance of complementary laboratory experiments and calculations to obtain basic molecular data is emphasized. PMID:16894165

  19. Protosteller Disks Under the Influence of Winds and UV Radiation

    NASA Technical Reports Server (NTRS)

    Yorke, H. W.

    2003-01-01

    Star formation and the creation of protostellar disks generally occur in a crowded environment. Nearby young stars and protostars can influence the disks of their closets neighbors by a combination of outflows and hard radiation. The central stars themselves can have a stellar wind and may produce sufficient UV and X-ray to ultimately destroy their surrounding disks. Here we describe the results of numerical simulations of the influence that an external UV source and a central star's wind can have on its circumstellar disk. The numerical method (axial symmetry assumed) is described elsewhere. We find that protostellar disks will be destroyed on a relatively short time scale ( 10(sup 5)yr) unless they are well shielded from O-stars. Initially isotropic T-Tauri winds do not significantly influence their disks, but instead are focused toward the rotation axis by the disk wind from photoevaporation.

  20. The VLA Nascent Disk and Multiplicity Survey (VANDAM): Resolved Candidate Disks around Class 0 and I Protostars

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The properties of young protostellar disks, particularly Class 0 disks, are not well studied observationally, and their expected properties are controversial. In particular, there is debate about whether or not the earliest disks are large and massive and about when and how disks form. To characterize the properties of the youngest disks and binaries we are conducting the VLA Nascent Disk and Multiplicity survey (VANDAM) toward all known protostars in the Perseus molecular cloud (d ~ 230 pc). The survey is the largest and most complete high-resolution millimeter/centimeter wavelength survey of protostellar disks and binaries. We present the dust emission results toward a sample of ~15 protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the VANDAM survey with ~0.05'' or 12 AU resolution. We have begun to confirm the disk candidacy of these sources by fitting the Ka-band 8 mm dust-continuum data in the uv-plane to a simple, parametrized model based on the Shakura-Sunyaev disk model. The seven candidate disks this analysis has been performed on are well-fit by the disk shaped model, and have estimated masses from the measured flux in agreement with masses of previously known disks. The inner-disk surface densities of the VANDAM candidate disks have shallower density profiles compared to disks around more evolved Class II systems. The best-fit model radii of the seven early-result candidate disks are R > 10 AU; at 8 mm, the radii reflect lower limits on the disk size since dust continuum emission is tied to grain size and large grains radially drift inwards. These disks, if confirmed kinematically, are inconsistent with theoretical models where the disk size is limited by strong magnetic braking to < 10 AU at early times.

  1. Initiation of bipolar flows by magnetic field twisting in protostellar nebulae

    NASA Technical Reports Server (NTRS)

    Newman, William I.; Newman, Alice L.; Lovelace, Richard V. E.

    1992-01-01

    A model is developed for the time-dependent twisting of an initial poloidal magnetic field threading a conducting protostellar disk. The region outside the disk is assumed to be filled, at least initially, with a low-density, force-free 'coronal' plasma. The differential rotation of the disk acts to twist the B field in the space outside the disk thus generating a toroidal magnetic field. In turn, the toroidal field acts to pinch the plasma and the poloidal field toward the system axis producing a collimated channel. This channel could facilitate the formation of bipolar flows. The magnitude and duration of the field twisting is expected to be limited by magnetohydrodynamic instability.

  2. Infall-driven protostellar accretion and the solution to the luminosity problem

    SciTech Connect

    Padoan, Paolo; Haugbølle, Troels; Nordlund, Åke

    2014-12-10

    We investigate the role of mass infall in the formation and evolution of protostars. To avoid ad hoc initial and boundary conditions, we consider the infall resulting self-consistently from modeling the formation of stellar clusters in turbulent molecular clouds. We show that infall rates in turbulent clouds are comparable to accretion rates inferred from protostellar luminosities or measured in pre-main-sequence stars. They should not be neglected in modeling the luminosity of protostars and the evolution of disks, even after the embedded protostellar phase. We find large variations of infall rates from protostar to protostar, and large fluctuations during the evolution of individual protostars. In most cases, the infall rate is initially of order 10{sup –5} M {sub ☉} yr{sup –1}, and may either decay rapidly in the formation of low-mass stars, or remain relatively large when more massive stars are formed. The simulation reproduces well the observed characteristic values and scatter of protostellar luminosities and matches the observed protostellar luminosity function. The luminosity problem is therefore solved once realistic protostellar infall histories are accounted for, with no need for extreme accretion episodes. These results are based on a simulation of randomly driven magnetohydrodynamic turbulence on a scale of 4 pc, including self-gravity, adaptive-mesh refinement to a resolution of 50 AU, and accreting sink particles. The simulation yields a low star formation rate, consistent with the observations, and a mass distribution of sink particles consistent with the observed stellar initial mass function during the whole duration of the simulation, forming nearly 1300 sink particles over 3.2 Myr.

  3. Do siblings always form and evolve simultaneously? Testing the coevality of multiple protostellar systems through SEDs

    NASA Astrophysics Data System (ADS)

    Murillo, N. M.; van Dishoeck, E. F.; Tobin, J. J.; Fedele, D.

    2016-07-01

    Context. Multiplicity is common in field stars and among protostellar systems. Models suggest two paths of formation: turbulent fragmentation and protostellar disk fragmentation. Aims: We attempt to find whether or not the coevality frequency of multiple protostellar systems can help to better understand their formation mechanism. The coevality frequency is determined by constraining the relative evolutionary stages of the components in a multiple system. Methods: Spectral energy distributions (SEDs) for known multiple protostars in Perseus were constructed from literature data. Herschel PACS photometric maps were used to sample the peak of the SED for systems with separations ≥7″, a crucial aspect in determining the evolutionary stage of a protostellar system. Inclination effects and the surrounding envelope and outflows were considered to decouple source geometry from evolution. This together with the shape and derived properties from the SED was used to determine each system's coevality as accurately as possible. SED models were used to examine the frequency of non-coevality that is due to geometry. Results: We find a non-coevality frequency of 33 ± 10% from the comparison of SED shapes of resolved multiple systems. Other source parameters suggest a somewhat lower frequency of non-coevality. The frequency of apparent non-coevality that is due to random inclination angle pairings of model SEDs is 17 ± 0.5%. Observations of the outflow of resolved multiple systems do not suggest significant misalignments within multiple systems. Effects of unresolved multiples on the SED shape are also investigated. Conclusions: We find that one-third of the multiple protostellar systems sampled here are non-coeval, which is more than expected from random geometric orientations. The other two-thirds are found to be coeval. Higher order multiples show a tendency to be non-coeval. The frequency of non-coevality found here is most likely due to formation and enhanced by

  4. A Model for Infall-Outflow Interactions in Protostellar Disks

    NASA Technical Reports Server (NTRS)

    Velusamy, W. Langer T.

    1997-01-01

    Recently we have shown(sup 1,2) from (sup 12)CO and C(sup 18)O OVRO-MMA observations evidence of infall-outflow interactions in the Young Stellar Object IRS1 in B5. We present new data obtained with the OVRO-MMA in (sup 13)CO(2-1) and (1-0) to trace the full extent of this infall-outflow interaction region.

  5. Use of CFD Analyses to Predict Disk Friction Loss of Centrifugal Compressor Impellers

    NASA Astrophysics Data System (ADS)

    Cho, Leesang; Lee, Seawook; Cho, Jinsoo

    To improve the total efficiency of centrifugal compressors, it is necessary to reduce disk friction loss, which is expressed as the power loss. In this study, to reduce the disk friction loss due to the effect of axial clearance and surface roughness is analyzed and methods to reduce disk friction loss are proposed. The rotating reference frame technique using a commercial CFD tool (FLUENT) is used for steady-state analysis of the centrifugal compressor. Numerical results of the CFD analysis are compared with theoretical results using established experimental empirical equations. The disk friction loss of the impeller is decreased in line with increments in axial clearance until the axial clearance between the impeller disk and the casing is smaller than the boundary layer thickness. In addition, the disk friction loss of the impeller is increased in line with the increments in surface roughness in a similar pattern as that of existing experimental empirical formulas. The disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. To minimize disk friction loss on the centrifugal compressor impeller, the axial clearance and the theoretical boundary layer thickness should be designed to be the same. The design of the impeller requires careful consideration in order to optimize axial clearance and minimize surface roughness.

  6. Predictions for shepherding planets in scattered light images of debris disks

    SciTech Connect

    Rodigas, Timothy J.; Hinz, Philip M.; Malhotra, Renu

    2014-01-01

    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 dust 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.

  7. An Evolutionary Algorithm for Feature Subset Selection in Hard Disk Drive Failure Prediction

    ERIC Educational Resources Information Center

    Bhasin, Harpreet

    2011-01-01

    Hard disk drives are used in everyday life to store critical data. Although they are reliable, failure of a hard disk drive can be catastrophic, especially in applications like medicine, banking, air traffic control systems, missile guidance systems, computer numerical controlled machines, and more. The use of Self-Monitoring, Analysis and…

  8. Disk Chemistry and Cometary Composition

    NASA Astrophysics Data System (ADS)

    Markwick, A. J.; Charnley, S. B.

    2003-05-01

    We will describe current chemical modelling of disks similar to the protosolar nebula. Calculations are being undertaken to determine the spatial and temporal chemistry of the gas and dust within the 5-40AU comet-forming region of the nebula. These theoretical studies aim to determine the contribution of pristine and partially-processed interstellar material from the cool outer nebula, as compared to that obtained from outward radial mixing of matter from the hot inner nebula. Reference Molecular distributions in the inner regions of protostellar disks, Markwick, A. J., Ilgner, M., Millar, T. J., Henning, Th. (2002), Astron. Astrophys., 385, 632.

  9. Disk Chemistry and Cometary Composition

    NASA Astrophysics Data System (ADS)

    Markwick, A. J.; Charnley, S. B.

    2005-01-01

    We will describe current chemical modelling of disks similar to the protosolar nebula. Calculations are being undertaken to determine the spatial and temporal chemistry of the gas and dust within the 5-40AU comet-forming region of the nebula. These theoretical studies aim to determine the contribution of pristine and partially-processed interstellar material from the cool outer nebula as compared to that obtained from outward radial mixing of matter from the hot inner nebula. Reference Molecular distributions in the inner regions of protostellar disks Markwick A. J. Ilgner M. Millar T. J. Henning Th. (2002) Astron. Astrophys. 385 632

  10. Spectroscopic diagnostics of organic chemistry in the protostellar environment

    NASA Technical Reports Server (NTRS)

    Charnley, S. B.; Ehrenfreund, P.; Kuan, Y. J.

    2001-01-01

    A combination of astronomical observations, laboratory studies, and theoretical modelling is necessary to determine the organic chemistry of dense molecular clouds. We present spectroscopic evidence for the composition and evolution of organic molecules in protostellar environments. The principal reaction pathways to complex molecule formation by catalysis on dust grains and by reactions in the interstellar gas are described. Protostellar cores, where warming of dust has induced evaporation of icy grain mantles, are excellent sites in which to study the interaction between gas phase and grain-surface chemistries. We investigate the link between organics that are observed as direct products of grain surface reactions and those which are formed by secondary gas phase reactions of evaporated surface products. Theory predicts observable correlations between specific interstellar molecules, and also which new organics are viable for detection. We discuss recent infrared observations obtained with the Infrared Space Observatory, laboratory studies of organic molecules, theories of molecule formation, and summarise recent radioastronomical searches for various complex molecules such as ethers, azaheterocyclic compounds, and amino acids.

  11. Towards Bayesian Machine Learning for Estimating Parameters of Accretion Disk Models for SPH Simulations

    NASA Astrophysics Data System (ADS)

    Goel, Amit; Montgomery, Michele; Wiegand, Paul

    2016-01-01

    Accretion disks are ubiquitous in Active Galactic Nuclei, in protostellar systems forming protoplanets, and in close binary star systems such as X-ray binaries, Cataclysmic Variables, and Algols, for example. Observations such as disk tilt are found in all of these different accreting system types, suggesting a common physics must be present. To understand the common connections between these different system types, which can help us understand their unique evolutions, we need to better understand the physics of accretion. For example, viscosity is typically a constant value in the disk of a system that is in a specific state such as a quiescent state. However, viscosity can't be constant throughout the disk, especially at the boundaries. To learn more about viscosity and other common parameters in these disk, we use Bayesian Inference and Markov Chain Monte Carlo techniques to make predictions of events to come in the numerical simulations of these accreting disks. In this work, we present our techniques and initial findings.

  12. OBSERVING SIMULATED PROTOSTARS WITH OUTFLOWS: HOW ACCURATE ARE PROTOSTELLAR PROPERTIES INFERRED FROM SEDs?

    SciTech Connect

    Offner, Stella S. R.; Robitaille, Thomas P.; Hansen, Charles E.; Klein, Richard I.; McKee, Christopher F.

    2012-07-10

    The properties of unresolved protostars and their local environment are frequently inferred from spectral energy distributions (SEDs) using radiative transfer modeling. In this paper, we use synthetic observations of realistic star formation simulations to evaluate the accuracy of properties inferred from fitting model SEDs to observations. We use ORION, an adaptive mesh refinement (AMR) three-dimensional gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud including the effects of protostellar outflows. To obtain the dust temperature distribution and SEDs of the forming protostars, we post-process the simulations using HYPERION, a state-of-the-art Monte Carlo radiative transfer code. We find that the ORION and HYPERION dust temperatures typically agree within a factor of two. We compare synthetic SEDs of embedded protostars for a range of evolutionary times, simulation resolutions, aperture sizes, and viewing angles. We demonstrate that complex, asymmetric gas morphology leads to a variety of classifications for individual objects as a function of viewing angle. We derive best-fit source parameters for each SED through comparison with a pre-computed grid of radiative transfer models. While the SED models correctly identify the evolutionary stage of the synthetic sources as embedded protostars, we show that the disk and stellar parameters can be very discrepant from the simulated values, which is expected since the disk and central source are obscured by the protostellar envelope. Parameters such as the stellar accretion rate, stellar mass, and disk mass show better agreement, but can still deviate significantly, and the agreement may in some cases be artificially good due to the limited range of parameters in the set of model SEDs. Lack of correlation between the model and simulation properties in many individual instances cautions against overinterpreting properties inferred from SEDs for unresolved protostellar

  13. VIBRATIONALLY EXCITED HCN AROUND AFGL 2591: A PROBE OF PROTOSTELLAR STRUCTURE

    SciTech Connect

    Veach, Todd J.; Groppi, Christopher E.; Hedden, Abigail

    2013-03-10

    Vibrationally excited molecules with submillimeter rotational transitions are potentially excellent probes of physical conditions near protostars. This study uses observations of the v = 1 and v = 2 ro-vibrational modes of HCN (4-3) to probe this environment. The presence or absence and relative strengths of these ro-vibrational lines probe the gas excitation mechanism and physical conditions in warm, dense material associated with protostellar disks. We present pilot observations from the Heinrich Hertz Submillimeter Telescope and follow-up observations from the Submillimeter Array. All vibrationally excited HCN (4-3) v = 0, v = 1, and v = 2 lines were observed. The existence of the three v = 2 lines at approximately equal intensity imply collisional excitation with a density of greater than (10{sup 10} cm{sup -3}) and a temperature of >1000 K for the emitting gas. This warm, high-density material should directly trace structures formed in the protostellar envelope and disk environment. Further, the line shapes of the v = 2 emission may suggest a Keplerian disk. This Letter demonstrates the utility of this technique which is of particular interest due to the recent inauguration of the Atacama Large Millimeter Array.

  14. Protostellar formation in rotating interstellar clouds. VII - Opacity and fragmentation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1988-01-01

    This paper investigates the effect of variations in the Rosseland mean opacity of dust grains on numerical models of three-dimensional protostellar collapse and fragmentation. In particular, it is found that increasing the dust grain opacity by factors of three to four has little effect upon the gross characteristics of protostellar fragmentation. Consequently, theoretical quantities such as the estimated minimum protostellar mass for Population I star formation are insensitive to the precise value of the opacity.

  15. Radiation-Hydrodynamic Simulations of Massive Star Formation with Protostellar Outflows

    SciTech Connect

    Cunningham, A J; Klein, R I; Krumholz, M R; McKee, C F

    2011-03-02

    We report the results of a series of AMR radiation-hydrodynamic simulations of the collapse of massive star forming clouds using the ORION code. These simulations are the first to include the feedback effects protostellar outflows, as well as protostellar radiative heating and radiation pressure exerted on the infalling, dusty gas. We find that that outflows evacuate polar cavities of reduced optical depth through the ambient core. These enhance the radiative flux in the poleward direction so that it is 1.7 to 15 times larger than that in the midplane. As a result the radiative heating and outward radiation force exerted on the protostellar disk and infalling cloud gas in the equatorial direction are greatly diminished. The simultaneously reduces the Eddington radiation pressure barrier to high-mass star formation and increases the minimum threshold surface density for radiative heating to suppress fragmentation compared to models that do not include outflows. The strength of both these effects depends on the initial core surface density. Lower surface density cores have longer free-fall times and thus massive stars formed within them undergo more Kelvin contraction as the core collapses, leading to more powerful outflows. Furthermore, in lower surface density clouds the ratio of the time required for the outflow to break out of the core to the core free-fall time is smaller, so that these clouds are consequently influenced by outflows at earlier stages of collapse. As a result, outflow effects are strongest in low surface density cores and weakest in high surface density one. We also find that radiation focusing in the direction of outflow cavities is sufficient to prevent the formation of radiation pressure-supported circumstellar gas bubbles, in contrast to models which neglect protostellar outflow feedback.

  16. Radiation-hydrodynamic Simulations of Massive Star Formation with Protostellar Outflows

    NASA Astrophysics Data System (ADS)

    Cunningham, Andrew J.; Klein, Richard I.; Krumholz, Mark R.; McKee, Christopher F.

    2011-10-01

    We report the results of a series of adaptive mesh refinement radiation-hydrodynamic simulations of the collapse of massive star-forming clouds using the ORION code. These simulations are the first to include the feedback effects protostellar outflows, as well as protostellar radiative heating and radiation pressure exerted on the infalling, dusty gas. We find that outflows evacuate polar cavities of reduced optical depth through the ambient core. These enhance the radiative flux in the poleward direction so that it is 1.7-15 times larger than that in the midplane. As a result the radiative heating and outward radiation force exerted on the protostellar disk and infalling cloud gas in the equatorial direction are greatly diminished. This simultaneously reduces the Eddington radiation pressure barrier to high-mass star formation and increases the minimum threshold surface density for radiative heating to suppress fragmentation compared to models that do not include outflows. The strength of both these effects depends on the initial core surface density. Lower surface density cores have longer free-fall times and thus massive stars formed within them undergo more Kelvin contraction as the core collapses, leading to more powerful outflows. Furthermore, in lower surface density clouds the ratio of the time required for the outflow to break out of the core to the core free-fall time is smaller, so that these clouds are consequently influenced by outflows at earlier stages of the collapse. As a result, outflow effects are strongest in low surface density cores and weakest in high surface density ones. We also find that radiation focusing in the direction of outflow cavities is sufficient to prevent the formation of radiation pressure-supported circumstellar gas bubbles, in contrast to models which neglect protostellar outflow feedback.

  17. The Herschel Orion Protostar Survey: Spectral Energy Distributions and Fits Using a Grid of Protostellar Models

    NASA Astrophysics Data System (ADS)

    Furlan, E.; Fischer, W. J.; Ali, B.; Stutz, A. M.; Stanke, T.; Tobin, J. J.; Megeath, S. T.; Osorio, M.; Hartmann, L.; Calvet, N.; Poteet, C. A.; Booker, J.; Manoj, P.; Watson, D. M.; Allen, L.

    2016-05-01

    We present key results from the Herschel Orion Protostar Survey: spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion molecular clouds. This is the largest sample of protostars studied in a single, nearby star formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX, our SEDs cover 1.2–870 μm and sample the peak of the protostellar envelope emission at ∼100 μm. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate constraints on protostellar envelope properties. We find that most protostars, and in particular the flat-spectrum sources, are well fit. The median envelope density and median inclination angle decrease from Class 0 to Class I to flat-spectrum protostars, despite the broad range in best-fit parameters in each of the three categories. We also discuss degeneracies in our model parameters. Our results confirm that the different protostellar classes generally correspond to an evolutionary sequence with a decreasing envelope infall rate, but the inclination angle also plays a role in the appearance, and thus interpretation, of the SEDs.

  18. Selected Papers on Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Cassen, P. M.; Wasson, J. T.; Woolum, D. S.; Klahr, H. H.; Henning, Th.

    2004-01-01

    Three papers present studies of thermal balances, dynamics, and electromagnetic spectra of protoplanetary disks, which comprise gas and dust orbiting young stars. One paper addresses the reprocessing, in a disk, of photons that originate in the disk itself in addition to photons that originate in the stellar object at the center. The shape of the disk is found to strongly affect the redistribution of energy. Another of the three papers reviews an increase in the optical luminosity of the young star FU Orionis. The increase began in the year 1936 and similar increases have since been observed in other stars. The paper summarizes astronomical, meteoric, and theoretical evidence that these increases are caused by increases in mass fluxes through the inner portions of the protoplanetary disks of these stars. The remaining paper presents a mathematical-modeling study of the structures of protostellar accretion disks, with emphasis on limits on disk flaring. Among the conclusions reached in the study are that (1) the radius at which a disk becomes shadowed from its central stellar object depends on radial mass flow and (2) most planet formation has occurred in environments unheated by stellar radiation.

  19. Efficiency of particle trapping in the outer regions of protoplanetary disks

    SciTech Connect

    Simon, Jacob B.; Armitage, Philip J.

    2014-03-20

    We investigate the strength of axisymmetric local pressure maxima (zonal flows) in the outer regions of protoplanetary disks, where ambipolar diffusion reduces turbulent stresses driven by the magnetorotational instability. Using local numerical simulations we show that in the absence of net vertical magnetic fields, the strength of turbulence in the ambipolar dominated region of the disk is low and any zonal flows that are present are weak. For net fields strong enough to yield observed protostellar accretion rates, however, zonal flows with a density amplitude of 10%-20% are formed. These strengths are comparable to those seen in simulations of ideal MHD disk turbulence. We investigate whether these zonal flows are able to reverse the inward radial drift of solids, leading to prolonged and enhanced concentration as a prelude to planetesimal formation. For commonly assumed mean surface density profiles (surface density Σ∝r {sup –1/2} or steeper) we find that the predicted perturbations to the background disk profile do not correspond to local pressure maxima. This is a consequence of radial width of the simulated zonal flows, which is larger than was assumed in prior analytic models of particle trapping. These larger scale flows would only trap particles for higher amplitude fluctuations than observed. We conclude that zonal flows are likely to be present in the outer regions of protoplanetary disks and are potentially large enough to be observable, but are unlikely to lead to strong particle trapping.

  20. Herniated disk

    MedlinePlus

    ... the disk. This may place pressure on nearby nerves or the spinal cord. ... Lumbar radiculopathy; Cervical radiculopathy; Herniated intervertebral disk; Prolapsed intervertebral disk; Slipped disk; Ruptured disk; Herniated nucleus pulposus

  1. A SPITZER INFRARED SPECTROGRAPH DETECTION OF CRYSTALLINE SILICATES IN A PROTOSTELLAR ENVELOPE

    SciTech Connect

    Poteet, Charles A.; Megeath, S. Thomas; Fischer, William J.; Bjorkman, Jon E.; Watson, Dan M.; Remming, Ian S.; McClure, Melissa K.; Calvet, Nuria; Hartmann, Lee; Tobin, John J.; Sargent, Benjamin A.; Muzerolle, James; Furlan, Elise; Allen, Lori E.; Ali, Babar

    2011-06-01

    We present the Spitzer Space Telescope Infrared Spectrograph spectrum of the Orion A protostar HOPS-68. The mid-infrared spectrum reveals crystalline substructure at 11.1, 16.1, 18.8, 23.6, 27.9, and 33.6 {mu}m superimposed on the broad 9.7 and 18 {mu}m amorphous silicate features; the substructure is well matched by the presence of the olivine end-member forsterite (Mg{sub 2}SiO{sub 4}). Crystalline silicates are often observed as infrared emission features around the circumstellar disks of Herbig Ae/Be stars and T Tauri stars. However, this is the first unambiguous detection of crystalline silicate absorption in a cold, infalling, protostellar envelope. We estimate the crystalline mass fraction along the line of sight by first assuming that the crystalline silicates are located in a cold absorbing screen and secondly by utilizing radiative transfer models. The resulting crystalline mass fractions of 0.14 and 0.17, respectively, are significantly greater than the upper limit found in the interstellar medium ({approx}<0.02-0.05). We propose that the amorphous silicates were annealed within the hot inner disk and/or envelope regions and subsequently transported outward into the envelope by entrainment in a protostellar outflow.

  2. GGD 37: AN EXTREME PROTOSTELLAR OUTFLOW

    SciTech Connect

    Green, J. D.; Watson, D. M.; Forrest, W. J.; Kim, K. H.; Bergin, E.; Maret, S.; Melnick, G.; Tolls, V.; Sonnentrucker, P.; Sargent, B. A.; Raines, S. N.

    2011-01-01

    We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne V]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne V] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s{sup -1}. The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.

  3. Numerical simulation of unsteady laminar flow through a tilting disk heart valve: prediction of vortex shedding.

    PubMed

    Huang, Z J; Merkle, C L; Abdallah, S; Tarbell, J M

    1994-04-01

    Heart valves induce flow disturbances which play a role in blood cell activation and damage, but questions of the magnitude and spatial distribution of fluid stresses (wall shear stress and turbulent stress) cannot be readily addressed with current experimental techniques. Therefore, a numerical simulation procedure for flow through artificial heart valves is presented. The algorithm employed is based on the Navier-Stokes equations in generalized curvilinear coordinates with artificial compressibility for coupling of velocity and pressure. The algorithm applies a finite-difference technique on a body-conforming composite grid around the heart valve disk on which the numerical simulations are performed. Steady laminar flow over a backward-facing step and unsteady laminar flow inside a square driven cavity are computed to validate the algorithm. Two-dimensional, time-accurate simulation of flow through a tilting disk valve with a steady upstream Reynolds number as high as 1000 reveals the complex behavior of 'vortex shedding'. By scaling the results at the Reynolds number of 1000 to peak systolic flow conditions, the maximum value of shear stress on the valve disk is estimated to be 770 dyn cm-2. The 'apparent' Reynolds stress associated with vortex shedding is estimated to be as high as 3900 dyn cm-2 with a vortex shedding frequency of about 26 Hz. The 'apparent' Reynolds stress value is of similar magnitude as reported in experiments but would not be expected to damage blood cells because the spatial scales associated with vortex shedding are much larger than blood cell dimensions. PMID:8188720

  4. [Prediction of outcomes of surgical treatment of degenerative lumbar disk disease].

    PubMed

    Zhuravlev, Iu I; Nazarenko, G I; Cherkashov, A M; Riazanov, V V; Nazarenko, A G

    2009-01-01

    The paper focuses on algorithms of outcomes assessment of surgical treatment of the patients with degenerative lumbar disk disease. From 1997 to 2006 389 patients with discogenic lumbar pain were operated in the Medical Center of Central Bank of Russia. 185 patients underwent radiofrequency destruction of facet nerves, laser percutaneous lumbar discectomy was performed in 39 patients, microdiscectomy -- in 131, and decompression combined with lumbar spine stabilization -- in 31 cases. Clinical and radiological data of each patient were recorded in the database using 3-point scale according to intensity of the feature. Assessment of patients' condition was performed pre- and postoperatively (after discharge and after 6, 12 and 24 months interval). Postoperative outcome was recorded for the current period in compliance with modified criteria of Kawabata et al. Obtained data were mathematically and statistically processed. Developed algorithms allowed assessment of postoperative outcome in the patients with degenerative lumbar disk disease. Outcome data can be used for evaluation of feasibility of surgical treatment as well as for selection of surgical technique. PMID:19505029

  5. Protostellar Outflow Evolution in Turbulent Environments

    SciTech Connect

    Cunningham, A; Frank, A; Carroll, J; Blackman, E; Quillen, A

    2008-04-11

    The link between turbulence in star formatting environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers-type turbulence and produces a driving scale-length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star forming environments. In the last section we contrast our work and its conclusions with previous studies which claim that jets can not be the source of turbulence.

  6. Protostellar Outflow Evolution in Turbulent Environments

    NASA Astrophysics Data System (ADS)

    Cunningham, Andrew J.; Frank, Adam; Carroll, Jonathan; Blackman, Eric G.; Quillen, Alice C.

    2009-02-01

    The link between turbulence in star-forming environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows, we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence and produces a driving scale length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star-forming environments. In the last section, we contrast our work and its conclusions with previous studies which claim that jets cannot be the source of turbulence.

  7. ASSEMBLY OF PROTOPLANETARY DISKS AND INCLINATIONS OF CIRCUMBINARY PLANETS

    SciTech Connect

    Foucart, Francois; Lai, Dong

    2013-02-10

    The Kepler satellite has discovered a number of transiting planets around close binary stars. These circumbinary systems have highly aligned planetary and binary orbits. In this paper, we explore how the mutual inclination between the planetary and binary orbits may reflect the physical conditions of the assembly of protoplanetary disks and the interaction between protostellar binaries and circumbinary disks. Given the turbulent nature of star-forming molecular clouds, it is possible that the gas falling onto the outer region of a circumbinary disk and the central protostellar binary have different axes of rotation. Thus, the newly assembled circumbinary disk can be misaligned with respect to the binary. However, the gravitational torque from the binary produces a warp and twist in the disk, and the back-reaction torque tends to align the disk and the binary orbital plane. We present a new, analytic calculation of this alignment torque and show that the binary-disk inclination angle can be reduced appreciably after the binary accretes a few percent of its mass from the disk. Our calculation suggests that in the absence of other disturbances, circumbinary disks and planets around close (sub-AU) stellar binaries, for which mass accretion onto the proto-binary is very likely to have occurred, are expected to be highly aligned with the binary orbits, while disks and planets around wide binaries can be misaligned. Measurements of the mutual inclinations of circumbinary planetary systems can provide a clue to the birth environments of such systems.

  8. A Protostellar Jet Emanating from a Hypercompact H ii Region

    NASA Astrophysics Data System (ADS)

    Guzmán, Andrés E.; Garay, Guido; Rodríguez, Luis F.; Contreras, Yanett; Dougados, Catherine; Cabrit, Sylvie

    2016-08-01

    We present radio continuum observations of the high-mass young stellar object (HMYSO) G345.4938+01.4677 obtained using the Australia Telescope Compact Array (ATCA) at 5, 9, 17, and 19 GHz. These observations provide definite evidence that the outer and inner pairs of radio lobes consist of shock-ionized material being excited by an underlying collimated and fast protostellar jet emanating from a hypercompact H ii region. By comparing with images taken 6 years earlier at 5 and 9 GHz using the same telescope, we assess the proper motions (PMs) of the radio sources. The outer west and east lobes exhibit PMs of 64 ± 12 and 48 ± 13 mas yr‑1, indicating velocities projected in the plane of the sky and receding from G345.4938+01.4677 of 520 and 390 {\\text{km s}}-1, respectively. The internal radio lobes also display PM signals consistently receding from the HMYSO with magnitudes of 17 ± 11 and 35 ± 10 mas yr‑1 for the inner west and east lobes, respectively. The morphology of the outer west lobe is that of a detached bow shock. At 17 and 19 GHz, the outer east lobe displays an arcuate morphology also suggesting a bow shock. These results show that disk accretion and jet acceleration—possibly occurring in a very similar way compared with low-mass protostars—is taking place in G345.4938+01.4677 despite the presence of ionizing radiation and the associated hypercompact H ii region.

  9. Probing Pre-Protostellar Cores with Formaldehyde

    NASA Astrophysics Data System (ADS)

    Young, K. E.; Lee, J.-E.; Evans, N. J., II; Goldsmith, P. F.; Doty, S. D.

    2004-05-01

    We present maps of the 6 cm and 1.3 mm transitions of H2CO toward three cold, dense pre-protostellar cores: L1498, L1512, and L1544. The 6 cm transition is uniquely suited to probe high density gas at low temperature. Our models indicate that H2CO is depleted in the interiors of PPCs. Depletion significantly affects how H2CO probes the earliest stages of star formation. Multi-stage, self-consistent models, including gas--dust energetics, of both H2CO transitions are presented, and the implications of the results discussed. This work was supported by the National Aeronautics and Space Administration, the National Science Foundation, and the Research Corporation.

  10. Spitzer IRAC Detection of Protostellar Outflows

    NASA Astrophysics Data System (ADS)

    Ybarra, Jason E.; Lada, E. A.; Balog, Z.

    2009-01-01

    We will discuss a method for detecting shocked H2 emission in IRAC band images and distinguishing H2 knots from stellar sources. Using this method we will present Spitzer IRAC imaging of a recently discovered parsec scale protostellar outflow. This outflow was detected in all four IRAC bands. The proposed source of the outflow is an embedded Class 0 object detected in the MIPS images. This work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by an award issued by JPL/Caltech and also a NASA LTSA Grant NNG05GD66G

  11. Disk Accretion and the Stellar Birthline

    NASA Astrophysics Data System (ADS)

    Hartmann, Lee; Cassen, Patrick; Kenyon, Scott J.

    1997-02-01

    We present a simplified analysis of some effects of disk accretion on the early evolution of fully convective, low-mass pre-main-sequence stars. Our analysis builds on the previous seminal work of Stahler, but it differs in that the accretion of material occurs over a small area of the stellar surface, such as through a disk or magnetospheric accretion column, so that most of the stellar photosphere is free to radiate to space. This boundary condition is similar to the limiting case considered by Palla & Stahler for intermediate-mass stars. We argue that for a wide variety of disk mass accretion rates, material will be added to the star with relatively small amounts of thermal energy. Protostellar evolution calculated assuming this ``low-temperature'' limit of accretion generally follows the results of Stahler because of the thermostatic nature of deuterium fusion, which prevents protostars from contracting below a ``birthline'' in the H-R diagram. Our calculated protostellar radii tend to fall below Stahler's at higher masses; the additional energy loss from the stellar photosphere in the case of disk accretion tends to make the protostar contract. The low-temperature disk accretion evolutionary tracks never fall below the deuterium-fusion birthline until the internal deuterium is depleted, but protostellar tracks can lie above the birthline in the H-R diagram if the initial radius of the protostellar core is large enough or if rapid disk accretion (such as might occur during FU Ori outbursts) adds significant amounts of thermal energy to the star. These possibilities cannot be ruled out by either theoretical arguments or observational constraints at present, so that individual protostars might evolve along a multiplicity of birthlines with a modest range of luminosity at a given mass. Our results indicate that there are large uncertainties in assigning ages for the youngest stars from H-R diagram positions, given the uncertainty in birthline positions. Our

  12. Disks around Massive Young Stellar Objects: Are They Common?

    NASA Astrophysics Data System (ADS)

    Jiang, Zhibo; Tamura, Motohide; Hoare, Melvin G.; Yao, Yongqiang; Ishii, Miki; Fang, Min; Yang, Ji

    2008-02-01

    We present K-band polarimetric images of several massive young stellar objects at resolutions ~0.1''-0.5''. The polarization vectors around these sources are nearly centrosymmetric, indicating they are dominating the illumination of each field. Three out of the four sources show elongated low-polarization structures passing through the centers, suggesting the presence of polarization disks. These structures and their surrounding reflection nebulae make up bipolar outflow/disk systems, supporting the collapse/accretion scenario as their low-mass siblings. In particular, S140 IRS 1 shows well-defined outflow cavity walls and a polarization disk which matches the direction of previously observed equatorial disk wind, thus confirming that the polarization disk is actually the circumstellar disk. To date, a dozen massive protostellar objects show evidence for the existence of disks; our work adds additional samples around massive young stellar objects equivalent to early B type stars.

  13. Numerical experiments on the stability of preplanetary disks

    NASA Technical Reports Server (NTRS)

    Cassen, P. M.; Smith, B. F.; Reynolds, R. T.; Miller, R. H.

    1981-01-01

    Gravitational stability of gaseous protostellar disks is relevant to theories of planetary formation. Stable gas disks favor formation of planetesimals by the accumulation of solid material; unstable disks allow the possibility of direct condensation of gaseous protoplanets. This paper presents the results of numerical experiments designed to test the stability of thin disks against large-scale, self-gravitational disruption. It is found that a disk as massive as 1 solar mass, surrounding a 1 solar mass protostar, can be stable against long-wavelength gravitational disruption if its temperature is about 300 K or greater. Stability of a cooler disk requires that it be less massive, but even at 100 K a stable disk can have an appreciable fraction (about 1/3) of a solar mass.

  14. Protostellar feedback halts the growth of the first stars in the universe.

    PubMed

    Hosokawa, Takashi; Omukai, Kazuyuki; Yoshida, Naoki; Yorke, Harold W

    2011-12-01

    The first stars fundamentally transformed the early universe by emitting the first light and by producing the first heavy elements. These effects were predetermined by the mass distribution of the first stars, which is thought to have been fixed by a complex interplay of gas accretion and protostellar radiation. We performed radiation-hydrodynamics simulations that followed the growth of a primordial protostar through to the early stages as a star with thermonuclear burning. The circumstellar accretion disk was evaporated by ultraviolet radiation from the star when its mass was 43 times that of the Sun. Such massive primordial stars, in contrast to the often-postulated extremely massive stars, may help explain the fact that there are no signatures of the pair-instability supernovae in abundance patterns of metal-poor stars in our galaxy. PMID:22075723

  15. 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.

  16. Imaging the water snow-line during a protostellar outburst.

    PubMed

    Cieza, Lucas A; Casassus, Simon; Tobin, John; Bos, Steven P; Williams, Jonathan P; Perez, Sebastian; Zhu, Zhaohuan; Caceres, Claudio; Canovas, Hector; Dunham, Michael M; Hales, Antonio; Prieto, Jose L; Principe, David A; Schreiber, Matthias R; Ruiz-Rodriguez, Dary; Zurlo, Alice

    2016-07-14

    A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation. PMID:27411631

  17. Imaging the water snow-line during a protostellar outburst

    NASA Astrophysics Data System (ADS)

    Cieza, Lucas A.; Casassus, Simon; Tobin, John; Bos, Steven P.; Williams, Jonathan P.; Perez, Sebastian; Zhu, Zhaohuan; Caceres, Claudio; Canovas, Hector; Dunham, Michael M.; Hales, Antonio; Prieto, Jose L.; Principe, David A.; Schreiber, Matthias R.; Ruiz-Rodriguez, Dary; Zurlo, Alice

    2016-07-01

    A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296 (refs 3, 10), at distances of about 30 astronomical units (AU) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 AU away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report images at 0.03-arcsec resolution (12 AU) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 AU, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation.

  18. DISENTANGLING THE ENTANGLED: OBSERVATIONS AND ANALYSIS OF THE TRIPLE NON-COEVAL PROTOSTELLAR SYSTEM VLA1623

    SciTech Connect

    Murillo, Nadia M.; Lai, Shih-Ping E-mail: slai@phys.nthu.edu.tw

    2013-02-10

    Commonplace at every evolutionary stage, multiple protostellar systems (MPSs) are thought to be formed through fragmentation, but it is unclear when and how. The youngest MPSs, which have not yet undergone much evolution, provide important constraints to this question. It is then of interest to disentangle early stage MPSs. In this Letter we present the results of our work on VLA1623 using our observations and archival data from the Submillimeter Array. Our continuum and line observations trace VLA1623's components, outflow, and envelope, revealing unexpected characteristics. We construct the spectral energy distribution (SED) for each component using the results of our work and data from literature, as well as derive physical parameters from continuum and perform a simple kinematical analysis of the circumstellar material. Our results show VLA1623 to be a triple non-coeval system composed of VLA1623A, B, and W, with each source driving its own outflow and unevenly distributed circumstellar material. From the SED, physical parameters, and IR emission we conclude that VLA1623A and W are Class 0 and Class I protostars, respectively, and together drive the bulk of the observed outflow. Furthermore, we find two surprising results, first the presence of a rotating disk-like structure about VLA1623A with indications of pure Keplerian rotation, which, if real, would make it one of the first evidence of Keplerian disk structures around Class 0 protostars. Second, we find VLA1623B to be a bona fide extremely young protostellar object between the starless core and Class 0 stages.

  19. Cluster Formation in Protostellar Outflow-driven Turbulence

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Yun; Nakamura, Fumitaka

    2006-04-01

    Most, perhaps all, stars go through a phase of vigorous outflow during formation. We examine, through three-dimensional MHD simulation, the effects of protostellar outflows on cluster formation. We find that the initial turbulence in the cluster-forming region is quickly replaced by motions generated by outflows. The protostellar outflow-driven turbulence (``protostellar turbulence'' for short) can keep the region close to a virial equilibrium long after the initial turbulence has decayed away. We argue that there exist two types of turbulence in star-forming clouds: a primordial (or ``interstellar'') turbulence and a protostellar turbulence, with the former transformed into the latter mostly in embedded clusters such as NGC 1333. Since the majority of stars are thought to form in clusters, an implication is that the stellar initial mass function is determined to a large extent by the stars themselves, through outflows that individually limit the mass accretion onto forming stars and collectively shape the environments (density structure and velocity field) in which most cluster members form. We speculate that massive cluster-forming clumps supported by protostellar turbulence gradually evolve toward a highly centrally condensed ``pivotal'' state, culminating in rapid formation of massive stars in the densest part through accretion.

  20. Role of the UV external radiation field on the presence of astrophysical ices in protostellars environments

    NASA Astrophysics Data System (ADS)

    Robson Monteiro Rocha, Will; Pilling, Sergio

    2016-07-01

    The astrophysical ices survival is directly related with the temperature and ionizing radiation field in protostellars environments such as disks and envelopes. Computational models has shown that pure volatile molecules like CO and CH _{4} should survive only inside densest regions of molecular clouds or protoplanetary disks On the other hand, solid molecules such as H _{2}O and CH _{3}OH can be placed around 5 - 10 AU from the central protostar. Unlike of the previous models, we investigate the role of the UV external radiation field on the presence of ices in disks and envelopes. Once that a star-forming region is composed by the formation of many protostars, the external radiation field should be an important component to understand the real localization of the ices along the sight line. To address this topic it was employed the radiative transfer code RADMC-3D based on the Monte Carlo method. The code was used to model the spectrum and the near-infrared image of Elias 29. The initial parameters of the disk and envelope was taken from our previous paper (Rocha & Pilling (2015), ApJ 803:18). The opacities of the ices were calculated from the complex refractive index obtained at laboratory experiments perfomed at Grand Accélerateur National d'Íons Lourds (GANIL), by using the NKABS code from Rocha & Pilling (2014), SAA 123:436. The partial conclusions that we have obtained shows that pure CO volatile molecule cannot be placed at disk or envelope of Elias 29, unlike shown in our paper about Elias 29. Once it was observed in Elias 29 spectrum obtained with Infrared Space Observatory (ISO) between 2.5 - 190 μm, this molecule should be placed in foreground molecular clouds or trapped in the water ice matrix. The next calculations will be able to show where are placed the ices such as CH _{3}OH and CH _{3}CHO observed in Elias 29 spectrum.

  1. Multilayer formation and evaporation of deuterated ices in prestellar and protostellar cores

    SciTech Connect

    Taquet, Vianney; Charnley, Steven B.; Sipilä, Olli

    2014-08-10

    Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H{sub 2} and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

  2. A Search for Protostellar Collapse in Late Class I Sources

    NASA Astrophysics Data System (ADS)

    Gregersen, E. M.; Mardones, D.; Evans, N. J., II; Myers, P. C.; Shirley, Y. L.; Wilson, C. D.

    2000-10-01

    Asymmetric spectra of optically thick spectral lines are associated with protostellar collapse in young stellar objects. Such asymmetries have been believed to be confined solely to the Class 0 stage, but collapse signatures have now been observed in Class I sources with Tbol < 200 K. We present partial results of a survey that extends earlier results in Class 0 and I sources of HCO+, a molecule that shows strong line asymmetry in simulations of collapsing clouds, to Class I sources with Tbol < 650 K to find when protostellar collapse ends and how infall motions change with time.

  3. The one dimensional collapse models of turbulent protostellar clouds

    NASA Astrophysics Data System (ADS)

    Zamozdra, S. N.

    The spherically-symmetric numerical modelling of the gravitational collapse of protostellar clouds is carried out, taking ambipolar diffusion and the pressure of Alfvenic turbulence into account. It is shown that the dependency of protostar formation time on ekg (the initial turbulent-to-gravitational energies ratio) is non-monotonic because it is determined by the complex interaction of large scale magnetosonic waves with the waves of turbulence amplification. Protostellar mass is almost independent on ekg while accretion rate variations with ekg can be of order of 10%.

  4. Dynamics of binary and planetary-system interaction with disks - Eccentricity changes

    NASA Technical Reports Server (NTRS)

    Atrymowicz, Pawel

    1992-01-01

    Protostellar and protoplanetary systems, as well as merging galactic nuclei, often interact tidally and resonantly with the astrophysical disks via gravity. Underlying our understanding of the formation processes of stars, planets, and some galaxies is a dynamical theory of such interactions. Its main goals are to determine the geometry of the binary-disk system and, through the torque calculations, the rate of change of orbital elements of the components. We present some recent developments in this field concentrating on eccentricity driving mechanisms in protoplanetary and protobinary systems. In those two types of systems the result of the interaction is opposite. A small body embedded in a disk suffers a decrease of orbital eccentricity, whereas newly formed binary stars surrounded by protostellar disks may undergo a significant orbital evolution increasing their eccentricities.

  5. Formation and Recondensation of Complex Organic Molecules during Protostellar Luminosity Outbursts

    NASA Astrophysics Data System (ADS)

    Taquet, Vianney; Wirström, Eva S.; Charnley, Steven B.

    2016-04-01

    During the formation of stars, the accretion of surrounding material toward the central object is thought to undergo strong luminosity outbursts followed by long periods of relative quiescence, even at the early stages of star formation when the protostar is still embedded in a large envelope. We investigated the gas-phase formation and recondensation of the complex organic molecules (COMs) di-methyl ether and methyl formate, induced by sudden ice evaporation processes occurring during luminosity outbursts of different amplitudes in protostellar envelopes. For this purpose, we updated a gas-phase chemical network forming COMs in which ammonia plays a key role. The model calculations presented here demonstrate that ion–molecule reactions alone could account for the observed presence of di-methyl ether and methyl formate in a large fraction of protostellar cores without recourse to grain-surface chemistry, although they depend on uncertain ice abundances and gas-phase reaction branching ratios. In spite of the short outburst timescales of about 100 years, abundance ratios of the considered species higher than 10% with respect to methanol are predicted during outbursts due to their low binding energies relative to water and methanol which delay their recondensation during cooling. Although the current luminosity of most embedded protostars would be too low to produce complex organics in the hot-core regions that are observable with current sub-millimetric interferometers, previous luminosity outburst events would induce the formation of COMs in extended regions of protostellar envelopes with sizes increasing by up to one order of magnitude.

  6. Signatures of Chemical Evolution in Protostellar Nebulae

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A., III; Johnson, Natasha

    2011-01-01

    A decade ago observers began to take serious notice of the presence of crystalline silicate grains in the dust flowing away from some comets. While crystallinity had been seen in such objects previously, starting with the recognitions by Campins and Ryan (1990) that the 10 micron feature of Comet Halley resembled that of the mineral forsterite, most such observations were either ignored or dismissed as no path to explain such crystalline grains was available in the literature. When it was first suggested that an outward flow must be present to carry annealed silicate grains from the innermost regions of the Solar Nebula out to the regions where comets could form (Nuth, 1999; 2001) this suggestion was also dismissed because no such transport mechanism was known at the time. Since then not only have new models of nebular dynamics demonstrated the reality of long distance outward transport (Ciesla, 2007; 2008; 2009) but examination of older models (Boss, 2004) showed that such transport had been present but had gone unrecognized for many years. The most unassailable evidence for outward nebular transport came with the return of the Stardust samples from Comet Wild2, a Kuiper-belt comet that contained micron-scale grains of high temperature minerals resembling the Calcium-Aluminum Inclusions found in primitive meteorites (Zolensky et aI., 2006) that formed at T > 1400K. Now that outward transport in protostellar nebulae has been firmly established, a re-examination of its consequences for nebular gas is in order that takes into account both the factors that regulate both the outward flow as well as those that likely control the chemical composition of the gas. Laboratory studies of surface catalyzed reactions suggest that a trend toward more highly reduced carbon and nitrogen compounds in the gas phase should be correlated with a general increase in the crystallinity of the dust (Nuth et aI., 2000), but is such a trend actually observable? Unlike the Fischer-Tropsch or

  7. DEUTERIUM CHEMISTRY IN PROTOPLANETARY DISKS. II. THE INNER 30 AU

    SciTech Connect

    Willacy, K.; Woods, P. M. E-mail: Paul.Woods@manchester.ac.u

    2009-09-20

    We present the results of models of the chemistry, including deuterium, in the inner regions of protostellar disks. We find good agreement with recent gas-phase observations of several (non-deuterated) species. We also compare our results with observations of comets and find that in the absence of other processing, e.g., in the accretion shock at the surface of the disk, or by mixing in the disk, the calculated D/H ratios in ices are higher than measured and reflect the D/H ratio set in the molecular cloud phase. Our models give quite different abundances and molecular distributions to other inner disk models because of the differences in physical conditions in the model disk. This emphasizes how changes in the assumptions about the density and temperature distribution can radically affect the results of chemical models.

  8. BIPOLAR JETS LAUNCHED FROM ACCRETION DISKS. II. THE FORMATION OF ASYMMETRIC JETS AND COUNTER JETS

    SciTech Connect

    Fendt, Christian; Sheikhnezami, Somayeh E-mail: nezami@mpia.de

    2013-09-01

    We investigate the jet launching from accretion disks, in particular the formation of intrinsically asymmetric jet/counter jet systems. We perform axisymmetric MHD simulations of the disk-jet structure on a bipolar computational domain covering both hemispheres. We apply various models such as asymmetric disks with (initially) different scale heights in each hemisphere, symmetric disks into which a local disturbance is injected, and jets launched into an asymmetric disk corona. We consider both a standard global magnetic diffusivity distribution and a novel local diffusivity model. Typical disk evolution first shows substantial disk warping and then results in asymmetric outflows with a 10%-30% mass flux difference. We find that the magnetic diffusivity profile is essential for establishing a long-term outflow asymmetry. We conclude that bipolar asymmetry in protostellar and extragalactic jets can indeed be generated intrinsically and maintained over a long time by disk asymmetries and the standard jet launching mechanism.

  9. THE LONG-TERM EVOLUTION OF PHOTOEVAPORATING PROTOPLANETARY DISKS

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu Zhaohuan; Gammie, Charles E-mail: lhartm@umich.edu E-mail: gammie@illinois.edu

    2013-09-01

    We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for {approx}< 20% of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that the initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly rotating cores. Accreting and non-accreting transitional disks show different evolutionary paths on the M-dot-R{sub wall} plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU.

  10. Herniated Disk

    MedlinePlus

    Your backbone, or spine, is made up of 26 bones called vertebrae. In between them are soft disks filled with a jelly-like substance. These disks cushion the vertebrae and keep them in place. As you age, ...

  11. 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.

  12. Star Formation in Low Mass Magnetized Cores: The Formation of Disks and Outflows

    NASA Astrophysics Data System (ADS)

    Duffin, Dennis F.

    2012-10-01

    Protostellar discs are generally thought to drive molecular outflows and jets observed in star forming regions, but there has been some debate as to how they form. The details of the driving and collimation of outflows help determine how much mass is cleared out and how much energy is fed back into the surroundings. Recently it has been argued that the magnetic brake is so strong that early protostellar disks cannot form. We have performed 3D ideal magnetohydrodynamic (MHD) simulations of collapsing Bonnor-Ebert spheres, employing sink particles within an AMR grid and using a cooling function to model radiative cooling of the gas. This allows us to follow the formation and early evolution of the accretion disc (2-8)×10^4 years further into the Class 0 phase of its evolution. We form a rotationally dominated disc with a radius of 100 AU embedded inside a transient, unstable, flattened, rotating structure extending out to 2000 AU. The inner disc becomes unstable to a warping instability due to the magnetic structure of the outflow, warping 30 deg with respect to the rotation-axis by the end of the simulation. The disc is unstable to a Parker instability and sheds magnetic loops, degrading the orientation of the mean threading field. This reduces and locally reverses the magnetic braking torque of the large scale field back upon the disc. The reduction of magnetic braking allows a nearly Keplerian disc to form and may be the key way in which low mass stellar systems produce rotationally dominated discs. We discuss the relevance of our disc misalignment concerning the formation of mis-aligned hot Jupiters. Protostellar outflows are implicated in clearing mass from collapsing cores, and limiting the final mass of newly formed stars. The details of the driving and collimation of outflows help determine how much mass is cleared out and how much energy is fed back into the surroundings. The simulations generate outflows which are precessing, kinked, contain internal

  13. Protostellar formation in rotating interstellar clouds. VIII - Inner core formation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1989-01-01

    The results are presented of a variety of spherically symmetric one-dimensional (1D) calculations intended to determine the robustness of the dynamical hiccup phenomenon in protostellar cores. The 1D models show that the phenomenon is relatively insensitive to changes in the equations of state, numerical resolution, initial density and temperature, and the radiative transfer approximation. In 1D, the hiccup results in an explosive destruction of the entire inner protostellar core. Inner core formation is studied with a sequence of three-dimensional models which show that rapid inner core rotation stabilizes the hiccup instability. Instead, the inner core becomes quite flat and undergoes a cycle of binary fragmentation, binary decay into a single object surrounded by a bar, breakup of the bar into a binary, etc. When lesser amounts of rotation are involved, the inner core does hiccup somewhat, but mass is ejected in only a few directions, leading to several broad streams of ejecta.

  14. Revealing the dynamics of Class 0 protostellar discs with ALMA

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Sánchez-Monge, Á.; Walch, S.; Banerjee, R.

    2016-06-01

    We present synthetic ALMA observations of Keplerian, protostellar discs in the Class 0 stage studying the emission of molecular tracers like 13CO, C18O, HCO+, H13CO+, N2H+, and H2CO. We model the emission of discs around low- and intermediate-mass protostars. We show that under optimal observing conditions ALMA is able to detect the discs already in the earliest stage of protostellar evolution, although the emission is often concentrated to the innermost 50 au. Therefore, a resolution of a few 0.1 arcsec might be too low to detect Keplerian discs around Class 0 objects. We also demonstrate that under optimal conditions for edge-on discs Keplerian rotation signatures are recognisable, from which protostellar masses can be inferred. For this we here introduce a new approach, which allows us to determine protostellar masses with higher fidelity than before. Furthermore, we show that it is possible to reveal Keplerian rotation even for strongly inclined discs and that ALMA should be able to detect possible signs of fragmentation in face-on discs. In order to give some guidance for future ALMA observations, we investigate the influence of varying observing conditions and source distances. We show that it is possible to probe Keplerian rotation in inclined discs with an observing time of 2 h and a resolution of 0.1 arcsec, even in the case of moderate weather conditions. Furthermore, we demonstrate that under optimal conditions, Keplerian discs around intermediate-mass protostars should be detectable up to kpc distances.

  15. CONVERGENCE STUDIES OF MASS TRANSPORT IN DISKS WITH GRAVITATIONAL INSTABILITIES. I. THE CONSTANT COOLING TIME CASE

    SciTech Connect

    Michael, Scott; Steiman-Cameron, Thomas Y.; Durisen, Richard H.; Boley, Aaron C. E-mail: tomsc@astro.indiana.edu E-mail: aaron.boley@gmail.com

    2012-02-10

    We conduct a convergence study of a protostellar disk, subject to a constant global cooling time and susceptible to gravitational instabilities (GIs), at a time when heating and cooling are roughly balanced. Our goal is to determine the gravitational torques produced by GIs, the level to which transport can be represented by a simple {alpha}-disk formulation, and to examine fragmentation criteria. Four simulations are conducted, identical except for the number of azimuthal computational grid points used. A Fourier decomposition of non-axisymmetric density structures in cos (m{phi}), sin (m{phi}) is performed to evaluate the amplitudes A{sub m} of these structures. The A{sub m} , gravitational torques, and the effective Shakura and Sunyaev {alpha} arising from gravitational stresses are determined for each resolution. We find nonzero A{sub m} for all m-values and that A{sub m} summed over all m is essentially independent of resolution. Because the number of measurable m-values is limited to half the number of azimuthal grid points, higher-resolution simulations have a larger fraction of their total amplitude in higher-order structures. These structures act more locally than lower-order structures. Therefore, as the resolution increases the total gravitational stress decreases as well, leading higher-resolution simulations to experience weaker average gravitational torques than lower-resolution simulations. The effective {alpha} also depends upon the magnitude of the stresses, thus {alpha}{sub eff} also decreases with increasing resolution. Our converged {alpha}{sub eff} is consistent with predictions from an analytic local theory for thin disks by Gammie, but only over many dynamic times when averaged over a substantial volume of the disk.

  16. DETECTION OF A MAGNETIZED DISK AROUND A VERY YOUNG PROTOSTAR

    SciTech Connect

    Rao, Ramprasad; Girart, Josep M.; Lai, Shih-Ping; Marrone, Daniel P. E-mail: girart@ice.cat

    2014-01-01

    We present subarcsecond resolution polarimetric observations of the 878 μm thermal dust continuum emission obtained with the Submillimeter Array toward the IRAS 16293–2422 protostellar binary system. We report the detection of linearly polarized dust emission arising from the circumstellar disk associated with the IRAS 16293–2422 B protostar. The fractional polarization of ≅ 1.4% is only slightly lower than that expected from theoretical calculations in such disks. The magnetic field structure on the plane of the sky derived from the dust polarization suggests a complex magnetic field geometry in the disk, possibly associated with a rotating disk that is wrapping the field lines as expected from the simulations. The polarization around IRAS 16293–2422 A at subarcsecond angular resolution is only marginally detected.

  17. A Study of Radio Polarization in Protostellar Jets

    NASA Astrophysics Data System (ADS)

    Cécere, Mariana; Velázquez, Pablo F.; Araudo, Anabella T.; De Colle, Fabio; Esquivel, Alejandro; Carrasco-González, Carlos; Rodríguez, Luis F.

    2016-01-01

    Synchrotron radiation is commonly observed in connection with shocks of different velocities, ranging from relativistic shocks associated with active galactic nuclei, gamma-ray bursts, or microquasars, to weakly or non-relativistic flows such as those observed in supernova remnants. Recent observations of synchrotron emission in protostellar jets are important not only because they extend the range over which the acceleration process works, but also because they allow us to determine the jet and/or interstellar magnetic field structure, thus giving insights into the jet ejection and collimation mechanisms. In this paper, we compute for the first time polarized (synchrotron) and non-polarized (thermal X-ray) synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. We consider models with different jet velocities and variability, as well as a toroidal or helical magnetic field. Our simulations show that variable, low-density jets with velocities of ˜1000 km s-1 and ˜10 times lighter than the environment can produce internal knots with significant synchrotron emission and thermal X-rays in the shocked region of the leading bow shock moving in a dense medium. While models with a purely toroidal magnetic field show a very large degree of polarization, models with a helical magnetic field show lower values and a decrease of the degree of polarization, in agreement with observations of protostellar jets.

  18. The Formation and Fragmentation of Primordial Protostellar Discs

    NASA Astrophysics Data System (ADS)

    Clark, Paul C.; Glover, Simon C. O.; Smith, Rowan J.; Greif, Thomas H.; Klessen, Ralf S.; Bromm, Volker

    2010-11-01

    We study the formation and evolution of the protostellar discs that form around the first stars in the Universe. Using sink particles, we replace the gravitationally bound gas at densities higher than 1015 cm-3 and radii greater than 3 AU from the central protostellar core, with an accreting point mass that is able to gravitationally interact with the surrounding gas. We find the disc is gravitationally (or `Toomre') unstable, and is dominated by a strong m = 2 spiral mode. Although the angular momentum transport is dominated by a combination of gravitational torques and Reynolds stresses, which are extremely efficient mechanisms, the disc is unable to process the infalling material and grows increasingly gravitationally unstable. During the build-up of the disc, the temperature in the gas is regulated by a combination of H2 line cooling, collision-induced emission and H2 dissociation, which together help to offset heating from the gravitational collapse and feedback from the protostar. Once the disc starts to fragment, H2 dissociation keeps the gas almost isothermal as the collapse of the fragment progresses. The fragmentation occurs when the protostar/disc system is only 230 yr old and at a distance of ~20 AU from its sibling, by which point the central protostar has a mass of ~1 Msolar. Given the angular momentum of the new protostellar system, it is likely that the protostars will grow to become a massive binary system.

  19. Spatial Distribution of Small Organics in Prestellar and Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Waalkes, William; Guzman, Viviana; Oberg, Karin I.

    2016-01-01

    In the interstellar medium, formaldehyde (H2CO) has efficient formation pathways in both the gas-phase and on the surfaces of dust grains. Methanol (CH3OH), on the other hand, is believed to form exclusively on grains as there are no efficient gas-phase reactions leading to CH3OH. We present observations taken with the IRAM 30m telescope of several H2CO and CH3OH lines in a prestellar and protostellar core. We investigated the formation pathways of H2CO and CH3OH by comparing their spatial distributions. We find that in the prestellar core, the two species are anti-correlated in the densest region, while their emission is correlated in the low-density region. In contrast, for the protostellar core we find a correlation in the distribution of both species. We conclude that in the protostellar source, H2CO and CH3OH form together on grains and have been thermally desorbed due to the central newly formed star. In the prestellar core, however, CH3OH forms on the ices and remains depleted in the coldest regions, while H2CO can form efficiently in the gas-phase. This work was supported in part by the NSF REU and DoD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution.

  20. Particle simulation of supersonic convection in the protostellar nebula

    NASA Astrophysics Data System (ADS)

    Riegger, J. M.

    1995-02-01

    For the simulation of compressible convection and a possible description of inner processes in meteorites a new algorithm for particle-in-cell methods in particle simulation is developed, which allows a direct description of the inner pressure by use of individual particle temperatures and therefore a description of gas dynamics without the approximations of perturbation theory. The simulation of nonadiabatic processes in superadiabatic stratified atmospheres leads to the self-organization of convection cells and to supersonic convection and instationary shock front systems for high Rayleigh numbers Ra > 5 × 10 5 as they are received by other numerical methods. The transport of material through shock fronts yields much faster temperature and pressure changes than ordinary convective transport in the subsonic range. Tracing the values of state along the pathlines shows that fast entropy increases occur either within shock fronts or due to local dissipation in turbulences. Transport through shock front systems results in multiple rapid temperature changes per cycle. Investigations on the local convective structure of the protostellar nebula with a simple radiative transfer and standard opacities and accretion rates indicate supersonic convection and multiple shock front systems in the outer layers of the solar nebula due to radiative cooling. Supersonic convection provides a very effective mechanism of dissipation for the protostellar nebula and makes a contribution to the discussion on the turbulent structure of the protostellar nebula and to the formation of chrondrules.

  1. Clarifying Massive Protostellar Evolution and Circumstellar Processing

    NASA Astrophysics Data System (ADS)

    Indebetouw, Remy; Brogan, Crystal; Hoare, Melvin; Lumsden, Stuart; Robitaille, Thomas; Sewilo, Marta; Urquhart, James; Viti, Serena; Whitney, Barbara

    2008-03-01

    Massive stars dominate the evolution of galaxies and even as protostars, their feedback can affect their own formation and that of their host clusters. We propose a systematic study of massive protostars through the stages of their early evolution, to derive a clearer evolutionary sequence and a better link between the state of the central source and physical conditions in circumstellar material. This experiment will improve over existing work by careful source selection to systematically span evolutionary parameter space, resulting in a more uniform and comprehensive sample. Sophisticated radiative transfer, ionization, and chemical modeling will be used to extract the full riches of each IRS spectrum and find trends in how massive stars form and process their natal material: We will be able to determine the temperature, density, and chemical state (heating history) of circumstellar dust and ice in the accretion disk and envelope, and at later evolutionary stages the ionizing and soft (PAH-exciting) ultraviolet radiation emitted by the protostars and how that radiation is quenched and shadowed by circumstellar material. This investigation is the key to realizing the full potential of previous infrared imaging surveys like MSX and Spitzer's GLIMPSE and MIPSGAL to study massive star formation. These surveys have provided a basis for us to select a large relatively unbiased sample spanning evolutionary state. In return, revealing the spectroscopic signature of massive YSOs will greatly clarify the modeling and interpretation of the thousands of other protostars in these imaging survey data.

  2. The development of a protoplanetary disk from its natal envelope.

    PubMed

    Watson, Dan M; Bohac, C J; Hull, C; Forrest, William J; Furlan, E; Najita, J; Calvet, Nuria; d'Alessio, Paola; Hartmann, Lee; Sargent, B; Green, Joel D; Kim, Kyoung Hee; Houck, J R

    2007-08-30

    Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid development from their initial, spheroidal configurations, and therefore are studied intensively for details of the formation of protoplanetary disks within protostellar envelopes. At millimetre wavelengths, kinematic signatures of collapse have been observed in several such protostars, through observations of molecular lines that probe their outer envelopes. It has been suggested that one or more components of the proto-multiple system NGC 1333-IRAS 4 (refs 1, 2) may display signs of an embedded region that is warmer and denser than the bulk of the envelope. Here we report observations that reveal details of the core on Solar System dimensions. We detect in NGC 1333-IRAS 4B a rich emission spectrum of H2O, at wavelengths 20-37 microm, which indicates an origin in extremely dense, warm gas. We can model the emission as infall from a protostellar envelope onto the surface of a deeply embedded, dense disk, and therefore see the development of a protoplanetary disk. This is the only example of mid-infrared water emission from a sample of 30 class 0 objects, perhaps arising from a favourable orientation; alternatively, this may be an early and short-lived stage in the evolution of a protoplanetary disk. PMID:17728752

  3. Methanol masers and millimetre lines : a common origin in protostellar envelopes

    NASA Astrophysics Data System (ADS)

    Torstensson, Karl Johan Erik

    2011-12-01

    In this thesis we study the earliest stages of high-mass star formation. Class II methanol masers are only associated with massive star formation and are a unique probe of these environments. Through observations we have studied where and when the methanol maser emission occur in relation to the protostar. We have found that for a fair fraction of the sources the methanol masers appear on size scales of ca. 1000 AU, in the equatorial region of the massive protostar. It appears that infall, rather than rotation, is the dominant motion. We propose that the maser emission occur close to or in a shock interface, possibly related to the accretion flow of the more extended gas in the protostellar envelope onto an accretion disk. The morphology and kinematics of the thermal methanol gas support the hypothesis that the maser region is also the region where the methanol molecules are released from the icy mantles of the du st grains. We have also estimated the temperature and column density of the methanol gas in the outflows and find evidence for radiative excitation of the methanol gas at the location of the maser emission.

  4. Optical Disks.

    ERIC Educational Resources Information Center

    Gale, John C.; And Others

    1985-01-01

    This four-article section focuses on information storage capacity of the optical disk covering the information workstation (uses microcomputer, optical disk, compact disc to provide reference information, information content, work product support); use of laser videodisc technology for dissemination of agricultural information; encoding databases…

  5. DISK-SATELLITE INTERACTION IN DISKS WITH DENSITY GAPS

    SciTech Connect

    Petrovich, Cristobal; Rafikov, Roman R.

    2012-10-10

    Gravitational coupling between a gaseous disk and an orbiting perturber leads to angular momentum exchange between them that can result in gap opening by planets in protoplanetary disks and clearing of gas by binary supermassive black holes (SMBHs) embedded in accretion disks. Understanding the co-evolution of the disk and the orbit of the perturber in these circumstances requires knowledge of the spatial distribution of the torque exerted by the latter on a highly non-uniform disk. Here we explore disk-satellite interaction in disks with gaps in linear approximation both in Fourier and in physical space, explicitly incorporating the disk non-uniformity in the fluid equations. Density gradients strongly displace the positions of Lindblad resonances in the disk (which often occur at multiple locations), and the waveforms of modes excited close to the gap edge get modified compared to the uniform disk case. The spatial distribution of the excitation torque density is found to be quite different from the existing prescriptions: most of the torque is exerted in a rather narrow region near the gap edge where Lindblad resonances accumulate, followed by an exponential falloff with the distance from the perturber. Despite these differences, for a given gap profile, the full integrated torque exerted on the disk agrees with the conventional uniform disk theory prediction at the level of {approx}10%. The nonlinearity of the density wave excited by the perturber is shown to decrease as the wave travels out of the gap, slowing down its nonlinear evolution and damping. Our results suggest that gap opening in protoplanetary disks and gas clearing around SMBH binaries can be more efficient than the existing theories predict. They pave the way for self-consistent calculations of the gap structure and the orbital evolution of the perturber using accurate prescription for the torque density behavior.

  6. The Impact of Protostellar Jets on their Environment

    NASA Astrophysics Data System (ADS)

    O'Connell, B. F.

    2005-06-01

    features aligning the outflow. In addition, [Fe II] emission at 1.644 μm has been detected but is restricted to isolated condensations. The ordered structure of the western outflow is modeled as a series of C-type shocks with J-type dissociative apices. Essentially the same conditions are predicted for each bow except for a systematic reduction in speed and density with distance from the driving source. Increased K-band extinctions are found in the bright regions, as high as 2.9 magnitudes, and suggest that the bow shocks become visible where the outflow impacts on dense clumps of cloud material. Integral field spectroscopy was performed on the highly symmetric HH 212 outflow. Narrow-band images and spectra were simultaneously obtained between 1.5 to 2.5 μm. Images in H2 and [Fe II] transition lines were compared in order to extract the excitation and extinction conditions. Collisional excitation was confirmed as the process leading to the radiation from the inner knots and bows. Lower excitation and extinction are found for the bows which appear to have exited from the dense inner gas. The peak flux positions are compared for all the transition lines detected. For the knots, a trend is found between the measured offsets and the upper level temperatures both along the outflow direction and transverse to the jet axis. An underlying shock structure is implied. A timescale for the Class O evolutionary stage is suggested which relates the envelope mass to the mass accretion rate as inferred from the outflow luminosity. The deduced timescales are in general agreement with the Class O lifetimes estimated from statistical surveys. It is proposed that in order to investigate the relationship between outflows and protostellar evolution, the individual environmental factors for each outflow need to be examined. Only then can the intrinsic luminosities be revealed and related to the evolution which may be different for each source.

  7. Rotation and Outflow Motions in the Very Low-Mass Class 0 Protostellar System HH 211 at Subarcsecond Resolution

    NASA Astrophysics Data System (ADS)

    Lee, Chin-Fei; Hirano, Naomi; Palau, Aina; Ho, Paul T. P.; Bourke, Tyler L.; Zhang, Qizhou; Shang, Hsien

    2009-07-01

    HH 211 is a nearby young protostellar system with a highly collimated jet. We have mapped it in 352 GHz continuum, SiO (J = 8 - 7), and HCO+ (J = 4 - 3) emission at up to ~0farcs2 resolution with the Submillimeter Array (SMA). The continuum source is now resolved into two sources, SMM1 and SMM2, with a separation of ~ 84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty disk around the protostar driving the jet. SMM2 is seen to the southwest of SMM1 and may trace an envelope-disk around a small binary companion. A flattened envelope-disk is seen in HCO+ around SMM1 with a radius of ~ 80 AU perpendicular to the jet axis. Its velocity structure is consistent with a rotation motion and can be fitted with a Keplerian law that yields a mass of ~50 ± 15 M Jup (a mass of a brown dwarf) for the protostar. Thus, the protostar could be the lowest mass source known to have a collimated jet and a rotating flattened envelope-disk. A small-scale (~200 AU) low-speed (~2 km s-1) outflow is seen in HCO+ around the jet axis extending from the envelope-disk. It seems to rotate in the same direction as the envelope-disk and may carry away part of the angular momentum from the envelope-disk. The jet is seen in SiO close to ~100 AU from SMM1. It is seen with a "C-shaped" bending. It has a transverse width of lsim 40 AU and a velocity of ~ 170 ± 60 km s-1. A possible velocity gradient is seen consistently across its innermost pair of knots, ~0.5 km s-1 at ~10 AU, consistent with the sense of rotation of the envelope-disk. If this gradient is an upper limit of the true rotational gradient of the jet, then the jet carries away a very small amount of angular momentum of lsim 5 AU km s-1 and thus must be launched from the very inner edge of the disk near the corotation radius.

  8. Simulating the Formation of Massive Protostars. I. Radiative Feedback and Accretion Disks

    NASA Astrophysics Data System (ADS)

    Klassen, Mikhail; Pudritz, Ralph E.; Kuiper, Rolf; Peters, Thomas; Banerjee, Robi

    2016-05-01

    We present radiation hydrodynamic simulations of collapsing protostellar cores with initial masses of 30, 100, and 200 M ⊙. We follow their gravitational collapse and the formation of a massive protostar and protostellar accretion disk. We employ a new hybrid radiative feedback method blending raytracing techniques with flux-limited diffusion for a more accurate treatment of the temperature and radiative force. In each case, the disk that forms becomes Toomre-unstable and develops spiral arms. This occurs between 0.35 and 0.55 freefall times and is accompanied by an increase in the accretion rate by a factor of 2–10. Although the disk becomes unstable, no other stars are formed. In the case of our 100 and 200 M ⊙ simulations, the star becomes highly super-Eddington and begins to drive bipolar outflow cavities that expand outwards. These radiatively driven bubbles appear stable, and appear to be channeling gas back onto the protostellar accretion disk. Accretion proceeds strongly through the disk. After 81.4 kyr of evolution, our 30 M ⊙ simulation shows a star with a mass of 5.48 M ⊙ and a disk of mass 3.3 M ⊙, while our 100 M ⊙ simulation forms a 28.8 M ⊙ mass star with a 15.8 M ⊙ disk over the course of 41.6 kyr, and our 200 M ⊙ simulation forms a 43.7 M ⊙ star with an 18 M ⊙ disk in 21.9 kyr. In the absence of magnetic fields or other forms of feedback, the masses of the stars in our simulation do not appear to be limited by their own luminosities.

  9. FROM PRESTELLAR TO PROTOSTELLAR CORES. II. TIME DEPENDENCE AND DEUTERIUM FRACTIONATION

    SciTech Connect

    Aikawa, Y.; Wakelam, V.; Hersant, F.; Garrod, R. T.; Herbst, E.

    2012-11-20

    We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from a dense molecular cloud core to a protostellar core, by solving a gas-grain reaction network applied to a one-dimensional radiative hydrodynamic model with infalling fluid parcels. Spatial distributions of gas and ice-mantle species are calculated at the first-core stage, and at times after the birth of a protostar. Gas-phase methanol and methane are more abundant than CO at radii r {approx}< 100 AU in the first-core stage, but gradually decrease with time, while abundances of larger organic species increase. The warm-up phase, when complex organic molecules are efficiently formed, is longer-lived for those fluid parcels infalling at later stages. The formation of unsaturated carbon chains (warm carbon-chain chemistry) is also more effective in later stages; C{sup +}, which reacts with CH{sub 4} to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are strongly deuterated, mainly due to high D/H ratios in the parent molecules, determined in the cold phase. We also extend our model to simulate simply the chemistry in circumstellar disks, by suspending the one-dimensional infall of a fluid parcel at constant disk radii. The species CH{sub 3}OCH{sub 3} and HCOOCH{sub 3} increase in abundance in 10{sup 4}-10{sup 5} yr at the fixed warm temperature; both also have high D/H ratios.

  10. Dynamics of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Nelson, Andrew F.; Benz, Willy; Adams, Fred C.; Arnett, David

    1998-07-01

    We present a series of two-dimensional hydrodynamic simulations of massive disks around protostars. We simulate the same physical problem using both a Piecewise Parabolic Method (PPM) code and a Smoothed Particle Hydrodynamic (SPH) code and analyze their differences. The disks studied here range in mass from 0.05M* to 1.0M* and in initial minimum Toomre Q value from 1.1 to 3.0. We adopt simple power laws for the initial density and temperature in the disk with an isothermal (γ = 1) equation of state. The disks are locally isothermal. We allow the central star to move freely in response to growing perturbations. The simulations using each code are compared to discover differences due to error in the methods used. For this problem, the strengths of the codes overlap only in a limited fashion, but similarities exist in their predictions, including spiral arm pattern speeds and morphological features. Our results represent limiting cases (i.e., systems evolved isothermally) rather than true physical systems. Disks become active from the inner regions outward. From the earliest times, their evolution is a strongly dynamic process rather than a smooth progression toward eventual nonlinear behavior. Processes that occur in both the extreme inner and outer radial regions affect the growth of instabilities over the entire disk. Effects important for the global morphology of the system can originate at quite small distances from the star. We calculate approximate growth rates for the spiral patterns; the one-armed (m = 1) spiral arm is not the fastest growing pattern of most disks. Nonetheless, it plays a significant role because of factors that can excite it more quickly than other patterns. A marked change in the character of spiral structure occurs with varying disk mass. Low-mass disks form filamentary spiral structures with many arms while high-mass disks form grand design spiral structures with few arms. In our SPH simulations, disks with initial minimum Q = 1.5 or

  11. Protostellar collapse of rotating cloud cores. Covering the complete first accretion period of the stellar core

    NASA Astrophysics Data System (ADS)

    Schönke, J.; Tscharnuter, W. M.

    2011-02-01

    Aims: We investigate the influence of turbulent viscosity on the collapse of a rotating molecular cloud core with axial symmetry, in particular, on the first and second collapse phase, as well as the evolution of the second (protostellar) core during its first accretion period. By using extensive numerical calculations, we monitor the intricate interactions between the newly formed protostar and the surrounding accretion disk (the first core) in which the star is embedded. Methods: We use a grid-based radiation-hydrodynamics code with a spatial grid designed to meet the high resolution required to study the second core. The radiative transfer is treated in the flux-limited diffusion approximation. A slightly supercritical Bonnor-Ebert sphere of 1 Msun and uniform rotation according to a fixed centrifugal radius of 100 AU serves as the initial condition without exception. In a parameter study, we vary the β-viscosity driving the angular momentum transport. Results: Without viscosity (β=0), a highly flattened accretion disk forms that fragments into several "cold" rings. For β = 10-4, a single "warm" ring forms that undergoes collapse due to hydrogen dissociation. For β = 10-3, ring formation is suppressed completely. The second collapse proceeds on the local thermal timescale, which is in contrast to the current view of a generally dynamical second collapse. During the first accretion period of the second core, the first core heats up globally and, as a consequence, a nearly spherical outflow occurs, destroying the structure of the former accretion disk completely. Finally, for β = 10-2, we see the classical dynamical second collapse and a shorter but more rapid accretion phase. The impact on the surrounding accretion disk is even more pronounced. We follow the resulting massive outflow up to several kyr after the second collapse, where the central parts (R < 0.7 AU) are now cut out and replaced with an appropriate inner boundary condition. Matter is found to

  12. Experimental verification of a non-axisymmetric displacement field predicted by finite element analysis of a composite disk subjected to an axisymmetric loading

    NASA Astrophysics Data System (ADS)

    Oliver, Stanley T.

    A finite element analysis of a circular quasi-isotropic composite disk that was clamped around its boundary and subjected to a uniform pressure was developed by the author prior to initiating this work. The analysis was performed as part of a program being developed to measure the permeability of materials. While investigating the results of the proposed configuration, it was determined that the allowable stress for the material to be tested would be exceeded close to the boundary. However, it was suggested that a pre-stress could be incorporated by tapering the clamped boundary so that, after the pressure was applied, the combined stress would fall within the material's allowable limit. Interestingly, the finite element analysis of the pre-stressed disk predicted an unexpected out-of-plane displacement that did not follow the principal material directions despite the fact that the disk was quasi-isotropic and loaded uniformly around the boundary. Further investigation revealed that this was due to variations in the terms contained in the bending stiffness matrix as a function of the angle measured relative to the principal material directions. The permeability test was subsequently adopted as part of the proposed test program and no failures have occurred to date near the boundary. However, since the initial finite element model developed for the pre-stressed condition does not accurately reflect the clamped condition currently found in practice, a more sophisticated model is needed. This dissertation focuses on the actual pre-stressed condition. After a thorough investigation is made of the bending stiffness matrix, two improved finite element models are developed using different analysis codes. The first model was developed in Nastran, mainly because the author used this package in his initial work. But the procedure to develop a nonlinear contact model for Nastran in Patran was found to be cumbersome. So, Abaqus was used because the associated pre

  13. Accretion and magnetic field morphology around Class 0 stage protostellar discs

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Banerjee, R.; Pudritz, R. E.; Klessen, R. S.

    2015-01-01

    We analyse simulations of turbulent, magnetized molecular cloud cores focusing on the formation of Class 0 stage protostellar discs and the physical conditions in their surroundings. We show that for a wide range of initial conditions Keplerian discs are formed in the Class 0 stage already. In particular, we show that even subsonic turbulent motions reduce the magnetic braking efficiency sufficiently in order to allow rotationally supported discs to form. We therefore suggest that already during the Class 0 stage the fraction of Keplerian discs is significantly higher than 50 per cent, consistent with recent observational trends but significantly higher than predictions based on simulations with misaligned magnetic fields, demonstrating the importance of turbulent motions for the formation of Keplerian discs. We show that the accretion of mass and angular momentum in the surroundings of protostellar discs occurs in a highly anisotropic manner, by means of a few narrow accretion channels. The magnetic field structure in the vicinity of the discs is highly disordered, revealing field reversals up to distances of 1000 au. These findings demonstrate that as soon as even mild turbulent motions are included, the classical disc formation scenario of a coherently rotating environment and a well-ordered magnetic field breaks down. Hence, it is highly questionable to assess the magnetic braking efficiency based on non-turbulent collapse simulation. We strongly suggest that, in addition to the global magnetic field properties, the small-scale accretion flow and detailed magnetic field structure have to be considered in order to assess the likelihood of Keplerian discs to be present.

  14. THE MASS DISTRIBUTION OF STARLESS AND PROTOSTELLAR CORES IN GOULD BELT CLOUDS

    SciTech Connect

    Sadavoy, Sarah I.; Di Francesco, James; Bontemps, Sylvain; Megeath, S. Thomas; Allgaier, Erin; Rebull, Luisa M.; Carey, Sean; McCabe, Caer-Eve; Noriega-Crespo, Alberto; Padgett, Deborah; Gutermuth, Robert; Hora, Joe; Huard, Tracy; Muzerolle, James; Terebey, Susan

    2010-02-20

    Using data from the SCUBA Legacy Catalogue (850 {mu}m) and Spitzer Space Telescope (3.6-70 {mu}m), we explore dense cores in the Ophiuchus, Taurus, Perseus, Serpens, and Orion molecular clouds. We develop a new method to discriminate submillimeter cores found by Submillimeter Common-User Bolometer Array (SCUBA) as starless or protostellar, using point source photometry from Spitzer wide field surveys. First, we identify infrared sources with red colors associated with embedded young stellar objects (YSOs). Second, we compare the positions of these YSO candidates to our submillimeter cores. With these identifications, we construct new, self-consistent starless and protostellar core mass functions (CMFs) for the five clouds. We find best-fit slopes to the high-mass end of the CMFs of -1.26 +- 0.20, -1.22 +- 0.06, -0.95 +- 0.20, and -1.67 +- 0.72 for Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are each consistent with the -1.35 power-law slope of the Salpeter initial mass function at higher masses, but suggest some differences. We examine a variety of trends between these CMF shapes and their parent cloud properties, potentially finding a correlation between the high-mass slope and core temperature. We also find a trend between core mass and effective size, but we are very limited by sensitivity. We make similar comparisons between core mass and size with visual extinction (for A{sub V} >= 3) and find no obvious trends. We also predict the numbers and mass distributions of cores that future surveys with SCUBA-2 may detect in each of these clouds.

  15. Magnetic disk

    NASA Technical Reports Server (NTRS)

    Mallinson, John C.

    1991-01-01

    Magnetic disk recording was invented in 1953 and has undergone intensive development ever since. As a result of this 38 years of development, the cost per byte and the areal density has halved and doubled, respectively every 2 to 2 1/2 years. Today, the cost per byte is lower than 10(exp -6) dollars per byte and area densities exceed 100 x 10(exp 6) bits per square inch. The recent achievements in magnetic disk recording will first be surveyed briefly. Then the principal areas of current technical development will be outlined. Finally, some comments will be made about the future of magnetic disk recording.

  16. The Anatomy of the Young Protostellar Outflow HH 211

    NASA Astrophysics Data System (ADS)

    Tappe, A.; Forbrich, J.; Martín, S.; Yuan, Y.; Lada, C. J.

    2012-05-01

    We present Spitzer Space Telescope 5-36 μm mapping observations toward the southeastern lobe of the young protostellar outflow HH 211. The southeastern terminal shock of the outflow shows a rich mid-infrared spectrum including molecular emission lines from OH, H2O, HCO+, CO2, H2, and HD. The spectrum also shows a rising infrared continuum toward 5 μm, which we interpret as unresolved emission lines from highly excited rotational levels of the CO v = 1-0 fundamental band. This interpretation is supported by a strong excess flux observed in the Spitzer/IRAC 4-5 μm channel 2 image compared to the other IRAC channels. The extremely high critical densities of the CO v = 1-0 ro-vibrational lines and a comparison to H2 and CO excitation models suggest jet densities larger than 106 cm-3 in the terminal shock. We also observed the southeastern terminal outflow shock with the Submillimeter Array and detected pure rotational emission from CO 2-1, HCO+ 3-2, and HCN 3-2. The rotationally excited CO traces the collimated outflow backbone as well as the terminal shock. HCN traces individual dense knots along the outflow and in the terminal shock, whereas HCO+ solely appears in the terminal shock. The unique combination of our mid-infrared and submillimeter observations with previously published near-infrared observations allow us to study the interaction of one of the youngest known protostellar outflows with its surrounding molecular cloud. Our results help us to understand the nature of some of the so-called green fuzzies (Extended Green Objects), and elucidate the physical conditions that cause high OH excitation and affect the chemical OH/H2O balance in protostellar outflows and young stellar objects. In an appendix to this paper, we summarize our Spitzer follow-up survey of protostellar outflow shocks to find further examples of highly excited OH occurring together with H2O and H2.

  17. THE ANATOMY OF THE YOUNG PROTOSTELLAR OUTFLOW HH 211

    SciTech Connect

    Tappe, A.; Forbrich, J.; Lada, C. J.; Martin, S.; Yuan, Y.

    2012-05-20

    We present Spitzer Space Telescope 5-36 {mu}m mapping observations toward the southeastern lobe of the young protostellar outflow HH 211. The southeastern terminal shock of the outflow shows a rich mid-infrared spectrum including molecular emission lines from OH, H{sub 2}O, HCO{sup +}, CO{sub 2}, H{sub 2}, and HD. The spectrum also shows a rising infrared continuum toward 5 {mu}m, which we interpret as unresolved emission lines from highly excited rotational levels of the CO v = 1-0 fundamental band. This interpretation is supported by a strong excess flux observed in the Spitzer/IRAC 4-5 {mu}m channel 2 image compared to the other IRAC channels. The extremely high critical densities of the CO v = 1-0 ro-vibrational lines and a comparison to H{sub 2} and CO excitation models suggest jet densities larger than 10{sup 6} cm{sup -3} in the terminal shock. We also observed the southeastern terminal outflow shock with the Submillimeter Array and detected pure rotational emission from CO 2-1, HCO{sup +} 3-2, and HCN 3-2. The rotationally excited CO traces the collimated outflow backbone as well as the terminal shock. HCN traces individual dense knots along the outflow and in the terminal shock, whereas HCO{sup +} solely appears in the terminal shock. The unique combination of our mid-infrared and submillimeter observations with previously published near-infrared observations allow us to study the interaction of one of the youngest known protostellar outflows with its surrounding molecular cloud. Our results help us to understand the nature of some of the so-called green fuzzies (Extended Green Objects), and elucidate the physical conditions that cause high OH excitation and affect the chemical OH/H{sub 2}O balance in protostellar outflows and young stellar objects. In an appendix to this paper, we summarize our Spitzer follow-up survey of protostellar outflow shocks to find further examples of highly excited OH occurring together with H{sub 2}O and H{sub 2}.

  18. ACCRETION OUTBURSTS IN CIRCUMPLANETARY DISKS

    SciTech Connect

    Lubow, S. H.; Martin, R. G.

    2012-04-20

    We describe a model for the long-term evolution of a circumplanetary disk that is fed mass from a circumstellar disk and contains regions of low turbulence (dead zones). We show that such disks can be subject to accretion-driven outbursts, analogous to outbursts previously modeled in the context of circumstellar disks to explain FU Ori phenomena. Circumplanetary disks around a proto-Jupiter can undergo outbursts for infall accretion rates onto the disks in the range M-dot{sub infall} approx. 10{sup -9} to 10{sup -7} M{sub Sun} yr{sup -1}, typical of accretion rates in the T Tauri phase. During outbursts, the accretion rate and disk luminosity increases by several orders of magnitude. Most of the planet mass growth during planetary gas accretion may occur via disk outbursts involving gas that is considerably hotter than predicted by steady state models. For low infall accretion rates M-dot{sub infall} {approx}< 10{sup -10} M{sub sun} yr{sup -1} that occur in late stages of disk accretion, disk outbursts are unlikely to occur, even if dead zones are present. Such conditions are favorable for the formation of icy satellites.

  19. Molecular ions in the protostellar shock L1157-B1

    NASA Astrophysics Data System (ADS)

    Podio, L.; Lefloch, B.; Ceccarelli, C.; Codella, C.; Bachiller, R.

    2014-05-01

    Aims: We perform a complete census of molecular ions with an abundance greater than ~10-10 in the protostellar shock L1157-B1. This allows us to study the ionisation structure and chemistry of the shock. Methods: An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30 m and Herschel/HIFI as part of the CHESS and ASAI large programmes allows searching for molecular ions emission. Then, by means of a radiative transfer code in the large velocity gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem. Results: We detect emission from HCO+, H13CO+, N2H+, HCS+, and for the first time in a shock, from HOCO+ and SO+. The bulk of the emission peaks at blue-shifted velocity, ~0.5-3 km s -1 with respect to systemic, has a width of ~3-7 km s-1 and is associated with the outflow cavities (Tkin ~ 20-70 K, nH2 ~ 105 cm-3). A high-velocity component up to -40 km s-1, associated with the primary jet, is detected in the HCO+ 1-0 line. Observed HCO+ and N2H+ abundances (XHCO+ ~ 0.7-3 × 10-8, XN2H+ ~ 0.4-8 × 10-9) agree with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionisation rate ζ = 3 × 10-16 s-1. HOCO+, SO+, and HCS+ observed abundances (XHOCO+ ~ 10-9, XSO+ ~ 8 × 10-10, XHCS+ ~ 3-7 × 10-10), instead, are 1-2 orders of magnitude larger than predicted in the cloud; on the other hand, they are strongly enhanced on timescales shorter than the shock age (~2000 years) if CO2, S or H2S, and OCS are sputtered off the dust grains in the shock. Conclusions: The performed analysis indicates that HCO+ and N2H+ are a fossil record of pre-shock gas in the outflow cavity, whilst HOCO+, SO+, and HCS+ are effective shock tracers that can be used to infer the amount of CO2 and sulphur

  20. PROTOSTELLAR OUTFLOW HEATING IN A GROWING MASSIVE PROTOCLUSTER

    SciTech Connect

    Wang Ke; Wu Yuefang; Zhang Huawei; Zhang Qizhou; Li Huabai

    2012-02-15

    The dense molecular clump P1 in the infrared dark cloud complex G28.34+0.06 harbors a massive protostellar cluster at its extreme youth. Our previous Submillimeter Array observations revealed several jet-like CO outflows emanating from the protostars, indicative of intense accretion and potential interaction with ambient natal materials. Here, we present the Expanded Very Large Array spectral line observations toward P1 in the NH{sub 3} (J,K) = (1,1), (2,2), (3,3) lines, as well as H{sub 2}O and class I CH{sub 3}OH masers. Multiple NH{sub 3} transitions reveal the heated gas widely spread in the 1 pc clump. The temperature distribution is highly structured; the heated gas is offset from the protostars, and morphologically matches the outflows very well. Hot spots of spatially compact, spectrally broad NH{sub 3} (3,3) emission features are also found coincident with the outflows. A weak NH{sub 3} (3,3) maser is discovered at the interface between an outflow jet and the ambient gas. These findings suggest that protostellar heating may not be effective in suppressing fragmentation during the formation of massive cores.

  1. Radiation magnetohydrodynamic simulations of protostellar collapse: Low-metallicity environments

    SciTech Connect

    Tomida, Kengo

    2014-05-10

    Among many physical processes involved in star formation, radiation transfer is one of the key processes because it dominantly controls the thermodynamics. Because metallicities control opacities, they are one of the important environmental parameters that affect star formation processes. In this work, I investigate protostellar collapse in solar-metallicity and low-metallicity (Z = 0.1 Z {sub ☉}) environments using three-dimensional radiation hydrodynamic and magnetohydrodynamic simulations. Because radiation cooling in high-density gas is more effective in low-metallicity environments, first cores are colder and have lower entropies. As a result, first cores are smaller, less massive, and have shorter lifetimes in low-metallicity clouds. Therefore, first cores would be less likely to be found in low-metallicity star forming clouds. This also implies that first cores tend to be more gravitationally unstable and susceptible to fragmentation. The evolution and structure of protostellar cores formed after the second collapse weakly depend on metallicities in the spherical and magnetized models, despite the large difference in the metallicities. Because this is due to the change of the heat capacity by dissociation and ionization of hydrogen, it is a general consequence of the second collapse as long as the effects of radiation cooling are not very large during the second collapse. On the other hand, the effects of different metallicities are more significant in the rotating models without magnetic fields, because they evolve slower than other models and therefore are more affected by radiation cooling.

  2. Ice Chemistry in Interstellar Dense Molecular Clouds, Protostellar Disks, and Comets

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.

    2015-01-01

    Despite the low temperatures (T less than 20K), low pressures, and low molecular densities found in much of the cosmos, considerable chemistry is expected to occur in many astronomical environments. Much of this chemistry happens in icy grain mantles on dust grains and is driven by ionizing radiation. This ionizing radiation breaks chemical bonds of molecules in the ices and creates a host of ions and radicals that can react at the ambient temperature or when the parent ice is subsequently warmed. Experiments that similar these conditions have demonstrated a rich chemistry associated with these environments that leads to a wide variety of organic products. Many of these products are of considerable interest to astrobiology. For example, the irradiation of simple ices has been shown to abiotically produce amino acids, nucleobases, quinones, and amphiphiles, all compounds that play key roles in modern biochemistry. This suggests extraterrestrial chemistry could have played a role in the origin of life on Earth and, by extension, do so on planets in other stellar systems.

  3. EARTH, MOON, SUN, AND CV ACCRETION DISKS

    SciTech Connect

    Montgomery, M. M.

    2009-11-01

    Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if

  4. Earth, Moon, Sun, and CV Accretion Disks

    NASA Astrophysics Data System (ADS)

    Montgomery, M. M.

    2009-11-01

    Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if

  5. A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys

    NASA Astrophysics Data System (ADS)

    Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

    2011-06-01

    Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

  6. Near-infrared multiwavelength imaging polarimetry of the low-mass proto-stellar object HL Tauri

    NASA Astrophysics Data System (ADS)

    Murakawa, K.; Oya, S.; Pyo, T.-S.; Ishii, M.

    2008-12-01

    We present the {JHK}-band high-resolution polarimetric images of the low-mass proto-stellar object HL Tau using the adaptive optics-equipped CIAO instrument on the Subaru telescope. Our polarization images show a butterfly-shaped polarization disk with an ˜0.9 arcsec × 3.0 arcsec extension. In the nebula, where polarization vectors are centro-symmetrically aligned, the polarization is as high as PJ ˜30%, P_H˜42%, and PK ˜55%. On the other hand, low polarizations of P<3% in the J, H, and K bands and a low color excess ratio of EJ-H/EH-K=1.1 compared to the standard cloud value of 1.75 are detected towards the central star. We estimated the upper limit of the grain sizes a_max to be 0.4 μm in the nebula and ⪆0.7 μm in the line of sight towards the central star. Our high-resolution polarimetric data, which spatially resolves the polarization disk, provides us with important information about grain growth in the region close to the central star.

  7. Predicting water quality by relating Secchi-Disk transparency and chlorophyll a measurements to satellite imagery for Michigan Inland Lakes, August 2002

    USGS Publications Warehouse

    Fuller, L.M.; Aichele, S.S.; Minnerick, R.J.

    2004-01-01

    Inland lakes are an important economic and environmental resource for Michigan. The U.S. Geological Survey and the Michigan Department of Environmental Quality have been cooperatively monitoring the quality of selected lakes in Michigan through the Lake Water Quality Assessment program. Through this program, approximately 730 of Michigan's 11,000 inland lakes will be monitored once during this 15-year study. Targeted lakes will be sampled during spring turnover and again in late summer to characterize water quality. Because more extensive and more frequent sampling is not economically feasible in the Lake Water Quality Assessment program, the U.S. Geological Survey and Michigan Department of Environmental Quality investigate the use of satellite imagery as a means of estimating water quality in unsampled lakes. Satellite imagery has been successfully used in Minnesota, Wisconsin, and elsewhere to compute the trophic state of inland lakes from predicted secchi-disk measurements. Previous attempts of this kind in Michigan resulted in a poorer fit between observed and predicted data than was found for Minnesota or Wisconsin. This study tested whether estimates could be improved by using atmospherically corrected satellite imagery, whether a more appropriate regression model could be obtained for Michigan, and whether chlorophyll a concentrations could be reliably predicted from satellite imagery in order to compute trophic state of inland lakes. Although the atmospheric-correction did not significantly improve estimates of lake-water quality, a new regression equation was identified that consistently yielded better results than an equation obtained from the literature. A stepwise regression was used to determine an equation that accurately predicts chlorophyll a concentrations in northern Lower Michigan.

  8. Tracing characteristic perturbations resulting from Planet-Disk and Binary-Disk interaction in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Ruge, Jan Philipp; Wolf, Sebastian; Uribe, Ana; Demidova, Tatiana; Klahr, Hubert; Grinin, Vladimir

    2013-07-01

    The perturbation by an additional, gravitating component (planet, binary star) within a protoplanetary disk induces characteristic large-scale structures in the disk density profile. We investigate the observability of these perturbations. On the basis of a large number of (M)HD and SPH simulations, we calculate synthetic scattered and polarized light images as well as thermal re-emission maps of these models and predict the observational results for different instruments from the optical to the (sub)mm wavelength range with a special focus on ALMA. In the first study (A) (Ruge et al., 2013a,c) we investigate the observability of the planet-disk interaction for different star-disk-planet configurations. We predict that ALMA is able to observe planet-induced gaps around stars of various types and for a large range of disk masses. Besides this, we find that ALMA can trace small, local perturbations indicating zonal flows in the disk. The detectability of gaps in scattered light is limited to a range of total disk masses between 1e-4 M_sun and 1e-6 M_sun. Gap detections in both wavelength ranges are feasible for M_disk ~ 1e-4 M_sun. In our second study (B) (Ruge et al. 2013b) we investigate the observability of perturbations in young circumbinary disks for several orbital elements of the binary system. We find that ALMA will allow one to trace characteristic AU-sized spiral arm features in disks in face-on orientation and also to detect binary-induced perturbations in the edge-on brightness profiles. We find that the technique of differential polarimetry offers the potential for significantly clearer detections of these disk structures than imaging in scattered light alone.

  9. Long-Wavelength Excesses of FU Orionis Objects: Flared Outer Disks or Infalling Envelopes?

    NASA Astrophysics Data System (ADS)

    Zhu, Zhaohuan; Hartmann, Lee; Calvet, Nuria; Hernandez, Jesus; Tannirkulam, Ajay-Kumar; D'Alessio, Paola

    2008-09-01

    The mid- to far-infrared emission of the outbursting FU Orionis objects has been attributed either to a flared outer disk or to an infalling envelope. We revisit this issue using detailed radiative transfer calculations to model the recent, high signal-to-noise ratio data from the IRS instrument on the Spitzer Space Telescope. In the case of FU Ori, we find that a physically plausible flared disk irradiated by the central accretion disk matches the observations. Building on our previous work, our accretion disk model with outer disk irradiation by the inner disk reproduces the spectral energy distribution between ~4000 Å and ~40 μm. Our model is consistent with near-infrared interferometry, but there are some inconsistencies with mid-infrared interferometric results. Including the outer disk allows us to refine our estimate of the outer radius of the outbursting, high mass accretion rate disk in FU Ori as ~0.5 AU, which is a crucial parameter in assessing theories of the FU Orionis phenomenon. We are able to place an upper limit on the mass infall rate of any remnant envelope infall rate to ~7 × 10-7 M⊙ yr -1 assuming a centrifugal radius of 200 AU. The FUor BBW 76 is also well modeled by a 0.6 AU inner disk and a flared outer disk. However, V1515 Cyg requires an envelope with an outflow cavity to adequately reproduce the IRS spectrum. In contrast with the suggestion by Green et al., we do not require a flattened envelope to match the observations; the inferred cavity shape is qualitatively consistent with typical protostellar envelopes. This variety of dusty structures suggests that the FU Orionis phase can be present at either early or late stages of protostellar evolution.

  10. Stem thrust prediction model for Westinghouse wedge gate valves with linkage type stem-to-disk connection

    SciTech Connect

    Wang, J.K.; Sharma, V.; Kalsi, M.S.

    1996-12-01

    The Electric Power Research Institute (EPRI) conducted a comprehensive research program with the objective of providing nuclear utilities with analytical methods to predict motor operated valve (MOV) performance under design basis conditions. This paper describes the stem thrust calculation model developed for evaluating the performance of one such valve, the Westinghouse flexible wedge gate valve. These procedures account for the unique functional characteristics of this valve design. In addition, model results are compared to available flow loop and in situ test data as a basis for evaluating the performance of the valve model.

  11. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  12. Accretion outbursts in self-gravitating protoplanetary disks

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Nelson, Richard P. E-mail: lhartm@umich.edu E-mail: r.p.nelson@qmul.ac.uk

    2014-11-01

    We improve on our previous treatments of the long-term evolution of protostellar disks by explicitly solving disk self-gravity in two dimensions. The current model is an extension of the one-dimensional layered accretion disk model of Bae et al. We find that gravitational instability (GI)-induced spiral density waves heat disks via compressional heating (i.e., PdV work), and can trigger accretion outbursts by activating the magnetorotational instability (MRI) in the magnetically inert disk dead zone. The GI-induced spiral waves propagate well inside of the gravitationally unstable region before they trigger outbursts at R ≲ 1 AU where GI cannot be sustained. This long-range propagation of waves cannot be reproduced with the previously used local α treatments for GI. In our standard model where zero dead-zone residual viscosity (α{sub rd}) is assumed, the GI-induced stress measured at the onset of outbursts is locally as large as 0.01 in terms of the generic α parameter. However, as suggested in our previous one-dimensional calculations, we confirm that the presence of a small but finite α{sub rd} triggers thermally driven bursts of accretion instead of the GI + MRI-driven outbursts that are observed when α{sub rd} = 0. The inclusion of non-zero residual viscosity in the dead zone decreases the importance of GI soon after mass feeding from the envelope cloud ceases. During the infall phase while the central protostar is still embedded, our models stay in a 'quiescent' accretion phase with M-dot {sub acc}∼10{sup −8}--10{sup −7} M{sub ⊙} yr{sup −1} over 60% of the time and spend less than 15% of the infall phase in accretion outbursts. While our models indicate that episodic mass accretion during protostellar evolution can qualitatively help explain the low accretion luminosities seen in most low-mass protostars, detailed tests of the mechanism will require model calculations for a range of protostellar masses with some constraint on the initial core

  13. Predicting Water Quality by Relating Secchi-Disk Transparency and Chlorophyll a Measurements to Landsat Satellite Imagery for Michigan Inland Lakes, 2001-2006

    USGS Publications Warehouse

    Fuller, L.M.; Minnerick, R.J.

    2007-01-01

    The State of Michigan has more than 11,000 inland lakes; approximately 3,500 of these lakes are greater than 25 acres. The USGS, in cooperation with the Michigan Department of Environmental Quality (MDEQ), has been monitoring the quality of inland lakes in Michigan through the Lake Water Quality Assessment monitoring program. Approximately 100 inland lakes will be sampled per year from 2001 to 2015. Volunteers coordinated by MDEQ started sampling lakes in 1974, and continue to sample to date approximately 250 inland lakes each year through the Cooperative Lakes Monitoring Program (CLMP), Michigan's volunteer lakes monitoring program. Despite this sampling effort, it is still impossible to physically collect the necessary water-quality measurements for all 3,500 Michigan inland lakes. Therefore, a technique was used by USGS, modeled after Olmanson and others (2001), in cooperation with MDEQ that uses satellite remote sensing to predict water quality in unsampled inland lakes greater than 25 acres. Water-quality characteristics that are associated with water clarity can be predicted for Michigan inland lakes by relating sampled measurements of secchi-disk transparency (SDT) and chlorophyll a concentrations (Chl-a), to satellite imagery. The trophic state index (TSI) which is an indicator of the biological productivity can be calculated based on SDT measurements, Chl-a concentrations, and total phosphorus (TP) concentrations measured near the lake's surface. Through this process, unsampled inland lakes within the fourteen Landsat satellite scenes encompassing Michigan can be translated into estimated TSI from either predicted SDT or Chl-a (fig. 1).

  14. Observations of Protostellar Outflow Feedback in Clustered Star Formation

    NASA Astrophysics Data System (ADS)

    Nakamura, F.

    2016-05-01

    We discuss the role of protostellar outflow feedback in clustered star formation using the observational data of recent molecular outflow surveys toward nearby cluster-forming clumps. We found that for almost all clumps, the outflow momentum injection rate is significantly larger than the turbulence dissipation rate. Therefore, the outflow feedback is likely to maintain supersonic turbulence in the clumps. For less massive clumps such as B59, L1551, and L1641N, the outflow kinetic energy is comparable to the clump gravitational energy. In such clumps, the outflow feedback probably affects significantly the clump dynamics. On the other hand, for clumps with masses larger than about 200 M⊙, the outflow kinetic energy is significantly smaller than the clump gravitational energy. Since the majority of stars form in such clumps, we conclude that outflow feedback cannot destroy the whole parent clump. These characteristics of the outflow feedback support the scenario of slow star formation.

  15. DIVERSE PROTOSTELLAR EVOLUTIONARY STATES IN THE YOUNG CLUSTER AFGL961

    SciTech Connect

    Williams, Jonathan P.; Mann, Rita K.; Beaumont, Christopher N.; Swift, Jonathan J.; Adams, Joseph D.; Hora, Joe; Kassis, Marc; Lada, Elizabeth A.; Roman-Zuniga, Carlos G.

    2009-07-10

    We present arcsecond resolution mid-infrared and millimeter observations of the center of the young stellar cluster AFGL961 in the Rosette molecular cloud. Within 0.2 pc of each other, we find an early B star embedded in a dense core, a neighboring star of similar luminosity with no millimeter counterpart, a protostar that has cleared out a cavity in the circumcluster envelope, and two massive, dense cores with no infrared counterparts. An outflow emanates from one of these cores, indicating a deeply embedded protostar, but the other is starless, bound, and appears to be collapsing. The diversity of states implies either that protostellar evolution is faster in clusters than in isolation or that clusters form via quasi-static rather than dynamic collapse. The existence of a pre-stellar core at the cluster center shows that some star formation continues after and in close proximity to massive, ionizing stars.

  16. Debris Disks and Hidden Planets

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2008-01-01

    When a planet orbits inside a debris disk like the disk around Vega or Beta Pictoris, the planet may be invisible, but the patterns it creates in the disk may give it away. Observing and decoding these patterns may be the only way we can detect exo-Neptunes orbiting more than 20 AU from their stars, and the only way we can spot planets in systems undergoing the late stages of planet formation. Fortunately, every few months, a new image of a debris disk appears with curious structures begging for explanation. I'll describe some new ideas in the theory of these planet-disk interactions and provide a buyers guide to the latest models (and the planets they predict).

  17. The formation of primordial binaries in globular clusters by star-disk interactions

    NASA Technical Reports Server (NTRS)

    Murray, Stephen D.; Clarke, C. J.; Pringle, J. E.

    1991-01-01

    The formation of primordial binaries in globular clusters is examined using simple numerical models. Clusters of protostars collapse until their velocity dispersion rises sufficiently to reverse the infall and the cluster reaches equilibrium. During the collapse, interactions between stars and protostellar disks lead to stellar capture. It is found that binary fraction of a few percent typically result. Binary formation is terminated when the velocity dispersion rises to a point at which most encounters result in disk destruction rather than capture. As a result, much gas is returned to the cluster ISM, limiting the star formation efficiency to a value significantly below 100 percent.

  18. CARMA OBSERVATIONS OF PROTOSTELLAR OUTFLOWS IN NGC 1333

    SciTech Connect

    Plunkett, Adele L.; Arce, Hector G.; Corder, Stuartt A.; Mardones, Diego; Sargent, Anneila I.; Schnee, Scott L.

    2013-09-01

    We present observations of outflows in the star-forming region NGC 1333 using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA). We combined the {sup 12}CO and {sup 13}CO (1-0) CARMA mosaics with data from the 14 m Five College Radio Astronomy Observatory to probe the central, most dense, and active region of this protostellar cluster at scales from 5'' to 7' (or 1000 AU to 0.5 pc at a distance of 235 pc). We map and identify {sup 12}CO outflows, and along with {sup 13}CO data we estimate their mass, momentum, and energy. Within the 7' Multiplication-Sign 7' map, the 5'' resolution allows for a detailed study of morphology and kinematics of outflows and outflow candidates, some of which were previously confused with other outflow emission in the region. In total, we identify 22 outflow lobes, as well as 9 dense circumstellar envelopes marked by continuum emission, of which 6 drive outflows. We calculate a total outflow mass, momentum, and energy within the mapped region of 6 M{sub Sun }, 19 M{sub Sun} km s{sup -1}, and 7 Multiplication-Sign 10{sup 44} erg, respectively. Within this same region, we compare outflow kinematics with turbulence and gravitational energy, and we suggest that outflows are likely important agents for the maintenance of turbulence in this region. In the earliest stages of star formation, outflows do not yet contribute enough energy to totally disrupt the clustered region where most star formation is happening, but have the potential to do so as the protostellar sources evolve. Our results can be used to constrain outflow properties, such as outflow strength, in numerical simulations of outflow-driven turbulence in clusters.

  19. THE IMPORTANCE OF DISK STRUCTURE IN STALLING TYPE I MIGRATION

    SciTech Connect

    Kretke, Katherine A.; Lin, D. N. C.

    2012-08-10

    As planets form they tidally interact with their natal disks. Though the tidal perturbation induced by Earth and super-Earth mass planets is generally too weak to significantly modify the structure of the disk, the interaction is potentially strong enough to cause the planets to undergo rapid type I migration. This physical process may provide a source of short-period super-Earths, though it may also pose a challenge to the emergence and retention of cores on long-period orbits with sufficient mass to evolve into gas giants. Previous numerical simulations have shown that the type I migration rate sensitively depends upon the circumstellar disk's properties, particularly the temperature and surface density gradients. Here, we derive these structure parameters for (1) a self-consistent viscous-disk model based on a constant {alpha} prescription, (2) an irradiated disk model that takes into account heating due to the absorption of stellar photons, and (3) a layered accretion disk model with variable {alpha} parameter. We show that in the inner viscously heated regions of typical protostellar disks, the horseshoe and corotation torques of super-Earths can exceed their differential Lindblad torque and cause them to undergo outward migration. However, the temperature profile due to passive stellar irradiation causes type I migration to be inward throughout much of the disk. For disks in which there is outward migration, we show that location and the mass range of the 'planet traps' depend on some uncertain assumptions adopted for these disk models. Competing physical effects may lead to dispersion in super-Earths' mass-period distribution.

  20. Comparison of Multi Disk Exponential Gas Distribution vs. Single Disk

    NASA Astrophysics Data System (ADS)

    Rao, Erica; O'Brien, James

    2013-04-01

    In fitting galactic rotation curves to data, most standard theories make use of a single exponential disk approximation of the gas distribution to account for the HI synthesis data observed at various radio telescope facilities. We take a sample of surface brightness profiles from The HI Nearby Galaxy Survey (THINGS), and apply both single disk exponentials and Multi-Disk exponentials, and use these various models to see how the modelling procedure changes the Newtonian prediction of the mass of the galaxy. Since the missing mass problem has not been fully explained in large spiral galaxies, different modelling procedures could account for some of the missing matter.

  1. Disk Dispersal Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    We first review the evidence pertaining to the lifetimes of planet-forming disks of gas and dust around young stars and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation caused by the heating of the disk surface by ultraviolet radiation. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks, and this talk focuses on the evaporation caused by the presence of a nearby, luminous star rather than the central star itself. We also focus on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We find a possible explanation for the differences between Neptune and Jupiter, and make a prediction concerning recent searches for giant planets in large clusters. We discuss recent models of the infrared spectra from gaseous disks around young stars.

  2. Disk filter

    DOEpatents

    Bergman, Werner

    1986-01-01

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  3. Disk filter

    DOEpatents

    Bergman, W.

    1985-01-09

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  4. ACCRETION DISK TEMPERATURES OF QSOs: CONSTRAINTS FROM THE EMISSION LINES

    SciTech Connect

    Bonning, E. W.; Shields, G. A.; Stevens, A. C.; Salviander, S. E-mail: shields@astro.as.utexas.edu E-mail: triples@astro.as.utexas.edu

    2013-06-10

    We compare QSO emission-line spectra to predictions based on theoretical ionizing continua of accretion disks. The observed line intensities do not show the expected trend of higher ionization with theoretical accretion disk temperature as predicted from the black hole mass and accretion rate. Consistent with earlier studies, this suggests that the inner disk does not reach temperatures as high as expected from standard disk theory. Modified radial temperature profiles, taking account of winds or advection in the inner disk, achieve better agreement with observation. The emission lines of radio-detected and radio-undetected sources show different trends as a function of the theoretically predicted disk temperature.

  5. SMA OBSERVATIONS OF CLASS 0 PROTOSTARS: A HIGH ANGULAR RESOLUTION SURVEY OF PROTOSTELLAR BINARY SYSTEMS

    SciTech Connect

    Chen Xuepeng; Arce, Hector G.; Dunham, Michael M.; Zhang Qizhou; Bourke, Tyler L.; Launhardt, Ralf; Henning, Thomas; Jorgensen, Jes K.; Lee, Chin-Fei; Foster, Jonathan B.; Pineda, Jaime E. E-mail: xuepeng.chen@yale.edu

    2013-05-10

    We present high angular resolution 1.3 mm and 850 {mu}m dust continuum data obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby clouds (distance < 500 pc), which represents so far the largest survey toward protostellar binary/multiple systems. The median angular resolution in the survey is 2.''5, while the median linear resolution is approximately 600 AU. Compact dust continuum emission is observed from all sources in the sample. Twenty-one sources in the sample show signatures of binarity/multiplicity, with separations ranging from 50 AU to 5000 AU. The numbers of singles, binaries, triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The derived multiplicity frequency (MF) and companion star fraction (CSF) for Class 0 protostars are 0.64 {+-} 0.08 and 0.91 {+-} 0.05, respectively, with no correction for completeness. The derived MF and CSF in this survey are approximately two times higher than the values found in the binary surveys toward Class I young stellar objects, and approximately three (for MF) and four (for CSF) times larger than the values found among main-sequence stars, with a similar range of separations. Furthermore, the observed fraction of high-order multiple systems to binary systems in Class 0 protostars (0.50 {+-} 0.09) is also larger than the fractions found in Class I young stellar objects (0.31 {+-} 0.07) and main-sequence stars ({<=}0.2). These results suggest that binary properties evolve as protostars evolve, as predicted by numerical simulations. The distribution of separations for Class 0 protostellar binary/multiple systems shows a general trend in which CSF increases with decreasing companion separation. We find that 67% {+-} 8% of the protobinary systems have circumstellar mass ratios below 0.5, implying that unequal-mass systems are preferred in the process of binary star formation. We suggest an empirical sequential fragmentation picture for binary star formation, based on this work and

  6. Chondrules and the Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Hewins, R. H.; Jones, Rhian; Scott, Ed

    2011-03-01

    Part I. Introduction: 1. Chondrules and the protoplanetary disk: An overview R. H. Hewins; Part. II. Chonrules, Ca-Al-Rich Inclusions and Protoplanetary Disks: 2. Astronomical observations of phenomena in protostellar disks L. Hartmann; 3. Overview of models of the solar nebula: potential chondrule-forming environments P. Cassen; 4. Large scale processes in the solar nebula A. P. Boss; 5. Turbulence, chondrules and planetisimals J. N. Cuzzi, A. R. Dobrovolskis and R. C. Hogan; 6. Chondrule formation: energetics and length scales J. T. Wasson; 7. Unresolved issues in the formation of chondrules and chondrites J. A. Wood; 8. Thermal processing in the solar nebula: constraints from refractory inclusions A. M. Davis and G. J. MacPherson; 9. Formation times of chondrules and Ca-Al-Rich inclusions: constraints from short-lived radionuclides T. D. Swindle, A. M. Davis, C. M. Hohenberg, G. J. MacPherson and L. E. Nyquist; 10. Formation of chondrules and chondrites in the protoplanetary nebula E. R. D. Scott, S. G. Love and A. N. Krot; Part III. Chondrule precursors and multiple melting: 11. Origin of refractory precursor components of chondrules K. Misawa and N. Nakamura; 12. Mass-independent isotopic effects in chondrites: the role of chemical processes M. H. Thiemens; 13. Agglomeratic chondrules: implications for the nature of chondrule precursors and formation by incomplete melting M. K. Weisberg and M. Prinz; 14. Constraints on chondrule precursors from experimental Data H. C. Connolly Jr. and R. H. Hewins; 15. Nature of matrix in unequilibrated chondrites and its possible relationship to chondrules A. J. Brearly; 16. Constraints on chondrite agglomeration from fine-grained chondrule Rims K. Metzler and A. Bischoff; 17. Relict grains in chondrules: evidence for chondrule recycling R. H. Jones; 18. Multiple heating of chondrules A. E. Rubin and A. N. Krot; 19. Microchondrule-bearing chondrule rims: constraints on chondrule formation A. N. Krot and A. E. Rubin; Part IV

  7. Spatially Resolved Magnetic Field Structure in the Disk of a T Tauri Star

    NASA Astrophysics Data System (ADS)

    Stephens, Ian; Looney, Leslie; Kwon, Woojin; Fernandez Lopez, Manuel; Hughes, A. Meredith; Mundy, Lee G.; Crutcher, Richard; Li, Zhi-Yun; Rao, Ramprasad; Segura-Cox, Dominique

    2015-01-01

    The formation of disks around protostars is thought to be regulated through magnetic fields, and theoretical models suggest that the fractional polarization should be approximately 2-3%. However, resolved observations of disks in T Tauri stars have remained undetected and are constrained to have fractional polarization of less than 1%. With CARMA observations of HL Tau, we recently found the first detection of a resolved magnetic field about a T Tauri Star. While poloidal field components appear to be completely absent for HL Tau at the 80 AU scale, a purely toroidal field does not fit the observations well either, suggesting the system is more complicated than theoretically expected. Incoming ALMA observations of both HL Tau and Class 0 protostellar disks will help disentangle the true magnetic field morphology in the disks of protostars.

  8. Photoevaporating Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2004-01-01

    Ultraviolet radiation from the central star or from a nearby massive star heats the surfaces of protoplanetary disks and causes the outer, less gravitationally bound part of the disks, to photoevaporate into interstellar space. Photoevaporation is likely the most important dispersal mechanism for the outer regions of disks. We focus in this talk on disks around low-mass stars like the Sun rather than high-mass stars, which we have treated previously. Stars often form in clusters and the ultraviolet flux from the most luminous star in the cluster can have a dramatic effect on the disk orbiting a nearby low-mass star. We apply our theoretical models to the evaporating protoplanetary disks (or "proplyds") in the Trapezium cluster in Orion, to the formation of gas giant planets like Jupiter around Sun-like stars in the Galaxy, and to the formation of Kuiper belts around low mass stars. We discuss recent models of the effects of the radiation from the central low mass star including both the predicted infrared spectra from the heated disks as well as preliminary results on the photoevaporation rates.

  9. Dark-disk universe.

    PubMed

    Fan, JiJi; Katz, Andrey; Randall, Lisa; Reece, Matthew

    2013-05-24

    We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally supported disk, much as baryons do. We call this proposed new dark matter component double-disk dark matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas. PMID:23745856

  10. AN ADAPTIVE OPTICS SURVEY FOR CLOSE PROTOSTELLAR BINARIES

    SciTech Connect

    Connelley, Michael S.; Reipurth, Bo; Tokunaga, Alan T.

    2009-11-15

    In order to test the hypothesis that Class I protostellar binary stars are a product of ejections during the dynamical decay of nonhierarchical multiple systems, we combined the results of new adaptive optics (AO) observations of Class I protostars with our previously published AO data to investigate whether Class I protostars with a widely separated companion (r > 200 AU) are more likely to also have a close companion (r < 200 AU). In total, we observed 47 embedded young stellar objects (YSOs) with either the Subaru natural guide star AO system or the Keck laser guide star AO system. We found that targets with a widely separated companion within 5000 AU are not more likely to have a close companion. However, targets with another YSO within a projected separation of 25,000 AU are much more likely to have a close companion. Most importantly, every target with a close companion has another YSO within a projected separation of 25,000 AU. We came to the same conclusions after considering a restricted sample of targets within 500 pc and close companions wider than 50 AU to minimize incompleteness effects. The Orion star-forming region was found to have an excess of both close binaries and YSOs within 25,000 AU compared to other star-forming regions. We interpret these observations as strong evidence that many close Class I binary stars form via ejections and that many of the ejected stars become unbound during the Class I phase.

  11. A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS

    SciTech Connect

    Bans, Alissa; Koenigl, Arieh E-mail: akonigl@uchicago.edu

    2012-10-20

    Protostellar systems, ranging from low-luminosity classical T Tauri and Herbig Ae stars to high-luminosity Herbig Be stars, exhibit a near-infrared (NIR) excess in their spectra that is dominated by a bump in the monochromatic luminosity with a peak near 3 {mu}m. The bump can be approximated by a thermal emission component of temperature {approx}1500 K that is of the order of the sublimation temperature of interstellar dust grains. In the currently popular 'puffed-up rim' scenario, the bump represents stellar radiation that propagates through the optically thin inner region of the surrounding accretion disk and is absorbed and reemitted by the dust that resides just beyond the dust sublimation radius r {sub sub}. However, this model cannot account for the strongest bumps measured in these sources, and it predicts a pronounced secondary bounce in the interferometric visibility curve that is not observed. In this paper we present an alternative interpretation, which attributes the bump to reemission of stellar radiation by dust that is uplifted from the disk by a centrifugally driven wind. Winds of this type are a leading candidate for the origin of the strong outflows associated with protostars, and there is observational evidence for disk winds originating on scales {approx}r {sub sub}. Using a newly constructed Monte Carlo radiative transfer code and focusing on low-luminosity sources, we show that this model can account for the NIR excess emission even in bright Herbig Ae stars such as AB Auriga and MWC 275, and that it successfully reproduces the basic features of the visibilities measured in these protostars. We argue that a robust dusty outflow in these sources could be self-limiting-through shielding of the stellar FUV photons-to a relatively narrow launching region between r {sub sub} and {approx}2 r {sub sub}. We also suggest that the NIR and scattered-light variability exhibited by a source like MWC 275 can be attributed in this picture to the uplifting of

  12. HERSCHEL FINDS EVIDENCE FOR STELLAR WIND PARTICLES IN A PROTOSTELLAR ENVELOPE: IS THIS WHAT HAPPENED TO THE YOUNG SUN?

    SciTech Connect

    Ceccarelli, C.; López-Sepulcre, A.; Dominik, C.; Kama, M.; Padovani, M.; Caux, E.; Caselli, P.

    2014-07-20

    There is evidence that the young Sun emitted a high flux of energetic (≥10 MeV) particles. The collisions of these particles with the material at the inner edge of the Protosolar Nebula disk induced spallation reactions that formed short-lived radionuclei, like {sup 10}Be, whose trace is now visible in some meteorites. However, it is poorly known exactly when this happened, and whether and how it affected the solar system. Here, we present indirect evidence for an ejection of energetic particles in the young protostar, OMC-2 FIR 4, similar to that experienced by the young solar system. In this case, the energetic particles collide with the material in the protostellar envelope, enhancing the abundance of two molecular ions, HCO{sup +} and N{sub 2}H{sup +}, whose presence is detected via Herschel observations. The flux of energetic particles at a distance of 1 AU from the emitting source, estimated from the measured abundance ratio of HCO{sup +} and N{sub 2}H{sup +}, can easily account for the irradiation required by meteoritic observations. These new observations demonstrate that the ejection of ≥10 MeV particles is a phenomenon occurring very early in the life of a protostar, before the disappearance of the envelope from which the future star accretes. The whole envelope is affected by the event, which sets constraints on the magnetic field geometry in the source and opens up the possibility that the spallation reactions are not limited to the inner edge of the Protosolar Nebula disk.

  13. Evaluation of Oxacillin and Cefoxitin Disk and MIC Breakpoints for Prediction of Methicillin Resistance in Human and Veterinary Isolates of Staphylococcus intermedius Group.

    PubMed

    Wu, M T; Burnham, C-A D; Westblade, L F; Dien Bard, J; Lawhon, S D; Wallace, M A; Stanley, T; Burd, E; Hindler, J; Humphries, R M

    2016-03-01

    Staphylococcus pseudintermedius is a coagulase-positive species that colonizes the nares and anal mucosa of healthy dogs and cats. Human infections with S. pseudintermedius range in severity from bite wounds and rhinosinusitis to endocarditis; historically, these infections were thought to be uncommon, but new laboratory methods suggest that their true incidence is underreported. Oxacillin and cefoxitin disk and MIC tests were evaluated for the detection of mecA- or mecC-mediated methicillin resistance in 115 human and animal isolates of the Staphylococcus intermedius group (SIG), including 111 Staphylococcus pseudintermediusand 4 Staphylococcus delphini isolates, 37 of which were mecA positive. The disk and MIC breakpoints evaluated included the Clinical and Laboratory Standards Institute (CLSI) M100-S25 Staphylococcus aureus/Staphylococcus lugdunensis oxacillin MIC breakpoints and cefoxitin disk and MIC breakpoints, the CLSI M100-S25 coagulase-negative Staphylococcus (CoNS) oxacillin MIC breakpoint and cefoxitin disk breakpoint, the CLSI VET01-S2 S. pseudintermedius oxacillin MIC and disk breakpoints, and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) S. pseudintermedius cefoxitin disk breakpoint. The oxacillin results interpreted by the VET01-S2 (disk and MIC) and M100-S25 CoNS (MIC) breakpoints agreed with the results of mecA/mecC PCR for all isolates, with the exception of one false-resistant result (1.3% of mecA/mecC PCR-negative isolates). In contrast, cefoxitin tests performed poorly, ranging from 3 to 89% false susceptibility (very major errors) and 0 to 48% false resistance (major errors). BD Phoenix, bioMérieux Vitek 2, and Beckman Coulter MicroScan commercial automated susceptibility test panel oxacillin MIC results were also evaluated and demonstrated >95% categorical agreement with mecA/mecC PCR results if interpreted by using the M100-S25 CoNS breakpoint. The Alere penicillin-binding protein 2a test accurately detected all

  14. Evaluation of Oxacillin and Cefoxitin Disk and MIC Breakpoints for Prediction of Methicillin Resistance in Human and Veterinary Isolates of Staphylococcus intermedius Group

    PubMed Central

    Wu, M. T.; Westblade, L. F.; Dien Bard, J.; Wallace, M. A.; Stanley, T.; Burd, E.; Hindler, J.

    2015-01-01

    Staphylococcus pseudintermedius is a coagulase-positive species that colonizes the nares and anal mucosa of healthy dogs and cats. Human infections with S. pseudintermedius range in severity from bite wounds and rhinosinusitis to endocarditis; historically, these infections were thought to be uncommon, but new laboratory methods suggest that their true incidence is underreported. Oxacillin and cefoxitin disk and MIC tests were evaluated for the detection of mecA- or mecC-mediated methicillin resistance in 115 human and animal isolates of the Staphylococcus intermedius group (SIG), including 111 Staphylococcus pseudintermediusand 4 Staphylococcus delphini isolates, 37 of which were mecA positive. The disk and MIC breakpoints evaluated included the Clinical and Laboratory Standards Institute (CLSI) M100-S25 Staphylococcus aureus/Staphylococcus lugdunensis oxacillin MIC breakpoints and cefoxitin disk and MIC breakpoints, the CLSI M100-S25 coagulase-negative Staphylococcus (CoNS) oxacillin MIC breakpoint and cefoxitin disk breakpoint, the CLSI VET01-S2 S. pseudintermedius oxacillin MIC and disk breakpoints, and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) S. pseudintermedius cefoxitin disk breakpoint. The oxacillin results interpreted by the VET01-S2 (disk and MIC) and M100-S25 CoNS (MIC) breakpoints agreed with the results of mecA/mecC PCR for all isolates, with the exception of one false-resistant result (1.3% of mecA/mecC PCR-negative isolates). In contrast, cefoxitin tests performed poorly, ranging from 3 to 89% false susceptibility (very major errors) and 0 to 48% false resistance (major errors). BD Phoenix, bioMérieux Vitek 2, and Beckman Coulter MicroScan commercial automated susceptibility test panel oxacillin MIC results were also evaluated and demonstrated >95% categorical agreement with mecA/mecC PCR results if interpreted by using the M100-S25 CoNS breakpoint. The Alere penicillin-binding protein 2a test accurately detected all

  15. Evidence for Infalling Gas of Low Angular Momentum toward the L1551 NE Keplerian Circumbinary Disk

    NASA Astrophysics Data System (ADS)

    Takakuwa, Shigehisa; Saito, Masao; Lim, Jeremy; Saigo, Kazuya

    2013-10-01

    We report follow-up C18O(3-2) line observations of the Class I binary protostellar system L1551 NE with the Submillimeter Array in its compact and subcompact configurations. Our previous observations at a higher angular resolution in the extended configuration revealed a circumbinary disk exhibiting Keplerian motion. The combined data, with more extensive spatial coverage (~140-2000 AU), verify the presence of a Keplerian circumbinary disk and reveal for the first time a distinct low-velocity (lsim ± 0.5 km s-1 from the systemic velocity) component that displays a velocity gradient along the minor axis of the circumbinary disk. Our simple model that reproduces the main features seen in the position-velocity diagrams comprises a circumbinary disk exhibiting Keplerian motion out to a radius of ~300 AU, beyond which the gas exhibits pure infall at a constant velocity of ~0.6 km s-1. This velocity is significantly smaller than the expected free-fall velocity of ~2.2 km s-1 onto the L1551 NE protostellar mass of ~0.8 M ⊙ at ~300 AU, suggesting that the infalling gas is decelerated as it moves into regions of high gas pressure in the circumbinary disk. The discontinuity in angular momenta between the outer infalling gas and the inner Keplerian circumbinary disk implies an abrupt transition in the effectiveness at which magnetic braking is able to transfer angular momentum outward, a result perhaps of the different plasma β values and the ionization fractions between the outer and inner regions of the circumbinary disk.

  16. Proper motions of embedded protostellar jets in Serpens

    NASA Astrophysics Data System (ADS)

    Djupvik, A. A.; Liimets, T.; Zinnecker, H.; Barzdis, A.; Rastorgueva-Foi, E. A.; Petersen, L. R.

    2016-03-01

    Aims: We determine the proper motion of protostellar jets around Class 0 and Class I sources in an active star forming region in Serpens. Methods: Multi-epoch deep images in the 2.122 μm line of molecular hydrogen, v = 1-0 S(1), obtained with the near-infrared instrument NOTCam on a timescale of 10 years, are used to determine the proper motion of knots and jets. K-band spectroscopy of the brighter knots is used to supply radial velocities, estimate extinction, excitation temperature, and H2 column densities towards these knots. Results: We measure the proper motion of 31 knots on different timescales (2, 4, 6, 8, and 10 years). The typical tangential velocity is around 50 km s-1 for the 10-year baseline, but for shorter timescales, a maximum tangential velocity up to 300 km s-1 is found for a few knots. Based on morphology, velocity information, and the locations of known protostars, we argue for the existence of at least three partly overlapping and deeply embedded flows, one Class 0 flow and two Class I flows. The multi-epoch proper motion results indicate time-variable velocities of the knots, for the first time directly measured for a Class 0 jet. We find in general higher velocities for the Class 0 jet than for the two Class I jets. While the bolometric luminosites of the three driving sources are about equal, the derived mass flow rate Ṁout is two orders of magnitude higher in the Class 0 flow than in the two Class I flows. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

  17. CCS Observations of the Protostellar Envelope of B335

    NASA Technical Reports Server (NTRS)

    Velusamy, T.; Kuiper, T. B. H.; Langer, W. D.

    1995-01-01

    Knowledge of the density, velocity and chemical profiles around protostars is of fundamental importance for testing dynamical models of protostar evolution and understanding the nature of the material falling onto circumstellar disks. Presented are single dish and interferometric spectral line observations of CCS towards the core of B335, a classic example of a young, low mass stellar object.

  18. Lyman edges - Signatures of accretion disks

    NASA Astrophysics Data System (ADS)

    Kinney, A. L.

    1992-05-01

    Accretion disks are thought to provide the ultraviolet emission seen in the big blue bump of quasars. However, observations of the UV spectra of quasars do not show the additional signatures predicted by the accretion disk models. This paper will concentrate on just one of those signatures - the Lyman edge. Two studies are briefly discussed which explore the Lyman edge region of both high and low redshift quasars (Antonucci, Kinney, and Ford 1989 and Koratkar, Kinney, and Bohlin 1992). Both studies find that Lyman edges are not present in quasar spectra as frequently as predicted by the models or at the strength predicted by accretion disk models.

  19. ALMA observations of a misaligned binary protoplanetary disk system in Orion

    SciTech Connect

    Williams, Jonathan P.; Mann, Rita K.; Francesco, James Di; Johnstone, Doug; Matthews, Brenda; Andrews, Sean M.; Ricci, Luca; Hughes, A. Meredith; Bally, John

    2014-12-01

    We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a wide binary system in Orion, with projected separation 440 AU, in which we detect submillimeter emission from the protoplanetary disks around each star. Both disks appear moderately massive and have strong line emission in CO 3-2, HCO{sup +} 4-3, and HCN 3-2. In addition, CS 7-6 is detected in one disk. The line-to-continuum ratios are similar for the two disks in each of the lines. From the resolved velocity gradients across each disk, we constrain the masses of the central stars, and show consistency with optical-infrared spectroscopy, both indicative of a high mass ratio ∼9. The small difference between the systemic velocities indicates that the binary orbital plane is close to face-on. The angle between the projected disk rotation axes is very high, ∼72°, showing that the system did not form from a single massive disk or a rigidly rotating cloud core. This finding, which adds to related evidence from disk geometries in other systems, protostellar outflows, stellar rotation, and similar recent ALMA results, demonstrates that turbulence or dynamical interactions act on small scales well below that of molecular cores during the early stages of star formation.

  20. Workshop on Physics of Accretion Disks Around Compact and Young Stars

    NASA Technical Reports Server (NTRS)

    Liang, E (Editor); Stepinski, T. F. (Editor)

    1995-01-01

    The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster presentations, and a list of workshop participants. Accretion disks are believed to surround many stars. Some of these disks form around compact stars, such as white dwarfs, neutron stars, or black holes that are members of binary systems and reveal themselves as a power source, especially in the x-ray and gamma regions of the spectrum. On the other hand, protostellar disks are believed to be accretion disks associated with young, pre-main-sequence stars and manifest themselves mostly in infrared and radio observations. These disks are considered to be a natural outcome of the star formation process. The focus of this workshop included theory and observations relevant to accretion disks around compact objects and newly forming stars, with the primary purpose of bringing the two communities together for intellectual cross-fertilization. The nature of the workshop was exploratory, to see how much interaction is possible between distinct communities and to better realize the local potential in this subject. A critical workshop activity was identification and documentation of key issues that are of mutual interest to both communities.

  1. Modeling Layered Accretion and the Magnetorotational Instability in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Lesniak, Michael V., III

    2012-05-01

    Understanding the temperature structure of protoplanetary disks (PPDs) is paramount to modeling disk evolution and future planet formation. PPDs around T Tauri stars have two primary heating sources, protostellar irradiation, which depends on the flaring of the disk, and accretional heating as viscous coupling between annuli dissipate energy. I have written a "1.5-D" radiative transfer code to calculate disk temperatures assuming hydrostatic and radiative equilibrium. The model solves for the temperature at all locations simultaneously using Rybicki's method, converges rapidly at high optical depth, and retains full frequency dependence. The likely cause of accretional heating in PPDs is the magnetorotational instability (MRI), which acts where gas ionization is sufficiently high for gas to couple to the magnetic field. This will occur in surface layers of the disk, leaving the interior portions of the disk inactive ("dead zone"). I calculate temperatures in PPDs undergoing such "layered accretion." Since the accretional heating is concentrated far from the midplane, temperatures in the disk's interior are lower than in PPDs modeled with vertically uniform accretion. The method is used to study for the first time disks evolving via the magnetorotational instability, which operates primarily in surface layers. I find that temperatures in layered accretion disks do not significantly differ from those of "passive disks," where no accretional heating exists. Emergent spectra are insensitive to active layer thickness, making it difficult to observationally identify disks undergoing layered vs. uniform accretion. I also calculate the ionization chemistry in PPDs, using an ionization network including multiple charge states of dust grains. Combined with a criterion for the onset of the MRI, I calculate where the MRI can be initiated and the extent of dead zones in PPDs. After accounting for feedback between temperature and active layer thickness, I find the surface

  2. Observing Planet Formation in Young Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Jang-Condell, Hannah; Kuchner, M. J.; Debes, J. H.

    2009-01-01

    Identification and observation of where and when gaps form in protoplanetary disks is vital for learning about the process of planet formation. We will present simulations of radiative transfer in gas-rich protoplanetary disks with embedded planets that predict and model observable signatures of planet formation. Depending on the mass of the planet, the perturbation may be a local dimple or an annular gap. We will demonstate that these features can already be detected in some nearby gas-rich disks. The appearance of disks with embedded planets varies with wavelength as it ranges from optical through infrared to radio because of optical depth effects. Shorter wavelengths reveal superficial surface features of disks, while longer wavelengths probe deeper in the disk. Confirmation of a planet-induced gap in a disk requires multi-wavelength observations. Imaging of the predicted features of planet formation in disks requires very high spatial resolution, and is currently most feasible in the optical and radio. However, data in the infrared is crucial for constraining the models. Deep gaps created by very massive planets may be detectable in SEDs. Confirmation of a planet-induced gap in a disk requires multi-wavelength observations.

  3. The near-infrared excitation of the HH 211 protostellar outflow

    NASA Astrophysics Data System (ADS)

    O'Connell, B.; Smith, M. D.; Froebrich, D.; Davis, C. J.; Eislöffel, J.

    2005-02-01

    The protostellar outflow HH 211 is of considerable interest since it is extremely young and highly collimated. Here, we explore the outflow through imaging and spectroscopy in the near-infrared to determine if there are further diagnostic signatures of youth. We confirm the detection of a near-infrared continuum of unknown origin. We propose that it is emitted by the driving millimeter source, escapes the core through tunnels, and illuminates features aligning the outflow. Narrow-band flux measurements of these features contain an unusually large amount of continuum emission. [FeII] emission at 1.644 μm has been detected and is restricted to isolated condensations. However, the characteristics of vibrational excitation of molecular hydrogen resemble those of older molecular outflows. We attempt to model the ordered structure of the western outflow as a series of shocks, finding that bow shocks with J-type dissociative apices and C-type flanks are consistent. Moreover, essentially the same conditions are predicted for all three bows except for a systematic reduction in speed and density with distance from the driving source. We find increased K-band extinctions in the bright regions as high as 2.9 mag and suggest that the bow shocks become visible where the outflow impacts on dense clumps of cloud material. We propose that the outflow is carved out by episodes of pulsating jets. The jets, driven by central explosive events, are responsible for excavating a central tunnel through which radiation temporarily penetrates. Based in part on observations collected at the German-Spanish Astronomical Center, Calar Alto, operated jointly by Max-Planck Institut für Astronomie and Instituto de Astrofísica de Andalucía (CSIC). Observations were also obtained with The United Kingdom Infrared Telescope, which is operated by the Joint Astronomy Centre on behalf of the UK Particle Physics and Astronomy Research Council.

  4. Molecules in protostellar shocks: the CHESS view on L1157-B1

    NASA Astrophysics Data System (ADS)

    Lefloch, B.; Benedettini, M.; Cabrit, S.; Caux, E.; Ceccarelli, C.; Cernicharo, J.; Codella, C.; Giannini, T.; Nisini, B.; Parise, B.; Salez, M.; Vasta, M.; Viti, S.; CHESS Team

    2011-05-01

    Shocks driven by protostellar outflows play an important role in the chemical evolution of molecular gas through temperature and density changes resulting from the activation of endothermic reactions, ionization, and dust destruction. These various processes lead to molecular abundance enhancements up to several orders of magnitude, as reported for various molecular species in "chemically active" outflows, whose archetype is the outflow of the low mass Class 0 protostar L1157. The opening up of the full far-infrared and submillimeter wavelength domains by Herschel has deep impact in the field by providing access to key spectral diagnostics of shock dynamics and chemistry at very high spectral resolution with HIFI and permitting to map the brightest features with the PACS and SPIRE multi-pixel spectrometers. We present the results of the spectral survey of the shock region L1157-B1 from 3.75mm up to 60 μm, carried out with the instruments onboard Herschel and with the IRAM 30m telescope, as part of the CHESS key project. The unprecedented sensitivity of these instruments brings new insight both on the molecular content and the physical conditions of this long studied region, thanks to the detection of hydrides (H2O, NH, HCl, ..) and of the high-excitation lines of heavy molecules (CO, CS, HCO+, HCN, ..). We will discuss the molecular content and the properties of the warm chemically enriched gas (abundance, excitation conditions). We will show how multi-transition analysis of the line profiles allows to constrain the shock physical conditions, the formation scenarios of various molecular species, including water, in relation with the predictions of MHD shock models.

  5. Evolution of Massive Protostars Via Disk Accretion

    NASA Astrophysics Data System (ADS)

    Hosokawa, Takashi; Yorke, Harold W.; Omukai, Kazuyuki

    2010-09-01

    Mass accretion onto (proto-)stars at high accretion rates \\dot{M}_* > 10^{-4} M_{⊙} yr^{-1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk accretion. We consider a limiting case of "cold" disk accretion, whereby most of the stellar photosphere can radiate freely with negligible backwarming from the accretion flow, and the accreting material settles onto the star with the same specific entropy as the photosphere. We compare our results to the calculated evolution via spherically symmetric accretion, the opposite limit, whereby the material accreting onto the star contains the entropy produced in the accretion shock front. We examine how different accretion geometries affect the evolution of massive protostars. For cold disk accretion at 10-3 M sun yr-1, the radius of a protostar is initially small, R *sime a few R sun. After several solar masses have accreted, the protostar begins to bloat up and for M * ~= 10 M sun the stellar radius attains its maximum of 30-400 R sun. The large radius ~100 R sun is also a feature of spherically symmetric accretion at the same accreted mass and accretion rate. Hence, expansion to a large radius is a robust feature of accreting massive protostars. At later times, the protostar eventually begins to contract and reaches the zero-age main sequence (ZAMS) for M * ~= 30 M sun, independent of the accretion geometry. For accretion rates exceeding several 10-3 M sun yr-1, the protostar never contracts to the ZAMS. The very large radius of several hundreds R sun results in the low effective temperature and low UV luminosity of the protostar. Such bloated protostars could well explain the existence of bright high-mass protostellar objects, which lack detectable H II regions.

  6. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  7. Identification of Gas Phase PAHs in Absorption Towards Protostellar Sources

    NASA Technical Reports Server (NTRS)

    Bregman, Jesse D.; Temi, Pasquale; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The infrared emission bands (also known as the UIR bands.) have recently been observed in absorption at 3.25 micrometers in the ices surrounding a few proto-stellar objects at 11.2 micrometers in MonR2, and at 6.2 micrometers towards two sources near the galactic center. The UIR bands have been observed in emission for many years, but identifying these bands has proven to be both difficult and contentious as no one has yet found a single material that provides a good match to the features. However, most investigators agree that some form of carbon-based material with aromatic bonds is the most likely candidate, and many arguments favor free molecules (polycyclic aromatic hydrocarbons, PAHs) as the carriers of at least the narrow emission bands. Since the emission arises not from a single molecule but from a family of molecules, identifying which PAHs are contributing to the infrared emission bands is difficult. The identification is further complicated by the fact that the emission at short wavelengths is dominated by small molecules while at long wavelengths it is dominated by large molecules. Thus, for example, the emission at 3.3 micrometers is from a different mix of molecules than those which produce the 11.2 micrometer band. To complicate matters further, the molecular mix includes both neutral and ionic species. In absorption, the same mixture of molecules contributes at all wavelengths and the molecules should be neutral, potentially simplifying comparisons with lab data. Also, absorption strengths measured in the lab are directly applicable to interstellar absorption bands without the need to model an emission spectrum of an unknown mixture of ionized and neutral PAHs. In this paper we show that a mixture of argon matrix isolated PAH molecules can reproduce the 3.25 micrometers absorption band seen in the ISO SWS spectra of four embedded Infrared sources, S140 IRS1, AFGL 2591, Elias 29, and AFGL 989. In section 2 we describe the ISO SWS data analysis and

  8. Evolutionary status of the pre-protostellar core L1498

    NASA Technical Reports Server (NTRS)

    Kuiper, T. B.; Langer, W. D.; Velusamy, T.; Levin, S. M. (Principal Investigator)

    1996-01-01

    L1498 is a classic example of a dense cold pre-protostellar core. To study the evolutionary status, the structure, dynamics, and chemical properties of this core we have obtained high spatial and high spectral resolution observations of molecules tracing densities of 10(3)-10(5) cm-3. We observed CCS, NH3, C3H2, and HC7N with NASA's DSN 70 m antennas. We also present large-scale maps of C18O and 13CO observed with the AT&T 7 m antenna. For the high spatial resolution maps of selected regions within the core we used the VLA for CCS at 22 GHz, and the Owens Valley Radio Observatory (OVRO) MMA for CCS at 94 GHz and CS (2-1). The 22 GHz CCS emission marks a high-density [n(H2) > 10(4) cm -3] core, which is elongated with a major axis along the SE-NW direction. NH3 and C3H2 emissions are located inside the boundary of the CCS emission. C18O emission traces a lower density gas extending beyond the CCS boundary. Along the major axis of the dense core, CCS, NH3 and C3H2 emission show evidence of limb brightening. The observations are consistent with a chemically differentiated onion-shell structure for the L1498 core, with NH3 in the inner and CCS in the outer parts of the core. The high angular resolution (9"-12") spectral line maps obtained by combining NASA Goldstone 70 m and VLA data resolve the CCS 22 GHz emission in the southeast and northwest boundaries into arclike enhancements, supporting the picture that CCS emission originates in a shell outside the NH3 emitting region. Interferometric maps of CCS at 94 GHz and CS at 98 GHz show that their emitting regions contain several small-scale dense condensations. We suggest that the differences between the CCS, CS, C3H2, and NH3 emission are caused by a time-dependent effect as the core evolves slowly. We interpret the chemical and physical properties of L1498 in terms of a quasi-static (or slowly contracting) dense core in which the outer envelope is still growing. The growth rate of the core is determined by the

  9. Evolutionary status of the pre-protostellar core L1498.

    PubMed

    Kuiper, T B; Langer, W D; Velusamy, T

    1996-09-10

    L1498 is a classic example of a dense cold pre-protostellar core. To study the evolutionary status, the structure, dynamics, and chemical properties of this core we have obtained high spatial and high spectral resolution observations of molecules tracing densities of 10(3)-10(5) cm-3. We observed CCS, NH3, C3H2, and HC7N with NASA's DSN 70 m antennas. We also present large-scale maps of C18O and 13CO observed with the AT&T 7 m antenna. For the high spatial resolution maps of selected regions within the core we used the VLA for CCS at 22 GHz, and the Owens Valley Radio Observatory (OVRO) MMA for CCS at 94 GHz and CS (2-1). The 22 GHz CCS emission marks a high-density [n(H2) > 10(4) cm -3] core, which is elongated with a major axis along the SE-NW direction. NH3 and C3H2 emissions are located inside the boundary of the CCS emission. C18O emission traces a lower density gas extending beyond the CCS boundary. Along the major axis of the dense core, CCS, NH3 and C3H2 emission show evidence of limb brightening. The observations are consistent with a chemically differentiated onion-shell structure for the L1498 core, with NH3 in the inner and CCS in the outer parts of the core. The high angular resolution (9"-12") spectral line maps obtained by combining NASA Goldstone 70 m and VLA data resolve the CCS 22 GHz emission in the southeast and northwest boundaries into arclike enhancements, supporting the picture that CCS emission originates in a shell outside the NH3 emitting region. Interferometric maps of CCS at 94 GHz and CS at 98 GHz show that their emitting regions contain several small-scale dense condensations. We suggest that the differences between the CCS, CS, C3H2, and NH3 emission are caused by a time-dependent effect as the core evolves slowly. We interpret the chemical and physical properties of L1498 in terms of a quasi-static (or slowly contracting) dense core in which the outer envelope is still growing. The growth rate of the core is determined by the

  10. Hydrodynamic Simulations of Jet- and Wind-driven Protostellar Outflows

    NASA Astrophysics Data System (ADS)

    Lee, Chin-Fei; Stone, James M.; Ostriker, Eve C.; Mundy, Lee G.

    2001-08-01

    We present two-dimensional hydrodynamic simulations of both jet- and wind-driven models for protostellar outflows in order to make detailed comparisons to the kinematics of observed molecular outflows. The simulations are performed with the ZEUS-2D hydrodynamic code using a simplified equation of state, simplified cooling and no external heating, and no self-gravity. In simulations of steady jets, swept-up ambient gas forms a thin shell that can be identified as a molecular outflow. We find a simple ballistic bow shock model is able to reproduce the structure and transverse velocity of the shell. Position-velocity (PV) diagrams for the shell cut along the outflow axis show a convex spur structure with the highest velocity at the bow tip and low-velocity red and blue components at any viewing angle. The power-law index of the mass-velocity (MV) relationship ranges from 1.5 to 3.5, depending strongly on the inclination. If the jet is time-variable, the PV diagrams show multiple convex spur structures, and the power-law index becomes smaller than the steady jet simulation. In simulations of isothermal steady wide-angle winds, swept-up ambient gas forms a thin shell that at early stages has a similar shape to the shell in the jet-driven model; it becomes broader at later times. We find the structure and kinematics of the shell is well described by a momentum-conserving model similar to that of Shu et al. (1991). In contrast to the results from jet simulations, the PV diagrams for the shell cut along the outflow axis show a lobe structure tilted with source inclination, with components that are primarily either red or blue unless the inclination is nearly in the plane of sky. The power-law index of the MV relationship ranges from 1.3 to 1.8. If the wind is time-variable, the PV diagrams also show multiple structures, and the power-law index becomes smaller than the steady wind simulation. Comparing the different simulations with observations, we find that some outflows

  11. Young stars and protostellar cores near NGC 2023

    NASA Astrophysics Data System (ADS)

    Mookerjea, B.; Sandell, G.; Jarrett, T. H.; McMullin, J. P.

    2009-12-01

    Context: We investigate the young (proto)stellar population in NGC 2023 and the L 1630 molecular cloud bordering the h ii region IC 434, using Spitzer IRAC and MIPS archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA observations of one of the Class 0 protostars, NGC 2023 MM 1. Aims: We study the distribution of gas, dust and young stars in this region to see where stars are forming, whether the expansion of the h ii region has triggered star formation, and whether dense cold cores have already formed stars. Methods: We have performed photometry of all IRAC and MIPS images, and used color-color diagrams to identify and classify all young stars seen within a 22'×26' field along the boundary between IC 434 and L 1630. For some stars, which have sufficient optical, IR, and/or sub-millimeter data we have also used the online SED fitting tool for a large 2D archive of axisymmetric radiative transfer models to perform more detailed modeling of the observed SEDs. We identify 5 sub-millimeter cores in our 850 and 450 μm SCUBA images, two of which have embedded class 0 or I protostars. Observations with BIMA are used to refine the position and characteristics of the Class 0 source NGC 2023 MM 1. These observations show that it is embedded in a very cold cloud core, which is strongly enhanced in NH2D. Results: We find that HD 37903 is the most massive member of a cluster with 20-30 PMS stars. We also find smaller groups of PMS stars formed from the Horsehead nebula and another elephant trunk structure to the north of the Horsehead. Star formation is also occurring in the dark lane seen in IRAC images and in the sub-millimeter continuum. We refine the spectral classification of HD 37903 to B2 Ve. We find that the star has a clear IR excess, and therefore it is a young Herbig Be star. Conclusions: Our study shows that the expansion of the IC 434 h ii region has triggered star formation in some of the dense elephant trunk structures and compressed gas

  12. MODELING PLANETARY SYSTEM FORMATION WITH N-BODY SIMULATIONS: ROLE OF GAS DISK AND STATISTICS COMPARED TO OBSERVATIONS

    SciTech Connect

    Liu Huigen; Zhou Jilin; Wang Su

    2011-05-10

    During the late stage of planet formation, when Mars-sized cores appear, interactions among planetary cores can excite their orbital eccentricities, accelerate their merging, and thus sculpt their final orbital architecture. This study contributes to the final assembling of planetary systems with N-body simulations, including the type I or II migration of planets and gas accretion of massive cores in a viscous disk. Statistics on the final distributions of planetary masses, semimajor axes, and eccentricities are derived and are comparable to those of the observed systems. Our simulations predict some new orbital signatures of planetary systems around solar mass stars: 36% of the surviving planets are giant planets (>10 M{sub +}). Most of the massive giant planets (>30 M{sub +}) are located at 1-10 AU. Terrestrial planets are distributed more or less evenly at <1-2 AU. Planets in inner orbits may accumulate at the inner edges of either the protostellar disk (3-5 days) or its magnetorotational instability dead zone (30-50 days). There is a planet desert in the mass-eccentricity diagram, i.e., a lack of planets with masses 0.005-0.08M{sub J} in highly eccentric orbits (e > 0.3-0.4). The average eccentricity ({approx}0.15) of the giant planets (>10 M{sub +}) is greater than that ({approx}0.05) of the terrestrial planets (<10 M{sub +}). A planetary system with more planets tends to have smaller planet masses and orbital eccentricities on average.

  13. HiRes deconvolved Spitzer images of 89 protostellar jets and outflows: New data on the evolution of the outflow morphology

    SciTech Connect

    Velusamy, T.; Langer, W. D.; Thompson, T. E-mail: William.D.Langer@jpl.nasa.gov

    2014-03-01

    To study the role of protosellar jets and outflows in the time evolution of the parent cores and the protostars, the astronomical community needs a large enough database of infrared images of protostars at the highest spatial resolution possible to reveal the details of their morphology. Spitzer provides unprecedented sensitivity in the infrared to study both the jet and outflow features, however, its spatial resolution is limited by its 0.85 m mirror. Here, we use a high-resolution deconvolution algorithm, 'HiRes,' to improve the visualization of spatial morphology by enhancing resolution (to subarcsecond levels in the IRAC bands) and removing the contaminating side lobes from bright sources in a sample of 89 protostellar objects. These reprocessed images are useful for detecting (1) wide-angle outflows seen in scattered light, (2) morphological details of H{sub 2} emission in jets and bow shocks, and (3) compact features in MIPS 24 μm images as protostar/disk and atomic/ionic line emission associated with the jets. The HiRes FITS image data of such a large homogeneous sample presented here will be useful to the community in studying these protostellar objects. To illustrate the utility of this HiRes sample, we show how the opening angle of the wide-angle outflows in 31 sources, all observed in the HiRes-processed Spitzer images, correlates with age. Our data suggest a power-law fit to opening angle versus age with an exponent of ∼0.32 and 0.02, respectively, for ages ≤8000 yr and ≥8000 yr.

  14. Optical Disk Testing System

    NASA Astrophysics Data System (ADS)

    Manns, Basil H.

    1987-01-01

    This paper describes the development of the basics of an optical disk testing system used to test 12 inch, write once, Alcatel Thomson Gigadisk (ATG) media that are used at the Library of Congress in a pilot document storage and retrieval system. Since very little is known regarding the longevity of optical disk media and the fact that disk manufacturers are still refining processing techniques, any conclusions regarding error patterns, failure modes, or longevity may be superceded by a new "batch" of disks. Therefore, this paper focuses on the development of procedures for testing disks that can be used as the write once optical disk technology continues to advance.

  15. Observations of Warm Water and Volatiles in Young Protoplanetary Disks, and the Connection to Disk Evolution and Planet Formation

    NASA Astrophysics Data System (ADS)

    Banzatti, Andrea; Meyer, M.; Pontoppidan, K.

    2014-01-01

    Recent analyses of mid-infrared spectra have shown that warm molecular gas (mainly water, OH, and simple organic molecules) is commonly detected in the inner regions of T Tauri disks and might be an important tracer for the chemical and physical evolution of the terrestrial planet formation region. Many studies suggest that the composition of gas and dust in circumstellar disks (inherited from the ISM and evolved through the protostellar phase) can be further altered by several processes relevant for planet formation. The outcome of this evolution may have important implications concerning the diversity of planetary systems, the composition of planetary surfaces and atmospheres, and on planet habitability. Molecular abundances in the inner disk are a privileged tracer of both the local irradiation environment and the radial transport of icy bodies that evaporate after crossing the snowline, the building blocks of rocky planets. Water and other molecules in the gas phase are therefore strongly connected to our understanding of disk evolution and planet formation processes. In this presentation I will show the highlights from the research I have done during my PhD, using mid-infrared spectroscopy from Spitzer and VLT-VISIR to address: 1) the effect of variable UV radiation in shaping the properties of the molecular gas in inner disks, during accretion phenomena in the T Tauri phase, and 2) the abundance of water vapor inward of the snowline as indicative of its origin through chemical (gas-phase reactions) and/or physical processes (ongoing inward migration of icy solids), and a potential tracer of disk evolution and planet formation processes.

  16. Observations of Warm Water in Young Protoplanetary Disks and its Connection to Disk Evolution and Planet Formation

    NASA Astrophysics Data System (ADS)

    Banzatti, Andrea; Meyer, Michael; Pontoppidan, Klaus; Bruderer, Simon

    2013-07-01

    Recent analyses of mid-infrared spectra have shown that warm molecular gas (mainly water, OH, and simple organic molecules) is commonly detected in the inner regions of T Tauri disks and might be an important tracer for the chemical and physical evolution of the terrestrial planet formation region. Many studies suggest that the composition of gas and dust in circumstellar disks (inherited from the ISM and evolved through the protostellar phase) can be further altered by several processes relevant for planet formation. The outcome of this evolution may have important implications concerning the architecture of planetary systems, the composition of surfaces and atmospheres of forming planets, and on planet habitability. The water abundance in the inner disk is a good tracer of both the local irradiation environment and the radial transport of icy bodies that evaporate after crossing the snowline, the building blocks of rocky planets. Water and other molecules in the gas phase are therefore strongly connected to our understanding of disk evolution and planet formation processes. Here I show the highlights from the research I have done during my PhD, using mid-infrared spectroscopy from Spitzer and VLT-VISIR to address: 1) the effect of variable UV radiation on gas molecules in the inner disk, during accretion phenomena in the T Tauri phase, and 2) the abundance of water vapor inward of the snowline as indicative of its origin through chemical (gas-phase reactions) and/or physical (ongoing inward migration of icy solids) processes, and a potential tracer of disk evolution and planet formation processes.

  17. Inner Structure of Protostellar Collapse Candidate B335 Derived from Millimeter-Wave Interferometry

    NASA Astrophysics Data System (ADS)

    Harvey, Daniel W. A.; Wilner, David J.; Myers, Philip C.; Tafalla, Mario; Mardones, Diego

    2003-02-01

    We present a study of the density structure of the protostellar collapse candidate B335 using continuum observations from the IRAM Plateau de Bure Interferometer made at wavelengths of 1.2 and 3.0 mm. We analyze these data, which probe spatial scales from 5000 to 500 AU, directly in the visibility domain by comparison with synthetic observations constructed from models that assume different physical conditions. This approach allows for much more stringent constraints to be derived from the data than from analysis of images. A single radial power law in density provides a good description of the data, with a best-fit power-law density index p=1.65+/-0.05. Through simulations, we quantify the sensitivity of this result to various model uncertainties, including assumptions of temperature distribution, outer boundary, dust opacity spectral index, and an unresolved central component. The largest uncertainty comes from the unknown presence of a centralized point source. The maximal point source, with 1.2 mm flux of F=12+/-7 mJy, reduces the power-law density index to p=1.47+/-0.07. The remaining sources of systematic uncertainty, of which the most important is the radial dependence of the temperature distribution, likely contribute a total uncertainty at the level of δp<~0.2. Taking into account the uncertainties, we find strong evidence that the power-law index of the density distribution within 5000 AU is significantly less than the value at larger radii, close to 2.0, from previous studies of dust emission and extinction. Images made from the data show clear departures from spherical symmetry, with the globule being slightly extended perpendicular to the outflow axis. The inclusion of a crude model of the outflow as a hollow bipolar cone of constant opening angle improves the fit and leaves the resulting density power-law index unchanged. These results conform well to the generic paradigm of isolated, low-mass star formation, which predicts a power-law density index

  18. Magnetic fields in primordial accretion disks

    NASA Astrophysics Data System (ADS)

    Latif, M. A.; Schleicher, D. R. G.

    2016-01-01

    Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α-Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10M⊙ and an accretion rate of 10-3M⊙ yr-1, and a supermassive star with 105M⊙ and an accretion rate of 10-1M⊙ yr-1. For the 10M⊙ Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100L⊙ and a mass outflow rate of 10-3.7M⊙ yr-1. For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ~106.0L⊙ and a mass outflow rate of 10-2.1M⊙ yr-1. We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.

  19. D/H Measurements in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Keane, Jacqueline

    2007-05-01

    It is generally accepted that a considerable fraction of early Earths water was delivered by asteroids, comets, and planetesimals. The local planets and comets were assembled from the material in circumstellar disks, which in turn evolved from the envelopes and clouds surrounding protostars. Here at the University of Hawaii-NASA Astrobiology Institute the key research goal is to connect the major aspects of starformation and planetary water, in effect aiming to understand the terms of a "watery Drake Equation". To achieve this goal, we use the infrared and submillimeter telescopes on Mauna Kea to survey several molecules in a variety of starforming clouds. Observations show that water is the most common interstellar ice component. Moreover, there is evidence for enhanced water ice formation in the inner parts of protostellar envelopes. Simple molecules form on the icy grain mantles from surface reactions or thermal annealing of the ice, in turn these molecules drive a rich gas phase chemistry that produces more complex prebiotic molecules. Ice bands, therefore, serve as unique tracers of the chemical and thermal history of circumstellar environments. Here we will discuss constraints on the reservoirs of water and organic molecules in starforming regions, taking in to account the latest observational and theoretical measurements. Recent observations of a number of deuterated molecules, including water, will be discussed in terms of grain surface chemistry and its role in driving the enhanced fractionation of methanol like species, while at the same time inhibiting the deuteration of water.

  20. GIANT PLANET MIGRATION, DISK EVOLUTION, AND THE ORIGIN OF TRANSITIONAL DISKS

    SciTech Connect

    Alexander, Richard D.; Armitage, Philip J.

    2009-10-20

    We present models of giant planet migration in evolving protoplanetary disks. Our disks evolve subject to viscous transport of angular momentum and photoevaporation, while planets undergo Type II migration. We use a Monte Carlo approach, running large numbers of models with a range in initial conditions. We find that relatively simple models can reproduce both the observed radial distribution of extrasolar giant planets, and the lifetimes and accretion histories of protoplanetary disks. The use of state-of-the-art photoevaporation models results in a degree of coupling between planet formation and disk clearing, which has not been found previously. Some accretion across planetary orbits is necessary if planets are to survive at radii approx<1.5 AU, and if planets of Jupiter mass or greater are to survive in our models they must be able to form at late times, when the disk surface density in the formation region is low. Our model forms two different types of 'transitional' disks, embedded planets and clearing disks, which show markedly different properties. We find that the observable properties of these systems are broadly consistent with current observations, and highlight useful observational diagnostics. We predict that young transition disks are more likely to contain embedded giant planets, while older transition disks are more likely to be undergoing disk clearing.

  1. Accretion disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Coroniti, F. V.

    1985-01-01

    Accretion disk electrodynamic phenomena are separable into two classes: (1) disks and coronas with turbulent magnetic fields; (2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an alpha-omega dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.

  2. Disk-loss and disk-renewal phases in classical Be stars. II. Contrasting with stable and variable disks

    SciTech Connect

    Draper, Zachary H.; Wisniewski, John P.; Bjorkman, Karen S.; Bjorkman, Jon E.; Meade, Marilyn R.; Haubois, Xavier; Mota, Bruno C.; Carciofi, Alex C. E-mail: karen.bjorkman@utoledo.edu E-mail: meade@astro.wisc.edu E-mail: carciofi@usp.br

    2014-05-10

    Recent observational and theoretical studies of classical Be stars have established the utility of polarization color diagrams (PCDs) in helping to constrain the time-dependent mass decretion rates of these systems. We expand on our pilot observational study of this phenomenon, and report the detailed analysis of a long-term (1989-2004) spectropolarimetric survey of nine additional classical Be stars, including systems exhibiting evidence of partial disk-loss/disk-growth episodes as well as systems exhibiting long-term stable disks. After carefully characterizing and removing the interstellar polarization along the line of sight to each of these targets, we analyze their intrinsic polarization behavior. We find that many steady-state Be disks pause at the top of the PCD, as predicted by theory. We also observe sharp declines in the Balmer jump polarization for later spectral type, near edge-on steady-state disks, again as recently predicted by theory, likely caused when the base density of the disk is very high, and the outer region of the edge-on disk starts to self absorb a significant number of Balmer jump photons. The intrinsic V-band polarization and polarization position angle of γ Cas exhibits variations that seem to phase with the orbital period of a known one-armed density structure in this disk, similar to the theoretical predictions of Halonen and Jones. We also observe stochastic jumps in the intrinsic polarization across the Balmer jump of several known Be+sdO systems, and speculate that the thermal inflation of part of the outer region of these disks could be responsible for producing this observational phenomenon. Finally, we estimate the base densities of this sample of stars to be between ≈8 × 10{sup –11} and ≈4 × 10{sup –12} g cm{sup –3} during quasi steady state periods given there maximum observed polarization.

  3. Chemistry in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Henning, Thomas; Semenov, Dmitry

    2013-12-01

    This comprehensive review summarizes our current understanding of the evolution of gas, solids and molecular ices in protoplanetary disks. Key findings related to disk physics and chemistry, both observationally and theoretically, are highlighted. We discuss which molecular probes are used to derive gas temperature, density, ionization state, kinematics, deuterium fractionation, and study organic matter in protoplanetary disks.

  4. Optical Disk Technology.

    ERIC Educational Resources Information Center

    Abbott, George L.; And Others

    1987-01-01

    This special feature focuses on recent developments in optical disk technology. Nine articles discuss current trends, large scale image processing, data structures for optical disks, the use of computer simulators to create optical disks, videodisk use in training, interactive audio video systems, impacts on federal information policy, and…

  5. Understanding Floppy Disks.

    ERIC Educational Resources Information Center

    Valentine, Pamela

    1980-01-01

    The author describes the floppy disk with an analogy to the phonograph record, and discusses the advantages, disadvantages, and capabilities of hard-sectored and soft-sectored floppy disks. She concludes that, at present, the floppy disk will continue to be the primary choice of personal computer manufacturers and their customers. (KC)

  6. Protoplanetary Disk Evolution: Singles vs. Binaries

    NASA Astrophysics Data System (ADS)

    Daemgen, Sebastian; Jayawardhana, Ray; Petr-Gotzens, Monika G.; Meyer, Elliot

    2016-01-01

    Based on a large number of observations carried out in the last decade it appears that the fraction of stars with protoplanetary disks declines steadily between ~1 Myr and ~10 Myr. We do, however, know that the multiplicity fraction of star-forming regions can be as high as >50% and that multiples have reduced disk lifetimes on average. As a consequence, the observed roughly exponential disk decay can be fully attributed neither to single nor binary stars and its functional form may need revision. Observational evidence for a non-exponential decay has been provided by Kraus et al. (2012), who statistically correct previous disk frequency measurements for the presence of binaries and find agreement with models that feature a constantly high disk fraction up to ~3 Myr, followed by a rapid (<~2 Myr) decline. We present results from our high angular resolution observational program to study the fraction of protoplanetary disks of single and binary stars separately. We find that disk evolution timescales of stars bound in close binaries (<100 AU) are significantly reduced compared to wider binaries. The frequencies of accretors among single stars and wide binaries appear indistinguishable, and are found to be lower than predicted from planet forming disk models governed by viscous evolution and photoevaporation.

  7. Floppy disk utility user's guide

    NASA Technical Reports Server (NTRS)

    Akers, J. W.

    1980-01-01

    A floppy disk utility program is described which transfers programs between files on a hard disk and floppy disk. It also copies the data on one floppy disk onto another floppy disk and compares the data. The program operates on the Data General NOVA-4X under the Real Time Disk Operating System. Sample operations are given.

  8. Floppy disk utility user's guide

    NASA Technical Reports Server (NTRS)

    Akers, J. W.

    1981-01-01

    The Floppy Disk Utility Program transfers programs between files on the hard disk and floppy disk. It also copies the data on one floppy disk onto another floppy disk and compares the data. The program operates on the Data General NOVA-4X under the Real Time Disk Operating System (RDOS).

  9. Photoevaporation and Disk Dispersal

    NASA Astrophysics Data System (ADS)

    Gorti, Uma

    2016-01-01

    Protoplanetary disks are depleted of their mass on short timescales by viscous accretion, which removes both gas and solids, and by photoevaporation which removes mainly gas. Photoevaporation may facilitate planetesimal formation by lowering the gas/dust mass ratio in disks. Disk dispersal sets constraints on planet formation timescales, and by controlling the availability of gas determines the type of planets that form in the disk. Photoevaporative wind mass loss rates are theoretically estimated to range from ~ 10-10 to 10-8 M ⊙, and disk lifetimes are typically ~ few Myr.

  10. Change in the chemical composition of infalling gas forming a disk around a protostar.

    PubMed

    Sakai, Nami; Sakai, Takeshi; Hirota, Tomoya; Watanabe, Yoshimasa; Ceccarelli, Cecilia; Kahane, Claudine; Bottinelli, Sandrine; Caux, Emmanuel; Demyk, Karine; Vastel, Charlotte; Coutens, Audrey; Taquet, Vianney; Ohashi, Nagayoshi; Takakuwa, Shigehisa; Yen, Hsi-Wei; Aikawa, Yuri; Yamamoto, Satoshi

    2014-03-01

    IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud, which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1 AU is the distance from Earth to the Sun), and is infalling and rotating. It also has a protostellar disk with a radius of 90 AU (ref. 6), from which a planetary system is expected to form. The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C3H2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20 AU), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there. PMID:24522533

  11. Protostellar Interferometric Line Survey (PILS): Constraining the formation of complex organic molecules with ALMA

    NASA Astrophysics Data System (ADS)

    Jorgensen, Jes K.; Coutens, Audrey; Bourke, Tyler L.; Favre, Cecile; Garrod, Robin; Lykke, Julie; Mueller, Holger; Oberg, Karin I.; Schmalzl, Markus; van der Wiel, Matthijs; van Dishoeck, Ewine; Wampfler, Susanne F.

    2015-08-01

    Understanding how, when and where complex organic and potentially prebiotic molecules are formed is a fundamental goal of astrochemistry and an integral part of origins of life studies. Already now ALMA is showing its capabilities for studies of the chemistry of solar-type stars with its high sensitivity for faint lines, high spectral resolution which limits line confusion, and high angular resolution making it possible to study the structure of young protostars on solar-system scales. We here present the first results from a large unbiased survey “Protostellar Interferometric Line Survey (PILS)” targeting one of the astrochemical template sources, the low-mass protostellar binary IRAS 16293-2422. The survey is more than an order of magnitude more sensitive than previous surveys of the source and provide imaging down to 25 AU scales (radius) around each of the two components of the binary. An example of one of the early highlights from the survey is unambiguous detections of the (related) prebiotic species glycolaldehyde, ethylene glycol (two lowest energy conformers), methyl formate and acetic acid. The glycolaldehyde-ethylene glycol abundance ratio is high in comparison to comets and other protostars - but agrees with previous measurements, e.g., in the Galactic Centre clouds possibly reflecting different environments and/or evolutionary histories. Complete mapping of this and other chemical networks in comparison with detailed chemical models and laboratory experiments will reveal the origin of complex organic molecules in a young protostellar system and investigate the link between these protostellar stages and the early Solar System.

  12. A survey of 44-GHz Class I methanol masers toward High Mass Protostellar Objects

    NASA Astrophysics Data System (ADS)

    Berenice Rodríguez Garza, Carolina; Kurtz, Stan

    2016-01-01

    We present preliminary results of 44-GHz Class I methanol maser observations made with the Very Large Array toward a sample of 55 High Mass Protostellar Objects. We found a 44% detection rate of methanol maser emission. We present a statistical description of our results, along with a comparison of the location of the 44-GHz masers with respect to shocked gas, traced by Extended Green Objects seen in the Spitzer/IRAC bands.

  13. Episodic molecular outflow in the very young protostellar cluster Serpens South.

    PubMed

    Plunkett, Adele L; Arce, Héctor G; Mardones, Diego; van Dokkum, Pieter; Dunham, Michael M; Fernández-López, Manuel; Gallardo, José; Corder, Stuartt A

    2015-11-01

    The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such 'episodic' ejection events have been observed during the class 0 protostellar phase (the early accretion stage), and continue during the subsequent class I phase that marks the first one million years of star formation. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. Outflows link protostars with their environment and provide a viable source of the turbulence that is necessary for regulating star formation in clusters, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a young, class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, shows unambiguous episodic events. The (12)C(16)O (J = 2-1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes--one of the first detectable signs of star formation--which originate from the peak of 1-mm continuum emission. Emission from the surrounding C(18)O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic, accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence. PMID:26536957

  14. Episodic molecular outflow in the very young protostellar cluster Serpens South

    NASA Astrophysics Data System (ADS)

    Plunkett, Adele L.; Arce, Héctor G.; Mardones, Diego; van Dokkum, Pieter; Dunham, Michael M.; Fernández-López, Manuel; Gallardo, José; Corder, Stuartt A.

    2015-11-01

    The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such `episodic' ejection events have been observed during the Class 0 protostellar phase (the early accretion stage), and continue during the subsequent class I phase that marks the first one million years of star formation. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. Outflows link protostars with their environment and provide a viable source of turbulence that is necessary for regulating star formation in clusters, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a very young class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, shows unambiguous episodic events. The 12CO (J=2-1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes --- one of the first detectable signs of star formation --- which originate from the peak of 1-mm continuum emission. Emission from the surrounding C18O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence.

  15. Kinematics of the Envelope and Two Bipolar Jets in the Class 0 Protostellar System L1157

    NASA Astrophysics Data System (ADS)

    Kwon, Woojin; Fernández-López, Manuel; Stephens, Ian W.; Looney, Leslie W.

    2015-11-01

    A massive envelope and a strong bipolar outflow are the two main structures characterizing the youngest protostellar systems. In order to understand the physical properties of a bipolar outflow and the relationship with those of the envelope, we obtained a mosaic map covering the whole bipolar outflow of the youngest protostellar system L1157 with about 5″ angular resolution in CO J = 2-1 using the Combined Array for Research in Millimeter-wave Astronomy. By utilizing these observations of the whole bipolar outflow, we estimate its physical properties and show that they are consistent with multiple jets. We also constrain a preferred precession direction. In addition, we observed the central envelope structure with 2″ resolution in the λ =1.3 and 3 mm continua and various molecular lines: C17O, C18O, 13CO, CS, CN, N2H+, CH3OH, H2O, SO, and SO2. All of the CO isotopes and CS, CN, and N2H+ have been detected and imaged. We marginally detected the features that can be interpreted as a rotating inner envelope in C17O and C18O and as an infalling outer envelope in N2H+. We also estimated the envelope and central protostellar masses and found that the dust-opacity spectral index changes with radius.

  16. Broad N2H+ Emission toward the Protostellar Shock L1157-B1

    NASA Astrophysics Data System (ADS)

    Codella, C.; Viti, S.; Ceccarelli, C.; Lefloch, B.; Benedettini, M.; Busquet, G.; Caselli, P.; Fontani, F.; Gómez-Ruiz, A.; Podio, L.; Vasta, M.

    2013-10-01

    We present the first detection of N2H+ toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ~0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N2H+(1-0) line originated from the dense (>=105 cm-3) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N2H+ column density of a few 1012 cm-2 corresponding to an abundance of (2-8) × 10-9. The N2H+ abundance can be matched by a model of quiescent gas evolved for more than 104 yr, i.e., for more than the shock kinematical age (sime2000 yr). Modeling of C-shocks confirms that the abundance of N2H+ is not increased by the passage of the shock. In summary, N2H+ is a fossil record of the pre-shock gas, formed when the density of the gas was around 104 cm-3, and then further compressed and accelerated by the shock.

  17. Deuterium Fractionation and Ionization Degree in Massive Protostellar/cluster Cores

    NASA Astrophysics Data System (ADS)

    Chen, Huei-Ru; Liu, Sheng-Yuan; Su, Yu-Nung

    2013-03-01

    We have conducted a survey of deuterium fractionation of N2H+, RD (N2H+) ≡ N(N2D+)/N(N2H+), with the Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) to assess the use of RD (N2H+) as an evolutionary tracer among massive protostellar/cluster cores in early stages. Our sample includes 32 dense cores in various evolutionary stages, from high-mass starless cores (HMSCs), high-mass protostellar objects (HMPOs), to ultra-compact (UC) HII regions, in infrared dark clouds (IRDCs) and high infrared extinction clouds. The results show a decreasing trend in deuterium fractionation with evolutionary stage traced by gas temperature and line width (Fig. 1). A moderate increasing trend of deuterium fractionation with the CO depletion factor is also found among cores in IRDCs and HMSCs. These suggest a general chemical behavior of deuterated species in low- and high-mass protostellar candidates. Upper limits to the ionization degree are also estimated to be in the range of 4 × 10-8 - 5 × 10-6.

  18. EVAPORATION OF GRAIN-SURFACE SPECIES BY SHOCK WAVES IN A PROTOPLANETARY DISK

    SciTech Connect

    Aota, Takuhiro; Aikawa, Yuri; Inoue, Tsuyoshi

    2015-02-01

    Recent Atacama Large Millimeter/submillimeter Array observations of young protostellar objects detected warm SO emission, which could be associated with a forming protostellar disk. In order to investigate if such warm gas can be produced by accretion shock onto the forming disk, we calculate the sputtering and thermal desorption of various grain-surface species in one-dimensional shock waves. We find that thermal desorption is much more efficient than the sputtering in the post-shock region. While H{sub 2}O can be thermally desorbed, if the accretion velocity is larger than 8 km s{sup –1} with the pre-shock gas number density of 10{sup 9} cm{sup –3}, SO is desorbed if the accretion velocity ≳2 km s{sup –1} and ≳4 km s{sup –1}, with the pre-shock density of 10{sup 9} cm{sup –3} and 10{sup 8} cm{sup –3}, respectively. We also find that the column density of hydrogen nuclei in warm post-shock gas is N {sub warm} ∼ 10{sup 21} cm{sup –2}.

  19. Water transport from collapsing prestellar cores to forming disks: evolution of the HDO/H2O ratio

    NASA Astrophysics Data System (ADS)

    Furuya, K.; Drozdovskaya, M. N.; Walsh, C.; van Dishoeck, E. F.

    2016-05-01

    We investigate the transport of H2O and HDO ices from the collapse of rotating cores to the formation of disks. We adopt a two-dimensional physical model in order to trace fluid parcels, in which molecular evolution is simulated using a gas-ice chemical model. We find that water ice accreting from the protostellar envelope onto the disks can have a variation of the HDO/H2O ratio, reproducing the variation of the HDO/H2O ratio observed in comets. The result suggests that processing of water in the disk itself is not necessarily required to account for the variation of the HDO/H2O ratio in comets.

  20. Two Jets from the Protostellar System L1551 IRS 5

    NASA Astrophysics Data System (ADS)

    Fridlund, C. V. Malcolm; Liseau, René

    1998-05-01

    Hubble Space Telescope and ground-based observations of the jet emanating from the young stellar object L1551 IRS 5 clearly show a structure with two components, one of which terminates in a working surface only 1500 AU from the originating sources. This particular jet is found to be less dense than the ambient medium. Its Mach disk is found to be very small, only ~45 AU. We show that this jet cannot be the driver of the large-scale molecular outflow in L1551 for two reasons: (1) the jet fails to provide the necessary momentum by at least a factor of 100, and, (2) having a dynamic age ~3 orders of magnitude less than that of the outflow, this jet has no causal relationship with the molecular flow. The morphology and velocity field of the two components are consistent with them being separate entities, and we suggest that there are in fact two jets, each possibly originating from a different young stellar object. Based on observations made with the Nordic Optical Telescope, operated jointly on the island of La Palma by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, and based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  1. Coronagraphic Polarimetry of HST-Resolved Circumstellar T Tauri and Debris Disks.

    NASA Astrophysics Data System (ADS)

    Schneider, Glenn; Hines, D. C.; 10852, HST/GO; 10847 Teams

    2007-12-01

    The formation of planetary systems is intimately linked to the dust population in circumstellar disks, thus understanding dust grain evolution is essential to advancing our understanding of how planets form. While it is well established that stars form in ISM-like protostellar environments, the connection to now observable light-scattering circumstellar disks and the processes of planet formation is still very uncertain. Mid-IR spectral studies suggest that disk grains are growing in the environments of young stellar objects during the putative planet-formation epoch. Structures revealed in well resolved images of older circumstellar debris disks suggest gravitational influences on the disks from putative co-orbital bodies of planetary mass. To further elucidate the dust and systemic properties in potentially planet-forming systems, we have undertaken two symbiotic HST imaging programs that exploit the recently commission capabilities of coronagraphic polarimetry with the Near Infrared Camera and Multi-Object Spectrometer, probing dust structures in T Tauri circumstellar disks during the early epochs of planet formation, and debris disks around older stars. We present the first observational results from these two programs in light of earlier commission observations of TW Hya, focusing on the scattered light disks around the T Tauri star GM Aur and the debris disk associated with HR 32297, along with optical (ACS) coronagraphic polarimetry of the unusual dust structure around HD 61005. Support for this work was provided by NASA through grant numbers GO-9768. 10847 and 10852 from the Space Telescope Science Institute, which is operated by Association of Universities for Research in Astronomy Incorporated, under NASA contract NAS5-26555.

  2. A Hot and Massive Accretion Disk around the High-mass Protostar IRAS 20126+4104

    NASA Astrophysics Data System (ADS)

    Chen, Huei-Ru Vivien; Keto, Eric; Zhang, Qizhou; Sridharan, T. K.; Liu, Sheng-Yuan; Su, Yu-Nung

    2016-06-01

    We present new spectral line observations of the CH3CN molecule in the accretion disk around the massive protostar IRAS 20126+4104 with the Submillimeter Array, which, for the first time, measure the disk density, temperature, and rotational velocity with sufficient resolution (0.″37, equivalent to ∼600 au) to assess the gravitational stability of the disk through the Toomre-Q parameter. Our observations resolve the central 2000 au region that shows steeper velocity gradients with increasing upper state energy, indicating an increase in the rotational velocity of the hotter gas nearer the star. Such spin-up motions are characteristics of an accretion flow in a rotationally supported disk. We compare the observed data with synthetic image cubes produced by three-dimensional radiative transfer models describing a thin flared disk in Keplerian motion enveloped within the centrifugal radius of an angular-momentum-conserving accretion flow. Given a luminosity of 1.3 × 104 L ⊙, the optimized model gives a disk mass of 1.5 M ⊙ and a radius of 858 au rotating about a 12.0 M ⊙ protostar with a disk mass accretion rate of 3.9 × 10‑5 M ⊙ yr‑1. Our study finds that, in contrast to some theoretical expectations, the disk is hot and stable to fragmentation with Q > 2.8 at all radii which permits a smooth accretion flow. These results put forward the first constraints on gravitational instabilities in massive protostellar disks, which are closely connected to the formation of companion stars and planetary systems by fragmentation.

  3. MODELING THE RESOLVED DISK AROUND THE CLASS 0 PROTOSTAR L1527

    SciTech Connect

    Tobin, John J.; Hartmann, Lee; Calvet, Nuria; Chiang, Hsin-Fang; Looney, Leslie W.; Wilner, David J.; Loinard, Laurent; D'Alessio, Paola

    2013-07-01

    We present high-resolution sub/millimeter interferometric imaging of the Class 0 protostar L1527 IRS (IRAS 04368+2557) at {lambda} = 870 {mu}m and 3.4 mm from the Submillimeter Array and Combined Array for Research in Millimeter Astronomy. We detect the signature of an edge-on disk surrounding the protostar with an observed diameter of 180 AU in the sub/millimeter images. The mass of the disk is estimated to be 0.007 M{sub Sun }, assuming optically thin, isothermal dust emission. The millimeter spectral index is observed to be quite shallow at all the spatial scales probed: {alpha} {approx} 2, implying a dust opacity spectral index {beta} {approx} 0. We model the emission from the disk and surrounding envelope using Monte Carlo radiative transfer codes, simultaneously fitting the sub/millimeter visibility amplitudes, sub/millimeter images, resolved L' image, spectral energy distribution, and mid-infrared spectrum. The best-fitting model has a disk radius of R = 125 AU, is highly flared (H{proportional_to}R {sup 1.3}), has a radial density profile {rho}{proportional_to}R {sup -2.5}, and has a mass of 0.0075 M{sub Sun }. The scale height at 100 AU is 48 AU, about a factor of two greater than vertical hydrostatic equilibrium. The resolved millimeter observations indicate that disks may grow rapidly throughout the Class 0 phase. The mass and radius of the young disk around L1527 are comparable to disks around pre-main-sequence stars; however, the disk is considerably more vertically extended, possibly due to a combination of lower protostellar mass, infall onto the disk upper layers, and little settling of {approx}1 {mu}m-sized dust grains.

  4. The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Pickett, Brian K.; Mejía, Annie C.; Durisen, Richard H.; Cassen, Patrick M.; Berry, Donald K.; Link, Robert P.

    2003-06-01

    cooling. The additional heating and cooling are applied to each model over the outer half of the disk or the entire disk. The models are subject to the rapid growth of a four-armed spiral instability; the subsequent evolution of the models depends on the thermal behavior of the disk. The cooling function tends to overwhelm the heating included in our artificial viscosity prescription, and as a result the spiral structure strengthens. The spiral disturbances transport mass at prodigious rates during the early nonlinear stages of development and significantly alter the disk's vertical surface. Although dense condensations of material can appear, their character depends on the extent of the volumetric cooling in the disk. In the simulation of the high-Q model with heating and cooling applied throughout the disk, thin, dense rings form at radii ranging from 1 to 3 AU and steadily increase in mass; later companion formation may occur in these rings as cooling drives them toward instability. When heating and cooling are applied only over the outer radial half of the disk, however, a succession of single condensations appears near 5 AU. Each clump has roughly the mass of Saturn, and some survive a complete orbit. Since the clumps form near the artificial boundary in the treatment of the disk gas physics, the production of a clump in this case is a numerical artifact. Nevertheless, radially abrupt transitions in disk gas characteristics, for example, in opacity, might mimic the artificial boundary effects in our simulations and favor the production of stable companions in actual protostellar and protoplanetary disks. The ultimate survival of condensations as eventual stellar or substellar companions to the central star is still largely an open question.

  5. Coupling the Weather Research and Forecasting (WRF) model and Large Eddy Simulations with Actuator Disk Model: predictions of wind farm power production

    NASA Astrophysics Data System (ADS)

    Garcia Cartagena, Edgardo Javier; Santoni, Christian; Ciri, Umberto; Iungo, Giacomo Valerio; Leonardi, Stefano

    2015-11-01

    A large-scale wind farm operating under realistic atmospheric conditions is studied by coupling a meso-scale and micro-scale models. For this purpose, the Weather Research and Forecasting model (WRF) is coupled with an in-house LES solver for wind farms. The code is based on a finite difference scheme, with a Runge-Kutta, fractional step and the Actuator Disk Model. The WRF model has been configured using seven one-way nested domains where the child domain has a mesh size one third of its parent domain. A horizontal resolution of 70 m is used in the innermost domain. A section from the smallest and finest nested domain, 7.5 diameters upwind of the wind farm is used as inlet boundary condition for the LES code. The wind farm consists in six-turbines aligned with the mean wind direction and streamwise spacing of 10 rotor diameters, (D), and 2.75D in the spanwise direction. Three simulations were performed by varying the velocity fluctuations at the inlet: random perturbations, precursor simulation, and recycling perturbation method. Results are compared with a simulation on the same wind farm with an ideal uniform wind speed to assess the importance of the time varying incoming wind velocity. Numerical simulations were performed at TACC (Grant CTS070066). This work was supported by NSF, (Grant IIA-1243482 WINDINSPIRE).

  6. Fast radial flows in transition disk holes

    SciTech Connect

    Rosenfeld, Katherine A.; Andrews, Sean M.; Chiang, Eugene

    2014-02-20

    Protoplanetary 'transition' disks have large, mass-depleted central cavities, yet also deliver gas onto their host stars at rates comparable to disks without holes. The paradox of simultaneous transparency and accretion can be explained if gas flows inward at much higher radial speeds inside the cavity than outside the cavity, since surface density (and by extension optical depth) varies inversely with inflow velocity at fixed accretion rate. Radial speeds within the cavity might even have to approach free-fall values to explain the huge surface density contrasts inferred for transition disks. We identify observational diagnostics of fast radial inflow in channel maps made in optically thick spectral lines. Signatures include (1) twisted isophotes in maps made at low systemic velocities and (2) rotation of structures observed between maps made in high-velocity line wings. As a test case, we apply our new diagnostic tools to archival Atacama Large Millimeter Array data on the transition disk HD 142527 and uncover evidence for free-fall radial velocities inside its cavity. Although the observed kinematics are also consistent with a disk warp, the radial inflow scenario is preferred because it predicts low surface densities that appear consistent with recent observations of optically thin CO isotopologues in this disk. How material in the disk cavity sheds its angular momentum wholesale to fall freely onto the star is an unsolved problem; gravitational torques exerted by giant planets or brown dwarfs are briefly discussed as a candidate mechanism.

  7. Dynamics of acoustically levitated disk samples.

    PubMed

    Xie, W J; Wei, B

    2004-10-01

    The acoustic levitation force on disk samples and the dynamics of large water drops in a planar standing wave are studied by solving the acoustic scattering problem through incorporating the boundary element method. The dependence of levitation force amplitude on the equivalent radius R of disks deviates seriously from the R3 law predicted by King's theory, and a larger force can be obtained for thin disks. When the disk aspect ratio gamma is larger than a critical value gamma(*) ( approximately 1.9 ) and the disk radius a is smaller than the critical value a(*) (gamma) , the levitation force per unit volume of the sample will increase with the enlargement of the disk. The acoustic levitation force on thin-disk samples ( gamma

  8. Ripples in disk galaxies

    SciTech Connect

    Schweizer, F.; Seitzer, P.

    1988-05-01

    Evidence is presented that ripples occur not only in ellipticals but also in disk galaxies of Hubble types S0, S0/Sa, and Sa, and probably even in the Sbc galaxy NGC 3310. It is argued that the ripples cannot usually have resulted from transient spiral waves or other forced vibrations in existing disks, but instead consist of extraneous sheetlike matter. The frequent presence of major disk-shaped companions suggests that ripple material may be acquired not only through wholesale mergers but also through mass transfer from neighbor galaxies. The implications of ripples in early-type disk galaxies are addressed. 40 references.

  9. Glass rupture disk

    DOEpatents

    Glass, S. Jill; Nicolaysen, Scott D.; Beauchamp, Edwin K.

    2002-01-01

    A frangible rupture disk and mounting apparatus for use in blocking fluid flow, generally in a fluid conducting conduit such as a well casing, a well tubing string or other conduits within subterranean boreholes. The disk can also be utilized in above-surface pipes or tanks where temporary and controllable fluid blockage is required. The frangible rupture disk is made from a pre-stressed glass with controllable rupture properties wherein the strength distribution has a standard deviation less than approximately 5% from the mean strength. The frangible rupture disk has controllable operating pressures and rupture pressures.

  10. Superalloy Disk With Dual-Grain Structure Spin Tested

    NASA Technical Reports Server (NTRS)

    Gayda, John; Kantzos, Pete T.

    2003-01-01

    Advanced nickel-base disk alloys for future gas turbine engines will require greater temperature capability than current alloys, but they must also continue to deliver safe, reliable operation. An advanced, nickel-base disk alloy, designated Alloy 10, was selected for evaluation in NASA s Ultra Safe Propulsion Project. Early studies on small test specimens showed that heat treatments that produced a fine grain microstructure promoted high strength and long fatigue life in the bore of a disk, whereas heat treatments that produced a coarse grain microstructure promoted optimal creep and crack growth resistance in the rim of a disk. On the basis of these results, the optimal combination of performance and safety might be achieved by utilizing a heat-treatment technology that could produce a fine grain bore and coarse grain rim in a nickel-base disk. Alloy 10 disks that were given a dual microstructure heat treatment (DMHT) were obtained from NASA s Ultra-Efficient Engine Technology (UEET) Program for preliminary evaluation. Data on small test specimens machined from a DMHT disk were encouraging. However, the benefit of the dual grain structure on the performance and reliability of the entire disk still needed to be demonstrated. For this reason, a high temperature spin test of a DMHT disk was run at 20 000 rpm and 1500 F at the Balancing Company of Dayton, Ohio, under the direction of NASA Glenn Research Center personnel. The results of that test showed that the DMHT disk exhibited significantly lower crack growth than a disk with a fine grain microstructure. In addition, the results of these tests could be accurately predicted using a two-dimensional, axisymmetric finite element analysis of the DMHT disk. Although the first spin test demonstrated a significant performance advantage associated with the DMHT technology, a second spin test on the DMHT disk was run to determine burst margin. The disk burst in the web at a very high speed, over 39 000 rpm, in line with

  11. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2016-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  12. Migration and growth of protoplanetary embryos. I. Convergence of embryos in protoplanetary disks

    SciTech Connect

    Zhang, Xiaojia; Lin, Douglas N. C.; Liu, Beibei; Li, Hui

    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} > 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.

  13. Migration and Growth of Protoplanetary Embryos. I. Convergence of Embryos in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojia; Liu, Beibei; Lin, Douglas N. C.; Li, Hui

    2014-12-01

    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 (Mp ) in the range of a few Earth masses (M ⊕) 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 Mp > 10 M ⊕, 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.

  14. Formation Process of the Circumstellar Disk: Long-term Simulations in the Main Accretion Phase of Star Formation

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki

    2010-12-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of gsim3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of ~0.005-0.1 M sun, while the protostar has a mass of ~10-3 M sun. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for ~105 yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  15. FORMATION PROCESS OF THE CIRCUMSTELLAR DISK: LONG-TERM SIMULATIONS IN THE MAIN ACCRETION PHASE OF STAR FORMATION

    SciTech Connect

    Machida, Masahiro N.; Inutsuka, Shu-ichiro; Matsumoto, Tomoaki E-mail: inutsuka@nagoya-u.j

    2010-12-01

    The formation and evolution of the circumstellar disk in unmagnetized molecular clouds is investigated using three-dimensional hydrodynamic simulations from the prestellar core until the end of the main accretion phase. In collapsing cloud cores, the first (adiabatic) core with a size of {approx}>3 AU forms prior to the formation of the protostar. At its formation, the first core has a thick disk-like structure and is mainly supported by the thermal pressure. After the protostar formation, it decreases the thickness gradually and becomes supported by the centrifugal force. We found that the first core is a precursor of the circumstellar disk with a size of >3 AU. This means that unmagnetized protoplanetary disk smaller than <3 AU does not exist. Reflecting the thermodynamics of the collapsing gas, at the protostar formation epoch, the first core (or the circumstellar disk) has a mass of {approx}0.005-0.1 M{sub sun}, while the protostar has a mass of {approx}10{sup -3} M{sub sun}. Thus, just after the protostar formation, the circumstellar disk is about 10-100 times more massive than the protostar. In the main accretion phase that lasts for {approx}10{sup 5} yr, the circumstellar disk mass initially tends to dominate the protostellar mass. Such a massive disk is unstable to gravitational instability and tends to show fragmentation. Our calculations indicate that the low-mass companions may form in the circumstellar disk in the main accretion phase. In addition, the mass accretion rate onto the protostar shows a strong time variability that is caused by the torque from the low-mass companions and/or the spiral arms in the circumstellar disk. Such variability provides an important signature for detecting the substellar mass companion in the circumstellar disk around very young protostars.

  16. Observational evidence for thin AGN disks

    NASA Technical Reports Server (NTRS)

    Netzer, Hagai

    1992-01-01

    AGN spectrum and spectral features, polarization, inclination, and X-ray line and continuum reflection features are discussed in a critical way in order to determine the ones that are the least model-dependent. The sign and strength of absorption and emission edges are found to be model-dependent, and relativistic broadening and shifting makes them hard to detect. The presence or absence of the predicted Lyman edge polarization feature may be used as a decisive test for thin, bare AGN disks. Other good model-independent tests are several inclination-related line and continuum correlations in big AGN samples. It is shown that electron temperature near the surface of the disk can greatly exceed the disk equilibrium temperature, which causes deviations from LTE. This effect must be incorporated into realistic disk models.

  17. Probabilistic Analysis of Aircraft Gas Turbine Disk Life and Reliability

    NASA Technical Reports Server (NTRS)

    Melis, Matthew E.; Zaretsky, Erwin V.; August, Richard

    1999-01-01

    Two series of low cycle fatigue (LCF) test data for two groups of different aircraft gas turbine engine compressor disk geometries were reanalyzed and compared using Weibull statistics. Both groups of disks were manufactured from titanium (Ti-6Al-4V) alloy. A NASA Glenn Research Center developed probabilistic computer code Probable Cause was used to predict disk life and reliability. A material-life factor A was determined for titanium (Ti-6Al-4V) alloy based upon fatigue disk data and successfully applied to predict the life of the disks as a function of speed. A comparison was made with the currently used life prediction method based upon crack growth rate. Applying an endurance limit to the computer code did not significantly affect the predicted lives under engine operating conditions. Failure location prediction correlates with those experimentally observed in the LCF tests. A reasonable correlation was obtained between the predicted disk lives using the Probable Cause code and a modified crack growth method for life prediction. Both methods slightly overpredict life for one disk group and significantly under predict it for the other.

  18. From Cores to Envelopes to Disks: A Multi-scale View of Magnetized Star Formation

    NASA Astrophysics Data System (ADS)

    Hull, Charles L. H.

    2014-12-01

    protostellar envelope may be a turning point: at larger scales B-fields may still retain the memory of the global B-field drawn in from the ambient medium; but at smaller scales the B-fields may be affected by the dynamics of both envelope and disk rotation. This sets the stage for ALMA (the Atacama Large Millimeter/submillimeter Array), which will soon reveal the morphology of B-fields in circumstellar disks themselves.

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

    SciTech Connect

    Romero, Gisela A.; Schreiber, Matthias R.; Rebassa-Mansergas, Alberto; Cieza, Lucas A.; Merin, Bruno; Smith Castelli, Analia V.; Allen, Lori E.; Morrell, Nidia

    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 transition 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.

  20. Elliptical accretion disks in active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Eracleous, Michael; Livio, Mario; Halpern, Jules P.; Storchi-Bergmann, Thaisa

    1995-01-01

    We present a calculation of the profiles of emission lines originating in a relativistic, eccentric disk, and show examples of the resulting model profiles. Our calculations are motivated by the fact that in about one-quarter of the double-peaked emission lines observed in radio-loud active galactic nuclei (and in the mildly active nucleus of NGC 1097), the red peak is stronger than the blue peak, which is contrary to the prediction of relativistic, circular disk models. Using the eccentric disk model we fit some of the observed profiles that cannot be fitted with a circular disk model. We propose two possible scenarios for the formation of an eccentric disk in an active galactic nucleus: (a) tidal perturbation of the disk around a supermassive black hole by a smaller binary companion, and (b) formation of an elliptical disk from the debris resulting from the tidal disruption of a star by the central black hole. In the former case we show that the eccentricity can be long-lived because of the presence of the binary companion. In the latter case, although the inner parts of the disk may circularize quickly, we estimate that the outer parts will maintain their eccentricity for times much longer than the local viscous time. We suggest that it may be possible to detect profile variability on much shorter timescales than those ranging from a decade to several centuries by comparing the evolution of the line profile with detailed model predictions. We argue that line-profile variability may also be the most promising discriminant among competing models for the origin of asymmetric, double-peaked emission lines.

  1. The SEEDS of Planet Formation: Observations of Transitional Disks

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.

    2011-01-01

    As part of its 5-year study, the Strategic Exploration of Exoplanets and Disk Systems (SEEDS) has already observed a number of YSOs with circumstellar disks, including 13 0.5-8 Myr old A-M stars with indications that they host wide gaps or central cavities in their circumstellar disks in millimeter or far-IR observations, or from deficits in warm dust thermal emission. For 8 of the disks, the 0.15" inner working angle of HiCIAO+A0188 samples material in the millimeter or mid-IR identified cavity. In one case we report detection of a previously unrecognized wide gap. For the remaining 4 stars, the SEEDS data sample the outer disk: in 3 cases, we present the first NIR imagery of the disks. The data for the youngest sample members 1-2 Myr) closely resemble coeval primordial disks. After approximately 3 Myr, the transitional disks show a wealth of structure including spiral features, rings, divots, and in some cases, largely cleared gaps in the disks which are not seen in coeval primordial disks. Some of these structural features are predicted consequences of Jovian-mass planets having formed in the disk, while others are novel features. We discuss the implications for massive planet formation timescales and mechanisms.

  2. The SEEDS of Planet Formation: Observations of Transitional Disks

    NASA Technical Reports Server (NTRS)

    Grady, Carol

    2011-01-01

    As part of its 5-year study, the Strategic Exploration of Exoplanets and Disk Systems (SEEDS) has already observed a number of YSOs with circumstellar disks, including 13 0.5- 8 Myr old A-M stars with indications that they host wide gaps or central cavities in their circumstellar disks in millimeter or far-IR observations, or from deficits in warm dust thermal emission. For 8 of the disks, the 0.15" inner working angle of HiCIAO+A0188 samples material in the millimeter or mid-IR identified cavity. In one case we reprt detection of a previously unrecognized wide gap. For the remaining 4 stars, the SEEDS data sample the outer disk: in 3 cases, we present the first NIR imagery of the disks. The data for the youngest sample members (less than 1-2 Myr) closely resemble coeval primordial disks. After approximately 3 Myr, the transitional disks show a wealth of structure including spiral features, rings, divots, and in some cases, largely cleared gaps in the disks which are not seen in coeval primordial disks. Some of these structural features are predicted consequences of lovianmass planets having formed in the disk, while others are novel features. We discuss the implications for massive planet formation timescales and mechanisms.

  3. The Milky Way disk

    NASA Astrophysics Data System (ADS)

    Carraro, G.

    2015-08-01

    This review summarises the invited presentation I gave on the Milky Way disc. The idea underneath was to touch those topics that can be considered hot nowadays in the Galactic disk research: the reality of the thick disk, the spiral structure of the Milky Way, and the properties of the outer Galactic disk. A lot of work has been done in recent years on these topics, but a coherent and clear picture is still missing. Detailed studies with high quality spectroscopic data seem to support a dual Galactic disk, with a clear separation into a thin and a thick component. Much confusion and very discrepant ideas still exist concerning the spiral structure of the Milky Way. Our location in the disk makes it impossible to observe it, and we can only infer it. This process of inference is still far from being mature, and depends a lot on the selected tracers, the adopted models and their limitations, which in many cases are neither properly accounted for, nor pondered enough. Finally, there are very different opinions on the size (scale length, truncation radius) of the Galactic disk, and on the interpretation of the observed outer disk stellar populations in terms either of external entities (Monoceros, Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk properties (e.g., warp and flare).

  4. Burst Testing of a Superalloy Disk with a Dual Grain Structure

    NASA Technical Reports Server (NTRS)

    Gayda, John; Kantzos, Pete

    2002-01-01

    Room temperature burst testing of an advanced nickel-base superalloy disk with a dual grain structure was conducted. The disk had a fine grain bore and a coarse grain rim. The results of this test showed that the disk burst at 39,100 rpm in line with predictions based on a 2-D finite element analysis. Further, significant growth of the disk was observed before failure which was also in line with predictions.

  5. Radio pulsar disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Michel, F. C.

    1983-01-01

    Macroscopic physics are discussed for the case of a disk close to an isolated, magnetized, rotating neutron star that acts as a Faraday disk dynamo, while the disk acts as both a load and a neutral sheet. This sheet allows the polar cap current to return to the neutron star, splitting a dipolar field into two monopolar halves. The dominant energy loss is from the stellar wind torque, and the next contribution is dissipation in the auroral zones, where the current returns to the star in a 5 cm-thick sheet. The disk itself may be a source of visible radiation comparable to that in pulsed radio frequency emission. As the pulsar ages, the disk expands and narrows into a ring which, it is suggested, may lead to a cessation of pulsed emission at periods of a few sec.

  6. Methylammonium methylcarbamate thermal formation in interstellar ice analogs: a glycine salt precursor in protostellar environments

    NASA Astrophysics Data System (ADS)

    Bossa, J.-B.; Duvernay, F.; Theulé, P.; Borget, F.; D'Hendecourt, L.; Chiavassa, T.

    2009-11-01

    Context: Analyses of dust cometary grains collected by the Stardust spacecraft have shown the presence of amines and amino acids molecules, and among them glycine (NH{2}CH{2}COOH). We show how the glycine molecule could be produced in the protostellar environments before its introduction into comets. Aims: We study the evolution of the interstellar ice analogues affected by both thermal heating and vacuum ultraviolet (VUV) photons, in addition to the nature of the formed molecules and the confrontation of our experimental results with astronomical observations. Methods: Infrared spectroscopy and mass spectrometry are used to monitor the evolution of the H{2}O:CO{2}:CH{3}NH{2} and CO{2}:CH{3}NH{2} ice mixtures during both warming processes and VUV photolysis. Results: We first show how carbon dioxide (CO{2}) and methylamine (CH{3}NH{2}) thermally react in water-dominated ice to form methylammonium methylcarbamate [ CH{3}NH{3}+] [ CH{3}NHCOO-] noted C. We then determine the reaction rate and activation energy. We show that C thermal formation can occurs in the 50-70 K temperature range of a protostellar environment. Secondly, we report that a VUV photolysis of a pure C sample produces a glycine salt, methylammonium glycinate [ CH{3}NH{3}+] [ NH{2}CH{2}COO-] noted G. We propose a scenario explaining how C and subsequently G can be synthesized in interstellar ices and precometary grains. Conclusions: [ CH{3}NH{3}+] [ CH{3}NHCOO-] could be readily formed and would act as a glycine salt precursor in protostellar environments dominated by thermal and UV processing. We propose a new pathway leading to a glycine salt, which is consistent with the detection of glycine and methylamine within the returned samples of comet 81P/Wild 2 from the Stardust mission.

  7. A protostellar jet model for the water masers in W49N

    NASA Technical Reports Server (NTRS)

    Low, Mordecai-Mark Mac; Elitzur, Moshe; Stone, James M.; Konigl, Arieh

    1994-01-01

    Observations by Gwinn, Moran, & Reid of the proper motions of water masers in W49N show that they have elongated distribution expanding from a common center. Features with high space velocity only occur far from the center, while low-velocity features occur at all distances. We propose that these observations can be interpreted in terms of a shell of shocked molecular gas that is driven by the expanding cocoon of a high-velocity protostellar jet. We present three-dimensional numerical simulations in support of this interpretation and argue that this source provides a unique oppurtunity for a detailed study of jet-driven cocoons.

  8. Search for massive protostellar candidates in the southern hemisphere. I. Association with dense gas

    NASA Astrophysics Data System (ADS)

    Fontani, F.; Beltrán, M. T.; Brand, J.; Cesaroni, R.; Testi, L.; Molinari, S.; Walmsley, C. M.

    2005-03-01

    We have observed two rotational transitions of both CS and C17O, and the 1.2 mm continuum emission towards a sample of 130 high-mass protostellar candidates with δ < -30°. This work represents the first step of the extension to the southern hemisphere of a project started more than a decade ago aimed at the identification of massive protostellar candidates. Following the same approach adopted for sources with δ ≥ -30°, we have selected from the IRAS Point Source Catalogue 429 sources which potentially are compact molecular clouds on the basis of their IR colours. The sample has then been divided into two groups according to the colour indices [25 12] and [60 12]: the 298 sources with [25 12] ≥ 0.57 and [60 12] ≥ 1.30 have been called High sources, the remaining 131 have been called Low sources. In this paper, we check the association with dense gas and dust in 130 Low sources. We have obtained a detection rate of ~85% in CS, demonstrating a tight association of the sources with dense molecular clumps. Among the sources detected in CS, ~76% have also been detected in C17O and ~93% in the 1.2 mm continuum. Millimeter-continuum maps show the presence of clumps with diameters in the range 0.2-2 pc and masses from a few M⊙ to 105 M⊙; H2 volume densities computed from CS line ratios lie between ~104.5 and 105.5 cm-3. The bolometric luminosities of the sources, derived from IRAS data, are in the range 103-106 L⊙, consistent with embedded high-mass objects. Based on our results and those found in the literature for other samples of high-mass young stellar objects, we conclude that our sources are massive objects in a very early evolutionary stage, probably prior to the formation of an Hii region. We propose a scenario in which High and Low sources are both made of a massive clump hosting a high-mass protostellar candidate and a nearby stellar cluster. The difference might be due to the fact that the 12 μm IRAS flux, the best discriminant between the two

  9. Where a Neutron Star's Accretion Disk Ends

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    In X-ray binaries that consist of a neutron star and a companion star, gas funnels from the companion into an accretion disk surrounding the neutron star, spiraling around until it is eventually accreted. How do the powerful magnetic fields threading through the neutron star affect this accretion disk? Recent observations provide evidence that they may push the accretion disk away from the neutron stars surface.Truncated DisksTheoretical models have indicated that neutron star accretion disks may not extend all the way in to the surface of a neutron star, but may instead be truncated at a distance. This prediction has been difficult to test observationally, however, due to the challenge of measuring the location of the inner disk edge in neutron-star X-ray binaries.In a new study, however, a team of scientists led by Ashley King (Einstein Fellow at Stanford University) has managed to measure the location of the inner edge of the disk in Aquila X-1, a neutron-star X-ray binary located 17,000 light-years away.Iron line feature detected by Swift (red) and NuSTAR (black). The symmetry of the line is one of the indicators that the disk is located far from the neutron star; if the inner regions of the disk were close to the neutron star, severe relativistic effects would skew the line to be asymmetric. [King et al. 2016]Measurements from ReflectionsKing and collaborators used observations made by NuSTAR and Swift/XRT both X-ray space observatories of Aquila X-1 during the peak of an X-ray outburst. By observing the reflection of Aquila X-1s emission off of the inner regions of the accretion disk, the authors were able to estimate the location of the inner edge of the disk.The authors find that this inner edge sits at ~15 gravitational radii. Since the neutron stars surface is at ~5 gravitational radii, this means that the accretion disk is truncated far from the stars surface. In spite of this truncation, material still manages to cross the gap and accrete onto the

  10. 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

  11. Warm Disks from Giant Impacts

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    mass ejected from colliding protoplanets is typically around 0.4 Earth masses. This mass is ejected in the form of fragments that then spread into the terrestrial planet region around the star. The fragments undergo cascading collisions as they orbit, forming an infrared-emitting debris disk at ~1 AU from the star.The authors then calculate the infrared flux profile expected from these simulated disks. They show that the warm disks can exist and radiate for up to ~100 Myr before the fragments are smashed into micrometer-sized pieces small enough to be blown out of the solar system by radiation pressure.The Spitzer Space Telescope has, thus far, observed tens of warm-debris-disk signatures roughly consistent with the authors predictions, primarily located at roughly 1 AU around stars with ages of 10100 Myr. This region is near the habitable zone of these stars, which makes it especially interesting that these systems may currently be undergoing a giant impact stage perhaps on the way to forming terrestrial planets.CitationH. Genda et al 2015 ApJ 810 136. doi:10.1088/0004-637X/810/2/136

  12. ALIGNMENT BETWEEN FLATTENED PROTOSTELLAR INFALL ENVELOPES AND AMBIENT MAGNETIC FIELDS

    SciTech Connect

    Chapman, Nicholas L.; Matthews, Tristan G.; Novak, Giles; Davidson, Jacqueline A.; Goldsmith, Paul F.; Houde, Martin; Kwon, Woojin; Looney, Leslie W.; Li Zhiyun; Matthews, Brenda; Peng Ruisheng; Vaillancourt, John E.; Volgenau, Nikolaus H.

    2013-06-20

    We present 350 {mu}m polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 {mu}m polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15 Degree-Sign ). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.

  13. CHASING DISK DISPERSAL INDICATORS: THE ORIGIN OF THE [OI] LOW-VELOCITY COMPONENT FROM YOUNG STELLAR OBJECTS

    NASA Astrophysics Data System (ADS)

    Rigliaco, Elisabetta; Pascucci, I.; Gorti, U.; Edwards, S.; Hollenbach, D. J.

    2014-01-01

    The formation time, masses, and location of planets are strongly impacted by the physical mechanisms that disperse protoplanetary disks and the timescale over which protoplanetary material is cleared out. Accretion of matter onto the central star, protostellar winds/jets, magnetic disk winds, and photoevaporative winds operate concurrently. Hence, disentangling their relative contribution to disk dispersal requires identifying diagnostics that trace different star-disk environments. Here, I will discuss the analysis the low velocity component (LVC) of the Oxygen optical forbidden lines, which is found to be blueshifted by a few km/s with respect to the stellar velocity. We find that the [OI] LVC profiles are different from those of other lines tracing disk and photoevaporative winds ([NeII] at 12.81μm and CO at 4.7μm), pointing to different origins for these gas lines. The analysis of the [OI] LVC, and the comparison with the stellar properties favor an origin of the [OI] LVC in a region where OH is photodissociated by stellar FUV photons and argue against thermal emission from an X-ray-heated layer. Detailed modeling of two spectra with the highest S/N and resolution shows that there are two components within the LVC: a broad, centrally peaked component that can be attributed to gas arising in a warm disk surface in Keplerian rotation, and a narrow component that may arise in a cool (<1,000 K) molecular wind.

  14. Hydrodynamic Stability and Magnetic Reconnection in Disks and Stars

    NASA Technical Reports Server (NTRS)

    Goodman, Jeremy; Kulsrud, Russell

    1999-01-01

    edges of disks in close binaries [2], and it may be important in disks of very low ionization such as protostellar disks, or even cataclysmic-variable disks in quiescence where the MHD mechanism may be ineffective [5]. All analyses up to 1996 were done in a local approximation where the orbital frequency, shear rate, and tidal field were treated as constants. The locally computed growth rate turns out to depend strongly on radius, and it was unclear how to average these local rates to obtain the correct global rate. This is a critical issue for accretion disks in close binaries, because the local growth rate is comparable to the orbital frequency towards the outer edge of the disk but decreases rapidly inwards. Paper #1 examined this issue in a simplified global model where the destabilizing terms vary with position. We found that the global growth rate is essentially equal to the maximum local rate, provided that the latter is smoothed over a radial range equal to the distance that the destabilized wave propagates at its group speed in one growth time. Thus, in an accretion disk, waves would grow rapidly in the outer parts but would propagate both inwards and outwards at a maximum group speed of order the disk thickness divided by the orbital period.

  15. VizieR Online Data Catalog: Wind-driving protostellar accretion discs (Salmeron+, 2011)

    NASA Astrophysics Data System (ADS)

    Salmeron, R.; Konigl, A.; Wardle, M.

    2011-10-01

    We continue our study of weakly ionized protostellar accretion discs that are threaded by a large-scale magnetic field and power a centrifugally driven wind. It has been argued that there is already evidence in several protostellar systems that such a wind transports a significant fraction of the angular momentum from at least some part of the disc. We model this situation by considering a radially localized disc model in which the matter is everywhere well coupled to the field and the wind is the main repository of excess angular momentum. We consider stationary configurations in which magnetic diffusivity counters the shearing and advection of the magnetic field lines. In Wardle & Koenigl (1997, ASP Conf. Ser., 121, 561) we analysed the disc structure in the hydrostatic approximation (vertical motions neglected inside the disc) and presented exact disc/wind solutions for the ambipolar diffusivity regime. In Koenigl, Salmeron & Wardle (Paper I, 2010MNRAS.401..479K) we generalized the hydrostatic analysis to the Hall and Ohm diffusivity domains and used it to identify the disc parameter sub-regimes in which viable solutions with distinct physical properties can be expected to occur. In this paper we test the results of Paper I by deriving full numerical solutions (integrated through the sonic critical surface) of the disc equations in the Hall domain. (1 data file).

  16. Limits on the location of planetesimal formation in self-gravitating protostellar discs

    NASA Astrophysics Data System (ADS)

    Clarke, C. J.; Lodato, G.

    2009-09-01

    In this Letter, we show that if planetesimals form in spiral features in self-gravitating discs, as previously suggested by the idealized simulations of Rice et al., then in realistic protostellar discs, this process will be restricted to the outer regions of the disc (i.e. at radii in excess of several tens of au). This restriction relates to the requirement that dust has to be concentrated in spiral features on a time-scale that is less than the (roughly dynamical) lifetime of such features, and that such rapid accumulation requires spiral features whose fractional amplitude is not much less than unity. This in turn requires that the cooling time-scale of the gas is relatively short, which restricts the process to the outer disc. We point out that the efficient conversion of a large fraction of the primordial dust in the disc into planetesimals could rescue this material from the well-known problem of rapid inward migration at an approximate metre-size scale and that in principle the collisional evolution of these objects could help to resupply small dust to the protostellar disc. We also point out the possible implications of this scenario for the location of planetesimal belts inferred in debris discs around main sequence stars, but stress that further dynamical studies are required in order to establish whether the disc retains a memory of the initial site of planetesimal creation.

  17. Millimeter-sized grains in the protostellar envelopes: Where do they come from?

    NASA Astrophysics Data System (ADS)

    Wong, Yi Hang Valerie; Hirashita, Hiroyuki; Li, Zhi-Yun

    2016-08-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as 1010 cm-3, instead of the typical density 105 cm-3, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to ≳0.1 M⊙. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed in the inner parts of the star-forming regions and transported to the envelopes before a significant mass growth of the central object, and that they survive in the envelopes.

  18. Millimeter-sized grains in the protostellar envelopes: Where do they come from?

    NASA Astrophysics Data System (ADS)

    Wong, Yi Hang Valerie; Hirashita, Hiroyuki; Li, Zhi-Yun

    2016-06-01

    Grain growth during star formation affects the physical and chemical processes in the evolution of star-forming clouds. We investigate the origin of the millimeter (mm)-sized grains recently observed in Class I protostellar envelopes. We use the coagulation model developed in our previous paper and find that a hydrogen number density of as high as 1010 cm-3, instead of the typical density 105 cm-3, is necessary for the formation of mm-sized grains. Thus, we test a hypothesis that such large grains are transported to the envelope from the inner, denser parts, finding that gas drag by outflow efficiently "launches" the large grains as long as the central object has not grown to ≳0.1 M⊙. By investigating the shattering effect on the mm-sized grains, we ensure that the large grains are not significantly fragmented after being injected in the envelope. We conclude that the mm-sized grains observed in the protostellar envelopes are not formed in the envelopes but formed in the inner parts of the star-forming regions and transported to the envelopes before a significant mass growth of the central object, and that they survive in the envelopes.

  19. Far infrared observations of pre-protostellar sources in Lynds 183

    NASA Astrophysics Data System (ADS)

    Lehtinen, K.; Mattila, K.; Lemke, D.; Juvela, M.; Prusti, T.; Laureijs, R.

    2003-02-01

    Using ISOPHOT maps at 100 and 200 mu m and raster scans at 100, 120, 150 and 200 mu m we have detected four unresolved far-infrared sources in the high latitude molecular cloud L 183. Two of the sources are identified with 1.3 mm continuum sources found by Ward-Thompson et al. (\\cite{wthompson94}, \\cite{wthompson00}) and are located near the temperature minimum and the coincident column density maximum of dust distribution. For these two sources, the ISO observations have enabled us to derive temperatures ( ~ 8.3 K) and masses ( ~ 1.4 and 2.4 Msun). They are found to have masses greater than or comparable to their virial masses and are thus expected to undergo gravitational collapse. We classify them as pre-protostellar sources. The two new sources are good candidates for pre-protostellar sources or protostars within L 183. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

  20. TF41 Engine Fan Disk Seeded Fault Crack Propagation Test

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.

    2003-01-01

    Uncontained engine failures, although rare in occurrence, can have a catastrophic effect on aircraft performance and safety. Engine disk cracks can eventually lead to these type of failures. A number of techniques to detect engine disk cracks have been developed in recent years. However, these technologies have only been validated by disk spin pit tests, not actual engine tests. Due to this, a project was established to perform seeded fault engine tests on a TF41 engine disk fan. A defect was machined in the first stage fan disk of a TF41 engine. The disk was run in a spin pit to initiate a crack. Once initiated, the disk was run in an actual engine test facility. The engine was cycled by a number of start and stops with the goal of propagating the crack to disk burst through low cycle fatigue. Various crack detection techniques were installed on the engine and run real-time during the test to validate their abilities to detect disk cracks. These techniques were based on methods such as change in mass imbalance using vibration or shaft displacement, change in blade position, acoustic emission, and torsional resonance. At the completion of 4474 test cycles, the crack in the TF41 disk was determined to have grown approximately 0.025 inches. This was far less the predicted crack growth based on a fracture mechanics analysis and finite element stress analysis.

  1. Instability and transition in rotating disk flow

    NASA Technical Reports Server (NTRS)

    Malik, M. R.

    1981-01-01

    The stability of three dimensional rotating disk flow and the effects of Coriolis forces and streamline curvature were investigated. It was shown that this analysis gives better growth rates than Orr-Sommerfeld equation. Results support the numerical prediction that the number of stationary vortices varies directly with the Reynolds number.

  2. Gas in Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Roberge, Aki

    2008-01-01

    Gas makes up the bulk of the mass in a protoplanetary disk, but it is much more difficult to observe than the smaller dust component. The l ifetime of gas in a disk has far-reaching consequences. including lim iting the time available for giant planet formation and controlling t he migration of planetary bodies of all sizes, from Jupiters to meter-sized planetesimals. Here I will discuss what is known about the gas component of protoplanetary disks, highlighting recent results from i nfrared studies with the Spitzer Space Telescope. Exciting upcoming o pportunities for gas studies will also be discussed. In particular, the first large far-IR survey of gas tracers from young disks will be p erformed using the Herschel Space Observatory, as part of the "Gas in Protoplanetary Systems" (GASPS) Open Time Key Project.

  3. Gas in Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Roberge, Aki

    2008-01-01

    Gas makes up the bulk of the mass in a protoplanetary disk, but it is much more difficult to observe than the smaller dust component. The lifetime of gas in a disk has far-reaching consequences, including limiting the time available for giant planet formation and controlling the migration of planetary bodies of all sizes, from Jupiters to meter-sized planetesimals. Here I will discuss what is known about the gas component of protoplanetary disks, highlighting recent results from infrared studies with the Spitzer Space Telescope. Exciting upcoming opportunities for gas studies will also be discussed. In particular, the first large far-IR survey of gas tracers from young disks will be performed using the Herschel Space Observatory, as part of the 'Gas in Protoplanetary Systems' (GASPS) Open Time Key Project.

  4. Organizing Your Hard Disk.

    ERIC Educational Resources Information Center

    Stocker, H. Robert; Hilton, Thomas S. E.

    1991-01-01

    Suggests strategies that make hard disk organization easy and efficient, such as making, changing, and removing directories; grouping files by subject; naming files effectively; backing up efficiently; and using PATH. (JOW)

  5. STIS Observations of the Disk and Outflow of the Herbig Ae Star HD163296

    NASA Technical Reports Server (NTRS)

    Kimble, Randy; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    Coronagraphic imaging with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope reveals a approx. 450 AU radius circumstellar disk around the Herbig Ae star HDI63296. The disk includes an annulus of reduced scattering at 325 AU and exhibits a flat trend of surface brightness in to 180-222 AU, consistent with a cleared central zone. The disk is accompanied by a chain of nebulosities ("knots") oriented roughly perpendicular to the disk. Followup spectroscopy in the visible and the far ultraviolet confirms the Herbig-Haro nature of the observed knots. The FUV data in particular reveal the presence of a collimated, bipolar outflow, with a blue-shifted Lyman alpha jet that can be traced to within 0.06 arcseconds (7.3 AU) of HD163296 and a red-shifted Lyman alpha component that may be due to infall or to a poorly collimated wind. If the estimated age of this system is correct, these data indicate that protostellar outflows may last up to 10 times longer than previously believed.

  6. DIAGNOSING CIRCUMSTELLAR DEBRIS DISKS

    SciTech Connect

    Hahn, Joseph M.

    2010-08-20

    A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting {beta} Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of radiation pressure, which is the dominant perturbation on the disk's smaller but abundant dust grains. Solving the resulting system of rate equations then provides the dust abundances versus grain size and dust abundances over time. Those solutions also provide the dust grains' collisional lifetime versus grain size, and the debris disk's optical depth and surface brightness versus distance from the star. Comparison to observations then yields estimates of the unseen planetesimal disk's radius, and the rate at which the disk sheds mass due to planetesimal grinding. The model can also be used to measure or else constrain the dust grain's physical and optical properties, such as the dust grains' strength, their light-scattering asymmetry parameter, and the grains' efficiency of light scattering Q{sub s}. The model is then applied to optical observations of the edge-on dust disk orbiting {beta} Pictoris, and good agreement is achieved when the unseen planetesimal disk is broad, with 75 {approx}< r {approx}< 150 AU. If it is assumed that the dust grains are bright like Saturn's icy rings (Q{sub s} = 0.7), then the cross section of dust in the disk is A{sub d} {approx_equal} 2 x 10{sup 20} km{sup 2} and its mass is M{sub d} {approx_equal} 11 lunar masses. In this case, the planetesimal disk's dust-production rate is quite heavy, M-dot {sub d{approx}}9 M {sub +} Myr{sup -1}, implying that there is or was a substantial amount of planetesimal mass there, at least 110 Earth masses. If the dust grains are darker than assumed, then the planetesimal disk's mass-loss rate and its total mass are heavier. In fact, the apparent dearth

  7. Protostars and Disks

    NASA Technical Reports Server (NTRS)

    Ho, Paul

    1997-01-01

    The research concentrated on high angular resolution (arc-second scale) studies of molecular cloud cores associated with very young star formation. New ways to study disks and protoplanetary systems were explored. Findings from the areas studied are briefly summarized: (1) molecular clouds; (2) gravitational contraction; (3) jets, winds, and outflows; (4) Circumstellar Disks (5) Extrasolar Planetary Systems. A bibliography of publications and submitted papers produced during the grant period is included.

  8. An Extremely High Velocity Molecular Jet Surrounded by an Ionized Cavity in the Protostellar Source Serpens SMM1

    NASA Astrophysics Data System (ADS)

    Hull, Charles L. H.; Girart, Josep M.; Kristensen, Lars E.; Dunham, Michael M.; Rodríguez-Kamenetzky, Adriana; Carrasco-González, Carlos; Cortés, Paulo C.; Li, Zhi-Yun; Plambeck, Richard L.

    2016-06-01

    We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of a one-sided, high-velocity (∼80 km s‑1) CO(J = 2\\to 1) jet powered by the intermediate-mass protostellar source Serpens SMM1-a. The highly collimated molecular jet is flanked at the base by a wide-angle cavity; the walls of the cavity can be seen in both 4 cm free–free emission detected by the Very Large Array and 1.3 mm thermal dust emission detected by ALMA. This is the first time that ionization of an outflow cavity has been directly detected via free–free emission in a very young, embedded Class 0 protostellar source that is still powering a molecular jet. The cavity walls are ionized either by UV photons escaping from the accreting protostellar source or by the precessing molecular jet impacting the walls. These observations suggest that ionized outflow cavities may be common in Class 0 protostellar sources, shedding further light on the radiation, outflow, and jet environments in the youngest, most embedded forming stars.

  9. 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

  10. Disk Precession in Pleione

    NASA Astrophysics Data System (ADS)

    Hirata, R.

    2007-03-01

    From the polarimetric observation of Pleione, we found that the intrinsic polarization angle varied from 60° to 130° in 1974-2003. The Hα profile also changed dramatically from the edge-on type (shell-line profile) to the surface-on type (wine-bottle profile). These facts clearly indicate the spatial motion of the disk axis. We interpret these variations in terms of the disk precession, caused by the secondary of this spectroscopic binary with a period of 218d. We performed the χ^2 minimization for the polarization angle, assuming uniform precession with an imposed condition that the shell maximum occurred at edge-on view. The resulting precession angle is 59° with a period of 81 years. Then, we can describe chronologically the spatial motion of disk axis. We also derived the Hα disk radius from the peak separation, assuming the Keplerian disk. The precession of the disk gives natural explanation of the mysterious long-term spectroscopic behaviors of this star.

  11. Young Planetary disks

    NASA Astrophysics Data System (ADS)

    Lecavelier Des Etangs, A.

    2007-07-01

    The present review focuses on UV observations of young planetary disks and consequently mostly on the gaseous content of those disks. Few examples are taken to illustrate the capability of the UV observatories to scrutinize in detail the gas content of low density circumstellar disks if they are seen edge-on or nearly edge-on. For instance, in the case of HD100546, FUSE observations re- vealed signatures of outflow and infall in the disk caused by interaction of the stellar magnetosphere with the circumstellar disk. Observations of numerous absorption lines from H2 around young stars give constrains on the gas temper- ature and density, and physical size of the absorbing layer. In the case of T-Tauri stars and one brown dwarf, emissions from exited H2 have been detected. In the case of Beta Pictoris, the observation of CO in the UV and search for H2 with FUSE demonstrated that the evaporation of frozen bodies like comets must produce the CO seen in the disk. Extensive observations of spectral variability of Beta Pictoris are now interpreted by extrasolar comets evaporating in the vicinity of the central star of this young planetary system.

  12. Chemistry in disks. X. The molecular content of protoplanetary disks in Taurus

    NASA Astrophysics Data System (ADS)

    Guilloteau, S.; Reboussin, L.; Dutrey, A.; Chapillon, E.; Wakelam, V.; Piétu, V.; Di Folco, E.; Semenov, D.; Henning, Th.

    2016-08-01

    Aims: We attempt to determine the molecular composition of disks around young low-mass stars. Methods: We used the IRAM 30 m radio telescope to perform a sensitive wideband survey of 30 stars in the Taurus Auriga region known to be surrounded by gaseous circumstellar disks. We simultaneously observed HCO+(3-2), HCN(3-2), C2H(3-2), CS(5-4), and two transitions of SO. We combined the results with a previous survey that observed 13CO (2-1), CN(2-1), two o-H2CO lines, and another transition of SO. We used available interferometric data to derive excitation temperatures of CN and C2H in several sources. We determined characteristic sizes of the gas disks and column densities of all molecules using a parametric power-law disk model. Our study is mostly sensitive to molecules at 200-400 au from the stars. We compared the derived column densities to the predictions of an extensive gas-grain chemical disk model under conditions representative of T Tauri disks. Results: This survey provides 20 new detections of HCO+ in disks, 18 in HCN, 11 in C2H, 8 in CS, and 4 in SO. HCO+ is detected in almost all sources and its J = 3-2 line is essentially optically thick, providing good estimates of the disk radii. The other transitions are (at least partially) optically thin. Large variations of the column density ratios are observed, but do not correlate with any specific property of the star or disk. Disks around Herbig Ae stars appear less rich in molecules than those around T Tauri stars, although the sample remains small. SO is only found in the (presumably younger) embedded objects, perhaps reflecting an evolution of the S chemistry due to increasing depletion with time. Overall, the molecular column densities, and in particular the CN/HCN and CN/C2H ratios, are well reproduced by gas-grain chemistry in cold disks. Conclusions: This study provides a comprehensive census of simple molecules in disks of radii >200-300 au. Extending that to smaller disks, or searching for less

  13. Evolution and precession of accretion disk in tidal disruption events

    NASA Astrophysics Data System (ADS)

    Shen, R.-F.; Matzner, C. D.

    2012-12-01

    In a supermassive black hole (BH) tidal disruption event (TDE), the tidally disrupted star feeds the BH via an accretion disk. Most often it is assumed that the accretion rate history, hence the emission light curve, tracks the rate at which new debris mass falls back onto the disk, notably the t-5/3 power law. But this is not the case when the disk evolution due to viscous spreading - the driving force for accretion - is carefully considered. We construct a simple analytical model that comprehensively describes the accretion rate history across 4 different phases of the disk evolution, in the presence of mass fallback and disk wind loss. Accretion rate evolves differently in those phases which are governed by how the disk heat energy is carried away, early on by advection and later by radiation. The accretion rate can decline as steeply as t-5/3 only if copious disk wind loss is present during the early advection-cooled phase. Later, the accretion rate history is t-8/7 or shallower. These have great implications on the TDE flare light curve. A TDE accretion disk is most likely misaligned with the equatorial plane of the spinning BH. Moreover, in the TDE the accretion rate is super- or near-Eddington thus the disk is geometrically thick, for which case the BH's frame dragging effect may cause the disk precess as a solid body, which may manifest itself as quasi-periodic signal in the TDE light curve. Our disk evolution model predicts the disk precession period increases with time, typically as ∝ t. The results are applied to the recently jetted TDE flare Swift transient J1644 + 57 which shows numerous, quasi-periodic dips in its long-term X-ray light curve. As the current TDE sample increases, the identification of the disk precession signature provides a unique way of measuring BH spin and studying BH accretion physics.

  14. Fast, Capacious Disk Memory Device

    NASA Technical Reports Server (NTRS)

    Muller, Ronald M.

    1990-01-01

    Device for recording digital data on, and playing back data from, memory disks has high recording or playback rate and utilizes available recording area more fully. Two disks, each with own reading/writing head, used to record data at same time. Head on disk A operates on one of tracks numbered from outside in; head on disk B operates on track of same number in sequence from inside out. Underlying concept of device applicable to magnetic or optical disks.

  15. High Temperature Spin Testing of a Superalloy Disk With a Dual Grain Structure

    NASA Technical Reports Server (NTRS)

    Gayda, John; Kantzos, Pete

    2002-01-01

    Comparative spin tests were run on superalloy disks at an elevated temperature to determine the benefits of a DMHT disk, with a fine grain bore and coarse grain rim, versus a traditional subsolvus disk with a fine grain structure in the bore and rim. The results of these tests showed that the DMHT disk exhibited significantly lower growth at 1500 F. Further, the results of these tests could be accurately predicted using a 2D viscoelastic finite element analysis. These results indicate DMHT technology can be used to extend disk operating temperatures when compared to traditional subsolvus heat treatment options for superalloy disks. However, additional research is required to ensure the safe operation of a DMHT disk under more realistic engine operating conditions. This includes testing to determine the burst margin and cyclic capability of DMHT disks in a spin pit, at a minimum, and ultimately running an engine test with a DMHT disk.

  16. SHADOWS CAST BY A WARP IN THE HD 142527 PROTOPLANETARY DISK

    SciTech Connect

    Marino, S.; Perez, S.; Casassus, S.

    2015-01-10

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in the H band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70° ± 5°. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.

  17. Shadows Cast by a Warp in the HD 142527 Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Marino, S.; Perez, S.; Casassus, S.

    2015-01-01

    Detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. One such feature is the two intensity nulls seen along the outer disk of the HD 142527 system, which are particularly well traced in polarized differential imaging. Here we propose that these are shadows cast by the inner disk. The inner and outer disk are thick, in terms of the unit-opacity surface in the H band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. Radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70° ± 5°. This finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions.

  18. Depletion of chlorine into HCl ice in a protostellar core. The CHESS spectral survey of OMC-2 FIR 4

    NASA Astrophysics Data System (ADS)

    Kama, M.; Caux, E.; López-Sepulcre, A.; Wakelam, V.; Dominik, C.; Ceccarelli, C.; Lanza, M.; Lique, F.; Ochsendorf, B. B.; Lis, D. C.; Caballero, R. N.; Tielens, A. G. G. M.

    2015-02-01

    Context. The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances <10-5 has not yet been well studied. Aims: Our aim here is to study the depletion of chlorine in the protostellar core, OMC-2 FIR 4. Methods: We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H2 hyperfine collisional excitation rate coefficients. Results: A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9 × 10-11, a factor of only 10-3 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous foreground cloud, where we find no depletion of volatile chlorine. Conclusions: Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores. Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the dark cloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage. About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with an abundance of ≲10-10 in most of the protostellar core. We find the [35Cl]/[37Cl] ratio in OMC-2 FIR 4 to be 3.2 ± 0.1, consistent with the solar system value. Appendices are available in electronic form at http://www.aanda.org

  19. Drag reduction of a hairy disk

    NASA Astrophysics Data System (ADS)

    Niu, Jun; Hu, David L.

    2011-10-01

    We investigate experimentally the hydrodynamics of a hairy disk immersed in a two-dimensional flowing soap film. Drag force is measured as a function of hair length, density, and coating area. An optimum combination of these parameters yields a drag reduction of 17%, which confirms previous numerical predictions (15%). Flow visualization indicates the primary mechanism for drag reduction is the bending, adhesion, and reinforcement of hairs trailing the disk, which reduces wake width and traps "dead water." Thus, the use of hairy coatings can substantially reduce an object's drag while negligibly increasing its weight.

  20. 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.

  1. Simulations of accretion disks in pseudo-complex General Relativity

    NASA Astrophysics Data System (ADS)

    Hess, P. O.; Algalán B., M.; Schönenbach, T.; Greiner, W.

    2015-11-01

    After a summary on pseudo-complex General Relativity (pc-GR), circular orbits and stable orbits in general are discussed, including predictions compared to observations. Using a modified version of a model for accretions disks, presented by Page and Thorne in 1974, we apply the raytracing technique in order to simulate the appearance of an accretion disk as it should be observed in a detector. In pc-GR we predict a dark ring near a very massive, rapidly rotating object.

  2. Water in high-mass pre- and proto-stellar cores from Hi-GAL

    NASA Astrophysics Data System (ADS)

    Persson, Carina M.; Olmi, Luca; Codella, Claudio

    2015-08-01

    As a part of our on-going investigation of the earliest phases of massive star formation, we present Herschel-HIFI data of H2O, NH3 and N2H+ towards a sample of high-mass starless cores and proto-stellar objects in two galactic fields, each containing objects in different evolutionary stages. We observed 17 sources in the l = 30° galactic field, and 35 sources in the l = 59° field. The clumps in the l = 59°region have lower luminosity and mass than the l = 30° objects. We find that the sources with detections have much higher mean luminosities than compared to the sources with no detection of any line, but the mean masses are similar. Most sources with detections are proto-stellar, and at least two of the detected sources in the l = 59° region are in a more advanced stage of evolution. For the l = 30° sources no preferential evolutionary phase is evident. None of these sources, however, appear to belong to the late phase of envelope dispersal.The detections show complex line shapes from the protostellar envelopes, molecular outflows and infall. All detections in the l = 59° field show similar water line profiles with broad outflows, whereas towards l = 30° no outflows are detected and all sources display very different line shapes. Both water and ammonia are also often self-absorbed, sometimes saturated, and some sources show an inverse or a regular P-Cygni line profile. N2H+ do not exhibit line asymmetries or absorption. The integrated intensities of the three lines are correlated, and we also find correlations between the water line luminosity and continuum temperature. The typical water luminosity towards the l = 30° sources is lower than compared to l = 59° sources, but their continuum temperature is higher, which may suggest a later evolutionary stage.In the sight-lines towards 11 sources in the l = 30° field, among which four have no detections in the star-forming regions, we also detect H2O and NH3 in absorption from interstellar gas. Since

  3. DEUTERIUM FRACTIONATION AS AN EVOLUTIONARY PROBE IN MASSIVE PROTOSTELLAR/CLUSTER CORES

    SciTech Connect

    Chen, Huei-Ru; Wang, Mei-Yan; Liu, Sheng-Yuan; Su, Yu-Nung

    2011-12-20

    Clouds of high infrared extinction are promising sites of massive star/cluster formation. A large number of cloud cores discovered in recent years allow for the investigation of a possible evolutionary sequence among cores in early phases. We have conducted a survey of deuterium fractionation toward 15 dense cores in various evolutionary stages, from high-mass starless cores to ultracompact H II regions, in the massive star-forming clouds of high extinction, G34.43+0.24, IRAS 18151-1208, and IRAS 18223-1243, with the Submillimeter Telescope. Spectra of N{sub 2}H{sup +} (3-2), N{sub 2}D{sup +} (3-2), and C{sup 18}O (2-1) were observed to derive the deuterium fractionation of N{sub 2}H{sup +}, D{sub frac} {identical_to} N(N{sub 2}D{sup +})/N(N{sub 2}H{sup +}), as well as the CO depletion factor for every selected core. Our results show a decreasing trend in D{sub frac} with both gas temperature and line width. Since colder and quiescent gas is likely to be associated with less evolved cores, larger D{sub frac} appears to correlate with early phases of core evolution. Such decreasing trend resembles the behavior of D{sub frac} in the low-mass protostellar cores and is consistent with several earlier studies in high-mass protostellar cores. We also find a moderate increasing trend of D{sub frac} with the CO depletion factor, suggesting that sublimation of ice mantles alters the competition in the chemical reactions and reduces D{sub frac}. Our findings suggest a general chemical behavior of deuterated species in both low- and high-mass protostellar candidates at early stages. In addition, upper limits to the ionization degree are estimated to be within 2 Multiplication-Sign 10{sup -7} and 5 Multiplication-Sign 10{sup -6}. The four quiescent cores have marginal field-neutral coupling and perhaps favor turbulent cooling flows.

  4. New Detection of an Extremely Blue-shift Dominated Jet in G353.273+0.641: A Possible Disk-Jet System on 100 AU Scale

    NASA Astrophysics Data System (ADS)

    Motogi, K.; Fujisawa, K.; Sugiyama, K.; Niinuma, K.; Sorai, K.; Honma, M.; Hirota, T.; Yonekura, Y.; Hachisuka, K.; Walsh, A. J.

    2013-10-01

    We report a new detection of an unusual molecular jet from a high mass protostellar object G353.273+0.641 using the NRO 45m telescope. Newly detected SiO (υ = 0, J = 2-1) jet shows highly blue-shift dominated spectrum similar to the associated 22 GHz maser emission. The remarkable blue-shift dominance in both of the maser and SiO emission can be caused by a compact (< 170 AU) and optically thick face-on disk, masking the red-shifted part of the jet.

  5. Life and reliability of rotating disks

    NASA Technical Reports Server (NTRS)

    Zaretsky, Erwin V.; Smith, Todd E.; August, Richard

    1988-01-01

    In aerospace applications, an engineer must be especially cognizant of size and weight constraints which affect design decisions. Although designing at or below the material fatigue limit may be desirable in most industrial applications, in aerospace application it is almost mandatory to design certain components for a finite life at an acceptable probability of survival. Zaretsky outlined such a methodology based in part on the work of W. Weibull (1939, 1951) and G. Lundberg and A. Palmgren (1947a, 1947b, 1952). It is the objective of this work to apply the method of Zaretsky (1987) to statistically predict the life of a generic solid disk with and without bolt holes; determine the effect of disk design variables, thermal loads, and speed on relative life; and develop a generalized equation for determining disk life by incorporating only these variables.

  6. Photoprocesses in protoplanetary disks.

    PubMed

    van Dishoeck, Ewine F; Jonkheid, Bastiaan; van Hemert, Marc C

    2006-01-01

    Circumstellar disks are exposed to intense ultraviolet (UV) radiation from the young star. In the inner disks, the UV radiation can be enhanced by more than seven orders of magnitude compared with the average interstellar radiation field, resulting in a physical and chemical structure that resembles that of a dense photon-dominated region (PDR). This intense UV field affects the chemistry, the vertical structure of the disk, and the gas temperature, especially in the surface layers. The parameters which make disks different from more traditional PDRs are discussed, including the shape of the UV radiation field, grain growth, the absence of PAHs, the gas/dust ratio and the presence of inner holes. Illustrative infrared spectra from the Spitzer Space Telescope are shown. New photodissociation cross sections for selected species, including simple ions, are presented. Also, a summary of cross sections at the Lyman alpha 1216 A line, known to be strong for some T Tauri stars, is made. Photodissociation and ionization rates are computed for different radiation fields with color temperatures ranging from 30000 to 4000 K and grain sizes up to a few microm. The importance of a proper treatment of the photoprocesses is illustrated for the transitional disk toward HD 141569A which includes grain growth. PMID:17191450

  7. PLANETESIMAL DISK MICROLENSING

    SciTech Connect

    Heng, Kevin; Keeton, Charles R. E-mail: keeton@physics.rutgers.ed

    2009-12-10

    Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

  8. The Chemistry of Nearby Disks

    NASA Astrophysics Data System (ADS)

    Öberg, Karin I.

    2016-01-01

    The gas and dust rich disks around young stars are the formation sites of planets. Observations of molecular trace species have great potential as probes of the disk structures and volatile compositions that together regulate planet formation. The disk around young star TW Hya has become a template for disk molecular studies due to a combination of proximity, a simple face-on geometry and richness in volatiles. It is unclear, however, how typical the chemistry of the TW disk is. In this proceeding, we review lessons learnt from exploring the TW Hya disk chemistry, focusing on the CO snowline, and on deuterium fractionation chemistry. We compare these results with new ALMA observations toward more distant, younger disks. We find that while all disks have some chemical structures in common, there are also substantial differences between the disks, which may be due to different initial conditions, structural or chemical evolutionary stages, or a combination of all three.

  9. Reprocessing of ices in turbulent protoplanetary disks: Carbon and nitrogen chemistry

    SciTech Connect

    Furuya, Kenji; Aikawa, Yuri

    2014-08-01

    We study the influence of the turbulent transport on ice chemistry in protoplanetary disks, focusing on carbon- and nitrogen-bearing molecules. Chemical rate equations are solved with the diffusion term, mimicking the turbulent mixing in the vertical direction. Turbulence can bring ice-coated dust grains from the midplane to the warm irradiated disk surface, and the ice mantles are reprocessed by photoreactions, thermal desorption, and surface reactions. The upward transport decreases the abundance of methanol and ammonia ices at r ≲ 30 AU because warm dust temperature prohibits their reformation on grain surfaces. This reprocessing could explain the smaller abundances of carbon and nitrogen bearing molecules in cometary coma than those in low-mass protostellar envelopes. We also show the effect of mixing on the synthesis of complex organic molecules (COMs) in two ways: (1) transport of ices from the midplane to the disk surface and (2) transport of atomic hydrogen from the surface to the midplane. The former enhances the COMs formation in the disk surface, while the latter suppresses it in the midplane. Then, when mixing is strong, COMs are predominantly formed in the disk surface, while their parent molecules are (re)formed in the midplane. This cycle expands the COMs distribution both vertically and radially outward compared with that in the non-turbulent model. We derive the timescale of the sink mechanism by which CO and N{sub 2} are converted to less volatile molecules to be depleted from the gas phase and find that the vertical mixing suppresses this mechanism in the inner disks.

  10. The FU Orionis Outburst as a Thermal Disk Accretion Event: Detailed Calculations and Comparison to Observations

    NASA Technical Reports Server (NTRS)

    Bell, K. R.

    1994-01-01

    FU Orionis outbursts are temporary large increases in luminosity: x(40-250) thought to occur repeatedly in all low mass young stellar systems. We discuss detailed calculations of viscous accretion disks suggesting that FU Ori events signify the existence of a protostellar disk transporting mass at a rate of (1-10) x 10(exp -6) Solar Mass/yr, in agreement with theoretical and observational estimates of molecular cloud core collapse rates. Accretion through the inner edge of disks subject to outburst is self-regulated through the thermal ionization instability such that long periods (approximately 1000 yrs) of low mass flux: (1-10) x 10(exp -8) Solar Mass/yr, are punctuated by short periods (approximately 100 yrs) of high mass flux: (1-10) x 10(exp -5) Solar Mass/yr. The unstable region of the disk extends radially only to a distance of approximately 1/4 AU. Beyond this region matter is transported stably at the infall rate. In systems for which M = 1 Solar Mass, with an inner disk edge of 3 Solar Radius, the critical rate for outbursts is 5 x 10(exp -7) Solar Mass/yr independent of the magnitude of the viscous alpha parameter consistent with estimates of boundary layer mass flux in T Tauri stars. We use timescales of observed outbursts to constrain the magnitude of the alpha parameter to be 10(exp -4) where hydrogen is neutral and 10(exp -3) where ionized. Light curves of V1515 Cyg, FU Ori, and V1057 Cyg are reproduced; the latter two require application of a small perturbation in surface density to produce observed rapid rise times. Detailed reply is made to objections to the accretion disk model for outbursts. Comparison to observations are made of time dependent spectral energy distributions, colors, and line-width velocity evolution.

  11. The FU Orionis Outburst as a Thermal Disk Accretion Event: Detailed Calculations and Comparison to Observations

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Cuzzi, Jeff (Technical Monitor)

    1994-01-01

    FU Orionis outbursts are temporary large increases in luminosity: x (40 - 250) thought to occur repeatedly in all low mass young stellar systems. We discuss detailed calculations of viscous accretion disks suggesting that FU Ori events signify the existence of a protostellar disk transporting mass at a rate of (1 - 10) x 10(exp 6) solar mass / yr, in agreement with theoretical and observational estimates of molecular cloud core collapse rates. Accretion through the inner edge of disks subject to outburst is self-regulated through the thermal ionization instability such that long periods (approx. 1000 yrs) of low mass flux: (1 - 10) x 10(exp -5) solar mass / yr, are punctuated by short periods (approx. 100 yrs) of high mass flux: (1-10) x 10(exp -5) solar mass / yr. The unstable region of the disk extends radially only to a distance of approx. = 1/4 AU. Beyond this region matter is transported stably at the infall rate. In systems for which M(sum *) = 1 solar mass with an inner disk edge of 3 solar radius, the critical rate for outbursts is 5 x 10(exp -7) solar mass / yr independent of the magnitude of the viscous ce parameter consistent with estimates of boundary layer mass flux in T Tauri stars. We use timescales of observed outbursts to constrain the magnitude of the alpha parameter to be 10(exp -4) where hydrogen is neutral and 10(exp -3) where ionized. Light curves of V1515 Cyg, FU Ori, and V1057 Cya are reproduced; the latter two require application of a small perturbation in surface density to produce observed rapid rise times. Detailed reply is made to objections to the accretion disk model for outbursts. Comparison to observations are made of time dependent spectral energy distributions, colors, and line-width velocity evolution.

  12. Study of Scattered Light from Known Debris Disks

    NASA Technical Reports Server (NTRS)

    Rodriguez, Joseph E.; Weinberger, Alycia J.; Roberge, Aki

    2011-01-01

    Using the Spitzer Space Telescope, a group of edge on debris disks, surrounding main-sequence shell stars have been discovered in the infrared. These disks are of high interest because they not only have dust, but an observed amount of circumstellar gas. HD158352 was an ideal target to try and image the disk because it was one of the closest stars in this group. Using the Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS), we attempted to take a direct image of the light scattered from the known disk in a broad optical bandpass. Studying these particular type of disks in high detail will allow us to learn more about gas-dust interactions. In particular, this will allow us to learn how the circumstellar gas evolves during the planet-forming phase. Even though it was predicted that the disk should have a magnitude of 20.5 at 3", no disk was seen in any of the optical images. This suggests that the parameters used to predict the brightness of the disk are not what we first anticipated and adjustments to the model must be performed. We also present the blue visible light spectrum of the scattered light from the debris disk surrounding Beta Pictoris. We are analyzing archival observations taken by Heap, using Hubble Space Telescope's STIS instrument. A long slit with a bar was used to occult Beta Pictoris as well as the PSF star. This was done because it is necessary to subtract a PSF observed the same way at the target to detect the disk. It appears that we have detected light from the disk but the work was in progress at the time of the abstract deadline.

  13. How The Inner Disk Communicates to the Outer Disk

    NASA Astrophysics Data System (ADS)

    Goto, Miwa

    2009-08-01

    We investigated how evolution in the outer disk has an influence on the inner disk of a protoplanetary disk system. Thanks to two-layer models that give the theoretical platform of disk geometry, we now have a good handle on how dust evolves in outer protoplanetary disks (>10 AU). It has long been thought that the outer and inner disks dissipate on roughly the same time scale as sub-mm observations of nearby T Tauri systems has suggested. However, new high spatial resolution observations point toward the dissipation of an inner disk as not being a simple extension of the outer disk. We performed preliminary tests of the differential disk evolution in gas and dust in the inner disks of Herbig Ae/Be stars using the CO vibrational band as the gas probe. The line luminosity of CO v = 1-0 P(30) has a reasonable correlation with the near-infrared excess over the stellar photosphere. It guarantees that the CO vibration band is a secure probe of the inner disk, as is expected from its high critical density, high excitation temperature, and kinematics. On the other hand, the line luminosity of P(30) does not show a clear trend either with far-infrared color, near-infrared/far-infrared-color, or the type of the spectral energy distribution (SED) (I/II). The inner disks (<1 AU) of Herbig Ae/Be stars of our sample are influenced little by the geometry of the outer disks.

  14. THE SPHERICALIZATION OF DARK MATTER HALOS BY GALAXY DISKS

    SciTech Connect

    Kazantzidis, Stelios; Abadi, Mario G.; Navarro, Julio F. E-mail: mario@oac.uncor.ed

    2010-09-01

    Cosmological simulations indicate that cold dark matter (CDM) halos should be triaxial. Validating this theoretical prediction is, however, less than straightforward because the assembly of galaxies is expected to modify halo shapes and to render them more axisymmetric. We use a suite of N-body simulations to quantitatively investigate the effect of the growth of a central disk galaxy on the shape of triaxial dark matter halos. In most circumstances, the halo responds to the presence of the disk by becoming more spherical. The net effect depends weakly on the timescale of the disk assembly but noticeably on the orientation of the disk relative to the halo principal axes, and it is maximal when the disk symmetry axis is aligned with the major axis of the halo. The effect depends most sensitively on the overall gravitational importance of the disk. Our results indicate that exponential disks whose contribution peaks at less than {approx}50% of their circular velocity are unable to noticeably modify the shape of the gravitational potential of their surrounding halos. Many dwarf and low surface brightness galaxies are expected to be in this regime, and therefore their detailed kinematics could be used to probe halo triaxiality, one of the basic predictions of the CDM paradigm. We argue that the complex disk kinematics of the dwarf galaxy NGC 2976 might be the reflection of a triaxial halo. Such signatures of halo triaxiality should be common in galaxies where the luminous component is subdominant.

  15. Far-infrared image restoration analysis of the protostellar cluster in S140

    NASA Technical Reports Server (NTRS)

    Lester, D. F.; Harvey, P. M.; Joy, M.; Ellis, H. B., Jr.

    1986-01-01

    Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented.

  16. The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity

    NASA Astrophysics Data System (ADS)

    Lefloch, B.; Gusdorf, A.; Codella, C.; Eislöffel, J.; Neri, R.; Gómez-Ruiz, A. I.; Güsten, R.; Leurini, S.; Risacher, C.; Benedettini, M.

    2015-09-01

    Context. Protostellar outflows are a crucial ingredient of the star-formation process. However, the physical conditions in the warm outflowing gas are still poorly known. Aims: We present a multi-transition, high spectral resolution CO study of the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow and to constrain the physical conditions of the various components in order to understand the origin of the mass-loss phenomenon. Methods: We have observed the J = 12-11, J = 13-12, and J = 16-15 CO lines at high spectral resolution with SOFIA/GREAT and the J = 5-4, J = 9-8, and J = 14-13 CO lines with HIFI/Herschel towards the position of the terminal bowshock HH377 in the southern outflow lobe. These observations were complemented with maps of CO transitions obtained with the IRAM 30 m telescope (J = 1-0, 2-1), the Plateau de Bure interferometer (J = 2-1), and the James Clerk Maxwell Telescope (J = 3-2, 4-3). Results: We identify three main components in the protostellar outflow: the jet, the cavity, and the bowshock, with a typical size of 1.7″ × 21″, 4.5″, and 22″ × 10″, respectively. In the jet, the emission from the low-J CO lines is dominated by a gas layer at Tkin = 80-100 K, column density N(CO) = 9 × 1016 cm-2, and density n(H2) = (0.5-1) × 105 cm-3; the emission of the high-J CO lines arises from a warmer (Tkin = 400-750 K), denser (n(H2) = (0.5-1) × 106 cm-3), lower column density (N(CO) = 1.5 × 1016 cm-2) gas component. Similarly, in the outflow cavity, two components are detected: the emission of the low-J lines is dominated by a gas layer of column density N(CO) = 7 × 1017 cm-2 at Tkin = 55-85 K and density in the range (1-8) × 105 cm-3; the emission of the high-J lines is dominated by a hot, denser gas layer with Tkin = 500-1500K, n(H2) = (1-5) × 106 cm-3, and N(CO) = 6 × 1016 cm-2. A temperature gradient as a function of the velocity is found in the high-excitation gas

  17. The Pivotal Onset of Protostellar Collapse: ISO's View and Complementary Observations

    NASA Astrophysics Data System (ADS)

    Wiesemeyer, H.; Gusten, R.; Cox, P.; Zylka, R.; Wright, M. C. H.

    We present {sc iso} observations of cloud cores in a stage of early accretion onto a central hydrostatic object. In order to study this pivotal phase of the dynamical protostellar collapse, we performed mid-{sc ir} imaging using the {sc isocam} {sc lw} array, and far-{sc ir} photometry with the {sc isophot} {sc pht-p} and {sc pht-c} sub-instruments towards extreme Class 0} objects in globular filament GF 9 (L 1082). With {sc isocam}, we detected the central accreting objects. {sc isophot} allowed for the identification of an extremely cold (~10 K) core. Complementary spectroscopic and continuum studies at lambda1.3 mm and 3 mm remove part of the remaining ambiguities.

  18. Laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic field.

    PubMed

    Albertazzi, B; Ciardi, A; Nakatsutsumi, M; Vinci, T; Béard, J; Bonito, R; Billette, J; Borghesi, M; Burkley, Z; Chen, S N; Cowan, T E; Herrmannsdörfer, T; Higginson, D P; Kroll, F; Pikuz, S A; Naughton, K; Romagnani, L; Riconda, C; Revet, G; Riquier, R; Schlenvoigt, H-P; Skobelev, I Yu; Faenov, A Ya; Soloviev, A; Huarte-Espinosa, M; Frank, A; Portugall, O; Pépin, H; Fuchs, J

    2014-10-17

    Although bipolar jets are seen emerging from a wide variety of astrophysical systems, the issue of their formation and morphology beyond their launching is still under study. Our scaled laboratory experiments, representative of young stellar object outflows, reveal that stable and narrow collimation of the entire flow can result from the presence of a poloidal magnetic field whose strength is consistent with observations. The laboratory plasma becomes focused with an interior cavity. This gives rise to a standing conical shock from which the jet emerges. Following simulations of the process at the full astrophysical scale, we conclude that it can also explain recently discovered x-ray emission features observed in low-density regions at the base of protostellar jets, such as the well-studied jet HH 154. PMID:25324383

  19. Induced velocities of grains embedded in a turbulent gas. [test particle theory application to protostellar clouds

    NASA Technical Reports Server (NTRS)

    Voelk, H. J.; Morfill, G.; Roeser, S.; Jones, F. C.

    1978-01-01

    A theory is presented for the dynamics of dust particles in an incompressible turbulent fluid. Grain-gas coupling occurs through friction forces that are proportional to the mean grain velocity relative to the gas. This test particle theory is applied to the case of Kolmogoroff spectrum in a protostellar cloud. The mean turbulence induced grain velocity and the mean turbulent relative velocity of two grains are calculated. Whereas the former should determine the dust scale height, grain-grain collisions are influenced by the latter. For a reasonable strength of turbulence, the mean induced relative velocity of two particles turns out to be at least as large as the corresponding terminal velocity difference during gravitational settling.

  20. Chemistry in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Semenov, D. A.

    2012-01-01

    In this lecture I discuss recent progress in the understanding of the chemical evolution of protoplanetary disks that resemble our Solar system during the first ten million years. At the verge of planet formation, strong variations of temperature, density, and radiation intensities in these disks lead to a layered chemical structure. In hot, dilute and heavily irradiated atmosphere only simple radicals, atoms, and atomic ions can survive, formed and destroyed by gas-phase processes. Beneath the atmosphere a partly UV-shielded, warm molecular layer is located, where high-energy radiation drives rich chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark disk midplane many molecules are frozen out, forming thick icy mantles where surface chemistry is active and where complex (organic) species are synthesized.

  1. Packings of soft disks

    NASA Astrophysics Data System (ADS)

    Ziherl, Primoz; Vidmar, Marija

    2011-03-01

    We explore the stability of 2D ordered structures formed by soft disks treated as isotropic solid bodies. Using a variational model, we compute the equilibrium shapes and the elastic energy of disks in regular columnar, honeycomb, square, and hexagonal lattice. The results reproduce the Hertzian interaction in the regime of small deformations. The phase diagram of elastic disks is characterized by broad regions of phase coexistence; its main feature is that the coordination number of the stable phases decreases with density. These results may provide an insight into structure of the non-close-packed lattices observed in certain nanocolloidal systems. This work was supported by Slovenian Research Agency (grant No. P1-0055) and by EU through ITN COMPLOIDS (grant FP7-People-ITN-2008 No. 234810).

  2. Premixed direct injection disk

    SciTech Connect

    York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Lacy, Benjamin; Zuo, Baifang; Uhm, Jong Ho

    2013-04-23

    A fuel/air mixing disk for use in a fuel/air mixing combustor assembly is provided. The disk includes a first face, a second face, and at least one fuel plenum disposed therebetween. A plurality of fuel/air mixing tubes extend through the pre-mixing disk, each mixing tube including an outer tube wall extending axially along a tube axis and in fluid communication with the at least one fuel plenum. At least a portion of the plurality of fuel/air mixing tubes further includes at least one fuel injection hole have a fuel injection hole diameter extending through said outer tube wall, the fuel injection hole having an injection angle relative to the tube axis. The invention provides good fuel air mixing with low combustion generated NOx and low flow pressure loss translating to a high gas turbine efficiency, that is durable, and resistant to flame holding and flash back.

  3. Supersized Disk (Artist's Concept)

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Annotated ImageData Graph

    This illustration compares the size of a gargantuan star and its surrounding dusty disk (top) to that of our solar system. Monstrous disks like this one were discovered around two 'hypergiant' stars by NASA's Spitzer Space Telescope. Astronomers believe these disks might contain the early 'seeds' of planets, or possibly leftover debris from planets that already formed.

    The hypergiant stars, called R 66 and R 126, are located about 170,000 light-years away in our Milky Way's nearest neighbor galaxy, the Large Magellanic Cloud. The stars are about 100 times wider than the sun, or big enough to encompass an orbit equivalent to Earth's. The plump stars are heavy, at 30 and 70 times the mass of the sun, respectively. They are the most massive stars known to sport disks.

    The disks themselves are also bloated, with masses equal to several Jupiters. The disks begin at a distance approximately 120 times greater than that between Earth and the sun, or 120 astronomical units, and terminate at a distance of about 2,500 astronomical units.

    Hypergiant stars are the puffed-up, aging descendants of the most massive class of stars, called 'O' stars. The stars are so massive that their cores ultimately collapse under their own weight, triggering incredible explosions called supernovae. If any planets circled near the stars during one of these blasts, they would most likely be destroyed.

    The orbital distances in this picture are plotted on a logarithmic scale. This means that a given distance shown here represents proportionally larger actual distances as you move to the right. The sun and planets in our solar system have been scaled up in size for better viewing. Little Dust Grains in Giant Stellar Disks The graph above of data from NASA's Spitzer Space Telescope shows the composition of a monstrous disk of what may be planet-forming dust circling the colossal 'hypergiant' star

  4. The Structure and Environmental Impacts of Protostellar Outflows in DR 21 and Orion

    NASA Astrophysics Data System (ADS)

    Wiseman, J. J.; Ho, P. T. P.; Brown, R.

    1997-12-01

    Regions of high-mass star formation are considerably more complicated than their low-mass counterparts. Recent HST NICMOS images of Orion-KL (Thompson et al. 1997) as well as sensitive ground-based infrared images of H_2 shock emission in the Orion outflow region (Chrysostomou et al. 1997, McCaughrean & Mac Low 1997, Schild et al. 1997) reveal intricate clumpy shock structures extending in nearly all radial directions from the source. The one radial direction in which the shock emission is particularly diminished is to the northeast, and it is precisely here that a molecular gas filament is present and highly heated, as though blocking the path of outflowing material from Orion-KL. We present our latest NH_3 (1,1), (2,2), and (3,3) VLA MEM mosaics of the Orion-KL region. We present evidence from temperature and chemical excitation gradients that the molecular gas cores along the filament extending to the northeast of Orion-KL are strongly heated by impacts from protostellar ejecta. These effects are seen in the core ``CS1'' 30'' northeast of IRc2 and also in cores at least twice as distant (1.5 pc). The DR 21 outflow region is also quite complex, with multiple molecular outflows extending from a multiple-component HII region. We present sensitive VLA maps of hydrogen recombination line emission, and we report the detection of bipolar ionized gas within the molecular outflow lobes. This detection gives observational evidence for the initial ionized inner structure of high mass protostellar outflows. Chrysostomou, A. et al. 1997, MNRAS, 289, 605 McCaughrean, M., & Mac Low, M.-M. 1997, AJ, 113, 391 Schild, H., Miller, S., & Tennyson, J. 1997, A&A, 319, 1037 Thompson, R., Rieke, M., Schneider, G., Stolovy, S., Erickson, E., & Axon, D. 1997, STSCI Early Release Observation PRC97-13

  5. Mathematical method for the study and teaching of stellar and protostellar structure

    NASA Astrophysics Data System (ADS)

    Doorish, John Francis

    The purpose of this thesis is to develop a relatively simple yet effective method of teaching stellar and protostellar structure. There are four differential equations describing the structure of a star. They are: These equations are linearly approximated in the following form: W = Wo (1 plus or minus wx). Here, W represents the pressure (P), temperature (T), mass (M), and/or luminosity (L) gradients within the star; W represents some initial value of these parameters expanded inwardly or outwardly from an initial point, ro; and w represents what is called the Motz Dimensionless Variables (MDV) which are directly derivable from the above set of equations. They are dimensionless, so, in the expansion, W has the same units as wo. The MDV appear below: As yet, there is no MDV for luminosity owing to the complicating energy generation factor, epsilon. In the above sets of equations, the mean molecular weight is micro; the opacity is kappa; the ratio of gas pressure to total pressure is beta; and the other symbols have their usual meanings. In the above set of equations describing the MDV, if the surface of the star is expanded to larger values, representing earlier, and therefore, protostellar stages of the star, by theoretically halting accretion, no dynamical factors need to be considered. The above set of equations describing a stellar structure in static equilibrium may then be used. This method was designed for college and early graduate students who have never before encountered the topic of stellar structure. This method was taught to a class of college physics majors in a local New York City college. The students had never before seen these equations. After the presentation, they were asked to attempt construction of sample stellar model using this method and also to complete a questionnaire concerning their general academic history and their opinions of the method. According to the questionnaire, most subjects felt that it was effective, yet simple enough, as

  6. MPP disk subsystem

    NASA Technical Reports Server (NTRS)

    Hudgins, W. A.

    1984-01-01

    A disk subsystem for the Massively Parallel processor (MPP) is designed to the block diagram level. The subsystem is capable of storing 4,992 megabytes of data, expandable to 39,936 megabytes. The subsystem is capable of transferring data to the MPP Staging Memory at a rate of 25 megabytes/second, expandable to 100 megabytes/second. A lower cost disk subsystem is also presented. This alternate subsystem is capable of storing 3,744 megabytes with a transfer rate of 10.6 megabyte/second.

  7. GIANT PLANET FORMATION BY DISK INSTABILITY IN LOW MASS DISKS?

    SciTech Connect

    Boss, Alan P.

    2010-12-20

    Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of 0.043 M{sub sun} from 4 to 20 AU in orbit around a 1 M{sub sun} protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk (T{sub o}) temperatures. Models with T{sub o} = 20 K are able to form a single self-gravitating clump, whereas models with T{sub o} = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least {approx}0.043 M{sub sun} inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer-disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.

  8. Internal and environmental secular evolution of disk galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2015-03-01

    that are available to them. They do this by spreading - the inner parts shrink while the outer parts expand. Significant changes happen only if some process efficiently transports energy or angular momentum outward. The consequences are very general: evolution by spreading happens in stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks. This meeting is about disk galaxies, so the evolution most often involves the redistribution of angular momentum. We now have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the center. Numerical simulations reproduce observed morphologies very well. Gas that is transported to small radii reaches high densities that are seen in CO observations. Star formation rates measured (e.g.) in the mid-infrared show that many barred and oval galaxies grow, on timescales of a few Gyr, dense central `pseudobulges' that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). Our resulting picture of secular evolution accounts for the richness observed in morphological classification schemes such as those of de Vaucouleurs (1959) and Sandage (1961). State-of-the art morphology discussions include the de Vaucouleurs Atlas of Galaxies (Buta et al. 2007) and Buta (2012, 2013). Pseudobulges as disk-grown alternatives to merger-built classical bulges are important because they impact many aspects of our understanding of galaxy evolution. For example, they are observed to contain supermassive black holes (BHs), but they do not show the well known, tight correlations between BH mass and host properties (Kormendy et al. 2011). We can distinguish between classical and pseudo bulges because the latter retain a `memory' of their disky origin. That is, they have one or more characteristics of disks: (1) flatter shapes than those of

  9. Plasmofluidic Disk Resonators

    PubMed Central

    Kwon, Min-Suk; Ku, Bonwoo; Kim, Yonghan

    2016-01-01

    Waveguide-coupled silicon ring or disk resonators have been used for optical signal processing and sensing. Large-scale integration of optical devices demands continuous reduction in their footprints, and ultimately they need to be replaced by silicon-based plasmonic resonators. However, few waveguide-coupled silicon-based plasmonic resonators have been realized until now. Moreover, fluid cannot interact effectively with them since their resonance modes are strongly confined in solid regions. To solve this problem, this paper reports realized plasmofluidic disk resonators (PDRs). The PDR consists of a submicrometer radius silicon disk and metal laterally surrounding the disk with a 30-nm-wide channel in between. The channel is filled with fluid, and the resonance mode of the PDR is strongly confined in the fluid. The PDR coupled to a metal-insulator-silicon-insulator-metal waveguide is implemented by using standard complementary metal oxide semiconductor technology. If the refractive index of the fluid increases by 0.141, the transmission spectrum of the waveguide coupled to the PDR of radius 0.9 μm red-shifts by 30 nm. The PDR can be used as a refractive index sensor requiring a very small amount of analyte. Plus, the PDR filled with liquid crystal may be an ultracompact intensity modulator which is effectively controlled by small driving voltage. PMID:26979929

  10. Accretion disk coronae

    NASA Technical Reports Server (NTRS)

    White, N. E.; Holt, S. S.

    1981-01-01

    Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains an ADC. The possible origin of an ADC is discussed and a simple hydrostatic evaporated ADC model is developed which, when applied to 4U1822-37, 4U2129+47 and Cyg X-3, can explain their temporal and spectral properties. The quasi-sinusoidal modulation of all three sources can be reconciled with the partial occultation of the ADC by a bulge at the edge of the accretion disk which is caused by the inflowing material. The height of this bulge is an order of magnitude larger than the hydrostatic disk height and is the result of turbulence in the outer region of the disk. The spectral properties of all three sources can be understood in terms of Compton scattering of the original source spectrum by the ADC. Spectral variations with epoch in Cyg X-3 are probably caused by changes in the optical depth of the corona. A consequence of our model is that any accreting neutron star X-ray source in a semi-detached binary system which is close to its Eddington limit most likely contains an optically thick ADC.

  11. Solar disk sextant

    NASA Technical Reports Server (NTRS)

    Sofia, S.; Chiu, H.-Y.; Maier, E.; Schatten, K. H.; Minott, P.; Endal, A. S.

    1984-01-01

    This paper presents the conceptual design of an instrument, called the solar disk sextant, to be used in space to measure the shape and the size of the sun and their variations. The instrumental parameters required to produce sufficient sensitivity to address the problems of solar oblateness, solar pulsations, and global size changes of climatic importance are given.

  12. Plasmofluidic Disk Resonators

    NASA Astrophysics Data System (ADS)

    Kwon, Min-Suk; Ku, Bonwoo; Kim, Yonghan

    2016-03-01

    Waveguide-coupled silicon ring or disk resonators have been used for optical signal processing and sensing. Large-scale integration of optical devices demands continuous reduction in their footprints, and ultimately they need to be replaced by silicon-based plasmonic resonators. However, few waveguide-coupled silicon-based plasmonic resonators have been realized until now. Moreover, fluid cannot interact effectively with them since their resonance modes are strongly confined in solid regions. To solve this problem, this paper reports realized plasmofluidic disk resonators (PDRs). The PDR consists of a submicrometer radius silicon disk and metal laterally surrounding the disk with a 30-nm-wide channel in between. The channel is filled with fluid, and the resonance mode of the PDR is strongly confined in the fluid. The PDR coupled to a metal-insulator-silicon-insulator-metal waveguide is implemented by using standard complementary metal oxide semiconductor technology. If the refractive index of the fluid increases by 0.141, the transmission spectrum of the waveguide coupled to the PDR of radius 0.9 μm red-shifts by 30 nm. The PDR can be used as a refractive index sensor requiring a very small amount of analyte. Plus, the PDR filled with liquid crystal may be an ultracompact intensity modulator which is effectively controlled by small driving voltage.

  13. Herniated disk repair (image)

    MedlinePlus

    ... one of the most common causes of lower back pain. The mainstay of treatment for herniated disks is an initial period of rest with pain and anti-inflammatory medications followed by physical therapy. If pain and symptoms persist, surgery to remove ...

  14. ALMA observations of infalling flows toward the Keplerian disk around the class I protostar L1489 IRS

    SciTech Connect

    Yen, Hsi-Wei; Takakuwa, Shigehisa; Ohashi, Nagayoshi; Aikawa, Yuri; Aso, Yusuke; Koyamatsu, Shin; Machida, Masahiro N.; Saigo, Kazuya; Saito, Masao; Tomida, Kengo; Tomisaka, Kohji

    2014-09-20

    We have conducted ALMA observations in the 1.3 mm continuum and {sup 12}CO (2-1), C{sup 18}O (2-1), and SO (5{sub 6}-4{sub 5}) lines toward L1489 IRS, a Class I protostar surrounded by a Keplerian disk and an infalling envelope. The Keplerian disk is clearly identified in the {sup 12}CO and C{sup 18}O emission, and its outer radius (∼700 AU) and mass (∼0.005 M {sub ☉}) are comparable to those of disks around T Tauri stars. The protostellar mass is estimated to be 1.6 M {sub ☉} with the inclination angle of 66°. In addition to the Keplerian disk, there are blueshifted and redshifted off-axis protrusions seen in the C{sup 18}O emission pointing toward the north and the south, respectively, adjunct to the middle part of the Keplerian disk. The shape and kinematics of these protrusions can be interpreted as streams of infalling flows with a conserved angular momentum following parabolic trajectories toward the Keplerian disk, and the mass infalling rate is estimated to be ∼5 × 10{sup –7} M {sub ☉} yr{sup –1}. The specific angular momentum of the infalling flows (∼2.5 × 10{sup –3} km s{sup –1} pc) is comparable to that at the outer radius of the Keplerian disk (∼4.8 × 10{sup –3} km s{sup –1} pc). The SO emission is elongated along the disk major axis and exhibits a linear velocity gradient along the axis, which is interpreted to mean that the SO emission primarily traces a ring region in the flared Keplerian disk at radii of ∼250-390 AU. The local enhancement of the SO abundance in the ring region can be due to the accretion shocks at the centrifugal radius where the infalling flows fall onto the disk. Our ALMA observations unveiled both the Keplerian disk and the infalling gas onto the disk, and the disk can further grow by accreting material and angular momenta from the infalling gas.

  15. On the Holmberg asymmetry of the satellites of disk galaxies

    NASA Technical Reports Server (NTRS)

    Byrd, Gene G.; Valtonen, Mauri J.

    1987-01-01

    A tidal explanation for the observation by Holmberg that the satellites of edge-on disk galaxies tend to avoid the sector within + or - 30 deg of the major axes of the disk galaxies is considered. It is shown that satellites with small orbit-to-disk inclinations are likely to become compact and consequently be left out in Holmberg's survey due to the resemblance to stars. The explanation is supported by the observation of an excess of compact galaxies near the major-axis direction of edge-on disk galaxies. The disk tidal explanation also predicts that the asymmetry should be weaker with larger satellites. It is found that the Karachentsev (1972, 1980) binary galaxy sample, where the typical companion is comparable to the primary galaxy, shows no Holmberg effect. The case of M32 as a compact satellite of the Andromeda galaxy is discussed as a nearby observationally supported example of the above processes.

  16. Compton heated winds and coronae above accretion disks. I Dynamics

    NASA Technical Reports Server (NTRS)

    Begelman, M. C.; Mckee, C. F.; Shields, G. A.

    1983-01-01

    X rays emitted in the inner part of an accretion disk system can heat the surface of the disk farther out, producing a corona and possibly driving off a strong wind. The dynamics of Compton-heated coronae and winds are analyzed using an approximate two-dimensional technique to estimate the mass loss rate as a function of distance from the source of X rays. The findings have important dynamical implications for accretion disks in quasars, active galactic nuclei, X ray binaries, and cataclysmic variables. These include: mass loss from the disk possibly comparable with or exceeding the net accretion rate onto the central compact object, which may lead to unstable accretion; sufficient angular momentum loss in some cases to truncate the disk in a semidetached binary at a smaller radius than that predicted by tidal truncation theories; and combined static plus ram pressure in the wind adequate to confine line-emitting clouds in quasars and Seyfert galaxies.

  17. The formation of a massive protostar through the disk accretion of gas.

    PubMed

    Chini, Rolf; Hoffmeister, Vera; Kimeswenger, Stefan; Nielbock, Markus; Nürnberger, Dieter; Schmidtobreick, Linda; Sterzik, Michael

    2004-05-13

    The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the formation of stars above ten solar masses through this mechanism, although some calculations have claimed that stars up to 40 solar masses can in principle be formed via accretion through a disk. Given this uncertainty and the fact that most massive stars are born in dense clusters, it was suggested that high-mass stars are the result of the runaway merging of intermediate-mass stars. Here we report observations that clearly show a massive star being born from a large rotating accretion disk. The protostar has already assembled about 20 solar masses, and the accretion process is still going on. The gas reservoir of the circumstellar disk contains at least 100 solar masses of additional gas, providing sufficient fuel for substantial further growth of the forming star. PMID:15141204

  18. Disk instability and the spectral evolution of the 1992 outburst of the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Kim, S.-W.; Wheeler, J. C.; Bruhweiler, F. C.; Fitzurka, M.; Beuermann, K.; Reinsch, K.; Mineshige, S.

    1994-01-01

    The disk instability model can explain the previous history of dwarf-nova-like outbursts in the intermediate polar GK Per, which occur about once every three years. Disk models that reproduce the recurrence time and outburst light curves suggest that GK Per has a large effective inner disk radius (approx. 30-40 white dwarf radii) truncated by a strong magnetic field (10(exp 7) G). In this context, the effective radius is that of the portion of the disk that participates in the disk thermal instability. The radius derived is larger than the corotation radius, which must be an upper limit on the true dynamical inner radius of the disk. Disk instability models with this large effective inner radius predict that the ultraviolet continuum should be rather flat. Here we compare the predictions of the disk instability model to IUE observations of the 1981 outburst and to IUE and ROSAT observations of the recent 1992 outburst of GK Per. The model disk continuum spectral evolution is consistent with the observed UV and optical spectra, especially at maximum and in the early decay phase of the outburst. The consistency of the model with the observed UV spectra suggests that the effective inner radius of the disk is almost constant, independent of mass accretion rate, and that whatever structure lies between the effective inner radius and the corotation radius neither participates in the disk instability nor radiates substantially in the UV. The related physics of the inner disk region will be briefly discussed.

  19. Bimodality of Circumstellar Disk Evolution Induced by the Hall Current

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Y.; Iwasaki, K.; Okuzumi, S.; Machida, M. N.; Inutsuka, S.

    2015-09-01

    The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of the circumstellar disk using three-dimensional simulations. In our simulations, all non-ideal effects, as well as the radiation transfer, are considered. The size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti-parallel. In the former case, only a very small disk (\\lt 1 {AU}) is formed. On the other hand, in the latter case, a massive and large (\\gt 20 {AU}) disk is formed in the early phase of protostar formation. Since the parallel and anti-parallel properties do not readily change, we expect that the parallel and anti-parallel properties are also important in the subsequent disk evolution and the difference between the two cases is maintained or enhanced. This result suggests that the disk size distribution of the Class 0 young stellar objects is bimodal. Thus, the disk evolution can be categorized into two cases and we may call the parallel and anti-parallel systems Ortho-disk and Para-disk, respectively. We also show that the anti-rotating envelopes against the disk rotation appear with a size of ≳ 200 {AU}. We predict that the anti-rotating envelope will be found in the future observations.

  20. Equilibrium Initialization and Stability of Three-Dimensional Gas Disks

    SciTech Connect

    Wang, Hsiang-Hsu; Klessen, Ralf S.; Dullemond, Cornelis P.; Bosch, Frank C.van den; Fuchs, Burkhard; /KIPAC, Menlo Park

    2010-08-25

    We present a new systematic way of setting up galactic gas disks based on the assumption of detailed hydrodynamic equilibrium. To do this, we need to specify the density distribution and the velocity field which supports the disk. We first show that the required circular velocity has no dependence on the height above or below the midplane so long as the gas pressure is a function of density only. The assumption of disks being very thin enables us to decouple the vertical structure from the radial direction. Based on that, the equation of hydrostatic equilibrium together with the reduced Poisson equation leads to two sets of second-order non-linear differential equation, which are easily integrated to set-up a stable disk. We call one approach 'density method' and the other one 'potential method'. Gas disks in detailed balance are especially suitable for investigating the onset of the gravitational instability. We revisit the question of global, axisymmetric instability using fully three-dimensional disk simulations. The impact of disk thickness on the disk instability and the formation of spontaneously induced spirals is studied systematically with or without the presence of the stellar potential. In our models, the numerical results show that the threshold value for disk instability is shifted from unity to 0.69 for self-gravitating thick disks and to 0.75 for combined stellar and gas thick disks. The simulations also show that self-induced spirals occur in the correct regions and with the right numbers as predicted by the analytic theory.

  1. Elastic and hydrodynamic torques on a colloidal disk within a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Rovner, Joel B.; Borgnia, Dan S.; Reich, Daniel H.; Leheny, Robert L.

    2012-10-01

    The orientationally dependent elastic energy and hydrodynamic behavior of colloidal disks with homeotropic surface anchoring suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) have been investigated. In the absence of external torques, the disks align with the normal of the disk face â parallel to the nematic director n̂. When a magnetic field is applied, the disks rotate â by an angle θ so that the magnetic torque and the elastic torque caused by distortion of the nematic director field are balanced. Over a broad range of angles, the elastic torque increases linearly with θ in quantitative agreement with a theoretical prediction based on an electrostatic analogy. When the disks are rotated to angles θ>(π)/(2), the resulting large elastic distortion makes the disk orientation unstable, and the director undergoes a topological transition in which θπ-θ. In the transition, a defect loop is shed from the disk surface, and the disks spin so that â sweeps through π radians as the loop collapses back onto the disk. Additional measurements of the angular relaxation of disks to θ=0 following removal of the external torque show a quasi-exponential time dependence from which an effective drag viscosity for the nematic can be extracted. The scaling of the angular time dependence with disk radius and observations of disks rotating about â indicate that the disk motion affects the director field at surprisingly modest Ericksen numbers.

  2. A debris disk around an isolated young neutron star.

    PubMed

    Wang, Zhongxiang; Chakrabarty, Deepto; Kaplan, David L

    2006-04-01

    Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (> or = 10(6) years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars. PMID:16598251

  3. The Evolution of Inner Disk Gas in Transition Disks

    NASA Astrophysics Data System (ADS)

    Hoadley, K.; France, K.; Alexander, R. D.; McJunkin, M.; Schneider, P. C.

    2015-10-01

    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 (H2) 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 H2 disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H2 emission in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H2 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 (rin and rout), describing where the bulk of the observed H2 emission arises in each disk, and we examine correlations between these and several observational disk evolution indicators, such as n13-31, rin, CO, and the mass accretion rate. We find strong, positive correlations between the H2 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 H2 inner radii are ˜4 times larger in transition systems, while the bulk of the H2 emission originates inside the dust gap radius for all transitional sources.

  4. THE DISCOVERY OF THE YOUNGEST MOLECULAR OUTFLOW ASSOCIATED WITH AN INTERMEDIATE-MASS PROTOSTELLAR CORE, MMS-6/OMC-3

    SciTech Connect

    Takahashi, Satoko; Ho, Paul T. P.

    2012-01-20

    We present subarcsecond resolution HCN (4-3) and CO (3-2) observations made with the Submillimeter Array, toward an extremely young intermediate-mass protostellar core, MMS 6-main, located in the Orion Molecular Cloud 3 region (OMC-3). We have successfully imaged a compact molecular outflow lobe ( Almost-Equal-To 1000 AU) associated with MMS 6-main, which is also the smallest molecular outflow ever found in the intermediate-mass protostellar cores. The dynamical timescale of this outflow is estimated to be {<=}100 yr. The line width dramatically increases downstream at the end of the molecular outflow ({Delta}v {approx} 25 km s{sup -1}) and clearly shows the bow-shock-type velocity structure. The estimated outflow mass ( Almost-Equal-To 10{sup -4} M{sub Sun }) and outflow size are approximately two to four orders and one to three orders of magnitude smaller, respectively, while the outflow force ( Almost-Equal-To 10{sup -4} M{sub Sun} km s{sup -1} yr{sup -1}) is similar, compared to the other molecular outflows studied in OMC-2/3. These results show that MMS 6-main is a protostellar core at the earliest evolutionary stage, most likely shortly after the second core formation.

  5. Effects of Turbulence on Cosmic Ray Propagation in Protostars and Young Star/Disk Systems

    NASA Astrophysics Data System (ADS)

    Fatuzzo, Marco; Adams, Fred C.

    2014-05-01

    The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: (1) the (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distribution of values. (2) The median of the mirror point distribution moves outward for sufficiently large fluctuation amplitudes (roughly when δB/B 0 > 0.2 at the location of the turbulence-free mirror point); the distribution becomes significantly non-Gaussian in this regime as well. These results may have significant consequences for the ionization fraction of the disk, which in turn dictates the efficiency with which disk material can accrete onto the central object. A similar reduction in cosmic ray flux can occur during the earlier protostellar stages; the decrease in ionization can help alleviate the magnetic braking problem that inhibits disk formation.

  6. Effects of turbulence on cosmic ray propagation in protostars and young star/disk systems

    SciTech Connect

    Fatuzzo, Marco; Adams, Fred C. E-mail: fca@umich.edu

    2014-05-20

    The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: (1) the (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distribution of values. (2) The median of the mirror point distribution moves outward for sufficiently large fluctuation amplitudes (roughly when δB/B {sub 0} > 0.2 at the location of the turbulence-free mirror point); the distribution becomes significantly non-Gaussian in this regime as well. These results may have significant consequences for the ionization fraction of the disk, which in turn dictates the efficiency with which disk material can accrete onto the central object. A similar reduction in cosmic ray flux can occur during the earlier protostellar stages; the decrease in ionization can help alleviate the magnetic braking problem that inhibits disk formation.

  7. Studies of Circumstellar Disk Evolution

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2005-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  8. Herschel-HIFI view of mid-IR quiet massive protostellar objects

    NASA Astrophysics Data System (ADS)

    Herpin, F.; Chavarría, L.; Jacq, T.; Braine, J.; van der Tak, F.; Wyrowski, F.; van Dishoeck, E. F.; Baudry, A.; Bontemps, S.; Kristensen, L.; Schmalzl, M.; Mata, J.

    2016-03-01

    Aims: We present Herschel/HIFI observations of 14 water lines in a small sample of Galactic massive protostellar objects: NGC 6334I(N), DR21(OH), IRAS 16272-4837, and IRAS 05358+3543. Using water as a tracer of the structure and kinematics, we individually study each of these objects with the aim to estimate the amount of water around them, but to also to shed light on the high-mass star formation process. Methods: We analyzed the gas dynamics from the line profiles using Herschel-HIFI observations acquired as part of the WISH key-project of 14 far-IR water lines (H_216O, H_217O, H_218O) and several other species. Then through modeling the observations using the RATRAN radiative transfer code, we estimated outflow, infall, turbulent velocities, and molecular abundances and investigated the correlation with the evolutionary status of each source. Results: The four sources (and the previously studied W43-MM1) have been ordered in terms of evolution based on their spectral energy distribution from youngest to older: 1) NGC 64334I(N); 2) W43-MM1; 3) DR21(OH); 4) IRAS 16272-4837; 5) IRAS 05358+3543. The molecular line profiles exhibit a broad component coming from the shocks along the cavity walls that is associated with the protostars, and an infalling (or expanding, for IRAS 05358+3543) and passively heated envelope component, with highly supersonic turbulence that probably increases with the distance from the center. Accretion rates between 6.3 × 10-5 and 5.6 × 10-4M⊙ yr-1 are derived from the infall observed in three of our sources. The outer water abundance is estimated to be at the typical value of a few 10-8, while the inner abundance varies from 1.7 × 10-6 to 1.4 × 10-4 with respect to H2 depending on the source. Conclusions: We confirm that regions of massive star formation are highly turbulent and that the turbulence probably increases in the envelope with the distance to the star. The inner abundances are lower than the expected, 10-4, perhaps because

  9. Brown dwarf disks with ALMA

    SciTech Connect

    Ricci, L.; Isella, A.; Testi, L.; De Gregorio-Monsalvo, I.; Natta, A.; Scholz, A.

    2014-08-10

    We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

  10. Erosion of circumstellar particle disks by interstellar dust

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Griffith, Caitlin A.

    1989-01-01

    Circumstellar particle disks appear to be a common phenomenon; however, their properties vary greatly. Models of the evolution of such systems focus on internal mechanisms such as interparticle collisions and Poynting-Robertson drag. Herein it is shown that 'sandblasting' by interstellar dust can be an important and even dominant contributor to the evolution of circumstellar particle disks. Stars spend up to about 3 percent of their main-sequence lifetimes within atomic clouds. Among an IRAS sample of 21 nearby main-sequence A stars, beta Pictoris has the brightest disk; it also possesses the smallest random velocity and therefore the slowest predicted erosion rate.

  11. Consistent dust and gas models for protoplanetary disks. I. Disk shape, dust settling, opacities, and PAHs

    NASA Astrophysics Data System (ADS)

    Woitke, P.; Min, M.; Pinte, C.; Thi, W.-F.; Kamp, I.; Rab, C.; Anthonioz, F.; Antonellini, S.; Baldovin-Saavedra, C.; Carmona, A.; Dominik, C.; Dionatos, O.; Greaves, J.; Güdel, M.; Ilee, J. D.; Liebhart, A.; Ménard, F.; Rigon, L.; Waters, L. B. F. M.; Aresu, G.; Meijerink, R.; Spaans, M.

    2016-02-01

    We propose a set of standard assumptions for the modelling of Class II and III protoplanetary disks, which includes detailed continuum radiative transfer, thermo-chemical modelling of gas and ice, and line radiative transfer from optical to cm wavelengths. The first paper of this series focuses on the assumptions about the shape of the disk, the dust opacities, dust settling, and polycyclic aromatic hydrocarbons (PAHs). In particular, we propose new standard dust opacities for disk models, we present a simplified treatment of PAHs in radiative equilibrium which is sufficient to reproduce the PAH emission features, and we suggest using a simple yet physically justified treatment of dust settling. We roughly adjust parameters to obtain a model that predicts continuum and line observations that resemble typical multi-wavelength continuum and line observations of Class II T Tauri stars. We systematically study the impact of each model parameter (disk mass, disk extension and shape, dust settling, dust size and opacity, gas/dust ratio, etc.) on all mainstream continuum and line observables, in particular on the SED, mm-slope, continuum visibilities, and emission lines including [OI] 63 μm, high-J CO lines, (sub-)mm CO isotopologue lines, and CO fundamental ro-vibrational lines. We find that evolved dust properties, i.e. large grains, often needed to fit the SED, have important consequences for disk chemistry and heating/cooling balance, leading to stronger near- to far-IR emission lines in general. Strong dust settling and missing disk flaring have similar effects on continuum observations, but opposite effects on far-IR gas emission lines. PAH molecules can efficiently shield the gas from stellar UV radiation because of their strong absorption and negligible scattering opacities in comparison to evolved dust. The observable millimetre-slope of the SED can become significantly more gentle in the case of cold disk midplanes, which we find regularly in our T Tauri models

  12. Mathematical Method for the Study and Teaching of Stellar and Protostellar Structure.

    NASA Astrophysics Data System (ADS)

    Doorish, John Francis

    The purpose of this thesis is to develop a relatively simple yet effective method of teaching stellar and protostellar structure. There are four differential equations describing the structure of a star. They are:. These equations are linearly approximated in the following form: W = W_{rm o} (1+/-wx). Here, W represents the pressure (P), temperature (T), mass (M), and/or luminosity (L) gradients within the star; W represents some initial value of these parameters expanded inwardly or outwardly from an initial point, r_{rm o}; and w represents what is called the Motz Dimensionless Variables (MDV) which are directly derivable from the above set of equations. They are dimensionless, so, in the expansion, W has the same units as w _{rm o}. The MDV appear below:. As yet, there is no MDV for luminosity owing to the complicating energy generation factor, varepsilon . In the above sets of equations, the mean molecular weight is mu; the opacity is kappa; the ratio of gas pressure to total pressure is beta; and the other symbols have their usual meanings. In the above set of equations describing the MDV, if the surface of the star is expanded to larger values, representing earlier, and therefore, protostellar stages of the star, by theoretically halting accretion, no dynamical factors need to be considered. The above set of equations describing a stellar structure in static equilibrium may then be used. This method was designed for college and early graduate students who have never before encountered the topic of stellar structure. This method was taught to a class of college physics majors in a local New York City college. The students had never before seen these equations. After the presentation, they were asked to attempt construction of a sample stellar model using this method and also to complete a questionnaire concerning their general academic history and their opinions of the method. According to the questionnaire, most subjects felt that it was effective, yet simple

  13. Structure and Stability of Steady Protostellar Accretion Flows - Part Three - Nonlinear Instabilities

    NASA Astrophysics Data System (ADS)

    Balluch, M.

    1991-03-01

    Recently, a global, linear stability analysis of the structure of spherically symmetric steady protostellar accretion flows with a shock discontinuity has been made (Balluch 1990b). A detailed non-linear time-dependent radiation hydrodynamics calculation is presented to complement this study. In the `ideal-case' with constant opacity, the shock front around the second, inner core appears unstable with respect to oscillation due to critical cooling, starting at the instant, when a cooling region occurs in the calculation (due to its resolution in the late stages of accretion) and lasting as long as the mass flow rate is larger than M ≥ 2.8 10-6 Msun yr-1. This is in best agreement with the results of the linear analysis. Next, a detailed calculation of the formation of the first, outer core using quasimolecular artificial viscosity length scales, is presented. In about twice the e-folding time of the unstable mode in the linear analysis, a significant growth of a disturbance can be seen. It appears first in the velocity and the radiation flux in the settling zone, accompanied by an oscillation of the radiation flux in the region upstream from the shock up to r = 1014 cm. Some time later, the shock front starts to move. Again, these characteristics are in best concordance with the linear results. In addition, the calculation shows the growth of these oscillations deep in the non-linear regime until the beginning of a rapid expansion of the whole protostellar core. At last, a calculation of the global evolution of this expansion of the first, outer core is presented. It is shown that the expansion is stopped when about twice the core mass is involved. Then another collapse follows, and the whole scenario of formation and expansion of the outer core starts anew. During this evolution, up to 3 shock fronts were present at the same time in the flow. The largest expansion leads to central physical quantities comparable to the initial ones of the interstellar medium. At

  14. Chemistry in Disks. VII. First Detection of HC3N in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Chapillon, Edwige; Dutrey, Anne; Guilloteau, Stéphane; Piétu, Vincent; Wakelam, Valentine; Hersant, Franck; Gueth, Fréderic; Henning, Thomas; Launhardt, Ralf; Schreyer, Katharina; Semenov, Dmitry

    2012-09-01

    Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30 m telescope by using the new broadband correlator (fast Fourier Transform Spectrometer) to search for so far undetected molecules in the protoplanetary disks surrounding the T Tauri stars DM Tau, GO Tau, LkCa 15, and the Herbig Ae star MWC 480. We report the first detection of HC3N at 5σ in the GO Tau and MWC 480 disks with the IRAM 30 m, and in the LkCa 15 disk (5σ), using the IRAM array, with derived column densities of the order of 1012 cm-2. We also obtain stringent upper limits on CCS (N < 1.5 × 1012 cm-3). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen- and sulfur-bearing molecule observations. The observed column densities of HC3N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H2S, and SO). Based on observations carried out with the IRAM 30 m radiotelescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  15. CHEMISTRY IN DISKS. VII. FIRST DETECTION OF HC{sub 3}N IN PROTOPLANETARY DISKS

    SciTech Connect

    Chapillon, Edwige; Dutrey, Anne; Guilloteau, Stephane E-mail: dutrey@obs.u-bordeaux1.fr; and others

    2012-09-01

    Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30 m telescope by using the new broadband correlator (fast Fourier Transform Spectrometer) to search for so far undetected molecules in the protoplanetary disks surrounding the T Tauri stars DM Tau, GO Tau, LkCa 15, and the Herbig Ae star MWC 480. We report the first detection of HC{sub 3}N at 5{sigma} in the GO Tau and MWC 480 disks with the IRAM 30 m, and in the LkCa 15 disk (5{sigma}), using the IRAM array, with derived column densities of the order of 10{sup 12} cm{sup -2}. We also obtain stringent upper limits on CCS (N < 1.5 Multiplication-Sign 10{sup 12} cm{sup -3}). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen- and sulfur-bearing molecule observations. The observed column densities of HC{sub 3}N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H{sub 2}S, and SO).

  16. Cooling Fronts in Accretion Disks and Constraints on the Disk Viscosity

    NASA Astrophysics Data System (ADS)

    Vishniac, E. T.; Wheeler, J. C.

    1996-12-01

    We examine the speed of inward traveling cooling fronts in accretion disks and the structure of the hot phase of the disk inside the cooling front. We show that the cooling front speed is determined by the rarefaction wave that precedes it and is approximately alpha_F c_F (H/r)(q) , where alpha_F is the dimensionless viscosity, c_F is the sound speed, r is the radial coordinate, H is the disk thickness, and all quantities are evaluated at the cooling front. The scaling exponent q lies in the interval [0,1], depending on the slope of the (T,Sigma ) relation in the hot state. For a Kramers law opacity and alpha ~ (H/r)(n) , where n is of order unity, we find that q ~ 1/2. In addition, we derive a similarity solution which is exact in the limit of a thin disk with power law opacities and allows us to predict the coefficient in the cooling front speed scaling law. Our results support the numerical work of Cannizzo, Chen, and Livio (1995) and their conclusion that n~ 3/2 is necessary to reproduce the exponential decay of luminosity in black hole X-ray binary systems. Our results are insensitive to the structure of the disk outside the radius where rapid cooling sets in. In particular, the width of the rapid cooling zone is a consequence of the cooling front speed rather than its cause. This implies that our conclusions depend only on the structure of the hot phase of the disk, which is relatively well understood. We discuss the implications of this result for theoretical models of disk viscosity.

  17. Flow between contrarotating disks

    SciTech Connect

    Gan, X.; Kilic, M.; Owen, J.M.

    1995-04-01

    The paper describes a combined experimental and computational study of laminar and turbulent flow between contrarotating disks. Laminar computations produce Batchelor-type flow: radial outflow occurs in boundary layers on the disks and inflow is confined to a thin shear layer in the midplane; between the boundary layers and the shear layer, two contrarotating cores of fluid are formed. Turbulent computations (using a low-Reynolds-number {kappa}-{epsilon} turbulence model) and LDA measurements provide no evidence for Batchelor-type flow, even for rotational Reynolds numbers as low as 2.2 {times} 10{sup 4}. While separate boundary layers are formed on the disks, radial inflow occurs in a single interior core that extends between the two boundary layers; in the core, rotational effects are weak. Although the flow in the core was always found to be turbulent, the flow in the boundary layers could remain laminar for rotational Reynolds numbers up to 1.2 {times} 10{sup 5}. For the case of a superposed outflow, there is a source region in which the radial component of velocity is everywhere positive; radially outward of this region, the flow is similar to that described above. Although the turbulence model exhibited premature transition from laminar to turbulent flow in the boundary layers, agreement between the computed and measured radial and tangential components of velocity was mainly good over a wide range of nondimensional flow rates and rotational Reynolds numbers.

  18. Macroscopic Velocity Amplification in Stacked Disks

    NASA Astrophysics Data System (ADS)

    Murthy, Srividya; White, Gary

    2015-04-01

    When a small sphere rests atop a larger sphere (for example, a basketball with a tennis ball balanced on top), and both are released from a height, the resulting ``velocity amplification'' of the small sphere when the pair rebound from a hard floor, is a staple of the physics demonstration toolkit--usually impressive, sometimes dangerous. While this phenomenon has been studied in the literature in some detail, we set out to explore this effect by constructing a device involving stacked disks falling in a plane, fashioned after an online design by Wayne Peterson of Brigham Young University. When two disks, stacked edge to edge atop one another and confined to a vertical plane, are dropped, the top disk rebounds to a much greater height than it started from, as expected. In this talk, we report on experiments conducted by dropping the disks and recording the heights to which they rise on rebound, and the comparison of these results with our theoretical predictions and computer simulations. Frances E. Walker Fellowship.

  19. DIAGNOSTIC LINE EMISSION FROM EXTREME ULTRAVIOLET AND X-RAY-ILLUMINATED DISKS AND SHOCKS AROUND LOW-MASS STARS

    SciTech Connect

    Hollenbach, David; Gorti, U.

    2009-10-01

    Extreme ultraviolet (EUV; 13.6 eV disks around young, low-mass stars to thousands of degrees and ionize species with ionization potentials greater than 13.6 eV. Shocks generated by protostellar winds can also heat and ionize the same species close to the star/disk system. These processes produce diagnostic lines (e.g., [Ne II] 12.8 {mu}m and [O I] 6300 A) that we model as functions of key parameters such as EUV luminosity and spectral shape, X-ray luminosity and spectral shape, and wind mass loss rate and shock speed. Comparing our models with observations, we conclude that either internal shocks in the winds or X-rays incident on the disk surfaces often produce the observed [Ne II] line, although there are cases where EUV may dominate. Shocks created by the oblique interaction of winds with disks are unlikely [Ne II] sources because these shocks are too weak to ionize Ne. Even if [Ne II] is mainly produced by X-rays or internal wind shocks, the neon observations typically place upper limits of {approx}<10{sup 42} s{sup -1} on the EUV photon luminosity of these young low-mass stars. The observed [O I] 6300 A line has both a low velocity component (LVC) and a high velocity component. The latter likely arises in internal wind shocks. For the former we find that X-rays likely produce more [O I] luminosity than either the EUV layer, the transition layer between the EUV and X-ray layer, or the shear layer where the protostellar wind shocks and entrains disk material in a radial flow across the surface of the disk. Our soft X-ray models produce [O I] LVCs with luminosities up to 10{sup -4} L{sub sun}, but may not be able to explain the most luminous LVCs.

  20. Modeling transiting circumstellar disks: characterizing the newly discovered eclipsing disk system OGLE LMC-ECL-11893

    SciTech Connect

    Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M.

    2014-12-10

    We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ∼1.4 mag, preceded by a plateau of ∼0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ∼150 Myr and mass ∼4 M {sub ☉}. The disk appears to have an outer radius of ∼0.2 AU with predicted temperatures of ∼1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.

  1. Modeling Transiting Circumstellar Disks: Characterizing the Newly Discovered Eclipsing Disk System OGLE LMC-ECL-11893

    NASA Astrophysics Data System (ADS)

    Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M.

    2014-12-01

    We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ~1.4 mag, preceded by a plateau of ~0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ~150 Myr and mass ~4 M ⊙. The disk appears to have an outer radius of ~0.2 AU with predicted temperatures of ~1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.

  2. Stellar Populations and Radial Migrations in Virgo Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Roediger, Joel C.; Courteau, Stéphane; Sánchez-Blázquez, Patricia; McDonald, Michael

    2012-10-01

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ("U-shapes") in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (<=36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (~11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (>=50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field

  3. Wobbling The Galactic Disk with Bombardment of Satellite Galaxies

    NASA Astrophysics Data System (ADS)

    D'Onghia, Elena

    We propose to assess the effect of impacts of large visible satellite galaxies on a disk, as well as the relevance of the continuing bombardment of the Galactic disk by dark matter clumps as predicted by the current cosmological framework that can wobble the disk, heating it and eventually exciting ragged spiral structures. In particular, we make detailed predictions for observable features such as spiral arms, rings and their associated stars in galactic disks and relate them to the physical processes that drive their formation and evolution in our Milky Way galaxy and nearby spirals. To do this, we will combine analytic methods and numerical simulations that allow us to calculate observables, which we will compare to present and forthcoming observations. Our methodology utilizes a combination of state of the art hydrodynamic simulations of galaxy evolution and multi- wavelength radiative transfer simulations. Our primary goals are: (1) To identify the physical processes that are responsible for spiral structure formation observed in our Milky Way and nearby disk galaxies, from the flocculent to grand- designed spiral galaxies and to provide observable signatures to be compared with data on nearby galaxies combining maps of 24 micron emission (Spitzer) and cold gas, CO (Heracles) and HI (THINGS). (2) To explore different morphologies of spiral galaxies: from the multi-armed galaxies to the Milky Way sized galaxies with few arms. (3) For a Milky Way disk we will assess the effect of impacts of substructures passing through the disk to origin the asymmetry in the number density of stars recently discovered from SDSS and SEGUE data and confirmed from RAVE data. We will also investigate the disk heating in the vertical plane due to the formation of vertical oscillations that are produced by the impact and migration of stars in the disk as consequence of the heating as compared to the classical stellar migration mechanism. (4) We will measure the spiral pattern speed

  4. STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES

    SciTech Connect

    Roediger, Joel C.; Courteau, Stephane; Sanchez-Blazquez, Patricia; McDonald, Michael E-mail: courteau@astro.queensu.ca E-mail: mcdonald@space.mit.edu

    2012-10-10

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely

  5. DVD - digital versatile disks

    SciTech Connect

    Gaunt, R.

    1997-05-01

    An international standard has emerged for the first true multimedia format. Digital Versatile Disk (by its official name), you may know it as Digital Video Disks. DVD has applications in movies, music, games, information CD-ROMS, and many other areas where massive amounts of digital information is needed. Did I say massive amounts of data? Would you believe over 17 gigabytes on a single piece of plastic the size of an audio-CD? That`s the promise, at least, by the group of nine electronics manufacturers who have agreed to the format specification, and who hope to make this goal a reality by 1998. In this major agreement, which didn`t come easily, the manufacturers will combine Sony and Phillip`s one side double-layer NMCD format with Toshiba and Matsushita`s double sided Super-Density disk. By Spring of this year, they plan to market the first 4.7 gigabyte units. The question is: Will DVD take off? Some believe that read-only disks recorded with movies will be about as popular as video laser disks. They say that until the eraseable/writable DVD arrives, the consumer will most likely not buy it. Also, DVD has a good market for replacement of CD- Roms. Back in the early 80`s, the international committee deciding the format of the audio compact disk decided its length would be 73 minutes. This, they declared, would allow Beethoven`s 9th Symphony to be contained entirely on a single CD. Similarly, today it was agreed that playback length of a single sided, single layer DVD would be 133 minutes, long enough to hold 94% of all feature-length movies. Further, audio can be in Dolby`s AC-3 stereo or 5.1 tracks of surround sound, better than CD-quality audio (16-bits at 48kHz). In addition, there are three to five language tracks, copy protection and parental ``locks`` for R rated movies. DVD will be backwards compatible with current CD-ROM and audio CD formats. Added versatility comes by way of multiple aspect rations: 4:3 pan-scan, 4:3 letterbox, and 16:9 widescreen. MPEG

  6. BINARIES AMONG DEBRIS DISK STARS

    SciTech Connect

    Rodriguez, David R.; Zuckerman, B.

    2012-02-01

    We have gathered a sample of 112 main-sequence stars with known debris disks. We collected published information and performed adaptive optics observations at Lick Observatory to determine if these debris disks are associated with binary or multiple stars. We discovered a previously unknown M-star companion to HD 1051 at a projected separation of 628 AU. We found that 25% {+-} 4% of our debris disk systems are binary or triple star systems, substantially less than the expected {approx}50%. The period distribution for these suggests a relative lack of systems with 1-100 AU separations. Only a few systems have blackbody disk radii comparable to the binary/triple separation. Together, these two characteristics suggest that binaries with intermediate separations of 1-100 AU readily clear out their disks. We find that the fractional disk luminosity, as a proxy for disk mass, is generally lower for multiple systems than for single stars at any given age. Hence, for a binary to possess a disk (or form planets) it must either be a very widely separated binary with disk particles orbiting a single star or it must be a small separation binary with a circumbinary disk.

  7. Double-Disk Dark Matter

    NASA Astrophysics Data System (ADS)

    Fan, JiJi; Katz, Andrey; Randall, Lisa; Reece, Matthew

    2013-09-01

    Based on observational tests of large scale structure and constraints on halo structure, dark matter is generally taken to be cold and essentially collisionless. On the other hand, given the large number of particles and forces in the visible world, a more complex dark sector could be a reasonable or even likely possibility. This hypothesis leads to testable consequences, perhaps portending the discovery of a rich hidden world neighboring our own. We consider a scenario that readily satisfies current bounds that we call Partially Interacting Dark Matter (PIDM). This scenario contains self-interacting dark matter, but it is not the dominant component. Even if PIDM contains only a fraction of the net dark matter density, comparable to the baryonic fraction, the subdominant component’s interactions can lead to interesting and potentially observable consequences. Our primary focus will be the special case of Double-Disk Dark Matter (DDDM), in which self-interactions allow the dark matter to lose enough energy to lead to dynamics similar to those in the baryonic sector. We explore a simple model in which DDDM can cool efficiently and form a disk within galaxies, and we evaluate some of the possible observational signatures. The most prominent signal of such a scenario could be an enhanced indirect detection signature with a distinctive spatial distribution. Even though subdominant, the enhanced density at the center of the galaxy and possibly throughout the plane of the galaxy (depending on precise alignment) can lead to large boost factors, and could even explain a signature as large as the 130 GeV Fermi line. Such scenarios also predict additional dark radiation degrees of freedom that could soon be detectable and would influence the interpretation of future data, such as that from Planck and from the Gaia satellite. We consider this to be the first step toward exploring a rich array of new possibilities for dark matter dynamics.

  8. Kinematic Mass Measurements of Inner and Outer Spiral Disks

    NASA Astrophysics Data System (ADS)

    Herrmann, Kimberly A.; Ciardullo, R.

    2010-01-01

    Our knowledge of the structure and kinematics of galactic disks and halos is quite limited. While integrated light spectroscopy has provided a large amount of information on inner disks, once outside 2.5 disk scale lengths, almost nothing is known. Does the mass-to-light ratio (M/L) stay constant in the outer regions? Does the stellar scale height stay constant or do disks flare? Are galactic disks really maximal and could there be any trends with Hubble type? Are dark matter halos fit better by NFW or pseudo-isothermal models? We have been using planetary nebulae (PNe) to probe the kinematic structure of face-on spiral disks by identifying large ( 100) samples of these objects via narrow-band imaging, and then measuring their radial velocities with follow-up, high-precision ( 5 km/s) spectroscopy. Our results for IC 342, M74, M83, M94, and M101 are quite interesting. With one exception (M101) the z-velocity dispersion (sigmaz) of galactic disks declines exponentially with the light out to 3 disk scale lengths. This is exactly as expected for a constant M/L, constant scale height disk. However, in the two galaxies with significant data past this radius, the values of sigmaz asymptote out at 20 km/s. Moreover, our analysis finds kinematic evidence for significant flaring in the outer regions, especially in M94. These observations are in excellent agreement with predictions derived from models of disk heating by halo substructure, and demonstrate how kinematic surveys in the outer disks of spirals can be used to test hierarchical models of galaxy formation. We also find that the disks of late-type galaxies are far from maximal, that the disks of early type spirals have higher M/L ratios than the disks of later-type objects, and that the unseen inner halos of spiral galaxies are better fit by pseudo-isothermal laws than by NFW models.

  9. A BIPOLAR OUTFLOW FROM THE MASSIVE PROTOSTELLAR CORE W51e2-E

    SciTech Connect

    Shi Hui; Han, J. L.; Zhao Junhui E-mail: hil@nao.cas.c

    2010-08-01

    We present high-resolution images of the bipolar outflow from W51e2, which are produced from the Submillimeter Array archival data observed for CO(3-2) and HCN(4-3) lines with angular resolutions of 0.''8 x 0.''6 and 0.''3 x 0.''2, respectively. The images show that the powerful outflow originates from the protostellar core W51e2-E rather than from the ultracompact H II region W51e2-W. The kinematic timescale of the outflow from W51e2-E is about 1000 yr, younger than the age ({approx}5000 yr) of the ultracompact H II region W51e2-W. A large mass-loss rate of {approx}1 x 10{sup -3} M{sub sun} yr{sup -1} and a high mechanical power of 120 L{sub sun} are inferred, suggesting that an O star or a cluster of B stars are forming in W51e2-E. The observed outflow activity along with the inferred large accretion rate indicates that at present W51e2-E is in a rapid phase of star formation.

  10. Champagne flutes and brandy snifters: modelling protostellar outflow-cloud chemical interfaces

    NASA Astrophysics Data System (ADS)

    Rollins, R. P.; Rawlings, J. M. C.; Williams, D. A.; Redman, M. P.

    2014-10-01

    A rich variety of molecular species has now been observed towards hot cores in star-forming regions and in the interstellar medium. An increasing body of evidence from millimetre interferometers suggests that many of these form at the interfaces between protostellar outflows and their natal molecular clouds. However, current models have remained unable to explain the origin of the observational bias towards wide-angled `brandy snifter' shaped outflows over narrower `champagne flute' shapes in carbon monoxide imaging. Furthermore, these wide-angled systems exhibit unusually high abundances of the molecular ion HCO+. We present results from a chemodynamic model of such regions where a rich chemistry arises naturally as a result of turbulent mixing between cold, dense molecular gas and the hot, ionized outflow material. The injecta drives a rich and rapid ion-neutral chemistry in qualitative and quantitative agreement with the observations. The observational bias towards wide-angled outflows is explained naturally by the geometry-dependent ion injection rate causing rapid dissociation of CO in the younger systems.

  11. Tracing Massive Protostellar Jets from Intermediate-Mass Protostars in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Reiter, A.

    2014-09-01

    We present new spectroscopy and imaging of four protostellar jets in the Carina nebula. Near-IR [Fe II] emission traces dense gas in the jet that is self-shielded from Lyman continuum photons from nearby O-type stars. New near-IR [Fe II] images reveal a substantial mass of dense, neutral gas that is not seen in the Halpha emission from these jets, leading to densities and mass-loss rate estimates an order of magnitude larger than those derived from the Halpha emission measure. Higher jet mass-loss rates require higher accretion rates, implying that these jets are driven by intermediate-mass (around 2 - 8 solar masses) protostars. Velocities from new proper motion and spectroscopic measurements fall among the velocities typically measured in lower-luminosity sources (100 - 200 km/s). We propose that these jets reflect essentially the same outflow phenomenon seen in low-mass protostars, but that the collimated atomic jet core is irradiated and rendered observable. Thus, the jets in Carina constitute a new view of collimated jets from intermediate-mass protostars that exist in a feedback-dominated environment, and offer strong additional evidence that stars up to 8 solar masses form by the same accretion mechanisms as low-mass stars.

  12. The dependence of protostellar luminosity on environment in the Cygnus-X star-forming complex

    SciTech Connect

    Kryukova, E.; Megeath, S. T.; Hora, J. L.; Smith, Howard A.; Gutermuth, R. A.; Bontemps, S.; Schneider, N.; Kraemer, K.; Hennemann, M.; Motte, F.

    2014-07-01

    The Cygnus-X star-forming complex is one of the most active regions of low- and high-mass star formation within 2 kpc of the Sun. Using mid-infrared photometry from the IRAC and MIPS Spitzer Cygnus-X Legacy Survey, we have identified over 1800 protostar candidates. We compare the protostellar luminosity functions of two regions within Cygnus-X: CygX-South and CygX-North. These two clouds show distinctly different morphologies suggestive of dissimilar star-forming environments. We find the luminosity functions of these two regions are statistically different. Furthermore, we compare the luminosity functions of protostars found in regions of high and low stellar density within Cygnus-X and find that the luminosity function in regions of high stellar density is biased to higher luminosities. In total, these observations provide further evidence that the luminosities of protostars depend on their natal environment. We discuss the implications this dependence has for the star formation process.

  13. Different-sized dust grains and the chemical evolution of protostellar objects

    NASA Astrophysics Data System (ADS)

    Kochina, O. V.; Wiebe, D. S.

    2014-04-01

    Results of modeling the chemical evolution of protostellar objects are presented. The models take into account the existence of different dust populations with distinct grain sizes, total mass fractions, and temperatures. In addition to "classical" dust grains, the models include an entirely different second dust population, with dust grain sizes of 30 Å and a higher temperature. Two chemical-evolution models are compared, one taking into account only classical dust and the other including both dust populations. The influence of a complex dust composition on the general evolution of the molecular contents of prestellar cores and the abundances of a number of chemical species is studied. At early evolutionary stages, differences are mainly determined by the modification changes in the photoprocesses' balance due to efficient UV absorption by the second population of dust grains and in collisional reactions with the dust grains. At late stages, distinctions between the models are also determined by the increasing dominance of additional reaction channels. The species that respond to the presence of small grains in different ways are separated into different groups. Allowing for the presence of small grains makes it possible to significantly lower the water abundance in the gas phase.

  14. A Self-Perpetuating Catalyst for the Production of Complex Organic Molecules in Protostellar Nebulae

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A.; Johnson, N. M.

    2010-01-01

    The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. Many mechanisms may contribute to the total organic content in protostellar nebulae, ranging from organics formed via ion-molecule and atom-molecule reactions in the cold dark clouds from which such nebulae collapse, to similar ion-molecule and atom-molecule reactions in the dark regions of the nebula far from the proto star, to gas phase reactions in sub-nebulae around growing giant planets and in the nebulae themselves. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. The Haber-Bosch catalytic reduction of N2 by hydrogen was thought to produce the reduced nitrogen found in meteorites. However, the clean iron metal surfaces that catalyze these reactions are easily poisoned via reaction with any number of molecules, including the very same complex organics that they produce and both reactions work more efficiently in the hot regions of the nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Although none work as well as pure iron grains, and all produce a wide range of organic products rather than just pure methane, these materials are not truly catalysts.

  15. A DENSITY DEPENDENCE FOR PROTOSTELLAR LUMINOSITY IN CLASS I SOURCES: COLLABORATIVE ACCRETION

    SciTech Connect

    Elmegreen, Bruce G.; Hurst, Rachel; Koenig, Xavier

    2014-02-10

    Class I protostars in three high-mass star-forming regions are found to have correlations among the local projected density of other Class I protostars, the summed flux from these other protostars, and the protostellar luminosity in the WISE 22 μm band. Brighter Class I sources form in higher-density and higher-flux regions, while low luminosity sources form anywhere. These correlations depend slightly on the number of neighbors considered (from 2 to 20) and could include a size-of-sample effect from the initial mass function (i.e., larger numbers include rarer and more massive stars). Luminosities seem to vary by neighborhood with nearby protostars having values proportional to each other and higher density regions having higher values. If Class I luminosity is partially related to the accretion rate, then this luminosity correlation is consistent with the competitive accretion model, although it is more collaborative than competitive. The correlation is also consistent with primordial mass segregation and could explain why the stellar initial mass function resembles the dense core mass function even when cores form multiple stars.

  16. A Theoretical Perspective on the Formation and Fragmentation of Protostellar Discs

    NASA Astrophysics Data System (ADS)

    Whitworth, A.; Lomax, O.

    2016-01-01

    We discuss the factors influencing the formation and gravitational fragmentation of protostellar discs. We start with a review of how observations of prestellar cores can be analysed statistically to yield plausible initial conditions for simulations of their subsequent collapse. Simulations based on these initial conditions show that, despite the low levels of turbulence in prestellar cores, they deliver primary protostars and associated discs which are routinely subject to stochastic impulsive perturbations; consequently misalignment of the spins and orbits of protostars are common. Also, the simulations produce protostars that collectively have a mass function and binary statistics matching those observed in nearby star-formation regions, but only if a significant fraction of the turbulent energy in the core is solenoidal, and accretion onto the primary protostar is episodic with a duty cycle ≳ 3 000 yr. Under this circumstance, a core typically spawns between 4 and 5 protostars, with high efficiency, and the lower mass protostars are mainly formed by disc fragmentation. The requirement that a proto-fragment in a disc lose thermal energy on a dynamical timescale dictates that there is a sweet spot for disc fragmentation at radii 70 AU ≲ R ≲ 100 AU and temperatures 10 K ≲ T ≲ 20 K, and this might explain the brown dwarf desert.

  17. Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157

    NASA Astrophysics Data System (ADS)

    Mendoza, Edgar; Lefloch, B.; López-Sepulcre, A.; Ceccarelli, C.; Codella, C.; Boechat-Roberty, H. M.; Bachiller, R.

    2014-11-01

    Interstellar molecules with a peptide link (-NH-C(=O)-), like formamide (NH2CHO), acetamide (NH2COCH3) and isocyanic acid (HNCO), are particularly interesting for their potential role in pre-biotic chemistry. We have studied their emission in the protostellar shock regions L1157-B1 and L1157-B2, with the IRAM 30 m telescope, as part of the ASAI Large Programme. Analysis of the line profiles shows that the emission arises from the outflow cavities associated with B1 and B2. Molecular abundances of ≈(0.4-1.1) × 10-8 and (3.3-8.8) × 10-8 are derived for formamide and isocyanic acid, respectively, from a simple rotational diagram analysis. Conversely, NH2COCH3 was not detected down to a relative abundance of a few ≤10-10. B1 and B2 appear to be among the richest Galactic sources of HNCO and NH2CHO molecules. A tight linear correlation between their abundances is observed, suggesting that the two species are chemically related. Comparison with astrochemical models favours molecule formation on icy grain mantles, with NH2CHO generated from hydrogenation of HNCO.

  18. FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS

    SciTech Connect

    Dekel, Avishai; Sari, Re'em; Ceverino, Daniel E-mail: sari@phys.huji.ac.i

    2009-09-20

    We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability, and bulge formation. Intense, relatively smooth streams maintain an unstable dense gas-rich disk. Instability with high turbulence and giant clumps, each a few percent of the disk mass, is self-regulated by gravitational interactions within the disk. The clumps migrate into a bulge in {approx}<10 dynamical times, or {approx}<0.5 Gyr. The cosmological streams replenish the draining disk and prolong the clumpy phase to several Gigayears in a steady state, with comparable masses in disk, bulge, and dark matter within the disk radius. The clumps form stars in dense subclumps following the overall accretion rate, {approx}100 M{sub sun} yr{sup -1}, and each clump converts into stars in {approx}0.5 Gyr. While the clumps coalesce dissipatively to a compact bulge, the star-forming disk is extended because the incoming streams keep the outer disk dense and susceptible to instability and because of angular momentum transport. Passive spheroid-dominated galaxies form when the streams are more clumpy: the external clumps merge into a massive bulge and stir up disk turbulence that stabilize the disk and suppress in situ clump and star formation. We predict a bimodality in galaxy type by z {approx} 3, involving giant-clump star-forming disks and spheroid-dominated galaxies of suppressed star formation. After z {approx} 1, the disks tend to be stabilized by the dominant stellar disks and bulges. Most of the high-z massive disks are likely to end up as today's early-type galaxies.

  19. ROTATION OF THE NGC 1333 IRAS 4A2 PROTOSTELLAR JET

    SciTech Connect

    Choi, Minho; Kang, Miju; Tatematsu, Ken'ichi

    2011-02-20

    The bipolar jet of the NGC 1333 IRAS 4A2 protostar shows a velocity gradient in the direction perpendicular to the jet axis. This lateral velocity gradient can be seen throughout the jet imaged in a silicon monoxide line, 2500-8700 AU from the driving source, and is consistent with the rotation of the accretion disk. If this gradient is caused by the rotation of the jet around its axis, the average specific angular momentum is about 1.5 x 10{sup 21} cm{sup 2} s{sup -1}. Comparison of the kinematics between the jet and the disk suggests that the jet-launching region on the disk has a radius of about 2 AU, which supports the disk-wind models. The angular momentum transported away by the jet seems to be large enough for the protostar to accrete matter from the disk, confirming the crucial role of jets in the early phase of the star formation process.

  20. THE COLLISIONAL EVOLUTION OF DEBRIS DISKS

    SciTech Connect

    Gaspar, Andras; Rieke, George H.; Balog, Zoltan E-mail: grieke@as.arizona.edu

    2013-05-01

    We explore the collisional decay of disk mass and infrared emission in debris disks. With models, we show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a slower value. The total disk mass falls off {proportional_to}t {sup -0.35} at its fastest point (where t is time) for our reference model, while the dust mass and its proxy-the infrared excess emission-fades significantly faster ({proportional_to}t {sup -0.8}). These later level off to a decay rate of M{sub tot}(t){proportional_to}t {sup -0.08} and M{sub dust}(t) or L{sub ir}(t){proportional_to}t {sup -0.6}. This is slower than the {proportional_to}t {sup -1} decay given for all three system parameters by traditional analytic models. We also compile an extensive catalog of Spitzer and Herschel 24, 70, and 100 {mu}m observations. Assuming a log-normal distribution of initial disk masses, we generate model population decay curves for the fraction of stars harboring debris disks detected at 24 {mu}m. We also model the distribution of measured excesses at the far-IR wavelengths (70-100 {mu}m) at certain age regimes. We show general agreement at 24 {mu}m between the decay of our numerical collisional population synthesis model and observations up to a Gyr. We associate offsets above a Gyr to stochastic events in a few select systems. We cannot fit the decay in the far-infrared convincingly with grain strength properties appropriate for silicates, but those of water ice give fits more consistent with the observations (other relatively weak grain materials would presumably also be successful). The oldest disks have a higher incidence of large excesses than predicted by the model; again, a plausible explanation is very late phases of high dynamical activity around a small number of stars. Finally, we constrain the variables of our numerical model by comparing the evolutionary trends generated from the exploration

  1. Ringed Accretion Disks: Instabilities

    NASA Astrophysics Data System (ADS)

    Pugliese, D.; Stuchlík, Z.

    2016-04-01

    We analyze the possibility that several instability points may be formed, due to the Paczyński mechanism of violation of mechanical equilibrium, in the orbiting matter around a supermassive Kerr black hole. We consider a recently proposed model of a ringed accretion disk, made up by several tori (rings) that can be corotating or counter-rotating relative to the Kerr attractor due to the history of the accretion process. Each torus is governed by the general relativistic hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. We prove that the number of the instability points is generally limited and depends on the dimensionless spin of the rotating attractor.

  2. Supermassive disk galaxies

    NASA Astrophysics Data System (ADS)

    Buson, L. M.; Galletta, G.; Saglia, R. P.; Zeilinger, W. W.

    1991-03-01

    In order to investigate the properties of supermassive disk galaxies (SDGs), an extensive optical survey of SDG candidates in the Southern Hemisphere was performed with the 2.2-m ESO/MPI telescope at La Silla. The question of whether SDGs have in general an unusually high content of dark matter in the inner regions or, perhaps, an unusual stellar population is addressed. It is suggested that SDGs are formed as the result of a series of accretion events, possibly induced also by the progressive deepening of the galaxy potential well.

  3. Upper lumbar disk herniations.

    PubMed

    Cedoz, M E; Larbre, J P; Lequin, C; Fischer, G; Llorca, G

    1996-06-01

    Specific features of upper lumbar disk herniations are reviewed based on data from the literature and from a retrospective study of 24 cases treated surgically between 1982 and 1994 (seven at L1-L2 and 17 at L2-L3). Clinical manifestations are polymorphic, misleading (abdominogenital pain suggestive of a visceral or psychogenic condition, meralgia paresthetica, isolated sciatica; femoral neuralgia is uncommon) and sometimes severe (five cases of cauda equina syndrome in our study group). The diagnostic usefulness of imaging studies (radiography, myelography, computed tomography, magnetic resonance imaging) and results of surgery are discussed. The risk of misdiagnosis and the encouraging results of surgery are emphasized. PMID:8817752

  4. Eccentric-Disk Models for the Nucleus of M31

    NASA Astrophysics Data System (ADS)

    Peiris, Hiranya V.; Tremaine, Scott

    2003-12-01

    We construct dynamical models of the ``double'' nucleus of M31 in which the nucleus consists of an eccentric disk of stars orbiting a central black hole. The principal approximation in these models is that the disk stars travel in a Keplerian potential; i.e., we neglect the mass of the disk relative to the black hole. We consider both ``aligned'' models, in which the eccentric disk lies in the plane of the large-scale M31 disk, and ``nonaligned'' models, in which the orientation of the eccentric disk is fitted to the data. Both types of model can reproduce the double structure and overall morphology seen in Hubble Space Telescope photometry. In comparison with the best available ground-based spectroscopy, the models reproduce the asymmetric rotation curve, the peak height of the dispersion profile, and the qualitative behavior of the Gauss-Hermite coefficients h3 and h4. Aligned models fail to reproduce the observation that the surface brightness at P1 is higher than at P2 and yield significantly poorer fits to the kinematics; thus, we favor nonaligned models. Eccentric-disk models fitted to ground-based spectroscopy are used to predict the kinematics observed at much higher resolution by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, and we find generally satisfactory agreement.

  5. Observations of Water Ice Distribution in the HD169142 Disk

    NASA Astrophysics Data System (ADS)

    Honda, Mitsuhiko

    2013-01-01

    Icy grains play an important role on planetesimal/planet formation and related matters. Therefore, to reveal ice dust distribution within a protoplanetary disk is an important work for understanding planet formation. However, observations of icy grain IN THE DISK are scarce due to various observational limitations. Here we propose observations to trace the icy grains by making K, H_2O ice, and L' imaging photometric observations of disk scattered light to derive H_2O ice dust distribution in a disk surface via 3.1 mu m absorption. For the moment, only Gemini/NICI is capable of such observations. We have already demonstrated the effectiveness of such observing method toward Herbig Fe star HD142527. Since some theoretical studies suggest that there are no ice grains at the surface of the disk around A/B stars due to intense UV irradiation, we propose to observe disks around Herbig Ae star HD169142. When we fail to detect the ice feature, it supports the theoretical prediction that photodesorption is important. While the ice feature is detected, it requires reconsideration of the theories and provides an important constraint for the disk chemistry.

  6. TEMPERATURE STRUCTURE OF PROTOPLANETARY DISKS UNDERGOING LAYERED ACCRETION

    SciTech Connect

    Lesniak, M. V.; Desch, S. J.

    2011-10-20

    We calculate the temperature structures of protoplanetary disks (PPDs) around T Tauri stars heated by both incident starlight and viscous dissipation. We present a new algorithm for calculating the temperatures in disks in hydrostatic and radiative equilibrium, based on Rybicki's method for iteratively calculating the vertical temperature structure within an annulus. At each iteration, the method solves for the temperature at all locations simultaneously, and converges rapidly even at high (>>10{sup 4}) optical depth. The method retains the full frequency dependence of the radiation field. We use this algorithm to study for the first time disks evolving via the magnetorotational instability. Because PPD midplanes are weakly ionized, this instability operates preferentially in their surface layers, and disks will undergo layered accretion. We find that the midplane temperatures T{sub mid} are strongly affected by the column density {Sigma}{sub a} of the active layers, even for fixed mass accretion rate M-dot . Models assuming uniform accretion predict midplane temperatures in the terrestrial planet forming region several x 10{sup 2} K higher than our layered accretion models do. For M-dot < 10{sup -7} M{sub sun} yr{sup -1} and the column densities {Sigma}{sub a} < 10 g cm{sup -2} associated with layered accretion, disk temperatures are indistinguishable from those of a passively heated disk. We find emergent spectra are insensitive to {Sigma}{sub a}, making it difficult to observationally identify disks undergoing layered versus uniform accretion.

  7. Comets as collisional fragments of a primordial planetesimal disk

    NASA Astrophysics Data System (ADS)

    Morbidelli, A.; Rickman, H.

    2015-11-01

    Context. The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. Aims: We investigate the collisional evolution experienced by the precursors of current comet nuclei during the early stages of the solar system in the context of the so-called Nice model. Methods: We considered two environments for the collisional evolution: (1) the transplanetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants; and (2) the dispersing disk during the time that the scattered disk was formed. We performed simulations using different methods in the two cases to determine the number of destructive collisions typically experienced by a comet nucleus of 2 km radius. Results: In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4 Gy ago, comet-sized planetesimals have a very low probability of surviving destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, a significant fraction of the planetesimals might have remained intact. However, these survivors would still bear the marks of many nondestructive impacts. Conclusions: The Nice model of solar system evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for future research is to investigate whether the observed properties of comet nuclei are compatible with such a collisional origin.

  8. A disk of scattered icy objects and the origin of Jupiter-family comets.

    PubMed

    Duncan, M J; Levison, H F

    1997-06-13

    Orbital integrations carried out for 4 billion years produced a disk of scattered objects beyond the orbit of Neptune. Objects in this disk can be distinguished from Kuiper belt objects by a greater range of eccentricities and inclinations. This disk was formed in the simulations by encounters with Neptune during the early evolution of the outer solar system. After particles first encountered Neptune, the simulations show that about 1 percent of the particles survive in this disk for the age of the solar system. A disk currently containing as few as approximately 6 x 10(8) objects could supply all of the observed Jupiter-family comets. Two recently discovered objects, 1996 RQ20 and 1996 TL66, have orbital elements similar to those predicted for objects in this disk, suggesting that they are thus far the only members of this disk to be identified. PMID:9180070

  9. Optical disk media research discussed

    NASA Astrophysics Data System (ADS)

    Hou, J.; Gan, F.

    1986-03-01

    A review of the current status of the research and development on various optical disk media is presented. It is noted that research around the world on the media for the nonerasable optical disk is almost over, and that the nonerasable optical disk has been successfully used for CD, LD player and DRAW devices. On the other hand, great efforts are now being made to search the more suitable media for erasable optical disks. Extensive experiments on various material systems including optical characteristic change, phase transition and magneto-optical recording media are under way. It is expected that fruitful results will appear in the next 2 or 3 years.

  10. Gravitational Instability in Planetesimal Disks

    NASA Astrophysics Data System (ADS)

    Bolin, Bryce T.; Lithwick, Yoram; Pan, Margaret; Rein, Hanno; Wu, Yanqin

    2014-11-01

    Gravitational instability (GI) has been proposed as a method of forming giant gas planets enhanced by disk thermodynamics in a protoplanetary disk (Boss, 1997, Science 276; Durisen et al., 2007, Protostars and Planets V) and as a method of forming planetesimals through the focusing of boulders by the interaction between solids and gases in a turbulent circumstellar disk (Johansen et al., 2007, Nature 448; Youdin & Goodman, 2005, Astrophys. J. 620). GI is mediated through a gaseous circumstellar disk in each each of these scenarios. We explore the possibility of GI occurring in a planetesimal disk devoid of gas. In this regime, mutual collisions between planetesimals are required to dissipate their orbital shear and velocity dispersion enough for collapse to occur as described by the Toomre stability criterion (Toomre, 1964, Astrophys. J. 139; Toomre, 1981, Structure and Evolution of Normal Galaxies). How frequent must collisions be between planetesimals in a gravitationally stable planetesimal disk for GI to occur? Are there collisional rates where GI is postponed indefinitely in an equilibrium state between gravitational stirring and collisional cooling? We present 3D shearing sheet simulations using the REBOUND N-body code with the symplectic epicyclic integrator (Rein & Liu, 2011, A&A 537; Rein & Tremaine, 2011, MNRAS 415) in which the candidate collision rates are within a few orders of magnitude of the disk dynamical lifetime. Our simulations suggest that collisions rate directly controls disk cooling. The shape of the disk cooling curve is independent of the collision rate when scaled to the collision time.

  11. Higher order diffractions from a circular disk

    NASA Technical Reports Server (NTRS)

    Marsland, Diane P.; Balanis, Constantine A.; Brumley, Stephen A.

    1987-01-01

    The backscattering from a circular disk is analyzed using the geometrical theory of diffraction. First-, second-, and third-order diffractions are included in the hard polarization analysis, while first-, second-, and third-order slope diffractions are included for soft polarization. Improvements in the prediction of the monostatic radar cross section over previous works are noted. For hard polarization, an excellent agreement is exhibited between experimental and theoretical results, while a very good agreement is noted for soft polarization. To further improve the soft polarization results for wide angles, a model for the creeping wave or circulating current on the edge of the disk is obtained and used to find an additional component of the backscattered field. The addition of this component significantly improves the results for wide angles, leading to excellent agreement for soft polarization also. An axial-caustic correction method using equivalent currents is also included in the analysis.

  12. [Disk calcifications in children].

    PubMed

    Schmit, P; Fauré, C; Denarnaud, L

    1985-05-01

    It is not unusual for intervertebral disk calcifications to be detected in pediatric practice, the 150 or so cases reported in the literature probably representing only a small proportion of lesions actually diagnosed. Case reports of 33 children with intervertebral disk calcifications were analyzed. In the majority of these patients (31 of 33) a diagnosis of "idiopathic" calcifications had been made, the cervical localization of the lesions being related to repeated ORL infections and/or trauma. A pre-existing pathologic factor was found in two cases (one child with juvenile rheumatoid arthritis treated by corticoids and one child with Williams and Van Beuren's syndrome). An uncomplicated course was noted in 31 cases, the symptomatology (pain, spinal stiffness and febricula) improving after several days. Complications developed in two cases: one child had very disabling dysphagia due to an anteriorly protruding cervical herniated disc and surgery was necessary; the other child developed cervicobrachial neuralgia due to herniated disc protrusion into the cervical spinal canal, but symptoms regressed within several days although calcifications persisted unaltered. These findings and the course of the rare complications documented in the literature suggest the need for the most conservative treatment possible in cases of disc calcifications in children. PMID:4032343

  13. Disk storage at CERN

    NASA Astrophysics Data System (ADS)

    Mascetti, L.; Cano, E.; Chan, B.; Espinal, X.; Fiorot, A.; González Labrador, H.; Iven, J.; Lamanna, M.; Lo Presti, G.; Mościcki, JT; Peters, AJ; Ponce, S.; Rousseau, H.; van der Ster, D.

    2015-12-01

    CERN IT DSS operates the main storage resources for data taking and physics analysis mainly via three system: AFS, CASTOR and EOS. The total usable space available on disk for users is about 100 PB (with relative ratios 1:20:120). EOS actively uses the two CERN Tier0 centres (Meyrin and Wigner) with 50:50 ratio. IT DSS also provide sizeable on-demand resources for IT services most notably OpenStack and NFS-based clients: this is provided by a Ceph infrastructure (3 PB) and few proprietary servers (NetApp). We will describe our operational experience and recent changes to these systems with special emphasis to the present usages for LHC data taking, the convergence to commodity hardware (nodes with 200-TB each with optional SSD) shared across all services. We also describe our experience in coupling commodity and home-grown solution (e.g. CERNBox integration in EOS, Ceph disk pools for AFS, CASTOR and NFS) and finally the future evolution of these systems for WLCG and beyond.

  14. Disk MHD generator study

    NASA Technical Reports Server (NTRS)

    Retallick, F. D.

    1980-01-01

    Directly-fired, separately-fired, and oxygen-augmented MHD power plants incorporating a disk geometry for the MHD generator were studied. The base parameters defined for four near-optimum-performance MHD steam power systems of various types are presented. The finally selected systems consisted of (1) two directly fired cases, one at 1920 K (2996F) preheat and the other at 1650 K (2500 F) preheat, (2) a separately-fired case where the air is preheated to the same level as the higher temperature directly-fired cases, and (3) an oxygen augmented case with the same generator inlet temperature of 2839 (4650F) as the high temperature directly-fired and separately-fired cases. Supersonic Mach numbers at the generator inlet, gas inlet swirl, and constant Hall field operation were specified based on disk generator optimization. System pressures were based on optimization of MHD net power. Supercritical reheat stream plants were used in all cases. Open and closed cycle component costs are summarized and compared.

  15. Integrability of motion around galactic razor-thin disks

    NASA Astrophysics Data System (ADS)

    Vieira, Ronaldo S. S.; Ramos-Caro, Javier

    2016-06-01

    We consider the three-dimensional bounded motion of a test particle around razor-thin disk configurations, by focusing on the adiabatic invariance of the vertical action associated with disk-crossing orbits. We find that it leads to an approximate third integral of motion predicting envelopes of the form Z(R)∝ [Σ (R)]^{-1/3} , where R is the radial galactocentric coordinate, Z is the z-amplitude (vertical amplitude) of the orbit and Σ represents the surface mass density of the thin disk. This third integral, which was previously formulated for the case of flattened 3D configurations, is tested for a variety of trajectories in different thin-disk models.

  16. Numerical evaluation of single central jet for turbine disk cooling

    NASA Astrophysics Data System (ADS)

    Subbaraman, M. R.; Hadid, A. H.; McConnaughey, P. K.

    The cooling arrangement of the Space Shuttle Main Engine High Pressure Oxidizer Turbopump (HPOTP) incorporates two jet rings, each of which produces 19 high-velocity coolant jets. At some operating conditions, the frequency of excitation associated with the 19 jets coincides with the natural frequency of the turbine blades, contributing to fatigue cracking of blade shanks. In this paper, an alternate turbine disk cooling arrangement, applicable to disk faces of zero hub radius, is evaluated, which consists of a single coolant jet impinging at the center of the turbine disk. Results of the CFD analysis show that replacing the jet ring with a single central coolant jet in the HPOTP leads to an acceptable thermal environment at the disk rim. Based on the predictions of flow and temperature fields for operating conditions, the single central jet cooling system was recommended for implementation into the development program of the Technology Test Bed Engine at NASA Marshall Space Flight Center.

  17. Testing accretion disk instabilities in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Bagińska, Patrycja; Różańska, Agata; Janiuk, Agnieszka; Czerny, Bożena

    2014-12-01

    We study disk instabilities in black hole binaries in which X-ray novae outbursts were observed. Typically, one outburst occurs in each light curve, with total duration from 30 up to 400 days. The shape of an outburst can be very regular fast rise exponential decay (FRED) characteristic for ionisation instability mechanism that occurs in accretion disks, or irregular suggesting that, beside FRED, additional flickering occurs. We use the model which predicts time dependent evolution of ionisation instability in an accretion disk around black hole, assuming viscosity parameter to be proportional to the total pressure. We test it in detail for two objects: GX 339-4 and XTE J1818-245. The modelled light curves agree with the collected RXTE light curves, indicating that disk instability works in those objects.

  18. Chemistry in disks. VIII. The CS molecule as an analytic tracer of turbulence in disks

    NASA Astrophysics Data System (ADS)

    Guilloteau, S.; Dutrey, A.; Wakelam, V.; Hersant, F.; Semenov, D.; Chapillon, E.; Henning, T.; Piétu, V.

    2012-12-01

    Context. Turbulence is thought to be a key driver of the evolution of protoplanetary disks, regulating the mass accretion process, the transport of angular momentum, and the growth of dust particles. Aims: We intend to determine the magnitude of the turbulent motions in the outer parts (>100 AU) of the disk surrounding DM Tau. Methods: Turbulent motions can be constrained by measuring the nonthermal broadening of line emission from heavy molecules. We used the IRAM Plateau de Bure interferometer to study emission from the CS molecule in the disk of DM Tau. High spatial (1.4 × 11.4 × 1 farcs) and spectral resolution (0.126 km s-1) CS J = 3-2 images provide constraints on the molecule distribution and velocity structure of the disk. A low sensitivity CS J = 5-4 image was used in conjunction to evaluate the excitation conditions. We analyzed the data in terms of two parametric disk models, and compared the results with detailed time-dependent chemical simulations. Results: The CS data confirm the relatively low temperature suggested by observations of other simple molecules. The intrinsic linewidth derived from the CS J = 3-2 data is much larger than expected from pure thermal broadening. The magnitude of the derived nonthermal component depends only weakly on assumptions about the location of the CS molecules with respect to the disk plane. Our results indicate turbulence with a Mach number around 0.4-0.5 in the molecular layer. Geometrical constraints suggest that this layer is located near one scale height, in reasonable agreement with chemical model predictions. Based on observations carried out with the IRAM Plateau de Bure interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

  19. A twisted disk equation that describes warped galaxy disks

    NASA Technical Reports Server (NTRS)

    Barker, K.

    1994-01-01

    Warped H1 gas layers in the outer regions of spiral galaxies usually display a noticeably twisted structure. This structure is thought to arise primarily as a result of differential precession in the H1 disk as it settles toward a 'preferred orientation' in an underlying dark halo potential well that is not spherically symmetric. In an attempt to better understand the structure and evolution of these twisted, warped disk structures, we have utilized the 'twist-equation' formalism. Specifically, we have generalized the twist equation to allow the treatment of non-Keplerian disks and from it have derived the steady-state structure of twisted disks that develop from free precession in a nonspherical, logarithmic halo potential. This generalized equation can also be used to examine the time-evolutionary behavior of warped galaxy disks.

  20. VISCOUS EVOLUTION AND PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS DUE TO EXTERNAL FAR ULTRAVIOLET RADIATION FIELDS

    SciTech Connect

    Anderson, Kassandra R.; Adams, Fred C.; Calvet, Nuria

    2013-09-01

    This paper explores the effects of FUV radiation fields from external stars on circumstellar disk evolution. Disks residing in young clusters can be exposed to extreme levels of FUV flux from nearby OB stars, and observations show that disks in such environments are being actively photoevaporated. Typical FUV flux levels can be factors of {approx}10{sup 2}-10{sup 4} higher than the interstellar value. These fields are effective in driving mass loss from circumstellar disks because they act at large radial distance from the host star, i.e., where most of the disk mass is located, and where the gravitational potential well is shallow. We combine viscous evolution (an {alpha}-disk model) with an existing FUV photoevaporation model to derive constraints on disk lifetimes, and to determine disk properties as functions of time, including mass-loss rates, disk masses, and radii. We also consider the effects of X-ray photoevaporation from the host star using an existing model, and show that for disks around solar-mass stars, externally generated FUV fields are often the dominant mechanism in depleting disk material. For sufficiently large viscosities, FUV fields can efficiently photoevaporate disks over the entire range of parameter space. Disks with viscosity parameter {alpha} = 10{sup -3} are effectively dispersed within 1-3 Myr; for higher viscosities ({alpha} = 10{sup -2}) disks are dispersed within {approx}0.25-0.5 Myr. Furthermore, disk radii are truncated to less than {approx}100 AU, which can possibly affect the formation of planets. Our model predictions are consistent with the range of observed masses and radii of proplyds in the Orion Nebula Cluster.

  1. OUTWARD MIGRATION OF JUPITER AND SATURN IN EVOLVED GASEOUS DISKS

    SciTech Connect

    D'Angelo, Gennaro; Marzari, Francesco E-mail: francesco.marzari@pd.infn.it

    2012-09-20

    The outward migration of a pair of resonant-orbit planets, driven by tidal interactions with a gas-dominated disk, is studied in the context of evolved solar nebula models. The planets' masses, M{sub 1} and M{sub 2}, correspond to those of Jupiter and Saturn. Hydrodynamical calculations in two and three dimensions are used to quantify the migration rates and analyze the conditions under which the outward migration mechanism may operate. The planets are taken to be fully formed after 10{sup 6} and before 3 Multiplication-Sign 10{sup 6} years. The orbital evolution of the planets in an evolving disk is then calculated until the disk's gas is completely dissipated. Orbital locking in the 3:2 mean motion resonance may lead to outward migration under appropriate conditions of disk viscosity and temperature. However, resonance locking does not necessarily result in outward migration. This is the case, for example, if convergent migration leads to locking in the 2:1 mean motion resonance, as post-formation disk conditions seem to suggest. Accretion of gas on the planets may deactivate the outward migration mechanism by raising the mass ratio M{sub 2}/M{sub 1} and/or by reducing the accretion rate toward the star, and hence depleting the inner disk. For migrating planets locked in the 3:2 mean motion resonance, there are stalling radii that depend on disk viscosity and on stellar irradiation, when it determines the disk's thermal balance. Planets locked in the 3:2 orbital resonance that start moving outward from within 1-2 AU may reach beyond Almost-Equal-To 5 AU only under favorable conditions. However, within the explored space of disk parameters, only a small fraction-less than a few percent-of the models predict that the interior planet reaches beyond Almost-Equal-To 4 AU.

  2. The Evolving Properties of Water in a Dynamic Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Ciesla, Fred

    2015-08-01

    Protoplanetary disks are dynamic objects, through which mass and angular momentum are transported as part of the final stages of pre-main sequence evolution of their central stars. These disks are also rich chemical factories, in which materials inherited from the interstellar medium are transformed through a series of reactions (involving, gases, solids, ions, and photons) to the eventual building blocks of the planets.The chemical and physical evolution of a protoplanetary disk are intimately connected. Both solids and gases are subjected to large-scale motions associated with disk evolution and diffusion within the gas. Solids also settle toward the disk midplane and migrate inwards due to gravity and gas drag. This dynamical evolution exposes primitive materials to a range of physical conditions (pressure, temperature, radiation environment) within the disk. It is the integrated effects of these environments that define the physical and chemical properties of a solid grain prior to its incorporation into a planetesimal or planet.Water serves as an interesting tracer of this evolution, as it would be processed in a variety of ways within a protoplanetary disk. I will discuss new methods that allow us to trace the dynamical movement of water vapor and ice throughout the lifetime of a protoplanetary disk and to determine the physical environments to which the water would be exposed. In particular, I will show how the early evolution of a protoplanetary disk impacts the D/H ratio of the water inherited by planetary materials. I will also explore how photodesorption of water by UV photons can lead to the formation of amorphous ice and thus the trapping of noble gases and other volatiles at levels that are much greater than predicted by equilibrium chemistry models. These effects combine to lead to constantly evolving properties of water during the early stages of planet formation. I will also discuss how the observed properties of Solar System bodies constrain these

  3. BROAD N{sub 2}H{sup +} EMISSION TOWARD THE PROTOSTELLAR SHOCK L1157-B1

    SciTech Connect

    Codella, C.; Fontani, F.; Gómez-Ruiz, A.; Vasta, M.; Viti, S.; Ceccarelli, C.; Lefloch, B.; Podio, L.; Caselli, P.

    2013-10-10

    We present the first detection of N{sub 2}H{sup +} toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ∼0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N{sub 2}H{sup +}(1-0) line originated from the dense (≥10{sup 5} cm{sup –3}) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N{sub 2}H{sup +} column density of a few 10{sup 12} cm{sup –2} corresponding to an abundance of (2-8) × 10{sup –9}. The N{sub 2}H{sup +} abundance can be matched by a model of quiescent gas evolved for more than 10{sup 4} yr, i.e., for more than the shock kinematical age (≅2000 yr). Modeling of C-shocks confirms that the abundance of N{sub 2}H{sup +} is not increased by the passage of the shock. In summary, N{sub 2}H{sup +} is a fossil record of the pre-shock gas, formed when the density of the gas was around 10{sup 4} cm{sup –3}, and then further compressed and accelerated by the shock.

  4. Molecular inventories and chemical evolution of low-mass protostellar envelopes

    NASA Astrophysics Data System (ADS)

    Jørgensen, J. K.; Schöier, F. L.; van Dishoeck, E. F.

    2004-03-01

    This paper presents the first substantial study of the chemistry of the envelopes around a sample of 18 low-mass pre- and protostellar objects for which physical properties have previously been derived from radiative transfer modeling of their dust continuum emission. Single-dish line observations of 24 transitions of 9 molecular species (not counting isotopes) including HCO+, N2H+, CS, SO, SO2, HCN, HNC, HC3N and CN are reported. The line intensities are used to constrain the molecular abundances by comparison to Monte Carlo radiative transfer modeling of the line strengths. In general the nitrogen-bearing species together with HCO+ and CO cannot be fitted by a constant fractional abundance when the lowest excitation transitions are included, but require radial dependences of their chemistry since the intensity of the lowest excitation lines are systematically underestimated in such models. A scenario is suggested in which these species are depleted in a specific region of the envelope where the density is high enough that the freeze-out timescale is shorter than the dynamical timescale and the temperature low enough that the molecule is not evaporated from the icy grain mantles. This can be simulated by a ``drop'' abundance profile with standard (undepleted) abundances in the inner- and outermost regions and a drop in abundance in between where the molecule freezes out. An empirical chemical network is constructed on the basis of correlations between the abundances of various species. For example, it is seen that the HCO+ and CO abundances are linearly correlated, both increasing with decreasing envelope mass. This is shown to be the case if the main formation route of HCO+ is through reactions between CO and H3+, and if the CO abundance still is low enough that reactions between H3+ and N2 are the main mechanism responsible for the removal of H3+. Species such as CS, SO and HCN show no trend with envelope mass. In particular no trend is seen between

  5. 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.

  6. The Composition of the Protosolar Disk and the Formation Conditions for Comets

    NASA Astrophysics Data System (ADS)

    Willacy, K.; Alexander, C.; Ali-Dib, M.; Ceccarelli, C.; Charnley, S. B.; Doronin, M.; Ellinger, Y.; Gast, P.; Gibb, E.; Milam, S. N.; Mousis, O.; Pauzat, F.; Tornow, C.; Wirström, E. S.; Zicler, E.

    2015-12-01

    Conditions in the protosolar nebula have left their mark in the composition of cometary volatiles, thought to be some of the most pristine material in the solar system. Cometary compositions represent the end point of processing that began in the parent molecular cloud core and continued through the collapse of that core to form the protosun and the solar nebula, and finally during the evolution of the solar nebula itself as the cometary bodies were accreting. Disentangling the effects of the various epochs on the final composition of a comet is complicated. But comets are not the only source of information about the solar nebula. Protostellar disks around young stars similar to the protosun provide a way of investigating the evolution of disks similar to the solar nebula while they are in the process of evolving to form their own solar systems. In this way we can learn about the physical and chemical conditions under which comets formed, and about the types of dynamical processing that shaped the solar system we see today.

  7. SCUBA and HIRES Results for Protostellar Cores in the MON OB1 Dark Cloud

    NASA Astrophysics Data System (ADS)

    Wolf-Chase, G.; Moriarty-Schieven, G.; Fich, M.; Barsony, M.

    1999-05-01

    We have used HIRES-processing of IRAS data and point-source modelling techniques (Hurt & Barsony 1996; O'Linger 1997; Barsony et al. 1998), together with submillimeter continuum imaging using the Submillimeter Common-User Bolometer Array (SCUBA) on the 15-meter James Clerk Maxwell Telescope (JCMT), to search CS cores in the Mon OB1 dark cloud (Wolf-Chase, Walker, & Lada 1995; Wolf-Chase & Walker 1995) for deeply embedded sources. These observations, as well as follow-up millimeter photometry at the National Radio Astronomy Observatory (NRAO) 12-meter telescope on Kitt Peak, have lead to the identification of two Class 0 protostellar candidates, which were previously unresolved from two brighter IRAS point sources (IRAS 06382+0939 & IRAS 06381+1039) in this cloud. Until now, only one Class 0 object had been confirmed in Mon OB1; the driving source of the highly-collimated outflow NGC 2264 G (Ward-Thompson, Eiroa, & Casali 1995; Margulis et al. 1990; Lada & Fich 1996), which lies well outside the extended CS cores. One of the new Class 0 candidates may be an intermediate-mass source associated with an H_2O maser, and the other object is a low-mass source which may be associated with a near-infrared jet, and possibly with a molecular outflow. We report accurate positions for the new Class 0 candidates, based on the SCUBA images, and present new SEDs for these sources, as well as for the brighter IRAS point sources. A portion of this work was performed while GWC held a President's Fellowship from the University of California. MB and GWC gratefully acknowledge financial support from MB's NSF CAREER Grant, AST97-9753229.

  8. From nearby low-mass protostars to high redshift starbursts: protostellar outflows tracing the IMF

    NASA Astrophysics Data System (ADS)

    Kristensen, Lars E.; Bergin, Edwin

    2015-08-01

    Embedded low-mass protostars are notoriously difficult to observe even in the nearest Galactic high-mass clusters where they outnumber the high-mass protostars by orders of magnitude. Thus, without a good tracer of the low-mass population, we do not have a good handle on the shape of the initial (core) mass function, leaving little hope for extrapolating to extragalactic regions where we will never have neither the sensitivity nor the resolution to directly observe this population. A good tracer of the low-mass population is needed.One such physical tracer is outflows. Outflow emission is directly proportional to envelope mass, and outflows are predominantly active during the deeply embedded phases of star formation. What is required for this method to work is species and transitions tracing outflows uniquely such that any signal is not diluted by the surrounding cloud, such as certain methanol transitions, water, high-J CO (J > 10).I will present a statistical model of a forming high-mass cluster. The model includes what we currently know about Galactic high-mass clusters and incorporates outflow emission from low-mass protostars. The latter component is obtained from observations of tens of nearby embedded low-mass protostellar outflows in the above-mentioned tracers. The model is benchmarked against ALMA and Herschel-HIFI observations of Galactic clusters proving the concept, and preliminary extrapolations to the extragalactic regime are presented. With this new probe, and traditional probes of the distant star formation which predominantly trace high mass stars, we will be able to explore the IMF in starburst galaxies from low to high redshift.

  9. Unveiling the Detailed Density and Velocity Structures of the Protostellar Core B335

    NASA Astrophysics Data System (ADS)

    Kurono, Yasutaka; Saito, Masao; Kamazaki, Takeshi; Morita, Koh-Ichiro; Kawabe, Ryohei

    2013-03-01

    We present an observational study of the protostellar core B335 harboring a low-mass Class 0 source. The observations of the H13CO+(J = 1-0) line emission were carried out using the Nobeyama 45 m telescope and Nobeyama Millimeter Array. Our combined image of the interferometer and single-dish data depicts detailed structures of the dense envelope within the core. We found that the core has a radial density profile of n(r)vpropr -p and a reliable difference in the power-law indices between the outer and inner regions of the core: p ≈ 2 for r >~ 4000 AU and p ≈ 1.5 for r <~ 4000 AU. The dense core shows a slight overall velocity gradient of ~1.0 km s-1 over the scale of 20, 000 AU across the outflow axis. We believe that this velocity gradient represents a solid-body-like rotation of the core. The dense envelope has a quite symmetrical velocity structure with a remarkable line broadening toward the core center, which is especially prominent in the position-velocity diagram across the outflow axis. The model calculations of position-velocity diagrams do a good job of reproducing observational results using the collapse model of an isothermal sphere in which the core has an inner free-fall region and an outer region conserving the conditions at the formation stage of a central stellar object. We derived a central stellar mass of ~0.1 M ⊙, and suggest a small inward velocity, v_{r ≥ r_inf}˜ 0 km s^{-1} in the outer core at >~ 4000 AU. We concluded that our data can be well explained by gravitational collapse with a quasi-static initial condition, such as Shu's model, or by the isothermal collapse of a marginally critical Bonnor-Ebert sphere.

  10. Tracing Carina's protostellar jets to the source with WFC3-IR

    NASA Astrophysics Data System (ADS)

    Smith, Nathan

    2010-09-01

    Based on a recent H-alpha imaging survey of the Carina Nebula with ACS, we discovered 39 new Herbig-Haro {HH} jets marking the bipolar outflows from newly formed low-mass stars. This provides a valuable sample of jets that are all at the same distance, allowing us to study the relationship between protostars and their outflows where nearby massive stars are shredding the molecular cloud as new stars are forming. Carina has been studied extensively with Spitzer and Chandra, providing IR spectral energy distributions and X-ray luminosities for all detectable sources in the field. However, 29 of the jets seen at visual wavelengths emerge from opaque clouds or dark globules seen in silhouette against the bright background H II region, so the protostellar driving sources are still embedded in their natal clouds and are not identifiable in optical images. This makes the identification of the driving sources in lower resolution Spitzer and Chandra images ambiguous. Three of these jets {HH666, HH901, and HH902} have already been imaged with WFC3 as ERO targets after the servicing mission, demonstrating that near-IR [Fe II] emission lines in the F126N and F164N filters provide an excellent way to trace the jet emission back into the cloud and to thereby identify which embedded star is driving the outflow. Here we propose to obtain WFC3-IR images of [Fe II] emission from the remaining embedded jets in order to link the jets to the protostars that launch them. This will then permit a comparison of the jet properties to protostar properties for the full sample. Additionally, the flux ratio of these two [Fe II] lines will probe the spatially dependent extinction through the cloud all the way back to the source, providing a map of the density structure in the protostar's extended circumstellar envelope.

  11. On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

    NASA Astrophysics Data System (ADS)

    Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

    2016-05-01

    The dynamical response of edge waves under the influence of self-gravity is examined in an idealized two-dimensional model of a proto-stellar disc, characterized in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius r0. The fluid in basic state is prescribed to rotate with a Keplerian profile $\\Omega_k(r)\\sim r^{-3/2}$ modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabilizer irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non- Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density, in addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect . Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

  12. Dense cavity walls traced by CS in the L1157-B1 protostellar shocked region

    NASA Astrophysics Data System (ADS)

    Gomez-Ruiz, Arturo; Codella, Claudio; Lefloch, Bertrand; Benedettini, Milena; Busquet, Gemma; Nisini, Brunella; Ceccarelli, Cecilia; Cabrit, Sylvie; Viti, Serena

    2013-07-01

    In the framework of the CHESS Key Program, an unbiased spectral survey performed with Herschel and IRAM, in the frequency range from 97 to 600 GHz, have provided a chemical census of the protostellar shock L1157-B1. Here we focus on the study of carbon monosulfide (CS), a standard tracer of high-density gas. We have detected a total of 18 emission lines, with E_u up to 183 K, due to four isotopologues (^12C^32S, ^12C^34S, ^13C^32S, and ^12C^33S). The unprecedented sensitivity of the survey allow us to carefully analyze the line profiles. These profiles can be well fitted by two exponential laws: I ∝ exp(-|v/v0|) with v0 = 4.4, and 2.5 km s-1. Remarkably these two exponential laws are the same as those found in the CO line profiles by Lefloch et al. (2012), and named g2 and g3 components, respectively. These components have been related to the cavity walls produced by the B1 shock and the older B2 shock, respectively. An important characteristic of the lines profiles is that the emission of high-J CS transitions (E_u > 60 K) comes only from the g2 component. Using the LVG approximation, the CS solutions constrain n >= 10^4.5 cm^-3. In addition, when contrasted with the CO results (that already constrained T_k of 90 K and 40 K for g2 and g3, respectively), we see that the LVG can provide strong constrains to the gas density, in this case about 5 x 10^5 cm^-3 for both g2 and g3 components. Thus, the combination of CO and CS is a powerful tool to constrain both n and T_k. Our CS observations show therefore that this molecule is highlighting the dense cavity walls produced by the episodic outflow.

  13. Inferring the Structure of the Pre-Protostellar Core L1498

    NASA Astrophysics Data System (ADS)

    Doty, Sandra L.; Doty, Steven D.; Perkett, Matthew J.

    2014-09-01

    We present a study of the pre-protostellar core (PPC) L1498. A series of self-consistent, three-dimensional continuum radiative transfer models are constructed. The outputs of these models are convolved with appropriate telescope beam responses, including the effect of beam chopping to simulate SCUBA observations. The simulated observations are compared with existing observational data. An automated search is conducted in the multi-dimensional parameter space to identify the best-fit model. Grids of models are constructed in the vicinity of the best fit in order to understand the sensitivity/uncertainty of the results. We find that the source is well fit by a prolate spheroid of cutoff (and thus approximately outer) radius rcut = 0.073 ± 0.005 pc, axis ratio q = 2.0 ± 0.2, a central luminosity L* < 10^-3 Lsun, and an optical depth in the visible of τv = 20 ± 5. We find that the PPC is illuminated by two external radiation fields: a uniform ISRF of strength s_ISRF = 0.5 ± 0.25 and a local plane-parallel radiation field s_PPRF = 1.0 ± 0.5. Both of these radiation fields are locally attenuated, with τ_ISRF = 1.0 ± 0.25, and τ_PPRF = 1.25± 0.75, consistent with the fact that L1498 is embedded in a larger cloud. Most interestingly, the density fall-off at the outer edge is extremely steep, having a power law of m > 10. This is effectively a "sharp edge" to the PPC, and together with the constant density interior, is interpreted as potential signs of a pressure-confined core.

  14. COMPLEX SCATTERED RADIATION FIELDS AND MULTIPLE MAGNETIC FIELDS IN THE PROTOSTELLAR CLUSTER IN NGC 2264

    SciTech Connect

    Kwon, Jungmi; Tamura, Motohide; Kandori, Ryo; Kusakabe, Nobuhiko; Hashimoto, Jun; Nakajima, Yasushi; Nakamura, Fumitaka; Nagayama, Takahiro; Nagata, Tetsuya; Hough, James H.; Werner, Michael W.; Teixeira, Paula S.

    2011-11-01

    Near-infrared imaging polarimetry in the J, H, and K{sub s} bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field (MF) structure of the molecular cloud. The mean polarization position angle of the point-like sources is 81 Degree-Sign {+-} 29 Degree-Sign in the cluster core, and 58 Degree-Sign {+-} 24 Degree-Sign in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the MF in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the MF strength to be about 100 {mu}G. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong MF. The local MF direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local MF direction runs roughly perpendicular to the Galactic MF direction.

  15. Supermassive star formation via episodic accretion: protostellar disc instability and radiative feedback efficiency

    NASA Astrophysics Data System (ADS)

    Sakurai, Y.; Vorobyov, E. I.; Hosokawa, T.; Yoshida, N.; Omukai, K.; Yorke, H. W.

    2016-06-01

    The formation of supermassive stars (SMSs) is a potential pathway to seed supermassive black holes in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper, we study the evolution of an accreting SMS and its UV emissivity with realistic variable accretion from a circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the protostellar accretion until the stellar mass exceeds 104 M⊙. The disc fragments by gravitational instability, creating many clumps that migrate inward to fall on to the star. The resulting accretion history is highly time-dependent: short episodic accretion bursts are followed by longer quiescent phases. We show that the disc for the direct collapse model is more unstable and generates greater variability than normal Pop III cases. Next, we conduct a stellar evolution calculation using the obtained accretion history. Our results show that, regardless of the variable accretion, the stellar radius monotonically increases with almost constant effective temperature at Teff ≃ 5000 K as the stellar mass increases. The resulting UV feedback is too weak to hinder accretion due to the low flux of stellar UV photons. The insensitivity of stellar evolution to variable accretion is attributed to the fact that time-scales of variability, ≲103 yr, are too short to affect the stellar structure. We argue that this evolution will continue until the SMS collapses to produce a black hole by the general relativistic instability after the mass reaches ≳105 M⊙.

  16. Identification of protostellar clusters in the inner part of the milky way : Interaction between the ISM and star forming regions.

    NASA Astrophysics Data System (ADS)

    Beuret, M.; Billot, N.; Cambrésy, L.; Elia, D.; Molinari, S.; Pezzuto, S.; Pestalozzi, M.; Schisano, E.

    2014-12-01

    Interactions between the interstellar medium (ISM) and young stellar objects (YSO) need to be investigated to better understand star formation. We used the Minimum Spanning Tree (MST) method to identify protostellar clusters in the inner part of galactic plane. Using heliocentric distance estimates, we obtained about 230 clusters over a 140 × 2 square degree region. Most of these clusters are correlated with Infrared Dark Cloud (IRDC) or H II regions. We conclude that clustering is more important for protostars than for prestellar clumps and that a strong correlation can be established between the distribution of H II regions, known star formation complexes and the YSOs identified in the Hi-GAL data.

  17. Scattering from Thin Dielectric Disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.

    1984-01-01

    A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectric properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T is sufficiently large the disk will always be in one or the other of these regimes (T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.

  18. Ringed Accretion Disks: Equilibrium Configurations

    NASA Astrophysics Data System (ADS)

    Pugliese, D.; Stuchlík, Z.

    2015-12-01

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  19. Multiwavelength search for protoplanetary disks

    NASA Technical Reports Server (NTRS)

    Neuhaeuser, Ralph; Schmidt-Kaler, Theodor

    1994-01-01

    Infrared emission of circumstellar dust was observed for almost one hundred T Tauri stars. This dust is interpreted to be part of a protoplanetary disk orbiting the central star. T Tauri stars are young stellar objects and evolve into solar type stars. Planets are believed to form in these disks. The spectral energy distribution of a disk depends on its temperature profile. Different disk regions emit at different wavelengths. The disk-star boundary layer is hot and emits H(alpha) radiation. Inner disk regions at around 1 AU with a temperature of a few hundred Kelvin can be probed in near infrared wavelength regimes. Outer disk regions at around 100 AU distance from the star are colder and emit far infrared and sub-millimeter radiation. Also, X-ray emission from the stellar surface can reveal information on disk properties. Emission from the stellar surface and the boundary layer may be shielded by circumstellar gas and dust. T Tauri stars with low H(alpha) emission, i.e. no boundary layer, show stronger X-ray emission than classical T Tauri stars, because the inner disk regions of weak emission-line T Tauri stars may be clear of material. In this paper, first ROSAT all sky survey results on the X-ray emission of T Tauri stars and correlations between X-ray luminosity and properties of T Tauri disks are presented. Due to atmospheric absorption, X-ray and most infrared observations cannot be carried out on Earth, but from Earth orbiting satellites (e.g. IRAS, ROSAT, ISO) or from lunar based observatories, which would have special advantages such as a stable environment.

  20. Berkeley Disk Resource Manager

    Energy Science and Technology Software Center (ESTSC)

    2004-02-27

    The Berkeley Disk Resource Manager (B-DRM) is a middleware component whose function is to provide dynamic space allocation and file management of a shared disk system on the Grid. It provides space allocation and dynamic information on storage availability for the planning and execution of Grid jobs. The B-DRM manages two types of resources: space and files. Vi1en managing space, the B-DRM allocates space to the requesting client based on a default space quota, Thenmore » managing files, the B-DRM allocates space for files, invokes file transfer services to move files into the space, pins files for a certain lifetime, releases files upon the client’s request, and uses file replacement policies to optimize the use of the shared space. The B-DRM is designed to provide effective sharing of files, by monitoring the activity of shared files, and making dynamic decisions on which files to replace when space is needed. In addition, the B-DRM performs automatic garbage collection of unused files when space is needed by removing selected files that were released by the client or whose lifetime has expired. The BDRM supports requests to get multiple files in a single call, manages a queue of the requested files, brings in as many files as the space quota permits, and continues to reuse the space when files are released to stream files to the client until the entire request is satisfied. Similarly, the B-DRM supports requests to put multiple files into its space, streaming files into the allocated space and reusing the space if necessary.« less

  1. RAID 7 disk array

    NASA Technical Reports Server (NTRS)

    Stout, Lloyd

    1993-01-01

    Each RAID level reflects a different design architecture. Associated with each is a backdrop of imposed limitations, as well as possibilities which may be exploited within the architectural constraints of that level. There are three unique features that differentiate RAID 7 from all other levels. RAID 7 is asynchronous with respect to usage of I/O data paths. Each I/O drive (includes all data and one parity drives) as well as each host interface (there may be multiple host interfaces) has independent control and data paths. This means that each can be accessed completely, independently, of the other. This is facilitated by a separate device cache for each device/interface as well. RAID 7 is asynchronous with respect to device hierarchy and data bus utilization. Each drive and each interface is connected to a high speed data bus controlled by the embedded operating system to make independent transfers to and from central cache. RAID 7 is asynchronous with respect to the operation of an embedded real time process oriented operating system. This means that exclusive and independent of the host, or multiple host paths, the embedded OS manages all I/O transfers asynchronously across the data and parity drives. A key factor to consider is that of the RAID 7's ability to anticipate and match host I/O usage patterns. This yields the following benefits over RAID's built around micro-code based architectures. RAID 7 appears to the host as a normally connected Big Fast Disk (BFD). RAID 7 appears, from the perspective of the individual disk devices, to minimize the total number of accesses and optimize read/write transfer requests. RAID 7 smoothly integrates the random demands of independent users with the principles of spatial and temporal locality. This optimizes small, large, and time sequenced I/O requests which results in users having an I/O performance which approaches performance to that of main memory.

  2. Berkeley Disk Resource Manager

    SciTech Connect

    Shoshani, Arie; Sim, Alex; Gu, Junmin

    2004-02-27

    The Berkeley Disk Resource Manager (B-DRM) is a middleware component whose function is to provide dynamic space allocation and file management of a shared disk system on the Grid. It provides space allocation and dynamic information on storage availability for the planning and execution of Grid jobs. The B-DRM manages two types of resources: space and files. Vi1en managing space, the B-DRM allocates space to the requesting client based on a default space quota, Then managing files, the B-DRM allocates space for files, invokes file transfer services to move files into the space, pins files for a certain lifetime, releases files upon the client’s request, and uses file replacement policies to optimize the use of the shared space. The B-DRM is designed to provide effective sharing of files, by monitoring the activity of shared files, and making dynamic decisions on which files to replace when space is needed. In addition, the B-DRM performs automatic garbage collection of unused files when space is needed by removing selected files that were released by the client or whose lifetime has expired. The BDRM supports requests to get multiple files in a single call, manages a queue of the requested files, brings in as many files as the space quota permits, and continues to reuse the space when files are released to stream files to the client until the entire request is satisfied. Similarly, the B-DRM supports requests to put multiple files into its space, streaming files into the allocated space and reusing the space if necessary.

  3. Accretion of solid materials onto circumplanetary disks from protoplanetary disks

    SciTech Connect

    Tanigawa, Takayuki; Maruta, Akito; Machida, Masahiro N.

    2014-04-01

    We investigate the accretion of solid materials onto circumplanetary disks from heliocentric orbits rotating in protoplanetary disks, which is a key process for the formation of regular satellite systems. In the late stage of the gas-capturing phase of giant planet formation, the accreting gas from protoplanetary disks forms circumplanetary disks. Since the accretion flow toward the circumplanetary disks affects the particle motion through gas drag force, we use hydrodynamic simulation data for the gas drag term to calculate the motion of solid materials. We consider a wide range of size for the solid particles (10{sup –2}-10{sup 6} m), and find that the accretion efficiency of the solid particles peaks around 10 m sized particles because energy dissipation of drag with circum-planetary disk gas in this size regime is most effective. The efficiency for particles larger than 10 m becomes lower because gas drag becomes less effective. For particles smaller than 10 m, the efficiency is lower because the particles are strongly coupled with the background gas flow, which prevents particles from accretion. We also find that the distance from the planet where the particles are captured by the circumplanetary disks is in a narrow range and well described as a function of the particle size.

  4. Low-state disks and low-beta disks

    NASA Technical Reports Server (NTRS)

    Mineshige, Shin; Kusnose, Masaaki; Matsumoto, Ryoji

    1995-01-01

    Stellar black hole candidates (BHCs) exhibit bimodal spectral states. We calculate nonthermal disk spectra, demonstrating that a large photon index (alpha (sub x) approximately 2-3) observed in the soft (high) state is due to a copious soft photon supply, whereas soft photon starvation leads to a smaller index (alpha (sub x) approximately 1.5-2) in the hard (low) state. Thus, the absence of the soft component flux in the low state cannot be due to obscuration. A possible disk configuration during the low state is discussed. We proposed that a low-state disk may be a low-beta disk in which magnetic pressure may exceed gas pressure becuase of the suppression of field escape by a strong shear. As a result, disk material will take the form of blobs constricted by mainly toroidal magnetic fields. Fields are dissipated mainly by occasional reconnection events with a huge energy release. This will account for large-amplitude, aperiodic X-ray variations (flickering) and high-energy radiation with small alpha(sub x) from hard state BHCs and possibly from active galactic nuclei. Further, we propose a hysteretic relation between the mass-flow rate and plasma-beta, a ratio of gas pressure to magnetic pressure, for the spectral evolution of transient BHCs. The disk is in the low-beta state in quiescence and early rise. The low-beta disk is optically thin and affected by advection. A hard-to-soft transition occurs before the peak luminosity, since there is no advection-dominated branch at higher luminosities. An optically thick, high-beta disk appears at small radii. In the decay phase of the light curve, the standard-type disk becomes effectively optically thin, when a soft-hard transition is triggered. High-beta plasmas in the main body shrink to form minute blobs, and low-beta coronal plasma fills interblob space.

  5. Particle on a boron disk: ring currents and disk aromaticity in B20(2-).

    PubMed

    Tai, Truong Ba; Havenith, Remco W A; Teunissen, Jos L; Dok, Ahmet R; Hallaert, Simon D; Nguyen, Minh Tho; Ceulemans, Arnout

    2013-09-16

    The B20(2-) cluster is predicted to exhibit a planar sheet-like structure with a circular circumference. Orbital plots and energy correlations demonstrate the close correspondence between the electronic structure of B20(2-) and the Bessel functions describing the waves of a quantum mechanical particle confined to a disk. The π-band of B20(2-), and its B19(-) congener, contains 12 π-electrons, forming a (1σ)(2)(1π)(4)(1δ)(4)(2σ)(2) configuration, which corresponds to a "disk aromaticity" electron count. The analogy not only applies to the π-band, but also extends to the 50 valence σ-electrons. The occupied σ-orbitals are assigned on the basis of radial and angular nodes of the scalar disk waves. The magnetic response of the cluster was examined by Nucleus Independent Chemical Shift (NICS) values and current density calculations based on the ipsocentric model. B20(2-) is found to exhibit a remarkable inner paratropic current in the σ-channel and an outer diatropic current in the π-channel. The orbital excitations responsible for the antiaromaticity in σ and the disk-aromaticity in π are identified. PMID:24011355

  6. Self-gravitational Force Calculation of Second-order Accuracy for Infinitesimally Thin Gaseous Disks in Polar Coordinates

    NASA Astrophysics Data System (ADS)

    Wang, Hsiang-Hsu; Yen, David C. C.; Taam, Ronald E.

    2015-11-01

    Investigating the evolution of disk galaxies and the dynamics of proto-stellar disks can involve the use of both a hydrodynamical and a Poisson solver. These systems are usually approximated as infinitesimally thin disks using two-dimensional Cartesian or polar coordinates. In Cartesian coordinates, the calculations of the hydrodynamics and self-gravitational forces are relatively straightforward for attaining second-order accuracy. However, in polar coordinates, a second-order calculation of self-gravitational forces is required for matching the second-order accuracy of hydrodynamical schemes. We present a direct algorithm for calculating self-gravitational forces with second-order accuracy without artificial boundary conditions. The Poisson integral in polar coordinates is expressed in a convolution form and the corresponding numerical complexity is nearly linear using a fast Fourier transform. Examples with analytic solutions are used to verify that the truncated error of this algorithm is of second order. The kernel integral around the singularity is applied to modify the particle method. The use of a softening length is avoided and the accuracy of the particle method is significantly improved.

  7. Evidence for a solar system-size accretion disk around the massive protostar G192.16-3.82.

    PubMed

    Shepherd, D S; Claussen, M J; Kurtz, S E

    2001-05-25

    Seven-millimeter continuum observations of a massive bipolar outflow source, G192.16-3.82, were made at a milli-arc-second resolution with a capability that links the National Radio Astronomy Observatory's Very Large Array radio interferometer with the Very Long Baseline Array antenna, located in Pie Town, New Mexico. The observations provide evidence for a true accretion disk that is about the size of our solar system and located around a massive star. A model of the radio emission suggests the presence of a binary protostellar system. The primary protostar, G192 S1, at the center of the outflow, with a protostar mass of about 8 to 10 times the solar mass, is surrounded by an accretion disk with a diameter of 130 astronomical units (AU). The mass of the disk is on the order of the protostar mass. The outflow is poorly collimated with a full opening angle of about 40 degrees; there is no indication of a more highly collimated jetlike component. The companion source, G192 S2, is located 80 AU north of the primary source. PMID:11375484

  8. Protoplanetary and Debris Disk Morphologies

    NASA Astrophysics Data System (ADS)

    Lomax, Jamie R.; Wisniewski, John P.; Grady, Carol A.; McElwain, Michael W.; Hashimoto, Jun; Donaldson, Jessica; Debes, John H.; Malumuth, Eliot; Roberge, Aki; Weinberger, Alycia J.; SEEDS Team

    2016-01-01

    The types of planets that form around other stars are highly dependent on their natal disk conditions. Therefore, the composition, morphology, and distribution of material in protoplanetary and debris disks are important for planet formation. Here we present the results of studies of two disk systems: AB Aur and AU Mic.The circumstellar disk around the Herbig Ae star AB Aur has many interesting features, including spirals, asymmetries, and non-uniformities. However, comparatively little is known about the envelope surrounding the system. Recent work by Tang et al (2012) has suggested that the observed spiral armss may not in fact be in the disk, but instead are due to areas of increased density in the envelope and projection effects. Using Monte Carlo modeling, we find that it is unlikely that the envelope holds enough material to be responsible for such features and that it is more plausible that they form from disk material. Given the likelihood that gravitational perturbations from planets cause the observed spiral morphology, we use archival H band observations of AB Aur with a baseline of 5.5 years to determine the locations of possible planets.The AU Mic debris disk also has many interesting morphological features. Because its disk is edge on, the system is an ideal candidate for color studies using coronagraphic spectroscopy. Spectra of the system were taken by placing a HST/STIS long slit parallel to and overlapping the disk while blocking out the central star with an occulting fiducial bar. Color gradients may reveal the chemical processing that is occuring within the disk. In addition, it may trace the potential composition and architecture of any planetary bodies in the system because collisional break up of planetesimals produces the observed dust in the system. We present the resulting optical reflected spectra (5200 to 10,200 angstroms) from this procedure at several disk locations. We find that the disk is bluest at the innermost locations of the

  9. Observations of Disks Around Pre--Main-Sequence Binary Stars

    NASA Astrophysics Data System (ADS)

    Jensen, Eric L. N.

    1996-08-01

    factor of four lower than from the spectroscopic binary. Since UZ Tau E and W have similar stellar masses, luminosities, and ages, we conclude that the mass of dust and gas associated with UZ Tau W is reduced solely by the influence of a companion with a separation comparable to a typical disk radius. The disk emission from UZ Tau E is similar to that from single T Tauri stars. In a 1 arcsec-resolution aperture synthesis map, CO (2 --> 1) emission is elongated with a size of 300 AU; a disk model fit to the continuum spectral energy distribution yields a disk mass of 0.06 Modot, larger than the ``minimum mass solar nebula''. In contrast, no CO emission is detected from UZ Tau W, and its 1.3 mm continuum emission is unresolved in a 1 arcsec (FWHM) beam (corresponding to a 70 AU radius). The small extent of the emission and dynamical considerations imply that the 50 AU binary cannot be surrounded by any appreciable circumbinary disk; its mm-wave emission is from circumstellar disks around one or both components with masses in the range of 0.002--0.04 Modot. Finally, we present a study of disk clearing by pre--main-sequence binaries with separations less than 1 AU null. Several binaries have spectral energy distributions (SEDs) with little or no infrared excess at λ = 1--5 microns, requiring that their inner disks be optically thin. In each case the inferred size of the cleared region is comparable to a few times the binary semimajor axis as predicted by theories of binary-disk interactions. Other binaries show large near- and mid-infrared excesses, with little evidence of cleared regions in their disks. The infrared excesses in these binaries can be reproduced by a model in which a gap is cleared by the binary but is partially filled with very low-surface-density dust; this hot, optically-thin dust also reproduces the 9.8 micron silicate emission features observed in two of these systems. Thus, all binaries studied show SEDs which are consistent with the presence of

  10. Constraining the Milky Way thick disk formation: Chemical characterization of the thick disk outside of the solar neighbourhood

    NASA Astrophysics Data System (ADS)

    Posbic, H.; Katz, D.; Haywood, M.; Bonifacio, P.; Caffau, E.; Gomez, A.; Sbordone, L.; Arenou, F.; Royer, F.

    2012-12-01

    The formation of the Milky Way disk is still an open question. Many scenarios are proposed. Different formation scenarios predict different disk chemical trends. This work aims to chemically characterize the Milky Way disk inside and outside the solar neighbourhood, to better constrain its formation scenario. This is possible thanks to high resolution spectra of 200 disk stars observed using the Giraffe spectrograph on the Very Large Telescope (VLT). They were selected to have galactic altitudes |Z| that cover both the thin and thick disk (|Z| up to 2 kpc). The new automatic spectra analysis software SPADES (Stellar PArameters DEtermination Software, Posbic et al. 2012) was used to determine the stellar parameters, and most importantly, the elemental abundances of these stars. The distances of these stars were also determined. The metallicity distribution function of the disk using this sample was calculated. It showed a large contribution of the thick disk stars and a smooth transition at the metallicity of the thick disk/halo interface. The vertical behaviour of the metallicity distribution function was also studied. A vertical metallicity gradient in the disk of partial [Fe/H] / partial |Z| = -0.19 ± 0.14 dex/kpc was marginally detected at the 1.4 sigma level. The [Ti/Fe] and [Ca/Fe] vs [Fe/H] trends for the stars are determined. The main result of the analysis is that the trends of [Ca/Fe] vs [Fe/H] and [Ti/Fe] vs [Fe/H] show no significant difference close (i.e. |Z| leq 1 kpc) and farther away (1 < |Z| < 2.5 kpc) from the Galactic plane. This suggests that thick disk gas and stars have been enriched by the same proportion of type II and type I super-novae from the galactic plane up to at least 2.5 kpc. These results support thick disk formation scenarios like collapse or gas-rich accretion and disfavour a thick disk formed of stars captured during a merger event.

  11. The birth and death of organic molecules in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Henning, Thomas; Semenov, Dmitry

    2008-10-01

    The most intriguing question related to the chemical evolution of protoplanetary disks is the genesis of pre-biotic organic molecules in the planet-forming zone. In this contribution we briefly review current observational knowledge of physical structure and chemical composition of disks and discuss whether organic molecules can be present in large amounts at the verge of planet formation. We predict that some molecules, including CO-bearing species such as H2CO, can be underabundant in inner regions of accreting protoplanetary disks around low-mass stars due to the high-energy stellar radiation and chemical processing on dust grain surfaces. These theoretical predictions are further compared with high-resolution observational data and the limitations of current models are discussed.

  12. Phase Stability of a Powder Metallurgy Disk Superalloy

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Gayda, John; Kantzos, P.; Telesman, Jack; Gang, Anita

    2006-01-01

    Advanced powder metallurgy superalloy disks in aerospace turbine engines now entering service can be exposed to temperatures approaching 700 C, higher than those previously encountered. They also have higher levels of refractory elements, which can increase mechanical properties at these temperatures but can also encourage phase instabilities during service. Microstructural changes including precipitation of topological close pack phase precipitation and coarsening of existing gamma' precipitates can be slow at these temperatures, yet potentially significant for anticipated disk service times exceeding 1,000 h. The ability to quantify and predict such potential phase instabilities and degradation of capabilities is needed to insure structural integrity and air worthiness of propulsion systems over the full life cycle. A prototypical advanced disk superalloy was subjected to high temperature exposures, and then evaluated. Microstructural changes and corresponding changes in mechanical properties were quantified. The results will be compared to predictions of microstructure modeling software.

  13. Magnetically Torqued Thin Accretion Disks

    NASA Astrophysics Data System (ADS)

    Kluźniak, W.; Rappaport, S.

    2007-12-01

    We compute the properties of a geometrically thin, steady accretion disk surrounding a central rotating, magnetized star. The magnetosphere is assumed to entrain the disk over a wide range of radii. The model is simplified in that we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal component of the magnetic field as a function of radial distance. We find a solution for the angular velocity profile tending to corotation close to the central star and smoothly matching a Keplerian curve at a radius where the viscous stress vanishes. The value of this ``transition'' radius is nearly the same for both of our adopted B-field models. We then solve analytically for the torques on the central star and for the disk luminosity due to gravity and magnetic torques. When expressed in a dimensionless form, the resulting quantities depend on one parameter alone, the ratio of the transition radius to the corotation radius. For rapid rotators, the accretion disk may be powered mostly by spin-down of the central star. These results are independent of the viscosity prescription in the disk. We also solve for the disk structure for the special case of an optically thick alpha disk. Our results are applicable to a range of astrophysical systems including accreting neutron stars, intermediate polar cataclysmic variables, and T Tauri systems.

  14. Simulations of Accretion Disk Wind Models

    NASA Astrophysics Data System (ADS)

    Brooks, Craig L.; Yong, Suk Yee; O'Dowd, Matthew; Webster, Rachel L.; Bate, Nicholas

    2016-01-01

    The kinematics of the broad emission line region (BELR) in quasars is largely unknown, however there is strong evidence that outflows may be a key component. For example, in approximately 15% of quasars we observe broad, blue-shifted absorption features which may be ubiquitous based on line-of-sight arguments. We use a new mathematical description of an outflowing disk-wind with an initial rotational component to predict surface brightness distributions of this wind at different orientations. These surface brightness distributions will allow us to simulate gravitational microlensing of BELR light, with a view to mapping the structure and better understanding the kinematics of these flows.

  15. Low extreme-ultraviolet luminosities impinging on protoplanetary disks

    SciTech Connect

    Pascucci, I.; Hendler, N. P.; Ricci, L.; Gorti, U.; Hollenbach, D.; Brooks, K. J.; Contreras, Y.

    2014-11-01

    The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the extreme-ultraviolet (EUV) luminosity impinging on 14 disks around young (∼2-10 Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 10{sup 42} photons s{sup –1} for all sources without jets and lower than 5 × 10{sup 40} photons s{sup –1} for the three older sources in our sample. These latter values are low for EUV-driven photoevaporation alone to clear out protoplanetary material in the timescale inferred by observations. In addition, our EUV upper limits are too low to reproduce the [Ne II] 12.81 μm luminosities from three disks with slow [Ne II]-detected winds. This indicates that the [Ne II] line in these sources primarily traces a mostly neutral wind where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative mass loss rates than those predicted by EUV-driven models alone. In summary, our results suggest that high-energy stellar photons other than EUV may dominate the dispersal of protoplanetary disks around sun-like stars.

  16. Low Extreme-ultraviolet Luminosities Impinging on Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Pascucci, I.; Ricci, L.; Gorti, U.; Hollenbach, D.; Hendler, N. P.; Brooks, K. J.; Contreras, Y.

    2014-11-01

    The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the extreme-ultraviolet (EUV) luminosity impinging on 14 disks around young (~2-10 Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 1042 photons s-1 for all sources without jets and lower than 5 × 1040 photons s-1 for the three older sources in our sample. These latter values are low for EUV-driven photoevaporation alone to clear out protoplanetary material in the timescale inferred by observations. In addition, our EUV upper limits are too low to reproduce the [Ne II] 12.81 μm luminosities from three disks with slow [Ne II]-detected winds. This indicates that the [Ne II] line in these sources primarily traces a mostly neutral wind where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative mass loss rates than those predicted by EUV-driven models alone. In summary, our results suggest that high-energy stellar photons other than EUV may dominate the dispersal of protoplanetary disks around sun-like stars.

  17. DiskJockey: Protoplanetary disk modeling for dynamical mass derivation

    NASA Astrophysics Data System (ADS)

    Czekala, Ian

    2016-03-01

    DiskJockey derives dynamical masses for T Tauri stars using the Keplerian motion of their circumstellar disks, applied to radio interferometric data from the Atacama Large Millimeter Array (ALMA) and the Submillimeter Array (SMA). The package relies on RADMC-3D (ascl:1202.015) to perform the radiative transfer of the disk model. DiskJockey is designed to work in a parallel environment where the calculations for each frequency channel can be distributed to independent processors. Due to the computationally expensive nature of the radiative synthesis, fitting sizable datasets (e.g., SMA and ALMA) will require a substantial amount of CPU cores to explore a posterior distribution in a reasonable timeframe.

  18. Future hard disk drive systems

    NASA Astrophysics Data System (ADS)

    Wood, Roger

    2009-03-01

    This paper briefly reviews the evolution of today's hard disk drive with the additional intention of orienting the reader to the overall mechanical and electrical architecture. The modern hard disk drive is a miracle of storage capacity and function together with remarkable economy of design. This paper presents a personal view of future customer requirements and the anticipated design evolution of the components. There are critical decisions and great challenges ahead for the key technologies of heads, media, head-disk interface, mechanics, and electronics.

  19. Gravitational asymmetries in gaseous disks.

    NASA Astrophysics Data System (ADS)

    Junqueira, S.; Combes, F.

    1997-12-01

    The authors report preliminary results of self-gravitating simulations of spiral galaxies modeled by two components, stellar and gaseous disks. One of the objectives of this work is to study asymmetries in the distribution of the gas, features observed for a number of spiral galaxies. The gas disk is simulated by the Beam-Scheme method, where the gas is considered as a fluid. The results suggest that very concentrated galactic disks can be unstable to the one-armed (m = 1) spiral perturbation, which may explain the asymmetric patterns observed in isolated galaxies.

  20. Properties of accretion disk coronae

    NASA Technical Reports Server (NTRS)

    Wilms, J.; Dove, J.; Staubert, R.; Begelman, M. C.

    1997-01-01

    The properties of accretion disk corona in a parameter regime suitable for Galactic black hole candidates are considered and the results of an analysis of these properties using a self-consistent Monte Carlo code are presented. Examples of the coronal temperature structure, the shape and angular dependency of the spectrum and the maximum temperature allowed for each optical depth of the corona are presented. It is shown that the observed spectrum of the Galactic black hole candidate Cygnus X-1 cannot be explained by accreting disk corona models with a slab geometry, where the accretion disk is sandwiched by the comptonizing medium.

  1. Recognizing Patterns in Debris Disks

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2009-01-01

    An extrasolar planet sculpts the famous debris dish around Fomalhaut; probably many other debris disks contain planets that we could locate if only we could better recognize their signatures in the dust that surrounds them. I will describe the latest 3-D models of debris dish dynamics / models that include planets, grain-grain collisions and even ISM-disk interactions. I will show why all these ingredients are needed to explain disk images--and what the images are telling us about planet formation.

  2. VLA and CARMA Observations of Protostars in the Cepheus Clouds: Sub-arcsecond Proto-binaries Formed via Disk Fragmentation

    NASA Astrophysics Data System (ADS)

    Tobin, John J.; Chandler, Claire J.; Wilner, David J.; Looney, Leslie W.; Loinard, Laurent; Chiang, Hsin-Fang; Hartmann, Lee; Calvet, Nuria; D'Alessio, Paola; Bourke, Tyler L.; Kwon, Woojin

    2013-12-01

    We present observations of three Class 0/I protostars (L1157-mm, CB230 IRS1, and L1165-SMM1) using the Karl G. Jansky Very Large Array (VLA) and observations of two (L1165-SMM1 and CB230 IRS1) with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The VLA observations were taken at wavelengths of λ = 7.3 mm, 1.4 cm, 3.3 cm, 4.0 cm, and 6.5 cm with a best resolution of ~0.''06 (18 AU) at 7.3 mm. The L1165-SMM1 CARMA observations were taken at λ = 1.3 mm with a best resolution of ~0.''3 (100 AU) and the CB230 IRS1 observations were taken at λ = 3.4 mm with a best resolution of ~3'' (900 AU). We find that L1165-SMM1 and CB230 IRS1 have probable binary companions at separations of ~0.''3 (100 AU) from detections of secondary peaks at multiple wavelengths. The position angles of these companions are nearly orthogonal to the direction of the observed bipolar outflows, consistent with the expected protostellar disk orientations. We suggest that these companions may have formed from disk fragmentation; turbulent fragmentation would not preferentially arrange the binary companions to be orthogonal to the outflow direction. For L1165-SMM1, both the 7.3 mm and 1.3 mm emission show evidence of a large (R > 100 AU) disk. For the L1165-SMM1 primary protostar and the CB230 IRS1 secondary protostar, the 7.3 mm emission is resolved into structures consistent with ~20 AU radius disks. For the other protostars, including L1157-mm, the emission is unresolved, suggesting disks with radii <20 AU.

  3. VLA and CARMA observations of protostars in the Cepheus clouds: Sub-arcsecond proto-binaries formed via disk fragmentation

    SciTech Connect

    Tobin, John J.; Looney, Leslie W.; Chandler, Claire J.; Wilner, David J.; Bourke, Tyler L.; Loinard, Laurent; D'Alessio, Paola; Chiang, Hsin-Fang; Hartmann, Lee; Calvet, Nuria; Kwon, Woojin

    2013-12-20

    We present observations of three Class 0/I protostars (L1157-mm, CB230 IRS1, and L1165-SMM1) using the Karl G. Jansky Very Large Array (VLA) and observations of two (L1165-SMM1 and CB230 IRS1) with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The VLA observations were taken at wavelengths of λ = 7.3 mm, 1.4 cm, 3.3 cm, 4.0 cm, and 6.5 cm with a best resolution of ∼0.''06 (18 AU) at 7.3 mm. The L1165-SMM1 CARMA observations were taken at λ = 1.3 mm with a best resolution of ∼0.''3 (100 AU) and the CB230 IRS1 observations were taken at λ = 3.4 mm with a best resolution of ∼3'' (900 AU). We find that L1165-SMM1 and CB230 IRS1 have probable binary companions at separations of ∼0.''3 (100 AU) from detections of secondary peaks at multiple wavelengths. The position angles of these companions are nearly orthogonal to the direction of the observed bipolar outflows, consistent with the expected protostellar disk orientations. We suggest that these companions may have formed from disk fragmentation; turbulent fragmentation would not preferentially arrange the binary companions to be orthogonal to the outflow direction. For L1165-SMM1, both the 7.3 mm and 1.3 mm emission show evidence of a large (R > 100 AU) disk. For the L1165-SMM1 primary protostar and the CB230 IRS1 secondary protostar, the 7.3 mm emission is resolved into structures consistent with ∼20 AU radius disks. For the other protostars, including L1157-mm, the emission is unresolved, suggesting disks with radii <20 AU.

  4. Stability of Galactic Gaseous Disks and the Formation of Massive Clusters

    SciTech Connect

    Escala, Andres; Larson, Richard B.

    2008-08-21

    We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.

  5. Propulsion Health Monitoring of a Turbine Engine Disk Using Spin Test Data

    NASA Technical Reports Server (NTRS)

    Abdul-Aziz, Ali; Woike, Mark R.; Oza, Nikunj; Matthews, Bryan; Baaklini, George Y.

    2010-01-01

    This paper considers data collected from an experimental study using high frequency capacitive sensor technology to capture blade tip clearance and tip timing measurements in a rotating turbine engine-like-disk-to predict the disk faults and assess its structural integrity. The experimental results collected at a range of rotational speeds from tests conducted at the NASA Glenn Research Center s Rotordynamics Laboratory are evaluated using multiple data-driven anomaly detection techniques to identify abnormalities in the disk. Further, this study presents a select evaluation of an online health monitoring scheme of a rotating disk using high caliber sensors and test the capability of the in-house spin system.

  6. Radiative Transfer in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Graziani, L.; Aiello, S.; Belleni-Morante, A.; Cecchi-Pestellini, C.

    2008-09-01

    Abstract Protoplanetary disks are the precursors of planetary systems. All building materials needed to assembly the planetary systems are supplied by these reservoirs, including many organic molecules [1,2]. Thus, the physical and chemical properties in Protoplanetary disks set the boundary conditions for the formation and evolution of planets and other solar system bodies. In standard radiative scenario structure and chemistry of protoplanetary disks depend strongly on the nature of central star around which they formed. The dust temperature is manly set by the stellar luminosity, while the chemistry of the whole disk depends on the UV and X ray fluxes [3,4,6,8]. Therefore, a knowledge as accurate as possible of the radiative transfer (RT) inside disks is a prerequisite for their modelling. Actually, real disks are complex, stratified and inhomogeneous environments requiring a detailed dust mixture modelling and the ability to follow the radiation transfer across radial and vertical gradients. Different energetic processes as the mass accretion processes onto the star surface, the viscous dissipative heating dominating the midplane region, and the flared atmospheres radiation reprocessing, have a significant role in the disk structuring [4,5,8]. During the last 10 years many authors suggested various numerical and analytical techniques to resolve the disk temperature structure providing vertical temperature profiles and disk SED databases [4,6]. In this work we present the results of our semi analytical and numerical model solving the radiative transfer problem in two separate interesting disk regions: 1) Disk atmospheres at large radius, r > 10 AU. 2) Vertical disk structure over 1 < r < 10 AU and 10 < r < 100 AU. A simplified analytical approach based on P-N approximation [7] for a rectified disk surface (suitable for limited range of r) is compared and contrasted with a more accurate Monte Carlo integration [5]. Our code can handle arbitrary dust

  7. DIGGING INTO NGC 6334 I(N): MULTIWAVELENGTH IMAGING OF A MASSIVE PROTOSTELLAR CLUSTER

    SciTech Connect

    Brogan, C. L.; Hunter, T. R.; Indebetouw, R.; Cyganowski, C. J.; Beuther, H.; Menten, K. M.; Thorwirth, S.

    2009-12-10

    We present a high-resolution, multi-wavelength study of the massive protostellar cluster NGC 6334 I(N) that combines new spectral line data from the Submillimeter Array (SMA) and VLA with a re-analysis of archival VLA continuum data, Two Micron All Sky Survey and Spitzer images. As shown previously, the brightest 1.3 mm source SMA1 contains substructure at subarcsecond resolution, and we report the first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm (SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be comprised of free-free and dust components, while SMA6 shows only dust emission. Our 1.''5 resolution 1.3 mm molecular line images reveal substantial hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH{sub 3}OH rotation temperatures of 165 +- 9 K and 145 +- 12 K for SMA1 and SMA2, respectively. We estimate a diameter of 1400 AU for the SMA1 hot-core emission, encompassing both SMA1b and SMA1d, and speculate that these sources comprise a approx>800 AU separation binary that may explain the previously suggested precession of the outflow emanating from the SMA1 region. Compact line emission from SMA4 is weak, and none is seen toward SMA6. The LSR velocities of SMA1, SMA2, and SMA4 all differ by 1-2 km s{sup -1}. Outflow activity from SMA1, SMA2, SMA4, and SMA6 is observed in several molecules including SiO(5-4) and IRAC 4.5 mum emission; 24 mum emission from SMA4 is also detected. Eleven water maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and SMA6, while two others are associated with the Sandell source SM2. We also detect a total of 83 Class I CH{sub 3}OH 44 GHz maser spots which likely result from the combined activity of many outflows. Our observations paint the portrait of multiple young hot cores in a protocluster prior to the stage where its members become visible in the near-infrared.

  8. UNVEILING THE DETAILED DENSITY AND VELOCITY STRUCTURES OF THE PROTOSTELLAR CORE B335

    SciTech Connect

    Kurono, Yasutaka; Saito, Masao; Kamazaki, Takeshi; Morita, Koh-Ichiro; Kawabe, Ryohei

    2013-03-10

    We present an observational study of the protostellar core B335 harboring a low-mass Class 0 source. The observations of the H{sup 13}CO{sup +}(J = 1-0) line emission were carried out using the Nobeyama 45 m telescope and Nobeyama Millimeter Array. Our combined image of the interferometer and single-dish data depicts detailed structures of the dense envelope within the core. We found that the core has a radial density profile of n(r){proportional_to}r {sup -p} and a reliable difference in the power-law indices between the outer and inner regions of the core: p Almost-Equal-To 2 for r {approx}> 4000 AU and p Almost-Equal-To 1.5 for r {approx}< 4000 AU. The dense core shows a slight overall velocity gradient of {approx}1.0 km s{sup -1} over the scale of 20, 000 AU across the outflow axis. We believe that this velocity gradient represents a solid-body-like rotation of the core. The dense envelope has a quite symmetrical velocity structure with a remarkable line broadening toward the core center, which is especially prominent in the position-velocity diagram across the outflow axis. The model calculations of position-velocity diagrams do a good job of reproducing observational results using the collapse model of an isothermal sphere in which the core has an inner free-fall region and an outer region conserving the conditions at the formation stage of a central stellar object. We derived a central stellar mass of {approx}0.1 M{sub Sun }, and suggest a small inward velocity, v{sub r{>=}r{sub i{sub n{sub f}}}}{approx}0 km s{sup -1} in the outer core at {approx}> 4000 AU. We concluded that our data can be well explained by gravitational collapse with a quasi-static initial condition, such as Shu's model, or by the isothermal collapse of a marginally critical Bonnor-Ebert sphere.

  9. The role of cosmic rays on magnetic field diffusion and the formation of protostellar discs

    NASA Astrophysics Data System (ADS)

    Padovani, M.; Galli, D.; Hennebelle, P.; Commerçon, B.; Joos, M.

    2014-11-01

    Context. The formation of protostellar discs is severely hampered by magnetic braking, as long as magnetic fields remain frozen in the gas. The latter condition depends on the levels of ionisation that characterise the innermost regions of a collapsing cloud. Aims: The chemistry of dense cloud cores and, in particular, the ionisation fraction is largely controlled by cosmic rays. The aim of this paper is to evaluate whether the attenuation of the flux of cosmic rays expected in the regions around a forming protostar is sufficient to decouple the field from the gas, thereby influencing the formation of centrifugally supported disc. Methods: We adopted the method developed in a former study to compute the attenuation of the cosmic-ray flux as a function of the column density and the field strength in clouds threaded by poloidal and toroidal magnetic fields. We applied this formalism to models of low- and high-mass star formation extracted from numerical simulations of gravitational collapse that include rotation and turbulence. Results: For each model we determine the size of the magnetic decoupling zone, where collapse or rotation motion becomes unaffected by the local magnetic field. In general, we find that decoupling only occurs when the attenuation of cosmic rays is taken into account with respect to a calculation in which the cosmic-ray ionisation rate is kept constant. The extent of the decoupling zone also depends on the dust grain size distribution and is larger if large grains (of radius ~10-5 cm) are formed by compression and coagulation during cloud collapse. The decoupling region disappears for the high-mass case. This is due to magnetic field diffusion caused by turbulence that is not included in the low-mass models. Conclusions: We conclude that a realistic treatment of cosmic-ray propagation and attenuation during cloud collapse may lead to a value of the resistivity of the gas in the innermost few hundred AU around a forming protostar that is higher

  10. SPITZER SPECTRAL LINE MAPPING OF PROTOSTELLAR OUTFLOWS. II. H{sub 2} EMISSION IN L1157

    SciTech Connect

    Nisini, Brunella; Giannini, Teresa; Antoniucci, Simone; Neufeld, David A.; Yuan Yuan; Bergin, Edwin A.; Melnick, Gary J.

    2010-11-20

    We present an analysis of Spitzer-IRS spectroscopic maps of the L1157 protostellar outflow in the H{sub 2} pure-rotational lines from S(0) to S(7). The aim of this work is to derive the physical conditions pertaining to the warm molecular gas and study their variations within the flow. The mid-IR H{sub 2} emission follows the morphology of the precessing flow, with peaks correlated with individual CO clumps and H{sub 2} 2.12 {mu}m ro-vibrational emission. More diffuse emission delineating the CO cavities is detected only in the low-laying transitions, with J{sub lower{<=}} 2. The H{sub 2} line images have been used to construct two-dimensional maps of N(H{sub 2}), H{sub 2} ortho-to-para ratio (OPR), and temperature spectral index {beta}, in the assumption of a gas temperature stratification where the H{sub 2} column density varies as T {sup -}{beta}. Variations of these parameters are observed along the flow. In particular, the OPR ranges from {approx}0.6 to 2.8, highlighting the presence of regions subject to recent shocks where the OPR has not had time yet to reach the equilibrium value. Near-IR spectroscopic data on ro-vibrational H{sub 2} emission have been combined with the mid-IR data and used to derive additional shock parameters in the brightest blueshifted and redshifted emission knots. A high abundance of atomic hydrogen (H/H{sub 2} {approx} 0.1-0.3) is implied by the observed H{sub 2} column densities, assuming n(H{sub 2}) values as derived by independent SiO observations. The presence of a high fraction of atomic hydrogen indicates that a partially dissociative shock component should be considered for the H{sub 2} excitation in these localized regions. However, planar shock models, either of C- or J-type, are not able to consistently reproduce all the physical parameters derived from our analysis of the H{sub 2} emission. Globally, H{sub 2} emission contributes to about 50% of the total shock radiated energy in the L1157 outflow. We find that the

  11. DISK MASSES AT THE END OF THE MAIN ACCRETION PHASE: CARMA OBSERVATIONS AND MULTI-WAVELENGTH MODELING OF CLASS I PROTOSTARS

    SciTech Connect

    Eisner, J. A.

    2012-08-10

    We present imaging observations at the 1.3 mm wavelength of Class I protostars in the Taurus star-forming region, obtained with the CARMA interferometer. Of an initial sample of 10 objects, we detected and imaged millimeter wavelength emission from 9. One of the nine is resolved into two sources and detailed analysis of this binary protostellar system is deferred to a future paper. For the remaining eight objects, we use the CARMA data to determine the basic morphology of the millimeter emission. Combining the millimeter data with 0.9 {mu}m images of scattered light, Spitzer Infrared Spectrograph spectra, and broadband spectral energy distributions (all from the literature), we attempt to determine the structure of the circumstellar material. We consider models including both circumstellar disks and envelopes, and constrain the masses (and other structural parameters) of each of these components. We show that the disk masses in our sample span a range from {approx}< 0.01 to {approx}> 0.1 M{sub Sun }. The disk masses for our sample are significantly higher than for samples of more evolved Class II objects. Thus, Class I disk masses probably provide a more accurate estimate of the initial mass budget for star and planet formation. However, the disk masses determined here are lower than required by theories of giant planet formation. The masses also appear too low for gravitational instability, which could lead to high mass accretion rates. Even in these Class I disks, substantial particle growth may have hidden much of the disk mass in hard-to-see larger bodies.

  12. Black hole accretion disks - Coronal stabilization of the Lightman-Eardley instability

    NASA Technical Reports Server (NTRS)

    Ionson, J. A.; Kuperus, M.

    1984-01-01

    Physical processes by which the presence of a corona around a black hole can raise the threshold of onset of the Lightman-Eardley (L-E, 1976) instability are explored analytically. The L-E model predicts that an optically thick disk becomes unstable when the disk radiation pressure exceeds the disk gas pressure. The model has important implications for the validity of either the coronal disk or two-temperature disk models for accretion zones around black holes. It is shown that a corona can dissipate accreting gravitational energy through radiative cooling. Specific ratios of hard/soft X-rays are quantified for stable and unstable conditions. X-ray spectra from Cyg X-1 are cited as residing below the instability threshold value and thus are supportive of the coronal disk model.

  13. THE OPACITY OF GALACTIC DISKS AT z {approx} 0.7

    SciTech Connect

    Sargent, M. T.; Schinnerer, E.; Carollo, C. M.; Kampczyk, P.; Lilly, S. J.; Oesch, P. A.; Scarlata, C.; Capak, P.; Scoville, N.; Ilbert, O.; Kneib, J.-P.; Koekemoer, A. M.; Leauthaud, A.; Massey, R.; Rhodes, J.; Taniguchi, Y.

    2010-05-01

    We compare the surface brightness-inclination relation for a sample of COSMOS pure disk galaxies at z {approx} 0.7 with an artificially redshifted sample of Sloan Digital Sky Survey (SDSS) disks well matched to the COSMOS sample in terms of rest-frame photometry and morphology, as well as their selection and analysis. The offset between the average surface brightness of face-on and edge-on disks in the redshifted SDSS sample matches that predicted by measurements of the optical depth of galactic disks in the nearby universe. In contrast, large disks at z {approx} 0.7 have a virtually flat surface brightness-inclination relation, suggesting that they are more opaque than their local counterparts. This could be explained by either an increased amount of optically thick material in disks at higher redshift or a different spatial distribution of the dust.

  14. Interstellar Methanol from the Lab to Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Drozdovskaya, Maria; Walsh, Catherine; Visser, Ruud; Harsono, Daniel; van Dishoeck, Ewine

    2015-08-01

    Interstellar methanol is considered to be a parent species of larger, more complex organic molecules. It holds a central role in many astrochemical models [e.g. 1]. Methanol has also been the focus of several laboratory studies [e.g. 2, 3] in an effort to gain insight into grain-surface chemistry, which potentially builds chemical complexity already in the cold, dark phases of protostellar evolution. The case of methanol is a prime example of experimental work having implications on astronomical scales. For this meeting, I would like to highlight how physical and chemical models can be unified to simulate infalling material during the birth of a low-mass protostar. An axisymmetric 2D semi-analytic collapse model [4], wavelength-dependent radiative transfer calculations with RADMC3D [5] and a comprehensive gas-grain chemical network [6] are used to study two physical scenarios. In the first case, the dominant disc growth mechanism is viscous spreading, while in the second, continuous infall of matter prevails. The results show that the infall path influences the abundance of methanol entering each type of disk, ranging from complete loss of methanol to an enhancement by a factor of >1 relative to the prestellar phase [7]. This work illustrates how the experimentally verified hydrogenation sequence of carbon monoxide leading to methanol influences the delivery of methanol ice to the planet- and comet-forming zones of protoplanetary disks. Such intriguing links will soon be tested by upcoming cometary data from the Rosetta mission and ALMA observations.[1] Garrod R. T., Herbst E., 2006, A&A, 457, 927[2] Watanabe N., Nagaoka A., Shiraki T., Kouchi A., 2004, ApJ, 616, 638[3] Fuchs G. W., Cuppen H. M., Ioppolo S., Romanzin C., Bisschop S. E., Andersson S., van Dishoeck E. F., Linnartz H., 2009, A&A, 505, 629[4] Visser R., van Dishoeck E. F., Doty S. D., Dullemond C. P., 2009, A&A, 495, 881[5] Dullemond C. P., Dominik C., 2004, A&A, 417, 159[6] Walsh C., Millar T. J

  15. Planet Formation Signposts: Observability of Circumplanetary Disks via Gas Kinematics

    NASA Astrophysics Data System (ADS)

    Perez, Sebastian; Dunhill, A.; Casassus, S.; Roman, P.; Szulágyi, J.; Flores, C.; Marino, S.; Montesinos, M.

    2015-09-01

    The identification of ongoing planet formation requires the finest angular resolutions and deepest sensitivities in observations inspired by state-of-the-art numerical simulations. Hydrodynamic simulations of planet-disk interactions predict the formation of circumplanetary disks (CPDs) around accreting planetary cores. These CPDs have eluded unequivocal detection—their identification requires predictions in CPD tracers. In this work, we aim to assess the observability of embedded CPDs with the Atacama Large Millimeter/submillimeter Array (ALMA) as features imprinted in the gas kinematics. We use 3D smooth particle hydrodynamic simulations of CPDs around 1 and 5 {M}{Jup} planets at large stellocentric radii in locally isothermal and adiabatic disks. The simulations are then connected with 3D radiative transfer for predictions in CO isotopologues. Observability is assessed by corrupting with realistic long baseline phase noise extracted from the recent HL Tau ALMA data. We find that the presence of a CPD produces distinct signposts: (1) a compact emission separated in velocity from the overall circumstellar disk’s Keplerian pattern, (2) a strong impact on the velocity pattern when the Doppler-shifted line emission sweeps across the CPD location, and (3) a local increase in the velocity dispersion. We test our predictions with a simulation tailored for HD 100546—which has a reported protoplanet candidate. We find that the CPDs are detectable in all three signposts with ALMA Cycle 3 capabilities for both 1 and 5 {M}{Jup} protoplanets, when embedded in an isothermal disk.

  16. A ∼0.2-solar-mass protostar with a Keplerian disk in the very young L1527 IRS system.

    PubMed

    Tobin, John J; Hartmann, Lee; Chiang, Hsin-Fang; Wilner, David J; Looney, Leslie W; Loinard, Laurent; Calvet, Nuria; D'Alessio, Paola

    2012-12-01

    In their earliest stages, protostars accrete mass from their surrounding envelopes through circumstellar disks. Until now, the smallest observed protostar-to-envelope mass ratio was about 2.1 (ref. 1). The protostar L1527 IRS is thought to be in the earliest stages of star formation. Its envelope contains about one solar mass of material within a radius of about 0.05 parsecs (refs 3, 4), and earlier observations suggested the presence of an edge-on disk. Here we report observations of dust continuum emission and (13)CO (rotational quantum number J = 2 → 1) line emission from the disk around L1527 IRS, from which we determine a protostellar mass of 0.19 ± 0.04 solar masses and a protostar-to-envelope mass ratio of about 0.2. We conclude that most of the luminosity is generated through the accretion process, with an accretion rate of about 6.6 × 10(-7) solar masses per year. If it has been accreting at that rate through much of its life, its age is approximately 300,000 years, although theory suggests larger accretion rates earlier, so it may be younger. The presence of a rotationally supported disk is confirmed, and significantly more mass may be added to its planet-forming region as well as to the protostar itself in the future. PMID:23222612

  17. Lumbar disk herniation surgery: outcome and predictors.

    PubMed

    Sedighi, Mahsa; Haghnegahdar, Ali

    2014-12-01

    Study Design A retrospective cohort study. Objectives To determine the outcome and any differences in the clinical results of three different surgical methods for lumbar disk herniation and to assess the effect of factors that could predict the outcome of surgery. Methods We evaluated 148 patients who had operations for lumbar disk herniation from March 2006 to March 2011 using three different surgical techniques (laminectomy, microscopically assisted percutaneous nucleotomy, and spinous process osteotomy) by using Japanese Orthopaedic Association (JOA) Back Pain Evaluation Questionnaire, Resumption of Activities of Daily Living scale and changes of visual analog scale (VAS) for low back pain and radicular pain. Our study questionnaire addressed patient subjective satisfaction with the operation, residual complaints, and job resumption. Data were analyzed with SPSS version 16.0 (SPSS, Inc., Chicago, Illinois, United States). Statistical significance was set at 0.05. For statistical analysis, chi-square test, Mann-Whitney U test, Kruskal-Wallis test, and repeated measure analysis were performed. For determining the confounding factors, univariate analysis by chi-square test was used and followed by logistic regression analysis. Results Ninety-four percent of our patients were satisfied with the results of their surgeries. VAS documented an overall 93.3% success rate for reduction of radicular pain. Laminectomy resulted in better outcome in terms of JOA Back Pain Evaluation Questionnaire. The outcome of surgery did not significantly differ by age, sex, level of education, preoperative VAS for back, preoperative VAS for radicular pain, return to previous job, or level of herniation. Conclusion Surgery for lumbar disk herniation is effective in reducing radicular pain (93.4%). All three surgical approaches resulted in significant decrease in preoperative radicular pain and low back pain, but intergroup variation in the outcome was not achieved. As indicated

  18. Persistent Patterns in Accretion Disks

    SciTech Connect

    Amin, Mustafa A.; Frolov, Andrei V.; /KIPAC, Menlo Park

    2006-04-03

    We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the central body. Their existence depends on general relativistic corrections to orbital motion and, if observed, could be used to probe the strong gravity region around a black hole. We also discuss a possible connection to the puzzle of quasi-periodic oscillations.

  19. Rewriteable optical disk recorder development

    NASA Technical Reports Server (NTRS)

    Shull, Thomas A.; Rinsland, Pamela L.

    1991-01-01

    A NASA program to develop a high performance (high rate, high capability) rewriteable optical disk recorder for spaceflight applications is presented. An expandable, adaptable system concept is proposed based on disk Drive modules and a modular Controller. Drive performance goals are 10 gigabyte capacity are up to 1.8 gigabits per second rate with concurrent I/O, synchronous data transfer, and 2 to 5 years operating life in orbit. Technology developments, design concepts, current status, and future plans are presented.

  20. Resolved Observations of Transition Disks

    NASA Astrophysics Data System (ADS)

    Casassus, Simon

    2016-04-01

    Resolved observations are bringing new constraints on the origin of radial gaps in protoplanetary disks. The kinematics, sampled in detail in one case-study, are indicative of non-Keplerian flows, corresponding to warped structures and accretion which may both play a role in the development of cavities. Disk asymmetries seen in the radio continuum are being interpreted in the context of dust segregation via aerodynamic trapping. We summarise recent observational progress, and describe prospects for improvements in the near term.