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Sample records for migration disk evolution

  1. Impact of radial migration on the chemical evolution of the Milky Way disk

    NASA Astrophysics Data System (ADS)

    Prantzos, N.; Kubryk, M.; Athanassoula, E.

    2014-07-01

    We study the role of radial migration of stars on the chemical evolution of the Milky Way disk with a 1D semi-analytical disk model. We describe radial migration with parametrised time- and radius-dependent diffusion coefficients, based on the analysis of a N-body+SPH simulation of a disk galaxy (analyzed by Kubryk et al. 2013). Our model reproduces well the present day values of most of the main global observables of the MW. Assuming that the thick disk is the oldest (>9 Gyr) part of the disk, we find that the adopted radial migration scheme can reproduce quantitatively the main local properties of the thin and thick disk: metallicity-distributions, dispersion in age-metallicity relation, "two-branch" behaviour in the O/Fe vs. Fe/H relation, local surface densities of stars, etc..

  2. Giant Planet Migration, Disk Evolution, and the Origin of Transitional Disks

    NASA Astrophysics Data System (ADS)

    Alexander, Richard D.; Armitage, Philip J.

    2009-10-01

    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 lsim1.5 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.

  3. 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.

  4. THE MIGRATION OF GAP-OPENING PLANETS IS NOT LOCKED TO VISCOUS DISK EVOLUTION

    SciTech Connect

    Duffell, Paul C.; MacFadyen, Andrew I.; Farris, Brian D.; Haiman, Zoltan; D'Orazio, Daniel J.

    2014-09-01

    Most standard descriptions of Type II migration state that massive, gap-opening planets must migrate at the viscous drift rate. This is based on the idea that the disk is separated into an inner and outer region and gas is considered unable to cross the gap. In fact, gas easily crosses the gap on horseshoe orbits, nullifying this necessary premise which would set the migration rate. In this work, it is demonstrated using highly accurate numerical calculations that the actual migration rate is dependent on disk and planet parameters, and can be significantly larger or smaller than the viscous drift rate. In the limiting case of a disk much more massive than the secondary, the migration rate saturates to a constant that is sensitive to disk parameters and is not necessarily of the order of the viscous rate. In the opposite limit of a low-mass disk, the migration rate decreases linearly with disk mass. Steady-state solutions in the low disk mass limit show no pile-up outside the secondary's orbit, and no corresponding drainage of the inner disk.

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

    NASA Astrophysics Data System (ADS)

    Russo, Matthew; Thompson, Christopher

    2015-12-01

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

  6. PROTOPLANETARY MIGRATION IN TURBULENT ISOTHERMAL DISKS

    SciTech Connect

    Baruteau, C.; Lin, D. N. C. E-mail: lin@ucolick.or

    2010-02-01

    In order to reproduce the statistical properties of the observed exoplanets, population synthesis models have shown that the migration of protoplanets should be significantly slowed down, and that processes stalling migration should be at work. Much current theoretical efforts have thus been dedicated to find physical effects that slow down, halt or even reverse migration. Many of these studies rely on the horseshoe drag, whose long-term evolution (saturated or not) is intimately related to the disk viscosity in laminar disk models. We investigate how the horseshoe drag exerted on a low-mass planet is altered by a more realistic treatment of the turbulence in protoplanetary disks. Two-dimensional hydrodynamic simulations are performed with a turbulence model that reproduces the main turbulence properties of three-dimensional magnetohydrodynamic calculations. We find that the horseshoe drag can remain unsaturated on the long term, depending on the turbulence strength. We show that the desaturation of the horseshoe drag by turbulence can be modeled by vortensity diffusion across the time-averaged planet's horseshoe region. At low-turbulence, the running-time-averaged torque is in good agreement with the total torque obtained for an equivalent laminar model, with a similar vortensity diffusion coefficient. At high turbulence, differences arise due to the time evolution of the averaged density profile with turbulence.

  7. PROTOPLANETARY DISK RESONANCES AND TYPE I MIGRATION

    SciTech Connect

    Tsang, David

    2011-11-10

    Waves reflected by the inner edge of a protoplanetary disk are shown to significantly modify Type I migration, even allowing the trapping of planets near the inner disk edge for small planets in a range of disk parameters. This may inform the distribution of planets close to their central stars, as observed recently by the Kepler mission.

  8. 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.

  9. ORBITAL MIGRATION OF PROTOPLANETS IN A MARGINALLY GRAVITATIONALLY UNSTABLE DISK

    SciTech Connect

    Boss, Alan P.

    2013-02-20

    Core accretion and disk instability require giant protoplanets to form in the presence of disk gas. Protoplanet migration models generally assume disk masses low enough that the disk's self-gravity can be neglected. However, disk instability requires a disk massive enough to be marginally gravitationally unstable (MGU). Even for core accretion, an FU Orionis outburst may require a brief MGU disk phase. We present a new set of three-dimensional, gravitational radiation hydrodynamics models of MGU disks with multiple protoplanets, which interact gravitationally with the disk and with each other, including disk gas mass accretion. Initial protoplanet masses are 0.01 to 10 M {sub Circled-Plus} for core accretion models, and 0.1 to 3 M {sub Jup} for Nice scenario models, starting on circular orbits with radii of 6, 8, 10, or 12 AU, inside a 0.091 M {sub Sun} disk extending from 4 to 20 AU around a 1 M {sub Sun} protostar. Evolutions are followed for up to {approx}4000 yr and involve phases of relative stability (e {approx} 0.1) interspersed with chaotic phases (e {approx} 0.4) of orbital interchanges. The 0.01 to 10 M {sub Circled-Plus} cores can orbit stably for {approx}1000 yr: monotonic inward or outward orbital migration of the type seen in low mass disks does not occur. A system with giant planet masses similar to our solar system (1.0, 0.33, 0.1, 0.1 M {sub Jup}) was stable for over 1000 yr, and a Jupiter-Saturn-like system was stable for over 3800 yr, implying that our giant planets might well survive an MGU disk phase.

  10. Stochastic Migration in a Dissipating Disk

    NASA Astrophysics Data System (ADS)

    Mills, Sean; Fabrycky, Daniel C.

    2016-10-01

    It is yet unclear whether the majority of planets formed in situ in their presently observed locations or if they formed distant from their current locations and migrated through the gas and dust protoplanetary disk extant early in their host star's lifetime. Migration simulations generally produce an abundance of planets near mean motion resonances (MMRs); however, statistical analysis of the observed population of exoplanets shows only a very modest enhancement of planets near MMRs and a large number in a continuum of period ratios. It has previously been suggested that migration through a turbulent, dissipating disk may disrupt the resonances formed via migration and approximately reproduce the period ratios of pairs of planets observed in planets observed by Kepler. Here we expand on this analysis to include more realistic dissipation and turbulence parameterizations and compare the results of our simulations to the architectures of higher multiplicity systems observed by Kepler as well as individual planet pairs. We thus place tighter constraints on the turbulence and dissipation properties of disks during planet formation and migration.

  11. 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

  12. 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

  13. 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

  14. Suppression of type I migration by disk winds

    NASA Astrophysics Data System (ADS)

    Ogihara, Masahiro; Morbidelli, Alessandro; Guillot, Tristan

    2015-12-01

    Context. Planets less massive than Saturn tend to rapidly migrate inward in protoplanetary disks. This is the so-called type I migration. Simulations attempting to reproduce the observed properties of exoplanets show that type I migration needs to be significantly reduced over a wide region of the disk for a long time. However, the mechanism capable of suppressing type I migration over a wide region has remained elusive. The recently found turbulence-driven disk winds offer new possibilities. Aims: We investigate the effects of disk winds on the disk profile and type I migration for a range of parameters that describe the strength of disk winds. We also examine the in situ formation of close-in super-Earths in disks that evolve through disk winds. Methods: The disk profile, which is regulated by viscous diffusion and disk winds, was derived by solving the diffusion equation. We carried out a number of simulations and plot here migration maps that indicate the type I migration rate. We also performed N-body simulations of the formation of close-in super-Earths from a population of planetesimals and planetary embryos. Results: We define a key parameter, Kw, which determines the ratio of strengths between the viscous diffusion and disk winds. For a wide range of Kw, the type I migration rate is presented in migration maps. These maps show that type I migration is suppressed over the whole close-in region when the effects of disk winds are relatively strong (Kw ≲ 100). From the results of N-body simulations, we see that type I migration is significantly slowed down assuming Kw = 40. We also show that the results of N-body simulations match statistical orbital distributions of close-in super-Earths.

  15. The effect of radial migration on galactic disks

    SciTech Connect

    Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio; Abadi, Mario

    2014-10-20

    We study the radial migration of stars driven by recurring multi-arm spiral features in an exponential disk embedded in a dark matter halo. The spiral perturbations redistribute angular momentum within the disk and lead to substantial radial displacements of individual stars, in a manner that largely preserves the circularity of their orbits and that results, after 5 Gyr (∼40 full rotations at the disk scale length), in little radial heating and no appreciable changes to the vertical or radial structure of the disk. Our results clarify a number of issues related to the spatial distribution and kinematics of migrators. In particular, we find that migrators are a heavily biased subset of stars with preferentially low vertical velocity dispersions. This 'provenance bias' for migrators is not surprising in hindsight, for stars with small vertical excursions spend more time near the disk plane, and thus respond more readily to non-axisymmetric perturbations. We also find that the vertical velocity dispersion of outward migrators always decreases, whereas the opposite holds for inward migrators. To first order, newly arrived migrators simply replace stars that have migrated off to other radii, thus inheriting the vertical bias of the latter. Extreme migrators might therefore be recognized, if present, by the unexpectedly small amplitude of their vertical excursions. Our results show that migration, understood as changes in angular momentum that preserve circularity, can strongly affect the thin disk, but cast doubts on models that envision the Galactic thick disk as a relic of radial migration.

  16. Accretion disks in Algols: Progenitors and evolution

    NASA Astrophysics Data System (ADS)

    Van Rensbergen, W.; De Greve, J. P.

    2016-08-01

    Context. There are only a few Algols with measured accretion disk parameters. These measurements provide additional constraints for tracing the origin of individual systems, narrowing down the initial parameter space. Aims: We investigate the origin and evolution of six Algol systems with accretion disks to find the initial parameters and evolutionary constraints for them. Methods: With a modified binary evolution code, series of close binary evolution are calculated to obtain the best match for observed individual systems. Results: Initial parameters for six Algol systems with accretion disks were determined matching both the present system parameters and the observed disk characteristics. Conclusions: When Roche lobe overflow (RLOF) starts during core hydrogen burning of the donor, the disk lifetime was found to be short. The disk luminosity is comparable to the luminosity of the gainer during a large fraction of the disk lifetime.

  17. THE EVOLUTION OF INNER DISK GAS IN TRANSITION DISKS

    SciTech Connect

    Hoadley, K.; France, K.; McJunkin, M.; Alexander, R. D.; Schneider, P. C.

    2015-10-10

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

  18. MIGRATION OF PLANETS EMBEDDED IN A CIRCUMSTELLAR DISK

    SciTech Connect

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

    2011-07-01

    Planetary migration poses a serious challenge to theories of planet formation. In gaseous and planetesimal disks, migration can remove planets as quickly as they form. To explore migration in a planetesimal disk, we combine analytic and numerical approaches. After deriving general analytic migration rates for isolated planets, we use N-body simulations to confirm these results for fast and slow migration modes. Migration rates scale as m{sup -1} (for massive planets) and (1 + (e{sub H}/3){sup 3}){sup -1}, where m is the mass of a planet and e{sub H} is the eccentricity of the background planetesimals in Hill units. When multiple planets stir the disk, our simulations yield the new result that large-scale migration ceases. Thus, growing planets do not migrate through planetesimal disks. To extend these results to migration in gaseous disks, we compare physical interactions and rates. Although migration through a gaseous disk is an important issue for the formation of gas giants, we conclude that migration has little impact on the formation of terrestrial planets.

  19. Radial migration and chemical evolution in the Milky Way

    NASA Astrophysics Data System (ADS)

    Prantzos, N.

    2016-09-01

    The role of radial migration on the chemical evolution of the Milky Way is studied with semi-analytical models of disk evolution, using several new/updated ingredients and parametrized prescriptions for blurring and churning. It is found that radial migration impacts on several properties of the local disk (shape and dispersion of the age-metallicity relation, metallicity distribution), it may explain some chemical properties of the local thin and thick disks (i.e. the two-branch shape of the O/Fe vs. Fe/H relation) and it affects the past abundance profiles of the stellar population.

  20. Type I planet migration in nearly laminar disks

    SciTech Connect

    Li, Hui; Li, Shengtai; Lubow, S H; Lin, D

    2008-01-01

    We describe two-dimensional hydrodynamic simulations of the migration of low-mass planets ({<=}30 M{sub {circle_plus}}) in nearly laminar disks (viscosity parameter {alpha} < 10{sup -3}) over timescales of several thousand orbit periods. We consider disk masses of 1, 2, and 5 times the minimum mass solar nebula, disk thickness parameters of H/r = 0.035 and 0.05, and a variety of {alpha} values and planet masses. Disk self-gravity is fully included. Previous analytic work has suggested that Type I planet migration can be halted in disks of sufficiently low turbulent viscosity, for {alpha} {approx} 10{sup -4}. The halting is due to a feedback effect of breaking density waves that results in a slight mass redistribution and consequently an increased outward torque contribution. The simulations confirm the existence of a critical mass (M{sub {alpha}} {approx} 10M{sub {circle_plus}}) beyond which migration halts in nearly laminar disks. For {alpha} {approx}> 10{sup -3}, density feedback effects are washed out and Type I migration persists. The critical masses are in good agreement with the analytic model of Rafikov. In addition, for {alpha} {approx}> 10{sup -4} steep density gradients produce a vortex instability, resulting in a small time-varying eccentricity in the planet's orbit and a slight outward migration. Migration in nearly laminar disks may be sufficiently slow to reconcile the timescales of migration theory with those of giant planet formation in the core accretion model.

  1. Dispersing the Gaseous Protoplanetary Disk and Halting Type II Migration

    NASA Astrophysics Data System (ADS)

    Lecar, M.; Sasselov, D. D.

    2003-10-01

    More than 30 extrasolar Jupiter-like planets have shorter periods than the planet Mercury. It is generally accepted that they formed farther out, past the ``snow line'' (~1 AU), and migrated inward. In order to be driven by tidal torques from the gaseous disk, the disk exterior to the planet had to contain about a planetary mass. The fact that the planets stopped migrating means that their outer disk was removed. We suggest, following the simulation by Kley and Bate et al., that the outer disk was accreted by the planet. This not only halts migration but removes the outer disk. For planets exterior to about 2 AU, the outer disk could have been removed by photoevaporation (Matsuyama et al.). Furthermore, as also shown by Bate et al., this process also provides an upper limit to planetary masses in agreement with the analysis of observed planetary masses by Zucker & Mazeh. In this scenario, the endgame is a race. The central star is accreting the inner disk and the planet, while the planet is accreting the outer disk. The planet survives if it accretes its outer disk before being accreted by the star. The winner is determined solely by the ratio of the mass of the outer disk to the local surface density of the disk. Some planets certainly lose the race and are eaten by the central star.

  2. Migration Traps in Disks around Supermassive Black Holes

    NASA Astrophysics Data System (ADS)

    Bellovary, Jillian M.; Mac Low, Mordecai-Mark; McKernan, Barry; Ford, K. E. Saavik

    2016-03-01

    Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20-300Rg, where Rg = 2GM/c2 is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.

  3. The dependence of giant planet migration on disk and planet properties

    NASA Astrophysics Data System (ADS)

    Moorhead, Althea; Ford, E. B.

    2010-05-01

    Given the severe challenges in forming giant planets so close to their host star, disk-induced migration is often invoked to explain their small semi-major axes. Migration theory is usually divided into two limiting cases: Type I migration, in which the planet remains embedded in the disk, and Type II migration, in which the planet is sufficiently massive that it clears a gap in the disk in the vicinity of its orbit and follows the viscous evolution of the disk. However, recent hydrodynamic simulations of giant planets in circumstellar disks do not seem to follow this prescription; giant planet migration rates show a dependence on planet mass that is inconsistent with migrration on a constant, viscous timescale (Edgar 2008). We use FARGO to extend the work of Edgar (2008) and Bate (2003) to higher viscosities and larger planet masses and present the results in the context of distinguishing between the standard description of giant planet migration and that of Edgar (2007). Additionally, we present simulations of planets on eccentric orbits and describe how eccentricity modifies giant planet migration.

  4. Asymmetric evolution of magnetic reconnection in collisionless accretion disk

    SciTech Connect

    Shirakawa, Keisuke Hoshino, Masahiro

    2014-05-15

    An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J{sub 0}×Ω{sub 0}, where J{sub 0} is the initial current density in the neutral sheet and Ω{sub 0} is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

  5. Verification of runaway migration in a massive disk

    SciTech Connect

    Li, Shengtai

    2009-01-01

    Runaway migration of a proto-planet was first proposed and observed by Masset and Papaloizou (2003). The semi-major axis of the proto-planet varies by 50% over just a few tens of orbits when runaway migration happens. More recent work by D'Angelo et al. (2005) solved the same problem with locally refined grid and found that the migration rate is sharply reduced and no runaway occurs when the grid cells surrounding the planet are refined enough. To verify these two seemly contradictory results, we independently perform high-resolution simulations, solving the same problem as Masset and Papaloizou (2003), with and without self-gravity. We find that the migration rate is highly dependent on the softening used in the gravitational force between thd disk and planet. When a small softening is used in a 2D massive disk, the mass of the circumplanetary disk (CPD) increases with time with enough resolution in the CPD region. It acts as the mass is continually accreted to the CPD, which cannot be settled down until after thousands of orbits. If the planet is held on a fixed orbit long enough, the mass of CPD will become so large that the condition for the runaway migration derived in Masset (2008) will not be satisfied, and hence the runaway migration will not be triggered. However, when a large softening is used, the mass of the CPD will begin to decrease after the initial increase stage. Our numerical results with and without disk-gravity confirm that the runaway migration indeed exists when the mass deficit is larger than the total mass of the planet and CPD. Our simulations results also show that the torque from the co-orbital region, in particular the planet's Hill sphere, is the main contributor to the runaway migration, and the CPD which is lagged behind by the planet becomes so asymmetric that it accelerates the migration.

  6. The Genesis of the Milky Way's Thick Disk Via Stellar Migration

    NASA Astrophysics Data System (ADS)

    Loebman, Sarah R.; Roškar, Rok; Debattista, Victor P.; Ivezić, Željko; Quinn, Thomas R.; Wadsley, James

    2011-08-01

    We compare the spatial, kinematic, and metallicity distributions of stars in the Milky Way disk, as observed by the Sloan Digital Sky Survey and Geneva-Copenhagen Survey, to predictions made by N-body simulations that naturally include radial migration as proposed by Sellwood & Binney. In these simulations, stars that migrate radially outward feel a decreased restoring force, consequentially they reach larger heights above the mid-plane. We find that this model is in qualitative agreement with observational data and can explain the disk's double-exponential vertical structure and other characteristics as due to internal evolution. In particular, the model reproduces observations of stars in the transition region between exponential components, which do not show a strong correlation between rotational velocity and metallicity. Although such a correlation is present in young stars because of epicyclic motions, radial migration efficiently mixes older stars and weakens the correlation. Classifying stars as members of the thin or thick disk by either velocity or metallicity leads to an apparent separation in the other property, as observed. We find a much stronger separation when using [α/Fe], which is a good proxy for stellar age. The model success is remarkable because the simulation was not tuned to reproduce the Galaxy, hinting that the thick disk may be a ubiquitous Galactic feature generated by stellar migration. Nonetheless, we cannot exclude the possibility that some fraction of the thick disk is a fossil of a more violent history, nor can radial migration explain thick disks in all galaxies, most strikingly those which counterrotate with respect to the thin disk.

  7. THE GENESIS OF THE MILKY WAY'S THICK DISK VIA STELLAR MIGRATION

    SciTech Connect

    Loebman, Sarah R.; Roskar, Rok; Ivezic, Zeljko; Quinn, Thomas R.; Debattista, Victor P.; Wadsley, James E-mail: roskar@physik.uzh.ch

    2011-08-10

    We compare the spatial, kinematic, and metallicity distributions of stars in the Milky Way disk, as observed by the Sloan Digital Sky Survey and Geneva-Copenhagen Survey, to predictions made by N-body simulations that naturally include radial migration as proposed by Sellwood and Binney. In these simulations, stars that migrate radially outward feel a decreased restoring force, consequentially they reach larger heights above the mid-plane. We find that this model is in qualitative agreement with observational data and can explain the disk's double-exponential vertical structure and other characteristics as due to internal evolution. In particular, the model reproduces observations of stars in the transition region between exponential components, which do not show a strong correlation between rotational velocity and metallicity. Although such a correlation is present in young stars because of epicyclic motions, radial migration efficiently mixes older stars and weakens the correlation. Classifying stars as members of the thin or thick disk by either velocity or metallicity leads to an apparent separation in the other property, as observed. We find a much stronger separation when using [{alpha}/Fe], which is a good proxy for stellar age. The model success is remarkable because the simulation was not tuned to reproduce the Galaxy, hinting that the thick disk may be a ubiquitous Galactic feature generated by stellar migration. Nonetheless, we cannot exclude the possibility that some fraction of the thick disk is a fossil of a more violent history, nor can radial migration explain thick disks in all galaxies, most strikingly those which counterrotate with respect to the thin disk.

  8. MIGRATION OF GAS GIANT PLANETS IN GRAVITATIONALLY UNSTABLE DISKS

    SciTech Connect

    Michael, Scott; Durisen, Richard H.; Boley, Aaron C. E-mail: durisen@astro.indiana.edu

    2011-08-20

    Characterization of migration in gravitationally unstable disks is necessary to understand the fate of protoplanets formed by disk instability. As part of a larger study, we are using a three-dimensional radiative hydrodynamics code to investigate how an embedded gas giant planet interacts with a gas disk that undergoes gravitational instabilities (GIs). This Letter presents results from simulations with a Jupiter-mass planet placed in orbit at 25 AU within a 0.14 M{sub sun} disk. The disk spans 5-40 AU around a 1 M{sub sun} star and is initially marginally unstable. In one simulation, the planet is inserted prior to the eruption of GIs; in another, it is inserted only after the disk has settled into a quasi-steady GI-active state, where heating by GIs roughly balances radiative cooling. When the planet is present from the beginning, its own wake stimulates growth of a particular global mode with which it strongly interacts, and the planet plunges inward 6 AU in about 10{sup 3} years. In both cases with embedded planets, there are times when the planet's radial motion is slow and varies in direction. At other times, when the planet appears to be interacting with strong spiral modes, migration both inward and outward can be relatively rapid, covering several AUs over hundreds of years. Migration in both cases appears to stall near the inner Lindblad resonance of a dominant low-order mode. Planet orbit eccentricities fluctuate rapidly between about 0.02 and 0.1 throughout the GI-active phases of the simulations.

  9. 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

  10. THICK-DISK EVOLUTION INDUCED BY THE GROWTH OF AN EMBEDDED THIN DISK

    SciTech Connect

    Villalobos, Alvaro; Helmi, Amina; Kazantzidis, Stelios E-mail: ahelmi@astro.rug.n E-mail: villalobos@oats.inaf.i

    2010-07-20

    We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically common 5:1 encounters between initially thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale lengths and scale heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation.

  11. 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.

  12. Orbital Survival of Meter-size and Larger Bodies During Gravitationally Unstable Phases of Protoplanetary Disk Evolution

    NASA Astrophysics Data System (ADS)

    Boss, Alan P.

    2015-07-01

    A long-standing problem in the collisional accretion of terrestrial planets is the possible loss of m-size bodies through their inward migration onto the protostar as a result of gas drag forces. Such inward migration can be halted, and indeed even reversed, in a protoplanetary disk with local pressure maxima, such as marginally gravitationally unstable (MGU) phases of evolution, e.g., FU Orionis events. Results are presented for a suite of three-dimensional models of MGU disks extending from 1 to 10 AU and containing solid particles with sizes of 1 cm, 10 cm, 1 m, or 10 m, subject to disk gas drag and gravitational forces. These hydrodynamical models show that over disk evolution time scales of ∼ 6× {10}3 years or longer, during which over half the gaseous disk mass is accreted by the protostar, very few 1 and 10 m bodies are lost through inward migration: most bodies survive and orbit stably in the outer disk. A greater fraction of 1 and 10 cm particles are lost to the central protostar during these time periods, as such particles are more closely tied to the disk gas accreting onto the protostar, but even in these cases, a significant fraction survive and undergo transport from the hot inner disk to the cold outer disk, perhaps explaining the presence of small refractory particles in Comet Wild 2. Evidently MGU disk phases offer a means to overcome the m-sized migration barrier to collisional accumulation.

  13. Chemodynamical evolution of the Milky Way disk. I. The solar vicinity

    NASA Astrophysics Data System (ADS)

    Minchev, I.; Chiappini, C.; Martig, M.

    2013-10-01

    In the first paper of this series, we present a new approach for studying the chemo-dynamical evolution in disk galaxies, which consists of fusing disk chemical evolution models with compatible numerical simulations of galactic disks. This method avoids known star formation and chemical enrichment problems encountered in simulations. Here we focus on the Milky Way, by using a detailed thin-disk chemical evolution model (matching local observables, which are weakly affected by radial migration) and a simulation in the cosmological context, with dynamical properties close to those of our Galaxy. We examine in detail the interplay between in situ chemical enrichment and radial migration and their impact on key observables in the solar neighborhood, e.g., the age-metallicity-velocity relation, the metallicity distribution, and gradients in the radial and vertical directions. We show that, due to radial migration from mergers at high redshift and the central bar at later times, a sizable fraction of old metal-poor high-[α/Fe] stars can reach the solar vicinity. This naturally accounts for a number of recent observations related to both the thin and thick disks, despite the fact that we use thin-disk chemistry only. Although significant radial mixing is present, the slope in the age-metallicity relation is only weakly affected, with a scatter compatible with recent observational work. While we find a smooth density distribution in the [O/Fe]-[Fe/H] plane, we can recover the observed discontinuity by selecting particles according to kinematic criteria used in high-resolution samples to define the thin and thick disks. We outline a new method for estimating the birth place of the Sun and predict that the most likely radius lies in the range 4.4 < r < 7.7 kpc (for a current location at r = 8 kpc). A new, unifying model for the Milky Way thick disk is offered, where both mergers and radial migration play a role at different stages of the disk evolution. We show that in the

  14. Self-consistent dynamical and thermodynamical evolutions of protoplanetary disks.

    NASA Astrophysics Data System (ADS)

    Baillie, K.; Charnoz, S.; Taillifet, E.; Piau, L.

    2012-09-01

    Astronomical observations reveal the diversity of protoplanetary disk evolutions. In order to understand the global evolution of these disks from their birth, during the collapse of the molecular cloud, to their evaporation because of the stellar radiation, many processes with different timescales must be coupled: stellar evolution, thermodynamical evolution, photoevaporation, cloud collapse, viscous spreading... Simulating all these processes simultaneously is beyond the capacity of modern computers. However, by modeling the results of large scale simulations and coupling them with models of viscous evolution, we have designed a one dimension full model of disk evolution. In order to generate the most realistic protoplanetary disk, we minimize the number of input parameters and try to calculate most of them from self-consistent processes, as early as possible in the history of the disk; starting with the collapse of the molecular cloud that feeds the disk in gas. We start from the Hueso and Guillot, 2005 [2] model of disk evolution and couple the radiative transfer description of Calvet et al, 1991 [1] allowing us to handle a non-isothermal disk which midplane temperature is defined by an irradiation term form the central star and a viscous heating term depending on the optical depth of the disk. Our new model of the disk photosphere profile allows us to estimate self-consistent photosphere heights and midplane temperatures at the same time. We then follow the disk evolution using an upgrade of the viscous spreading equation from Lynden-Bell and Pringle, 1981 [3]. In particular, the molecular cloud collapse adds a time varying term to the temporal variation of the surface mass density of the disk, in the same manner that photo-evaporation introduces a density loss term. The central star itself is modeled using recent stellar evolution code described in Piau et al, 2011 [4]. Using the same temperature model in the vertical direction, we estimate 2D thermal maps of

  15. Self-consistent Dynamical And Thermodynamical Evolutions Of Protoplanetary Disks.

    NASA Astrophysics Data System (ADS)

    Baillie, Kevin; Charnoz, S.; Taillifet, E.; Piau, L.

    2012-10-01

    Astronomical observations reveal the diversity of protoplanetary disk evolutions. In order to understand the global evolution of these disks from their birth, during the collapse of the molecular cloud, to their evaporation because of the stellar radiation, many processes with different timescales must be coupled: stellar evolution, thermodynamical evolution, photoevaporation, cloud collapse, viscous spreading...By modeling the results of large scale simulations and coupling them with models of viscous evolution, we have designed a one dimension full model of disk evolution for which most parameters are self-consistently calculated at each time step. We integrate the Hueso and Guillot, 2005 model of disk evolution and couple the radiative transfer description of Calvet et al, 1991 allowing us to handle a non-isothermal disk. We also take into account the collapse of the molecular cloud that feeds the disk. Using the same temperature model in the vertical direction, we estimate 2D thermal maps of the disk. The central star itself is modeled using recent stellar evolution code described in Piau et al, 2011. We first test our model in the case of an already formed Minimum Mass solar Nebula, trying to match the observational constraints on the radial surface density gradients and photosphere height profiles of the Taurus-Auriga or Ophiucus disks for instance. We then follow the full long-term evolution of a disk fed by the collapse of the molecular cloud. We estimate disk temperatures and accretion rates and try to constrain the favourable zone for the formation of the first solids. This will help targeting future JWST observations.

  16. Self-consistent dynamical and thermodynamical evolutions of protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Baillié, K.; Charnoz, S.; Taillifet, E.; Piau, L.

    2012-12-01

    Astronomical observations reveal the diversity of protoplanetary disk evolutions. In order to understand the global evolution of these disks from their birth, during the collapse of the molecular cloud, to their evaporation because of the stellar radiation, many processes with different timescales must be coupled: stellar evolution, thermodynamical evolution, photoevaporation, cloud collapse, viscous spreading... By modeling the results of large scale simulations and coupling them with models of viscous evolution, we have designed a one dimension full model of disk evolution for which most parameters are self-consistently calculated at each time step. We integrate the Hueso and Guillot, 2005 model of disk evolution and couple the radiative transfer description of Calvet et al, 1991 allowing us to handle a non-isothermal disk. We also take into account the collapse of the molecular cloud that feeds the disk. Using the same temperature model in the vertical direction, we estimate 2D thermal maps of the disk. The central star itself is modeled using recent stellar evolution code described in Piau et al, 2011. We first test our model in the case of an already formed Minimum Mass solar Nebula, trying to match the observational constraints on the radial surface density gradients and photosphere height profiles of the Taurus-Auriga or Ophiucus disks for instance. We then follow the full long-term evolution of a disk fed by the collapse of the molecular cloud. We estimate disk temperatures and accretion rates and try to constrain the favourable zone for the formation of the first solids. This will help targeting future JWST observations.

  17. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2003-01-01

    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.

  18. Evolution of Vega-like disks

    NASA Astrophysics Data System (ADS)

    Dominik, C.; Habing, H. J.; Hjhvega Consortium

    Vega-like stars are main-sequence stars with IR excesses usually attributed to the presence of a circumstellar debris disk. According to the results from the IRAS database, approximately 30 % or more of all main sequence stars should show such an excess (Aumann & Good 1990, AJ 350, 408; Aumann 1988, AJ 96, 1414) however, a more recent re-evaluation of this problem indicates numbers clearly below 20 % (Plets 1997, PHD-thesis, University Leuven). One of the problems of the IRAS studies was that the samples used to study the phenomenon usually were poorly defined. This was also prohibitive to a detailed statistical study of age effects these stars. We have undertaken the study of a volume-limited sample with ISO. Studying this sample and theoretical models we will show in this contribution that: 1. There is an age-excess relation for main sequence stars. We find a fraction of excess stars in our sample of approximately 20 %, higher for young stars. 2. By example of a particular G type star we show that the inner hole in the disk required to fit the observations needs not only to be created when the stars forms, but also needs to be maintained over the history of the stars evolution. 3. We present calculations which indicate that the sun was a Vega-like star when it was young, but that the current amount of material is too little to produce an amount of dust which would be observable with current technology (ISO) from a nearby star.

  19. Tatooine Nurseries: Structure and Evolution of Circumbinary Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Vartanyan, David; Garmilla, José A.; Rafikov, Roman R.

    2016-01-01

    Recent discoveries of circumbinary planets by the Kepler mission provide motivation for understanding their birthplaces—protoplanetary disks around stellar binaries with separations ≲ 1 {{AU}}. We explore properties and evolution of such circumbinary disks focusing on modification of their structure caused by tidal coupling to the binary. We develop a set of analytical scaling relations describing viscous evolution of the disk properties, which are verified and calibrated using 1D numerical calculations with realistic inputs. Injection of angular momentum by the central binary suppresses mass accretion onto the binary and causes radial distribution of the viscous angular momentum flux {F}J to be different from that in a standard accretion disk around a single star with no torque at the center. Disks with no mass accretion at the center develop an {F}J profile that is flat in radius. Radial profiles of temperature and surface density are also quite different from those in disks around single stars. Damping of the density waves driven by the binary and viscous dissipation dominates heating of the inner disk (within 1-2 AU), pushing the ice line beyond 3-5 AU, depending on disk mass and age. Irradiation by the binary governs disk thermodynamics beyond ˜10 AU. However, self-shadowing by the hot inner disk may render central illumination irrelevant out to ˜20 AU. Spectral energy distribution of a circumbinary disk exhibits a distinctive bump around 10 μm, which may facilitate identification of such disks around unresolved binaries. Efficient tidal coupling to the disk drives orbital inspiral of the binary and may cause low-mass and relatively compact binaries to merge into a single star within the disk lifetime. We generally find that circumbinary disks present favorable sites for planet formation (despite their wider zone of volatile depletion), in agreement with the statistics of Kepler circumbinary planets.

  20. Gap formation in a self-gravitating disk and the associated migration of the embedded giant planet

    NASA Astrophysics Data System (ADS)

    Zhang, Hui; Liu, Hui-Gen; Zhou, Ji-Lin; Wittenmyer, Robert A.

    2014-04-01

    We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk's self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We select several surface densities and focus on the gravitationally stable region. To obtain more reliable gravity torques exerted on the planet, a refined treatment of the disk's gravity is adopted in the vicinity of the planet. Our results indicate that the net effect of the disk's self-gravity on the gap formation process depends on the surface density of the disk. We notice that there are two critical values, ΣI and ΣII. When the surface density of the disk is lower than the first one, Σ0 < ΣI, the effect of self-gravity suppresses the formation of a gap. When Σ0 > ΣI, the self-gravity of the gas tends to benefit the gap formation process and enlarges the width/depth of the gap. According to our 1-D and 2-D simulations, we estimate the first critical surface density to be ΣI ≈ 0.8 MMSN. This effect increases until the surface density reaches the second critical value ΣII. When Σ0 > ΣII, the gravitational turbulence in the disk becomes dominant and the gap formation process is suppressed again. Our 2-D simulations show that this critical surface density is around 3.5 MMSN. We also study the associated orbital evolution of a giant planet. Under the effect of the disk's self-gravity, the migration rate of the giant planet increases when the disk is dominated by gravitational turbulence. We show that the migration timescale correlates with the effective viscosity and can be up to 104 yr.

  1. 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.

  2. 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.

  3. MIGRATION OF EXTRASOLAR PLANETS: EFFECTS FROM X-WIND ACCRETION DISKS

    SciTech Connect

    Adams, Fred C.; Cai, Mike J.; Lizano, Susana

    2009-09-10

    Magnetic fields are dragged in from the interstellar medium during the gravitational collapse that forms star/disk systems. Consideration of mean field magnetohydrodynamics in these disks shows that magnetic effects produce sub-Keplerian rotation curves and truncate the inner disk. This Letter explores the ramifications of these predicted disk properties for the migration of extrasolar planets. Sub-Keplerian flow in gaseous disks drives a new migration mechanism for embedded planets and modifies the gap-opening processes for larger planets. This sub-Keplerian migration mechanism dominates over Type I migration for sufficiently small planets (m{sub P} {approx}< 1 M {sub +}) and/or close orbits (r {approx}< 1 AU). Although the inclusion of sub-Keplerian torques shortens the total migration time by only a moderate amount, the mass accreted by migrating planetary cores is significantly reduced. Truncation of the inner disk edge (for typical system parameters) naturally explains final planetary orbits with periods P {approx} 4 days. Planets with shorter periods, P {approx} 2 days, can be explained by migration during FU-Orionis outbursts, when the mass accretion rate is high and the disk edge moves inward. Finally, the midplane density is greatly increased at the inner truncation point of the disk (the X-point); this enhancement, in conjunction with continuing flow of gas and solids through the region, supports the in situ formation of giant planets.

  4. The Importance of Radial Migration to the Evolution of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Daniel, Kathryne J.; Wyse, Rosemary F. G.

    2016-01-01

    Spiral galaxy evolution is frequently considered in the context of environment, but internal processes may also play an important role. Radial migration is one such internal process, wherein a transient spiral arm rearranges the angular momentum distribution of the disk around corotation without causing kinematic heating. The efficiency of radial migration depends on both the duty cycle for transient patterns and the RMS change in orbital angular momentum induced by each pattern. Should radial migration be efficient, it could cause a substantial fraction of disk stars to move large radial distances over the lifetime of the disk, thus having significant impact on its kinematic, structural and chemical evolution.In this talk, I will summarize a subset of work focusing on the physics that determines the magnitude of the RMS change in orbital angular momentum from each spiral pattern. I have derived an analytic "capture criterion" that predicts whether or not a disk star with finite random orbital energy is in a "trapped orbit" (i.e. the orbital family induced by the spiral pattern that can lead to radial migration). I will present this criterion and show that it is primarily a star's orbital angular momentum that determines whether or not it is in a trapped orbit. The capture criterion could be used to better understand the role of radial migration in N-body simulations as well as applied to models of galaxy evolution. I will describe an example study wherein I applied the capture criterion, in a series of disk galaxy models, to find the fraction of an ensemble of stars that is in trapped orbits. I found that this fraction decreases linearly with increasing radial velocity dispersion and conclude that radial migration may play a role in the evolution of disk galaxies, but it is insignificant to the evolution of high velocity dispersion populations.

  5. Two-body Relaxation Driven Evolution of the Young Stellar Disk in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Šubr, Ladislav; Haas, Jaroslav

    2014-05-01

    The center of our Galaxy hosts almost two hundred very young stars, a subset of which is orbiting the central supermassive black hole (SMBH) in a relatively thin disk-like structure. First analyses indicated a power-law surface density profile of the disk, ΣvpropR β with β = -2. Recently, however, doubts about this profile arose. In particular, it now seems to be better described by a sort of broken power law. By means of both analytical arguments and numerical N-body modeling, we show that such a broken power-law profile is a natural consequence of the two-body relaxation of the disk. Due to the small relative velocities of the nearby stars in co-planar Keplerian orbits around the SMBH, two-body relaxation is effective enough to affect the evolution of the disk on timescales comparable to its estimated age. In the inner, densest part of the disk, the profile becomes rather flat (β ≈ -1) while the outer parts keep imprints of the initial state. Our numerical models show that the observed projected surface density profile of the young stellar disk can result from two-body relaxation driven evolution of a disk with initial single power-law profile with -2 <~ β <~ -1.5. In addition, we suggest that two-body relaxation may have caused a significant radial migration of the S-stars toward the central SMBH, thus playing an important role in their formation scenario.

  6. PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL

    SciTech Connect

    Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya.; Zhukovska, S.; Semenov, D.; Henning, Th.; Vasyunin, A.; Birnstiel, T. E-mail: dwiebe@inasan.ru E-mail: zhukovska@mpia.de E-mail: henning@mpia.de E-mail: tbirnstiel@cfa.harvard.edu

    2013-03-20

    We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R {approx}< 50 AU) and lower in the outer disk (R {approx}> 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO{sub 2}, NH{sub 2}CN, HNO, H{sub 2}O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

  7. OUTWARD MIGRATION OF JUPITER AND SATURN IN 3:2 OR 2:1 RESONANCE IN RADIATIVE DISKS: IMPLICATIONS FOR THE GRAND TACK AND NICE MODELS

    SciTech Connect

    Pierens, Arnaud; Raymond, Sean N.; Nesvorny, David; Morbidelli, Alessandro

    2014-11-01

    Embedded in the gaseous protoplanetary disk, Jupiter and Saturn naturally become trapped in 3:2 resonance and migrate outward. This serves as the basis of the Grand Tack model. However, previous hydrodynamical simulations were restricted to isothermal disks, with moderate aspect ratio and viscosity. Here we simulate the orbital evolution of the gas giants in disks with viscous heating and radiative cooling. We find that Jupiter and Saturn migrate outward in 3:2 resonance in modest-mass (M {sub disk} ≈ M {sub MMSN}, where MMSN is the {sup m}inimum-mass solar nebula{sup )} disks with viscous stress parameter α between 10{sup –3} and 10{sup –2}. In disks with relatively low-mass (M {sub disk} ≲ M {sub MMSN}), Jupiter and Saturn get captured in 2:1 resonance and can even migrate outward in low-viscosity disks (α ≤ 10{sup –4}). Such disks have a very small aspect ratio (h ∼ 0.02-0.03) that favors outward migration after capture in 2:1 resonance, as confirmed by isothermal runs which resulted in a similar outcome for h ∼ 0.02 and α ≤ 10{sup –4}. We also performed N-body runs of the outer solar system starting from the results of our hydrodynamical simulations and including 2-3 ice giants. After dispersal of the gaseous disk, a Nice model instability starting with Jupiter and Saturn in 2:1 resonance results in good solar systems analogs. We conclude that in a cold solar nebula, the 2:1 resonance between Jupiter and Saturn can lead to outward migration of the system, and this may represent an alternative scenario for the evolution of the solar system.

  8. Protoplanetary Disk Heating and Evolution Driven by Spiral Density Waves

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2016-11-01

    Scattered light imaging of protoplanetary disks often reveals prominent spiral arms, likely excited by massive planets or stellar companions. Assuming that these arms are density waves, evolving into spiral shocks, we assess their effect on the thermodynamics, accretion, and global evolution of the disk. We derive analytical expressions for the direct (irreversible) heating, angular momentum transport, and mass accretion rate induced by disk shocks of arbitrary amplitude. These processes are very sensitive to the shock strength. We show that waves of moderate strength (density jump at the shock ΔΣ/Σ ∼ 1) result in negligible disk heating (contributing at the ∼1% level to the energy budget) in passive, irradiated protoplanetary disks on ∼100 au scales, but become important within several au. However, shock heating is a significant (or even dominant) energy source in disks of cataclysmic variables, stellar X-ray binaries, and supermassive black hole binaries, heated mainly by viscous dissipation. Mass accretion induced by the spiral shocks is comparable to (or exceeds) the mass inflow due to viscous stresses. Protoplanetary disks featuring prominent global spirals must be evolving rapidly, in ≲0.5 Myr at ∼100 au. A direct upper limit on the evolution timescale can be established by measuring the gravitational torque due to the spiral arms from the imaging data. We find that, regardless of their origin, global spiral waves must be important agents of the protoplanetary disk evolution. They may serve as an effective mechanism of disk dispersal and could be related to the phenomenon of transitional disks.

  9. THE ROLE OF MULTIPLICITY IN DISK EVOLUTION AND PLANET FORMATION

    SciTech Connect

    Kraus, Adam L.; Ireland, Michael J.; Hillenbrand, Lynne A.; Martinache, Frantz

    2012-01-20

    The past decade has seen a revolution in our understanding of protoplanetary disk evolution and planet formation in single-star systems. However, the majority of solar-type stars form in binary systems, so the impact of binary companions on protoplanetary disks is an important element in our understanding of planet formation. We have compiled a combined multiplicity/disk census of Taurus-Auriga, plus a restricted sample of close binaries in other regions, in order to explore the role of multiplicity in disk evolution. Our results imply that the tidal influence of a close ({approx}<40 AU) binary companion significantly hastens the process of protoplanetary disk dispersal, as {approx}2/3 of all close binaries promptly disperse their disks within {approx}<1 Myr after formation. However, prompt disk dispersal only occurs for a small fraction of wide binaries and single stars, with {approx}80%-90% retaining their disks for at least {approx}2-3 Myr (but rarely for more than {approx}5 Myr). Our new constraints on the disk clearing timescale have significant implications for giant planet formation; most single stars have 3-5 Myr within which to form giant planets, whereas most close binary systems would have to form giant planets within {approx}<1 Myr. If core accretion is the primary mode for giant planet formation, then gas giants in close binaries should be rare. Conversely, since almost all single stars have a similar period of time within which to form gas giants, their relative rarity in radial velocity (RV) surveys indicates either that the giant planet formation timescale is very well matched to the disk dispersal timescale or that features beyond the disk lifetime set the likelihood of giant planet formation.

  10. Imprint of accretion disk-induced migration on gravitational waves from extreme mass ratio inspirals.

    PubMed

    Yunes, Nicolás; Kocsis, Bence; Loeb, Abraham; Haiman, Zoltán

    2011-10-21

    We study the effects of a thin gaseous accretion disk on the inspiral of a stellar-mass black hole into a supermassive black hole. We construct a phenomenological angular momentum transport equation that reproduces known disk effects. Disk torques modify the gravitational wave phase evolution to detectable levels with LISA for reasonable disk parameters. The Fourier transform of disk-modified waveforms acquires a correction with a different frequency trend than post-Newtonian vacuum terms. Such inspirals could be used to detect accretion disks with LISA and to probe their physical parameters. PMID:22107500

  11. The Evolution of FU Orionis Disks

    NASA Astrophysics Data System (ADS)

    Green, Joel D.

    2016-06-01

    Do protoplanetary disks undergo regular (or irregular) bursts of accretion? FU Orionis objects (FUors) are the strongest direct evidence for episodic accretion in low mass young stellar objects. FUors exhibit rapid changes in disk chemistry, both because they are temporarily bright IR sources relative to their core mass, and vary on day, month, year, and decade timescales. With improved spatial and spectral resolution from FORCAST, and a ten year time baseline compared with Spitzer-IRS data, we can observe and constrain the properties of silicate dust, and disk profiles, as they are altered by the outburst. We also consider the occurrence of binarity and whether any connection exists between multiplicity and evidence of recent outburst behavior.

  12. Evolution of protoplanetary disks with dynamo magnetic fields

    NASA Technical Reports Server (NTRS)

    Reyes-Ruiz, M.; Stepinski, Tomasz F.

    1994-01-01

    The notion that planetary systems are formed within dusty disks is certainly not a new one; the modern planet formation paradigm is based on suggestions made by Laplace more than 200 years ago. More recently, the foundations of accretion disk theory where initially developed with this problem in mind, and in the last decade astronomical observations have indicated that many young stars have disks around them. Such observations support the generally accepted model of a viscous Keplerian accretion disk for the early stages of planetary system formation. However, one of the major uncertainties remaining in understanding the dynamical evolution of protoplanetary disks is the mechanism responsible for the transport of angular momentum and subsequent mass accretion through the disk. This is a fundamental piece of the planetary system genesis problem since such mechanisms will determine the environment in which planets are formed. Among the mechanisms suggested for this effect is the Maxwell stress associated with a magnetic field treading the disk. Due to the low internal temperatures through most of the disk, even the question of the existence of a magnetic field must be seriously studied before including magnetic effects in the disk dynamics. On the other hand, from meteoritic evidence it is believed that magnetic fields of significant magnitude existed in the earliest, PP-disk-like, stage of our own solar system's evolution. Hence, the hypothesis that PP disks are magnetized is not made solely on the basis of theory. Previous studies have addressed the problem of the existence of a magnetic field in a steady-state disk and have found that the low conductivity results in a fast diffusion of the magnetic field on timescales much shorter than the evolutionary timescale. Hence the only way for a magnetic field to exist in PP disks for a considerable portion of their lifetimes is for it to be continuously regenerated. In the present work, we present results on the self

  13. On the growth and orbital evolution of giant planets in layered protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Pierens, A.; Nelson, R. P.

    2010-09-01

    Aims: We present the results of hydrodynamic simulations of the growth and orbital evolution of giant planets embedded in a protoplanetary disk with a dead-zone. The aim is to examine to what extent the presence of a dead-zone affects the rates of mass accretion and migration for giant planets. Methods: We performed 3D numerical simulations using a grid-based hydrodynamics code. In these simulations of laminar, non-magnetised disks, the dead-zone is treated as a region where the vertical profile of the viscosity depends on the distance from the equatorial plane. We consider dead-zones with vertical sizes, HDZ, ranging from 0 to HDZ = 2.3 H, where H is the disk scale-height. For all models, the vertically integrated viscous stress, and the related mass flux through the disk, have the same value (equivalent to 10-8 M⊙ yr-1), such that the simulations test the dependence of planetary mass accretion and migration on the vertical distribution of the viscous stress (and mass flux). For each model, an embedded 30 M_⊕ planet on a fixed circular orbit is allowed to accrete gas from the disk. Once the planet mass becomes equal to that of Saturn or Jupiter, we allow the planet orbit to evolve due to gravitational interaction with the disk. Results: We find that the time scale over which a protoplanet grows to become a giant planet is essentially independent of the dead-zone size, and depends only on the total rate at which the disk viscously supplies material to the planet. For Saturn-mass planets, the migration rate depends only weakly on the size of the dead-zone for HDZ ≤ 1.5 H, but becomes noticeably slower when HDZ = 2.3 H. This effect is apparently due to the desaturation of corotation torques which originate from residual material in the partial-gap region. For Jupiter-mass planets, there is a clear tendency for the migration to proceed more slowly as the size of the dead-zone increases, with migration rates differing by approximately 40% for models with HDZ = 0

  14. OUTER-DISK POPULATIONS IN NGC 7793: EVIDENCE FOR STELLAR RADIAL MIGRATION

    SciTech Connect

    Radburn-Smith, David J.; Dalcanton, Julianne J.; Roskar, Rok; Debattista, Victor P.; Streich, David; De Jong, Roelof S.; Vlajic, Marija; Holwerda, Benne W.; Purcell, Chris W.; Dolphin, Andrew E.; Zucker, Daniel B.

    2012-07-10

    We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280'' ({approx}5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars of NGC 7793 extend significantly farther than the underlying H I disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.

  15. CHEMICAL EVOLUTION OF PROTOPLANETARY DISKS-THE EFFECTS OF VISCOUS ACCRETION, TURBULENT MIXING, AND DISK WINDS

    SciTech Connect

    Heinzeller, D.; Nomura, H.; Walsh, C.; Millar, T. J.

    2011-04-20

    We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing, and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared local thermodynamic equilibrium line emission spectra and compare these with recent Spitzer observations. Our results show that if H{sub 2} formation on warm grains is taken into consideration, the H{sub 2}O and OH abundances in the disk surface increase significantly. We find that the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line emission from the disk and subsequently improving agreement with observations. We find that NH{sub 3}, CH{sub 3}OH, C{sub 2}H{sub 2}, and sulfur-containing species are greatly enhanced by the inclusion of turbulent mixing. We demonstrate that disk winds potentially affect the disk chemistry and the resulting molecular line emission in a manner similar to that found when mixing is included.

  16. THE INFLUENCE OF RADIAL STELLAR MIGRATION ON THE CHEMICAL EVOLUTION OF THE MILKY WAY

    SciTech Connect

    Wang Yue; Zhao Gang

    2013-05-20

    Stellar migration is an important dynamical process in the Galactic disk. Here we model radial stellar migration in the Galactic disk with an analytical method, then add it to a detailed Galactic chemical evolution model to study the influence of radial stellar migration on the chemical evolution of the Milky Way, especially for the abundance gradients. We found that the radial stellar migration in the Galactic disk can make the profile of the G-dwarf metallicity distribution of the solar neighborhood taller and narrower, and thus it becomes another solution to the ''G-dwarf problem''. It can also scatter the age-metallicity relation. However, after migration, the abundance distributions along the Galactic radius do not change much; namely, the abundance gradients would not be flattened by the radial stellar migration, which is different from the predictions of many theoretical works. However, it can flatten the radial gradients of the mean chemical abundance of stars, and older stars possess flatter abundance gradients than younger stars. The most significant effect of radial stellar migration on the chemical abundance is that at a certain position it scatters the abundance of stars from a relatively concentrated value to a range.

  17. The role of resonances in the evolution of galactic disks

    NASA Astrophysics Data System (ADS)

    Lepine, Jacques; Scarano, Sergio; Andrievsky, Sergei; de Barros, Douglas A.; Junqueira, Thiago C.

    2015-03-01

    Resonances play an important role in the evolution of the disks of spiral galaxies, and in particular in the chemical abundance evolution. The dominant effect is that of corotation; this effect can be even used as a tool to estimate the age of the present spiral arm pattern, which are usually found to be long-lived, contrary to a recent common belief. We investigated a sample of galaxies for which the corotation radius is known and for which there are available in the literature measurements of abundance gradients for Oxygen. A very good correlation is found between corotation radii and the radii at which there is a break in the slope of the gradients. The gradients are usually decreasing in the inner regions and become flat or rising at larger radii. In several galaxies, including the Milky Way, one observes not only a change in the slope of the abundance gradient, but also an abrupt step in metallicity, at corotation. This step is due to the fact that corotation separates the disk of a galaxy in two regions (inside corotation and outside corotation) which are isolated one from the other, so that the two sides evolve in an independent way. The barrier between the two regions is produced by the flow of gas in opposite directions in the two sides and by the ring-shaped void of gas observed at corotation. Besides this, an independent effect of corotation is a minimum of star formation associated with the minimum velocity at which the spiral arms (seen as potential wells) are fed with interstellar gas. Still another effect is the scattering of stars by the resonance, which causes their migration to different galactic radii. Other resonances, like 4:1, have properties almost opposite to corotation; they stimulate star-formation, and tend to gather the stars in the resonant orbit, instead of scattering them out, as shown by numerical simulations. Due to this property, one can see arms which have the shape of resonant stellar orbits, which depart from logarithmic spirals.

  18. Dust Evolution Can Produce Scattered Light Gaps in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Birnstiel, Tilman; Andrews, Sean M.; Pinilla, Paola; Kama, Mihkel

    2015-11-01

    Recent imaging of protoplanetary disks with high resolution and contrast have revealed a striking variety of substructure. Of particular interest are cases where near-infrared scattered light images show evidence for low-intensity annular “gaps.” The origins of such structures are still uncertain, but the interaction of the gas disk with planets is a common interpretation. We study the impact that the evolution of the solid material can have on the observable properties of disks in a simple scenario without any gravitational or hydrodynamical disturbances to the gas disk structure. Even with a smooth and continuous gas density profile, we find that the scattered light emission produced by small dust grains can exhibit ring-like depressions similar to those presented in recent observations. The physical mechanisms responsible for these features rely on the inefficient fragmentation of dust particles. The occurrence and position of the proposed “gap” features depend most strongly on the dust-to-gas ratio, the fragmentation threshold velocity, the strength of the turbulence, and the age of the disk, and should be generic (at some radius) for typically adopted disk parameters. The same physical processes can affect the thermal emission at optically thin wavelengths (˜1 mm), although the behavior can be more complex; unlike for disk-planet interactions, a “gap” should not be present at these longer wavelengths.

  19. Internal and environmental secular evolution of disk galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2015-03-01

    This Special Session is devoted to the secular evolution of disk galaxies. Here `secular' means `slow' i.e., evolution on time scales that are generally much longer than the galaxy crossing or rotation time. Internal and environmentally driven evolution both are covered. I am indebted to Albert Bosma for reminding me at the 2011 Canary Islands Winter School on Secular Evolution that our subject first appeared in print in a comment made by Ivan King (1977) in his introductory talk at the Yale University meeting on The Evolution of Galaxies and Stellar Populations: `John Kormendy would like us to consider the possibility that a galaxy can interact with itself.. . . I'm not at all convinced, but John can show you some interesting pictures.' Two of the earliest papers that followed were Kormendy (1979a, b); the first discusses the interaction of galaxy components with each other, and the second studies these phenomena in the context of a morphological survey of barred galaxies. The earliest modeling paper that we still use regularly is Combes & Sanders (1981), which introduces the now well known idea that box-shaped bulges in edge-on galaxies are side-on, vertically thickened bars. It is gratifying to see how this subject has grown since that time. Hundreds of papers have been written, and the topic features prominently at many meetings (e.g., Block et al. 2004; Falcoń-Barroso & Knapen 2012, and this Special Session). My talk here introduces both internal and environmental secular evolution; a brief abstract follows. My Canary Islands Winter School review covers both subjects in more detail (Kormendy 2012). Kormendy & Kennicutt (2004) is a comprehensive review of internal secular evolution, and Kormendy & Bender (2012) covers environmental evolution. Both of these subject make significant progress at this meeting. Secular evolution happens because self-gravitating systems evolve toward the most tightly bound configuration that is reachable by the evolution processes

  20. Magnetic Field and Early Evolution of Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Yusuke

    2016-03-01

    The magnetic field plays a central role in the formation and evolution of circumstellar disks. The magnetic field connects the rapidly rotating central region with the outer envelope and extracts angular momentum from the central region during gravitational collapse of the cloud core. This process is known as magnetic braking. Both analytical and multidimensional simulations have shown that disk formation is strongly suppressed by magnetic braking in moderately magnetised cloud cores in the ideal magnetohydrodynamic limit. On the other hand, recent observations have provided growing evidence of a relatively large disk several tens of astronomical units in size existing in some Class 0 young stellar objects. This introduces a serious discrepancy between the theoretical study and observations. Various physical mechanisms have been proposed to solve the problem of catastrophic magnetic braking, such as misalignment between the magnetic field and the rotation axis, turbulence, and non-ideal effect. In this paper, we review the mechanism of magnetic braking, its effect on disk formation and early evolution, and the mechanisms that resolve the magnetic braking problem. In particular, we emphasise the importance of non-ideal effects. The combination of magnetic diffusion and thermal evolution during gravitational collapse provides a robust formation process for the circumstellar disk at the very early phase of protostar formation. The rotation induced by the Hall effect can supply a sufficient amount of angular momentum for typical circumstellar disks around T Tauri stars. By examining the combination of the suggested mechanisms, we conclude that the circumstellar disks commonly form in the very early phase of protostar formation.

  1. On the evolution of eccentric and inclined protoplanets embedded in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Cresswell, P.; Dirksen, G.; Kley, W.; Nelson, R. P.

    2007-10-01

    Context: Young planets embedded in their protoplanetary disk interact gravitationally with it leading to energy and angular momentum exchange. This interaction determines the evolution of the planet through changes to the orbital parameters. Aims: We investigate changes in the orbital elements of a 20 Earth-mass planet due to the torques from the disk. We focus on the non-linear evolution of initially non-vanishing eccentricity, e, and/or inclination, i. Methods: We treat the disk as a two- or three-dimensional viscous fluid and perform hydrodynamical simulations using finite difference methods. The planetary orbit is updated according to the gravitational torque exerted by the disk. We monitor the time evolution of the orbital elements of the planet. Results: We find rapid exponential decay of the planet orbital eccentricity and inclination for small initial values of e and i, in agreement with linear theory. For larger values of e > 0.1 the decay time increases and the decay rate scales as dot{e} ∝ e-2, consistent with existing theoretical models. For large inclinations (i > 6°) the inclination decay rate shows an identical scaling di/dt ∝ i-2. We find an interesting dependence of the migration on the eccentricity. In a disk with aspect ratio H/r=0.05 the migration rate is enhanced for small non-zero eccentricities (e < 0.1), while for larger values we see a significant reduction by a factor of 4. We find no indication for a reversal of the migration for large e, although the torque experienced by the planet becomes positive when e ≃ 0.3. This inward migration is caused by the persisting energy loss of the planet. Conclusions: For non gap forming planets, eccentricity and inclination damping occurs on a time scale that is very much shorter than the migration time scale. The results of non linear hydrodynamic simulations are in very good agreement with linear theory for values of e and i for which the theory is applicable (i.e. e and i ≤ H/r).

  2. Forming Gaps in Debris Disks with Fewer Planets via Planet Migration

    NASA Astrophysics Data System (ADS)

    Morrison, Sarah J.; Kratter, Kaitlin M.

    2016-10-01

    Debris disks across a wide range of ages can possess wide gaps of several AU or more; these gaps have been attributed to the presence of multiple planets. While at least two planets are likely needed for maintaining the edges of such gaps, large gaps may require more than two in more dynamically packed configurations to be able to have cleared material within the gap in the present day. As an alternative to currently packed planets occupying gaps in debris disks, we assess whether planetesimal and dynamical instability-driven planet migration could produce wide gaps with lower mass, fewer planets on relevant timescales to be consistent with the observed properties of debris disk systems. We also discuss implications for the disk properties in which these mechanisms could operate within the broader evolutionary context linking planets, debris disks, and the protoplanetary disks from which they originated.

  3. Two-body relaxation driven evolution of the young stellar disk in the galactic center

    SciTech Connect

    Šubr, Ladislav; Haas, Jaroslav

    2014-05-10

    The center of our Galaxy hosts almost two hundred very young stars, a subset of which is orbiting the central supermassive black hole (SMBH) in a relatively thin disk-like structure. First analyses indicated a power-law surface density profile of the disk, Σ∝R {sup β} with β = –2. Recently, however, doubts about this profile arose. In particular, it now seems to be better described by a sort of broken power law. By means of both analytical arguments and numerical N-body modeling, we show that such a broken power-law profile is a natural consequence of the two-body relaxation of the disk. Due to the small relative velocities of the nearby stars in co-planar Keplerian orbits around the SMBH, two-body relaxation is effective enough to affect the evolution of the disk on timescales comparable to its estimated age. In the inner, densest part of the disk, the profile becomes rather flat (β ≈ –1) while the outer parts keep imprints of the initial state. Our numerical models show that the observed projected surface density profile of the young stellar disk can result from two-body relaxation driven evolution of a disk with initial single power-law profile with –2 ≲ β ≲ –1.5. In addition, we suggest that two-body relaxation may have caused a significant radial migration of the S-stars toward the central SMBH, thus playing an important role in their formation scenario.

  4. DEAD ZONES AS THERMAL BARRIERS TO RAPID PLANETARY MIGRATION IN PROTOPLANETARY DISKS

    SciTech Connect

    Hasegawa, Yasuhiro; Pudritz, Ralph E. E-mail: pudritz@physics.mcmaster.ca

    2010-02-20

    Planetary migration in standard models of gaseous protoplanetary disks is known to be very rapid ({approx}10{sup 5} years), jeopardizing the existence of planetary systems. We present a new mechanism for significantly slowing rapid planetary migration, discovered by means of radiative transfer calculations of the thermal structure of protoplanetary disks irradiated by their central stars. Rapid dust settling in a disk's dead zone-a region with very little turbulence-leaves a dusty wall at its outer edge. We show that the back-heating of the dead zone by this irradiated wall produces a positive gradient of the disk temperature, which acts as a thermal barrier to planetary migration which persists for the disk lifetime. Although we analyze in detail the migration of a super-Earth in a low-mass disk around an M star, our findings can apply to a wide variety of young planetary systems. We compare our findings with other potentially important stopping mechanisms and show that there are large parameter spaces for which dead zones are likely to play the most important role for reproducing the observed mass-period relation in longer planetary periods.

  5. DUST EVOLUTION CAN PRODUCE SCATTERED LIGHT GAPS IN PROTOPLANETARY DISKS

    SciTech Connect

    Birnstiel, Tilman; Andrews, Sean M.; Pinilla, Paola; Kama, Mihkel E-mail: sandrews@cfa.harvard.edu E-mail: mkama@strw.leidenuniv.nl

    2015-11-01

    Recent imaging of protoplanetary disks with high resolution and contrast have revealed a striking variety of substructure. Of particular interest are cases where near-infrared scattered light images show evidence for low-intensity annular “gaps.” The origins of such structures are still uncertain, but the interaction of the gas disk with planets is a common interpretation. We study the impact that the evolution of the solid material can have on the observable properties of disks in a simple scenario without any gravitational or hydrodynamical disturbances to the gas disk structure. Even with a smooth and continuous gas density profile, we find that the scattered light emission produced by small dust grains can exhibit ring-like depressions similar to those presented in recent observations. The physical mechanisms responsible for these features rely on the inefficient fragmentation of dust particles. The occurrence and position of the proposed “gap” features depend most strongly on the dust-to-gas ratio, the fragmentation threshold velocity, the strength of the turbulence, and the age of the disk, and should be generic (at some radius) for typically adopted disk parameters. The same physical processes can affect the thermal emission at optically thin wavelengths (∼1 mm), although the behavior can be more complex; unlike for disk–planet interactions, a “gap” should not be present at these longer wavelengths.

  6. Evolution of accretion disks in tidal disruption events

    SciTech Connect

    Shen, Rong-Feng; Matzner, Christopher D. E-mail: matzner@astro.utoronto.ca

    2014-04-01

    During a stellar tidal disruption event (TDE), an accretion disk forms as stellar debris returns to the disruption site and circularizes. Rather than being confined within the circularizing radius, the disk can spread to larger radii to conserve angular momentum. A spreading disk is a source of matter for re-accretion at rates that may exceed the later stellar fallback rate, although a disk wind can suppress its contribution to the central black hole accretion rate. A spreading disk is detectible through a break in the central accretion rate history or, at longer wavelengths, by its own emission. We model the evolution of TDE disk size and accretion rate by accounting for the time-dependent fallback rate, for the influence of wind losses in the early advective stage, and for the possibility of thermal instability for accretion rates intermediate between the advection-dominated and gas-pressure-dominated states. The model provides a dynamic basis for modeling TDE light curves. All or part of a young TDE disk will precess as a solid body because of the Lense-Thirring effect, and precession may manifest itself as a quasi-periodic modulation of the light curve. The precession period increases with time. Applying our results to the jetted TDE candidate Swift J1644+57, whose X-ray light curve shows numerous quasi-periodic dips, we argue that the data best fit a scenario in which a main-sequence star was fully disrupted by an intermediate mass black hole on an orbit significantly inclined from the black hole equator, with the apparent jet shutoff at t = 500 days corresponding to a disk transition from the advective state to the gas-pressure-dominated state.

  7. EVOLUTION OF SNOW LINE IN OPTICALLY THICK PROTOPLANETARY DISKS: EFFECTS OF WATER ICE OPACITY AND DUST GRAIN SIZE

    SciTech Connect

    Oka, Akinori; Nakamoto, Taishi; Ida, Shigeru E-mail: nakamoto@geo.titech.ac.jp

    2011-09-10

    Evolution of a snow line in an optically thick protoplanetary disk is investigated with numerical simulations. The ice-condensing region in the disk is obtained by calculating the temperature and the density with the 1+1D approach. The snow line migrates as the mass accretion rate ( M-dot ) in the disk decreases with time. Calculations are carried out from an early phase with high disk accretion rates ( M-dot {approx}10{sup -7} M{sub sun} yr{sup -1}) to a later phase with low disk accretion rates ( M-dot {approx}10{sup -12} M{sub sun} yr{sup -1}) using the same numerical method. It is found that the snow line moves inward for M-dot {approx}>10{sup -10} M{sub sun} yr{sup -1}, while it gradually moves outward in the later evolution phase with M-dot {approx}<10{sup -10} M{sub sun} yr{sup -1}. In addition to the silicate opacity, the ice opacity is taken into consideration. In the inward migration phase, the additional ice opacity increases the distance of the snow line from the central star by a factor of 1.3 for dust grains {approx}< 10 {mu}m in size and of 1.6 for {approx}> 100 {mu}m. It is inevitable that the snow line comes inside Earth's orbit in the course of the disk evolution if the viscosity parameter {alpha} is in the range 0.001-0.1, the dust-to-gas mass ratio is higher than a tenth of the solar abundance value, and the dust grains are smaller than 1 mm. The formation of water-devoid planetesimals in the terrestrial planet region seems to be difficult throughout the disk evolution, which imposes a new challenge to planet formation theory.

  8. Metallicity evolution in mergers of disk galaxies with black holes

    NASA Astrophysics Data System (ADS)

    Rantala, Antti; Johansson, Peter H.

    2016-10-01

    We use the TreeSPH simulation code Gadget-3 including a recently improved smoothed particle hydrodynamics (SPH) module, a detailed metallicity evolution model and sophisticated subresolution feedback models for supernovae and supermassive black holes in order to study the metallicity evolution in disk galaxy mergers. In addition, we examine the simulated morphology, star formation histories, metallicity gradients and kinematic properties of merging galaxies and merger remnants. We will compare our simulation results with observations of the early-type Centaurus A galaxy and the currently colliding Antennae galaxies.

  9. Internal and environmental secular evolution of disk galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2015-03-01

    This Special Session is devoted to the secular evolution of disk galaxies. Here `secular' means `slow' i.e., evolution on time scales that are generally much longer than the galaxy crossing or rotation time. Internal and environmentally driven evolution both are covered. I am indebted to Albert Bosma for reminding me at the 2011 Canary Islands Winter School on Secular Evolution that our subject first appeared in print in a comment made by Ivan King (1977) in his introductory talk at the Yale University meeting on The Evolution of Galaxies and Stellar Populations: `John Kormendy would like us to consider the possibility that a galaxy can interact with itself.. . . I'm not at all convinced, but John can show you some interesting pictures.' Two of the earliest papers that followed were Kormendy (1979a, b); the first discusses the interaction of galaxy components with each other, and the second studies these phenomena in the context of a morphological survey of barred galaxies. The earliest modeling paper that we still use regularly is Combes & Sanders (1981), which introduces the now well known idea that box-shaped bulges in edge-on galaxies are side-on, vertically thickened bars. It is gratifying to see how this subject has grown since that time. Hundreds of papers have been written, and the topic features prominently at many meetings (e.g., Block et al. 2004; Falcoń-Barroso & Knapen 2012, and this Special Session). My talk here introduces both internal and environmental secular evolution; a brief abstract follows. My Canary Islands Winter School review covers both subjects in more detail (Kormendy 2012). Kormendy & Kennicutt (2004) is a comprehensive review of internal secular evolution, and Kormendy & Bender (2012) covers environmental evolution. Both of these subject make significant progress at this meeting. Secular evolution happens because self-gravitating systems evolve toward the most tightly bound configuration that is reachable by the evolution processes

  10. Coupling Dynamical And Collisional Evolution Of Dust In Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Charnoz, Sebastien

    2010-10-01

    Gaseous circumstellar disks are rich in dust and are thought to be both accretionaly and dynamically active. Unfortunately large bodies that could be embedded in these disks are still difficult to observe and their putative properties are indirectly inferred from the observable small dust content. It is why constraining the size distribution coupled with dust-dynamics is so critical. Unfortunately, coupling effects such as a realistic time-dependant dynamics, fragmentation and coagulation, has been recognized as numerically challenging and almost no attempt really succeeded with a generic approach. In these disks, the dust dynamics is driven by a variety of processes (gravity, gas drag, radiation pressure..) inducing a size-dependant dynamics, and, at the same time collisional evolution changes the local size distributions. These two effects are intimately coupled because the local dynamics and size-distribution determines the local collision rates, that, in-turn, determines the size-distribution and modifies the particle's dynamics. Here we report on a new algorithm that overcomes these difficulties by using a hybrid approach extending the work of Charnoz & Morbidelli (Icarus, 2004, 2007). We will briefly present the method and focus on gaseous protoplanetary disks either laminar or turbulent (the time dependant transport and dust evolution will be shown) . We will show how the taking into account of a 3D dynamics helps to determine disantengle the dust size-distribution in the disk's photosphere and in the midplane and thus may provide observational signatures of accretion. We will show how the coupling of turbulence with fragmentation may significantly affect the dust/ratio for the smallest bodies. Finally, we will show that an accurate description of the time dependant dynamics of larger dusts (those with Stokes numbers >= 1) may provide a possible path to the formation of bodies larger than the accretion barrier, through accretion in a transitory regime.

  11. Consequences of tidal interaction between disks and orbiting protoplanets for the evolution of multi-planet systems with architecture resembling that of Kepler 444

    NASA Astrophysics Data System (ADS)

    Papaloizou, J. C. B.

    2016-11-01

    We study orbital evolution of multi-planet systems with masses in the terrestrial planet regime induced through tidal interaction with a protoplanetary disk assuming that this is the dominant mechanism for producing orbital migration and circularization. We develop a simple analytic model for a system that maintains consecutive pairs in resonance while undergoing orbital circularization and migration. This model enables migration times for each planet to be estimated once planet masses, circularization times and the migration time for the innermost planet are specified. We applied it to a system with the current architecture of Kepler 444 adopting a simple protoplanetary disk model and planet masses that yield migration times inversely proportional to the planet mass, as expected if they result from torques due to tidal interaction with the protoplanetary disk. Furthermore the evolution time for the system as a whole is comparable to current protoplanetary disk lifetimes. In addition we have performed a number of numerical simulations with input data obtained from this model. These indicate that although the analytic model is inexact, relatively small corrections to the estimated migration rates yield systems for which period ratios vary by a minimal extent. Because of relatively large deviations from exact resonance in the observed system of up to 2 %, the migration times obtained in this way indicate only weak convergent migration such that a system for which the planets did not interact would contract by only {˜ }1 % although undergoing significant inward migration as a whole. We have also performed additional simulations to investigate conditions under which the system could undergo significant convergent migration before reaching its final state. These indicate that migration times have to be significantly shorter and resonances between planet pairs significantly closer during such an evolutionary phase. Relative migration rates would then have to decrease

  12. Consequences of tidal interaction between disks and orbiting protoplanets for the evolution of multi-planet systems with architecture resembling that of Kepler 444

    NASA Astrophysics Data System (ADS)

    Papaloizou, J. C. B.

    2016-05-01

    We study orbital evolution of multi-planet systems with masses in the terrestrial planet regime induced through tidal interaction with a protoplanetary disk assuming that this is the dominant mechanism for producing orbital migration and circularization. We develop a simple analytic model for a system that maintains consecutive pairs in resonance while undergoing orbital circularization and migration. This model enables migration times for each planet to be estimated once planet masses, circularization times and the migration time for the innermost planet are specified. We applied it to a system with the current architecture of Kepler 444 adopting a simple protoplanetary disk model and planet masses that yield migration times inversely proportional to the planet mass, as expected if they result from torques due to tidal interaction with the protoplanetary disk. Furthermore the evolution time for the system as a whole is comparable to current protoplanetary disk lifetimes. In addition we have performed a number of numerical simulations with input data obtained from this model. These indicate that although the analytic model is inexact, relatively small corrections to the estimated migration rates yield systems for which period ratios vary by a minimal extent. Because of relatively large deviations from exact resonance in the observed system of up to 2 %, the migration times obtained in this way indicate only weak convergent migration such that a system for which the planets did not interact would contract by only {˜ }1 % although undergoing significant inward migration as a whole. We have also performed additional simulations to investigate conditions under which the system could undergo significant convergent migration before reaching its final state. These indicate that migration times have to be significantly shorter and resonances between planet pairs significantly closer during such an evolutionary phase. Relative migration rates would then have to decrease

  13. Evolution of migration rate in a spatially realistic metapopulation model.

    PubMed

    Heino, M; Hanski, I

    2001-05-01

    We use an individual-based, spatially realistic metapopulation model to study the evolution of migration rate. We first explore the consequences of habitat change in hypothetical patch networks on a regular lattice. If the primary consequence of habitat change is an increase in local extinction risk as a result of decreased local population sizes, migration rate increases. A nonmonotonic response, with migration rate decreasing at high extinction rate, was obtained only by assuming very frequent catastrophes. If the quality of the matrix habitat deteriorates, leading to increased mortality during migration, the evolutionary response is more complex. As long as habitat patch occupancy does not decrease markedly with increased migration mortality, reduced migration rate evolves. However, once mortality becomes so high that empty patches remain uncolonized for a long time, evolution tends to increase migration rate, which may lead to an "evolutionary rescue" in a fragmented landscape. Kin competition has a quantitative effect on the evolution of migration rate in our model, but these patterns in the evolution of migration rate appear to be primarily caused by spatiotemporal variation in fitness and mortality during migration. We apply the model to real habitat patch networks occupied by two checkerspot butterfly (Melitaea) species, for which sufficient data are available to estimate rigorously most of the model parameters. The model-predicted migration rate is not significantly different from the empirically observed one. Regional variation in patch areas and connectivities leads to regional variation in the optimal migration rate, predictions that can be tested empirically. PMID:18707258

  14. THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF PLANET MIGRATION IN TURBULENT STRATIFIED DISKS

    SciTech Connect

    Uribe, A. L.; Klahr, H.; Flock, M.; Henning, Th.

    2011-08-01

    We performed three-dimensional magnetohydrodynamic simulations of planet migration in stratified disks using the Godunov code PLUTO, where the disk is turbulent due to the magnetorotational instability. We study the migration for planets with different planet-star mass ratios q = M{sub p} /M{sub s} . In agreement with previous studies, for the low-mass planet cases (q = 5 x 10{sup -6} and 10{sup -5}), migration is dominated by random fluctuations in the torque. For a Jupiter-mass planet (q = M{sub p} /M{sub s} = 10{sup -3} for M{sub s} = 1M{sub sun}), we find a reduction of the magnetic stress inside the orbit of the planet and around the gap region. After an initial stage where the torque on the planet is positive, it reverses and we recover migration rates similar to those found in disks where the turbulent viscosity is modeled by an {alpha} viscosity. For the intermediate-mass planets (q = 5 x 10{sup -5}, 10{sup -4}, and 2 x 10{sup -4}), we find a new and so far unexpected behavior. In some cases they experience sustained and systematic outward migration for the entire duration of the simulation. For this case, the horseshoe region is resolved and torques coming from the corotation region can remain unsaturated due to the stresses in the disk. These stresses are generated directly by the magnetic field. The magnitude of the horseshoe drag can overcome the negative Lindblad contribution when the local surface density profile is flat or increasing outward, which we see in certain locations in our simulations due to the presence of a zonal flow. The intermediate-mass planet is migrating radially outward in locations where there is a positive gradient of a pressure bump (zonal flow).

  15. Spatially Resolved Spectroscopic Star Formation Histories of nearby Disks: Hints of Stellar Migration

    NASA Astrophysics Data System (ADS)

    Yoachim, Peter; Roškar, Rok; Debattista, Victor P.

    2012-06-01

    We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk galaxies. We successfully measure ages in the outer disk in six systems. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations that are best fit with star formation histories that decline with time. The observed increase in average stellar ages beyond a profile break is similar to theoretical models that predict surface brightness breaks are caused by stellar migration, with the outer disk being populated from scattered old interior stars. In three more cases (IC 1132, NGC 4904, and NGC 6691), we find no significant change in the stellar population as one crosses the break radius. In these galaxies, both the inner and outer disks are dominated by active star formation and younger stellar populations. While radial migration can contribute to the stellar populations beyond the break, it appears that more than one mechanism is required to explain all of our observed stellar profile breaks. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.

  16. SPATIALLY RESOLVED SPECTROSCOPIC STAR FORMATION HISTORIES OF NEARBY DISKS: HINTS OF STELLAR MIGRATION

    SciTech Connect

    Yoachim, Peter; Roskar, Rok; Debattista, Victor P.

    2012-06-20

    We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk galaxies. We successfully measure ages in the outer disk in six systems. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations that are best fit with star formation histories that decline with time. The observed increase in average stellar ages beyond a profile break is similar to theoretical models that predict surface brightness breaks are caused by stellar migration, with the outer disk being populated from scattered old interior stars. In three more cases (IC 1132, NGC 4904, and NGC 6691), we find no significant change in the stellar population as one crosses the break radius. In these galaxies, both the inner and outer disks are dominated by active star formation and younger stellar populations. While radial migration can contribute to the stellar populations beyond the break, it appears that more than one mechanism is required to explain all of our observed stellar profile breaks.

  17. A SEMI-ANALYTICAL DESCRIPTION FOR THE FORMATION AND GRAVITATIONAL EVOLUTION OF PROTOPLANETARY DISKS

    SciTech Connect

    Takahashi, Sanemichi Z.; Inutsuka, Shu-ichiro; Machida, Masahiro N. E-mail: inutsuka@nagoya-u.jp E-mail: machida.masahiro.018@m.kyushu-u.ac.jp

    2013-06-10

    We investigate the formation process of self-gravitating protoplanetary disks in unmagnetized molecular clouds. The angular momentum is redistributed by the action of gravitational torques in the massive disk during its early formation. We develop a simplified one-dimensional accretion disk model that takes into account the infall of gas from the envelope onto the disk and the transfer of angular momentum in the disk with an effective viscosity. First we evaluate the gas accretion rate from the cloud core onto the disk by approximately estimating the effects of gas pressure and gravity acting on the cloud core. We formulate the effective viscosity as a function of the Toomre Q parameter that measures the local gravitational stability of the rotating thin disk. We use a function for viscosity that changes sensitively with Q when the disk is gravitationally unstable. We find a strong self-regulation mechanism in the disk evolution. During the formation stage of protoplanetary disks, the evolution of the surface density does not depend on the other details of the modeling of effective viscosity, such as the prefactor of the viscosity coefficient. Next, to verify our model, we compare the time evolution of the disk calculated with our formulation with that of three-dimensional hydrodynamical simulations. The structures of the resultant disks from the one-dimensional accretion disk model agree well with those of the three-dimensional simulations. Our model is a useful tool for the further modeling of chemistry, radiative transfer, and planet formation in protoplanetary disks.

  18. Understanding the Structure and Evolution of Nearby Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Zheng, Zheng

    2014-01-01

    In order to understand the structure and evolution of disk galaxies, we studied the stellar and gaseous components as well as the star formation rate in nearby disk galaxies. We used PS1 medium deep survey images to derive five-band (grizy) surface brightness profiles down to 30 ABmag/arcsec^2 for about 700 galaxies. From these stellar mass and mass-to-light ratio radial profiles are derived. The stellar mass radial profiles tend to bend-up at large radii, this often traces an extended old stellar population. The mass-to-light ratio profiles tend to rise outside the r25 radii. We also find a larger fraction of up-bending surface brightness profiles than Polen & Trujillo (2006). This may be because their sample is biased towards low surface brightness galaxies. We used HIPASS data as well as VLA HI 21cm data to study the gas component and dynamics of disk galaxies. We used the GALEX UV images to study the star formation of a HI-selected star-forming sample of about 400 galaxies, compiling a database of FUV and NUV radial profiles and related parameters. We used this to study the star forming efficiency (SFE, star formation rate per unit area divided by gas surface mass density) of the sample galaxies. We found that the UV based SFE has a tighter relationship with HI mass than an H_alpha based SFE as typically used in previous studies and the UV SFE is flat across wide range of stellar mass. We constructed a simple model to predict the distribution of interstellar medium and star formation rate in an equilibrium disk with constant two-fluid Toomre Q. This model can reproduces the SFE relations we derived.

  19. Oxygen abundance in local disk and bulge: chemical evolution with a strictly universal IMF

    NASA Astrophysics Data System (ADS)

    Caimmi, R.; Milanese, E.

    2009-09-01

    , or enhanced in, forming stars at different rates with respect to a selected reference case. Models involving a strictly universal IMF (i.e. gas neither inhibited from, nor enhanced in, forming stars with respect to a selected reference case) can also reproduce the data to an acceptable extent. Our main conclusions are (1) different models are necessary to fit the (incomplete) halo sample, which is consistent with the idea of two distinct halo components: an inner, flattened halo in slow prograde rotation, and an outer, spherical halo in net retrograde rotation (Carollo et al. in Nature 450:1020, 2007); (2) the oxygen enrichment within the inner SN halo, the SN thick disk, and the bulge, was similar and coeval within the same metallicity range, as inferred from observations (Prochaska et al. in Astron. J. 120:2513, 2000); (3) the fit to thin disk data implies an oxygen abundance range similar to its thick disk counterpart, with the extension of conclusion (2) to the thin disk, and the evolution of the thick + thin disk as a whole (Haywood in Mon. Not. R. Astron. Soc. 388:1175, 2008) cannot be excluded; (4) leaving outside the outer halo, a fit to the data related to different environments is provided by models with a strictly universal IMF but different probabilities of a region being active, which implies different global efficiencies of the star formation rate; (5) a special case of stellar migration across the disk can be described by models with enhanced star formation, where a fraction of currently observed SN stars were born in situ and a comparable fraction is due to the net effect of stellar migration, according to recent results based on high-resolution N-body + smooth particle hydrodynamics simulations (Ro\\vskar et al. in Astrophys. J. Lett. 684:L79, 2008).

  20. 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.

  1. CHEMICAL EVOLUTION OF TURBULENT PROTOPLANETARY DISKS AND THE SOLAR NEBULA

    SciTech Connect

    Semenov, D.; Wiebe, D. E-mail: dwiebe@inasan.ru

    2011-10-01

    We study the influence of transport processes on the chemical evolution of DM Tau-like protoplanetary disks. Turbulent transport of gases and ices is implicitly modeled in full two dimensions (2D), using the mixing-length approximation, along with the time-dependent chemistry. We find that turbulent transport enhances abundances and column densities of many gas-phase species and ices, particularly, complex ones. The influence of turbulent mixing on disk chemistry is more pronounced in the inner, planet-forming disk region where gradients of temperature and high-energy radiation intensities are steeper than in the outer region. The molecules that are unresponsive to transport include, e.g., C{sub 2}H, C{sup +}, CH{sub 4}, CN, CO, HCN, HNC, H{sub 2}CO, OH, as well as water and ammonia ice. Their column densities computed with the laminar and 2D mixing model differ by a factor of {approx}< 2-5. Molecules whose vertical column densities in the laminar and dynamical models differ by up to two orders of magnitude include, e.g., C{sub 2}H{sub 2}, some carbon chains, CS, H{sub 2}CS, H{sub 2}O, HCO{sup +}, HCOOH, HNCO, N{sub 2}H{sup +}, NH{sub 3}, CO ice, H{sub 2}CO ice, CH{sub 3}OH ice, and electrons. Molecules whose column densities are altered by diffusion by more than two orders of magnitude include, e.g., C{sub 2}S, C{sub 3}S, C{sub 6}H{sub 6}, CO{sub 2}, O{sub 2}, SiO, SO, SO{sub 2}, long carbon chain ices, CH{sub 3}CHO ice, HCOOH ice, O{sub 2} ice, and OCN ice. We indicate several observable or potentially detectable tracers of transport processes in protoplanetary disks and the solar nebula, such as heavy hydrocarbon ices, complex organics, CO{sub 2}, O{sub 2}, SO, SO{sub 2}, C{sub 2}S, C{sub 3}S compared to CO and water ice.

  2. Consumer resource interactions and the evolution of migration

    PubMed Central

    Drown, Devin M.; Dybdahl, Mark F.; Gomulkiewicz, Richard

    2013-01-01

    Theoretical studies have demonstrated that selection will favor increased migration when fitnesses vary both temporally and spatially, but it is far from clear how pervasive those theoretical conditions are in nature. While consumer-resource interactions are omnipresent in nature and can generate spatial and temporal variation, it is unknown even in theory whether these dynamics favor the evolution of migration. We develop a mathematical model to address whether and how migration evolves when variability in fitness is determined at least in part by consumer-resource coevolutionary interactions. Our analyses show that such interactions can drive the evolution of migration in the resource, consumer, or both species and thus supplies a general explanation for the pervasiveness of migration. Over short time scales, we show the direction of change in migration rate is determined primarily by the state of local adaptation of the species involved: rates increase when a species is locally maladapted and decrease when locally adapted. Our results reveal that long-term evolutionary trends in migration rates can differ dramatically depending on the strength or weakness of interspecific interactions and suggest an explanation for the evolutionary divergence of migration rates among interacting species. PMID:24152008

  3. Consumer-resource interactions and the evolution of migration.

    PubMed

    Drown, Devin M; Dybdahl, Mark F; Gomulkiewicz, Richard

    2013-11-01

    Theoretical studies have demonstrated that selection will favor increased migration when fitnesses vary both temporally and spatially, but it is far from clear how pervasive those theoretical conditions are in nature. Although consumer-resource interactions are omnipresent in nature and can generate spatial and temporal variation, it is unknown even in theory whether these dynamics favor the evolution of migration. We develop a mathematical model to address whether and how migration evolves when variability in fitness is determined at least in part by consumer-resource coevolutionary interactions. Our analyses show that such interactions can drive the evolution of migration in the resource, consumer, or both species and thus supplies a general explanation for the pervasiveness of migration. Over short time scales, we show the direction of change in migration rate is determined primarily by the state of local adaptation of the species involved: rates increase when a species is locally maladapted and decrease when locally adapted. Our results reveal that long-term evolutionary trends in migration rates can differ dramatically depending on the strength or weakness of interspecific interactions and suggest an explanation for the evolutionary divergence of migration rates among interacting species.

  4. Hydrocarbon Emission Rings in Protoplanetary Disks Induced by Dust Evolution

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  5. ON THE ORBITAL EVOLUTION OF A GIANT PLANET PAIR EMBEDDED IN A GASEOUS DISK. II. A SATURN-JUPITER CONFIGURATION

    SciTech Connect

    Zhang Hui; Zhou Jilin

    2010-08-10

    We carry out a series of high-resolution (1024 x 1024) hydrodynamic simulations to investigate the orbital evolution of a Saturn-Jupiter pair embedded in a gaseous disk. This work extends the results of our previous work by exploring a different orbital configuration-Jupiter lies outside Saturn (q < 1, where q {identical_to} M{sub i} /M{sub o} is the mass ratio of the inner planet and the outer one). We focus on the effects of different initial separations (d) between the two planets and the various surface density profiles of the disk, where {sigma} {proportional_to} r {sup -}{alpha}. We also compare the results of different orbital configurations of the planet pair. Our results show that (1) when the initial separation is relatively large (d>d {sub iLr}, where d {sub iLr} is the distance between Jupiter and its first inner Lindblad resonance), the two planets undergo divergent migration. However, the inward migration of Saturn could be halted when Jupiter compresses the inner disk in which Saturn is embedded. (2) Convergent migration occurs when the initial separation is smaller (d < d {sub iLr}) and the density slope of the disk is nearly flat ({alpha} < 1/2). Saturn is then forced by Jupiter to migrate inward where the two planets are trapped into mean motion resonances (MMRs), and Saturn may get very close to the central star. (3) In the case of q < 1, the eccentricity of Saturn could be excited to a very high value (e{sub S} {approx} 0.4-0.5) by the MMRs and the system could maintain stability. These results explain the formation of MMRs in the exoplanet systems where the outer planet is more massive than the inner one. It also helps us to understand the origin of the 'hot Jupiter/Saturn' with a highly eccentric orbit.

  6. Evolution of the protolunar disk: Dynamics, cooling timescale and implantation of volatiles onto the Earth

    NASA Astrophysics Data System (ADS)

    Charnoz, Sébastien; Michaut, Chloé

    2015-11-01

    It is thought that the Moon accreted from the protolunar disk that was assembled after the last giant impact on Earth. Due to its high temperature, the protolunar disk may act as a thermochemical reactor in which the material is processed before being incorporated into the Moon. Outstanding issues like devolatilisation and istotopic evolution are tied to the disk evolution, however its lifetime, dynamics and thermodynamics are unknown. Here, we numerically explore the long term viscous evolution of the protolunar disk using a one dimensional model where the different phases (vapor and condensed) are vertically stratified. Viscous heating, radiative cooling, phase transitions and gravitational instability are accounted for whereas Moon's accretion is not considered for the moment. The viscosity of the gas, liquid and solid phases dictates the disk evolution. We find that (1) the vapor condenses into liquid in ∼10 years, (2) a large fraction of the disk mass flows inward forming a hot and compact liquid disk between 1 and 1.7 Earth's radii, a region where the liquid is gravitationally stable and can accumulate, (3) the disk finally solidifies in 103 to 105 years. Viscous heating is never balanced by radiative cooling. If the vapor phase is abnormally viscous, due to magneto-rotational instability for instance, most of the disk volatile components are transported to Earth leaving a disk enriched in refractory elements. This opens a way to form a volatile-depleted Moon and would suggest that the missing Moon's volatiles are buried today into the Earth. The disk cooling timescale may be long enough to allow for planet/disk isotopic equilibration. However large uncertainties on the disk physics remain because of the complexity of its multi-phased structure.

  7. 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.

  8. Evolution of cooperation driven by social-welfare-based migration

    NASA Astrophysics Data System (ADS)

    Li, Yan; Ye, Hang; Zhang, Hong

    2016-03-01

    Individuals' migration behavior may play a significant role in the evolution of cooperation. In reality, individuals' migration behavior may depend on their perceptions of social welfare. To study the relationship between social-welfare-based migration and the evolution of cooperation, we consider an evolutionary prisoner's dilemma game (PDG) in which an individual's migration depends on social welfare but not on the individual's own payoff. By introducing three important social welfare functions (SWFs) that are commonly studied in social science, we find that social-welfare-based migration can promote cooperation under a wide range of parameter values. In addition, these three SWFs have different effects on cooperation, especially through the different spatial patterns formed by migration. Because the relative efficiency of the three SWFs will change if the parameter values are changed, we cannot determine which SWF is optimal for supporting cooperation. We also show that memory capacity, which is needed to evaluate individual welfare, may affect cooperation levels in opposite directions under different SWFs. Our work should be helpful for understanding the evolution of human cooperation and bridging the chasm between studies of social preferences and studies of social cooperation.

  9. 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.

  10. AN ANALYTIC MODEL FOR THE EVOLUTION OF A VISCOUS, IRRADIATED DISK

    SciTech Connect

    Chambers, J. E.

    2009-11-10

    We describe an analytic model for the evolution of a protoplanetary disk heated by viscous accretion and radiation from the central star. The disk is assumed to be flared and viscosity is assumed to follow an 'alpha' model, where viscosity is proportional to the local sound speed and scale height. In the inner disk, the midplane temperature is mainly determined by the energy released by the viscous accretion of material through the disk and onto the star. In the outer disk, stellar irradiation is the dominant heat source. A third regime is present in the innermost part of the disk, where viscous heating dominates but the opacity declines rapidly with increasing temperature due to dust grain sublimation. Changes in the protostellar radius and luminosity over time are readily incorporated into the model, although these have a relatively minor effect on the disk evolution. The model yields the surface density and midplane temperature at any point in space and time during the lifetime of the disk. It is especially suited to studies of planet formation that require a self-consistent model of disk evolution with minimal computational expense.

  11. The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

    NASA Astrophysics Data System (ADS)

    Xiang, Mao-Sheng; Liu, Xiao-Wei; Yuan, Hai-Bo; Huang, Yang; Wang, Chun; Ren, Juan-Juan; Chen, Bing-Qiu; Sun, Ning-Chen; Zhang, Hua-Wei; Huo, Zhi-Ying; Rebassa-Mansergas, Alberto

    2015-08-01

    Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to determine the radial and vertical gradients of stellar metallicity, Δ[Fe/H]/ΔR and Δ[Fe/H]/Δ|Z| of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages (≳ 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages (≳ 11 Gyr) are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R. After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum (steepest) at age 7-8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are

  12. Social interactions, information use, and the evolution of collective migration

    PubMed Central

    Guttal, Vishwesha; Couzin, Iain D.

    2010-01-01

    Migration of organisms (or cells) is typically an adaptive response to spatiotemporal variation in resources that requires individuals to detect and respond to long-range and noisy environmental gradients. Many organisms, from wildebeest to bacteria, migrate en masse in a process that can involve a vast number of individuals. Despite the ubiquity of collective migration, and the key function it plays in the ecology of many species, it is still unclear what role social interactions play in the evolution of migratory strategies. Here, we explore the evolution of migratory behavior using an individual-based spatially explicit model that incorporates the costs and benefits of obtaining directional cues from the environment and evolvable social interactions among migrating individuals. We demonstrate that collective migratory strategies evolve under a wide range of ecological scenarios, even when social encounters are rare. Although collective migration appears to be a shared navigational process, populations typically consist of small proportions of individuals actively acquiring directional information from their environment, whereas the majorities use a socially facilitated movement behavior. Because many migratory species face severe threat through anthropogenic influences, we also explore the microevolutionary response of migratory strategies to environmental pressures. We predict a gradual decline of migration due to increasing habitat destruction and argue that much greater restoration is required to recover lost behaviors (i.e., a strong hysteresis effect). Our results provide insights into both the proximate and ultimate factors that underlie evolved migratory behavior in nature. PMID:20713700

  13. DISK EVOLUTION IN THE THREE NEARBY STAR-FORMING REGIONS OF TAURUS, CHAMAELEON, AND OPHIUCHUS

    SciTech Connect

    Furlan, E.; Watson, Dan M.; McClure, M. K. E-mail: dmw@pas.rochester.ed

    2009-10-01

    We analyze samples of Spitzer Infrared Spectrograph spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1-2 Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31 {mu}m and the equivalent width of the 10 {mu}m silicate emission feature to identify objects whose disk configuration departs from that of a continuous, optically thick accretion disk. Transitional disks, whose steep 13-31 {mu}m spectral slope and near-IR flux deficit reveal inner disk clearing, occur with about the same frequency of a few percent in all three regions. Objects with unusually large 10 {mu}m equivalent widths are more common (20%-30%); they could reveal the presence of disk gaps filled with optically thin dust. Based on their medians and fraction of evolved disks, T Tauri stars in Taurus and Chamaeleon I are very alike. Disk evolution sets in early, since already the youngest region, the Ophiuchus core (L1688), has more settled disks with larger grains. Our results indicate that protoplanetary disks show clear signs of dust evolution at an age of a few Myr, even as early as approx1 Myr, but age is not the only factor determining the degree of evolution during the first few million years of a disk's lifetime.

  14. Protoplanetary disk formation and evolution models: DM Tau and GM Aur

    NASA Astrophysics Data System (ADS)

    Hueso, R.; Guillot, T.

    2002-09-01

    We study the formation and evolution of protoplanetary disks using an axisymmetric turbulent disk model. We compare model results with observational parameters derived for the DM Tau and GM Aur systems. These are relatively old T Tauri stars with large and massive protoplanetary disks. Early disk formation is studied in the standard scenario of slowly rotating isothermal collapsing spheres and is strongly dependent on the initial angular momentum and the collapse accretion rate. The viscous evolution of the disk is integrated in time using the classical Alpha prescription of turbulence. We follow the temporal evolution of the disks until their characteristics fit the observed characteristics of DM Tau and GM Aur. We therefore obtain the set of model parameters that are able to explain the present state of these disks. We also study the disk evolution under the Beta parameterization of turbulence, recently proposed for sheared flows on protoplanetary disks. Both parameterizations allow explaining the present state of both DM Tau and GM Aur. We infer a value of Alpha between 5x10-3 to 0.02 for DM Tau and one order of magnitude smaller for GM Aur. Values of the Beta parameter are in accordance with theoretical predictions of Beta around 2x10-5 but with a larger dispersion on other model parameters, which make us favor the Alpha parameterization of turbulence. Implications for planetary system development in these systems are presented. In particular, GM Aur is a massive and slowly evolving disk where conditions are very favorable for planetesimal growth. The large value of present disk mass and the relatively small observed accretion rate of this system may also be indicative of the presence of an inner gas giant planet. Acknowledgements: This work has been supported by Programme Nationale de Planetologie. R. Hueso acknowledges a post-doctoral fellowship from Gobierno Vasco.

  15. Migration and the evolution of duetting in songbirds.

    PubMed

    Logue, David M; Hall, Michelle L

    2014-05-01

    Many groups of animals defend shared resources with coordinated signals. The best-studied of these signals are the vocal duets produced by mated pairs of birds. Duets are believed to be more common among tropical-breeding species, but a comprehensive test of this hypothesis is lacking, and the mechanisms that generate latitudinal patterns in duetting are not known. We used a stratified sample of 372 songbird species to conduct the first broad-scale, phylogenetically explicit analysis of duet evolution. We found that duetting evolves in association with the absence of migration, but not with sexual monochromatism or tropical breeding. We conclude that the evolution of migration exerts a major influence on the evolution of duetting. The perceived association between tropical breeding and duetting may be a by-product of the migration-duetting relationship. Migration reduces the average duration of partnerships, potentially reducing the benefits of cooperative behaviour, including duetting. Ultimately, the evolution of coordinated resource-defence signals in songbirds may be driven by ecological conditions that favour sedentary lifestyles and social stability.

  16. Five steps in the evolution from protoplanetary to debris disk

    NASA Astrophysics Data System (ADS)

    Wyatt, M. C.; Panić, O.; Kennedy, G. M.; Matrà, L.

    2015-06-01

    The protoplanetary disks seen around Herbig Ae stars eventually dissipate leaving just a tenuous debris disk, comprised of planetesimals and the dust derived from them, as well as possibly gas and planets. This paper uses the properties of the youngest (10-20 Myr) A star debris disks to consider the transition from protoplanetary to debris disk. It is argued that the physical distinction between these two classes should rest on the presence of primordial gas in sufficient quantities to dominate the motion of small dust grains (rather than on the secondary nature of the dust or its level of stirring). This motivates an observational classification based on the dust emission spectrum which is empirically defined so that A star debris disks require fractional excesses <3 at 12 μm and <2000 at 70 μm. We also propose that a useful hypothesis to test is that the planet and planetesimal systems seen on the main sequence are already in place during the protoplanetary disk phase, but are obscured or overwhelmed by the rest of the disk. This may be only weakly true if the architecture of the planetary system continues to change until frozen at the epoch of disk dispersal, or completely false if planets and planetesimals form during the relatively short dispersal phase. Five steps in the transition are discussed: (i) the well-known carving of an inner hole to form a transition disk; (ii) depletion of mm-sized dust in the outer disk, where it is noted that it is of critical importance to ascertain whether this mass ends up in larger planetesimals or is collisionally depleted; (iii) final clearing of inner regions, where it is noted that multiple debris-like mechanisms exist to replenish moderate levels of hot dust at later phases, and that these likely also operate in protoplanetary disks; (iv) disappearance of the gas, noting the recent discoveries of both primordial and secondary gas in debris disks which highlight our ignorance in this area and its impending enlightenment

  17. Evolution of the Milky Way with radial motions of stars and gas. I. The solar neighbourhood and the thin and thick disks

    NASA Astrophysics Data System (ADS)

    Kubryk, M.; Prantzos, N.; Athanassoula, E.

    2015-08-01

    Context. We study the role of radial migration of stars on the chemical evolution of the Milky Way disk. Aims: We are interested in the impact of that process on the local properties of the disk (age-metallicity relation and its dispersion, metallicity distribution, evolution of abundance ratios) and on the morphological properties of the resulting thick and thin disks. Methods: We use a model with several new or up-dated ingredients: atomic and molecular gas phases, star formation that depends on molecular gas, yields from a recent homogeneous grid and observationally inferred SNIa rates. We describe radial migration with parametrised time- and radius-dependent diffusion coefficients, based on the analysis of an N-body+SPH simulation. We also consider parametrised radial gas flows, induced by the action of the Galactic bar. Results: Our model reproduces current values of most of the main global observables of the MW disk and bulge, and also the observed "stacked" evolution of MW-type galaxies. The azimuthally averaged radial velocity of gas inflow is constrained to less than a few tenths of km s-1. Radial migration is constrained by the observed dispersion in the age-metallicity relation. Assuming that the thick disk is the oldest (>9 Gyr) part of the disk, we find that the adopted radial migration scheme can quantitatively reproduce the main local properties of the thin and thick disk: metallicity distributions, "two-branch" behaviour in the O/Fe vs. Fe/H relation and the local surface densities of stars. The thick disk extends up to ~11 kpc and has a scale length of 1.8 kpc, which is considerably shorter than the thin disk, because of the inside-out formation scheme. We also show how, in this framework, current and forthcoming spectroscopic observations can constrain the nucleosynthesis yields of massive stars for the metallicity range of 0.1 Z⊙ to 2-3 Z⊙. Appendices are available in electronic form at http://www.aanda.org

  18. COLLISIONAL AND LUMINOSITY EVOLUTION OF A DEBRIS DISK: THE CASE OF HD 12039

    SciTech Connect

    Weidenschilling, S. J.

    2010-10-20

    Extrasolar debris disks that are bright enough to be observed are dense enough to be collision-dominated; i.e., the small grains that produce their infrared excess have collisional lifetimes shorter than their Poynting-Robertson decay times. This paper describes a numerical code for the modeling of such disks, including accretion and gravitational stirring as well as disruptive collisions. A constraint relating the mass of a debris disk and the sizes of the largest embedded bodies to its luminosity is demonstrated. The collisional code is applied to the debris disk around HD 12039, which has been intensively observed by the Spitzer Space Telescope. The evolution in time of the disk's luminosity is computed for a range of initial disk masses and planetesimal sizes. The luminosity at a given age depends on both the initial disk mass and the initial size of the planetesimals. Luminosity decays more rapidly for massive disks due to the combination of collisional depletion of small bodies and their accretion by bodies too large to contribute to dust production. Disks with low initial masses evolve slowly and can maintain their luminosities for {approx} Gyr timescales. This behavior may explain the lack of correlation between stellar metallicity and the abundance of debris disks.

  19. Formation and evolution of inclined accretion disks in intermediate polars

    NASA Astrophysics Data System (ADS)

    Fateeva, A. M.; Zhilkin, A. G.; Bisikalo, D. V.

    2016-01-01

    The results of 3D modeling of the formation of the accretion disks of intermediate polars are presented. A model with misaligned rotation axes of accretor and the orbit is onsidered, in which it is assumed that the white dwarf has a dipolar magnetic field with its symmetry axis inclined to the whitedwarf rotation and orbital axes. The computations show that, in the early stages of formation of the disk, the action of magnetic field is able to create the initial (seed) inclination of the disk. This inclination is then supported mainly by the dynamical pressure of the flow from the inner Lagrangian point L1. As themass of the disk increases, the inclination disappears. Under certain conditions, the disk inclination does not arise in systems with misaligned white-dwarf rotation and orbital axes. The influence of the magnetic field and asynchronous rotation of the accretor may result in the formation of spiral waves in the disk with amplitudes sufficient to be detected observationally.

  20. Migration and the evolution of duetting in songbirds

    PubMed Central

    Logue, David M.; Hall, Michelle L.

    2014-01-01

    Many groups of animals defend shared resources with coordinated signals. The best-studied of these signals are the vocal duets produced by mated pairs of birds. Duets are believed to be more common among tropical-breeding species, but a comprehensive test of this hypothesis is lacking, and the mechanisms that generate latitudinal patterns in duetting are not known. We used a stratified sample of 372 songbird species to conduct the first broad-scale, phylogenetically explicit analysis of duet evolution. We found that duetting evolves in association with the absence of migration, but not with sexual monochromatism or tropical breeding. We conclude that the evolution of migration exerts a major influence on the evolution of duetting. The perceived association between tropical breeding and duetting may be a by-product of the migration–duetting relationship. Migration reduces the average duration of partnerships, potentially reducing the benefits of cooperative behaviour, including duetting. Ultimately, the evolution of coordinated resource-defence signals in songbirds may be driven by ecological conditions that favour sedentary lifestyles and social stability. PMID:24619447

  1. The Evolution of a Planet-Forming Disk (Artist's Concept Animation)

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This animation shows the evolution of a planet-forming disk around a star. Initially, the young disk is bright and thick with dust, providing raw materials for building planets. In the first 10 million years or so, gaps appear within the disk as newborn planets coalesce out of the dust, clearing out a path.

    In time, this planetary 'debris disk' thins out as gravitational interactions with numerous planets slowly sweep away the dust. Steady pressure from the starlight and solar winds also blows out the dust. After a few billion years, only a thin ring remains in the outermost reaches of the system, a faint echo of the once-brilliant disk.

    Our own solar system has a similar debris disk -- a ring of comets called the Kuiper Belt. Leftover dust in the inner portion of the solar system is known as 'zodiacal dust.'

    Bright, young disks can be imaged directly by visible-light telescopes, such as NASA's Hubble Space Telescope. Older, fainter debris disks can be detected only by infrared telescopes like NASA's Spitzer Space Telescope, which sense the disks' dim heat.

  2. LONG-TERM EVOLUTION OF PLANET-INDUCED VORTICES IN PROTOPLANETARY DISKS

    SciTech Connect

    Fu, Wen; Li, Hui; Li, Shengtai; Lubow, Stephen

    2014-06-20

    Recent observations of large-scale asymmetric features in protoplanetary disks suggest that large-scale vortices exist in such disks. Massive planets are known to be able to produce deep gaps in protoplanetary disks. The gap edges could become hydrodynamically unstable to the Rossby wave/vortex instability and form large-scale vortices. In this study we examine the long-term evolution of these vortices by carrying out high-resolution two-dimensional hydrodynamic simulations that last more than 10{sup 4} orbits (measured at the planet's orbit). We find that the disk viscosity has a strong influence on both the emergence and lifetime of vortices. In the outer disk region where asymmetric features are observed, our simulation results suggest that the disk viscous α needs to be low, ∼10{sup –5}-10{sup –4}, to sustain vortices to thousands and up to 10{sup 4} orbits in certain cases. The chance of finding a vortex feature in a disk then decreases with smaller planet orbital radius. For α ∼ 10{sup –3} or larger, even planets with masses of 5 M {sub J} will have difficulty either producing or sustaining vortices. We have also studied the effects of different disk temperatures and planet masses. We discuss the implications of our findings on current and future protoplanetary disk observations.

  3. THE TRANSITIONAL PROTOPLANETARY DISK FREQUENCY AS A FUNCTION OF AGE: DISK EVOLUTION IN THE CORONET CLUSTER, TAURUS, AND OTHER 1-8 Myr OLD REGIONS

    SciTech Connect

    Currie, Thayne; Sicilia-Aguilar, Aurora

    2011-05-01

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

  4. The Torquing of Circumnuclear Accretion Disks by Stars and the Evolution of Massive Black Holes

    NASA Astrophysics Data System (ADS)

    Bregman, Michal; Alexander, Tal

    2012-03-01

    An accreting massive black hole (MBH) in a galactic nucleus is surrounded by a dense stellar cluster. We analyze and simulate numerically the evolution of a thin accretion disk due to its internal viscous torques, due to the frame-dragging torques of a spinning MBH (the Bardeen-Petterson effect), and due to the orbit-averaged gravitational torques by the stars (resonant relaxation). We show that the evolution of the MBH mass accretion rate, the MBH spin growth rate, and the covering fraction of the disk relative to the central ionizing continuum source, are all strongly coupled to the stochastic fluctuations of the stellar potential via the warps that the stellar torques excite in the disk. These lead to fluctuations by factors of up to a few in these quantities over a wide range of timescales, with most of the power on timescales >~ (M •/Md )P(Rd ), where M • and Md are the masses of the MBH and disk, and P is the orbital period at the disk's mass-weighted mean radius Rd . The response of the disk is stronger the lighter it is and the more centrally concentrated the stellar cusp. As proof of concept, we simulate the evolution of the low-mass maser disk in NGC 4258 and show that its observed O(10°) warp can be driven by the stellar torques. We also show that the frame dragging of a massive active galactic nucleus disk couples the stochastic stellar torques to the MBH spin and can excite a jitter of a few degrees in its direction relative to that of the disk's outer regions.

  5. THE TORQUING OF CIRCUMNUCLEAR ACCRETION DISKS BY STARS AND THE EVOLUTION OF MASSIVE BLACK HOLES

    SciTech Connect

    Bregman, Michal; Alexander, Tal

    2012-03-20

    An accreting massive black hole (MBH) in a galactic nucleus is surrounded by a dense stellar cluster. We analyze and simulate numerically the evolution of a thin accretion disk due to its internal viscous torques, due to the frame-dragging torques of a spinning MBH (the Bardeen-Petterson effect), and due to the orbit-averaged gravitational torques by the stars (resonant relaxation). We show that the evolution of the MBH mass accretion rate, the MBH spin growth rate, and the covering fraction of the disk relative to the central ionizing continuum source, are all strongly coupled to the stochastic fluctuations of the stellar potential via the warps that the stellar torques excite in the disk. These lead to fluctuations by factors of up to a few in these quantities over a wide range of timescales, with most of the power on timescales {approx}> (M{sub .}/M{sub d} )P(R{sub d} ), where M{sub .} and M{sub d} are the masses of the MBH and disk, and P is the orbital period at the disk's mass-weighted mean radius R{sub d}. The response of the disk is stronger the lighter it is and the more centrally concentrated the stellar cusp. As proof of concept, we simulate the evolution of the low-mass maser disk in NGC 4258 and show that its observed O(10 Degree-Sign ) warp can be driven by the stellar torques. We also show that the frame dragging of a massive active galactic nucleus disk couples the stochastic stellar torques to the MBH spin and can excite a jitter of a few degrees in its direction relative to that of the disk's outer regions.

  6. THE DIFFERENT EVOLUTION OF GAS AND DUST IN DISKS AROUND SUN-LIKE AND COOL STARS

    SciTech Connect

    Pascucci, I.; Apai, D.; Luhman, K.; Henning, Th.; Bouwman, J.; Meyer, M. R.; Lahuis, F.; Natta, A.

    2009-05-01

    Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk properties vary with stellar parameters remains poorly known. Here, we present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks around young Sun-like stars (K1-M5) and cool stars/brown dwarfs (M5-M9). The comparison of these two large samples of over 60 sources reveal major differences in the evolution of both the dust and gas components. We report the first detection of organic molecules in disks around brown dwarfs. The detection rate statistics and the line flux ratios of HCN and C{sub 2}H{sub 2} show a striking difference between the two samples, demonstrating a significant underabundance of HCN relative to C{sub 2}H{sub 2} in the disk surface of cool stars. We propose this to originate from the large difference in the UV irradiation around the two types of sources. The statistical comparison of the 10 {mu}m silicate emission features also reveals a difference between the two samples. Cool stars and brown dwarfs show weaker features arising from more processed silicate grains in the disk atmosphere. These findings complement previous indications of flatter disk structures and longer disk lifetimes around cool stars. Our results highlight important differences in the chemical and physical evolution of protoplanetary disks as a function of stellar mass, temperature, and radiation field which should be taken into account in planet formation models. We note that the different chemistry of preplanetary materials in the disk may also influence the bulk composition and volatile content of the forming planets. In particular, if exogenous HCN has played a key role in the synthesis of prebiotic molecules on Earth as proposed, then prebiotic chemistry may unfold differently on planets around cool stars.

  7. The Key Roles of the Gas Disk in the Formation and Evolution of Planetary Systems

    NASA Astrophysics Data System (ADS)

    Liu, H. G.

    2012-11-01

    The detection of exoplanets becomes hotter and hotter, especially the detection of Earth-like exoplanets. With the accumulation of observational data and the progress of Kepler mission of NASA, more exoplanets can be found or confirmed. The understanding of formation and evolution of exoplanets will be largely improved when much more samples are provided. According to the acknowledged theories of planet formation, the protoplanet is formed in the protoplanetary disc. Due to the interactions between the disc and protoplanets, the property of the disc plays a key role during the formation and evolution of planets. We investigate the later stage of planet formation, when the Mars-sized cores appear and the gas disc has not been depleted yet. Interactions among the planetary cores can excite their orbital eccentricities, accelerate their mergings, and thus sculpture their final orbital architecture. The interactions between the cores and gas discs lead to the type I and II migrations as well as the eccentricity damping. However, the rates of type I, II migrations are still uncertain in different disc models. In chapter 1, we introduce the main methods of exoplanet detection and the achievements of Kepler space telescope. We also list some examples of exoplanetary systems to show their diversity. The acknowledged theories of planet formation, including the gravitational instability and core accretion scenarios, are presented in detail in chapter 2. The studies in chapter 3 contribute to the final assembling of planetary systems with N-body simulations, including the type I and II migrations of planets, the eccentricity damping, and the gas accretion of massive cores in a viscous disk. In order to compare the observations in statistics, we use the Monte Carlo method to set a distribution of different discs. Our results of simulations interpret the distribution of exoplanets and may be a guidance for the further observations. In chapter 5, considering the uncertainty of

  8. Dynamical evolution of viscous disks around be stars. II. Polarimetry

    SciTech Connect

    Haubois, X.; Mota, B. C.; Carciofi, A. C.; Bednarski, D.; Draper, Z. H.; Wisniewski, J. P.; Rivinius, Th.

    2014-04-10

    Be stars exhibit variability for a great number of observables. Putting the pieces of the disk dynamics together is not an easy task and requires arduous modeling before achieving a good fit to the observational data. In order to guide the modeling process and make it more efficient, it is very instructive to investigate reference dynamical cases. This paper focuses on continuum polarimetric quantities and is the second of a series that aims to demonstrate the capacity of deriving the dynamical history and fundamental parameters of a classical Be star through follow-up of various observables. After a detailed study of the different opacities at play in the formation of polarized spectra, we investigate predictions of polarimetric observables in the continuum for different dynamical scenarios. Our models are based on a coupling of a hydrodynamic viscous decretion simulations in a disk and a three-dimensional non-LTE radiative transfer code. Through introduction of the polarization color diagram (PCD), we show that certain combinations of polarimetric observables exhibit features that are characteristic of a mass-loss history. This diagram also enables estimates of fundamental parameters such as the inclination angle, disk density scale, and the α viscous diffusion parameter. We present the PCD as a powerful diagnosis tool to track the dynamical phases of a Be star, such as disk build-up, dissipation, periodic, and episodic outbursts. Finally, we confront our models with observations of four Be stars that exhibited long-term polarimetric activity.

  9. GALACTIC ULTRACOMPACT X-RAY BINARIES: DISK STABILITY AND EVOLUTION

    SciTech Connect

    Heinke, C. O.; Ivanova, N.; Engel, M. C.; Pavlovskii, K.; Sivakoff, G. R.; Gladstone, J. C.; Cartwright, T. F.

    2013-05-10

    We study the mass-transfer rates and disk stability conditions of ultracompact X-ray binaries (UCXBs) using empirical time-averaged X-ray luminosities from Paper I and compiled information from the literature. The majority of UCXBs are consistent with evolutionary tracks for white dwarf donors. Three UCXBs with orbital periods longer than 40 minutes have mass-transfer rates above 10{sup -10} M{sub Sun} yr{sup -1}, inconsistent with white dwarf donor tracks. We show that if helium star donors can retain their initial high entropy, they can explain the observed mass-transfer rates of these UCXBs. Several UCXBs show persistent luminosities apparently below the disk instability limit for irradiated He accretion disks. We point out that a predominantly C and/or O disk (as observed in the optical spectra of several) lowers the disk instability limit, explaining this disagreement. The orbital period and low time-averaged mass-transfer rate of 2S 0918-549 provide evidence that the donor star is a low-entropy C/O white dwarf, consistent with optical spectra. We combine existing information to constrain the masses of the donors in 4U 1916-053 (0.064 {+-} 0.010 M{sub Sun }) and 4U 1626-67 (<0.036 M{sub Sun} for a 1.4 M{sub Sun} neutron star). We show that 4U 1626-67 is indeed persistent, and not undergoing a transient outburst, leaving He star models as the best explanation for the donor.

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

    NASA Technical Reports Server (NTRS)

    Currie, Thayne; Sicilia-Aguilar, Auora

    2011-01-01

    We present Spitzer 3.6-24 micron photometry and spectroscopy for stars in the 1-3 Myr-old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. (2008). Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. (2008) to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters - IC 348, NGC 2362, and eta Cha -- to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks -- those with inner holes and those that are homologously depleted. The percentage of disks in the transitional phase increases from approx.15-20% at 1-2 Myr to > 50% at 5-8 Myr; the mean transitional disk lifetime is closer to approx. 1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. (2009) and Sicilia-Aguilar et al. (2009). In the Coronet Cluster and IC 348, transitional disks are more numerous for very low-mass M3--M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically-thick primordial disks is Mdisk approx. 0.001-0.003 M*. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full SED modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.

  11. EVOLUTION OF X-RAY AND FAR-ULTRAVIOLET DISK-DISPERSING RADIATION FIELDS

    SciTech Connect

    Ingleby, Laura; Calvet, Nuria; Miller, Jon; Bergin, Edwin; Hartmann, Lee; Hernandez, Jesus; Briceno, Cesar; Espaillat, Catherine E-mail: ncalvet@umich.edu E-mail: ebergin@umich.edu E-mail: jesush@cida.ve E-mail: cespaillat@cfa.harvard.edu

    2011-04-15

    We present new X-ray and far-ultraviolet (FUV) observations of T Tauri stars covering the age range 1-10 Myr. Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the circumstellar disk and to assess the feasibility of current photoevaporation models, focusing on X-ray and UV radiation. We greatly increase the number of 7-10 Myr old T Tauri stars observed in X-rays by including observations of the well-populated 25 Ori aggregate in the Orion OB1a subassociation. With these new 7-10 Myr objects, we confirm that X-ray emission remains constant from 1 to 10 Myr. We also show, for the first time, observational evidence for the evolution of FUV radiation fields with a sample of 56 accreting and non-accreting young stars spanning 1 Myr to 1 Gyr. We find that the FUV emission decreases on timescales consistent with the decline of accretion in classical T Tauri stars until reaching the chromospheric level in weak T Tauri stars and debris disks. Overall, we find that the observed strength of high-energy radiation is consistent with that required by photoevaporation models to dissipate the disks in timescales of approximately 10 Myr. Finally, we find that the high-energy fields that affect gas evolution are not similarly affecting dust evolution; in particular, we find that disks with inner clearings, transitional disks, have similar levels of FUV emission as full disks.

  12. ON THE ORBITAL EVOLUTION OF A GIANT PLANET PAIR EMBEDDED IN A GASEOUS DISK. I. JUPITER-SATURN CONFIGURATION

    SciTech Connect

    Zhang Hui; Zhou Jilin

    2010-05-01

    We carry out a series of high-resolution (1024 x 1024) hydrodynamical simulations to investigate the orbital evolution of Jupiter and Saturn embedded in a gaseous protostellar disk. Our work extends the results in the classical papers of Masset and Snellgrove and Morbidelli and Crida by exploring various surface density profiles ({sigma}), where {sigma} {proportional_to} r {sup -{alpha}}. The stability of the mean motion resonances (MMRs) caused by the convergent migration of the two planets is studied as well. Our results show that (1) the gap formation process of Saturn is greatly delayed by the tidal perturbation of Jupiter. These perturbations cause inward or outward runaway migration of Saturn, depending on the density profiles on the disk. (2) The convergent migration rate increases as {alpha} increases and the type of MMRs depends on {alpha} as well. When 0 < {alpha} < 1, the convergent migration speed of Jupiter and Saturn is relatively slow, thus they are trapped into 2:1 MMR. When {alpha}>4/3, Saturn passes through the 2:1 MMR with Jupiter and is captured into the 3:2 MMR. (3) The 3:2 MMR turns out to be unstable when the eccentricity of Saturn (e{sub s} ) increases too high. The critical value above which instability will set in is e{sub s} {approx} 0.15. We also observe that the two planets are trapped into 2:1 MMR after the break of 3:2 MMR. This process may provide useful information for the formation of orbital configuration between Jupiter and Saturn in the solar system.

  13. A TREND BETWEEN COLD DEBRIS DISK TEMPERATURE AND STELLAR TYPE: IMPLICATIONS FOR THE FORMATION AND EVOLUTION OF WIDE-ORBIT PLANETS

    SciTech Connect

    Ballering, Nicholas P.; Rieke, George H.; Su, Kate Y. L.; Montiel, Edward

    2013-09-20

    Cold debris disks trace the limits of planet formation or migration in the outer regions of planetary systems, and thus have the potential to answer many of the outstanding questions in wide-orbit planet formation and evolution. We characterized the infrared excess spectral energy distributions of 174 cold debris disks around 546 main-sequence stars observed by both the Spitzer Infrared Spectrograph and the Multiband Imaging Photometer for Spitzer. We found a trend between the temperature of the inner edges of cold debris disks and the stellar type of the stars they orbit. This argues against the importance of strictly temperature-dependent processes (e.g., non-water ice lines) in setting the dimensions of cold debris disks. Also, we found no evidence that delayed stirring causes the trend. The trend may result from outward planet migration that traces the extent of the primordial protoplanetary disk, or it may result from planet formation that halts at an orbital radius limited by the efficiency of core accretion.

  14. Galaxy Zoo Hubble: First results of the redshift evolution of disk fraction in the red sequence

    NASA Astrophysics Data System (ADS)

    Galloway, Melanie; Willett, Kyle; Fortson, Lucy; Scarlata, Claudia; Beck, Melanie; Masters, Karen; Melvin, Tom

    2016-01-01

    The transition of galaxies from the blue cloud to the red sequence is commonly linked to a morphological transformation from disk to elliptical structure. However, the correlation between color and morphology is not one-to-one, as evidenced by the existence of a significant population of red disks. As this stage in a galaxy's evolution is likely to be transitory, the mechanism by which red disks are formed offers insight to the processes that trigger quenching of star formation and the galaxy's position on the star-forming sequence. To study the population of disk galaxies in the red sequence as a function of cosmic time, we utilize data from the Galaxy Zoo: Hubble project, which uses crowdsourced visual classifications of images of galaxies selected from the AEGIS, COSMOS, GEMS, and GOODS surveys. We construct a large sample of over 10,000 disk galaxies spanning a wide (0 < z < 1.0) redshift range. We use this sample to examine the change in the fraction of disks in the red sequence with respect to all disks from z˜1 to the present day. Preliminary results confirm that the fraction of disks in the red sequence decreases as the Universe evolves. We discuss the quenching processes which may explain this trend, and which morphological transformations are most affected by it.

  15. ON THE EVOLUTION OF DUST MINERALOGY, FROM PROTOPLANETARY DISKS TO PLANETARY SYSTEMS

    SciTech Connect

    Oliveira, Isa; Van Dishoeck, Ewine F.; Olofsson, Johan; Pontoppidan, Klaus M.; Augereau, Jean-Charles

    2011-06-10

    Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and solar system bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites, and interplanetary dust particles indicates a modification of the almost completely amorphous interstellar medium dust from which they formed. The production of crystalline silicates, thus, must happen in protoplanetary disks, where dust evolves to build planets and planetesimals. Different scenarios have been proposed, but it is still unclear how and when this happens. This paper presents dust grain mineralogy (composition, crystallinity, and grain size distribution) of a complete sample of protoplanetary disks in the young Serpens cluster. These results are compared to those in the young Taurus region and to sources that have retained their protoplanetary disks in the older Upper Scorpius and {eta} Chamaeleontis stellar clusters, using the same analysis technique for all samples. This comparison allows an investigation of the grain mineralogy evolution with time for a total sample of 139 disks. The mean cluster age and disk fraction are used as indicators of the evolutionary stage of the different populations. Our results show that the disks in the different regions have similar distributions of mean grain sizes and crystallinity fractions ({approx}10%-20%) despite the spread in mean ages. Furthermore, there is no evidence of preferential grain sizes for any given disk geometry nor for the mean cluster crystallinity fraction to increase with mean age in the 1-8 Myr range. The main implication is that a modest level of crystallinity is established in the disk surface early on ({<=}1 Myr), reaching an equilibrium that is independent of what may be happening in the disk midplane. These results are discussed in the context of planet formation, in comparison with mineralogical results from small bodies in our own solar

  16. THE INNER DISK STRUCTURE, DISK-PLANET INTERACTIONS, AND TEMPORAL EVOLUTION IN THE β PICTORIS SYSTEM: A TWO-EPOCH HST/STIS CORONAGRAPHIC STUDY

    SciTech Connect

    Apai, Dániel; Schneider, Glenn; Grady, Carol A.; Wyatt, Mark C.; Lagrange, Anne-Marie; Kuchner, Marc J.; Stark, Christopher J.; Lubow, Stephen H.

    2015-02-20

    We present deep Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphic images of the β Pic debris disk obtained at two epochs separated by 15 yr. The new images and the re-reduction of the 1997 data provide the most sensitive and detailed views of the disk at optical wavelengths as well as the yet smallest inner working angle optical coronagraphic image of the disk. Our observations characterize the large-scale and inner-disk asymmetries and we identify multiple breaks in the disk radial surface brightness profile. We study in detail the radial and vertical disk structure and show that the disk is warped. We explore the disk at the location of the β Pic b super-Jupiter and find that the disk surface brightness slope is continuous between 0.''5 and 2.''0, arguing for no change at the separations where β Pic b orbits. The two epoch images constrain the disk's surface brightness evolution on orbital and radiation pressure blow-out timescales. We place an upper limit of 3% on the disk surface brightness change between 3'' and 5'', including the locations of the disk warp, and the CO and dust clumps. We discuss the new observations in the context of high-resolution multi-wavelength images and divide the disk asymmetries in two groups: axisymmetric and non-axisymmetric. The axisymmetric structures (warp, large-scale butterfly, etc.) are consistent with disk structure models that include interactions of a planetesimal belt and a non-coplanar giant planet. The non-axisymmetric features, however, require a different explanation.

  17. Chemical evolution models for spiral disks: the Milky Way, M 31, and M 33

    NASA Astrophysics Data System (ADS)

    Marcon-Uchida, M. M.; Matteucci, F.; Costa, R. D. D.

    2010-09-01

    Context. The distribution of chemical abundances and their variation with time are important tools for understanding the chemical evolution of galaxies. In particular, the study of chemical evolution models can improve our understanding of the basic assumptions made when modelling our Galaxy and other spirals. Aims: We test a standard chemical evolution model for spiral disks in the Local Universe and study the influence of a threshold gas density and different efficiencies in the star formation rate (SFR) law on radial gradients of abundance, gas, and SFR. The model is then applied to specific galaxies. Methods: We adopt a one-infall chemical evolution model where the Galactic disk forms inside-out by means of infall of gas, and we test different thresholds and efficiencies in the SFR. The model is scaled to the disk properties of three Local Group galaxies (the Milky Way, M 31 and M 33) by varying its dependence on the star formation efficiency and the timescale for the infall of gas onto the disk. Results: Using this simple model, we are able to reproduce most of the observed constraints available in the literature for the studied galaxies. The radial oxygen abundance gradients and their time evolution are studied in detail. The present day abundance gradients are more sensitive to the threshold than to other parameters, while their temporal evolutions are more dependent on the chosen SFR efficiency. A variable efficiency along the galaxy radius can reproduce the present day gas distribution in the disk of spirals with prominent arms. The steepness in the distribution of stellar surface density differs from massive to lower mass disks, owing to the different star formation histories. Conclusions: The most massive disks seem to have evolved faster (i.e., with more efficient star formation) than the less massive ones, thus suggesting a downsizing in star formation for spirals. The threshold and the efficiency of star formation play a very important role in the

  18. On the Chemical Evolution of the Impact-Generated Protolunar Disk

    NASA Astrophysics Data System (ADS)

    Brugger, B.; Mousis, O.; Charnoz, S.; Ali-Dib, M.

    2014-04-01

    The giant impact theory suggests that the Moon was formed from a silicate disk resulting from the collision between the young Earth and a Mars-sized body. Here, we investigated the chemical composition of the two-phase silicate disk consisting of a melt layer surrounded by a vapor atmosphere. To do so, we used the disk's thermodynamic properties and the same number of elements (O, Na, Mg, Al, Si, K, Ca, Ti, Fe, and Zn) as those proposed by [1]. In order to compute the disk's equilibrium composition, we utilized the commercial software HSC Chemistry, which is widely used in the fields of geophysics and planetary science. When comparing our equilibrium calculations against those made by [1] with their own house code, we found that both sets of results are very close in the temperature range explored by these authors (1800-4200 K). Because recent models suggest that the silicate disk's temperature range could be more extended, we also investigated the disk's chemical composition in the 1000-4500 K range. We finally determined the partition of the elements found both in vapor and melt phases in this temperature range in order to trace back the evolution of volatiles and refractories throughout the disk.

  19. Effects of massive star radiation on circumstellar disks evolution in the Eagle Nebula

    NASA Astrophysics Data System (ADS)

    Guarcello, Mario

    2007-09-01

    We will determine the frequency of disk and disk-less stars in the outer regions (relatively poor of massive stars) of the young cluster NGC 6611, with the aim to study the effects of UV flux due to massive stars on the evolution of circumstellar disks around low mass stars. Our previous results for the central region of the cluster show that this effect may be present, but we need to observe stars at larger distance from massive stars. This cluster is particularly well suited for our study, thanks to the irregular spatial distribution of its OB stars. CHANDRA observations are crucial for identifying the disk-less population undetectable with other method.

  20. ON THE EVOLUTION OF THE CO SNOW LINE IN PROTOPLANETARY DISKS

    SciTech Connect

    Martin, Rebecca G.; Livio, Mario

    2014-03-10

    CO is thought to be a vital building block for prebiotic molecules that are necessary for life. Thus, understanding where CO existed in a solid phase within the solar nebula is important for understanding the origin of life. We model the evolution of the CO snow line in a protoplanetary disk. We find that the current observed location of the CO snow line in our solar system, and in the solar system analog TW Hydra, cannot be explained by a fully turbulent disk model. With time-dependent disk models we find that the inclusion of a dead zone (a region of low turbulence) can resolve this problem. Furthermore, we obtain a fully analytic solution for the CO snow line radius for late disk evolutionary times. This will be useful for future observational attempts to characterize the demographics and predict the composition and habitability of exoplanets.

  1. On the Evolution of the CO Snow Line in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Martin, Rebecca G.; Livio, Mario

    2014-03-01

    CO is thought to be a vital building block for prebiotic molecules that are necessary for life. Thus, understanding where CO existed in a solid phase within the solar nebula is important for understanding the origin of life. We model the evolution of the CO snow line in a protoplanetary disk. We find that the current observed location of the CO snow line in our solar system, and in the solar system analog TW Hydra, cannot be explained by a fully turbulent disk model. With time-dependent disk models we find that the inclusion of a dead zone (a region of low turbulence) can resolve this problem. Furthermore, we obtain a fully analytic solution for the CO snow line radius for late disk evolutionary times. This will be useful for future observational attempts to characterize the demographics and predict the composition and habitability of exoplanets.

  2. ON THE EVOLUTION AND SURVIVAL OF PROTOPLANETS EMBEDDED IN A PROTOPLANETARY DISK

    SciTech Connect

    Vazan, A.; Helled, R.

    2012-09-01

    We model the evolution of a Jupiter-mass protoplanet formed by the disk instability mechanism at various radial distances accounting for the presence of the disk. Using three different disk models, it is found that a newly formed Jupiter-mass protoplanet at a radial distance of {approx}<5-10 AU cannot undergo a dynamical collapse and evolve further to become a gravitational bound planet. We therefore conclude that giant planets, if formed by the gravitational instability mechanism, must form and remain at large radial distances during the first {approx}10{sup 5}-10{sup 6} years of their evolution. The minimum radial distances in which protoplanets of 1 Saturn-mass, 3 and 5 Jupiter-mass protoplanets can evolve using a disk model with M-dot = 10{sup -6} M{sub Sun} yr{sup -1} and {alpha} = 10{sup -2} are found to be 12, 9, and 7 AU, respectively. The effect of gas accretion on the planetary evolution of a Jupiter-mass protoplanet is also investigated. It is shown that gas accretion can shorten the pre-collapse timescale substantially. Our study suggests that the timescale of the pre-collapse stage does not only depend on the planetary mass, but is greatly affected by the presence of the disk and efficient gas accretion.

  3. Circumbinary dust disks - reconciling the theory of close binary evolution with observation

    NASA Astrophysics Data System (ADS)

    Brinkworth, Carolyn; Hoard, Donald; Marsh, Tom

    2008-03-01

    The evolution of all close binary systems is driven by the loss of angular momentum from the system. Standard theory invokes two mechanisms for this loss - gravitational radiation and magnetic braking - and forms the backbone of virtually all studies based on binary evolution rates. Recent studies, however, have shown that the extrapolations in which the standard theory is based are wrong, suggesting that the true evolutionary rate of binary systems should be 10 - 10000 slower than previously predicted. To confuse the matter further, observational studies show that binary systems are actually evolving around 1000 times faster than this revised theory suggests, leading to the speculation that there is another angular momentum loss mechanism at work. One of the more likely candidates is the presence of a cool, dusty disk around the binary, which drains angular momentum from the system via tidal coupling. We propose to combine a Spitzer search for circumbinary dust disks with results from an ongoing project to directly measure the evolutionary rates of a number of detached binary systems. By modelling these disks, we will be able to test for any correlation between disk mass and evolutionary rate, and test whether the presence of these dusty disks could finally bring the theory of close binary evolution into line with observation.

  4. Nature vs. Nurture: The influence of OB star environments on proto-planetary disk evolution.

    NASA Astrophysics Data System (ADS)

    Bouwman, Jeroen; Feigelson, Eric; Getman, Kostantin; Henning, Thomas; Lawson, Warrick; Linz, Hendrik; Luhman, Kevin; Roccatagliata, Veronica; Sicilia Aguilar, Aurora; Townsley, Leisa; Wang, Junfeng

    2006-05-01

    A natural approach for understanding the origin and diversity of planetary systems is to study the birth sites of planetary systems under varying environmental conditions. Dust grains in protoplanetary disks, the building blocks of planets, are structurally and chemically altered, and grow through coagulation into planetesimals. The disk geometry may change from a flaring to a more flattened structure, gaps may develop under the gravitational influence of protoplanets, and eventually the disk will dissipate, terminating the planet formation process. While the infrared properties of disks in quiet cloud environments have been extensively studied, investigations under the conditions of strong UV radiation and stellar winds in the proximity of OB stars have been limited. We propose a combined IRAC/IRS study of a large, well-defined and unbiased X-ray selected sample of pre-main-sequence stars in three OB associations: Pismis 24 in NGC 6357, NGC 2244 in the Rosette Nebula, and IC 1795 in the W3 complex. The samples are based on recent Chandra X-ray Observatory studies which reliably identify hundreds of cluster members and were carefully chosen to avoid high infrared nebular background. A new Chandra exposure of IC 1795 is requested, and an optical followup to characterise the host stars is planned. Modelling the Spitzer findings will provide the composition and size of dust present as well as the geometry, mass, and gaps in the global structure of the disk. As hundreds of cluster members will be covered with IRAC and dozens with IRS, good statistics on the disk evolution and dispersal as a function of location with respect to OB stars will be obtained. Comparison of disk properties within our sample and with existing Spitzer studies of quiescent star-forming regions should significantly advance the aim of characterising the influence of the environment on the evolution of protoplanetary disks. This effort relies on a powerful synergy between the Chandra and Spitzer

  5. Adaptive network dynamics and evolution of leadership in collective migration

    NASA Astrophysics Data System (ADS)

    Pais, Darren; Leonard, Naomi E.

    2014-01-01

    The evolution of leadership in migratory populations depends not only on costs and benefits of leadership investments but also on the opportunities for individuals to rely on cues from others through social interactions. We derive an analytically tractable adaptive dynamic network model of collective migration with fast timescale migration dynamics and slow timescale adaptive dynamics of individual leadership investment and social interaction. For large populations, our analysis of bifurcations with respect to investment cost explains the observed hysteretic effect associated with recovery of migration in fragmented environments. Further, we show a minimum connectivity threshold above which there is evolutionary branching into leader and follower populations. For small populations, we show how the topology of the underlying social interaction network influences the emergence and location of leaders in the adaptive system. Our model and analysis can be extended to study the dynamics of collective tracking or collective learning more generally. Thus, this work may inform the design of robotic networks where agents use decentralized strategies that balance direct environmental measurements with agent interactions.

  6. DISK EVOLUTION IN OB ASSOCIATIONS: DEEP SPITZER/IRAC OBSERVATIONS OF IC 1795

    SciTech Connect

    Roccatagliata, Veronica; Bouwman, Jeroen; Henning, Thomas; Gennaro, Mario; Sicilia-Aguilar, Aurora; Feigelson, Eric; Kim, Jinyoung Serena; Lawson, Warrick A.

    2011-06-01

    We present a deep Spitzer/Infrared Array Camera (IRAC) survey of the OB association IC 1795 carried out to investigate the evolution of protoplanetary disks in regions of massive star formation. Combining Spitzer/IRAC data with Chandra/Advanced CCD Imaging Spectrometer observations, we find 289 cluster members. An additional 340 sources with an infrared excess, but without X-ray counterpart, are classified as cluster member candidates. Both surveys are complete down to stellar masses of about 1 M{sub sun}. We present pre-main-sequence isochrones computed for the first time in the Spitzer/IRAC colors. The age of the cluster, determined via the location of the Class III sources in the [3.6]-[4.5]/[3.6] color-magnitude diagram, is in the range of 3-5 Myr. As theoretically expected, we do not find any systematic variation in the spatial distribution of disks within 0.6 pc of either O-type star in the association. However, the disk fraction in IC 1795 does depend on the stellar mass: sources with masses >2 M{sub sun} have a disk fraction of {approx}20%, while lower mass objects (2-0.8 M{sub sun}) have a disk fraction of {approx}50%. This implies that disks around massive stars have a shorter dissipation timescale.

  7. Chronology of star formation and disk evolution in the Eagle Nebula

    NASA Astrophysics Data System (ADS)

    Guarcello, M. G.; Micela, G.; Peres, G.; Prisinzano, L.; Sciortino, S.

    2010-10-01

    Context. Massive star-forming regions are characterized by intense ionizing fluxes, strong stellar winds and, occasionally, supernovae explosions, all of which have important effects on the surrounding media, on the star-formation process and on the evolution of young stars and their circumstellar disks. We present a multiband study of the massive young cluster NGC 6611 and its parental cloud (the Eagle Nebula) with the aim of studying how OB stars affect the early stellar evolution and the formation of other stars. Aims: We search for evidence of triggering of star formation by the massive stars inside NGC 6611 on a large spatial scale (~10 parsec) and ongoing disk photoevaporation in NGC 6611 and how its efficiency depends on the mass of the central stars. Methods: We assemble a multiband catalog of the Eagle Nebula with photometric data, ranging from B band to 8.0 μm, and X-ray data obtained with two new and one archival Chandra/ACIS-I observation. We select the stars with disks from infrared photometry and disk-less ones from X-ray emission, which are associated both with NGC 6611 and the outer region of the Eagle Nebula. We study induced photoevaporation searching for the spatial variation of disk frequency for distinct stellar mass ranges. The triggering of star formation by OB stars has been investigated by deriving the history of star formation across the nebula. Results: We find evidence of sequential star formation in the Eagle Nebula going from the southeast (2.6 Myears) to the northwest (0.3 Myears), with the median age of NGC 6611 members ~1 Myear. In NGC 6611, we observe a drop of the disk frequency close to massive stars (up to an average distance of 1 parsec), without observable effects at larger distances. Furthermore, disks are more frequent around low-mass stars (≤ 1 M⊙) than around high-mass stars, regardless of the distance from OB stars. Conclusions: The star-formation chronology we find in the Eagle Nebula does not support the hypothesis

  8. The co-evolution of spiral structure and mass distribution in disk galaxies

    NASA Astrophysics Data System (ADS)

    Seigar, Marc

    2005-07-01

    We propose to use a new diagnostic tool to study the mass buildup in disk galaxies as a function of look-back time out to z 1. The tight correlation between spiral arm pitch angle and rotation curve shear rate {Seigar et al. 2005} demonstrates that the tightness of spiral structure in disk galaxies depends on the central mass concentration {including dark matter}, as this determines the shear rate. Galaxies with high central mass concentration have a higher shear rate and more tightly wound spiral structure than those with low mass concentration. As a result, the evolution of spiral structure over time can be used to search for evolution in the mass distribution in spiral galaxies. The main goal of this project is to determine evolution in the mass distribution of disk galaxies, using spiral arm pitch angles as a quanitative indicator. In order to do this we will use nearly face-on disk galaxies with measurable spiral structure, observed in the GOODS fields.

  9. Dynamic-chemical evolution of the early protoplanetary disk and chemical diversity of asteroids

    NASA Astrophysics Data System (ADS)

    Nagahara, Hiroko

    2015-08-01

    Evolution of a protoplanetary disk is dynamic, where angular momentum is transported outward whereas masses are inward. Although the overall material transport is inward, a significant amount of outward transporation occurs due to diffusion, which resulted in mixing of materials with different degree of thermal processing.In the present study, we investigate the mixing of materials in a protoplanetary disk by combining fluid dynamics and themodynamics, and discuss the chemical evolution of the disk as a function of time and space and the conditions to generate chemical heterogeneity in the 2-4 AU within 106 years.The essence of the model is of a standard disk evolution model, which is combined with particle tracking model by Ciesla (2010). It enables us to track all the movement of individual particles. The chemical composition of dust particles is assumed with chemical equilibrium calculation. Summing up the number of grains with different chemical compositions, we trace the temporal and spatial change of chemical composition of the disk.The results show that some fraction of dust grains were transported to ~13AU after 105 years, ~50 AU after 5x105 years, and ~100 AU after a million years, though the most of them were fallen into the proto-sun. The flux of inward and outward dust transportation is significant within 105 years. The chemical composition of the disk is relatively enriched in refractory elements due to the outward transport of significant amounts of grains heated to high temperatures, and more heterogeneous at the early stage due to various degree of mixing of high temperature and low temperature components. It becomes homogeneous with unfractionated composition with time.Carbonaceous chondrites are thought to be fragments of asteroids, which are remnants of planetesimals. The chemical composition of carbonaceous chondrites are successfully reproduced with the present model, but only at the early stage of disk evolution (<105 years) unless the disk

  10. SATURATED TORQUE FORMULA FOR PLANETARY MIGRATION IN VISCOUS DISKS WITH THERMAL DIFFUSION: RECIPE FOR PROTOPLANET POPULATION SYNTHESIS

    SciTech Connect

    Masset, F. S.; Casoli, J. E-mail: jules.casoli@cea.f

    2010-11-10

    We provide torque formulae for low-mass planets undergoing type I migration in gaseous disks. These torque formulae put special emphasis on the horseshoe drag, which is prone to saturation: the asymptotic value reached by the horseshoe drag depends on a balance between coorbital dynamics (which tends to cancel out or saturate the torque) and diffusive processes (which tend to restore the unperturbed disk profiles, thereby desaturating the torque). We entertain the question of this asymptotic value and derive torque formulae that give the total torque as a function of the disk's viscosity and thermal diffusivity. The horseshoe drag features two components: one that scales with the vortensity gradient and another that scales with the entropy gradient and constitutes the most promising candidate for halting inward type I migration. Our analysis, which is complemented by numerical simulations, recovers characteristics already noted by numericists, namely, that the viscous timescale across the horseshoe region must be shorter than the libration time in order to avoid saturation and that, provided this condition is satisfied, the entropy-related part of the horseshoe drag remains large if the thermal timescale is shorter than the libration time. Side results include a study of the Lindblad torque as a function of thermal diffusivity and a contribution to the corotation torque arising from vortensity viscously created at the contact discontinuities that appear at the horseshoe separatrices. For the convenience of the reader mostly interested in the torque formulae, Section 8 is self-contained.

  11. Coupling protoplanetary disk formation with early protostellar evolution: influence on planet traps

    NASA Astrophysics Data System (ADS)

    Baillie, Kevin; Piau, Laurent

    2016-10-01

    Protoplanetary disk structures are known to be shaped by various thermal and compositional effects such as (though not limited to) shadowed regions, sublimation lines, density bumps... The resulting irregularities in the surface mass density and temperature profiles are key elements to determine the location where planetary embryos can be trapped. These traps provide hints of which planets are most likely to survive, at what distance from the star, and potentially with what composition (Baillié, Charnoz, Pantin, 2015, A&A 577, A65; Baillié, Charnoz, Pantin, 2016, A&A 590, A60). These structures are determined by the viscous spreading of the disk, that is initially formed by the collapse of the molecular cloud.Starting from the numerical hydrodynamical model detailed in Baillié & Charnoz., 2014, ApJ 786, 35 which couples the disk thermodynamics, its photosphere geometry, its dynamics and its dust composition in order to follow its long-term evolution, we now consider the early stages of the central star. We model the joint formation of the disk and the star: their mass are directly derived from the collapse of the molecular cloud while the star temperature, radius and brightness are interpolated over pre-calculated stellar evolutions. Therefore, our simulations no longer depend on the initial profile of the "Minimum Mass Solar Nebula", and allow us to model the influence of the forming star on the protoplanetary disk. In particular, we will present the resulting distribution of the sublimation lines of the main dust species, as well as the locations of the planet traps at various disk ages. In the longer term, we intend to investigate the influence of the star properties on the selection of the surviving planets.

  12. The Minimum-Mass Surface Density of the Solar Nebula using the Disk Evolution Equation

    NASA Technical Reports Server (NTRS)

    Davis, Sanford S.

    2005-01-01

    The Hayashi minimum-mass power law representation of the pre-solar nebula (Hayashi 1981, Prog. Theo. Phys.70,35) is revisited using analytic solutions of the disk evolution equation. A new cumulative-planetary-mass-model (an integrated form of the surface density) is shown to predict a smoother surface density compared with methods based on direct estimates of surface density from planetary data. First, a best-fit transcendental function is applied directly to the cumulative planetary mass data with the surface density obtained by direct differentiation. Next a solution to the time-dependent disk evolution equation is parametrically adapted to the planetary data. The latter model indicates a decay rate of r -1/2 in the inner disk followed by a rapid decay which results in a sharper outer boundary than predicted by the minimum mass model. The model is shown to be a good approximation to the finite-size early Solar Nebula and by extension to extra solar protoplanetary disks.

  13. Community Evolution in International Migration Top1 Networks.

    PubMed

    Peres, Mihaela; Xu, Helian; Wu, Gang

    2016-01-01

    Focusing on each country's topmost destination/origin migration relation with other countries, this study builds top1 destination networks and top1 origin networks in order to understand their skeletal construction and community dynamics. Each top1 network covers approximately 50% of the complete migrant network stock for each decade between 1960 and 2000. We investigate the community structure by implementing the Girvan-Newman algorithm and compare the number of components and communities to illustrate their differences. We find that (i) both top1 networks (origin and destination) exhibited communities with a clear structure and a surprising evolution, although 80% edges persist between each decade; (ii) top1 destination networks focused on developed countries exhibiting shorter paths and preferring more advance countries, while top1 origin networks focused both on developed as well as more substantial developing nations that presented a longer path and more stable groups; (iii) only few countries have a decisive influence on community evolution of both top1 networks. USA took the leading position as a destination country in top1 destination networks, while China and India were the main Asian emigration countries in top1 origin networks; European countries and the Russian Federation played an important role in both. PMID:26859406

  14. Community Evolution in International Migration Top1 Networks.

    PubMed

    Peres, Mihaela; Xu, Helian; Wu, Gang

    2016-01-01

    Focusing on each country's topmost destination/origin migration relation with other countries, this study builds top1 destination networks and top1 origin networks in order to understand their skeletal construction and community dynamics. Each top1 network covers approximately 50% of the complete migrant network stock for each decade between 1960 and 2000. We investigate the community structure by implementing the Girvan-Newman algorithm and compare the number of components and communities to illustrate their differences. We find that (i) both top1 networks (origin and destination) exhibited communities with a clear structure and a surprising evolution, although 80% edges persist between each decade; (ii) top1 destination networks focused on developed countries exhibiting shorter paths and preferring more advance countries, while top1 origin networks focused both on developed as well as more substantial developing nations that presented a longer path and more stable groups; (iii) only few countries have a decisive influence on community evolution of both top1 networks. USA took the leading position as a destination country in top1 destination networks, while China and India were the main Asian emigration countries in top1 origin networks; European countries and the Russian Federation played an important role in both.

  15. Community Evolution in International Migration Top1 Networks

    PubMed Central

    Xu, Helian

    2016-01-01

    Focusing on each country’s topmost destination/origin migration relation with other countries, this study builds top1 destination networks and top1 origin networks in order to understand their skeletal construction and community dynamics. Each top1 network covers approximately 50% of the complete migrant network stock for each decade between 1960 and 2000. We investigate the community structure by implementing the Girvan-Newman algorithm and compare the number of components and communities to illustrate their differences. We find that (i) both top1 networks (origin and destination) exhibited communities with a clear structure and a surprising evolution, although 80% edges persist between each decade; (ii) top1 destination networks focused on developed countries exhibiting shorter paths and preferring more advance countries, while top1 origin networks focused both on developed as well as more substantial developing nations that presented a longer path and more stable groups; (iii) only few countries have a decisive influence on community evolution of both top1 networks. USA took the leading position as a destination country in top1 destination networks, while China and India were the main Asian emigration countries in top1 origin networks; European countries and the Russian Federation played an important role in both. PMID:26859406

  16. IMPACT OF GRAIN EVOLUTION ON THE CHEMICAL STRUCTURE OF PROTOPLANETARY DISKS

    SciTech Connect

    Vasyunin, A. I.; Birnstiel, T.; Zhukovska, S.; Henning, T.; Dullemond, C. P.; Wiebe, D. S. E-mail: zhukovska@mpia.de E-mail: dullemon@mpia.de E-mail: dwiebe@inasan.ru

    2011-02-01

    We study the impact of dust evolution in a protoplanetary disk (PPD) around a T Tauri star on the disk's chemical composition. For the first time, we utilize a comprehensive model of dust evolution, which includes growth, fragmentation, and sedimentation. Specific attention is paid to the influence of grain evolution on the penetration of the UV field in the disk. A chemical model that includes a comprehensive set of gas-phase and grain-surface chemical reactions is used to simulate the chemical structure of the disk. The main effect of grain evolution on the disk's chemical composition comes from sedimentation and, to a lesser degree, from reduction of the total grain-surface area. The net effect of grain growth is suppressed by the fragmentation process which maintains a population of small grains, dominating the total grain surface area. We consider three models of dust properties. In model GS, both growth and sedimentation are taken into account. In models A5 and A4, all grains are assumed to be the same size (10{sup -5} cm and 10{sup -4} cm, respectively) with a constant gas-to-dust mass ratio of 100. As in previous studies, the 'three-layer' pattern (cold midplane, warm molecular layer, and hot atmosphere) in the disk-chemical structure is preserved in all models, but shifted closer to the midplane in models with increased grain size (GS and A4). Unlike other similar studies, we find that in models GS and A4, the column densities of most gas-phase species are enhanced by 1-3 orders of magnitude relative to those in a model with pristine dust (A5), while column densities of their surface counterparts are decreased. We show that column densities of certain species, such as C{sub 2}H, HC{sub 2n+1}N (n = 0-3), H{sub 2}O, and some other molecules, as well as the C{sub 2}H{sub 2}/HCN abundance ratio, all of which are accessible with Herschel and ALMA, can be used as observational tracers of early stages of the grain evolution process in PPDs.

  17. The Evolution of the Number Density of Large Disk Galaxies in COSMOS

    NASA Astrophysics Data System (ADS)

    Sargent, M. T.; Carollo, C. M.; Lilly, S. J.; Scarlata, C.; Feldmann, R.; Kampczyk, P.; Koekemoer, A. M.; Scoville, N.; Kneib, J.-P.; Leauthaud, A.; Massey, R.; Rhodes, J.; Tasca, L. A. M.; Capak, P.; McCracken, H. J.; Porciani, C.; Renzini, A.; Taniguchi, Y.; Thompson, D. J.; Sheth, K.

    2007-09-01

    We study a sample of approximately 16,500 galaxies with IACS,AB<=22.5 in the central 38% of the COSMOS field, which are extracted from a catalog constructed from the Cycle 12 ACS F814W COSMOS data set. Structural information on the galaxies is derived by fitting single Sérsic models to their two-dimensional surface brightness distributions. In this paper we focus on the disk galaxy population (as classified by the Zurich Estimator of Structural Types), and investigate the evolution of the number density of disk galaxies larger than approximately 5 kpc between redshift z~1 and the present epoch. Specifically, we use the measurements of the half-light radii derived from the Sérsic fits to construct, as a function of redshift, the size function Φ(r1/2, z) of both the total disk galaxy population and of disk galaxies split in four bins of bulge-to-disk ratio. In each redshift bin, the size function specifies the number of galaxies per unit comoving volume and per unit half-light radius r1/2. Furthermore, we use a selected sample of roughly 1800 SDSS galaxies to calibrate our results with respect to the local universe. We find the following: (1) The number density of disk galaxies with intermediate sizes (r1/2~5-7 kpc) remains nearly constant from z~1 to today. Unless the growth and destruction of such systems exactly balanced in the last eight billion years, they must have neither grown nor been destroyed over this period. (2) The number density of the largest disks (r1/2>7 kpc) decreases by a factor of about 2 out to z~1. (3) There is a constancy-or even slight increase-in the number density of large bulgeless disks out to z~1 the deficit of large disks at early epochs seems to arise from a smaller number of bulged disks. Our results indicate that the bulk of the large disk galaxy population has completed its growth by z~1 and support the theory that secular evolution processes produce-or at least add stellar mass to-the bulge components of disk galaxies. Based on

  18. THE WELL-ALIGNED ORBIT OF WASP-84b: EVIDENCE FOR DISK MIGRATION OF A HOT JUPITER

    SciTech Connect

    Anderson, D. R.; Triaud, A. H. M. J.; Turner, O. D.; Brown, D. J. A.; Clark, B. J. M.; Smalley, B.; Cameron, A. Collier; Doyle, A. P.; Gillon, M.; Hellier, C.; Lovis, C.; Maxted, P. F. L.; Pollacco, D.; Queloz, D.; Smith, A. M. S.

    2015-02-10

    We report the sky-projected orbital obliquity (spin–orbit angle) of WASP-84 b, a 0.69M{sub Jup} planet in an 8.52 day orbit around a G9V/K0V star, to be λ = −0.3 ± 1.7°. We obtain a true obliquity of ψ = 17.3 ± 7.7° from a measurement of the inclination of the stellar spin axis with respect to the sky plane. Due to the young age and the weak tidal forcing of the system, we suggest that the orbit of WASP-84b is unlikely to have both realigned and circularized from the misaligned and/or eccentric orbit likely to have arisen from high-eccentricity migration. Therefore we conclude that the planet probably migrated via interaction with the protoplanetary disk. This would make it the first “hot Jupiter” (P<10 d) to have been shown to have migrated via this pathway. Further, we argue that the distribution of obliquities for planets orbiting cool stars (T{sub eff} < 6250 K) suggests that high-eccentricity migration is an important pathway for the formation of short-orbit, giant planets.

  19. Stellar evolution in N-body simulations of disk galaxies. I

    NASA Technical Reports Server (NTRS)

    Comins, N. F.

    1983-01-01

    The Kalnajs (1972, 1976) Omega models of global mass and velocity distributions are employed in the present two-dimensional N-body simulation, which allows for a spectrum of particle masses, stellar explosions, explosion remnant interactions with an interstellar medium, and the creation of new stars from the gas. Two sequences of runs using the Omega values of 0.8 and 0.9 examine the separate and combined effects of particle mass distribution, the gravitational influence of an interstellar gas distribution on the N-body particles, and stellar evolution, allowing for stellar explosions and star formation from the gas. It is found that both Omega values' nonequilibrium results dramatically change when evolution is allowed to occur. These results call for more realistic coupled N-body and evolution simulations in order to improve the understanding of disk galaxy evolution.

  20. Modelling circumbinary protoplanetary disks. II. Gas disk feedback on planetesimal dynamical and collisional evolution in the circumbinary systems Kepler-16 and 34

    NASA Astrophysics Data System (ADS)

    Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.

    2016-05-01

    Aims: We investigate the feasibility of planetesimal growth in circumbinary protoplanetary disks around the observed systems Kepler-16 and Kepler-34 under the gravitational influence of a precessing eccentric gas disk. Methods: We embed the results of our previous hydrodynamical simulations of protoplanetary disks around binaries into an N-body code to perform 3D, high-resolution, inter-particle gravity-enabled simulations of planetesimal growth and dynamics that include the gravitational force imparted by the gas. Results: Including the full, precessing asymmetric gas disk generates high eccentricity orbits for planetesimals orbiting at the edge of the circumbinary cavity, where the gas surface density and eccentricity have their largest values. The gas disk is able to efficiently align planetesimal pericenters in some regions leading to phased, non-interacting orbits. Outside of these areas eccentric planetesimal orbits become misaligned and overlap leading to crossing orbits and high relative velocities during planetesimal collisions. This can lead to an increase in the number of erosive collisions that far outweighs the number of collisions that result in growth. Gravitational focusing from the static axisymmetric gas disk is weak and does not significantly alter collision outcomes from the gas free case. Conclusions: Due to asymmetries in the gas disk, planetesimals are strongly perturbed onto highly eccentric orbits. Where planetesimals orbits are not well aligned, orbit crossings lead to an increase in the number of erosive collisions. This makes it difficult for sustained planetesimal accretion to occur at the location of Kepler-16b and Kepler-34b and we therefore rule out in situ growth. This adds further support to our initial suggestions that most circumbinary planets should form further out in the disk and migrate inwards.

  1. WITNESSING THE DIFFERENTIAL EVOLUTION OF DISK GALAXIES IN LUMINOSITY AND SIZE VIA GRAVITATIONAL LENSING

    SciTech Connect

    Bandara, Kaushala; Crampton, David; Peng, Chien; Simard, Luc

    2013-11-01

    We take advantage of the magnification in size and flux of a galaxy provided by gravitational lensing to analyze the properties of 62 strongly lensed galaxies from the Sloan Lens ACS (SLACS) Survey. The sample of lensed galaxies spans a redshift range of 0.20 ≤ z ≤ 1.20 with a median redshift of z = 0.61. We use the lens modeling code LENSFIT to derive the luminosities, sizes, and Sérsic indices of the lensed galaxies. The measured properties of the lensed galaxies show a primarily compact, {sup d}isk{sup -}like population with the peaks of the size and Sérsic index distributions corresponding to ∼1.50 kpc and n ∼ 1, respectively. Comparison of the SLACS galaxies to a non-lensing, broadband imaging survey shows that a lensing survey allows us to probe a galaxy population that reaches ∼2 mag fainter. Our analysis allows us to compare the (z) = 0.61 disk galaxy sample (n ≤ 2.5) to an unprecedented local galaxy sample of ∼670, 000 SDSS galaxies at z ∼ 0.1; this analysis indicates that the evolution of the luminosity-size relation since z ∼ 1 may not be fully explained by a pure-size or pure-luminosity evolution but may instead require a combination of both. Our observations are also in agreement with recent numerical simulations of disk galaxies that show evidence of a mass-dependent evolution since z ∼ 1, where high-mass disk galaxies (M{sub *} > 10{sup 9} M{sub ☉}) evolve more in size and low-mass disk galaxies (M{sub *} ≤ 10{sup 9} M{sub ☉}) evolve more in luminosity.

  2. 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

  3. THE EVOLUTION OF STELLAR POPULATIONS IN THE OUTER DISKS OF SPIRAL GALAXIES

    SciTech Connect

    Alberts, Stacey; Calzetti, Daniela; Dong Hui; Johnson, L. C.; Dale, Daniel A.; Bianchi, Luciana; Thilker, David; Chandar, Rupali; Kennicutt, Robert C.; Meurer, Gerhardt R.; Regan, Michael

    2011-04-10

    We investigate recent star formation in the extended ultraviolet (XUV) disks of five nearby galaxies (NGC 0628, NGC 2090, NGC 2841, NGC 3621, and NGC 5055) using a long wavelength baseline comprised of ultraviolet and mid-infrared imaging from the Galaxy Evolution Explorer and the Spitzer Infrared Array Camera. We identify 229 unresolved stellar complexes across targeted portions of their XUV disks and utilize spectral energy distribution fitting to measure their stellar ages and masses through comparison with Starburst99 population synthesis models of instantaneous burst populations. We find that the median age of outer-disk associations in our sample is {approx}100 Myr with a large dispersion that spans the entire range of our models (1 Myr to 1 Gyr). This relatively evolved state for most associations addresses the observed dearth of H{alpha} emission in some outer disks, as H{alpha} can only be observed in star-forming regions younger than {approx}10 Myr. The large age dispersion is robust against variations in extinction (in the range E(B - V) = 0-0.3 mag) and variations in the upper end of the stellar initial mass function (IMF). In particular, we demonstrate that the age dispersion is insensitive to steepening of the IMF, up to extreme slopes.

  4. ELECTROSTATIC BARRIER AGAINST DUST GROWTH IN PROTOPLANETARY DISKS. I. CLASSIFYING THE EVOLUTION OF SIZE DISTRIBUTION

    SciTech Connect

    Okuzumi, Satoshi; Sakagami, Masa-aki; Tanaka, Hidekazu; Takeuchi, Taku

    2011-04-20

    Collisional growth of submicron-sized dust grains into macroscopic aggregates is the first step of planet formation in protoplanetary disks. These grains are expected to carry nonzero negative charges in the weakly ionized disks, but its effect on their collisional growth has not been fully understood so far. In this paper, we investigate how the charging affects the evolution of the dust size distribution properly taking into account the charging mechanism in a weakly ionized gas as well as porosity evolution through low-energy collisions. To clarify the role of the size distribution, we divide our analysis into two steps. First, we analyze the collisional growth of charged aggregates assuming a monodisperse (i.e., narrow) size distribution. We show that the monodisperse growth stalls due to the electrostatic repulsion when a certain condition is met, as was already expected in our previous work. Second, we numerically simulate dust coagulation using Smoluchowski's method to see how the outcome changes when the size distribution is allowed to freely evolve. We find that, under certain conditions, the dust undergoes bimodal growth where only a limited number of aggregates continue to grow, carrying a major part of the dust mass in the system. This occurs because remaining small aggregates efficiently sweep up free electrons to prevent the larger aggregates from being strongly charged. We obtain a set of simple criteria that allows us to predict how the size distribution evolves for a given condition. In Paper II, we apply these criteria to dust growth in protoplanetary disks.

  5. Open Cluster Neutron Capture Element Abundances and Milky Way Disk Evolution

    NASA Astrophysics Data System (ADS)

    Jacobson, Heather R.; Friel, E. D.

    2012-01-01

    Open clusters, whose ages and distances can be precisely determined, are useful probes of the chemical evolution of the Milky Way disk. The sample sizes of clusters subject to homogeneous analysis of high resolution spectra have grown in recent years, and increased attention has turned to measuring the abundances of neutron capture elements. The relative abundances of r-process elements (e.g., europium) to s-process elements (e.g., barium, lanthanum and zirconium) in cluster stars reveal the relative contributions of Type II supernovae and low-mass AGB stars to the chemical evolution of the galactic disk. A recent study of cluster s-process element abundances has revealed a surprising trend of increasing s-process element abundance ([s/Fe]) with decreasing cluster age, at odds with current s-process yield predictions (D'Orazi et al. 2009, Maiorca et al. 2011). We have undertaken an analysis of Zr, Ba, La, and Eu abundances in 17 open clusters based on high resolution optical spectra. The sample spans 700 Myr to 10 Gyr in age and Rgc 7-22 kpc in galactocentric distance, allowing for the exploration of neutron capture [x/Fe] ratios as a function of age and location in the disk. Preliminary results confirm the trend of enhanced [s/Fe] with decreasing cluster age found by other studies, though with a weaker correlation. Here we present the latest results of this analysis, including newly-determined abundances for the r-process element Eu for an expanded cluster sample that includes outer disk objects. This research is supported by a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship to HRJ under award AST-0901919.

  6. Planet signatures and effect of the chemical evolution of the Galactic thin-disk stars

    NASA Astrophysics Data System (ADS)

    Spina, Lorenzo; Meléndez, Jorge; Ramírez, Ivan

    2016-01-01

    Context. Studies based on high-precision abundance determinations revealed that chemical patterns of solar twins are characterised by the correlation between the differential abundances relative to the Sun and the condensation temperatures (Tc) of the elements. It has been suggested that the origin of this relation is related to the chemical evolution of the Galactic disk, but other processes, associated with the presence of planets around stars, might also be involved. Aims: We analyse HIRES spectra of 14 solar twins and the Sun to provide new insights on the mechanisms that can determine the relation between [X/H] and Tc. Methods: Our spectroscopic analysis produced stellar parameters (Teff, log g, [Fe/H], and ξ), ages, masses, and abundances of 22 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, and Ba). We used these determinations to place new constraints on the chemical evolution of the Galactic disk and to verify whether this process alone can explain the different [X/H]-Tc slopes observed so far. Results: We confirm that the [X/Fe] ratios of all the species correlate with age. The slopes of these relations allow us to describe the effect that the chemical evolution of the Galactic disk has on the chemical patterns of the solar twins. After subtracting the chemical evolution effect, we find that the unevolved [X/H]-Tc slope values do not depend on the stellar ages anymore. However, the wide diversity among these [X/H]-Tc slopes, covering a range of ± 4 × 10-5 dex K-1, indicates that processes in addition to the chemical evolution may affect the [X/H]-Tc slopes. Conclusions: The wide range of unevolved [X/H]-Tc slope values spanned at all ages by our sample could reflect the wide diversity among exo-planetary systems observed so far and the variety of fates that the matter in circumstellar disks can experience.

  7. Migration and the evolution of sexual dichromatism: evolutionary loss of female coloration with migration among wood-warblers

    PubMed Central

    Simpson, Richard K.; Johnson, Michele A.; Murphy, Troy G.

    2015-01-01

    The mechanisms underlying evolutionary changes in sexual dimorphism have long been of interest to biologists. A striking gradient in sexual dichromatism exists among songbirds in North America, including the wood-warblers (Parulidae): males are generally more colourful than females at northern latitudes, while the sexes are similarly ornamented at lower latitudes. We use phylogenetically controlled comparative analysis to test three non-mutually exclusive hypotheses for the evolution of sexual dichromatism among wood-warblers. The first two hypotheses focus on the loss of female coloration with the evolution of migration, either owing to the costs imposed by visual predators during migration, or owing to the relaxation of selection for female social signalling at higher latitudes. The third hypothesis focuses on whether sexual dichromatism evolved owing to changes in male ornamentation as the strength of sexual selection increases with breeding latitude. To test these hypotheses, we compared sexual dichromatism to three variables: the presence of migration, migration distance, and breeding latitude. We found that the presence of migration and migration distance were both positively correlated with sexual dichromatism, but models including breeding latitude alone were not strongly supported. Ancestral state reconstruction supports the hypothesis that the ancestral wood-warblers were monochromatic, with both colourful males and females. Combined, these results are consistent with the hypotheses that the evolution of migration is associated with the relaxation of selection for social signalling among females and that there are increased predatory costs along longer migratory routes for colourful females. These results suggest that loss of female ornamentation can be a driver of sexual dichromatism and that social or natural selection may be a stronger contributor to variation in dichromatism than sexual selection. PMID:26019159

  8. Migration and the evolution of sexual dichromatism: evolutionary loss of female coloration with migration among wood-warblers.

    PubMed

    Simpson, Richard K; Johnson, Michele A; Murphy, Troy G

    2015-06-22

    The mechanisms underlying evolutionary changes in sexual dimorphism have long been of interest to biologists. A striking gradient in sexual dichromatism exists among songbirds in North America, including the wood-warblers (Parulidae): males are generally more colourful than females at northern latitudes, while the sexes are similarly ornamented at lower latitudes. We use phylogenetically controlled comparative analysis to test three non-mutually exclusive hypotheses for the evolution of sexual dichromatism among wood-warblers. The first two hypotheses focus on the loss of female coloration with the evolution of migration, either owing to the costs imposed by visual predators during migration, or owing to the relaxation of selection for female social signalling at higher latitudes. The third hypothesis focuses on whether sexual dichromatism evolved owing to changes in male ornamentation as the strength of sexual selection increases with breeding latitude. To test these hypotheses, we compared sexual dichromatism to three variables: the presence of migration, migration distance, and breeding latitude. We found that the presence of migration and migration distance were both positively correlated with sexual dichromatism, but models including breeding latitude alone were not strongly supported. Ancestral state reconstruction supports the hypothesis that the ancestral wood-warblers were monochromatic, with both colourful males and females. Combined, these results are consistent with the hypotheses that the evolution of migration is associated with the relaxation of selection for social signalling among females and that there are increased predatory costs along longer migratory routes for colourful females. These results suggest that loss of female ornamentation can be a driver of sexual dichromatism and that social or natural selection may be a stronger contributor to variation in dichromatism than sexual selection.

  9. The Gaia-ESO Survey: Separating disk chemical substructures with cluster models. Evidence of a separate evolution in the metal-poor thin disk

    NASA Astrophysics Data System (ADS)

    Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.

    2016-02-01

    Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC< 10 kpc) from the Gaia-ESO survey (GES) internal data release 2 (iDR2). We aim at decomposing it into data groups highlighting number density and/or slope variations in the abundance-metallicity plane. An independent sample of disk red clump stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) was used to cross-check the identified features. Results: We find that the sample is separated into five groups associated with major Galactic components; the metal-rich end of the halo, the thick disk, and three subgroups for the thin disk sequence. This is confirmed with the sample of red clump stars from APOGEE. The three thin disk groups served to explore this sequence in more detail. The two metal-intermediate and metal-rich groups of the thin disk decomposition ([Fe/H] > -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] < -0.25 dex) is shifted to larger distances than those of the more metal-rich parts. Moreover, the metal-poor part of the thin disk presents indications of a scale height

  10. ON THE HORSESHOE DRAG OF A LOW-MASS PLANET. I. MIGRATION IN ISOTHERMAL DISKS

    SciTech Connect

    Casoli, J.; Masset, F. S. E-mail: frederic.masset@cea.f

    2009-09-20

    We investigate the unsaturated horseshoe drag exerted on a low-mass planet by an isothermal gaseous disk. In the globally isothermal case, we use a formalism, based on the use of a Bernoulli invariant, that takes into account pressure effects, and that extends the torque estimate to a region wider than the horseshoe region. We find a result that is strictly identical to the standard horseshoe drag. This shows that the horseshoe drag accounts for the torque of the whole corotation region, and not only of the horseshoe region, thereby deserving to be called corotation torque. We find that evanescent waves launched downstream of the horseshoe U-turns by the perturbations of vortensity exert a feedback on the upstream region, that render the horseshoe region asymmetric. This asymmetry scales with the vortensity gradient and with the disk's aspect ratio. It does not depend on the planetary mass, and it does not have any impact on the horseshoe drag. Since the horseshoe drag has a steep dependence on the width of the horseshoe region, we provide an adequate definition of the width that needs to be used in horseshoe drag estimates. We then consider the case of locally isothermal disks, in which the temperature is constant in time but depends on the distance to the star. The horseshoe drag appears to be different from the case of a globally isothermal disk. The difference, which is due to the driving of vortensity in the vicinity of the planet, is intimately linked to the topology of the flow. We provide a descriptive interpretation of these effects, as well as a crude estimate of the dependency of the excess on the temperature gradient.

  11. Propeller peregrinations: Ongoing observations of disk-embedded migration in Saturn's rings

    NASA Astrophysics Data System (ADS)

    Tiscareno, Matthew S.; Cassini Imaging Team

    2016-10-01

    The "propeller" moons within Saturn's rings are the first objects ever to have their orbits tracked while embedded in a disk, rather than moving through empty space (Tiscareno et al. 2010, ApJL). The km-sized "giant propellers" whose orbits have been tracked in the outer-A ring, as well as their smaller 0.1-km-sized brethren swarming in the mid-A ring, are not seen directly; rather, their locations are inferred by means of the propeller-shaped disturbances they create in the surrounding ring material (Tiscareno et al. 2006, Nature; Sremcevic et al. 2007, Nature; Tiscareno et al. 2008, AJ). The orbits of giant propellers are primarily Keplerian, but with clear excursions of up to several degrees longitude over a decade of observations. Most theories that have been proposed to explain the non-Keplerian motion of propeller moons (e.g., Pan et al. 2012, MNRAS; Tiscareno 2013, P&SS) rely on gravitational and/or collisional interactions between the moon and the surrounding disk, and thus hold out the prospect for directly observing processes that are important in protoplanetary scenarios and other disk systems. We will review the current dynamical models and report on recent ongoing observations by the Cassini imaging camera.

  12. Propeller peregrinations: Ongoing observations of disk-embedded migration in Saturn’s rings

    NASA Astrophysics Data System (ADS)

    Tiscareno, Matthew S.

    2016-05-01

    The "propeller" moons within Saturn's rings are the first objects ever to have their orbits tracked while embedded in a disk, rather than moving through empty space (Tiscareno et al. 2010, ApJL). The km-sized "giant propellers" whose orbits have been tracked in the outer-A ring, as well as their smaller 0.1-km-sized brethren swarming in the mid-A ring, are not seen directly; rather, their locations are inferred by means of the propeller-shaped disturbances they create in the surrounding ring material (Tiscareno et al. 2006, Nature; Sremcevic et al. 2007, Nature; Tiscareno et al. 2008, AJ). The orbits of giant propellers are primarily Keplerian, but with clear excursions of up to several degrees longitude over a decade of observations. Most theories that have been proposed to explain the non-Keplerian motion of propeller moons (e.g., Pan et al. 2012, MNRAS; Tiscareno 2013, P&SS) rely on gravitational and/or collisional interactions between the moon and the surrounding disk, and thus hold out the prospect for directly observing processes that are important in protoplanetary scenarios and other disk systems. We will review the current dynamical models and report on recent ongoing observations by the Cassini imaging camera.

  13. Disk evolution, element abundances and cloud properties of young gas giant planets.

    PubMed

    Helling, Christiane; Woitke, Peter; Rimmer, Paul B; Kamp, Inga; Thi, Wing-Fai; Meijerink, Rowin

    2014-04-14

    We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. PRODIMO protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The DRIFT cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models.

  14. Disk Evolution, Element Abundances and Cloud Properties of Young Gas Giant Planets

    PubMed Central

    Helling, Christiane; Woitke, Peter; Rimmer, Paul B.; Kamp, Inga; Thi, Wing-Fai; Meijerink, Rowin

    2014-01-01

    We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. ProDiMo protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The Drift cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models. PMID:25370190

  15. Migratory Recovery from Infection as a Selective Pressure for the Evolution of Migration.

    PubMed

    Shaw, Allison K; Binning, Sandra A

    2016-04-01

    Migration, a widespread animal behavior, can influence how individuals acquire and transmit pathogens. Past work has demonstrated that migration can reduce the costs of pathogen or parasite infection through two processes: migratory escape from infected areas or individuals and migratory culling of infected individuals. Here, we propose a third process: migratory recovery, where infected individuals lose their parasites and recover from infection during migration. Recovery can occur when parasites and/or their intermediate hosts cannot support changes in the migratory host's internal or external environment during migration. Thus, parasite mortality increases with migration. Although migratory recovery is likely widespread across species, it remains challenging to empirically test it as a selective force promoting migration. We develop a model and determine the conditions under which migratory recovery theoretically favors the evolution of migration. We show that incorporating migratory recovery into a model of migratory escape increases the range of biologically realistic conditions favoring migration and leads to scenarios where partial migration can evolve. Motivated by empirical estimates of infection costs, our model shows how recovery from infection could drive the evolution of migration. We suggest a number of future directions for both theoretical and empirical research in this area.

  16. THE RISE AND FALL OF PASSIVE DISK GALAXIES: MORPHOLOGICAL EVOLUTION ALONG THE RED SEQUENCE REVEALED BY COSMOS

    SciTech Connect

    Bundy, Kevin; Hopkins, Philip; Ma, Chung-Pei; Scarlata, Claudia; Capak, Peter; Carollo, C. M.; Oesch, Pascal; Ellis, Richard S.; Salvato, Mara; Scoville, Nick; Drory, Niv; Leauthaud, Alexie; Koekemoer, Anton M.; Murray, Norman; Ilbert, Olivier; Pozzetti, Lucia

    2010-08-20

    The increasing abundance of passive 'red-sequence' galaxies since z {approx} 1-2 is mirrored by a coincident rise in the number of galaxies with spheroidal morphologies. In this paper, however, we show in detail, that, the correspondence between galaxy morphology and color is not perfect, providing insight into the physical origin of this evolution. Using the COSMOS survey, we study a significant population of red-sequence galaxies with disk-like morphologies. These passive disks typically have Sa-Sb morphological types with large bulges, but they are not confined to dense environments. They represent nearly one-half of all red-sequence galaxies and dominate at lower masses ({approx}<10{sup 10} M{sub sun}) where they are increasingly disk-dominated. As a function of time, the abundance of passive disks with M {sub *} {approx}< 10{sup 11} M{sub sun} increases, but not as fast as red-sequence spheroidals in the same mass range. At higher mass, the passive disk population has declined since z {approx} 1, likely because they transform into spheroidals. Based on these trends, we estimate that as much as 60% of galaxies transitioning onto the red sequence evolve through a passive disk phase. The origin of passive disks therefore has broad implications for our understanding of how star formation shuts down. Because passive disks tend to be more bulge-dominated than their star-forming counterparts, a simple fading of blue disks does not fully explain their origin. We explore the strengths and weaknesses of several more sophisticated explanations, including environmental effects, internal stabilization, and disk regrowth during gas-rich mergers. While previous work has sought to explain color and morphological transformations with a single process, these observations open the way to new insight by highlighting the fact that galaxy evolution may actually proceed through several separate stages.

  17. Insights into Planet Formation from Debris Disks: I. The Solar System as an Archetype for Planetesimal Evolution

    NASA Astrophysics Data System (ADS)

    Matthews, Brenda C.; Kavelaars, JJ

    2016-05-01

    Circumstellar disks have long been regarded as windows into planetary systems. The advent of high sensitivity, high resolution imaging in the submillimeter where both the solid and gas components of disks can be detected opens up new possibilities for understanding the dynamical histories of these systems and therefore, a better ability to place our own solar system, which hosts a highly evolved debris disk, in context. Comparisons of dust masses from protoplanetary and debris disks have revealed a stark downturn in mass in millimeter-sized grains around a stellar age of 10 Myr, ostensibly in the "transition disk" phase, suggesting a period of rapid accretion of such grains onto planetesimals. This rapid formation phase is in keeping with radionucleide studies of Kuiper Belt Objects in the solar system. Importantly, this suggests that any thermal gradients in the gas of disks of this era will be "frozen in" to the planetesimals as they rapidly accrete from the solids and ices in their vicinity. Measurements of radial gradients in thermal tracers such as DHO, DCN and other tracers can therefore provide insight into the nascent solar system's abundances. In studies of dynamical evolution of the solar system, it is tacitly assumed that such abundances can reveal the location of formation for bodies now found in the asteroid belt and Kuiper belt. Similarly, evidence of gas detected from collisional evolution in young debris disks could potentially reveal how rapidly objects have dynamically evolved in those systems, most of which will be significantly younger than the solar system.

  18. STRUCTURE AND EVOLUTION OF DEBRIS DISKS AROUND F-TYPE STARS. I. OBSERVATIONS, DATABASE, AND BASIC EVOLUTIONARY ASPECTS

    SciTech Connect

    Moor, A.; Abraham, P.; Kiss, L. L.; Kiss, Cs.; Pascucci, I.; Apai, D.; Kospal, A.; Csengeri, T.; Henning, Th.; Juhasz, A.; Bayliss, D.; Kovacs, J.; Szalai, T.

    2011-03-15

    Although photometric and spectroscopic surveys with the Spitzer Space Telescope remarkably increased the number of well-studied debris disks around A-type and Sun-like stars, detailed analyses of debris disks around F-type stars remained less frequent. Using the MIPS camera and the Infrared Spectrograph (IRS) spectrograph, we searched for debris dust around 82 F-type stars with Spitzer. We found 27 stars that harbor debris disks, nine of which are new discoveries. The dust distribution around two of our stars, HD 50571 and HD 170773, was found to be marginally extended on the 70 {mu}m MIPS images. Combining the MIPS and IRS measurements with additional infrared and submillimeter data, we achieved excellent spectral coverage for most of our debris systems. We have modeled the excess emission of 22 debris disks using a single temperature dust ring model and of five debris systems with two-temperature models. The latter systems may contain two dust rings around the star. In accordance with the expected trends, the fractional luminosity of the disks declines with time, exhibiting a decay rate consistent with the range of model predictions. We found the distribution of radial dust distances as a function of age to be consistent with the predictions of both the self-stirred and the planetary-stirred disk evolution models. A more comprehensive investigation of the evolution of debris disks around F-type stars, partly based on the presented data set, will be the subject of an upcoming paper.

  19. The Properties of Local Barred Disks in the Field and Dense Environments: Implications for Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Marinova, I.; Jogee, S.; Barazza, F. D.; Heiderman, A.; Gray, M. E.; Barden, M.; Wolf, C.; Peng, C. Y.; Bacon, D.; Balogh, M.; Bell, E. F.; Böhm, A.; Caldwell, J. A. R.; Häußler, B.; Heymans, C.; Jahnke, K.; van Kampen, E.; Lane, K.; McIntosh, D. H.; Meisenheimer, K.; Sánchez, S. F.; Sommerville, R. S.; Taylor, A.; Wisotzki, L.; Zheng, X.

    2009-12-01

    Stellar bars are the most efficient internal drivers of disk evolution because they redistribute material and angular momentum within the galaxy and dark matter halo. Mounting evidence suggests that processes other than major mergers, such as minor mergers, secular processes driven by bars, and clump coalescence, as well as smooth accretion, play an important role in galaxy evolution since z = 2. As a key step toward characterizing this evolution and constraining theoretical models, we determine the frequency and properties of bars in the local Universe in both field and cluster environment, based on three of our studies: Marinova & Jogee (2007), Barazza, Jogee, & Marinova (2008) and Marinova et al. (2009). Among field spirals of intermediate Hubble types in the OSU survey, we find using ellipse fitting that the bar fraction is 44% in the optical and 60% in the NIR, giving an extinction correction factor of approximately 1.4 at z ˜ 0. Using data from the Abell 901/902 cluster system at z ˜ 0.165 from the HST ACS survey STAGES, we find that the optical bar fraction is a strong trend of both absolute magnitude and host bulge-to-total ratio, increasing for galaxies that are brighter and/or more disk-dominated. The latter trend is also found in the field from SDSS. For bright early types and faint late types the optical bar fraction in the cluster is similar to that in the field. We find that between the core region and the virial radii of the clusters the optical bar fraction is not a strong function of local environment density. We discuss the implications of our results in the context of theoretical models of the impact of bars on galaxy evolution.

  20. Chemo-Dynamical Evolution of Disk Galaxies, Smoothed Particles Hydrodynamics Approach

    NASA Astrophysics Data System (ADS)

    Berczik, P.

    In this paper I present, the new Chemo-Dynamical code, incorporated to the standard Smoothed Particle Hydrodynamics (CD-SPH). This code used to modelling the complex evolution of disk galaxy systems. The more detailed description of SPH code and the Star Formation (SF) and Super Novae (SN) algorithms you can find in our earlier work Berczik P. & Kravchuk S.G., 1996, ApSpSci, 245, 27. The galaxy presented via tree component system. The Dark Matter Halo described as an external gravitational potential with distribution of Dark Matter density (Burkert A. 1995, ApJ, 447, L25): ρDM (r) = frac ρ0 (1 + r / r0) cdot (1 + r / r0)2. The total mass of Dark Matter Halo is 1012 Modot. The second component is a hot coronal gas, with Thot ~106 K. This component presented as a uniformly distributed SPH gas with initial solid body rotation and with additisional random velocity component Δ V ~100 km/sec. The total mass of this component is 5 cdot 1010 Modot. The last component is a cold gas (Tcold ~104 K). This component presented also as a uniformly distributed SPH gas with initial solid body rotation and with additional random velocity component Δ V ~10 km/sec. The total mass of this component also is 5 cdot 1010 Modot. In the paper presented a more complex and may be more realistic incorporation of SF & SN in the SPH code. The presented calculation is clearly show, what the some interestiong and important properties of isolated disk galaxies we can explain using this simple, tree component "collapsing" model. In the frame of this approach we are able to reproduce the presently observed kinematics of star and gaseous components as well as their distributions and heavy element abundances. The developed model provide the realystic description of dynamics and chemical evolution of typical disk galaxies over the Hubble timescale.

  1. Global Evolution of Solid Matter in Turbulent Protoplanetry Disks. Part 1; Aerodynamics of Solid Particles

    NASA Technical Reports Server (NTRS)

    Stepinski, T. F.; Valageas, P.

    1996-01-01

    The problem of planetary system formation and its subsequent character can only be addressed by studying the global evolution of solid material entrained in gaseous protoplanetary disks. We start to investigate this problem by considering the space-time development of aerodynamic forces that cause solid particles to decouple from the gas. The aim of this work is to demonstrate that only the smallest particles are attached to the gas, or that the radial distribution of the solid matter has no momentary relation to the radial distribution of the gas. We present the illustrative example wherein a gaseous disk of 0.245 solar mass and angular momentum of 5.6 x 10(exp 52) g/sq cm/s is allowed to evolve due to turbulent viscosity characterized by either alpha = 10(exp -2) or alpha = 10(exp -3). The motion of solid particles suspended in a viscously evolving gaseous disk is calculated numerically for particles of different sizes. In addition we calculate the global evolution of single-sized, noncoagulating particles. We find that particles smaller than 0.1 cm move with the gas; larger particles have significant radial velocities relative to the gas. Particles larger than 0.1 cm but smaller than 10(exp 3) cm have inward radial velocities much larger than the gas, whereas particles larger than 10(exp 4) cm have inward velocities much smaller than the gas. A significant difference in the form of the radial distribution of solids and the gas develops with time. It is the radial distribution of solids, rather than the gas, that determines the character of an emerging planetary system.

  2. Evolution of second-generation stars in stellar disks of globular and nuclear clusters: ω Centauri as a test case

    SciTech Connect

    Mastrobuono-Battisti, Alessandra; Perets, Hagai B.

    2013-12-10

    Globular clusters (GCs) and many nuclear clusters (NCs) show evidence of hosting multiple generations of stellar populations. Younger stellar populations in NCs appear to reside in disk-like structures, including the NC in our own Galactic center as well as in M31. Kinematic studies of the anomalous GC ω Centauri, thought to possibly be a former dwarf galaxy (or a galactic nucleus), show evidence of hosting a central, kinematically cold disk component. These observations suggest that formation of second- (or multiple) generation stars may occur in flattened disk-like structures. Here, we use detailed N-body simulations to explore the possible evolution of such stellar disks embedded in GCs. We follow the long-term evolution of a disk-like structure similar to that observed in ω Centauri and study its properties. We find that a stellar-disk-like origin for second-generation stellar populations can leave behind significant kinematic signatures in properties of the clusters, including an anisotropic distribution and lower velocity dispersions, which can be used to constrain the origin of second-generations stars and their dynamical evolution.

  3. OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO

    SciTech Connect

    Ramirez, I.; Lambert, D. L.; Allende Prieto, C.

    2013-02-10

    Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777 nm O I triplet lines. We assign a kinematic probability for the stars to be thin-disk (P {sub 1}), thick-disk (P {sub 2}), and halo (P {sub 3}) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P {sub 2} > 0.5) relative to thin-disk (P {sub 1} > 0.5) stars with [Fe/H] {approx}< -0.2, as well as a 'knee' that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H] {approx}> -0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with 'intermediate' kinematics (P {sub 1} < 0.7, P {sub 2} < 0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P {sub 3} > 0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V < -200 km s{sup -1}; halo stars with V > -200 km s{sup -1} follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with 'ambiguous' kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.

  4. The Global Perspective on the Evolution of Solids in a Protoplanetary Disk

    NASA Technical Reports Server (NTRS)

    Stepinski, T. F.; Valageas, P.

    1996-01-01

    It is currently thought that planets around solar-type stars form by the accumulation of solid matter entrained in a gaseous, turbulent protoplanetary disk. We have developed a model designed to simulate the part of this process that starts from small particles suspended in the gaseous disk at the end of the formation stage, and ends up with most of the solid material aggregated into 1-10-km planetesimals. The major novelty of our approach is its emphasis on the global, comprehensive treatment of the problem, as our model simultaneously keeps track of the evolution of gas and solid particles due to gas-solid coupling, coagulation, sedimentation, and evaporation/condensation. The result of our calculations is the radial distribution of solid material circumnavigating a star in the form of a planetesimal swarm. Such a distribution should well approximate the radial apportionment of condensed components of the planets spread over the radial extent of the mature planetary system. Therefore we view our calculations as an attempt to predict the large-scale architecture of planetary systems and to assess their potential diversity. In particular, we have found that some initial conditions lead to all solids being lost to the star, but we can also identify initial conditions leading to a radial distribution of solid material quite reminiscent of what is found in our solar system.

  5. Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system's terrestrial planets

    NASA Astrophysics Data System (ADS)

    Ogihara, Masahiro; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Suzuki, Takeru K.

    2015-07-01

    Context. Recent three-dimensional magnetohydrodynamical simulations have identified a disk wind by which gas materials are lost from the surface of a protoplanetary disk, which can significantly alter the evolution of the inner disk and the formation of terrestrial planets. A simultaneous description of the realistic evolution of the gaseous and solid components in a disk may provide a clue for solving the problem of the mass concentration of the terrestrial planets in the solar system. Aims: We simulate the formation of terrestrial planets from planetary embryos in a disk that evolves via magnetorotational instability and a disk wind. The aim is to examine the effects of a disk wind on the orbital evolution and final configuration of planetary systems. Methods: We perform N-body simulations of sixty 0.1 Earth-mass embryos in an evolving disk. The evolution of the gas surface density of the disk is tracked by solving a one-dimensional diffusion equation with a sink term that accounts for the disk wind. Results: We find that even in the case of a weak disk wind, the radial slope of the gas surface density of the inner disk becomes shallower, which slows or halts the Type I migration of embryos. If the effect of the disk wind is strong, the disk profile is significantly altered (e.g., positive surface density gradient, inside-out evacuation), leading to outward migration of embryos inside ~1 AU. Conclusions: Disk winds play an essential role in terrestrial planet formation inside a few AU by changing the disk profile. In addition, embryos can undergo convergent migration to ~1 AU in certainly probable conditions. In such a case, the characteristic features of the solar system's terrestrial planets (e.g., mass concentration around 1 AU, late giant impact) may be reproduced.

  6. Soft X-Ray Irradiation of Silicates: Implications for Dust Evolution in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Ciaravella, A.; Cecchi-Pestellini, C.; Chen, Y.-J.; Muñoz Caro, G. M.; Huang, C.-H.; Jiménez-Escobar, A.; Venezia, A. M.

    2016-09-01

    The processing of energetic photons on bare silicate grains was simulated experimentally on silicate films submitted to soft X-rays of energies up to 1.25 keV. The silicate material was prepared by means of a microwave assisted sol-gel technique. Its chemical composition reflects the Mg2SiO4 stoichiometry with residual impurities due to the synthesis method. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan. We found that soft X-ray irradiation induces structural changes that can be interpreted as an amorphization of the processed silicate material. The present results may have relevant implications in the evolution of silicate materials in X-ray-irradiated protoplanetary disks.

  7. Soft X-Ray Irradiation of Silicates: Implications for Dust Evolution in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Ciaravella, A.; Cecchi-Pestellini, C.; Chen, Y.-J.; Muñoz Caro, G. M.; Huang, C.-H.; Jiménez-Escobar, A.; Venezia, A. M.

    2016-09-01

    The processing of energetic photons on bare silicate grains was simulated experimentally on silicate films submitted to soft X-rays of energies up to 1.25 keV. The silicate material was prepared by means of a microwave assisted sol–gel technique. Its chemical composition reflects the Mg2SiO4 stoichiometry with residual impurities due to the synthesis method. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan. We found that soft X-ray irradiation induces structural changes that can be interpreted as an amorphization of the processed silicate material. The present results may have relevant implications in the evolution of silicate materials in X-ray-irradiated protoplanetary disks.

  8. DO GIANT PLANETS SURVIVE TYPE II MIGRATION?

    SciTech Connect

    Hasegawa, Yasuhiro; Ida, Shigeru E-mail: ida@geo.titech.ac.jp

    2013-09-10

    Planetary migration is one of the most serious problems to systematically understand the observations of exoplanets. We clarify that the theoretically predicted type II, migration (like type I migration) is too fast, by developing detailed analytical arguments in which the timescale of type II migration is compared with the disk lifetime. In the disk-dominated regime, the type II migration timescale is characterized by a local viscous diffusion timescale, while the disk lifetime is characterized by a global diffusion timescale that is much longer than the local one. Even in the planet-dominated regime where the inertia of the planet mass reduces the migration speed, the timescale is still shorter than the disk lifetime except in the final disk evolution stage where the total disk mass decays below the planet mass. This suggests that most giant planets plunge into the central stars within the disk lifetime, and it contradicts the exoplanet observations that gas giants are piled up at r {approx}> 1 AU. We examine additional processes that may arise in protoplanetary disks: dead zones, photoevaporation of gas, and gas flow across a gap formed by a type II migrator. Although they make the type II migration timescale closer to the disk lifetime, we show that none of them can act as an effective barrier for rapid type II migration with the current knowledge of these processes. We point out that gas flow across a gap and the fraction of the flow accreted onto the planets are uncertain and they may have the potential to solve the problem. Much more detailed investigation for each process may be needed to explain the observed distribution of gas giants in extrasolar planetary systems.

  9. THE EVOLUTION OF CIRCUMPLANETARY DISKS AROUND PLANETS IN WIDE ORBITS: IMPLICATIONS FOR FORMATION THEORY, OBSERVATIONS, AND MOON SYSTEMS

    SciTech Connect

    Shabram, Megan; Boley, Aaron C.

    2013-04-10

    Using radiation hydrodynamics simulations, we explore the evolution of circumplanetary disks around wide-orbit proto-gas giants. At large distances from the star ({approx}100 AU), gravitational instability followed by disk fragmentation can form low-mass substellar companions (massive gas giants and/or brown dwarfs) that are likely to host large disks. We examine the initial evolution of these subdisks and their role in regulating the growth of their substellar companions, as well as explore consequences of their interactions with circumstellar material. We find that subdisks that form in the context of GIs evolve quickly from a very massive state. Long-term accretion rates from the subdisk onto the proto-gas giant reach {approx}0.3 Jupiter masses kyr{sup -1}. We also find consistency with previous simulations, demonstrating that subdisks are truncated at {approx}1/3 of the companion's Hill radius and are thick, with (h/r) of {approx}> 0.2. The thickness of subdisks draws to question the use of thin-disk approximations for understanding the behavior of subdisks, and the morphology of subdisks has implications for the formation and extent of satellite systems. These subdisks create heating events in otherwise cold regions of the circumstellar disk and serve as planet formation beacons that can be detected by instruments such as ALMA.

  10. EVOLUTION OF WARPED ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI. I. ROLES OF FEEDING AT THE OUTER BOUNDARIES

    SciTech Connect

    Li, Yan-Rong; Wang, Jian-Min; Cheng, Cheng; Qiu, Jie

    2013-02-10

    We investigate the alignment processes of spinning black holes and their surrounding warped accretion disks in a frame of two different types of feeding at the outer boundaries. We consider (1) fixed flows in which gas is continually fed with a preferred angular momentum, and (2) free flows in which there is no gas supply and the disks diffuse freely at their outer edges. As expected, we find that for the cases of fixed flows the black hole disk systems always align on timescales of several 10{sup 6} yr, irrespective of the initial inclinations. If the initial inclination angles are larger than {pi}/2, the black hole accretion transits from retrograde to prograde fashion, and the accreted mass onto the black holes during these two phases is comparable. On the other hand, for the cases of free flows, both alignments and anti-alignments can occur, depending on the initial inclinations and the ratios of the angular momentum of the disks to that of the black holes. In such cases, the disks will be consumed within timescales of 10{sup 6} yr by black holes accreting at the Eddington limit. We propose that there is a close connection between the black hole spin and the lifetime for which the feeding persists, which determines the observable episodic lifetimes of active galactic nuclei. We conclude that careful inclusion of the disk feeding at the outer boundaries is crucial for modeling the evolution of the black hole spin.

  11. Time-Dependent Simulations of the Formation and Evolution of Disk-Accreted Atmospheres Around Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Stoekl, Alexander; Dorfi, Ernst

    2014-05-01

    In the early, embedded phase of evolution of terrestrial planets, the planetary core accumulates gas from the circumstellar disk into a planetary envelope. This atmosphere is very significant for the further thermal evolution of the planet by forming an insulation around the rocky core. The disk-captured envelope is also the staring point for the atmospheric evolution where the atmosphere is modified by outgassing from the planetary core and atmospheric mass loss once the planet is exposed to the radiation field of the host star. The final amount of persistent atmosphere around the evolved planet very much characterizes the planet and is a key criterion for habitability. The established way to study disk accumulated atmospheres are hydrostatic models, even though in many cases the assumption of stationarity is unlikely to be fulfilled. We present, for the first time, time-dependent radiation hydrodynamics simulations of the accumulation process and the interaction between the disk-nebula gas and the planetary core. The calculations were performed with the TAPIR-Code (short for The adaptive, implicit RHD-Code) in spherical symmetry solving the equations of hydrodynamics, gray radiative transport, and convective energy transport. The models range from the surface of the solid core up to the Hill radius where the planetary envelope merges into the surrounding protoplanetary disk. Our results show that the time-scale of gas capturing and atmospheric growth strongly depends on the mass of the solid core. The amount of atmosphere accumulated during the lifetime of the protoplanetary disk (typically a few Myr) varies accordingly with the mass of the planet. Thus, a core with Mars-mass will end up with about 10 bar of atmosphere while for an Earth-mass core, the surface pressure reaches several 1000 bar. Even larger planets with several Earth masses quickly capture massive envelopes which in turn become gravitationally unstable leading to runaway accretion and the eventual

  12. Tracing chemical evolution over the extent of the Milky Way's disk with apogee red clump stars

    SciTech Connect

    Nidever, David L.; Bovy, Jo; Bird, Jonathan C.; Andrews, Brett H.; Johnson, Jennifer A.; Weinberg, David H.; Hayden, Michael; Holtzman, Jon; Feuillet, Diane; Majewski, Steven R.; García Pérez, Ana E.; Smith, Verne; Robin, Annie C.; Sobeck, Jennifer; Cunha, Katia; Allende Prieto, Carlos; Zasowski, Gail; Schiavon, Ricardo P.; Schneider, Donald P.; Shetrone, Matthew; and others

    2014-11-20

    We employ the first two years of data from the near-infrared, high-resolution SDSS-III/APOGEE spectroscopic survey to investigate the distribution of metallicity and α-element abundances of stars over a large part of the Milky Way disk. Using a sample of ≈10, 000 kinematically unbiased red-clump stars with ∼5% distance accuracy as tracers, the [α/Fe] versus [Fe/H] distribution of this sample exhibits a bimodality in [α/Fe] at intermediate metallicities, –0.9 < [Fe/H] <–0.2, but at higher metallicities ([Fe/H] ∼+0.2) the two sequences smoothly merge. We investigate the effects of the APOGEE selection function and volume filling fraction and find that these have little qualitative impact on the α-element abundance patterns. The described abundance pattern is found throughout the range 5 < R < 11 kpc and 0 < |Z| < 2 kpc across the Galaxy. The [α/Fe] trend of the high-α sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (∼10%). Using simple galactic chemical evolution models, we derive an average star-formation efficiency (SFE) in the high-α sequence of ∼4.5 × 10{sup –10} yr{sup –1}, which is quite close to the nearly constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the early evolution of the Milky Way disk was characterized by stars that shared a similar star-formation history and were formed in a well-mixed, turbulent, and molecular-dominated ISM with a gas consumption timescale (SFE{sup –1}) of ∼2 Gyr. Finally, while the two α-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track, this cannot hold in the outer Galaxy, requiring, instead, a mix of two or more populations with distinct enrichment histories.

  13. Evolution of blue E/S0 galaxies from z ~ 1: merger remnants or disk-rebuilding galaxies?

    NASA Astrophysics Data System (ADS)

    Huertas-Company, M.; Aguerri, J. A. L.; Tresse, L.; Bolzonella, M.; Koekemoer, A. M.; Maier, C.

    2010-06-01

    Context. Studying outliers from the bimodal distribution of galaxies in the color-mass space, such as morphological early-type galaxies residing in the blue cloud (blue E/S0s), can help for better understanding the physical mechanisms that lead galaxy migrations in this space. Aims: In this paper we try to bring new clues to studying the evolution of the properties of a significant sample of blue E/S0 galaxies in the COSMOS field. Methods: We define blue E/S0 galaxies as objects having a clear early-type morphology on the HST/ACS images (according to our automated classification scheme galSVM) but with a blue rest-frame color (defined by using the SED best-fit template on the COSMOS primary photometric catalogs). Combining these two measurements with spectroscopic redshifts from the zCOSMOS 10k release, we isolated 210 IAB < 22 blue early-type galaxies with M_*/M_⊙ > 1010 in three redshift bins (0.2 < z < 0.55, 0.55 < z < 0.8, 0.8 < z < 1.4) and studied the evolution of their properties (number density, SFR, morphology, size). Results: The threshold mass (Mt), defined at z = 0 in previous studies as the mass below which the population of blue early-type galaxies starts to be abundant relative to passive E/S0s, evolves from log (M_*/M_⊙) ~ 10.1 ± 0.35 at z ~ 0.3 to log (M_*/M_⊙) ~ 10.9 ± 0.35 at z ~ 1. Interestingly, it follows the evolution of the crossover mass between the early and late type populations (bimodality mass) indicating that the abundance of blue E/S0 is another measure of the downsizing effect in the build-up of the red sequence. There seems to be a turn-over mass in the nature of blue E/S0 galaxies. Above log (M_*/M_⊙) ~ 10.8 blue E/S0 resemble to merger remnants probably migrating to the red sequence on a time scale of ˜3 Gyr. Below this mass, they seem to be closer to normal late-type galaxies, as if they were the result of minor mergers that triggered the central star formation and built a central bulge component or were (re)building a

  14. A METHOD FOR COUPLING DYNAMICAL AND COLLISIONAL EVOLUTION OF DUST IN CIRCUMSTELLAR DISKS: THE EFFECT OF A DEAD ZONE

    SciTech Connect

    Charnoz, Sebastien; Taillifet, Esther

    2012-07-10

    Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics are size-dependent (because of gas drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid Lagrangian/Eulerian code is presented that overcomes some of these difficulties. The particles representing 'dust clouds' are tracked individually in a Lagrangian way. This system is then mapped on an Eulerian spatial grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete Lagrangian particles, keeping their number constant. An application example of dust growth in a turbulent protoplanetary disk at 1 AU is presented. First, the growth of dust is considered in the absence of a dead zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of a millimeter in size. Then the same case with an embedded dead zone is investigated and it is found that coagulation is much more efficient and produces, in a short timescale, 1-10 cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryo-sized objects inside large-scale turbulent structures as shown recently.

  15. Accretion dynamics and disk evolution in NGC 2264: a study based on CoRoT photometric observations

    NASA Astrophysics Data System (ADS)

    Alencar, S. H. P.; Teixeira, P. S.; Guimarães, M. M.; McGinnis, P. T.; Gameiro, J. F.; Bouvier, J.; Aigrain, S.; Flaccomio, E.; Favata, F.

    2010-09-01

    Context. The young cluster NGC 2264 was observed with the CoRoT satellite for 23 days uninterruptedly in March 2008 with unprecedented photometric accuracy. We present the first results of our analysis of the accreting population belonging to the cluster as observed by CoRoT. Aims: We search for possible light curve variability of the same nature as that observed in the classical T Tauri star AA Tau, which was attributed to a magnetically controlled inner disk warp. The inner warp dynamics is supposed to be directly associated with the interaction between the stellar magnetic field and the inner disk region. Methods: We analyzed the CoRoT light curves of 83 previously known classical T Tauri stars that belong to NGC 2264 classifying them according to their light-curve morphology. We also studied the CoRoT light-curve morphology as a function of a Spitzer-based classification of the star-disk systems. Results: The classification derived on the basis of the CoRoT light-curve morphology agrees very well with the Spitzer IRAC-based classification of the systems. The percentage of AA Tau-like light curves decreases as the inner disk dissipates, from 40% ± 10% in systems with thick inner disks to 36% ± 16% in systems with anemic disks and zero in naked photosphere systems. Indeed, 91% ± 29% of the CTTS with naked photospheres exhibit pure spot-like variability, while only 18% ± 7% of the thick disk systems do so, presumably those seen at low inclination and thus free of variable obscuration. Conclusions: AA Tau-like light curves are found to be fairly common, with a frequency of at least ~30 to 40% in young stars with inner dusty disks. The temporal evolution of the light curves indicates that the structure of the inner disk warp, located close to the corotation radius and responsible for the obscuration episodes, varies over a timescale of a few (~1-3) rotational periods. This probably reflects the highly dynamical nature of the star-disk magnetospheric interaction

  16. Shape evolution of zinc oxide from twinned disks to single spindles through solvothermal synthesis in binary solvents

    NASA Astrophysics Data System (ADS)

    Huang, Aisheng; Caro, Jürgen

    2010-10-01

    Shape evolution of ZnO crystals from twinned disks to single spindles was studied through solvothermal synthesis in binary solvents N,N-diethylformamide (DEF) and methanol (MeOH). The MeOH content in DEF had large influence on the morphology of the obtained ZnO crystals. In MeOH-free DEF, well-shaped ZnO twinned disks with perfect mirror symmetry could be formed through the assembly of ZnO 46--julolidinium-ZnO 46- growth units on the (0 0 0 1) growth interfaces. For small amounts of MeOH (MeOH/DEF=0.04), elongated twinned disks were formed since the growth along the polar c-axis was enhanced. With increasing MeOH content (MeOH/DEF=0.1), twinned rods with reduced mirror symmetry were formed. When a large amount of MeOH was added to DEF (MeOH/DEF=0.5), single spindles rather than twinned disks or twinned rods were obtained. A similar shape evolution of zinc oxide was observed in binary solvents DEF and N,N-dimethylformamide (DMF), suggesting that the growth of ZnO crystals with tuneable shape and size can be controlled by the composition of the binary solvent mixture.

  17. SHAPE EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES: CONFIRMATION OF INCREASED DISK PREVALENCE AT z > 1

    SciTech Connect

    Chang, Yu-Yen; Van der Wel, Arjen; Rix, Hans-Walter; Ramkumar, Balasubramanian; Wuyts, Stijn; Zibetti, Stefano; Holden, Bradford

    2013-01-10

    We use high-resolution K-band VLT/HAWK-I imaging over 0.25 deg{sup 2} to study the structural evolution of massive early-type galaxies since z {approx} 2. Mass-selected samples, complete down to log(M/M {sub Sun }) {approx} 10.7 such that 'typical' (L*) galaxies are included at all redshifts, are drawn from pre-existing photometric redshift surveys. We then separate the samples into different redshift slices and classify them as late- or early-type galaxies on the basis of their specific star formation rate. Axis-ratio measurements for the {approx}400 early-type galaxies in the redshift range 0.6 < z < 1.8 are accurate to 0.1 or better. The projected axis-ratio distributions are then compared with lower redshift samples. We find strong evidence for evolution of the population properties: early-type galaxies at z > 1 are, on average, flatter than at z < 1 and the median projected axis ratio at a fixed mass decreases with redshift. However, we also find that at all epochs z {approx}< 2, the most massive early-type galaxies (log(M/M {sub Sun }) > 11.3) are the roundest, with a pronounced lack of galaxies that are flat in projection. Merging is a plausible mechanism that can explain both results: at all epochs, merging is required for early-type galaxies to grow beyond log(M/M {sub Sun }) {approx} 11.3, and all early types over time gradually and partially lose their disk-like characteristics.

  18. Shape Evolution of Massive Early-type Galaxies: Confirmation of Increased Disk Prevalence at z > 1

    NASA Astrophysics Data System (ADS)

    Chang, Yu-Yen; van der Wel, Arjen; Rix, Hans-Walter; Wuyts, Stijn; Zibetti, Stefano; Ramkumar, Balasubramanian; Holden, Bradford

    2013-01-01

    We use high-resolution K-band VLT/HAWK-I imaging over 0.25 deg2 to study the structural evolution of massive early-type galaxies since z ~ 2. Mass-selected samples, complete down to log(M/M ⊙) ~ 10.7 such that "typical" (L*) galaxies are included at all redshifts, are drawn from pre-existing photometric redshift surveys. We then separate the samples into different redshift slices and classify them as late- or early-type galaxies on the basis of their specific star formation rate. Axis-ratio measurements for the ~400 early-type galaxies in the redshift range 0.6 < z < 1.8 are accurate to 0.1 or better. The projected axis-ratio distributions are then compared with lower redshift samples. We find strong evidence for evolution of the population properties: early-type galaxies at z > 1 are, on average, flatter than at z < 1 and the median projected axis ratio at a fixed mass decreases with redshift. However, we also find that at all epochs z <~ 2, the most massive early-type galaxies (log(M/M ⊙) > 11.3) are the roundest, with a pronounced lack of galaxies that are flat in projection. Merging is a plausible mechanism that can explain both results: at all epochs, merging is required for early-type galaxies to grow beyond log(M/M ⊙) ~ 11.3, and all early types over time gradually and partially lose their disk-like characteristics.

  19. Dust and gas density evolution at a radial pressure bump in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Taki, Tetsuo; Fujimoto, Masaki; Ida, Shigeru

    2016-06-01

    We investigate the simultaneous evolution of dust and gas density profiles at a radial pressure bump located in a protoplanetary disk. If dust particles are treated as test particles, a radial pressure bump traps dust particles that drift radially inward. As the dust particles become more concentrated at the gas pressure bump, however, the drag force from dust to gas (back-reaction), which is ignored in a test-particle approach, deforms the pressure bump. We find that the pressure bump is completely deformed by the back-reaction when the dust-to-gas mass ratio reaches ~ 1 for a slower bump restoration. The direct gravitational instability of dust particles is inhibited by the bump destruction. In the dust-enriched region, the radial pressure support becomes ~ 10-100 times lower than the global value set initially. Although the pressure bump is a favorable place for streaming instability (SI), the flattened pressure gradient inhibits SI from forming large particle clumps corresponding to 100-1000 km sized bodies, which has been previously proposed. If SI occurs there, the dust clumps formed would be 10-100 times smaller, that is, of about 1-100 km.

  20. A Hot Big Bang Theory: Magnetic Fields and the Early Evolution of the Protolunar Disk

    NASA Astrophysics Data System (ADS)

    Gammie, C. F.; Liao, Wei-Ting; Ricker, P. M.

    2016-09-01

    The leading theory for the formation of Earth’s Moon invokes a collision between a Mars-sized body and the proto-Earth to produce a disk of orbiting material that later condenses to form the Moon. We show that the disk opacity is large, and cooling is therefore inefficient ({t}{cool}{{Ω }}\\gg 1). In this regime, angular momentum transport in the disk leads to steady heating unless α \\lt {({t}{cool}{{Ω }})}-1\\ll 1. Following earlier work by Charnoz and Michaut, and Carballido et al., we show that once the disk is completely vaporized it is well coupled to the magnetic field. We consider a scenario in which turbulence driven by magnetic fields leads to a brief, hot phase where the disk is geometrically thick, with strong turbulent mixing. The disk cools by spreading until it decouples from the field. We point out that approximately half the accretion energy is dissipated in the boundary layer where the disk meets the Earth’s surface. This creates high entropy material close to the Earth, driving convection and mixing. Finally, a hot magnetized disk could drive bipolar outflows that remove mass and angular momentum from the Earth-Moon system.

  1. A Hot Big Bang Theory: Magnetic Fields and the Early Evolution of the Protolunar Disk

    NASA Astrophysics Data System (ADS)

    Gammie, C. F.; Liao, Wei-Ting; Ricker, P. M.

    2016-09-01

    The leading theory for the formation of Earth’s Moon invokes a collision between a Mars-sized body and the proto-Earth to produce a disk of orbiting material that later condenses to form the Moon. We show that the disk opacity is large, and cooling is therefore inefficient ({t}{cool}{{Ω }}\\gg 1). In this regime, angular momentum transport in the disk leads to steady heating unless α \\lt {({t}{cool}{{Ω }})}-1\\ll 1. Following earlier work by Charnoz and Michaut, and Carballido et al., we show that once the disk is completely vaporized it is well coupled to the magnetic field. We consider a scenario in which turbulence driven by magnetic fields leads to a brief, hot phase where the disk is geometrically thick, with strong turbulent mixing. The disk cools by spreading until it decouples from the field. We point out that approximately half the accretion energy is dissipated in the boundary layer where the disk meets the Earth’s surface. This creates high entropy material close to the Earth, driving convection and mixing. Finally, a hot magnetized disk could drive bipolar outflows that remove mass and angular momentum from the Earth–Moon system.

  2. External Photoevaporation of the Solar Nebula. II. Effects on Disk Structure and Evolution with Non-uniform Turbulent Viscosity due to the Magnetorotational Instability

    NASA Astrophysics Data System (ADS)

    Kalyaan, A.; Desch, S. J.; Monga, N.

    2015-12-01

    The structure and evolution of protoplanetary disks, especially the radial flows of gas through them, are sensitive to a number of factors. One that has been considered only occasionally in the literature is external photoevaporation by far-ultraviolet (FUV) radiation from nearby, massive stars, despite the fact that nearly half of disks will experience photoevaporation. Another effect apparently not considered in the literature is a spatially and temporally varying value of α in the disk (where the turbulent viscosity ν is α times the sound speed C times the disk scale height H). Here we use the formulation of Bai & Stone to relate α to the ionization fraction in the disk, assuming turbulent transport of angular momentum is due to the magnetorotational instability. We calculate the ionization fraction of the disk gas under various assumptions about ionization sources and dust grain properties. Disk evolution is most sensitive to the surface area of dust. We find that typically α ≲ 10-5 in the inner disk (<2 AU), rising to ˜10-1 beyond 20 AU. This drastically alters the structure of the disk and the flow of mass through it: while the outer disk rapidly viscously spreads, the inner disk hardly evolves; this leads to a steep surface density profile ({{Σ }}\\propto {r}-< p> with < p> ≈ 2-5 in the 5-30 AU region) that is made steeper by external photoevaporation. We also find that the combination of variable α and external photoevaporation eventually causes gas as close as 3 AU, previously accreting inward, to be drawn outward to the photoevaporated outer edge of the disk. These effects have drastic consequences for planet formation and volatile transport in protoplanetary disks.

  3. Evolution of a semilinear parabolic system for migration and selection without dominance

    NASA Astrophysics Data System (ADS)

    Lou, Yuan; Nagylaki, Thomas

    The semilinear parabolic system that describes the evolution of the gene frequencies in the diffusion approximation for migration and selection at a multiallelic locus without dominance is investigated. The population occupies a finite habitat of arbitrary dimensionality and shape (i.e., a bounded, open domain in R). The selection coefficients depend on position; the drift and diffusion coefficients may depend on position. The primary focus of this paper is the dependence of the evolution of the gene frequencies on λ, the strength of selection relative to that of migration. It is proved that if migration is sufficiently strong (i.e., λ is sufficiently small) and the migration operator is in divergence form, then the allele with the greatest spatially averaged selection coefficient is ultimately fixed. The stability of each vertex (i.e., an equilibrium with exactly one allele present) is completely specified. The stability of each edge equilibrium (i.e., one with exactly two alleles present) is fully described when either (i) migration is sufficiently weak (i.e., λ is sufficiently large) or (ii) the equilibrium has just appeared as λ increases. The existence of unexpected, complex phenomena is established: even if there are only three alleles and migration is homogeneous and isotropic (corresponding to the Laplacian), (i) as λ increases, arbitrarily many changes of stability of the edge equilibria and corresponding appearance of an internal equilibrium can occur and (ii) the conditions for protection or loss of an allele can both depend nonmonotonically on λ. Neither of these phenomena can occur in the diallelic case.

  4. EFFECTS OF CIRCUMNUCLEAR DISK GAS EVOLUTION ON THE SPIN OF CENTRAL BLACK HOLES

    SciTech Connect

    Maio, Umberto; Dotti, Massimo; Petkova, Margarita; Perego, Albino; Volonteri, Marta

    2013-04-10

    Mass and spin are the only two parameters needed to completely characterize black holes (BHs) in general relativity. However, the interaction between BHs and their environment is where complexity lies, as the relevant physical processes occur over a large range of scales. That is particularly relevant in the case of supermassive black holes (SMBHs), hosted in galaxy centers, and surrounded by swirling gas and various generations of stars. These compete with the SMBH for gas consumption and affect both dynamics and thermodynamics of the gas itself. How the behavior of such a fiery environment influences the angular momentum of the gas accreted onto SMBHs, and, hence, BH spins, is uncertain. We explore the interaction between SMBHs and their environment via first three-dimensional sub-parsec resolution simulations (ranging from {approx}0.1 pc to {approx}1 kpc scales) that study the evolution of the SMBH spin by including the effects of star formation, stellar feedback, radiative transfer, and metal pollution according to the proper stellar yields and lifetimes. This approach is crucial in investigating the impact of star formation processes and feedback effects on the angular momentum of the material that could accrete on the central hole. We find that star formation and feedback mechanisms can locally inject significant amounts of entropy in the surrounding medium, and impact the inflow inclination angles and Eddington fractions. As a consequence, the resulting trends show upper-intermediate equilibrium values for the spin parameter of a {approx_equal} 0.6-0.9, corresponding to radiative efficiencies {epsilon} {approx_equal} 9%-15%. These results suggest that star formation feedback taking place in the circumnuclear disk during the infall alone cannot induce very strong chaotic trends in the gas flow, quite independently from the different numerical parameters.

  5. Linear corotation torques in non-barotropic disks

    SciTech Connect

    Tsang, David

    2014-02-20

    A fully analytic expression for the linear corotation torque to first order in eccentricity for planets in non-barotropic protoplanetary disks is derived, taking into account the effect of disk entropy gradients. This torque formula is applicable to both the co-orbital, corotation torques and the non-co-orbital, corotation torques—for planets in orbits with non-zero eccentricity—in disks where the thermal diffusivity and viscosity are sufficient to maintain the linearity of these interactions. While the co-orbital, corotation torque is important for migration of planets in Type I migration, the non-co-orbital, corotation torque plays an important role in the eccentricity evolution of giant planets that have opened gaps in the disk. The presence of an entropy gradient in the disk can significantly modify the corotation torque in both these cases.

  6. A SPITZER IRS SURVEY OF NGC 1333: INSIGHTS INTO DISK EVOLUTION FROM A VERY YOUNG CLUSTER

    SciTech Connect

    Arnold, L. A.; Watson, Dan M.; Kim, K. H.; Manoj, P.; Remming, I.; Sheehan, P.; Forrest, W. J.; Mamajek, E.; Adame, L.; McClure, M.; Furlan, E.; Espaillat, C.; Ausfeld, K.; Rapson, V. A. E-mail: dmw@pas.rochester.edu

    2012-08-01

    We report on the {lambda} = 5-36 {mu}m Spitzer Infrared Spectrograph (IRS) spectra of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC 1333's youth enables the study of early protoplanetary disk properties, such as the degree of settling and the formation of gaps and clearings. We construct spectral energy distributions (SEDs) using our IRS data as well as published photometry and classify our sample into SED classes. Using 'extinction-free' spectral indices, we determine whether the disk, envelope, or photosphere dominates the spectrum. We analyze the dereddened spectra of objects that show disk-dominated emission using spectral indices and properties of silicate features in order to study the vertical and radial structure of protoplanetary disks in NGC 1333. At least nine objects in our sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in their inner disk. Disks with radial gaps in NGC 1333 show more nearly pristine silicate dust than their radially continuous counterparts. We compare properties of disks in NGC 1333 to those in three other well-studied regions, Taurus-Auriga, Ophiuchus, and Chamaeleon I, and find no difference in their degree of sedimentation and dust processing.

  7. TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR

    SciTech Connect

    Gorti, U.; Dullemond, C. P.; Hollenbach, D.

    2009-11-10

    We present the time evolution of viscously accreting circumstellar disks as they are irradiated by ultraviolet and X-ray photons from a low-mass central star. Our model is a hybrid of a one-dimensional (1D) time-dependent viscous disk model coupled to a 1+1D disk vertical structure model used for calculating the disk structure and photoevaporation rates. We find that disks of initial mass 0.1 M{sub sun} around approx1 M{sub sun} stars survive for approx4 x 10{sup 6} yr, assuming a viscosity parameter alpha = 0.01, a time-dependent FUV luminosity L{sub FUV} approx 10{sup -2}-10{sup -3} L{sub sun} and with X-ray and EUV luminosities L{sub X} approx L{sub EUV} approx 10{sup -3} L{sub sun}. We find that FUV/X-ray-induced photoevaporation and viscous accretion are both important in depleting disk mass. Photoevaporation rates are most significant at approx1-10 AU and at approx>30 AU. Viscosity spreads the disk which causes mass loss by accretion onto the central star and feeds mass loss by photoevaporation in the outer disk. We find that FUV photons can create gaps in the inner, planet-forming regions of the disk (approx1-10 AU) at relatively early epochs in disk evolution while disk masses are still substantial. EUV and X-ray photons are also capable of driving gaps, but EUV can only do so at late, low accretion-rate epochs after the disk mass has already declined substantially. Disks around stars with predominantly soft X-ray fields experience enhanced photoevaporative mass loss. We follow disk evolution around stars of different masses, and find that disk survival time is relatively independent of mass for stars with M{sub *}approx< 3 M{sub sun}; for M{sub *}approx> 3 M{sub sun} the disks are short-lived (approx10{sup 5} yr).

  8. The collapse of clouds and the formation and evolution of stars and disks

    NASA Technical Reports Server (NTRS)

    Shu, Frank; Najita, Joan; Galli, Daniele; Ostriker, Eve; Lizano, Susana

    1993-01-01

    We consider the interrelationships among the structure of molecular clouds; the collapse of rotating cloud cores; the formation of stars and disks; the origin of molecular outflows, protostellar winds, and highly collimated jets; the birth of planetary and binary systems; and the dynamics of star/disk/satellite interactions. Our discussion interweaves theory with the results of observations that span from millimeter wavelengths to X-rays.

  9. Secular Evolution in the Milky Way

    NASA Astrophysics Data System (ADS)

    Debattista, Victor

    2015-03-01

    I will review the secular evolution of the Milky Way disk and bulge with particular attention to the bulge and disk. Evidence for the importance of stellar migration in the Solar neighbourhood will be presented. The upcoming Gaia satellite will lead to a wealth of new data with which to explore these effects.

  10. Nonlinear evolution of tidally distorted accretion disks: Two-dimensional simulations

    NASA Technical Reports Server (NTRS)

    Ryu, Dongsu; Goodman, Jeremy

    1994-01-01

    According to a previously published linear analysis, the tidal distortion of accretion disks in binary star systems produces a local hydrodynamic instability to m = 1 internal waves, which may have arbitrarily small wavelengths in the absence of viscosity. The instability is three-dimensional and approximately incrompressible. To explore the nonlinear outcome of this instability, we develop a shearing-sheet approximation on scales comparable to the disk thickness. The large-scale azimuthal variation of the disk is represented by varying the local metric with time (local orbital phase). The hydrodynamic equations can then be posed two-dimensionally on local meridional planes. We solve these equations with a second-order gasdynamical code based on the Total-Variation-Diminishing scheme. Our simulations confirm the predicted linear growth rate. The modes saturate chaotically at velocities scaling as the product of the linear growth rate and the wavelength. If the wavelength is small compared with the disk thickness, the modes remain nearly incompressible even when nonlinear. The two-dimensional power spectrum of velocities after saturation is roughly isotropic and extends over a broad range of scales in an approximately power-law fashion. We measure the heating rate associated with the nonlinear dissipation of the modes. The dissipation implies a secular torque on the disk and a return of angular momentum to the secondary star via the tidal potential. The estimated torque is somewhat larger than the tidal torque produced by maximal disk viscosity (alpha approximately 1). At least in these two-dimensional simulations, however, there is no significant angular momentum flux within the disk.

  11. A robust tool highlights the influence of bird migration on influenza A virus evolution.

    PubMed

    Dugan, Vivien G

    2012-12-01

    One of the fundamental unknowns in the field of influenza biology is a panoramic understanding of the role wild birds play in the global maintenance and spread of influenza A viruses. Wild aquatic birds are considered a reservoir host for all lowly pathogenic avian influenza A viruses (AIV) and thus serve as a potential source of zoonotic AIV, such as Australasian-origin H5N1 responsible for morbidity and mortality in both poultry and humans, as well as genes that may contribute to the emergence of pandemic viruses. Years of broad, in-depth wild bird AIV surveillance have helped to decipher key observations and ideas regarding AIV evolution and viral ecology including the trending of viral lineages, patterns of gene flow within and between migratory flyways and the role of geographic boundaries in shaping viral evolution (Bahl et al. 2009; Lam et al. 2012). While these generally 'virus-centric' studies have ultimately advanced our broader understanding of AIV dynamics, recent studies have been more host-focused, directed at determining the potential impact of host behaviour on AIV, specifically, the influence of bird migration upon AIV maintenance and transmission. A large number of surveillance studies have taken place in Alaska, United States-a region where several global flyways overlap-with the aim of detecting the introduction of novel, Australasian-origin highly pathogenic H5N1 AIV into North America. By targeting bird species with known migration habits, long-distance migrators were determined to be involved in the intercontinental movement of individual AIV gene segments, but not entire viruses, between the Australasian and North American flyways (Koehler et al. 2008; Pearce et al. 2010). Yet, bird movement is not solely limited to long-distance migration, and the relationship of resident or nonmigratory and intermediate-distance migrant populations with AIV ecology has only recently been explored by Hill et al. (2012) in this issue of Molecular Ecology

  12. Metallicity gradients in local Universe galaxies: Time evolution and effects of radial migration

    NASA Astrophysics Data System (ADS)

    Magrini, Laura; Coccato, Lodovico; Stanghellini, Letizia; Casasola, Viviana; Galli, Daniele

    2016-04-01

    Context. Our knowledge of the shape of radial metallicity gradients in disc galaxies has recently improved. Conversely, the understanding of their time evolution is more complex, since it requires analysis of stellar populations with different ages or systematic studies of galaxies at different redshifts. In the local Universe, H ii regions and planetary nebulae (PNe) are important tools to investigate radial metallicity gradients in disc galaxies. Aims: We present an in-depth study of all nearby spiral galaxies (M33, M31, NGC 300, and M81) with direct-method nebular abundances of both populations, aiming at studying the evolution of their radial metallicity gradients. For the first time, we also evaluate the radial migration of PN populations. Methods: For the selected galaxies, we analysed H ii region and PN properties to: determine whether oxygen in PNe is a reliable tracer for past interstellar medium (ISM) composition; homogenise published datasets; estimate the migration of the oldest stellar populations; and determine the overall chemical enrichment and slope evolution. Results: We confirm that oxygen in PNe is a reliable tracer for past ISM metallicity. We find that PN gradients are flatter than or equal to those of H ii regions. When radial motions are negligible, this result provides a direct measurement of the time evolution of the gradient. For galaxies with dominant radial motions, we provide upper limits on the gradient evolution. Finally, the total metal content increases with time in all target galaxies, and early morphological types have a larger increment Δ(O/H) than late-type galaxies. Conclusions: Our findings provide important constraints to discriminate among different galactic evolutionary scenarios, favouring cosmological models with enhanced feedback from supernovae. The advent of extremely large telescopes allows us to include galaxies in a wider range of morphologies and environments, thus putting firmer constraints on galaxy formation

  13. A determination of the thick disk chemical abundance distribution: Implications for galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gilmore, Gerard; Wyse, Rosemary F. G.; Jones, Bryn J.

    1995-01-01

    We present a determination of the thick disk iron abundance distribution obtained from an in situ sample of F/G stars. These stars are faint, 15 less than or approximately = V less than or approximately = 18, selected on the basis of color, being a subset of the larger survey of Gilmore and Wyse designed to determine the properties of the stellar populations several kiloparsecs from the Sun. The fields studied in the present paper probe the iron abundance distribution of the stellar populations of the galaxy at 500-3000 pc above the plane, at the solar Galactocentric distance. The derived chemical abundance distributions are consistent with no metallicity gradients in the thick disk over this range of vertical distance, and with an iron abundance distribution for the thick disk that has a peak at -0.7 dex. The lack of a vertical gradient argues against slow, dissipational settling as a mechanism for the formation of the thick disk. The photometric and metallicity data support a turn-off of the thick disk that is comparable in age to the metal-rich globular clusters, or greater than or approximately = 12 Gyr, and are consistent with a spread to older ages.

  14. EVIDENCE FOR EVOLUTION AMONG PRIMORDIAL DISKS IN THE 5 Myr OLD UPPER SCORPIUS OB ASSOCIATION

    SciTech Connect

    Dahm, S. E.

    2010-11-15

    Moderate-resolution, near-infrared spectra between 0.8 and 5.2 {mu}m were obtained for 12 late-type (K0-M3) disk-bearing members of the {approx}5 Myr old Upper Scorpius OB association using SpeX on the NASA Infrared Telescope Facility. For most sources, continuum excess emission first becomes apparent between {approx}2.2 and 4.5 {mu}m and is consistent with that produced by single-temperature blackbodies having characteristic temperatures ranging from {approx}500 to 1300 K. The near-infrared spectra for 5 of 12 Upper Scorpius sources exhibit Pa{gamma}, Pa{beta}, and Br{gamma} emission, indicators of disk accretion. Using a correlation between Pa{beta} and Br{gamma} emission line luminosity and accretion luminosity, mass accretion rates ( M-dot ) are derived for these sources that range from M-dot = 3.5x10{sup -10} to 1.5 x 10{sup -8} M{sub sun} yr{sup -1}. Merging the SpeX observations with Spitzer Space Telescope mid-infrared (5.4-37.0 {mu}m) spectroscopy and 24 and 70 {mu}m broadband photometry, the observed spectral energy distributions (SEDs) are compared with those predicted by two-dimensional, radiative transfer accretion disk models. Of the nine Upper Scorpius sources examined in this analysis, three exhibit SEDs that are most consistent with models having inner disk radii that substantially exceed their respective dust sublimation radii. The remaining Upper Scorpius members possess SEDs that either show significant dispersion among predicted inner disk radii or are best described by models having inner disk rims coincident with the dust sublimation radius.

  15. The Evolution of the FU Orionis Disk, and the Seeds of Planet Formation

    NASA Astrophysics Data System (ADS)

    Green, Joel D.

    2016-10-01

    Young stars form new planetary systems during the collapse of a giant cloud of gas and dust. Tiny dust particles and gas parcels collide and stick together, growing slowly into planetary cores and then full-size planets. But is this process a steady and slow one, or are there bumps in the road to planet construction? In 1936, the young star FU Orionis (FU Ori) became 100 times brighter in only a few short months. Although astronomers didn't realize at the time, FU Ori was undergoing a "burst" of accretion -- instead of a slow trickle of material falling into the central star, nearly 20 Jupiters worth of material have fallen in and burned since 1936. This sustained flow is a large fraction of the entire measureable disk mass (both gas and dust) surrounding FU Ori. FU Ori has slowly faded over the past 80 years, reducing by approximately 1 mag. in B. But what changes did this increased brightness wreak upon FU Ori's disk, and what implications would it have for any planets that might have formed or form later? Unlike most observed young stars, FU Ori and its (~ 10) brethren with similar behavior show no evidence of crystalline dust grains like forsterite (peridot), and the temperatures at an Earth-equivalent distance would have risen from room temperature to a scalding 1000 degrees Kelvin.Our study with SOFIA/FORCAST, in comparison with our previous study with Spitzer/IRS, provides the first multi-epoch infrared spectroscopic study of an FUor, as it appeared in 2004 and 2016. First, the continuum (the energy emitted by viscous heating in the disk) has decreased by 13% but is still fit by a 7200 K blackbody at 13% less strength; second, the heating source behind disk's atmosphere (similar to a stellar atmosphere, as the superheated inner disk is at the same temperature as a typical star) has also decreased, exciting less high temperature water vapor. This change has not completely propagated to the rest of the disk. The silicate dust remains unchanged. We conclude

  16. The Evolution of Disks and Winds in Dwarf Nova Outbursts - FUSE

    NASA Technical Reports Server (NTRS)

    Long, Knox

    2002-01-01

    This project was a project to study the FUV spectra of two proto-typical dwarf novae, U Gem and SS Cygni, through an outburst cycle. The luminosity of the boundary layer in the two systems, as evidenced by earlier EUVE observations, is different in the two systems. Our intensive study of the two systems was intended to (1) probe the ionization and kinematic structure of the wind as a function of system brightness, (2) isolate the contributions of the disk to the FUV spectra, and (3) examine physical conditions and abundances of material just being accreted onto the disk from the secondary. The U Gem and SS Cyg observations took place in March and October 2000, respectively. The data obtained with FUSE was of excellent quality. Analysis of the both observations is now essentially complete, although some modeling of the SS Cyg spectra is ongoing, as we complete an ApJ manuscript on this object. Our main results for U Gem are as follows: The plateau spectra have continuum shapes and fluxes that are approximated by steady state accretion disk model spectra with an accretion rate 7x10(exp 9) Msolar/yr. The spectra also show numerous absorption lines of H I, He II, and 2-5 times ionized transitions of C, N, O, P, S, and Si. There are no emission features in the spectra, with the possible exception of a weak feature on the red wing of the 0 VI doublet. The absorption lines are narrow (FWHM approx. 50 km/s), too narrow to arise from the disk photosphere, and at low velocities (less than or equal to 700 km/s). The S VI and O VI doublets are optically thick. The absorption lines in the plateau spectra show orbital variability: in spectra obtained at orbital phases between 0.53 and 0.79, low-ionization absorption lines appear and the central depths of the preexisting lines increase. The increase in line absorption occurs at the same orbital phases as previously observed EUV and X-ray light-curve dips. If the absorbing material is in (near-) Keplerian rotation around the disk

  17. 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

  18. Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?

    NASA Astrophysics Data System (ADS)

    Eistrup, Christian; Walsh, Catherine; van Dishoeck, Ewine F.

    2016-11-01

    Context. The atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. Such pebbles are also the building blocks of comets. The chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. However, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases. Aims: To investigate if and how chemical evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2-30 AU range. Methods: A disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. A full chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Both molecular (inheritance from the parent cloud) and atomic (chemical reset) initial conditions are investigated. Results: Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of chemical reaction types included are all factors that affect the chemical evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. The grain temperature plays an important role, especially in the critical 20-28 K region where atomic H no longer sticks long enough to the surface to react, but atomic O does. Above 28 K, efficient grain-surface production of CO2 ice is seen, as well as O2 gas and ice under certain conditions, at the expense of H2O and CO. H2O ice is produced on grain surfaces only below 28 K. For high ionisation levels at intermediate disk radii, CH4 gas is

  19. Cepheus OB2: Disk Evolution and Accretion at 3-10 Myr

    NASA Technical Reports Server (NTRS)

    Sicilia-Aguilar, A.

    2005-01-01

    We presented the results of MMT observations of young stars for our study of protoplanetary disks at ages 1-10 Myr in Tr 37 and NGC 7160. Using low-resolution optical spectra from the Hectospec multifiber spectrograph, we have tripled the number of known low-mass cluster members, identifying 130 new members in Tr 37 and 30 in NGC 7160. We used indicators of youth to identify and classify the low-mass cluster members. With the extended samples, we estimated the disk fraction in the clusters, finding that 40% of the low-mass stars in Tr 37 are actively accreting, whereas only 1 of the 55 low-mass stars in NGC 7160 shows indications of accretion. Optical photometry and theoretical isochrones are used to refine the ages of the clusters, confirming the estimates of 4 Myr for Tr 37 and 10 Myr for NGC 7160.

  20. WIND-SHEARING IN GASEOUS PROTOPLANETARY DISKS AND THE EVOLUTION OF BINARY PLANETESIMALS

    SciTech Connect

    Perets, Hagai B.; Murray-Clay, Ruth A.

    2011-05-20

    One of the first stages of planet formation is the growth of small planetesimals and their accumulation into large planetesimals and planetary embryos. This early stage occurs much before the dispersal of most of the gas from the protoplanetary disk. Due to their different aerodynamic properties, planetesimals of different sizes and shapes experience different drag forces from the gas during this time. Such differential forces produce a wind-shearing (WISH) effect between close by, different-sized planetesimals. For any two planetesimals, a WISH radius can be considered at which the differential acceleration due to the wind becomes greater than the mutual gravitational pull between the planetesimals. We find that the WISH radius could be much smaller than the gravitational shearing radius by the star (the Hill radius). In other words, during the gas-phase of the disk, WISH could play a more important role than tidal perturbations by the star. Here, we study the WISH radii for planetesimal pairs of different sizes and compare the effects of wind and gravitational shearing (drag force versus gravitational tidal force). We then discuss the role of WISH for the stability and survival of binary planetesimals. Binaries are sheared apart by the wind if they are wider than their WISH radius. WISH-stable binaries can also inspiral, and possibly coalesce, due to gas drag. Here, we calculate the WISH radius and the gas-drag-induced merger timescale, providing stability and survival criteria for gas-embedded binary planetesimals. Our results suggest that even WISH-stable binaries may merge in times shorter than the lifetime of the gaseous disk. This may constrain currently observed binary planetesimals to have formed far from the star or at a late stage after the dispersal of most of the disk gas. We note that the WISH radius may also be important for other processes such as planetesimal erosion and planetesimal encounters and collisions in a gaseous environment.

  1. THE EVOLUTION OF ASTEROIDS IN THE JUMPING-JUPITER MIGRATION MODEL

    SciTech Connect

    Roig, Fernando; Nesvorný, David E-mail: davidn@boulder.swri.edu

    2015-12-15

    In this work, we investigate the evolution of a primordial belt of asteroids, represented by a large number of massless test particles, under the gravitational effect of migrating Jovian planets in the framework of the jumping-Jupiter model. We perform several simulations considering test particles distributed in the Main Belt, as well as in the Hilda and Trojan groups. The simulations start with Jupiter and Saturn locked in the mutual 3:2 mean motion resonance plus three Neptune-mass planets in a compact orbital configuration. Mutual planetary interactions during migration led one of the Neptunes to be ejected in less than 10 Myr of evolution, causing Jupiter to jump by about 0.3 AU in semimajor axis. This introduces a large-scale instability in the studied populations of small bodies. After the migration phase, the simulations are extended over 4 Gyr, and we compare the final orbital structure of the simulated test particles to the current Main Belt of asteroids with absolute magnitude H < 9.7. The results indicate that, in order to reproduce the present Main Belt, the primordial belt should have had a distribution peaked at ∼10° in inclination and at ∼0.1 in eccentricity. We discuss the implications of this for the Grand Tack model. The results also indicate that neither primordial Hildas, nor Trojans, survive the instability, confirming the idea that such populations must have been implanted from other sources. In particular, we address the possibility of implantation of Hildas and Trojans from the Main Belt population, but find that this contribution should be minor.

  2. Temporal Evolution of Photons Emerging out of Two Component Advective Disks

    NASA Astrophysics Data System (ADS)

    Chatterjee, Arka; Chakrabarti, Sandip Kumar; Ghosh, Himadri

    2016-07-01

    For outbursting cases, time lead and lag for hard photons to that of soft photons carries major information about the geometry of the system and the process that photons have undergone before they reach the detector. We construct a standard Keplerian disk as the source of soft photons which are Comptonized inside relativistic thick disks used as a proxy of the CENtrifugal BOundary supported Layer or CENBOL. Comptonization is computed by Monte-Carlo method. Finally, when the Comptonized photons leave the system and detected by a distant observer, their paths are guided by null geodesic equations. Time stamps on generated photons are put for different energy bands. We present difference of time in the arrival of soft photons to that of hard photons for various sizes of accretion disks. We compare our simulated results with the observational data available in literature. We also study the effects of inclination angle. Our aim is to develop a total time dependent outburst scenario to study the temporal properties of the observed photons.

  3. Type II Migration and Giant Planet Survival

    NASA Technical Reports Server (NTRS)

    Ward, William R.

    2003-01-01

    Type II migration, in which a newly formed large planet opens a gap in its precursor circumstellar nebula and subsequently evolves with it, has been implicated as a delivery mechanism responsible for close stellar companions. Large scale migration is possible in a viscously spreading disk of surface density sigma (r,t) when most of it is sacrificed to the primary in order to promote a small portion of the disk to much higher angular momentum orbits. Embedded planets generally follow its evolution unless their own angular momentum is comparable to that of the disk. The fraction of the starting disk mass, M (sub d) = 2pi integral rsigma(r,0)dr, that is consumed by the star depends on the distance at which material escapes the disk's outer boundary. If the disk is allowed to expand indefinitely, virtually all of the disk will fall into the primary in order to send a vanishingly small portion to infinity. For such a case, it is difficult to explain the survival of any giant planets, including Jupiter and Saturn. Realistically, however, there are processes that could truncate a disk at a finite distance, r(sub d). Recent numerical modeling has illustrated that planets can survive in this case. We show here that much of these results can be understood by simple conservation arguments.

  4. PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL UNSTRATIFIED DISKS

    SciTech Connect

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen E-mail: mordecai@amnh.or

    2009-12-20

    The dynamics of planetesimals and planetary cores may be strongly influenced by density perturbations driven by magneto-rotational turbulence in their natal protoplanetary gas disks. Using the local shearing box approximation, we perform numerical simulations of planetesimals moving as massless particles in a turbulent, magnetized, unstratified gas disk. Our fiducial disk model shows turbulent accretion characterized by a Shakura-Sunyaev viscosity parameter of alpha approx 10{sup -2}, with rms density perturbations of approx10%. We measure the statistical evolution of particle orbital properties in our simulations including mean radius, eccentricity, and velocity dispersion. We confirm random walk growth in time of all three properties, the first time that this has been done with direct orbital integration in a local model. We find that the growth rate increases with the box size used at least up to boxes of eight scale heights in horizontal size. However, even our largest boxes show velocity dispersions sufficiently low that collisional destruction of planetesimals should be unimportant in the inner disk throughout its lifetime. Our direct integrations agree with earlier torque measurements showing that type I migration dominates over diffusive migration by stochastic torques for most objects in the planetary core and terrestrial planet mass range. Diffusive migration remains important for objects in the mass range of kilometer-sized planetesimals. Discrepancies in the derived magnitude of turbulence between local and global simulations of magneto-rotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

  5. Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk: Ideal Unstratified Disks

    NASA Astrophysics Data System (ADS)

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen

    2009-12-01

    The dynamics of planetesimals and planetary cores may be strongly influenced by density perturbations driven by magneto-rotational turbulence in their natal protoplanetary gas disks. Using the local shearing box approximation, we perform numerical simulations of planetesimals moving as massless particles in a turbulent, magnetized, unstratified gas disk. Our fiducial disk model shows turbulent accretion characterized by a Shakura-Sunyaev viscosity parameter of α ~ 10-2, with rms density perturbations of ~10%. We measure the statistical evolution of particle orbital properties in our simulations including mean radius, eccentricity, and velocity dispersion. We confirm random walk growth in time of all three properties, the first time that this has been done with direct orbital integration in a local model. We find that the growth rate increases with the box size used at least up to boxes of eight scale heights in horizontal size. However, even our largest boxes show velocity dispersions sufficiently low that collisional destruction of planetesimals should be unimportant in the inner disk throughout its lifetime. Our direct integrations agree with earlier torque measurements showing that type I migration dominates over diffusive migration by stochastic torques for most objects in the planetary core and terrestrial planet mass range. Diffusive migration remains important for objects in the mass range of kilometer-sized planetesimals. Discrepancies in the derived magnitude of turbulence between local and global simulations of magneto-rotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

  6. The evolution of a Pluto-like system during the migration of the ice giants

    NASA Astrophysics Data System (ADS)

    Pires, Pryscilla; Giuliatti Winter, Silvia M.; Gomes, Rodney S.

    2015-01-01

    The planetary migration of the Solar System giant planets in the framework of the Nice model (Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F. [2005]. Nature 435,459-461; Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R. [2005]. Nature 435, 462-465; Gomes, R., Levison, H.F., Tsiganis, K., Morbidelli, A. [2005]. Nature 435, 466-469) creates a dynamical mechanism which can be used to explain the distribution of objects currently observed in the Kuiper belt (e.g., Levison, H.F., Morbidelli, A., Vanlaerhoven, C., Gomes, R., Tsiganis, K. [2008]. Icarus 196, 258-273). Through this mechanism the planetesimals within the disk, heliocentric distance ranging from beyond Neptune's orbit to approximately 34 AU, are delivered to the belt after a temporary eccentric phase of Uranus and Neptune's orbits. We reproduced the mechanism proposed by Levison et al. to implant bodies into the Kuiper belt. The capture of Pluto into the external 3:2 mean motion resonance with Neptune is associated with this gravitational scattering model. We verified the existence of several close encounters between the ice giants and the planetesimals during their outward radial migration, then we believe that the analysis of the dynamical history of the plutonian satellites during this kind of migration is important, and would provide some constrains about their place of formation - within the primordial planetesimal disk or in situ. We performed N-body simulations and recorded the trajectories of the planetesimals during close approaches with Uranus and Neptune. Close encounters with Neptune are the most common, reaching approximately 1200 in total. A Pluto similarly sized body assumed the hyperbolic trajectories of the former primordial planetesimal with respect to those giant planets. We assumed the current mutual orbital configuration and sizes for Pluto's satellites, then we found that the rate of destruction of systems similar to that of Pluto with closest approaches to Uranus or Neptune

  7. THREE-DIMENSIONAL DISK-PLANET TORQUES IN A LOCALLY ISOTHERMAL DISK

    SciTech Connect

    D'Angelo, Gennaro; Lubow, Stephen H. E-mail: lubow@stsci.ed

    2010-11-20

    We determine an expression for the Type I planet migration torque involving a locally isothermal disk, with moderate turbulent viscosity (5 x 10{sup -4} {approx}< {alpha} {approx}< 0.05), based on three-dimensional nonlinear hydrodynamical simulations. The radial gradients (in a dimensionless logarithmic form) of density and temperature are assumed to be constant near the planet. We find that the torque is roughly equally sensitive to the surface density and temperature radial gradients. Both gradients contribute to inward migration when they are negative. Our results indicate that two-dimensional calculations with a smoothed planet potential, used to account for the effects of the third dimension, do not accurately determine the effects of density and temperature gradients on the three-dimensional torque. The results suggest that substantially slowing or stopping planet migration by means of changes in disk opacity or shadowing is difficult and appears unlikely for a disk that is locally isothermal. The scalings of the torque and torque density with planet mass and gas sound speed follow the expectations of linear theory. We also determine an improved formula for the torque density distribution that can be used in one-dimensional long-term evolution studies of planets embedded in locally isothermal disks. This formula can be also applied in the presence of mildly varying radial gradients and of planets that open gaps. We illustrate its use in the case of migrating super-Earths and determine some conditions sufficient for survival.

  8. The age of the Galactic disk - Inflow, chemical evolution, astration, and radioactivity

    NASA Technical Reports Server (NTRS)

    Clayton, Donald D.

    1989-01-01

    Theoretical models of Galactic evolution and observational data on the age of the Galaxy are compared, with a focus on recent results. Topics addressed include the infall of material and its effects on the age-metallicity relation, the distribution of metallicity, the present gas fraction and metallicity, and the age spectrum of interstellar nuclei; the chemical evolution of the solar neighborhood; the key results of nuclear cosmochronology; and astration effects on Galactic age. It is found that both nuclear cosmochronology and detailed stellar and Galactic evolution models tend to support an age of 12-16 Gyr.

  9. Evolution and Instability of Galactic Gas Disks inresponse to A Spiral Density-wave Potential

    NASA Astrophysics Data System (ADS)

    Yuan, Chi; Yen, D. C.; Wang, H. H.

    2006-12-01

    We revisit the classic problem of the response of the gas in a galactic disk to an imposed spiral density-wave potential of stellar origin. The results show the distinct difference between waves generated by resonance excitation and forced oscillation. To avoid the confusion of mixing these two types of waves, we systematically reduce the strength of the spiral potential or the force near the primary Lindblad resonances. So we can study the original problem of shock formation and star formation problem formulated by Roberts (1969). For the cases without self-gravitation of the gas disk, in addition to the primary doubly periodic shocks, the presence of the branch-like structures which correspond to the ultra-harmonic resonances is pronounced. On the other hand, once the self-gravitation is included, unlike the work of Chakrabarti et al. (2003), the sub-structures associated with the ultra-harmonics are not necessarily enhanced by the self-gravity. Their growth may be deteriorated by the growth of the primary shocks. Sub-structures other than those identified with the ultra-harmonics may result from shear instability of Rayleigh's kind or gravitational instability of Toomre's kind. They are responsible for the branches, feathers or chaotic sub-structures observed in nearby galaxies in far infra-red. The work is in parts supported by a grant from National Science Council, Taiwan NSC95-2752-M-001-009-PAE.

  10. Steepening of the 820 μm continuum surface brightness profile signals dust evolution in TW Hydrae's disk

    NASA Astrophysics Data System (ADS)

    Hogerheijde, Michiel R.; Bekkers, David; Pinilla, Paola; Salinas, Vachail N.; Kama, Mihkel; Andrews, Sean M.; Qi, Chunhua; Wilner, David J.

    2016-02-01

    Context. Grain growth in planet-forming disks is the first step toward the formation of planets. The growth of grains and their inward drift leaves a distinct imprint on the dust surface density distribution and the resulting surface brightness profile of the thermal continuum emission. Aims: We determine the surface brightness profile of the continuum emission using resolved observations at millimeter wavelengths of the disk around TW Hya, and infer the signature of dust evolution on the surface density and dust opacity. Methods: Archival ALMA observations at 820 μm on baselines up to 410 kλ are compared to parameterized disk models to determine the surface brightness profile. Results: Under the assumption of a constant dust opacity, a broken radial power law best describes the dust surface density with a slope of -0.53 ± 0.01 from the 4.1 au radius of the already known inner hole to a turn-over radius of 47.1 ± 0.2 au, steepening to -8.0 ± 0.1 at larger radii. The emission drops below the detection limit beyond ~60 au. Conclusions: The shape of the dust surface density is consistent with theoretical expectations for grain growth, fragmentation, and drift, but its total dust content and its turn-over radius are too large for TW Hya's age of 8-10 Myr even when taking into account a radially varying dust opacity. Higher resolution imaging with ALMA of TW Hya and other disks is required to establish whether unseen gaps associated with, e.g., embedded planets trap grains at large radii or whether locally enhanced grain growth associated with the CO snow line explains the extent of the millimeter continuum surface brightness profile. In the latter case, population studies should reveal a correlation between the location of the CO snow line and the extent of the millimeter continuum. In the former case, and if CO freeze-out promotes planet formation, this correlation should extend to the location of gaps as well.

  11. Evolution of salt and hydrocarbon migration: Sweet Lake area, Cameron Parish, Louisiana

    SciTech Connect

    Spencer, J.A.; Sharpe, C.L.

    1996-09-01

    The interpretation of seismic, gravity, and well data in northern Cameron Parish, Louisiana suggest that lateral salt flow has influenced the area`s structural evolution, depositional patterns, and hydrocarbon migration. Sweet Lake Field has produced over 46 MMBO and 15 BCFG from Middle Miocene deltaic sands. The structural closure is a downthrown anticline on a fault controlled by the underlying salt feature. Sweet Lake Field overlies an allochthonous salt mass that was probably once part of an ancestral salt ridge extending from Hackberry to Big Lake fields. Nine wells encountering top of salt and several seismic lines define a detached salt feature underlying over twenty square miles at depths from 8500-18,000 ft. Salt withdrawal in the East Hackberry-Big Lake area influenced the depositional patterns of the Oligocene lower Hackberry channel systems. Progradation of thick Middle Oligocene Camerina (A) and Miogypsinoides sands into the area caused salt thinning and withdrawal resulting in the development and orientation of the large Marginulina-Miogypsinoides growth fault northwest of Sweet Lake. Additional evidence for the southeast trend of the salt is a well approximately two miles southeast of Sweet Lake which encountered salt at approximately 19,800 ft. High quality 2-D and 3-D seismic data will continue to enhance the regional understanding of the evolving salt structures in the onshore Gulf Coast and the local understanding of hydrocarbon migration. Additional examples of lateral salt flow will be recognized and some may prove to have subsalt hydrocarbon potential.

  12. ON THE TEMPORAL EVOLUTION OF THE DISK COUNTERPART OF TYPE II SPICULES IN THE QUIET SUN

    SciTech Connect

    Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.

    2013-02-20

    The newly established type II spicule has been speculated to provide enough hot plasma to play an important role in the mass loading and heating of the solar corona. With the identification of rapid blueshifted excursions (RBEs) as the on-disk counterpart of type II spicules we have analyzed three different high-quality timeseries with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish Solar Telescope on La Palma and subjected to an automated detection routine to detect a large number of RBEs for statistical purposes. Our observations are of a quiet-Sun region at disk center and we find lower Doppler velocities, 15-40 km s{sup -1}, and Doppler widths, 2-15 km s{sup -1}, of RBEs than in earlier coronal hole studies, 30-50 km s{sup -1} and 7-23 km s{sup -1}, respectively. In addition, we examine the spatial dependence of Doppler velocities and widths along the RBE axis and conclude that there is no clear trend to this over the field of view or in individual RBEs in the quiet Sun at disk center. These differences with previous coronal hole studies are attributed to the more varying magnetic field configuration in quiet-Sun conditions. Using an extremely high-cadence data set has allowed us to improve greatly on the determination of lifetimes of RBEs, which we find to range from 5 to 60 s with an average lifetime of 30 s, as well as the transverse motions in RBEs, with transverse velocities up to 55 km s{sup -1} and averaging 12 km s{sup -1}. Furthermore, our measurements of the recurrence rates of RBEs provide important new constraints on coronal heating by spicules. We also see many examples of a sinusoidal wave pattern in the transverse motion of RBEs with periods averaging 54 s and amplitudes from 21.5 to 129 km which agrees well with previous studies of wave motion in spicules at the limb. We interpret the appearance of RBEs over their full length within a few seconds as the result of a combination of three kinds of motions as is earlier reported for

  13. Long-term and Large-scale Hydrodynamical Simulations of Migrating Planets

    NASA Astrophysics Data System (ADS)

    Benítez-Llambay, Pablo; Ramos, Ximena S.; Beaugé, Cristian; Masset, Frédéric S.

    2016-07-01

    We present a new method that allows for long-term and large-scale hydrodynamical simulations of migrating planets over a grid-based Eulerian code. This technique, which consists of a remapping of the disk by tracking the planetary migration, enables runs of migrating planets over a time comparable to the age of protoplanetary disks. This method also has the potential to address efficiency problems related to the migration of multi-planet systems in gaseous disks and to improve the current results of the migration of massive planets by including global viscous evolution as well as detailed studies of the co-orbital region during migration. We perform different tests using the public code FARGO3D to validate this method and compare its results with those obtained using a classical fixed grid.

  14. SELF-GRAVITY, RESONANCES AND ORBITAL DIFFUSION IN STELLAR DISKS

    SciTech Connect

    Fouvry, Jean-Baptiste; Pichon, Christophe; Binney, James

    2015-06-10

    Fluctuations in a stellar system's gravitational field cause the orbits of stars to evolve. The resulting evolution of the system can be computed with the orbit-averaged Fokker–Planck equation once the diffusion tensor is known. We present the formalism that enables one to compute the diffusion tensor from a given source of noise in the gravitational field when the system's dynamical response to that noise is included. In the case of a cool stellar disk we are able to reduce the computation of the diffusion tensor to a one-dimensional integral. We implement this formula for a tapered Mestel disk that is exposed to shot noise and find that we are able to explain analytically the principal features of a numerical simulation of such a disk. In particular the formation of narrow ridges of enhanced density in action space is recovered. As the disk's value of Toomre's Q is reduced and the disk becomes more responsive, there is a transition from a regime of heating in the inner regions of the disk through the inner Lindblad resonance to one of radial migration of near-circular orbits via the corotation resonance in the intermediate regions of the disk. The formalism developed here provides the ideal framework in which to study the long-term evolution of all kinds of stellar disks.

  15. A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution

    NASA Technical Reports Server (NTRS)

    Balbus, Steven A.; Hawley, John F.

    1991-01-01

    A broad class of astronomical accretion disks is presently shown to be dynamically unstable to axisymmetric disturbances in the presence of a weak magnetic field, an insight with consequently broad applicability to gaseous, differentially-rotating systems. In the first part of this work, a linear analysis is presented of the instability, which is local and extremely powerful; the maximum growth rate, which is of the order of the angular rotation velocity, is independent of the strength of the magnetic field. Fluid motions associated with the instability directly generate both poloidal and toroidal field components. In the second part of this investigation, the scaling relation between the instability's wavenumber and the Alfven velocity is demonstrated, and the independence of the maximum growth rate from magnetic field strength is confirmed.

  16. TAGGING THE CHEMICAL EVOLUTION HISTORY OF THE LARGE MAGELLANIC CLOUD DISK

    SciTech Connect

    Lapenna, Emilio; Mucciarelli, Alessio; Ferraro, Francesco R.; Origlia, Livia E-mail: alessio.mucciarelli2@unibo.it E-mail: livia.origlia@oabo.inaf.it

    2012-12-10

    We have used high-resolution spectra obtained with the multifiber facility FLAMES at the Very Large Telescope of the European Southern Observatory to derive kinematic properties and chemical abundances of Fe, O, Mg, and Si for 89 stars in the disk of the Large Magellanic Cloud (LMC). The derived metallicity and [{alpha}/Fe], obtained as the average of O, Mg, and Si abundances, allow us to draw a preliminary scheme of the star formation history of this region of the LMC. The derived metallicity distribution shows two main components: one component (comprising {approx}84% of the sample) peaks at [Fe/H] = -0.48 dex and it shows an [{alpha}/Fe] ratio slightly under solar ([{alpha}/Fe] {approx} -0.1 dex). This population probably originated in the main star formation event that occurred 3-4 Gyr ago (possibly triggered by tidal capture of the Small Magellanic Cloud). The other component (comprising {approx}16% of the sample) peaks at [Fe/H] {approx} -0 dex and it shows an [{alpha}/Fe] {approx}0.2 dex. This population was probably generated during the long quiescent epoch of star formation between the first episode and the most recent bursts. Indeed, in our sample we do not find stars with chemical properties similar to the old LMC globular clusters nor to the iron-rich and {alpha}-poor stars recently found in the LMC globular cluster NGC 1718 and also predicted to be in the LMC field, thus suggesting that both of these components are small (<1%) in the LMC disk population.

  17. 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.

  18. Shaping Disk Galaxy Stellar Populations via Internal and External Processes

    NASA Astrophysics Data System (ADS)

    Roškar, Rok

    2015-03-01

    In recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

  19. Amphioxus and lamprey AP-2 genes: implications for neural crest evolution and migration patterns

    NASA Technical Reports Server (NTRS)

    Meulemans, Daniel; Bronner-Fraser, Marianne

    2002-01-01

    The neural crest is a uniquely vertebrate cell type present in the most basal vertebrates, but not in cephalochordates. We have studied differences in regulation of the neural crest marker AP-2 across two evolutionary transitions: invertebrate to vertebrate, and agnathan to gnathostome. Isolation and comparison of amphioxus, lamprey and axolotl AP-2 reveals its extensive expansion in the vertebrate dorsal neural tube and pharyngeal arches, implying co-option of AP-2 genes by neural crest cells early in vertebrate evolution. Expression in non-neural ectoderm is a conserved feature in amphioxus and vertebrates, suggesting an ancient role for AP-2 genes in this tissue. There is also common expression in subsets of ventrolateral neurons in the anterior neural tube, consistent with a primitive role in brain development. Comparison of AP-2 expression in axolotl and lamprey suggests an elaboration of cranial neural crest patterning in gnathostomes. However, migration of AP-2-expressing neural crest cells medial to the pharyngeal arch mesoderm appears to be a primitive feature retained in all vertebrates. Because AP-2 has essential roles in cranial neural crest differentiation and proliferation, the co-option of AP-2 by neural crest cells in the vertebrate lineage was a potentially crucial event in vertebrate evolution.

  20. X-RAYING AN ACCRETION DISK IN REALTIME: THE EVOLUTION OF IONIZED REFLECTION DURING A SUPERBURST FROM 4U 1636-536

    SciTech Connect

    Keek, L.; Ballantyne, D. R.; Kuulkers, E.; Strohmayer, T. E.

    2014-12-20

    When a thermonuclear X-ray burst ignites on an accreting neutron star, the accretion disk undergoes sudden strong X-ray illumination, which can drive a range of processes in the disk. Observations of superbursts, with durations of several hours, provide the best opportunity to study these processes and to probe accretion physics. Using detailed models of X-ray reflection, we perform time resolved spectroscopy of the superburst observed from 4U 1636-536 in 2001 with the Rossi X-Ray Timing Explorer. The spectra are consistent with a blackbody reflecting off a photoionized accretion disk, with the ionization state dropping with time. The evolution of the reflection fraction indicates that the initial reflection occurs from a part of the disk at larger radius, subsequently transitioning to reflection from an inner region of the disk. Even though this superburst did not reach the Eddington limit, we find that a strong local absorber develops during the superburst. Including this event, only two superbursts have been observed by an instrument with sufficient collecting area to allow for this analysis. It highlights the exciting opportunity for future X-ray observatories to investigate the processes in accretion disks when illuminated by superbursts.

  1. Decoupling of a giant planet from its disk in an inclined binary system

    NASA Astrophysics Data System (ADS)

    Picogna, G.; Marzari, F.

    2015-11-01

    Context. We explore the dynamical evolution of a planet that is embedded in a circumstellar disk, as part of a binary system where the orbital plane of the companion star is significantly tilted with respect to the initial disk plane. Aims: Our aim is to test whether the planet remains within the disk and continues to migrate towards the star in a Type I/II mode, in spite of the secular perturbations of the companion star. Our findings, could explain why observed exoplanets have significant inclination in relation to the equatorial plane of their host star. Methods: We used two different smoothed particle hydrodynamic codes, VINE and PHANTOM, to model the evolution of a star+disk+planet system with a companion star over time. Results: After an initial coupled evolution, the inclinations of the disk and the planet begin to differ significantly. The period of oscillation of the disk inclination, in relation to the initial plane, becomes shorter for the planet, which evolves independently after about 104 yr, following a perturbed N-body behaviour. However, the planet continues to migrate towards the star because, during its orbital motion, it crosses the disk plane, and friction with the gas causes angular momentum loss. Conclusions: In a significantly inclined binary system, disks and planets are not dynamically coupled for small binary separations but evolve almost independently. The planet abandons the disk, and because of the onset of a significant mutual inclination, it interacts with the gas only when its orbit intersects the disk plane. The drift of the planet towards the star is not due to Type I/II, where the planet is embedded in the disk, but to the friction with the gas while crossing the disk.

  2. 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

  3. Final Masses of Giant Planets II: Jupiter Formation in a Gas-Depleted Disk

    NASA Astrophysics Data System (ADS)

    Tanigawa, Takayuki; Tanaka, Hidekazu

    2015-12-01

    Firstly, we study the final masses of giant planets growing in protoplanetary disks through capture of disk gas, by employing an empirical formula for the gas capture rate and a shallow disk gap model, which are both based on hydrodynamical simulations. The shallow disk gaps cannot terminate growth of giant planets. For planets less massive than 10 Jupiter masses, their growth rates are mainly controlled by the gas supply through the global disk accretion, rather than their gaps. The insufficient gas supply compared with the rapid gas capture causes a depletion of the gas surface density even at the outside of the gap, which can create an inner hole in the protoplanetary disk. Our model can also predict how deep the inner hole is for a given planet mass. Secondly, our findings are applied to the formation of our solar system. For the formation of Jupiter, a very low-mass gas disk with a few or several Jupiter masses is required at the beginning of its gas capture because of the non-stopping capture. Such a low-mass gas disk with sufficient solid material can be formed through viscous evolution from an initially ˜10AU-sized compact disk with the solar composition. By the viscous evolution with a moderate viscosity of α˜10-3, most of disk gas accretes onto the sun and a widely spread low-mass gas disk remains when the solid core of Jupiter starts gas capture at t˜107 yrs. The depletion of the disk gas is suitable for explaining the high metallicity in giant planets of our solar system. A very low-mass gas disk also provides a plausible path where type I and II planetary migrations are both suppressed significantly. In particular, we also show that the type II migration of Jupiter-size planets becomes inefficient because of the additional gas depletion due to the rapid gas capture by themselves.

  4. Evolution of planetesimals. I - Dynamics: Relaxation in a thin disk. II - Numerical simulations

    NASA Astrophysics Data System (ADS)

    Palmer, P. L.; Lin, D. N. C.; Aarseth, S. J.

    1993-01-01

    The study examines the effects of density inhomogeneity and differential rotation as well as inelastic collisions on the dynamical evolution of planetesimals. Consideration is given to a three-step analysis: the dynamical evolution of the planetesimals, collisions and mass accumulation, and interaction with gas. It is shown that the velocity dispersion of a cold system of planetesimals increases rapidly due to elastic gravitational scattering. When the dispersion in the epicycle amplitude becomes comparable to the planetesimals' Roche radius, energy is transferred from the systematic Keplerian shear to the dispersive motion. With a numerical N-body scheme, gravitational scattering and physical collisions among a system of planetesimals is simulated. It is shown that dynamical equilibrium is attained with a velocity dispersion comparable to the surface escape velocity of those planetesimals which contribute most of the system mass.

  5. Migration Theories

    NASA Astrophysics Data System (ADS)

    Crida, Aurélien

    2015-08-01

    The great variety of the architectures of the extra-solar planetary systems has revealed the fundamental role played by planetary migration: the interactions between the planets and the gaseous disk in which they form leads to a modification of their orbits. Here, I will review the basic processes and the most recent results in this area.Planets up to ~50 Earth masses are prone to so-called type I migration.I will describe the processes at play, namely the Lindblad and corotation torques, and explain how the total torque depends on the planet mass and the local disk structure. Application to realistic disks shows one or two sweet spot(s) for outward migration of planets roughly between 5 and 30 Earth masses around the snowline ; this is confirmed by dedicated 3D numerical simulations. This has strong consequences on the formation of hot Super-Earths or mini-Neptunes.For smaller mass planets, it has been recently proposed that the heating of the neighboring gas by the luminous planet can lead to a positive torque, hence promoting outward migration. On the other hand, if the planet is not a heat source, a cold finger appears, whose resulting torque is negative. Applications of these two recent results should be discussed.Giant planets open gaps in the proto-planetary disk, and then are supposedly subject to type II migration, following the viscous accretion of the disk. This standard picture has been questioned recently, as gas appears to drift through the gap. Although the gap opening process is well understood in 2D for a planet on a fixed orbit, recent results on 3D simulations or migrating planets make the picture more accurate.Our ever better understanding of planet-disk interactions is of crucial importance as the statistics on extra solar systems keep growing and the results of these interactions are now imaged.

  6. Evolution of heavy-element abundances in the Galactic halo and disk

    NASA Technical Reports Server (NTRS)

    Mathews, G. J.; Cowan, J. J.; Schramm, D. N.

    1988-01-01

    The constraints on the universal energy density and cosmological constant from cosmochronological ages and the Hubble age are reviewed. Observational evidence for the galactic chemical evolution of the heavy-element chronometers is descirbed in the context of numerical models. The viability of the recently discovered Th/Nd stellar chronometer is discussed, along with the suggestion that high r-process abundances in metal-poor stars may have resulted from a primordial r-process, as may be required by some inhomogeneous cosmologies.

  7. STABILITY OF THE OUTER PLANETS IN MULTIRESONANT CONFIGURATIONS WITH A SELF-GRAVITATING PLANETESIMAL DISK

    SciTech Connect

    Reyes-Ruiz, M.; Aceves, H.; Chavez, C. E.

    2015-05-10

    We study the effect of a massive planetesimal disk on the dynamical stability of the outer planets in a system representing the early solar system assuming, as has been suggested recently, that these planets were initially locked in a compact and multiresonant configuration as a result of gas-driven migration in a protoplanetary disk. The planetesimal disk is represented by an ensemble of 2000 lunar mass bodies for which the gravitational interaction is calculated self-consistently using the Mercury6.5 code. Several initial multiresonant configurations and planetesimal disk models are considered. Under such conditions a strong dynamical instability, manifested as a rapid giant planet migration and planetesimal disk dispersal, develops on a timescale of less than 40 Myr in most cases. Dynamical disk heating due to the gravitational interactions among planetesimals leads to more frequent interactions between the planetesimals and the ice giants, in comparison to models in which planetesimal–planetesimal interactions are neglected. The number of particles used to represent the planetesimal disk has implications for our results, and although our studies represent the first self-consistent calculations of unstable planetesimal-driven migration, our results point toward the need for using more realistic treatments of the planetesimal disk. Finally, in the framework of our model, we discuss the possible implications of our results on the early evolution of the solar system.

  8. Satellite And Propeller Migration In Saturn's Rings

    NASA Astrophysics Data System (ADS)

    Crida, Aurelien; Charnoz, S.; Papaloizou, J.; Salmon, J.

    2009-09-01

    Saturn's rings host satellites like Pan and Daphnis, and smaller bodies like the recently discovered propellers (Tiscareno et al. 2006). These bodies interact gravitationally with the rings. Actually, the resulting perturbations on the ring system have revealed the presence of embedded objects (the Encke and Keeler gaps associated with Pan and Daphnis respectively, the little two-folded structures called propellers tracing the scattering of ring particles by some embedded small objects). Reciprocally, the rings must act on the embedded bodies, leading to their migration. Here, we study how the standard theory of planetary migration applies in Saturn's ring, where the pressure is negligible in contrast with standard protoplanetary disks. Pan and Daphnis should be in standard type II migration, governed by the global disk evolution. Therefore, their presence and position provide constraints on the history of the A-ring, which can be studied using numerical simulations of disk-satellite interactions. The propellers are fully embedded in the disc, and therefore should be subject to type I migration. The simple impulse approximation used by Lin and Papaloi zou (1979) to derive the one-sided torque is particularly suited to this case. Refining their calculation, taking density variations into account, and discussing the possibility for these bodies to enter the type III, runaway regime of migration, we aim at estimating a possible migration rate for these propellers, to be compared to the system life time.

  9. Radially Magnetized Protoplanetary Disk: Vertical Profile

    NASA Astrophysics Data System (ADS)

    Russo, Matthew; Thompson, Christopher

    2015-11-01

    This paper studies the response of a thin accretion disk to an external radial magnetic field. Our focus is on protoplanetary disks (PPDs), which are exposed during their later evolution to an intense, magnetized wind from the central star. A radial magnetic field is mixed into a thin surface layer, wound up by the disk shear, and pushed downward by a combination of turbulent mixing and ambipolar and ohmic drift. The toroidal field reaches much greater strengths than the seed vertical field that is usually invoked in PPD models, even becoming superthermal. Linear stability analysis indicates that the disk experiences the magnetorotational instability (MRI) at a higher magnetization than a vertically magnetized disk when both the effects of ambipolar and Hall drift are taken into account. Steady vertical profiles of density and magnetic field are obtained at several radii between 0.06 and 1 AU in response to a wind magnetic field Br ˜ (10-4-10-2)(r/ AU)-2 G. Careful attention is given to the radial and vertical ionization structure resulting from irradiation by stellar X-rays. The disk is more strongly magnetized closer to the star, where it can support a higher rate of mass transfer. As a result, the inner ˜1 AU of a PPD is found to evolve toward lower surface density. Mass transfer rates around 10-8 M⊙ yr-1 are obtained under conservative assumptions about the MRI-generated stress. The evolution of the disk and the implications for planet migration are investigated in the accompanying paper.

  10. The origin and evolution of r- and s-process elements in the Milky Way stellar disk

    NASA Astrophysics Data System (ADS)

    Battistini, Chiara; Bensby, Thomas

    2016-02-01

    Context. Elements heavier than iron are produced through neutron-capture processes in the different phases of stellar evolution. Asymptotic giant branch (AGB) stars are believed to be mainly responsible for elements that form through the slow neutron-capture process, while the elements created in the rapid neutron-capture process have production sites that are less understood. Knowledge of abundance ratios as functions of metallicity can lead to insight into the origin and evolution of our Galaxy and its stellar populations. Aims: We aim to trace the chemical evolution of the neutron-capture elements Sr, Zr, La, Ce, Nd, Sm, and Eu in the Milky Way stellar disk. This will allow us to constrain the formation sites of these elements, as well as to probe the evolution of the Galactic thin and thick disks. Methods: Using spectra of high resolution (42 000 ≲ R ≲ 65 000) and high signal-to-noise (S/N ≳ 200) obtained with the MIKE and the FEROS spectrographs, we determine Sr, Zr, La, Ce, Nd, Sm, and Eu abundances for a sample of 593 F and G dwarf stars in the solar neighborhood. The abundance analysis is based on spectral synthesis using one-dimensional, plane-parallel, local thermodynamic equilibrium (LTE) model stellar atmospheres calculated with the MARCS 2012 code. Results: We present abundance results for Sr (156 stars), Zr (311 stars), La (242 stars), Ce (365 stars), Nd (395 stars), Sm (280 stars), and Eu (378 stars). We find that Nd, Sm, and Eu show trends similar to what is observed for the α elements in the [X/Fe]-[Fe/H] abundance plane. For [Sr/Fe] and [Zr/Fe], we find decreasing abundance ratios for increasing metallicity, reaching sub-solar values at super-solar metallicities. [La/Fe] and [Ce/Fe] do not show any clear trend with metallicity, and they are close to solar values at all [Fe/H]. The trends of abundance ratios [X/Fe] as a function of stellar ages present different slopes before and after 8 Gyr. Conclusions: The rapid neutron-capture process is

  11. EFFECTS OF DUST FEEDBACK ON VORTICES IN PROTOPLANETARY DISKS

    SciTech Connect

    Fu, Wen; Liang, Edison; Li, Hui; Li, Shengtai; Lubow, Stephen

    2014-11-10

    We carried out two-dimensional, high-resolution simulations to study the effect of dust feedback on the evolution of vortices induced by massive planets in protoplanetary disks. Various initial dust to gas disk surface density ratios (0.001-0.01) and dust particle sizes (Stokes number 4 × 10{sup –4}-0.16) are considered. We found that while dust particles migrate inward, vortices are very effective at collecting them. When dust density becomes comparable to gas density within the vortex, a dynamical instability is excited and it alters the coherent vorticity pattern and destroys the vortex. This dust feedback effect is stronger with a higher initial dust/gas density ratio and larger dust grain. Consequently, we found that the disk vortex lifetime can be reduced up to a factor of 10. We discuss the implications of our findings on the survivability of vortices in protoplanetary disks and planet formation.

  12. Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Yang, Chao-Chin; Mac Low, M.; Menou, K.

    2010-01-01

    In core accretion scenario of planet formation, kilometer-sized planetesimals are the building blocks toward planetary cores. Their dynamics, however, are strongly influenced by their natal protoplanetary gas disks. It is generally believed that these disks are turbulent, most likely due to magnetorotational instability. The resulting density perturbations in the gas render the movement of the particles a random process. Depending on its strength, this process might cause several interesting consequences in the course of planet formation, specifically the survivability of objects under rapid inward type-I migration and/or collisional destruction. Using the local-shearing-box approximation, we conduct numerical simulations of planetesimals moving in a turbulent, magnetized gas disk, either unstratified or vertically stratified. We produce a fiducial disk model with turbulent accretion of Shakura-Sunyaev alpha about 10-2 and root-mean-square density perturbation of about 10% and statistically characterize the evolution of the orbital properties of the particles moving in the disk. These measurements result in accurate calibration of the random process of particle orbital change, indicating noticeably smaller magnitudes than predicted by global simulations, although the results may depend on the size of the shearing box. We apply these results to revisit the survivability of planetesimals under collisional destruction or protoplanets under type-I migration. Planetesimals are probably secure from collisional destruction, except for kilometer-sized objects situated in the outer regions of a young protoplanetary disk. On the other hand, we confirm earlier studies of local models in that type-I migration probably dominates diffusive migration due to stochastic torques for most planetary cores and terrestrial planets. Discrepancies in the derived magnitude of turbulence between local and global simulations of magnetorotationally unstable disks remains an open issue, with

  13. 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.

  14. Chemo -- dynamical, multi -- fragmented SPH code for evolution of star forming disk galaxies

    NASA Astrophysics Data System (ADS)

    Berczik, P.

    The problem of chemical and dynamical evolution of galaxies is one of the most attracting and complex problems of modern astrophysics. Within the framework of the given paper the standard dynamic Smoothed Particle Hydrodynamics (SPH) code (Monaghan J.J. 1992, ARAA, 30, 543) is noticeably expanded. Our work concernes with the changes and incorporation of new ideas into the algorithmic inclusion of Star Formation (SF) and Super Novae (SN) explosions in SPH (Berczik P. & Kravchuk S.G., 1996, ApSpSci, 245, 27). The proposed energy criterion for definition of a place and efficiency of SF results in the successfully explain Star Formation History (SFH) in isolated galaxies of different types. On the base of original ideas we expand a code in a more realistic way of the description of effects of return of a hot, chemical enriched gas in Interstellar Matter (ISM). In addition to the account of SNII, we offer the self-agreed account of SNIa and PN. This allows to describe not only the ISM content of O^16 but also the content of Fe^56 . This model will allow to investigate adequately also a well known G - dwarf problem.

  15. The impact of galactic fountains on the global evolution of galaxy disks

    NASA Astrophysics Data System (ADS)

    Fraternali, F.

    2016-06-01

    The evolution of the Milky Way, and its thin disc in particular, is a history of continuous accretion of fresh gas from the surrounding environment. Evidence for this accretion taking place include high-velocity clouds (HVCs) that appear to be raining down from the halo. I present a model that explains the formation of the prototypical HVC Complex C as gas cooling of the Galactic corona triggered by the explosion of a superbubble in the Outer arm occurred 150 Myr ago. This result is obtained with a new galactic fountain model combined with high-resolution hydrodynamical simulations. The material ejected by the superbubble has triggered the condensation of a large portion of the circumgalactic medium and caused its subsequent accretion on to the disc. This is a local manifestation of fountain-driven cooling of the lower Galactic corona that can contribute significantly in brining fresh low-metallicity gas to the disc of our Galaxy. The same model also reproduces the global-scale kinematics of the extraplanar gas and predicts a gas accretion that evolves inside-out.

  16. UNSTABLE PLANETARY SYSTEMS EMERGING OUT OF GAS DISKS

    SciTech Connect

    Matsumura, Soko; Thommes, Edward W.; Chatterjee, Sourav; Rasio, Frederic A.

    2010-05-01

    The discovery of over 400 extrasolar planets allows us to statistically test our understanding of the formation and dynamics of planetary systems via numerical simulations. Traditional N-body simulations of multiple-planet systems without gas disks have successfully reproduced the eccentricity (e) distribution of the observed systems by assuming that the planetary systems are relatively closely packed when the gas disk dissipates, so that they become dynamically unstable within the stellar lifetime. However, such studies cannot explain the small semimajor axes a of extrasolar planetary systems, if planets are formed, as the standard planet formation theory suggests, beyond the ice line. In this paper, we numerically study the evolution of three-planet systems in dissipating gas disks, and constrain the initial conditions that reproduce the observed a and e distributions simultaneously. We adopt initial conditions that are motivated by the standard planet formation theory, and self-consistently simulate the disk evolution and planet migration, by using a hybrid N-body and one-dimensional gas disk code. We also take into account eccentricity damping, and investigate the effect of saturation of corotation resonances on the evolution of planetary systems. We find that the a distribution is largely determined in a gas disk, while the e distribution is determined after the disk dissipation. We also find that there may be an optimum disk mass which leads to the observed a-e distribution. Our simulations generate a larger fraction of planetary systems trapped in mean-motion resonances (MMRs) than the observations, indicating that the disk's perturbation to the planetary orbits may be important to explain the observed rate of MMRs. We also find a much lower occurrence of planets on retrograde orbits than the current observations of close-in planets suggest.

  17. Migration or residency? The evolution of movement behavior and information usage in seasonal environments.

    PubMed

    Shaw, Allison K; Couzin, Iain D

    2013-01-01

    Migration, the seasonal movement of individuals among different locations, is a behavior found throughout the animal kingdom. Although migration is widely studied at taxonomically restricted levels, cross-taxonomic syntheses of migration are less common. As a result, we lack answers to broad questions such as what ultimate factors generally drive animal migration. Here we present such a synthesis by using a spatially explicit, individual-based model in which we evolve behavior rules via simulations under a wide range of ecological conditions to answer two questions. First, under what types of ecological conditions can an individual maximize its fitness by migrating (vs. being a resident)? Second, what types of information do individuals use to guide their movement? We show that migration is selected for when resource distributions are dominated more by seasonality than by local patchiness, and residency (nonmigratory behavior) is selected for when the reverse is true. When selected for, migration evolves as both a movement behavior and an information usage strategy. We also find that different types of migration can evolve, depending on the ecological conditions and availability of information. Finally, we present empirical support for our main results, drawn from migration patterns exhibited by a variety of taxonomic groups.

  18. Final Masses of Giant Planets. II. Jupiter Formation in a Gas-depleted Disk

    NASA Astrophysics Data System (ADS)

    Tanigawa, Takayuki; Tanaka, Hidekazu

    2016-05-01

    First, we study the final masses of giant planets growing in protoplanetary disks through capture of disk gas, by employing empirical formulae for the gas capture rate and a shallow disk gap model, which are both based on hydrodynamic simulations. We find that, for planets less massive than 10 Jupiter masses, their growth rates are mainly controlled by the gas supply through the global disk accretion, and the gap opening does not limit the accretion. The insufficient gas supply compared with the rapid gas capture causes a depletion of the gas surface density even at the outside the gap, which can create an inner hole in the disk. Second, our findings are applied to the formation of our solar system. For the formation of Jupiter, a very low-mass gas disk of several Jupiter masses is required at the beginning of its gas capture because of the continual capture. Such a low-mass gas disk with sufficient solid material can be formed through viscous evolution from a compact disk of initial size ˜10 au. By viscous evolution with a moderate viscosity of α ˜ 10‑3, most of the disk gas accretes onto the Sun and a widely spread low-mass gas disk remains when the solid core of Jupiter starts gas capture at t ˜ 107 yr. A very low-mass gas disk also provides a plausible path where type I and II planetary migrations are both suppressed significantly. In particular, the type II migration of Jupiter-size planets becomes inefficient because of the additional gas depletion due to the rapid gas capture by such planets.

  19. Formation and evolution of a circumterrestrial disk Constraints on the origin of the moon in geocentric orbit

    NASA Technical Reports Server (NTRS)

    Herbert, Floyd; Davis, Donald R.; Weidenschilling, Stuart J.

    1986-01-01

    A data base of about 25,000 numerically integrated trajectories of earth-encountering planetesimals is used to study the angular momentum problem of forming the moon out of material captured into a circumterrestrial disk from heliocentric orbits. Mass-orbital element distributions of incoming planetesimals are combined with this data base to calculate, as a function of distance from earth, the net geocentric specific angular momentum of disk-encountering material on heliocentric orbits. Results suggest that a permanent disk population is not possible.

  20. DUSTY DISKS AROUND WHITE DWARFS. I. ORIGIN OF DEBRIS DISKS

    SciTech Connect

    Dong Ruobing; Wang Yan; Lin, D. N. C.; Liu, X.-W. E-mail: yuw123@psu.ed E-mail: liuxw@bac.pku.edu.c

    2010-06-01

    A significant fraction of the mature FGK stars have cool dusty disks at least an order of magnitude brighter than the solar system's outer zodiacal light. Since such dusts must be continually replenished, they are generally assumed to be the collisional fragments of residual planetesimals analogous to the Kuiper-Belt objects. At least 10% of solar-type stars also bear gas giant planets. The fraction of stars with known gas giants or detectable debris disks (or both) appears to increase with the stellar mass. Here, we examine the dynamical evolution of systems of long-period gas giant planets and residual planetesimals as their host stars evolve off the main sequence, lose mass, and form planetary nebula around remnant white dwarf cores. The orbits of distant gas giant planets and super-km-size planetesimals expand adiabatically. During the most intense asymptotic giant branch mass-loss phase, sub-meter-size particles migrate toward their host stars due to the strong hydrodynamical drag by the intense stellar wind. Along their migration paths, gas giant planets capture and sweep up sub-km-size planetesimals onto their mean-motion resonances. These planetesimals also acquire modest eccentricities which are determined by the mass of the perturbing planets, and the rate and speed of stellar mass loss. The swept-up planetesimals undergo disruptive collisions which lead to the production of grains with an extended size range. The radiation drag on these particles is ineffective against the planets' resonant barrier and they form 30-50 AU size rings which can effectively reprocess the stellar irradiation in the form of FIR continuum. We identify the recently discovered dust ring around the white dwarf WD 2226-210 at the center of the Helix nebula as a prototype of such disks and suggest such rings may be common.

  1. PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL STRATIFIED DISKS

    SciTech Connect

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen E-mail: mordecai@amnh.org

    2012-04-01

    Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion L{sub h} /R {approx} O(1), where L{sub h} is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

  2. Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk: Ideal Stratified Disks

    NASA Astrophysics Data System (ADS)

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen

    2012-04-01

    Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion Lh /R ~ O(1), where Lh is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

  3. Grain growth and dust trapping in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Pinilla, Paola

    2015-08-01

    Circumstellar disks around young stars are known to be the birthplace of planets. Planet formation starts with the coagulation of micron-sized particles to larger dust aggregates. This process, which covers more than forty orders of magnitude in mass, has different physical challenges. One of the oldest mysteries is how planetesimals are formed, in spite of fragmentation collisions and rapid inward drift. Radial drift theory is in disagreement with the observations of millimetre grains in the cold regions of protoplanetary disks. Nevertheless, a disk model that includes dust coagulation, fragmentation, and the presence of long-lived pressure bumps, which moderate the rapid inward migration of particles, leads to a better agreement between observations and theory. Disks with a dust depleted inner cavity, known as transition disks, are excellent candidates to investigate the dust evolution under the existence of a pressure bump. Millimetre observations of transition disks reveal crescent- and ring-shaped emissions that lend credence to the notion than planetesimals may form in localised hotspots or pressure traps. Recent ALMA observations have showed astonishing dust structures in transition disks, which together with data of CO and its isotopologues, have been giving major support for particle trapping induced by embedded planets, which can solve the old paradigm of radial drift.

  4. The status of circular migration in the evolution of Melanesian towns: an attempt at explanation.

    PubMed

    Walsh, A C

    1992-01-01

    "This article proposes a model of Melanesian urbanization and associated forms of migration, both permanent and temporary/circular. The model describes four stages of urban development, spanning the arrival of capitalism to a futuristic city of the next century. The author links the future of circular migration in Melanesia to the relative strengths of the precapitalist and capitalist modes of production and associated social relations, particularly the wantok [kinship network]." PMID:12343908

  5. Migration of lymphocytes on fibronectin-coated surfaces: temporal evolution of migratory parameters

    NASA Technical Reports Server (NTRS)

    Bergman, A. J.; Zygourakis, K.; McIntire, L. V. (Principal Investigator)

    1999-01-01

    Lymphocytes typically interact with implanted biomaterials through adsorbed exogenous proteins. To provide a more complete characterization of these interactions, analysis of lymphocyte migration on adsorbed extracellular matrix proteins must accompany the commonly performed adhesion studies. We report here a comparison of the migratory and adhesion behavior of Jurkat cells (a T lymphoblastoid cell line) on tissue culture treated and untreated polystyrene surfaces coated with various concentrations of fibronectin. The average speed of cell locomotion showed a biphasic response to substrate adhesiveness for cells migrating on untreated polystyrene and a monotonic decrease for cells migrating on tissue culture-treated polystyrene. A modified approach to the persistent random walk model was implemented to determine the time dependence of cell migration parameters. The random motility coefficient showed significant increases with time when cells migrated on tissue culture-treated polystyrene surfaces, while it remained relatively constant for experiments with untreated polystyrene plates. Finally, a cell migration computer model was developed to verify our modified persistent random walk analysis. Simulation results suggest that our experimental data were consistent with temporally increasing random motility coefficients.

  6. Morphological evolution and migration of void in bi-piezoelectric interface based on nonlocal phase field method

    NASA Astrophysics Data System (ADS)

    Li, H. B.; Wang, X.

    2016-05-01

    This paper reports the result of investigation into the morphological evolution and migration of void in bi-piezoelectric material interface by utilizing nonlocal phase field model and finite element method (FEM), where the small scale effect containing the long-range forces among atoms is considered. The nonlocal elastic strain energy and the nonlocal electric energy around the void are firstly calculated by the finite element method. Then based on the finite difference method (FDM), the thermodynamic equilibrium equation containing the surface energy and anisotropic diffusivity is solved to simulate the morphological evolution and migration of elliptical void in bi-piezoelectric films interface. Results show that the way of load condition plays a significant role in the evolution process, and the boundary of void's long axis gradually collapses toward the center of ellipse. In addition, the evolutionary speed of left boundary gradually decreases with scale effect coefficient growth. This work can provide references for the safety evaluation of piezoelectric materials in micro electro mechanical system.

  7. ORBITAL MIGRATION OF LOW-MASS PLANETS IN EVOLUTIONARY RADIATIVE MODELS: AVOIDING CATASTROPHIC INFALL

    SciTech Connect

    Lyra, Wladimir; Mac Low, Mordecai-Mark; Paardekooper, Sijme-Jan E-mail: mordecai@amnh.or

    2010-06-01

    Outward migration of low-mass planets has recently been shown to be a possibility in non-barotropic disks. We examine the consequences of this result in evolutionary models of protoplanetary disks. Planet migration occurs toward equilibrium radii with zero torque. These radii themselves migrate inwards because of viscous accretion and photoevaporation. We show that as the surface density and temperature fall the planet orbital migration and disk depletion timescales eventually become comparable, with the precise timing depending on the mass of the planet. When this occurs, the planet decouples from the equilibrium radius. At this time, however, the gas surface density is already too low to drive substantial further migration. A higher mass planet, of 10 M {sub +}, can open a gap during the late evolution of the disk, and stops migrating. Low-mass planets, with 1 or 0.1 M {sub +}, released beyond 1 AU in our models avoid migrating into the star. Our results provide support for the reduced migration rates adopted in recent planet population synthesis models.

  8. Measuring the Relative Contributions of Viscous Accretion and Photoevaporation to the Dispersal of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Simon, M. N.; Pascucci, I.; Rigliaco, E.; Gorti, U.; Hollenbach, D.

    2014-03-01

    Models of protoplanetary disk evolution suggest that photoevaporation driven by the central star and viscous evolution via gas accretion onto the star are the main mechanisms that drive disk dispersal. Viscous evolution has the ability to smoothly decrease the disk surface density, but photoevaporation can drastically change it by creating gaps in planet-forming regions that widen quickly over time. This quick gas dispersal can stop the migration of giant planets whose location affects the final delivery of volatiles (including water) to terrestrial planets. We selected a sample of twenty protoplanetary disks around T. Tauri stars in the Taurus region spanning all three main disk evolutionary stages, with a range of mass accretion rates. For this sample we have acquired high-resolution optical spectra with Keck/HIRES covering gas lines that trace both accretion and photoevaporation. We will present an analysis of the forbidden OI, SII, and NII lines and provide empirically determined mass loss rates as a function of disk evolutionary stage and mass accretion rate. This will enhance our understanding of the disk stage at which photoevaporation starts to dominate over viscous accretion.

  9. A behavior-oriented dynamic model for sandbar migration and 2DH evolution

    USGS Publications Warehouse

    Splinter, K.D.; Holman, R.A.; Plant, N.G.

    2011-01-01

    A nonlinear model is developed to study the time-dependent relationship between the alongshore variability of a sandbar, a(t), and alongshore-averaged sandbar position, xc(t). Sediment transport equations are derived from energetics-based formulations. A link between this continuous physical representation and a parametric form describing the migration of sandbars of constant shape is established through a simple transformation of variables. The model is driven by offshore wave conditions. The parametric equations are dynamically coupled such that changes in one term (i.e., xc) drive changes in the other (i.e., a(t)). The model is tested on 566 days of data from Palm Beach, New South Wales, Australia. Using weighted nonlinear least squares to estimate best fit model coefficients, the model explained 49% and 41% of the variance in measured xc and a(t), respectively. Comparisons against a 1-D horizontal (1DH) version of the model showed significant improvements when the 2DH terms were included (1DH and 2DH Brier skill scores were -0.12 and 0.42, respectively). Onshore bar migration was not predicted in the 1DH model, while the 2DH model correctly predicted onshore migration in the presence of 2DH morphology and allowed the bar to remain closer to shore for a given amount of breaking, providing an important hysteresis to the system. The model is consistent with observations that active bar migration occurs under breaking waves with onshore migration occurring at timescales of days to weeks and increasing 2DH morphology, while offshore migration occurs rapidly under high waves and coincides with a reduction in 2DH morphology. Copyright ?? 2011 by the American Geophysical Union.

  10. Hillslope response to knickpoint migration in the Southern Appalachians: Implications for the evolution of post-orogenic landscapes

    USGS Publications Warehouse

    Wegmann, S.F.G.; Franke, K.L.; Hughes, S.; Lewis, R.Q.; Lyons, N.; Paris, P.; Ross, K.; Bauer, J.B.; Witt, A.C.

    2011-01-01

    The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post-orogenic landscape remain enigmatic. The non-glaciated Cullasaja River basin of south-western North Carolina, with uniform lithology, frequent debris flows, and the availability of high-resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post-orogenic landscape through the lens of hillslope-channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km2, a conservative estimate of the transition from fluvial to debris-flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint-driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area-elevation and slope distributions is presented that may be representative of post-orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel- hillslope coupling is an important factor in tectonically-inactive (i

  11. 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.

  12. 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.

  13. Circumstellar disks of the most vigorously accreting young stars.

    PubMed

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-02-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood. PMID:26989772

  14. Circumstellar disks of the most vigorously accreting young stars

    PubMed Central

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I.; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M.; Karr, Jennifer L.; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-01-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood. PMID:26989772

  15. Circumstellar disks of the most vigorously accreting young stars.

    PubMed

    Liu, Hauyu Baobab; Takami, Michihiro; Kudo, Tomoyuki; Hashimoto, Jun; Dong, Ruobing; Vorobyov, Eduard I; Pyo, Tae-Soo; Fukagawa, Misato; Tamura, Motohide; Henning, Thomas; Dunham, Michael M; Karr, Jennifer L; Kusakabe, Nobuhiko; Tsuribe, Toru

    2016-02-01

    Stars may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. Our high-resolution near-infrared imaging has verified the presence of the key associated features, large-scale arms and arcs surrounding four young stellar objects undergoing luminous outbursts. Our hydrodynamics simulations and radiative transfer models show that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood.

  16. DISK GALAXIES WITH BROKEN LUMINOSITY PROFILES FROM COSMOLOGICAL SIMULATIONS

    SciTech Connect

    Martinez-Serrano, F. J.; Serna, A.; Domenech-Moral, M.; Dominguez-Tenreiro, R.

    2009-11-10

    We present smoothed particle hydrodynamics cosmological simulations of the formation of three disk galaxies with a detailed treatment of chemical evolution and cooling. The resulting galaxies have properties compatible with observations: relatively high disk-to-total ratios, thin stellar disks, and good agreement with the Tully-Fisher and the luminosity-size relations. They present a break in the luminosity profile at 3.0 +- 0.5 disk scale lengths while showing an exponential mass profile without any apparent breaks, which is in line with recent observational results. Since the stellar mass profile is exponential, only differences in the stellar populations can be the cause of the luminosity break. Although we find a cutoff for the star formation rate (SFR) imposed by a density threshold in our star formation model, it does not coincide with the luminosity break and is located at 4.3 +- 0.4 disk scale lengths, with star formation going on between both radii. The color profiles and the age profiles are 'U-shaped', with the minimum for both profiles located approximately at the break radius. The SFR to stellar mass ratio increases until the break, explaining the coincidence of the break with the minimum of the age profile. Beyond the break, we find a steep decline in the gas density and, consequently, a decline in the SFR and redder colors. We show that most stars (64%-78%) in the outer disk originate in the inner disk and afterward migrate there. Such stellar migrations are likely the main origin of the U-shaped age profile and, therefore, of the luminosity break.

  17. THE DYNAMICAL EVOLUTION OF LOW-MASS HYDROGEN-BURNING STARS, BROWN DWARFS, AND PLANETARY-MASS OBJECTS FORMED THROUGH DISK FRAGMENTATION

    SciTech Connect

    Li, Yun; Kouwenhoven, M. B. N.; Stamatellos, D.; Goodwin, S. P.

    2015-06-01

    Theory and simulations suggest that it is possible to form low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) via disk fragmentation. As disk fragmentation results in the formation of several bodies at comparable distances to the host star, their orbits are generally unstable. Here, we study the dynamical evolution of these objects. We set up the initial conditions based on the outcomes of the smoothed-particle hydrodynamics simulations of Stamatellos and Whitworth, and for comparison we also study the evolution of systems resulting from lower-mass fragmenting disks. We refer to these two sets of simulations as set 1 and set 2, respectively. At 10 Myr, approximately half of the host stars have one companion left, and approximately 22% (set 1) to 9.8% (set 2) of the host stars are single. Systems with multiple secondaries in relatively stable configurations are common (about 30% and 44%, respectively). The majority of the companions are ejected within 1 Myr with velocities mostly below 5 km s{sup −1}, with some runaway escapers with velocities over 30 km s{sup −1}. Roughly 6% (set 1) and 2% (set 2) of the companions pair up into very low-mass binary systems, resulting in respective binary fractions of 3.2% and 1.2%. The majority of these pairs escape as very low-mass binaries, while others remain bound to the host star in hierarchical configurations (often with retrograde inner orbits). Physical collisions with the host star (0.43 and 0.18 events per host star for set 1 and set 2, respectively) and between companions (0.08 and 0.04 events per host star for set 1 and set 2, respectively) are relatively common and their frequency increases with increasing disk mass. Our study predicts observable properties of very low-mass binaries, low-mass hierarchical systems, the BD desert, and free-floating BDs and PMOs in and near young stellar groupings, which can be used to distinguish between different formation scenarios of very low

  18. 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.

  19. Herniated Disk

    MedlinePlus

    ... keep them in place. As you age, the disks break down or degenerate. As they do, they lose their cushioning ability. This can lead to pain if the back is stressed. A herniated disk is a disk that ruptures. This allows the ...

  20. Decoupling of a giant planet from its disk in an inclined binary system

    NASA Astrophysics Data System (ADS)

    Marzari, F.; Picogna, G.

    According to \\cite{Triaud_2010} and \\cite{Albrecht_2012} about 40% of hot Jupiters have orbits significantly tilted respect to the equatorial plane of the star. It has been suggested \\cite{Batygin_2012} that the evolution of a protoplanetary disk under the perturbations of a binary companion may be responsible for the observed spin-orbit misalignment of these exoplanets. A fundamental requirement for this model to work is that the planet is kept within the disk during its precession. In this way the planet would continue its migration by tidal interaction with the disk and, at the same time, once the disk is dissipated it would maintain its inclination. Previous studies seem to suggest that indeed a giant planet is forced to evolve within the disks even in presence of strong perturbing forces as those induced by a companion star. By using two different SPH codes (VINE and phantom) we show that on the long term the planet definitively decouples from the disk evolution and its orbital plane significantly departs from that of the disk. For a detailed analysis an discussion we refer to \\cite{Picogna_2015}.

  1. A hinge migration mechanism unlocks the evolution of green-to-red photoconversion in GFP-like proteins

    PubMed Central

    Kim, Hanseong; Zou, Taisong; Modi, Chintan; Dörner, Katerina; Grunkemeyer, Timothy J.; Chen, Liqing; Fromme, Raimund; Matz, Mikhail V.; Ozkan, S. Banu; Wachter, Rebekka M.

    2015-01-01

    Summary In proteins, functional divergence involves mutations that modify structure and dynamics. Here, we provide experimental evidence for an evolutionary mechanism driven solely by long-range dynamic motions without significant backbone adjustments, catalytic group rearrangements, or changes in subunit assembly. Crystallographic structures were determined for several reconstructed ancestral proteins belonging to a GFP class frequently employed in superresolution microscopy. Their chain flexibility was analyzed using molecular dynamics and perturbation response scanning. The green-tored photoconvertible phenotype appears to have arisen from a common green ancestor by migration of a knob-like anchoring region away from the active site diagonally across the beta-barrel fold. The allosterically coupled mutational sites provide active site conformational mobility via epistasis. We propose that light-induced chromophore twisting is enhanced in a reverse-protonated subpopulation, activating internal acid-base chemistry and backbone cleavage to enlarge the chromophore. Dynamics-driven hinge migration may represent a more general platform for the evolution of novel enzyme activities. PMID:25565105

  2. A hinge migration mechanism unlocks the evolution of green-to-red photoconversion in GFP-like proteins.

    PubMed

    Kim, Hanseong; Zou, Taisong; Modi, Chintan; Dörner, Katerina; Grunkemeyer, Timothy J; Chen, Liqing; Fromme, Raimund; Matz, Mikhail V; Ozkan, S Banu; Wachter, Rebekka M

    2015-01-01

    In proteins, functional divergence involves mutations that modify structure and dynamics. Here we provide experimental evidence for an evolutionary mechanism driven solely by long-range dynamic motions without significant backbone adjustments, catalytic group rearrangements, or changes in subunit assembly. Crystallographic structures were determined for several reconstructed ancestral proteins belonging to a GFP class frequently employed in superresolution microscopy. Their chain flexibility was analyzed using molecular dynamics and perturbation response scanning. The green-to-red photoconvertible phenotype appears to have arisen from a common green ancestor by migration of a knob-like anchoring region away from the active site diagonally across the β barrel fold. The allosterically coupled mutational sites provide active site conformational mobility via epistasis. We propose that light-induced chromophore twisting is enhanced in a reverse-protonated subpopulation, activating internal acid-base chemistry and backbone cleavage to enlarge the chromophore. Dynamics-driven hinge migration may represent a more general platform for the evolution of novel enzyme activities.

  3. Rapid Circumstellar Disk Evolution and an Accelerating Star Formation Rate in the Infrared Dark Cloud M17 SWex

    NASA Astrophysics Data System (ADS)

    Povich, Matthew S.; Townsley, Leisa K.; Robitaille, Thomas P.; Broos, Patrick S.; Orbin, Wesley T.; King, Robert R.; Naylor, Tim; Whitney, Barbara A.

    2016-07-01

    We present a catalog of 840 X-ray sources and first results from a 100 ks Chandra X-ray Observatory imaging study of the filamentary infrared (IR) dark cloud G014.225-00.506, which forms the central regions of a larger cloud complex known as the M17 southwest extension (M17 SWex). In addition to the rich population of protostars and young stellar objects with dusty circumstellar disks revealed by archival data from the Spitzer Space Telescope, we discover a population of X-ray-emitting, intermediate-mass pre-main-sequence stars that lack IR excess emission from circumstellar disks. We model the IR spectral energy distributions of this source population to measure its mass function and place new constraints on the destruction timescales for the inner dust disk for 2-8 M ⊙ stars. We also place a lower limit on the star formation rate (SFR) and find that it is quite high (\\dot{M}≥slant 0.007 M ⊙ yr-1), equivalent to several Orion Nebula Clusters in G14.225-0.506 alone, and likely accelerating. The cloud complex has not produced a population of massive, O-type stars commensurate with its SFR. This absence of very massive (≳20 M ⊙) stars suggests that either (1) M17 SWex is an example of a distributed mode of star formation that will produce a large OB association dominated by intermediate-mass stars but relatively few massive clusters, or (2) the massive cores are still in the process of accreting sufficient mass to form massive clusters hosting O stars.

  4. Wide-angle seismic constraints on the evolution of the deep San Andreas plate boundary by Mendocino triple junction migration

    USGS Publications Warehouse

    Hole, J.A.; Beaudoin, B.C.; Henstock, T.J.

    1998-01-01

    Recent wide-angle seismic observations that constrain the existence and structure of a mafic layer in the lower crust place strong constraints on the evolution of the San Andreas plate boundary system in northern and central California. Northward migration of the Mendocino Triple Junction and the subducted Juan de Fuca lithospheric slab creates a gap under the continent in the new strike-slip system. This gap must be filled by either asthenospheric upwelling or a northward migrating slab attached to the Pacific plate. Both processes emplace a mafic layer, either magmatic underplating or oceanic crust, beneath the California Coast Ranges. A slab of oceanic lithosphere attached to the Pacific plate is inconsistent with the seismic observation that the strike-slip faults cut through the mafic layer to the mantle, detaching the layer from the Pacific plate. The layer could only be attached to the Pacific plate if large vertical offsets and other complex structures observed beneath several strike-slip faults are original oceanic structures that are not caused by the faults. Otherwise, if oceanic slabs exist beneath California, they do not migrate north to fill the growing slab gap. The extreme heat pulse created by asthenospheric upwelling is inconsistent with several constraints from the seismic data, including a shallower depth to the slab gap than is predicted by heat flow models, seismic velocity and structure that are inconsistent with melting or metamorphism of the overlying silicic crust, and a high seismic velocity in the upper mantle. Yet either the Pacific slab model or the asthenospheric upwelling model must be correct. While the mafic material in the lower crust could have been emplaced prior to triple junction migration, the deeper slab gap must still be filled. A preexisting mafic layer does not reduce the inconsistencies of the Pacific slab model. Such material could, however, compensate for the decrease in mafic magma that would be produced if

  5. INTERACTION OF A GIANT PLANET IN AN INCLINED ORBIT WITH A CIRCUMSTELLAR DISK

    SciTech Connect

    Marzari, F.; Nelson, Andrew F. E-mail: andy.nelson@lanl.go

    2009-11-10

    We investigate the dynamical evolution of a Jovian-mass planet injected into an orbit highly inclined with respect to its nesting gaseous disk. Planet-planet scattering induced by convergent planetary migration and mean motion resonances may push a planet into such an out-of-plane configuration with inclinations as large as 20{sup 0}-30{sup 0}. In this scenario, the tidal interaction of the planet with the disk is more complex and, in addition to the usual Lindblad and corotation resonances, it also involves inclination resonances responsible for bending waves. We have performed three-dimensional hydrodynamic simulations of the disk and of its interactions with the planet with a smoothed particle hydrodynamics code. A main result is that the initial large eccentricity and inclination of the planetary orbit are rapidly damped on a timescale of the order of 10{sup 3} yr, almost independently of the initial semimajor axis and eccentricity of the planet. The disk is warped in response to the planet perturbations and it precesses. Inward migration also occurs when the planet is inclined, and it has a drift rate that is intermediate between type I and type II migration. The planet is not able to open a gap until its inclination becomes lower than approx10{sup 0}, when it also begins to accrete a significant amount of mass from the disk.

  6. Comparing the Evolution of the Galaxy Disk Sizes with Cold Dark Matter Models: The Hubble Deep Field.

    PubMed

    Giallongo; Menci; Poli; D'Odorico; Fontana

    2000-02-20

    The intrinsic sizes of the field galaxies with Idisk sizes at different cosmic epochs is within the range predicted by typical CDM models. However, the observed size distribution of faint (MB>-19) galaxies is skewed with respect to the CDM predictions, and an excess of small-size disks (Rd<2 kpc) is already present at z approximately 0.5. The excess persists up to z approximately 3 and involves brighter galaxies. Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physical mechanisms governing the star formation history in CDM models. PMID:10655168

  7. 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.

  8. The atomic and molecular content of disks around very low-mass stars and brown dwarfs

    SciTech Connect

    Pascucci, I.; Herczeg, G.; Carr, J. S.; Bruderer, S.

    2013-12-20

    There is growing observational evidence that disk evolution is stellar-mass-dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from eight very low mass star and brown dwarf disks. We report the first detections of Ne{sup +}, H{sub 2}, CO{sub 2}, and tentative detections of H{sub 2}O toward these faint and low-mass disks. Two of our [Ne II] 12.81 μm emission lines likely trace the hot (≥5000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H{sub 2} S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [Ne II] emission in gas at ∼600 K. We confirm the higher C{sub 2}H{sub 2}/HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H{sub 2}O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H{sub 2}O lines trace warm ≥600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks, which may result from a more efficient formation of non-migrating icy planetesimals. An O/C = 1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low mass stars and brown dwarfs.

  9. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    SciTech Connect

    Pugliese, D.; Stuchlík, Z. E-mail: zdenek.stuchlik@physics.cz

    2015-12-15

    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.

  10. Evidence of local short-distance spawning migration of tropical freshwater eels, and implications for the evolution of freshwater eel migration

    PubMed Central

    Arai, Takaomi

    2014-01-01

    Freshwater eels have fascinated biologists for centuries due to the spectacular long-distance migrations between the eels’ freshwater habitats and their spawning areas far out in the ocean and the mysteries of their ecology. The spawning areas of Atlantic eels and Japanese eel were located far offshore in the Atlantic Ocean and the Pacific Ocean, respectively, and their reproduction took place thousands of kilometers away from their growth habitats. Phylogenetic studies have revealed that freshwater eels originated in the Indonesian region. However, remarkably little is known about the life histories of tropical freshwater eels despite the fact that tropical eels are key to understanding the nature of primitive forms of catadromous migration. This study found spawning-condition tropical freshwater eels in Lake Poso, central Sulawesi, Indonesia, with considerably high gonadosomatic index values and with histologically fully developed gonads. This study provides the first evidence that under certain conditions, freshwater eels have conditions that are immediately able to spawn even in river downstream. The results suggest that, in contrast to the migrations made by the Atlantic and Japanese eels, freshwater eels originally migrated only short distances of <100 kilometers to local spawning areas adjacent to their freshwater growth habitats. Ancestral eels most likely underwent a catadromous migration from local short-distance movements in tropical coastal waters to the long-distance migrations characteristic of present-day temperate eels, which has been well established as occurring in subtropical gyres in both hemispheres. PMID:25614795

  11. 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.

  12. 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…

  13. The origin and evolution of the odd-Z iron-peak elements Sc, V, Mn, and Co in the Milky Way stellar disk

    NASA Astrophysics Data System (ADS)

    Battistini, Chiara; Bensby, Thomas

    2015-05-01

    Context. Elements heavier than Li are produced in the interiors of stars. However, for many elements the exact production sites and the timescales on which they are dispersed into the interstellar medium are unknown. Having a clear picture on the origins of the elements is important for our ability to trace and understand the formation and chemical evolution of the Milky Way and its stellar populations. Aims: The aim of this study is to investigate the origin and evolution of Sc, V, Mn, and Co for a homogeneous and statistically significant sample of stars probing the different populations of the Milky Way, in particular the thin and thick disks. Methods: Using high-resolution spectra obtained with the MIKE, FEROS, SOFIN, FIES, UVES, and HARPS spectrographs, we determine Sc, V, Mn, and Co abundances for a large sample of F and G dwarfs in the solar neighborhood. The method is based on spectral synthesis and using one-dimensional, plane-parallel, local thermodynamic equilibrium (LTE) model stellar atmospheres calculated with the MARCS 2012 code. The non-LTE (NLTE) corrections from the literature were applied to Mn and Co. Results: We find that the abundance trends derived for Sc (594 stars), V (466 stars), and Co (567 stars) are very similar to what has been observed for the α-elements in the thin and thick disks. On the contrary, Mn (569 stars) is generally underabundant relative to the Sun (i.e., [ Mn/Fe ] < 0) for [ Fe/H ] < 0. In addition, for Mn, when NLTE corrections are applied, the trend changes and is almost flat over the entire metallicity range of the stars in our sample (-2 ≲ [ Fe/H ] ≲ + 0.4). The [Sc/Fe]-[Fe/H] abundance trends show a small separation between the thin and thick disks, while for V and Co they completely overlap. For Mn there is a small difference in [Mn/Fe], but only when NLTE corrections are used. Comparisons with Ti as a reference element show flat trends for all the elements except for Mn that show well separated [Mn

  14. Variable extinction in HD 45677 and the evolution of dust grains in pre-main-sequence disks

    NASA Technical Reports Server (NTRS)

    Sitko, Michael L.; Halbedel, Elaine M.; Lawrence, Geoffrey F.; Smith, J. Allyn; Yanow, Ken

    1994-01-01

    Changes in the UV extinction and IR emission were sought in the Herbig Ae/Be star candidate HD 45677 (= FS CMa) by comparing UV, optical, and IR observations made approximately 10 yr apart. HD 45677 varied significantly, becoming more than 50% brighter in the UV and optical than it was a decade ago. A comparison of the observations between epochs indicates that if the variations are due to changes in dust obscuration, the dust acts as a gray absorber into the near-IR and must be depleted in grains smaller than 1 micron. This is similar to the results obtained on the circumstellar disks of stars like Vega and Beta Pic, and suggests that radiation pressure may be responsible for the small-grain depletion. In addition, the total IR flux seems to have declined, indicating a decrease in the total mass of the dust envelope that contributes to the IR emission in this part of the spectrum. Due to the anomalous nature of the extinction, the use of normal extinction curves to deredden the spectral energy distributions of stars with circumstellar dust may lead to significant errors and should be used with great caution.

  15. SPIN EVOLUTION OF MILLISECOND MAGNETARS WITH HYPERACCRETING FALLBACK DISKS: IMPLICATIONS FOR EARLY AFTERGLOWS OF GAMMA-RAY BURSTS

    SciTech Connect

    Dai, Z. G.; Liu Ruoyu E-mail: ryliu@nju.edu.cn

    2012-11-01

    The shallow decay phase or plateau phase of early afterglows of gamma-ray bursts (GRBs), discovered by Swift, is currently understood as being due to energy injection to a relativistic blast wave. One natural scenario for energy injection invokes a millisecond magnetar as the central engine of GRBs because the conventional model of a pulsar predicts a nearly constant magnetic-dipole-radiation luminosity within the spin-down timescale. However, we note that significant brightening occurs in some early afterglows, which apparently conflicts with the above scenario. Here we propose a new model to explain this significant brightening phenomena by considering a hyperaccreting fallback disk around a newborn millisecond magnetar. We show that for typical values of the model parameters, sufficient angular momentum of the accreted matter is transferred to the magnetar and spins it up. It is this spin-up that leads to a dramatic increase of the magnetic-dipole-radiation luminosity with time and thus significant brightening of an early afterglow. Based on this model, we carry out numerical calculations and fit well early afterglows of 12 GRBs assuming sufficiently strong fallback accretion. If the accretion is very weak, our model turns out to be the conventional energy-injection scenario of a pulsar. Therefore, our model can provide a unified explanation for the shallow decay phase, plateaus, and significant brightening of early afterglows.

  16. POPULATION SYNTHESIS OF YOUNG ISOLATED NEUTRON STARS: THE EFFECT OF FALLBACK DISK ACCRETION AND MAGNETIC FIELD EVOLUTION

    SciTech Connect

    Fu, Lei; Li, Xiang-Dong

    2013-10-01

    The spin evolution of isolated neutron stars (NSs) is dominated by their magnetic fields. The measured braking indices of young NSs show that the spin-down mechanism due to magnetic dipole radiation with constant magnetic fields is inadequate. Assuming that the NS magnetic field is buried by supernova fallback matter and re-emerges after accretion stops, we carry out a Monte Carlo simulation of the evolution of young NSs, and show that most of the pulsars have braking indices ranging from –1 to 3. The results are compatible with the observational data of NSs associated with supernova remnants. They also suggest that the initial spin periods of NSs might occupy a relatively wide range.

  17. Evolution of the hormonal control of animal performance: insights from the seaward migration of salmon

    USGS Publications Warehouse

    McCormick, S.D.

    2009-01-01

    The endocrine system is the key mediator of environmental and developmental (internal) information, and is likely to be involved in altering the performance of animals when selection has favored phenotypic plasticity. The endocrine control of performance should be especially pronounced in animals that undergo a developmental shift in niche, such as occurs in migratory species. By way of example, I review the developmental and environmental control of the preparatory changes for seawater entry of juvenile salmon (known as smolting) and its hormonal regulation. There is a size threshold for smolt development in juvenile Atlantic salmon that results in greater sensitivity of the growth hormone and cortisol axes to changes in daylength. These hormones, in turn, have broad effects on survival, ion homeostasis, growth and swimming performance during entry into seawater. Migratory niche shifts and metamorphic events are extreme examples of the role of hormones in animal performance and represent one end of a continuum. A framework for predicting when hormones will be involved in performance of animals is presented. Endocrine involvement in performance will be more substantial when (1) selection differentials on traits underlying performance are high and temporally discontinuous over an animal's lifetime, (2) the energetic and fitness costs of maintaining performance plasticity are less than those of constant performance, (3) cues for altering performance are reliable indicators of critical environmental conditions, require neurosensory input, and minimize effects of lag, and (4) the need for coordination of organs, tissues and cells to achieve increased performance is greater. By examining these impacts of selection, endocrinologists have an opportunity to contribute to the understanding of performance, phenotypic plasticity, and the evolution of life-history traits.

  18. Extinct Beringian wolf morphotype found in the continental U.S. has implications for wolf migration and evolution.

    PubMed

    Meachen, Julie A; Brannick, Alexandria L; Fry, Trent J

    2016-05-01

    Pleistocene diversity was much higher than today, for example there were three distinct wolf morphotypes (dire, gray, Beringian) in North America versus one today (gray). Previous fossil evidence suggested that these three groups overlapped ecologically, but split the landscape geographically. The Natural Trap Cave (NTC) fossil site in Wyoming, USA is an ideally placed late Pleistocene site to study the geographical movement of species from northern to middle North America before, during, and after the last glacial maximum. Until now, it has been unclear what type of wolf was present at NTC. We analyzed morphometrics of three wolf groups (dire, extant North American gray, Alaskan Beringian) to determine which wolves were present at NTC and what this indicates about wolf diversity and migration in Pleistocene North America. Results show NTC wolves group with Alaskan Beringian wolves. This provides the first morphological evidence for Beringian wolves in mid-continental North America. Their location at NTC and their radiocarbon ages suggest that they followed a temporary channel through the glaciers. Results suggest high levels of competition and diversity in Pleistocene North American wolves. The presence of mid-continental Beringian morphotypes adds important data for untangling the history of immigration and evolution of Canis in North America. PMID:27252837

  19. Spectral Energy Distributions of Young Stars in IC 348: The Role of Disks in Angular Momentum Evolution of Young, Low-mass Stars

    NASA Astrophysics Data System (ADS)

    Le Blanc, Thompson S.; Covey, Kevin R.; Stassun, Keivan G.

    2011-08-01

    Theoretical work suggests that a young star's angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these "disk-locking" theories is that a disk-locked star will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young stars' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating stars possess close-in disks that enforce the star's slow rotation, whereas rapidly rotating stars possess anemic or evacuated inner disks that are unable to brake the stars and instead the stars spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young stars in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each star, we match the observed SED, typically sampling 0.6-8.0 μm, to a grid of 200,000 pre-computed star+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the star's measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of stars with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 stars in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the

  20. The Ellipticities of Cluster Early-type Galaxies from z ~ 1 to z ~ 0: No Evolution in the Overall Distribution of Bulge-to-Disk Ratios

    NASA Astrophysics Data System (ADS)

    Holden, B. P.; Franx, M.; Illingworth, G. D.; Postman, M.; van der Wel, A.; Kelson, D. D.; Blakeslee, J. P.; Ford, H.; Demarco, R.; Mei, S.

    2009-03-01

    We have compiled a sample of early-type cluster galaxies from 0 < z < 1.3 and measured the evolution of their ellipticity distributions. Our sample contains 487 galaxies in 17 z>0.3 clusters with high-quality space-based imaging and a comparable sample of 210 galaxies in 10 clusters at z < 0.05. We select early-type galaxies (elliptical and S0 galaxies) that fall within the cluster R 200, and which lie on the red-sequence in the magnitude range -19.3>MB > - 21, after correcting for luminosity evolution as measured by the fundamental plane. Our ellipticity measurements are made in a consistent manner over our whole sample. We perform extensive simulations to quantify the systematic and statistical errors, and find that it is crucial to use point-spread function (PSF)-corrected model fits; determinations of the ellipticity from Hubble Space Telescope image data that do not account for the PSF "blurring" are systematically and significantly biased to rounder ellipticities at redshifts z>0.3. We find that neither the median ellipticity, nor the shape of the ellipticity distribution of cluster early-type galaxies evolves with redshift from z ~ 0 to z>1 (i.e., over the last ~8 Gyr). The median ellipticity at z>0.3 is statistically identical with that at z < 0.05, being higher by only 0.01 ± 0.02 or 3 ± 6%, while the distribution of ellipticities at z>0.3 agrees with the shape of the z < 0.05 distribution at the 1-2% level (i.e., the probability that they are drawn from the same distribution is 98-99%). These results are strongly suggestive of an unchanging overall bulge-to-disk ratio distribution for cluster early-type galaxies over the last ~8 Gyr from z ~ 1 to z ~ 0. This result contrasts with that from visual classifications which show that the fraction of morphologically-selected disk-dominated early-type galaxies, or S0s, is significantly lower at z>0.4 than at z ~ 0. We find that the median disk-dominated early-type, or S0, galaxy has a somewhat higher

  1. USING KUIPER BELT BINARIES TO CONSTRAIN NEPTUNE'S MIGRATION HISTORY

    SciTech Connect

    Murray-Clay, Ruth A.; Schlichting, Hilke E.

    2011-04-01

    Approximately 10%-20% of all Kuiper Belt objects (KBOs) occupy mean-motion resonances with Neptune. This dynamical configuration likely resulted from resonance capture as Neptune migrated outward during the late stages of planet formation. The details of Neptune's planetesimal-driven migration, including its radial extent and the concurrent eccentricity evolution of the planet, are the subject of considerable debate. Two qualitatively different proposals for resonance capture have been proposed-migration-induced capture driven by smooth outward evolution of Neptune's orbit and chaotic capture driven by damping of the planet's eccentricity near its current semi-major axis. We demonstrate that the distribution of comparable-mass, wide-separation binaries occupying resonant orbits can differentiate between these two scenarios. If migration-induced capture occurred, this fraction records information about the formation locations of different populations of KBOs. Chaotic capture, in contrast, randomizes the orbits of bodies as they are placed in resonance. In particular, if KBO binaries are formed by dynamical capture in a protoplanetary disk with a surface mass density typical of observed extrasolar disks, then migration-induced capture produces the following signatures. The 2:1 resonance should contain a dynamically cold component, with inclinations less than 5{sup 0}-10{sup 0}, having a binary fraction comparable to that among cold classical KBOs. If the 3:2 resonance also hosts a cold component, its binary fraction should be 20%-30% lower than in the cold classical belt. Among cold 2:1 (and if present 3:2) KBOs, objects with eccentricities e < 0.2 should have a binary fraction {approx}20% larger than those with e>0.2. Other binary formation scenarios and disk surface density profiles can generate analogous signatures but produce quantitatively different results. Searches for cold components in the binary fractions of resonant KBOs are currently practical. The

  2. Vortex cycles at the inner edges of dead zones in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Faure, Julien; Fromang, Sébastien; Latter, Henrik; Meheut, Heloise

    2015-01-01

    Context. In protoplanetary disks, the inner boundary between the turbulent and laminar regions is a promising site for planet formation because solids may become trapped at the interface itself or in vortices generated by the Rossby wave instability. The disk thermodynamics and the turbulent dynamics at that location are entwined because of the importance of turbulent dissipation to thermal ionization and, conversely, of thermal ionization to turbulence. However, most previous work has neglected this dynamical coupling and have thus missed a crucial element of the physics in this region. Aims: In this paper, we aim to determine how the interplay between ionization and turbulence affects the formation and evolution of vortices at the interface between the active and the dead zones. Methods: Using the Godunov code RAMSES, we performed a 3D magnetohydrodynamic global numerical simulation of a cylindrical model of an MRI-turbulent protoplanetary disk, including thermodynamical effects and a temperature-dependant resistivity. The comparison with an analogous 2D viscous simulation was extensively used to help identify the relevant physical processes and the disk's long-term evolution. Results: We find that a vortex forms at the interface as a result of Rossby wave instability, migrates inward, and penetrates the active zone where it is destroyed by turbulent motions. Subsequently, a new vortex emerges a few tens of orbits later at the interface, and the new vortex migrates inward too. The sequence repeats itself, resulting in cycles of vortex formation, migration, and disruption. This surprising behaviour is successfully reproduced using two different codes. We characterize this vortex life cycle and discuss its implications for planet formation at the dead-active interface. Our results also call for a better understanding of vortex migration in complex thermodynamical environments. Conclusions: Our simulations highlight the importance of thermodynamical processes for

  3. Thermodynamical Structure of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Hirose, S.; Turner, N.

    2009-12-01

    The thermodynamics of protoplanetary disks determines chemical and physical evolution of dust and gas in the disks, and thus is relevant for understanding the origin and formation of planetary systems. In this paper, the thermodynamical structure of protoplanetary disks around low-mass stars is studied using three-dimensional radiation magnetohydrodynamic (MHD) simulations. Local patches of the disk are modeled using the shearing box approximation with vertical gravity. For simplicity, the dust and gas are well mixed and have the same temperature, and ideal MHD is assumed. The frequency-integrated radiation field is evolved using the flux-limited diffusion approximation, adopting thermally averaged opacities. The heating arises from the dissipation of MHD turbulence driven by magnetorotational instability due to differential rotation of the disk, and the cooling comes from infrared radiation losses. Irradiation by the central star is treated by injecting appropriate amount of thermal energy near the disk photosphere for visible lights. The results indicate the heating is more concentrated in the disk atmosphere than in the classical model. The single-point heating rate in the atmosphere fluctuates by orders of magnitude over time intervals comparable to the orbital period due to magnetic reconnection and shocks, while the patch of disk overall sustains dynamical and thermodynamical equilibrium over many cooling times. We will discuss implications of our numerical results for line and continuum emission from protoplanetary disks.

  4. 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.

  5. Herniated disk

    MedlinePlus

    ... roots. Slipped disks occur more often in middle-aged and older men, usually after strenuous activity. Other ... calm the nerves Muscle relaxants to relieve back spasms LIFESTYLE CHANGES If you are overweight, diet and ...

  6. 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.

  7. Global Simulations of Protoplanetary Disks With Ohmic Resistivity and Ambipolar Diffusion

    NASA Astrophysics Data System (ADS)

    Gressel, Oliver; Turner, Neal J.; Nelson, Richard P.; McNally, Colin P.

    2015-03-01

    Protoplanetary disks (PPDs) are believed to accrete onto their central T Tauri star because of magnetic stresses. Recently published shearing box simulations indicate that Ohmic resistivity, ambipolar diffusion (AD) and the Hall effect all play important roles in disk evolution. In the presence of a vertical magnetic field, the disk remains laminar between 1-5 AU, and a magnetocentrifugal disk wind forms that provides an important mechanism for removing angular momentum. Questions remain, however, about the establishment of a true physical wind solution in the shearing box simulations because of the symmetries inherent in the local approximation. We present global MHD simulations of PPDs that include Ohmic resistivity and AD, where the time-dependent gas-phase electron and ion fractions are computed under FUV and X-ray ionization with a simplified recombination chemistry. Our results show that the disk remains laminar, and that a physical wind solution arises naturally in global disk models. The wind is sufficiently efficient to explain the observed accretion rates. Furthermore, the ionization fraction at intermediate disk heights is large enough for magneto-rotational channel modes to grow and subsequently develop into belts of horizontal field. Depending on the ionization fraction, these can remain quasi-global, or break-up into discrete islands of coherent field polarity. The disk models we present here show a dramatic departure from our earlier models including Ohmic resistivity only. It will be important to examine how the Hall effect modifies the evolution, and to explore the influence this has on the observational appearance of such systems, and on planet formation and migration.

  8. Tracking the Distribution of 26Al and 60Fe during the Early Phases of Star and Disk Evolution

    NASA Astrophysics Data System (ADS)

    Kuffmeier, Michael; Frostholm Mogensen, Troels; Haugbølle, Troels; Bizzarro, Martin; Nordlund, Åke

    2016-07-01

    The short-lived 26Al and 60Fe radionuclides are synthesized and expelled into the interstellar medium by core-collapse supernova events. The solar system’s first solids, calcium-aluminum refractory inclusions (CAIs), contain evidence for the former presence of the 26 Al nuclide defining the canonical 26Al/27 Al ratio of ˜ 5× {10}-5. A different class of objects temporally related to canonical CAIs are CAIs with fractionation and unidentified nuclear effects (FUN CAIs), which record a low initial 26Al/27Al of 10-6. The contrasting level of 26Al between these objects is often interpreted as reflecting the admixing of the 26Al nuclides during the early formative phase of the Sun. We use giant molecular cloud scale adaptive mesh-refinement numerical simulations to trace the abundance of 26Al and 60Fe in star-forming gas during the early stages of accretion of individual low-mass protostars. We find that the 26Al/27Al and 60Fe/56Fe ratios of accreting gas within a vicinity of 1000 au of the stars follow the predicted decay curves of the initial abundances at the time of star formation without evidence of spatial or temporal heterogeneities for the first 100 kyr of star formation. Therefore, the observed differences in 26Al/27Al ratios between FUN and canonical CAIs are likely not caused by admixing of supernova material during the early evolution of the proto-Sun. Selective thermal processing of dust grains is a more viable scenario to account for the heterogeneity in 26Al/27Al ratios at the time of solar system formation.

  9. Protoplanetary Nebula Evolution using the Beta Viscosity Model

    NASA Technical Reports Server (NTRS)

    Davis, Sanford S.

    2003-01-01

    The evolutionary dynamics of a protoplanetary disk is an important component of the planet formation process. In particular, the dynamic and thermodynamic field plays a critical role in chemical evolution, the migration of dust particles in the nebula, and the radial transport of meteoritic components. The dynamic evolution is investigated using analytical solutions of the surface density transport equations using a turbulence model based on hydrodynamic generation of turbulence. It captures the major properties of the disk including region of separation between radial inflow and-outflow and the evolution of the central plane temperature. The analytical formulas are compared with available numerical solutions based on the alpha viscosity model. The beta viscosity model, heretofore used for steady-state disks, is shown to be a useful approximation for unsteady problems.

  10. Millimetre spectral indices of transition disks and their relation to the cavity radius

    NASA Astrophysics Data System (ADS)

    Pinilla, P.; Benisty, M.; Birnstiel, T.; Ricci, L.; Isella, A.; Natta, A.; Dullemond, C. P.; Quiroga-Nuñez, L. H.; Henning, T.; Testi, L.

    2014-04-01

    Context. Transition disks are protoplanetary disks with inner depleted dust cavities that are excellent candidates for investigating the dust evolution when there is a pressure bump. A pressure bump at the outer edge of the cavity allows dust grains from the outer regions to stop their rapid inward migration towards the star and to efficiently grow to millimetre sizes. Dynamical interactions with planet(s) have been one of the most exciting theories to explain the clearing of the inner disk. Aims: We look for evidence of millimetre dust particles in transition disks by measuring their spectral index αmm with new and available photometric data. We investigate the influence of the size of the dust depleted cavity on the disk integrated millimetre spectral index. Methods: We present the 3-mm (100 GHz) photometric observations carried out with the Plateau de Bure Interferometer of four transition disks: LkHα 330, UX Tau A, LRLL 31, and LRLL 67. We used the available values of their fluxes at 345 GHz to calculate their spectral index, as well as the spectral index for a sample of twenty transition disks. We compared the observations with two kinds of models. In the first set of models, we considered coagulation and fragmentation of dust in a disk in which a cavity is formed by a massive planet located at different positions. The second set of models assumes disks with truncated inner parts at different radii and with power-law dust-size distributions, where the maximum size of grains is calculated considering turbulence as the source of destructive collisions. Results: We show that the integrated spectral index is higher for transition disks (TD) than for regular protoplanetary disks (PD) with mean values of bar{αmmTD} = 2.70 ± 0.13 and bar{αmmPD} = 2.20 ± 0.07 respectively. For transition disks, the probability that the measured spectral index is positively correlated with the cavity radius is 95%. High angular resolution imaging of transition disks is needed to

  11. Migratory intradural disk herniation and a strategy for intraoperative localization.

    PubMed

    Daffner, Scott D; Sedney, Cara L; Rosen, Charles L

    2015-02-01

    Study Design Case report. Objective Describe a case of intradural disk herniation and a method for intraoperative localization. Methods Intradural disk herniations are uncommon but well described. The diagnosis of these lesions is often difficult, and sometimes they may be diagnosed only through an intradural exploration after an expected disk fragment cannot be located. We report the case of an intradural disk herniation with an additional diagnostic difficulty-a migrated intradural disk. Results We present the first intraoperative imaging evidence of disk migration and propose a strategy to locate intradural disk fragments prior to durotomy. Conclusion Intradural disk herniations should be suspected when intraoperative findings are not congruent with imaging findings. An intraoperative myelogram may be helpful. PMID:25648315

  12. Generalized Similarity for Accretion/Decretion Disks

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2016-10-01

    Decretion (or external) disks are gas disks freely expanding to large radii due to their internal stresses. They are expected to naturally arise in tidal disruption events, around Be stars, in mass-losing post-main-sequence binaries, as a result of supernova fallback, etc. Their evolution is theoretically understood in two regimes: when the central object does not exert torque on the disk (a standard assumption for conventional accretion disks) or when no mass inflow (or outflow) occurs at the disk center. However, many astrophysical objects—circumbinary disks, Be stars, neutron stars accreting in a propeller regime, etc.—feature non-zero torque simultaneously with the non-zero accretion (or ejection of mass) at the disk center. We provide a general description for the evolution of such disks (both linear and nonlinear) in the self-similar regime, to which the disk should asymptotically converge with time. We identify a similarity parameter λ, which is uniquely related to the degree, to which the central mass accretion is suppressed by the non-zero central torque. The known decretion disk solutions correspond to the two discrete values of λ, while our new solutions cover a continuum of its physically allowed values, corresponding to either accretion or mass ejection by the central object. A direct relationship between λ and central \\dot{M} and torque is also established. We describe the time evolution of the various disk characteristics for different λ, and show that the observable properties (spectrum and luminosity evolution) of the decretion disks, in general, are different from the standard accretion disks with no central torque.

  13. The Matryoshka Disk: Keck/NIRC2 Discovery of a Solar-system-scale, Radially Segregated Residual Protoplanetary Disk around HD 141569A

    NASA Astrophysics Data System (ADS)

    Currie, Thayne; Grady, Carol A.; Cloutier, Ryan; Konishi, Mihoko; Stassun, Keivan; Debes, John; van der Marel, Nienke; Muto, Takayuki; Jayawardhana, Ray; Ratzka, Thorsten

    2016-03-01

    Using Keck/NIRC2 {L}\\prime (3.78 μm) data, we report the direct imaging discovery of a scattered-light-resolved, solar-system-scale residual protoplanetary disk around the young A-type star HD 141569A, interior to and concentric with the two ring-like structures at wider separations. The disk is resolved down to ∼0.″25 and appears as an arc-like rim with attached hook-like features. It is located at an angular separation intermediate between that of warm CO gas identified from spatially resolved mid-infrared spectroscopy and diffuse dust emission recently discovered with the Hubble Space Telescope. The inner disk has a radius of ∼39 au, a position angle consistent with north up, and an inclination of i ∼ 56o and has a center offset from the star. Forward modeling of the disk favors a thick torus-like emission sharply truncated at separations beyond the torus’s photocenter and heavily depleted at smaller separations. In particular, the best-fit density power law for the dust suggests that the inner disk dust and gas (as probed by CO) are radially segregated, a feature consistent with the dust trapping mechanism inferred from observations of “canonical” transitional disks. However, the inner disk component may instead be explained by radiation pressure-induced migration in optically thin conditions, in contrast to the two stellar companion/planet-influenced ring-like structures at wider separations. HD 141569A’s circumstellar environment—with three nested, gapped, concentric dust populations—is an excellent laboratory for understanding the relationship between planet formation and the evolution of both dust grains and disk architecture.

  14. Star formation in gravitationally unstable disk galaxies: From clouds to disks

    NASA Astrophysics Data System (ADS)

    Goldbaum, Nathan J.

    In Part I, I examine the dynamics of giant molecular clouds through simplified semianalytic models. I focus on the growth of clouds as they accrete gas. Our model clouds reproduce the scaling relations observed in both galactic and extragalactic clouds: clouds attain virial equilibrium and grow maintaining roughly constant surface densities, Sigma ≃ 50--200 M[special character omitted]pc-2 and that clouds grow along the well-known linewidth-size relation. We compare our models to observations of giant molecular clouds and associated young star clusters in the Large Magellanic Cloud, finding good agreement between our models and the relationship between H ii regions, young star clusters, and giant molecular clouds. The role of gravitational-instability driven turbulence in determining the structure and evolution of disk galaxies, and the extent to which gravity rather than feed- back can explain galaxy properties, remains an open question. To address it, in Part II I present high resolution adaptive mesh refinement simulations of Milky Way-like isolated disk galaxies, including realistic heating and cooling rates and a physically motivated prescription for star formation. The simulations resolve densities typical of the transition from atomic to molecular hydrogen, capturing the formation of gravitationally bound clouds. We present simulations both with and without stellar feedback from Type II supernova blast waves. We find gravitational instability alone can drive substantial turbulence in galactic disks and reproduce some properties of nearby star forming galaxies: Qtotal [special character omitted] 1, ceff ˜ 10 km/s, without stellar feedback. Including feedback produces an ISM with a structure similar to observed disks, with the bulk of the gas in the warm or cold atomic phase, and the remainder locked up in short-lived gravitationally bound clouds. We investigate radial flows of gas and find that radial migration of gas due to gravitational instability can

  15. HIGH-RESOLUTION STUDY OF THE CLUSTER COMPLEXES IN A LENSED SPIRAL AT REDSHIFT 1.5: CONSTRAINTS ON THE BULGE FORMATION AND DISK EVOLUTION

    SciTech Connect

    Adamo, Angela; Oestlin, G.; Zackrisson, E.; Guaita, L.; Bastian, N.; Livermore, R. C.

    2013-04-01

    We analyze the clump population of the spiral galaxy Sp 1149 at redshift 1.5. Located behind the galaxy cluster MACS J1149.5+2223, Sp 1149 has been significantly magnified allowing us to study the galaxy on physical scales down to {approx}100 pc. The galaxy cluster frame is among the targets of the Cluster Lensing And Supernova survey with Hubble (CLASH), an ongoing Hubble Space Telescope (HST) Multi-Cycle Treasury program. We have used the publicly available multi-band imaging data set to reconstruct the spectral energy distributions of the clumps in Sp 1149, and derive, by means of stellar evolutionary models, their physical properties. We found that 40% of the clumps observed in Sp 1149 are older than 30 Myr and can be as old as 300 Myr. These are also the more massive (luminous) clumps in the galaxy. Among the complexes in the local reference sample, the star-forming knots in luminous blue compact galaxies could be considered progenitor analogs of these long-lived clumps. The remaining 60% of clumps have colors comparable to local cluster complexes, suggesting a similar young age. We observe that the Sp 1149 clumps follow the M{proportional_to}R {sup 2} relation similar to local cluster complexes, suggesting similar formation mechanisms although they may have different initial conditions (e.g., higher gas surface densities). We suggest that the galaxy is experiencing a slow decline in star formation rate and a likely transitional phase toward a more quiescent star formation mode. The older clumps have survived between 6 and 20 dynamical times and are all located at projected distances smaller than 4 kpc from the center. Their current location suggests migration toward the center and the possibility of being the building blocks of the bulge. On the other hand, the dynamical timescale of the younger clumps is significantly shorter, meaning that they are quite close to their birthplace. We show that the clumps of Sp 1149 may account for the expected metal

  16. Magnetic and gravitational disk-star interactions: an interdependence of PMS stellar rotation rates and spin-orbit misalignments

    SciTech Connect

    Batygin, Konstantin; Adams, Fred C. E-mail: fca@umich.edu

    2013-12-01

    The presence of giant gaseous planets that reside in close proximity to their host stars, i.e., hot Jupiters, may be a consequence of large-scale radial migration through the protoplanetary nebulae. Within the framework of this picture, significant orbital obliquities characteristic of a substantial fraction of such planets can be attributed to external torques that perturb the natal disks out of alignment with the spin axes of their host stars. Therefore, the acquisition of orbital obliquity likely exhibits sensitive dependence on the physics of disk-star interactions. Here, we analyze the primordial excitation of spin-orbit misalignment of Sun-like stars in light of disk-star angular momentum transfer. We begin by calculating the stellar pre-main-sequence rotational evolution, accounting for spin-up due to gravitational contraction and accretion as well as spin-down due to magnetic star-disk coupling. We devote particular attention to angular momentum transfer by accretion, and show that while generally subdominant to gravitational contraction, this process is largely controlled by the morphology of the stellar magnetic field (that is, specific angular momentum accreted by stars with octupole-dominated surface fields is smaller than that accreted by dipole-dominated stars by an order of magnitude). Subsequently, we examine the secular spin-axis dynamics of disk-bearing stars, accounting for the time-evolution of stellar and disk properties, and demonstrate that misalignments are preferentially excited in systems where stellar rotation is not overwhelmingly rapid. Moreover, we show that the excitation of spin-orbit misalignment occurs impulsively through an encounter with a resonance between the stellar precession frequency and the disk-torquing frequency. Cumulatively, the model developed herein opens up a previously unexplored avenue toward understanding star-disk evolution and its consequences in a unified manner.

  17. Recent Observational Progress on Accretion Disks Around Compact Objects

    NASA Astrophysics Data System (ADS)

    Miller, Jon M.

    2016-04-01

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

  18. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Naoz, Smadar; Vican, Laura; Farr, Will M.

    2016-07-01

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

  19. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Naoz, Smadar; Vican, Laura; Farr, Will M.

    2016-07-01

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai-Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai-Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai-Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

  20. Radial Motions in Disk Stars: Ellipticity or Secular Flows?

    NASA Astrophysics Data System (ADS)

    López-Corredoira, M.; González-Fernández, C.

    2016-06-01

    Average stellar orbits of the Galactic disk may have some small intrinsic ellipticity which breaks the exact axisymmetry and there may also be some migration of stars inwards or outwards. Both phenomena can be detected through kinematic analyses. We use the red clump stars selected spectroscopically from the APO Galactic Evolution Experiment, with known distances and radial velocities, to measure the radial component of the Galactocentric velocities within 5 kpc < R < 16 kpc, | b| \\lt 5^\\circ , and within 20° from the Sun–Galactic center line. The average Galactocentric radial velocity is VR = (1.48 ± 0.35)[R(kpc) ‑ (8.8 ± 2.7)] km s‑1 outwards in the explored range, with a higher contribution from stars below the Galactic plane. Two possible explanations can be given for this result: (i) the mean orbit of the disk stars is intrinsically elliptical with a Galactocentric radial gradient of eccentricity around 0.01 kpc‑1 or (ii) there is a net secular expansion of the disk, in which stars within R ≈ 9–11 kpc are migrating to the region R ≳ 11 kpc at the rate of ∼2 M⊙ yr‑1, and stars with R ≲ 9 kpc are falling toward the center of the Galaxy. This migration ratio would be unattainable for a long time and should decelerate, otherwise the Galaxy would fade away in around 1 Gyr. At present, both hypotheses are speculative and one would need data on the Galactocentric radial velocities for other azimuths different to the center or anticenter in order to confirm one of the scenarios.

  1. Radial Motions in Disk Stars: Ellipticity or Secular Flows?

    NASA Astrophysics Data System (ADS)

    López-Corredoira, M.; González-Fernández, C.

    2016-06-01

    Average stellar orbits of the Galactic disk may have some small intrinsic ellipticity which breaks the exact axisymmetry and there may also be some migration of stars inwards or outwards. Both phenomena can be detected through kinematic analyses. We use the red clump stars selected spectroscopically from the APO Galactic Evolution Experiment, with known distances and radial velocities, to measure the radial component of the Galactocentric velocities within 5 kpc < R < 16 kpc, | b| \\lt 5^\\circ , and within 20° from the Sun-Galactic center line. The average Galactocentric radial velocity is VR = (1.48 ± 0.35)[R(kpc) - (8.8 ± 2.7)] km s-1 outwards in the explored range, with a higher contribution from stars below the Galactic plane. Two possible explanations can be given for this result: (i) the mean orbit of the disk stars is intrinsically elliptical with a Galactocentric radial gradient of eccentricity around 0.01 kpc-1 or (ii) there is a net secular expansion of the disk, in which stars within R ≈ 9-11 kpc are migrating to the region R ≳ 11 kpc at the rate of ˜2 M⊙ yr-1, and stars with R ≲ 9 kpc are falling toward the center of the Galaxy. This migration ratio would be unattainable for a long time and should decelerate, otherwise the Galaxy would fade away in around 1 Gyr. At present, both hypotheses are speculative and one would need data on the Galactocentric radial velocities for other azimuths different to the center or anticenter in order to confirm one of the scenarios.

  2. Accretion disk thermal instability in galactic nuclei

    NASA Astrophysics Data System (ADS)

    Mineshige, S.; Shields, G. A.

    1990-03-01

    The nonlinear evolution and spatial propagation of the thermal instability in accretion disks in galactic nuclei are investigated. Integrations of the vertical structure of the disks are described for different alpha prescriptions, and the thermal stability is examined. Global time-dependent calculations of the unstable disks are performed which show that there are two distinct types of behavior according to the assumed prescription for the viscosity parameter: the 'purr' type and the 'roar' type. The roar type is analyzed in some detail.

  3. Disk Dispersal Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; Yorke, Harold W.; Johnstone, Doug; DeVincenzi, Donald L. (Technical Monitor)

    1999-01-01

    We review the evidence pertaining to the lifetimes of planet-forming disks and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the, inner disk (r approx. less than A 10 AU), while photoevaporation is the principal process of disk dispersal outside of r approximately greater than 10 AU. Disk dispersed timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed the solar nebula is called into question.

  4. 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.

  5. Disk-planet interaction: new results and implications for gap opening

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman

    2013-07-01

    Gravitational disk-planet coupling has been a subject of intense investigation for more than three decades. Our understanding of very important phenomena such as planet migration and gap opening crucially relies on our knowledge of disk-planet interaction. Despite that, some interesting new results have emerged in this field recently. Three of them are reviewed in this poster. (1) Numerical verification of the nonlinear density wave evolution for small mass planets, which is found to be in excellent agreement with the analytical theory of this phenomenon developed by Goodman & Rafikov (2001). (2) A discovery and physical explanation of the "negative torque density phenomenon" - the change of sign of the torque density produced by the planet at moderate separation away from it, completely overlooked in all previous disk-satellite coupling theories. (3) Calculation of the torque density profile in a non-homogeneous disk with a wide gap and demonstration of its difference from the conventional Goldreich & Tremaine (1980) torque prescription, widely used in literature. Implications of these results for planet migration and gap opening are covered as well.

  6. 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.

  7. 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.

  8. SANs and Large Scale Data Migration at the NASA Center for Computational Sciences

    NASA Technical Reports Server (NTRS)

    Salmon, Ellen M.

    2004-01-01

    Evolution and migration are a way of life for provisioners of high-performance mass storage systems that serve high-end computers used by climate and Earth and space science researchers: the compute engines come and go, but the data remains. At the NASA Center for Computational Sciences (NCCS), disk and tape SANs are deployed to provide high-speed I/O for the compute engines and the hierarchical storage management systems. Along with gigabit Ethernet, they also enable the NCCS's latest significant migration: the transparent transfer of 300 Til3 of legacy HSM data into the new Sun SAM-QFS cluster.

  9. 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.

  10. Gravitational Instabilities in Circumstellar Disks

    NASA Astrophysics Data System (ADS)

    Kratter, Kaitlin; Lodato, Giuseppe

    2016-09-01

    Star and planet formation are the complex outcomes of gravitational collapse and angular momentum transport mediated by protostellar and protoplanetary disks. In this review, we focus on the role of gravitational instability in this process. We begin with a brief overview of the observational evidence for massive disks that might be subject to gravitational instability and then highlight the diverse ways in which the instability manifests itself in protostellar and protoplanetary disks: the generation of spiral arms, small-scale turbulence-like density fluctuations, and fragmentation of the disk itself. We present the analytic theory that describes the linear growth phase of the instability supplemented with a survey of numerical simulations that aim to capture the nonlinear evolution. We emphasize the role of thermodynamics and large-scale infall in controlling the outcome of the instability. Despite apparent controversies in the literature, we show a remarkable level of agreement between analytic predictions and numerical results. In the next part of our review, we focus on the astrophysical consequences of the instability. We show that the disks most likely to be gravitationally unstable are young and relatively massive compared with their host star, Md/M*≥0.1. They will develop quasi-stable spiral arms that process infall from the background cloud. Although instability is less likely at later times, once infall becomes less important, the manifestations of the instability are more varied. In this regime, the disk thermodynamics, often regulated by stellar irradiation, dictates the development and evolution of the instability. In some cases the instability may lead to fragmentation into bound companions. These companions are more likely to be brown dwarfs or stars than planetary mass objects. Finally, we highlight open questions related to the development of a turbulent cascade in thin disks and the role of mode-mode coupling in setting the maximum angular

  11. Towards a Global Evolutionary Model of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Bai, Xue-Ning

    2016-04-01

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

  12. Influence of viscosity and the adiabatic index on planetary migration

    NASA Astrophysics Data System (ADS)

    Bitsch, B.; Boley, A.; Kley, W.

    2013-02-01

    Context. The strength and direction of migration of low mass embedded planets depends on the disk's thermodynamic state. It has been shown that in active disks, where the internal dissipation is balanced by radiative transport, migration can be directed outwards, a process which extends the lifetime of growing embryos. Very important parameters determining the structure of disks, and hence the direction of migration, are the viscosity and the adiabatic index. Aims: In this paper we investigate the influence of different viscosity prescriptions (α-type and constant) and adiabatic indices on disk structures. We then determine how this affects the migration rate of planets embedded in such disks. Methods: We perform three-dimensional numerical simulations of accretion disks with embedded planets. We use the explicit/implicit hydrodynamical code NIRVANA that includes full tensor viscosity and radiation transport in the flux-limited diffusion approximation, as well as a proper equation of state for molecular hydrogen. The migration of embedded 20 MEarth planets is studied. Results: Low-viscosity disks have cooler temperatures and the migration rates of embedded planets tend toward the isothermal limit. Hence, in these disks, planets migrate inwards even in the fully radiative case. The effect of outward migration can only be sustained if the viscosity in the disk is large. Overall, the differences between the treatments for the equation of state seem to play a more important role in disks with higher viscosity. A change in the adiabatic index and in the viscosity changes the zero-torque radius that separates inward from outward migration. Conclusions: For larger viscosities, temperatures in the disk become higher and the zero-torque radius moves to larger radii, allowing outward migration of a 20-MEarth planet to persist over an extended radial range. In combination with large disk masses, this may allow for an extended period of the outward migration of growing

  13. Evolution.

    ERIC Educational Resources Information Center

    Mayr, Ernst

    1978-01-01

    Traces the history of evolution theory from Lamarck and Darwin to the present. Discusses natural selection in detail. Suggests that, besides biological evolution, there is also a cultural evolution which is more rapid than the former. (MA)

  14. Geometrical Structures of Chemically Decomposed Thick and Thin Disk Populations

    NASA Astrophysics Data System (ADS)

    Kawata, D.; Brook, C. B.; Rahimi, A.; Gibson, B. K.

    2016-10-01

    We summarize the thick and thin disk formation commonly seen in cosmological N-body simulations. As suggested in Brook et al. (2004), a hierarchical clustering scenario causes multiple minor gas-rich mergers, and leads to the formation of a kinematically hot disk, thick disk population, at a high redshift. Once the mergers become less significant at a later epoch, the thin disk population starts building up. Because in this scenario the thick disk population forms intensively at high redshift through multiple gas-rich mergers, the thick disk population is compact and has systematically higher [α/Fe] abundance than the thin disk population. We discuss that the thick disk population would be affected by the formation of the thin disk and suffer from the radial migration, which helps the thick disk population to be observed in the solar neighborhood. In addition, we show that the current cosmological simulations also naturally predict that the thin disk population is flaring at the outer region. As shown in Rahimi et al. (2014), at high vertical height from the disk plane, the compact thick disk population (low metallicity and high [α/Fe]) is dominant in the inner region and the flaring thin disk population (high metallicity and low [α/Fe]) contributes more in the outer region. This helps to explain the positive radial metallicity gradient and negative radial [α/Fe] gradient observed at high vertical height in the Milky Way stellar disk.

  15. STRUCTURE OF MAGNETOROTATIONAL INSTABILITY ACTIVE PROTOPLANETARY DISKS

    SciTech Connect

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

    2010-10-01

    The radial drift of planetary cores poses a challenge to efficient planet formation in standard disk models. However, the rate of this migration is sensitive to both the surface density and temperature profiles of protoplanetary disks. In this paper, we present a new model to self-consistently calculate the structure of a protoplanetary disk in which the magnetorotational instability (MRI) drives angular momentum transport. In this model, we calculate a quasi-steady-state disk model including a schematic representation involving efficient angular momentum transport in the active region with decreased (but non-zero) angular momentum transport in the dead zone. We find that MRI affects not only the surface density distribution but also the temperature profile. In this paper, we present our method and the key novel features evident in our fiducial model. In subsequent papers, we will use this model to study the impact of MRI on the formation and migration of planets.

  16. The Plio-Pleistocene evolution of the Crotone Basin (southern Italy): Interplay between sedimentation, tectonics and eustasy in the frame of Calabrian Arc migration

    NASA Astrophysics Data System (ADS)

    Zecchin, Massimo; Caffau, Mauro; Civile, Dario; Critelli, Salvatore; Di Stefano, Agata; Maniscalco, Rosanna; Muto, Francesco; Sturiale, Giovanni; Roda, Cesare

    2012-12-01

    The Crotone Basin is the exposed part of a larger Neogene forearc basin developed in the Ionian Sea in the frame of the SE-ward migration of the Calabrian Arc, which led to the subduction of the Ionian lithosphere and the spreading of the Tyrrhenian back-arc Basin (central Mediterranean). Taking into account the geologic context that accompanied its accumulation, the Plio-Pleistocene part of the Crotone Basin succession is exceptionally well preserved, and consists of a suite of continental, paralic, shallow-marine and deep-marine deposits organized to form unconformity bounded stratal units that in turn compose two main tectono-stratigraphic cycles. The unconformities separating these units are well recognizable along the basin margin and tend to vanish basinwards, and they record phases of basin reorganization linked to large-scale tectonics. In particular, the basin evolution was characterized by a cyclic pattern consisting of an alternation between longer subsidence phases, that favored the accumulation of stratal units, and uplift phases that led to base-level falls and the generation of unconformities. These phases were strictly related to an alternation between active subduction of the Ionian lithosphere below the Calabrian Arc, accompanied by the spreading of the Tyrrhenian back-arc Basin and by extension and subsidence in the forearc basin, and regional-scale compressional and transpressional events, during which the Arc migration temporarily stopped. The younger uplift of the basin, started during middle Pleistocene and still active, was characterized by extensional tectonics, and its interplay with glacio-eustasy controlled the formation of marine terraces. Since the Plio-Pleistocene tectonic episodes affecting the Calabrian Arc during its SE-ward migration seem to be all recorded in the Crotone Basin, the recognition of their effects on the basin fill and their time constraint become both critical, representing a reference to develop a clearer picture

  17. OT2_dardila_2: PACS Photometry of Transiting-Planet Systems with Warm Debris Disks

    NASA Astrophysics Data System (ADS)

    Ardila, D.

    2011-09-01

    Dust in debris disks is produced by colliding or evaporating planetesimals, the remnant of the planet formation process. Warm dust disks, known by their emission at =<24 mic, are rare (4% of FGK main-sequence stars), and specially interesting because they trace material in the region likely to host terrestrial planets, where the dust has very short dynamical lifetimes. Dust in this region comes from very recent asteroidal collisions, migrating Kuiper Belt planetesimals, or migrating dust. NASA's Kepler mission has just released a list of 1235 candidate transiting planets, and in parallel, the Wide-Field Infrared Survey Explorer (WISE) has just completed a sensitive all-sky mapping in the 3.4, 4.6, 12, and 22 micron bands. By cross-identifying the WISE sources with Kepler candidates as well as with other transiting planetary systems we have identified 21 transiting planet hosts with previously unknown warm debris disks. We propose Herschel/PACS 100 and 160 micron photometry of this sample, to determine whether the warm dust in these systems represents stochastic outbursts of local dust production, or simply the Wien side of emission from a cold outer dust belt. These data will allow us to put constraints in the dust temperature and infrared luminosity of these systems, allowing them to be understood in the context of other debris disks and disk evolution theory. This program represents a unique opportunity to exploit the synergy between three great space facilities: Herschel, Kepler, and WISE. The transiting planet sample hosts will remain among the most studied group of stars for the years to come, and our knowledge of their planetary architecture will remain incomplete if we do not understand the characteristics of their debris disks.

  18. Magneto-thermal Disk Winds from Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Bai, Xue-Ning; Ye, Jiani; Goodman, Jeremy; Yuan, Feng

    2016-02-01

    The global evolution and dispersal of protoplanetary disks (PPDs) are governed by disk angular-momentum transport and mass-loss processes. Recent numerical studies suggest that angular-momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal Alfvén speed vAp, (2) the sound speed cs near the wind base, and (3) how rapidly poloidal field lines diverge (achieve {R}-2 scaling). When {v}{Ap}\\gg {c}{{s}}, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. In both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. For typical PPD accretion-rate and wind-launching conditions, we expect vAp to be comparable to cs at the wind base. The resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. Implications for modeling global disk evolution and planet formation are also discussed.

  19. Rest-frame ultraviolet morphologies: connecting local galaxies with the epoch of disk formation

    NASA Astrophysics Data System (ADS)

    Fernandes Demello, Duilia; Soto, Emmaris

    2015-08-01

    At all redshifts rest-frame ultraviolet morphologies tend to be patchy and clumpy or extremely compact in nature. These morphological signatures could result from either merger interactions between two or multiple systems that trigger star formation, cloud collapse via gravitational instabilities in a gaseous disk that is fed by cold gas spiraling inwards along filamentary structures, or another mechanism still to be determined. Theoretical simulations of clumpy galaxy evolution suggest they could have evolved secularly through cold gas accretion onto rotating disks. Clumps in disks could have migrated to the center of the potential well of a galaxy and combined to form a bulge, or, if gravitationally unstable, could have dissipated forming the disk component. We are exploring potential correlations amongst different morphological properties at intermediate-z which is pivotal in bridging observations at high-z to the local extragalactic universe. We will show how flocculent galaxies, starburst galaxies and compact groups of galaxies may resemble clumpy disks at intermediate redshifts in the rest-frame UV.

  20. THE STAR-FORMING HISTORIES OF THE NUCLEUS, BULGE, AND INNER DISK OF NGC 5102: CLUES TO THE EVOLUTION OF A NEARBY LENTICULAR GALAXY {sup ,} {sup ,}

    SciTech Connect

    Davidge, T. J.

    2015-01-20

    Long slit spectra recorded with the Gemini Multi-Object Spectrograph on Gemini South are used to examine the star-forming history (SFH) of the lenticular galaxy NGC 5102. Structural and supplemental photometric information are obtained from archival Spitzer [3.6] images. Absorption features at blue and visible wavelengths are traced out along the minor axis to galactocentric radii ∼60 arcsec (∼0.9 kpc), sampling the nucleus, bulge, and disk components. Comparisons with model spectra point to luminosity-weighted metallicities that are consistent with the colors of resolved red giant branch stars in the disk. The nucleus has a luminosity-weighted age at visible wavelengths of ∼1{sub −0.1}{sup +0.2} Gyr, and the integrated light is dominated by stars that formed over a time period of only a few hundred Myr. For comparison, the luminosity-weighted ages of the bulge and disk are ∼2{sub −0.2}{sup +0.5} Gyr and 10{sub −2}{sup +2} Gyr, respectively. The g' – [3.6] colors of the nucleus and bulge are consistent with the spectroscopically based ages. In contrast to the nucleus, models that assume star-forming activity spanning many Gyr provide a better match to the spectra of the bulge and disk than simple stellar population models. Isophotes in the bulge have a disky shape, hinting that the bulge was assembled from material with significant rotational support. The SFHs of the bulge and disk are consistent with the bulge forming from the collapse of a long-lived bar, rather than from the collapse of a transient structure that formed as the result of a tidal interaction. It is thus suggested that the progenitor of NGC 5102 was a barred disk galaxy that morphed into a lenticular galaxy through the buckling of its bar.

  1. Evidence for dust grain growth in young circumstellar disks.

    PubMed

    Throop, H B; Bally, J; Esposito, L W; McCaughrean, M J

    2001-06-01

    Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

  2. Proteinquakes in the Evolution of Influenza Virus Hemagglutinin (A/H1N1) under Opposing Migration and Vaccination Pressures

    PubMed Central

    Phillips, J. C.

    2015-01-01

    Influenza virus contains two highly variable envelope glycoproteins, hemagglutinin (HA) and neuraminidase (NA). Here we show that, while HA evolution is much more complex than NA evolution, it still shows abrupt punctuation changes linked to punctuation changes of NA. HA exhibits proteinquakes, which resemble earthquakes and are related to hydropathic shifting of sialic acid binding regions. HA proteinquakes based on shifting sialic acid interactions are required for optimal balance between the receptor-binding and receptor-destroying activities of HA and NA for efficient virus replication. Our comprehensive results present a historical (1945–2011) panorama of HA evolution over thousands of strains and are consistent with many studies of HA and NA interactions based on a few mutations of a few strains. PMID:25654090

  3. Warm Circumstellar Debris Disks: Dynamical Excitation by Massive External Perturbers?

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika; Naoz, Smadar; Vican, Laura; Vican, Laura; Zuckerman, Ben M.; Holmbeck, Erika

    2016-01-01

    Observations of circumstellar debris disks have revealed that a subset of this population are warm disks (~300 K). A dynamically excited disk may indicate the presence of an exoplanet orbiting within and stirring the disk. However, observations suggest another possible mechanism for heating a debris disk: an external stellar-mass perturber exciting the eccentricities and inclinations of the particles in a disk.We explore the consequences of an external perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. The perturber excites the eccentricities of the particles in the disk via the Kozai-Lidov mechanism, triggering a collisional cascade among the planetesimals. These collisions produce smaller dust grains and damp the particles' larger eccentricities.We present the results of our study and discuss the connections to observations of warm disks and the implications for planet formation.

  4. Collisional Cascade in a Debris Disk from an External Perturber

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika; Naoz, Smadar; Vican, Laura; Zuckerman, Benjamin; Holmbeck, Erika

    2015-11-01

    The study of circumstellar debris disks has often been coupled with the study of planet formation. A thermally warm debris disk (~300 K) may indicate the presence of an exoplanet orbiting within and stirring the disk. However, there is another possible mechanism for heating a debris disk: an external stellar-mass perturber exciting the eccentricities and inclinations of the particles in a disk.We explore the consequences of an external perturber on the evolution of a debris disk. The perturber excites the eccentricities of the particles in the disk via the Kozai-Lidov mechanism, triggering a collisional cascade among the planetesimals. These collisions produce smaller dust grains and damp the particles’ larger eccentricities.We present the results of our study of a such a disk using secular analysis and collisional N-body simulations. We will discuss the connections to observations of warm disks and the implications for planet formation.

  5. Star formation rates and abundance gradients in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

  6. The Star-forming Histories of the Nucleus, Bulge, and Inner Disk of NGC 5102: Clues to the Evolution of a Nearby Lenticular Galaxy

    NASA Astrophysics Data System (ADS)

    Davidge, T. J.

    2015-01-01

    Long slit spectra recorded with the Gemini Multi-Object Spectrograph on Gemini South are used to examine the star-forming history (SFH) of the lenticular galaxy NGC 5102. Structural and supplemental photometric information are obtained from archival Spitzer [3.6] images. Absorption features at blue and visible wavelengths are traced out along the minor axis to galactocentric radii ~60 arcsec (~0.9 kpc), sampling the nucleus, bulge, and disk components. Comparisons with model spectra point to luminosity-weighted metallicities that are consistent with the colors of resolved red giant branch stars in the disk. The nucleus has a luminosity-weighted age at visible wavelengths of {˜ } 1+0.2-0.1 Gyr, and the integrated light is dominated by stars that formed over a time period of only a few hundred Myr. For comparison, the luminosity-weighted ages of the bulge and disk are {˜ } 2+0.5-0.2 Gyr and 10+2-2 Gyr, respectively. The g' - [3.6] colors of the nucleus and bulge are consistent with the spectroscopically based ages. In contrast to the nucleus, models that assume star-forming activity spanning many Gyr provide a better match to the spectra of the bulge and disk than simple stellar population models. Isophotes in the bulge have a disky shape, hinting that the bulge was assembled from material with significant rotational support. The SFHs of the bulge and disk are consistent with the bulge forming from the collapse of a long-lived bar, rather than from the collapse of a transient structure that formed as the result of a tidal interaction. It is thus suggested that the progenitor of NGC 5102 was a barred disk galaxy that morphed into a lenticular galaxy through the buckling of its bar. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

  7. Why do primordial germ cells migrate through an embryo and what does it mean for biological evolution?

    PubMed

    Olovnikov, A M

    2013-10-01

    An explanation of the role of primordial germ cell (PGC) migration during embryogenesis is proposed. According to the hypothesis, various PGCs during their migrations through an early embryo are contacting with anlagen of organs and acquiring nonidentical organ specificities. An individual PGC gets such an organ specificity, which corresponds to specificity of the first anlage with which this PGC has the first contact. As a result, the cellular descendants of PGCs (oocytes or spermatocytes) will express nonidentical organ-specific receptors, hence becoming functionally heterogeneous. Therefore, each clone of germ cells becomes capable of recognizing specifically the molecular signals that correspond only to "its" organ of the body. Such signals are produced by the body's organ when it functions in an extreme mode. Signals from the "exercising" organ of the body are delivered to the gonad only via the brain retransmitter, which is composed of neurons grouped as virtual organs of a homunculus. Homunculi are so-called somatotopic maps of the skeletomotor and other parts of the body represented in the brain. Signals, as complexes of regulatory RNAs and proteins, are transported from the "exercising" organ of the body to the corresponding virtual organ of the homunculus where they are processed and then forwarded to the gonad. The organ-specific signal will be selectively recognized by certain gametocytes according to their organ specificity, and then it will initiate the directed epimutation in the gametocyte genome. The nonrandomness of the gene order in chromosomes, that is the synteny and genetic map, is controlled by the so-called creatron that consolidates the soma and germline into a united system, providing the possibility of evolutionary responses of an organism to environmental influences. PMID:24237154

  8. Why do primordial germ cells migrate through an embryo and what does it mean for biological evolution?

    PubMed

    Olovnikov, A M

    2013-10-01

    An explanation of the role of primordial germ cell (PGC) migration during embryogenesis is proposed. According to the hypothesis, various PGCs during their migrations through an early embryo are contacting with anlagen of organs and acquiring nonidentical organ specificities. An individual PGC gets such an organ specificity, which corresponds to specificity of the first anlage with which this PGC has the first contact. As a result, the cellular descendants of PGCs (oocytes or spermatocytes) will express nonidentical organ-specific receptors, hence becoming functionally heterogeneous. Therefore, each clone of germ cells becomes capable of recognizing specifically the molecular signals that correspond only to "its" organ of the body. Such signals are produced by the body's organ when it functions in an extreme mode. Signals from the "exercising" organ of the body are delivered to the gonad only via the brain retransmitter, which is composed of neurons grouped as virtual organs of a homunculus. Homunculi are so-called somatotopic maps of the skeletomotor and other parts of the body represented in the brain. Signals, as complexes of regulatory RNAs and proteins, are transported from the "exercising" organ of the body to the corresponding virtual organ of the homunculus where they are processed and then forwarded to the gonad. The organ-specific signal will be selectively recognized by certain gametocytes according to their organ specificity, and then it will initiate the directed epimutation in the gametocyte genome. The nonrandomness of the gene order in chromosomes, that is the synteny and genetic map, is controlled by the so-called creatron that consolidates the soma and germline into a united system, providing the possibility of evolutionary responses of an organism to environmental influences.

  9. Trapping planets in an evolving protoplanetary disk: preferred time, locations, and planet mass

    NASA Astrophysics Data System (ADS)

    Baillié, K.; Charnoz, S.; Pantin, E.

    2016-05-01

    Context. Planet traps are necessary to prevent forming planets from falling onto their host star by type I inward migration. Surface mass density and temperature gradient irregularities favor the apparition of traps (planet accumulation region) and deserts (planet depletion zone). These features are found at the dust sublimation lines and heat transition barriers. Aims: We study how planets may remain trapped or escape these traps as they grow and as the disk evolves viscously with time. Methods: We numerically model the temporal viscous evolution of a protoplanetary disk by coupling its dynamics, thermodynamics, geometry, and composition. The resulting midplane density and temperature profiles allow the modeling of the interactions of this type of evolving disk with potential planets, even before the steady state is reached. Results: We follow the viscous evolution of a minimum mass solar nebula and compute the Lindblad and corotation torques that this type of disk would exert on potential planets of various masses that are located within the planetary formation region. We determine the position of planet traps and deserts in relationship with the sublimation lines, shadowed regions, and heat transition barriers. We notice that the planet mass affects the trapping potential of the mentioned structures through the saturation of the corotation torque. Planets that are a few tens of Earth masses can be trapped at the sublimation lines until they reach a certain mass while planets that are more massive than 100 M⊕ can only be trapped permanently at the heat transition barriers. They may also open gaps beyond 5 au and enter type II migration. Conclusions: Coupling a bimodal planetary migration model with a self-consistent evolved disk, we were able to distinguish several potential planet populations after five million years of evolution: two populations of giant planets that could stay trapped around 5.5 and 9 au and possibly open gaps, some super-Earths trapped

  10. A New M Dwarf Debris Disk Candidate in a Young Moving Group Discovered with Disk Detective

    NASA Astrophysics Data System (ADS)

    Silverberg, Steven M.; Kuchner, Marc J.; Wisniewski, John P.; Gagné, Jonathan; Bans, Alissa S.; Bhattacharjee, Shambo; Currie, Thayne R.; Debes, John R.; Biggs, Joseph R.; Bosch, Milton; Doll, Katharina; Durantini-Luca, Hugo A.; Enachioaie, Alexandru; Griffith, Philip, Sr.; Hyogo, Michiharu; Piñiero, Fernanda; Disk Detective Collaboration

    2016-10-01

    We used the Disk Detective citizen science project and the BANYAN II Bayesian analysis tool to identify a new candidate member of a nearby young association with infrared excess. WISE J080822.18-644357.3, an M5.5-type debris disk system with significant excess at both 12 and 22 μm, is a likely member (∼ 90 % BANYAN II probability) of the ∼45 Myr old Carina association. Since this would be the oldest M dwarf debris disk detected in a moving group, this discovery could be an important constraint on our understanding of M dwarf debris disk evolution.

  11. Lightcurves of Extreme Debris Disks

    NASA Astrophysics Data System (ADS)

    Rieke, George; Meng, Huan; Su, Kate

    2012-12-01

    We have recently discovered that some planetary debris disks with extreme fractional luminosities are variable on the timescale of a few years. This behavior opens a new possibility to understand planet building. Two of the known variable disks are around solar-like stars in the age range of 30 to 100+ Myr, which is the expected era of the final stages of terrestrial planet building. Such variability can be attributed to violent collisions (up to ones on the scale of the Moon-forming event between the proto-Earth and another proto-planet). The collisional cascades that are the aftermaths of these events can produce large clouds of tiny dust grains, possibly even condensed from silica vapor. A Spitzer pilot program has obtained the lightcurve of such a debris disk and caught two minor outbursts. Here we propose to continue the lightcurve monitoring with higher sampling rates and to expand it to more disks. The proposed time domain observations are a new dimension of debris disk studies that can bring unique insight to their evolution, providing important constraints on the collisional and dynamical models of terrestrial planet formation.

  12. MOLECULAR GAS IN YOUNG DEBRIS DISKS

    SciTech Connect

    Moor, A.; Abraham, P.; Kiss, Cs.; Juhasz, A.; Kospal, A.; Pascucci, I.; Apai, D.; Henning, Th.; Csengeri, T.; Grady, C.

    2011-10-10

    Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old ({approx}>8 Myr), gaseous dust disks. From our results, neither primordial origin nor steady secondary production from icy planetesimals can unequivocally explain the presence of CO gas in the disk of HD21997.

  13. ON THE FORMATION OF GALACTIC THICK DISKS

    SciTech Connect

    Minchev, I.; Streich, D.; Scannapieco, C.; De Jong, R. S.; Steinmetz, M.; Martig, M.

    2015-05-01

    Recent spectroscopic observations in the Milky Way suggest that the chemically defined thick disk (stars that have high [α/Fe] ratios and are thus old) has a significantly smaller scale-length than the thin disk. This is in apparent contradiction with observations of external edge-on galaxies, where the thin and thick components have comparable scale-lengths. Moreover, while observed disks do not flare (scale-height does not increase with radius), numerical simulations suggest that disk flaring is unavoidable, resulting from both environmental effects and secular evolution. Here we address these problems by studying two different suites of simulated galactic disks formed in the cosmological context. We show that the scale-heights of coeval populations always increase with radius. However, the total population can be decomposed morphologically into thin and thick disks, which do not flare. We relate this to the disk inside-out formation, where younger populations have increasingly larger scale-lengths and flare at progressively larger radii. In this new picture, thick disks are composed of the imbedded flares of mono-age stellar populations. Assuming that disks form inside out, we predict that morphologically defined thick disks must show a decrease in age (or [α/Fe] ratios) with radius and that coeval populations should always flare. This also explains the observed inversion in the metallicity and [α/Fe] gradients for stars away from the disk midplane in the Milky Way. The results of this work are directly linked to, and can be seen as evidence of, inside-out disk growth.

  14. Molecular Gas in Young Debris Disks

    NASA Technical Reports Server (NTRS)

    Moor, A.; Abraham, P.; Juhasz, A.; Kiss, Cs.; Pascucci, I.; Kospal, A.; Apai, D.; Henning, T.; Csengeri, T.; Grady, C.

    2011-01-01

    Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old > or approx.8 Myr), gaseous dust disks. From our results, neither primordia1 origin nor steady secondary production from icy planetesima1s can unequivocally explain the presence of CO gas in the disk ofHD21997.

  15. 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.

  16. Modeling Gas Distribution in Protoplanetary Accretion Disks

    NASA Astrophysics Data System (ADS)

    Kronberg, Martin; Lewis, Josiah; Brittain, Sean

    2010-07-01

    Protoplanetary accretion disks are disks of dust and gas which surround and feed material onto a forming star in the earliest stages of its evolution. One of the most useful methods for studying these disks is near infrared spectroscopy of rovibrational CO emission. This paper presents the methods in which synthetically generated spectra are modeled and fit to spectral data gathered from protoplanetary disks. This paper also discussed the methods in which this code can be improved by modifying the code to run a Monte Carlo analysis of best fit across the CONDOR cluster at Clemson University, thereby allowing for the creation of a catalog of protoplanetary disks with detailed information about them as gathered from the model.

  17. Observational constraints on black hole accretion disks

    NASA Technical Reports Server (NTRS)

    Liang, Edison P.

    1994-01-01

    We review the empirical constraints on accretion disk models of stellar-mass black holes based on recent multiwavelength observational results. In addition to time-averaged emission spectra, the time evolutions of the intensity and spectrum provide critical information about the structure, stability, and dynamics of the disk. Using the basic thermal Keplerian disk paradigm, we consider in particular generalizations of the standard optically thin disk models needed to accommodate the extremely rich variety of dynamical phenomena exhibited by black hole candidates ranging from flares of electron-positron annihilations and quasiperiodic oscillations in the X-ray intensity to X-ray novae activity. These in turn provide probes of the disk structure and global geometry. The goal is to construct a single unified framework to interpret a large variety of black hole phenomena. This paper will concentrate on the interface between basic theory and observational data modeling.

  18. Protostellar Disk Instabilities and the Formation of Substellar Companions

    NASA Astrophysics Data System (ADS)

    Pickett, Brian K.; Durisen, Richard H.; Cassen, Patrick; Mejia, Annie C.

    2000-09-01

    Recent numerical simulations of self-gravitating protostellar disks have suggested that gravitational instabilities can lead to the production of substellar companions. In these simulations, the disk is typically assumed to be locally isothermal; i.e., the initial, axisymmetric temperature in the disk remains everywhere unchanged. Such an idealized condition implies extremely efficient cooling for outwardly moving parcels of gas. While we have seen disk disruption in our own locally isothermal simulations of a small, massive protostellar disk, no long-lived companions formed as a result of the instabilities. Instead, thermal and tidal effects and the complex interactions of the disk material prevented permanent condensations from forming, despite the vigorous growth of spiral instabilities. In order to compare our results more directly with those of other authors, we here present three-dimensional evolutions of an older, larger, but less massive protostellar disk. We show that potentially long-lived condensations form only for the extreme of local isothermality, and then only when severe restrictions are placed on the natural tendency of the protostellar disk to expand in response to gravitational instabilities. A more realistic adiabatic evolution leads to vertical and radial expansion of the disk but no clump formation. We conclude that isothermal disk calculations cannot demonstrate companion formation by disk fragmentation but only suggest it at best. It will be necessary in future numerical work on this problem to treat the disk thermodynamics more realistically.

  19. Dynamics of gas disks in triaxial galaxies

    SciTech Connect

    Steiman-Cameron, T.Y.

    1984-01-01

    Increasing evidence has accumulated since the mid 1970's arguing that many, if not all, undisturbed galaxies may have triaxial mass distributions. The steady state configurations (preferred planes) of gas disks in triaxial galaxies with static and rotating surface figures is determined. In addition, the evolution of a gas disk as it settles into the steady state is followed for both axisymmetric and triaxial galaxies. Observational tests are provided for triaxial galactic geometry and give more accurate measures of settling times than those previously published. The preferred planes for gas disks in static and tumbling triaxial galaxies are determined using an analytic method derived from celestial mechanics. The evolution of gas disks which are not in the steady state is followed using numerical methods.

  20. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    SciTech Connect

    Perets, Hagai B.; Kenyon, Scott J.

    2013-02-20

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10{sup -5}-10{sup -3} M {sub Sun }, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M {sub Sun }. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  1. Effects of Photoevaporation on Planet Migration

    NASA Astrophysics Data System (ADS)

    Wise, Alexander; Dodson-Robinson, Sarah E.

    2015-01-01

    The final locations of planets may be influenced by turning points in their migration tracks called 'planet traps' (Hasegawa & Pudritz 2013, 2014). We explore a new planet trap caused by photoevaporation of a protoplanetary disk. Near the end of the lifetime of the gas disk, photoevaporation rates on the inner disk begin to exceed viscous accretion rates, initially resulting in a gap being formed at ~1 AU. Disk material inside the gap is quickly drained and then the gap widens until the gas disk is entirely blown away. Using a combination of analytical calculations and numerical simulations, we show that the variations of disk density resulting from this process affect the migration tracks of planets. In particular, the initial photoevaporative gap at ~1 AU stops planets from migrating inward from the gap for tens of thousands of years, until photoevaporation disperses the remaining disk and the planets lose their primary source of migration. This process may explain the apparent pileup of exoplanets at ~1 AU.

  2. On the Evolution of the Inner Disk Radius with Flux in the Neutron Star Low-mass X-Ray Binary Serpens X-1

    NASA Astrophysics Data System (ADS)

    Chiang, Chia-Ying; Morgan, Robert A.; Cackett, Edward M.; Miller, Jon M.; Bhattacharyya, Sudip; Strohmayer, Tod E.

    2016-11-01

    We analyze the latest Suzaku observation of the bright neutron star (NS) low-mass X-ray binary Serpens X-1 taken in 2013 October and 2014 April. The observation was taken using the burst mode and only suffered mild pile-up effects. A broad iron line is clearly detected in the X-ray spectrum. We test different models and find that the iron line is asymmetric and best interpreted by relativistic reflection. The relativistically broadened iron line is generally believed to originate from the innermost regions of the accretion disk, where strong gravity causes a series of special and general relativistic effects. The iron line profile indicates an inner radius of ∼8 R G, which gives an upper limit on the size of the NS. The asymmetric iron line has been observed in a number of previous observations, which gives several inner radius measurements at different flux states. We find that the inner radius of Serpens X-1 does not evolve significantly over the range of L/L Edd ∼ 0.4–0.6, and the lack of flux dependence of the inner radius implies that the accretion disk may be truncated outside of the innermost stable circular orbit by the boundary layer, rather than the stellar magnetic field.

  3. Fluid flow, element migration, and petrotectonic evolution of the Early Mesozoic central Klamath Island arc, northwesternmost California. Progress report

    SciTech Connect

    Ernst, W.G.

    1992-12-11

    Investigations in the central Klamath Mountains (KM) have documented the presence of a polymetamorphosed suite of highly magnesian basaltic rocks, the Yellow Dog greenstones, in the Sawyers Bar (SB) terrane of the western Triassic and Paleozoic belt. The assemblage was laid down, altered and metasomatized during the hypothesized collapse of a Phillipine Sea-type back-arc basin which brought the westerly SB oceanic arc terrane into juxtaposition with the inboard, pre-existing Stuart Fork subduction complex, and more easterly KM terranes in an immature island arc setting. Supporting research has concentrated on elucidating the areal extent and structural/stratigraphic relations of these mafic/ultramafic Yellow Dog metavolcanic units, and has documented the insignificant degree of crustal contamination of the melts by associated terrigenous metasediments. The thermal structure and its evolution in the central KM evidently reflects surfaceward advective transport of magmatic energy derived from the partly fused downgoing oceanic slab, as well as hydrothermal fluid circulation. Clarification of the thermal evolution of this crust-constructional event in the immature basaltic island arc are the goals of the research now underway, emptying both field and geochemical methods. Continuing work is documenting the flow and P-T history of aqueous fluids through the evolving KM arc, utilizing electron microprobe and oxygen isotopic data. The authors have nearly finished a regional reconnaissance map showing the distribution of the lavas throughout the California part of the KM. Application of the terrane concept to the central KM has also been reevaluated in the light of regional petrotectonic relationships. Investigations of the regional and contact metamorphism/metasomatism of the SB metasedimentary pile are in progress.

  4. Disk Alloy Development

    NASA Technical Reports Server (NTRS)

    Gabb, Tim; Gayda, John; Telesman, Jack

    2001-01-01

    The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA HSR/EPM disk program to have extended durability at 1150 to 1250 "Fin large disks. Scaled-up disks of this alloy were produced at the conclusion of this program to demonstrate these properties in realistic disk shapes. The objective of the UEET disk program was to assess the mechanical properties of these ME3 disks as functions of temperature, in order to estimate the maximum temperature capabilities of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor / Turbine Disk program were sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. Additional sub-scale disks and blanks were processed and tested to explore the effects of several processing variations on mechanical properties. Scaled-up disks of an advanced regional disk alloy, Alloy 10, were used to evaluate dual microstructure heat treatments. This allowed demonstration of an improved balance of properties in disks with higher strength and fatigue resistance in the bores and higher creep and dwell fatigue crack growth resistance in the rims. Results indicate the baseline ME3 alloy and process has 1300 to 1350 O F temperature capabilities, dependent on detailed disk and engine design property requirements. Chemistry and process enhancements show promise for further increasing temperature capabilities.

  5. Poynting Jets from Accretion Disks

    NASA Astrophysics Data System (ADS)

    Lovelace, R. V. E.; Li, H.; Koldoba, A. V.; Ustyugova, G. V.; Romanova, M. M.

    2002-06-01

    We give further consideration to the problem of the evolution of a coronal, force-free magnetic field that threads a differentially rotating, conducting Keplerian disk, extending the recent work of Li and coworkers. This situation is described by the force-free Grad-Shafranov (GS) equation for the flux function Ψ(r, z) that labels the poloidal field lines (in cylindrical coordinates). The GS equation involves a function H(Ψ) describing the distribution of the poloidal current, which is determined by the differential rotation or ``twist'' of the disk that increases linearly with time. We numerically solve the GS equation in a sequence of volumes of increasing size corresponding to the expansion of the outer perfectly conducting boundaries at (Rm, Zm). The outer boundaries model the influence of an external nonmagnetized plasma. The sequence of GS solutions provides a model for the dynamical evolution of the magnetic field in response to (1) the increasing twist of the disk and (2) the pressure of external plasma. We find solutions with magnetically collimated Poynting jets in which there is a continuous outflow of energy, angular momentum, and toroidal magnetic flux from the disk into the external space. This behavior contradicts the commonly accepted ``theorem'' of solar plasma physics that the motion of the footpoints of a magnetic loop structure leads to a stationary magnetic field configuration with zero power, angular momentum, and flux outflows. In addition, we discuss magnetohydrodynamic simulations that show quasi-stationary collimated Poynting jets similar to our GS solutions. In contrast with the GS solutions, the simulations show a steady uncollimated hydromagnetic (nonforce-free) outflow from the outer part of the disk. The Poynting jets are of interest for the understanding of the jets from active galactic nuclei, microquasars, and possibly gamma-ray burst sources.

  6. 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.

  7. ALMA observations of protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Hogerheijde, Michiel

    2015-08-01

    The Universe is filled with planetary systems, as recent detections of exo-planets have shown. Such systems grow out of disks of gas and dust that surround newly formed stars. The ground work for our understanding of the structure, composition, and evolution of such disks has been laid with infrared telescopes in the 1980's, 1990's, and 2000's, as well as with millimeter interferometers operating in the United States, France, and Japan. With the construction of the Atacama Large Millimeter / submillimeter Array, a new era of studying planet-forming disks has started. The unprecedented leap in sensitivity and angular resolution that ALMA offers, has truely revolutionized our understanding of disks. No longer featureless objects consisting of gas and smalll dust, they are now seen to harbor a rich structure and chemistry. The ongoing planet-formation process sculpts many disks into systems of rings and arcs; grains grown to millimeter-sizes collect in high-pressure areas where they could grow out to asteroids or comets or further generations of planets. This wealth of new information directly addresses bottlenecks in our theoretical understanding of planet formation, such as the question how grains can grow past the 'meter-sized' barrier or overcome the 'drift barrier', and how gas and ice evolve together and ultimately determine the elemental compositions of both giant and terrestrial planets. I will review the recent ALMA results on protoplanetary disks, presenting results on individual objects and from the first populations studies. I will conclude with a forward look, on what we might expect from ALMA in this area for the years and decades to come.

  8. Dispersal of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; DeVincenzi, D. (Technical Monitor)

    2002-01-01

    We review the evidence pertaining to the lifetimes of planet-forming disks 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 by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the inner disk (r approx. or less than 10 AU), while photoevaporation is the principal process of disk dispersal outside of r approx. or greater than 10 AU for low mass stars. Disk dispersal timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed he solar nebula is called into question. Finally, we model the small bright objects ('proplyds') observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV (ultraviolet) photons from the nearby massive star Theta(1)C.

  9. Dispersal of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2001-01-01

    We review the evidence pertaining to the lifetimes of planet-forming disks 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 by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the inner disk (r < or approx. equals 10 AU), while photoevaporation is the principal process of disk dispersal outside of r > or approx. equals 10 AU for low mass stars. Disk dispersal timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed the solar nebula is called into question. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1)C.

  10. Return migration.

    PubMed

    Gmelch, G

    1980-01-01

    The author reviews the findings of the growing literature on return migration. Topics covered include typologies of return migrants, reasons for return, adaptation and readjustment of returnees, and the impact of return migration on the migrants' home societies. The focus of the study is on international return migration, migration to Northern Europe and northeastern North America, and return migration to the southern and eastern fringes of Europe and the Caribbean

  11. Formation waters from Mississippian-Pennsylvanian reservoirs, Illinois basin, USA: Chemical and isotopic constraints on evolution and migration

    SciTech Connect

    Stueber, A.M. ); Walter, L.M.; Huston, T.J. ); Pushkar, P. )

    1993-02-01

    We have analyzed a suite of seventy-four formation-water samples from Mississippian and Pennsylvanian carbonate and siliciclastic strata in the Illinois basin for major, minor, and trace element concentrations and for strontium isotopic composition. A subset of these samples was also analyzed for boron isotopic composition. Data are used to interpret origin of salinity and chemical and Sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from Silurian-Devonian reservoirs. Systematics of Cl-Br-Na show that present Mississippian-Pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporation short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle Mississippian St. Louis Limestone, along with extensive dilution by mixing with meteoric waters. Additional diagenetic modifications in the subsurface interpreted from cation/Br ratios include K depletion through interaction with clay minerals, Ca enrichment, and Mg depletion by dolomitization, and Sr enrichment through CaCO[sub 3] recrystallization and dolomitization. Ste. Genevieve Limestone (middle Mississippian) formation waters show [sup 87]Sr/[sup 86]Sr ratios in the range 0.70782-0.70900, whereas waters from the siliciclastic reservoirs are in the rante 0.70900-0.71052. Inverse correlations between [sup 87]Sr/[sup 86]Sr and B,Li, and Mg concentrations suggest that the brines acquired radiogenic [sup 87]Sr through interaction with siliciclastic minerals. Completely unsystematic relations between [sup 87]Fr/[sup 86]Sr and 1/Sr are observed; Sr concentrations in Ste. Genevieve and Aux Vases (middle Mississippian) waters appear to be buffered by equilibrium with respect to SrSo[sub 4]. These formation waters are distinguished from Silurian-Devonian brines in the basin by elevated Cl/Br and Na/Br ratios and by unsystematic Sr isotope relationships.

  12. Moon formation coupled with the protolular disk

    NASA Astrophysics Data System (ADS)

    Charnoz, Sebastien; Bugnet, Lisa; Michaut, Chloé

    2015-11-01

    It is thought that the Moon accreted from the protolunar disk that was assembled after the last giant impact on Earth. Due to its high temperature, the protolunar disk may act as a thermochemical reactor in which the material is processed before being incorporated into the Moon. Outstanding issues like devolatilisation and istotopic evolution are tied to the disk evolution, however its lifetime, dynamics and thermodynamics are unknown. Here, we numerically explore the long term viscous evolution of the protolunar disk using a one dimensional model where the different phases (vapor and condensed) are vertically stratified.Our major innovation is that we compute at the same time the proto-moon growth along with the disk evolution, and calculate the thermodynamical equilibrium of the proto-lunar seed as it grows.We will discuss the long term dynamics, thermodynamics, cooling timescale and possibility for volatile depletion. We will show that due to different effective viscosities substantial fractionation of volatiles and refractory material is possible.Finally we will compare different scenarios of moon impacts (standard, sub-earths, fast spinning Earth) and their different advantages for explaining today’s moon material content.

  13. THE DISPERSAL OF PROTOPLANETARY DISKS AROUND BINARY STARS

    SciTech Connect

    Alexander, Richard

    2012-10-01

    I present models of disk evolution around young binary stars. I show that the primary factor in determining circumbinary disk lifetimes is the rate of disk photoevaporation. I also find that photoevaporative clearing leaves a signature on the distribution of circumbinary disk lifetimes, with a sharp increase in disk lifetimes for binary separations a {approx}< 0.3-1 AU. Observations of young binary stars can therefore be used to test models of disk evolution, and I show that current data set a strong upper limit to the rate of on-going photoevaporation (<10{sup -9} M{sub Sun} yr{sup -1}). Finally I discuss the implications of these results for planet formation and suggest that circumbinary planets around close (a {approx}< 1 AU) binaries should be relatively common.

  14. DRAMATIC EVOLUTION OF THE DISK-SHAPED SECONDARY IN THE ORION TRAPEZIUM STAR {theta}{sup 1} Ori B{sub 1} (BM Ori): MOST SATELLITE OBSERVATIONS

    SciTech Connect

    Windemuth, Diana; Herbst, William; Tingle, Evan; Fuechsl, Rachel; Kilgard, Roy; Pinette, Melanie; Templeton, Matthew; Henden, Arne

    2013-05-01

    The eclipsing binary {theta}{sup 1} Orionis B{sub 1}, variable star designation BM Ori, is the faintest of the four well-known Trapezium stars at the heart of the Orion Nebula. The primary is a B3 star ({approx}6 M{sub Sun }) but the nature of the secondary ({approx}2 M{sub Sun }) has long been mysterious, since the duration and shape of primary eclipse are inappropriate for any sort of ordinary star. Here we report nearly continuous photometric observations obtained with the MOST satellite over {approx}4 cycles of the 6.47 d binary period. The light curve is of unprecedented quality, revealing a deep, symmetric primary eclipse as well as a clear reflection effect and secondary eclipse. In addition, there are other small disturbances, some of which repeat at the same phase over the four cycles monitored. The shape of the primary light curve has clearly evolved significantly over the past 40 years. While its overall duration and depth have remained roughly constant, the slopes of the descent and ascent phases are significantly shallower now than in the past and its distinctive flat-bottomed ''pseudo-totality'' is much less obvious or even absent in the most recent data. We further demonstrate that the primary eclipse was detected at X-ray wavelengths during the Chandra Orion Ultradeep Project (COUP) study. The light curve continues to be well modeled by a self-luminous and reflective disk-shaped object seen nearly edge-on orbiting the B3 primary. The dramatic change in shape over four decades is modeled as an opacity variation in a tenuous outer envelope or disk of the secondary object. We presume that the secondary is an extremely young protostar at an earlier evolutionary phase than can be commonly observed elsewhere in the Galaxy and that the opacity variations observed are related to its digestion of some accreted matter over the last 50-100 years. Indeed, this object deserves continued observational and theoretical attention as the youngest known eclipsing

  15. 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)

  16. Origins of the thick disk of the Milky Way Galaxy as traced by the elemental abundances of metal-poor stars

    NASA Astrophysics Data System (ADS)

    Ruchti, Gregory Randal

    2010-12-01

    Understanding the formation and evolution of disks in galaxies in the early universe is very important for understanding the forms of galaxies today. Recent studies of the Milky Way Galaxy, an ideal galaxy for analyzing individual stars within its disk, indicate that the formation of the Galactic disk is very complex. Most of these studies, however, contain very few stars at low metallicities. Metal-poor stars are important, because they are potential survivors of the earliest star formation in the disk of the Milky Way Galaxy. I therefore measured elemental abundances of a statistically significant sample of metal-poor ([Fe/H] ≲ - 1.0) stars in the disk of the Galaxy, chosen from the RAVE survey in order to study the early formation history of the Galactic disk. I report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 dwarf/sub-giant metal-poor thick-disk candidate stars. I found that the [alpha/Fe] ratios are enhanced implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the interstellar medium prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star initial mass function. I further looked for radial or vertical gradients in metallicity or alpha-enhancement for the metal-poor thick disk, never before done for such a sample. I found no radial gradient and a moderate vertical gradient in my derived iron abundance, and only minimal-amplitude gradients in [alpha/Fe]. In addition, I show that the distribution of orbital eccentricities for my metal-poor thick-disk stars requires that the thick disk was formed primarily in situ, with direct accretion being extremely minimal. I conclude that the alpha-enhancement of the metal-poor thick disk, and the lack of obvious radial or

  17. Why Do T Tauri Disks Accrete?

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee; D'Alessio, Paola; Calvet, Nuria; Muzerolle, James

    2006-01-01

    Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks scales roughly with the square of the central stellar mass. No dependence of accretion rate on stellar mass is predicted by the simplest version of the Gammie layered disk model, in which nonthermal ionization of upper disk layers allows accretion to occur via the magnetorotational instability. We show that a minor modification of Gaminie's model to include heating by irradiation from the central star yields a modest dependence of accretion on the mass of the central star. A purely viscous disk model could provide a strong dependence of accretion rate on stellar mass if the initial disk radius (before much viscous evolution has occurred) has a strong dependence on stellar mass. However, it is far from clear that at least the most massive pre-main-sequence disks can be totally magnetically activated by X-rays or cosmic rays. We suggest that a combination of effects are responsible for the observed dependence, with the lowest mass stars having the lowest mass disks, which can be thoroughly magnetically active, while the higher mass stars have higher mass disks that have layered accret,ion and relatively inactive or "dead" central zones at some radii. In such dead zones, we suggest that gravitational instabilities may play a role in allowing accretion to proceed. In this connection, we emphasize the uncertainty in disk masses derived from dust emission and argue that T Tauri disk masses have been systematically underestimated by conventional analyses. Furtlier study of accretion rates, especially in the lowest mass stars, would help to clarify the mechanisms of accretion in T Tauri stars.

  18. 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

  19. The Stellar Population Structure of the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Bovy, Jo; Rix, Hans-Walter; Schlafly, Edward F.; Nidever, David L.; Holtzman, Jon A.; Shetrone, Matthew; Beers, Timothy C.

    2016-05-01

    The spatial structure of stellar populations with different chemical abundances in the Milky Way (MW) contains a wealth of information on Galactic evolution over cosmic time. We use data on 14,699 red-clump stars from the APOGEE survey, covering 4 {kpc}≲ R≲ 15 {kpc}, to determine the structure of mono-abundance populations (MAPs)—stars in narrow bins in [α /{Fe}] and [{Fe}/{{H}}]—accounting for the complex effects of the APOGEE selection function and the spatially variable dust obscuration. We determine that all MAPs with enhanced [α /{Fe}] are centrally concentrated and are well-described as exponentials with a scale length of 2.2+/- 0.2 {kpc} over the whole radial range of the disk. We discover that the surface-density profiles of low-[α /{Fe}] MAPs are complex: they do not monotonically decrease outwards, but rather display a peak radius ranging from ≈ 5 to ≈ 13 {kpc} at low [{Fe}/{{H}}]. The extensive radial coverage of the data allows us to measure radial trends in the thickness of each MAP. While high-[α /{Fe}] MAPs have constant scale heights, low-[α /{Fe}] MAPs flare. We confirm, now with high-precision abundances, previous results that each MAP contains only a single vertical scale height and that low-[{Fe}/{{H}}], low-[α /{Fe}] and high-[{Fe}/{{H}}], high-[α /{Fe}] MAPs have intermediate ({h}Z≈ 300{--}600 {pc}) scale heights that smoothly bridge the traditional thin- and thick-disk divide. That the high-[α /{Fe}], thick disk components do not flare is strong evidence against their thickness being caused by radial migration. The correspondence between the radial structure and chemical-enrichment age of stellar populations is clear confirmation of the inside-out growth of galactic disks. The details of these relations will constrain the variety of physical conditions under which stars form throughout the MW disk.

  20. Accretion disk viscosity and internal waves in disks

    NASA Astrophysics Data System (ADS)

    Huang, Min

    1992-01-01

    Recently, Vishniac, Jin and Diamond suggested that internal waves in accretion disks play a critical role in generating magnetic fields, and consequently are indirectly responsible for angular momentum transfer in thin, conducting, and non-self-gravitational disk systems. A project in which we will construct a quantitative model of the internal wave spectrum in accretion disks is started. It includes two aspects of work. The physical properties of the waves in a thin, non-self-gravitational, and non-magnetized accretion disk with realistic vertical structure is cataloged and examined. Besides the low frequency internal waves discovered by Vishniac and Diamond, it was found that sound waves with low frequency and low axisymmetry (with small absolute value of m) are capable of a driving dynamo because they are (1) well confined in a layer with thickness 2(absolute value of m)H where H is the disk scale height; (2) highly dispersive so they may survive the strong dissipation caused by the coherent nonlinear interaction their high frequency partners experience; and (3) elliptically polarized because they are confined in the z-direction. As a first step towards constructing a quantitative theory of this dynamo effect, a framework of calculating resonant nonlinear interaction among waves in disk is established. We are developing a numerical code which will compute the steady spectrum of the wave field in this framework. For simplicity, we only include the low frequency internal waves suggested by Vishniac and Diamond in the present stage. In the vicinity of the static state, the time step whose length is determined by the evolution of the modes with the largest amplitudes is too large for the modes with smaller amplitudes and overshooting occurs. Through nonlinear coupling, this overshooting is amplified and appears as a numerical instability affecting the evolution of the large amplitude modes. Shorter time steps may delay the appearance of the instability but not cure

  1. Ultra-violet radiation is responsible for the differences in global epidemiology of chickenpox and the evolution of varicella-zoster virus as man migrated out of Africa

    PubMed Central

    2011-01-01

    Background Of the eight human herpes viruses, varicella-zoster virus, which causes chickenpox and zoster, has a unique epidemiology. Primary infection is much less common in children in the tropics compared with temperate areas. This results in increased adult susceptibility causing outbreaks, for example in health-care workers migrating from tropical to temperate countries. The recent demonstration that there are different genotypes of varicella-zoster virus and their geographic segregation into tropical and temperate areas suggests a distinct, yet previously unconsidered climatic factor may be responsible for both the clinical and molecular epidemiological features of this virus infection. Presentation of the hypothesis Unlike other human herpes viruses, varicella-zoster virus does not require intimate contact for infection to occur indicating that transmission may be interrupted by a geographically restricted climatic factor. The factor with the largest difference between tropical and temperate zones is ultra-violet radiation. This could reduce the infectiousness of chickenpox cases by inactivating virus in vesicles, before or after rupture. This would explain decreased transmissibility in the tropics and why the peak chickenpox incidence in temperate zones occurs during winter and spring, when ultra-violet radiation is at its lowest. The evolution of geographically restricted genotypes is also explained by ultra-violet radiation driving natural selection of different virus genotypes with varying degrees of resistance to inactivation, tropical genotypes being the most resistant. Consequently, temperate viruses should be more sensitive to its effects. This is supported by the observation that temperate genotypes are found in the tropics only in specific circumstances, namely where ultra-violet radiation has either been excluded or significantly reduced in intensity. Testing the Hypothesis The hypothesis is testable by exposing different virus genotypes to ultra

  2. What determines the bulge to disk ratio of galaxies

    NASA Technical Reports Server (NTRS)

    Roos, Nico

    1990-01-01

    Galaxies having the same luminosity may have very different bulge to disk ratios, while the mean bulge to disk ratio slowly increases with total luminosity (Schecter and Dressler, 1987, Sandage et al., 1985). Such a behavior is expected if ellipticals and the spheroidal components of disk galaxies are produced by secondary accretion of galaxies by larger galaxies. This is illustrated using a simple toy model of the evolution of the mass function of galaxies due to galaxy mergers.

  3. Vertical Structure of Magnetized Accretion Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    Lizano, S.; Tapia, C.; Boehler, Y.; D'Alessio, P.

    2016-01-01

    We model the vertical structure of the magnetized accretion disks that are subject to viscous and resistive heating and irradiation by the central star. We apply our formalism to the radial structure of the magnetized accretion disks that are threaded by the poloidal magnetic field dragged during the process of star formation, which was developed by Shu and coworkers. We consider disks around low-mass protostars, T Tauri, and FU Orionis stars, as well as two levels of disk magnetization: {λ }{sys}=4 (strongly magnetized disks) and {λ }{sys}=12 (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk, and the T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7% of the viscous heating. In these models, the T Tauri disk has a larger aspect ratio, which is consistent with that inferred from observations. All the disks have spatially extended hot atmospheres where the irradiation flux is absorbed, although most of the mass (˜90%-95%) is in the disk midplane. With the advent of ALMA one expects direct measurements of magnetic fields and their morphology at disk scales. It will then be possible to determine the mass-to-flux ratio of magnetized accretion disks around young stars, an essential parameter for their structure and evolution. Our models contribute to the understanding of the vertical structure and emission of these disks.

  4. 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.

  5. 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).

  6. Migration and Survival of Planets near Magnetized Protostars

    NASA Astrophysics Data System (ADS)

    Romanova, Marina

    A significant fraction of observed exoplanets are located very close to the star with a clear peak at 0.05AU. This peak may be an imprint of the past history of the protostar and its disk, when it had a strong magnetic field and cleared a magnetic cavity of very low density. Planets which migrate to this region can survive for millions of years, until the disk is dispersed. This proposal plans to systematically investigate the migration of close- in planets inside the magnetospheric cavity caused by the star's magnetic field. We plan to investigate the cases of dipole and more complex multipole magnetic fields, as well as regimes of unstable accretion when cavities can have a very low density or can be partially filled with matter. In the second part of the proposal, we plan to investigate the migration of planets in the inner disks around rotating stars with misaligned dipole field. A rotating star with a tilted magnetic field excites a strong bending wave (a warp) that propagates outward to large distances in the disk. The wave has super-Keplerian angular velocity. We plan to analyze whether this bending wave may halt or reverse the inward migration of a planet. Also, we plan to investigate cases where the rotational axis of the star is tilted relative to the disk's axis. In this case, a new type of bending wave forms. In both cases, the close-in planet gets multiple kicks in the vertical direction, and this may change the inclination of the planet's orbit. We also plan to study the case where the massive planet clears the gap while interacting with the lower-mass inner parts of the disk. Solutions of these problems require global multidimensional simulations. Our group has developed state-of-the-art global axisymmetric and three-dimensional Godunov type codes, which are oriented to the investigation of plasma flow around rotating magnetized stars. Recently, we developed a module that calculates planetary orbits in our MHD simulations. These powerful tools and

  7. 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

  8. HNC IN PROTOPLANETARY DISKS

    SciTech Connect

    Graninger, Dawn; Öberg, Karin I.; Qi, Chunhua; Kastner, Joel

    2015-07-01

    The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3–2 toward the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3–2 and IRAM 30 m observations of HCN and HNC 1–0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1–0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. However, to realize the full potential of HNC as a disk tracer requires a combination of high SNR spatially resolved observations of HNC and HCN and disk-specific HNC chemical modeling.

  9. Rolling and slipping motion of Euler's disk

    NASA Astrophysics Data System (ADS)

    Caps, H.; Dorbolo, S.; Ponte, S.; Croisier, H.; Vandewalle, N.

    2004-05-01

    We present an experimental study of the motion of a circular disk spun onto a table. With the help of a high speed video system, the temporal evolution of (i) the inclination angle α , (ii) the angular velocity ω , and (iii) the precession rate Ω are studied. The influence of the mass of the disk as well as the friction between the disk and the supporting surface are considered. Both inclination angle and angular velocity are observed to decrease according to a power law. We also show that the precession rate diverges as the motion stops. Measurements are performed very near the collapse as well as on long range times. Times to collapse have been also measured. Results are compared with previous theoretical and experimental works. The major source of energy dissipation is found to be the slipping of the disk on the plane.

  10. BONDI-HOYLE-LYTTLETON ACCRETION ONTO A PROTOPLANETARY DISK

    SciTech Connect

    Moeckel, Nickolas; Throop, Henry B.

    2009-12-10

    Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival the amount in the initial protoplanetary disk; the potential importance of this 'tail-end' accretion for planet formation was recently highlighted by Throop and Bally. While accretion onto a point mass is successfully modeled by the classical Bondi-Hoyle-Lyttleton solutions, the more complicated case of accretion onto a star-disk system defies analytic solution. In this paper, we investigate via direct hydrodynamic simulations the accretion of dense interstellar material onto a star with an associated gaseous protoplanetary disk. We discuss the changes to the structure of the accretion flow caused by the disk, and vice versa. We find that immersion in a dense accretion flow can redistribute disk material such that outer disk migrates inward, increasing the inner disk surface density and reducing the outer radius. The accretion flow also triggers the development of spiral density features, and changes to the disk inclination. The mean accretion rate onto the star remains roughly the same with and without the presence of a disk. We discuss the potential impact of this process on planet formation, including the possibility of triggered gravitational instability, inclination differences between the disk and the star, and the appearance of spiral structure in a gravitationally stable system.

  11. Origin of the moon from a circumterrestrial disk

    NASA Technical Reports Server (NTRS)

    Weidenschilling, S. J.; Greenberg, R.; Chapman, C. R.; Davis, D. R.; Hartmann, W. K.

    1986-01-01

    The paper reveals the possibility that the moon could have formed from the long-term evolution of a circumterrestrial disk emplaced during the earth's final stages of formation. A model is presented which emphasizes silicate enrichment (or iron depletion) of lunar material within the disk. This model depends on the late-stage planetesimal population being dominated by small bodies.

  12. Three steps toward understanding the dynamical structure of the Kuiper belt (and what it means for Neptune's migration)

    NASA Astrophysics Data System (ADS)

    Nesvorny, David

    2015-11-01

    Much of the dynamical structure of the Kuiper belt can be explained if Neptune migrated over several AU, and/or if Neptune was scattered to an eccentric orbit during planetary instability.Step 1: An outstanding problem with the previous migration/instability models is that the distribution of orbital inclinations they predict is narrower than the one inferred from observations. Here we perform numerical simulations of the Kuiper belt formation starting from an initial state with Neptune at 20disk extending from beyond a_N to 30 AU. Neptune's orbit is migrated into the disk on an e-folding timescale 1 < tau < 100 Myr. A small fraction of the disk planetesimals become implanted into the Kuiper belt in the simulations. We find that the inclination constraint implies that Neptune's migration was slow (tau > 10 Myr) and long range (a_N < 25 AU).Step 2: A particularly puzzling and up-to-now unexplained feature of the Kuiper belt is the so-called `kernel', a concentration of orbits with semimajor axes a=44 AU, eccentricities e=0.05, and inclinations i<5 deg. Here we show that the Kuiper belt kernel can be explained if Neptune's migration was interrupted by a discontinuous change of Neptune's semimajor axis when Neptune reached 28 AU (jumping-Neptune model).Step 3: The existing migration/instability models invariably predict an excessively large resonant population, while observations show that the non-resonant orbits are in fact more common (e.g., Plutinos in the 3:2 resonance represent only ~1/3 of the main belt population). Here we show that the observed population statistic implies that Neptune's migration was grainy, as expected from scattering encounters of Neptune with massive planetesimals. Our preferred fit to observations suggests that the outer planetesimal disk below 30 AU contained ~2000 bodies with mass comparable to that of Pluto.Together, these results imply that Neptune's migration was slow, long-range and grainy

  13. The Nature of Transition Disks in Nearby Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Cieza, Lucas A.; Schreiber, M. R.; Romero, G. A.; Orellana, M.; Williams, J. P.; Merin, B.

    2011-01-01

    We present an update on our ongoing project to characterize a large sample of Spitzer selected transition disks located in several star-forming regions. Transition objects are pre-main-sequence stars with optically thin inner disks and optically thick outer disks. Different mechanisms have been proposed to explain their inner opacity holes: planet formation, grain growth, photoevaporation, and tidal truncation in tight binaries. These mechanisms, all relevant to disk evolution in general, can be distinguished when disk masses, accretion rates, and multiplicity information are available. We have already completed our study of Ophiuchus objects, presenting the results from Adaptive Optics (AO) imaging, submillimeter photometry, and echelle spectroscopy observations. We are currently working on several other regions, including Taurus-Auriga, Perseus, Serpens, and Lupus. Our results show that transition disks are a very heterogeneous group of objects with a wide range of SED morphologies, disk masses ( < 0.5 to 40 Mjup), and accretion rates (<10E-11 to 10E-7 Msolar/yr). Since the properties of our transition disks point toward distinct processes driving the evolution of each disk, we have been able to identify very strong candidates for the following disk categories: circumbinary disks, grain-growth dominated disks, photoevaporating disks, debris disks, and (giant) planet-forming disks.

  14. Are all flaring Herbig disks transitional?

    NASA Astrophysics Data System (ADS)

    Maaskant, K. M.; Honda, M.; Waters, L. B. F. M.; Tielens, A. G. G. M.; Dominik, Carsten; Min, M.; Verhoeff, A.; Meeus, G.; Ancker, M. E.

    2013-07-01

    Context: The evolution of young massive protoplanetary disks toward planetary systems is expected to correspond to structural changes in observational appearance, which includes the formation of gaps and the depletion of dust and gas. Aims. A special group of disks around Herbig Ae/Be stars do not show prominent silicate emission features, although they still bear signs of flaring disks, the presence of gas, and small grains. We focus our attention on four key Herbig Ae/Be stars to understand the structural properties responsible for the absence of silicate feature emission. Methods: We investigate Q- and N-band images taken with Subaru/COMICS, Gemini South/T-ReCS, and VLT/VISIR. We perform radiative transfer modeling to examine the radial distribution of dust and polycyclic aromatic hydrocarbons (PAHs). Our solutions require a separation of inner- and outer- disks by a large gap. From this, we characterize the radial density structure of dust and PAHs in the disk. Results: The inner edge of the outer disk has a high surface brightness and a typical temperature between ˜100-150 K and therefore, dominates the emission in the Q-band. All four disks are characterized by large gaps. We derive radii of the inner edge of the outer disk of 34+4 , 23+3 , 30+5 and 63+4 AU for HD 97048, HD 169142, HD 135344 B, and Oph IRS 48, respectively. For HD 97048 this is the first -4 -5 -3 -4 detection of a disk gap. The large gaps deplete the entire population of silicate particles with temperatures suitable for prominent mid- infrared feature emission, while small carbonaceous grains and PAHs can still show prominent emission at mid-infrared wavelengths. The continuum emission in the N-band is not due to emission in the wings of PAHs. This continuum emission can be due to very small grains or to thermal emission from the inner disk. We find that PAH emission is not always dominated by PAHs on the surface of the outer disk. Conclusions: The absence of silicate emission features is

  15. THE EXTENDED OPTICAL DISK OF M101

    SciTech Connect

    Mihos, J. Christopher; Harding, Paul; Spengler, Chelsea E.; Rudick, Craig S.; Feldmeier, John J. E-mail: paul.harding@case.edu E-mail: craig.rudick@phys.ethz.ch

    2013-01-10

    We have used deep, wide-field optical imaging to study the faint outskirts of the luminous spiral galaxy M101 (NGC 5457) as well as its surrounding environment. Over 6 deg{sup 2}, our imaging has a limiting surface brightness of {mu} {sub B} {approx} 29.5 mag arcsec{sup -2}, and has revealed the stellar structure of M101's disk out to nearly 25' (50 kpc), 3 times our measured R {sub 25} isophotal size of the optical disk. At these radii, the well-known asymmetry of the inner disk slews 180 Degree-Sign , resulting in an asymmetric plume of light at large radius which follows the very extended H I disk to the northeast of M101. This plume has very blue colors (B - V {approx} 0.2), suggesting that it is the somewhat more evolved (few hundred Myr to {approx}1 Gyr) counterpart of the young far-ultraviolet emitting population traced by Galaxy Evolution Explorer imaging. We also detect another, redder spur of extended light to the east of the disk, and both structures are reminiscent of features produced during fly-by galaxy interactions. However, we see no evidence of very extended tidal tails around M101 or any of its companions which might be expected from a recent encounter with a massive companion. We consider the properties of M101's outer disk in light of possible past interactions with the nearby companion galaxies NGC 5477 and NGC 5474. The detection of optical starlight at such large radii gives us the ability to study star formation histories and stellar populations in outer disks over longer timescales than those traced by the UV or H{alpha} emitting populations. Our data suggest an ongoing buildup of M101's outer disk due to encounters in the group environment triggering extended star formation and tidal heating of existing disk populations.

  16. 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.

  17. SUPERMASSIVE BLACK HOLES IN A STAR-FORMING GASEOUS CIRCUMNUCLEAR DISK

    SciTech Connect

    Del Valle, L.; Escala, A.; Molina, J.; Maureira-Fredes, C.; Amaro-Seoane, P.; Cuadra, J.

    2015-09-20

    Using N-body/smoothed particle hydrodynamics simulations we study the evolution of the separation of a pair of supermassive black holes (SMBHs) embedded in a star-forming circumnuclear disk (CND). This type of disk is expected to be formed in the central kiloparsec of the remnant of gas-rich galaxy mergers. Our simulations indicate that orbital decay of the SMBHs occurs more quickly when the mean density of the CND is higher, due to increased dynamical friction. However, in simulations where the CND is fragmented in high-density gaseous clumps (clumpy CND), the orbits of the SMBHs are erratically perturbed by the gravitational interaction with these clumps, delaying, in some cases, the orbital decay of the SMBHs. The densities of these gaseous clumps in our simulations and in recent studies of clumpy CNDs are two orders of magnitude higher than the observed density of molecular clouds in isolated galaxies or ultraluminous infrared galaxies (ULIRGs), thus, we expect that SMBH orbits are perturbed less in real CNDs than in the simulated CNDs of this study and other recent studies. We also find that the migration timescale has a weak dependence on the star formation rate of the CND. Furthermore, the migration timescale of an SMBH pair in a star-forming clumpy CND is at most a factor of three longer than the migration timescale of a pair of SMBHs in a CND modeled with more simple gas physics. Therefore, we estimate that the migration timescale of the SMBHs in a clumpy CND is on the order of 10{sup 7} years.

  18. Accretion Disks and the Formation of Stellar Systems

    NASA Astrophysics Data System (ADS)

    Kratter, Kaitlin Michelle

    2011-02-01

    In this thesis, we examine the role of accretion disks in the formation of stellar systems, focusing on young massive disks which regulate the flow of material from the parent molecular core down to the star. We study the evolution of disks with high infall rates that develop strong gravitational instabilities. We begin in chapter 1 with a review of the observations and theory which underpin models for the earliest phases of star formation and provide a brief review of basic accretion disk physics, and the numerical methods that we employ. In chapter 2 we outline the current models of binary and multiple star formation, and review their successes and shortcomings from a theoretical and observational perspective. In chapter 3 we begin with a relatively simple analytic model for disks around young, high mass stars, showing that instability in these disks may be responsible for the higher multiplicity fraction of massive stars, and perhaps the upper mass to which they grow. We extend these models in chapter 4 to explore the properties of disks and the formation of binary companions across a broad range of stellar masses. In particular, we model the role of global and local mechanisms for angular momentum transport in regulating the relative masses of disks and stars. We follow the evolution of these disks throughout the main accretion phase of the system, and predict the trajectory of disks through parameter space. We follow up on the predictions made in our analytic models with a series of high resolution, global numerical experiments in chapter 5. Here we propose and test a new parameterization for describing rapidly accreting, gravitationally unstable disks. We find that disk properties and system multiplicity can be mapped out well in this parameter space. Finally, in chapter 6, we address whether our studies of unstable disks are relevant to recently detected massive planets on wide orbits around their central stars.

  19. THE THICK DISKS OF SPIRAL GALAXIES AS RELICS FROM GAS-RICH, TURBULENT, CLUMPY DISKS AT HIGH REDSHIFT

    SciTech Connect

    Bournaud, Frederic; Martig, Marie; Elmegreen, Bruce G.

    2009-12-10

    The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendicular forcing and disk-gravity resistance are both proportional to the disk column density, so the resulting scale height is independent of this density. In the case of mergers, perpendicular forcing is independent of the column density and the low-density regions get thicker; the resulting flaring is inconsistent with observations. Late-stage gas accretion and thin-disk growth are shown to preserve the constant scale heights of thick disks formed by internal evolution. These results reinforce the idea that disk galaxies accrete most of their mass smoothly and acquire their structure by internal processes, in particular through turbulent and clumpy phases at high redshift.

  20. Formation of giant planets by fragmentation of protoplanetary disks.

    PubMed

    Mayer, Lucio; Quinn, Thomas; Wadsley, James; Stadel, Joachim

    2002-11-29

    The evolution of gravitationally unstable protoplanetary gaseous disks has been studied with the use of three-dimensional smoothed particle hydrodynamics simulations with unprecedented resolution. We have considered disks with initial masses and temperature profiles consistent with those inferred for the protosolar nebula and for other protoplanetary disks. We show that long-lasting, self-gravitating protoplanets arise after a few disk orbital periods if cooling is efficient enough to maintain the temperature close to 50 K. The resulting bodies have masses and orbital eccentricities similar to those of detected extrasolar planets.

  1. Circumstellar Debris Disks and SIRTF

    NASA Astrophysics Data System (ADS)

    Backman, D. E.

    2000-05-01

    At least 15% of nearby main sequence stars are found to have far-IR excesses representing thermal emission from optically thin dust clouds. Famous prototypes of this class of objects include the Vega and beta Pictoris systems. Because destruction times for observed grains are much shorter than the system ages, the dust is known to be ``2nd generation" material released recently from hypothetical asteroid or comet parent bodies and not primordial grains persisting since system formation. The best local analogs to the main sequence debris disk systems are the inner solar system's zodiacal dust cloud and a presumed dust component of the Kuiper Belt. Planetary masses are probably required to drive planetesimals into shattering collisions and star-grazing orbits that produce dust, thus debris disks may allow inference of presence and location of planets. SIRTF will give us much-improved understanding of the frequency of debris disks around field main sequence stars, as well as the amount, size and composition of dust grains versus stellar age. This will help place our solar system into context of evolution of planetary material around normal stars.

  2. Astounding Jumping Disk.

    ERIC Educational Resources Information Center

    Guzdziol, Edward S.

    1991-01-01

    Activities involving concave rubber disks are utilized to illustrate the scientific principles of kinetic and potential energy. Provides teacher instructions and questions related to the activity. (MDH)

  3. 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.

  4. Age-dependent metallicity gradients of the MilkyWay disk from main sequence turn-off stars in LSS-GAC

    NASA Astrophysics Data System (ADS)

    Xiang, Maosheng; Liu, Xiaowei

    2015-08-01

    The stellar metallicity gradient plays an important role on constraining the formation and assemblage history of the Galactic disk. We use 297, 042 main sequence turn-off stars from LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to study the radial metallicity gradient, [Fe/H]/R, and the vertical metallicity gradient, [Fe/H]/|Z|, of the Galactic disk in the anti-center direction. We carry out age determination for these turnoff stars via isochrone fitting and study the age-dependent metallicity gradients. We have implemented a detailed analysis on the sample selection effect to account for the target selection in the color - magnitude diagram (CMD) and the potential bias on metallicity gradients of a magnitude limited sample. Our results show that both the radial and vertical gradients have strong spatial and temporal evolution. The radial gradients of the oldest (age > 11Gyr) stars are almost zero at all heights above the Galactic disk plane, while those of the younger stars are always negative. The vertical gradients of the oldest stars are negative and show very weak evolution with the Galactocentric distance in the disk plane, R, while those of the younger stars show strong evolution with R. At the early epoch, the radial gradient steepens as the age becomes younger, with a maximum occurs at 7 - 8Gyr, after then it becomes flatter. Similar trend with age is also presented in the vertical gradients. We infer that the formation of the Galactic disk has experienced at least two phases. The earlier phase is probably a slow, pressure-supported collapse of gas, where the gas settle down to the disk from the vertical direction. In the later phase, there is significant radial flow of gas. Transition of the gas behaviors between the two phases occurs between 8 and 11Gyr. The two phases are responsible for the formation of the Galactic thick and thin disks, respectively, and consequently, we recommend that the age is a natural, physical criterion to

  5. Neptune's Orbital Migration Was Grainy, Not Smooth

    NASA Astrophysics Data System (ADS)

    Nesvorný, David; Vokrouhlický, David

    2016-07-01

    The Kuiper Belt is a population of icy bodies beyond the orbit of Neptune. The complex orbital structure of the Kuiper Belt, including several categories of objects inside and outside of resonances with Neptune, emerged as a result of Neptune’s migration into an outer planetesimal disk. An outstanding problem with the existing migration models is that they invariably predict excessively large resonant populations, while observations show that the non-resonant orbits are in fact common (e.g., the main belt population is ≃2-4 times larger than Plutinos in the 3:2 resonance). Here we show that this problem can be resolved if it is assumed that Neptune’s migration was grainy, as expected from scattering encounters of Neptune with massive planetesimals. The grainy migration acts to destabilize resonant bodies with large libration amplitudes, a fraction of which ends up on stable non-resonant orbits. Thus, the non-resonant-to-resonant ratio obtained with the grainy migration is higher, up to ˜10 times higher for the range of parameters investigated here, than in a model with smooth migration. In addition, the grainy migration leads to a narrower distribution of the libration amplitudes in the 3:2 resonance. The best fit to observations is obtained when it is assumed that the outer planetesimal disk below 30 au contained 1000-4000 Plutos. We estimate that the combined mass of Pluto-class objects in the original disk represented 10%-40% of the estimated disk mass ({M}{{disk}}≃ 20 {M}{{Earth}}). This constraint can be used to better understand the accretion processes in the outer solar system.

  6. Neptune's Orbital Migration Was Grainy, Not Smooth

    NASA Astrophysics Data System (ADS)

    Nesvorný, David; Vokrouhlický, David

    2016-07-01

    The Kuiper Belt is a population of icy bodies beyond the orbit of Neptune. The complex orbital structure of the Kuiper Belt, including several categories of objects inside and outside of resonances with Neptune, emerged as a result of Neptune’s migration into an outer planetesimal disk. An outstanding problem with the existing migration models is that they invariably predict excessively large resonant populations, while observations show that the non-resonant orbits are in fact common (e.g., the main belt population is ≃2–4 times larger than Plutinos in the 3:2 resonance). Here we show that this problem can be resolved if it is assumed that Neptune’s migration was grainy, as expected from scattering encounters of Neptune with massive planetesimals. The grainy migration acts to destabilize resonant bodies with large libration amplitudes, a fraction of which ends up on stable non-resonant orbits. Thus, the non-resonant-to-resonant ratio obtained with the grainy migration is higher, up to ˜10 times higher for the range of parameters investigated here, than in a model with smooth migration. In addition, the grainy migration leads to a narrower distribution of the libration amplitudes in the 3:2 resonance. The best fit to observations is obtained when it is assumed that the outer planetesimal disk below 30 au contained 1000–4000 Plutos. We estimate that the combined mass of Pluto-class objects in the original disk represented 10%–40% of the estimated disk mass ({M}{{disk}}≃ 20 {M}{{Earth}}). This constraint can be used to better understand the accretion processes in the outer solar system.

  7. TOWARD CHEMICAL CONSTRAINTS ON HOT JUPITER MIGRATION

    SciTech Connect

    Madhusudhan, Nikku; Amin, Mustafa A.; Kennedy, Grant M.

    2014-10-10

    The origin of hot Jupiters—gas giant exoplanets orbiting very close to their host stars—is a long-standing puzzle. Planet formation theories suggest that such planets are unlikely to have formed in situ but instead may have formed at large orbital separations beyond the snow line and migrated inward to their present orbits. Two competing hypotheses suggest that the planets migrated either through interaction with the protoplanetary disk during their formation, or by disk-free mechanisms such as gravitational interactions with a third body. Observations of eccentricities and spin-orbit misalignments of hot Jupiter systems have been unable to differentiate between the two hypotheses. In the present work, we suggest that chemical depletions in hot Jupiter atmospheres might be able to constrain their migration mechanisms. We find that sub-solar carbon and oxygen abundances in Jovian-mass hot Jupiters around Sun-like stars are hard to explain by disk migration. Instead, such abundances are more readily explained by giant planets forming at large orbital separations, either by core accretion or gravitational instability, and migrating to close-in orbits via disk-free mechanisms involving dynamical encounters. Such planets also contain solar or super-solar C/O ratios. On the contrary, hot Jupiters with super-solar O and C abundances can be explained by a variety of formation-migration pathways which, however, lead to solar or sub-solar C/O ratios. Current estimates of low oxygen abundances in hot Jupiter atmospheres may be indicative of disk-free migration mechanisms. We discuss open questions in this area which future studies will need to investigate.

  8. DISK-PLANETS INTERACTIONS AND THE DIVERSITY OF PERIOD RATIOS IN KEPLER'S MULTI-PLANETARY SYSTEMS

    SciTech Connect

    Baruteau, Clement; Papaloizou, John C. B. E-mail: J.C.B.Papaloizou@damtp.cam.ac.uk

    2013-11-20

    The Kepler mission is dramatically increasing the number of planets known in multi-planetary systems. Many adjacent planets have orbital period ratios near resonant values, with a tendency to be larger than required for exact first-order mean-motion resonances. This feature has been shown to be a natural outcome of orbital circularization of resonant planetary pairs due to star-planet tidal interactions. However, this feature holds in multi-planetary systems with periods longer than 10 days, in which tidal circularization is unlikely to provide efficient divergent evolution of the planets' orbits to explain these orbital period ratios. Gravitational interactions between planets and their parent protoplanetary disk may instead provide efficient divergent evolution. For a planet pair embedded in a disk, we show that interactions between a planet and the wake of its companion can reverse convergent migration and significantly increase the period ratio from a near-resonant value. Divergent evolution due to wake-planet interactions is particularly efficient when at least one of the planets opens a partial gap around its orbit. This mechanism could help account for the diversity of period ratios in Kepler's multiple systems from super-Earth to sub-Jovian planets with periods greater than about 10 days. Diversity is also expected for pairs of planets massive enough to merge their gap. The efficiency of wake-planet interactions is then much reduced, but convergent migration may stall with a variety of period ratios depending on the density structure in the common gap. This is illustrated for the Kepler-46 system, for which we reproduce the period ratio of Kepler-46b and c.

  9. Disk Evaporation in Star Forming Regions

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Young stars produce sufficient ultraviolet photon luminosity and mechanical luminosity in their winds to significantly affect the structure and evolution of the accretion disks surrounding them. The Lyman continuum photons create a nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk at small distances from the star. Further out, they create a photoevaporative flow which relatively rapidly destroys the disk. The resulting slow (10-50 km/s) ionized outflow, which persists for approx. greater than 10(exp 5) years for disk masses M(sub d) approx. 0.3M(sub *), may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We apply the results to Ae and Be stars in order to determine the lifetimes of disks around such stars. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1) C.

  10. Signposts of Multiple Planets in Debris Disks

    NASA Astrophysics Data System (ADS)

    Su, Kate Y. L.; Rieke, G. H.

    2014-01-01

    We review the nearby debris disk structures revealed by multi-wavelength images from Spitzer and Herschel, and complemented with detailed spectral energy distribution modeling. Similar to the definition of habitable zones around stars, debris disk structures should be identified and characterized in terms of dust temperatures rather than physical distances so that the heating power of different spectral type of stars is taken into account and common features in disks can be discussed and compared directly. Common features, such as warm (~150 K) dust belts near the water-ice line and cold (~50 K) Kuiper-belt analogs, give rise to our emerging understanding of the levels of order in debris disk structures and illuminate various processes about the formation and evolution of exoplanetary systems. In light of the disk structures in the debris disk twins (Vega and Fomalhaut), and the current limits on the masses of planetary objects, we suggest that the large gap between the warm and cold dust belts is the best signpost for multiple (low-mass) planets beyond the water-ice line.

  11. Cell Migration

    PubMed Central

    Trepat, Xavier; Chen, Zaozao; Jacobson, Ken

    2015-01-01

    Cell migration is fundamental to establishing and maintaining the proper organization of multicellular organisms. Morphogenesis can be viewed as a consequence, in part, of cell locomotion, from large-scale migrations of epithelial sheets during gastrulation, to the movement of individual cells during development of the nervous system. In an adult organism, cell migration is essential for proper immune response, wound repair, and tissue homeostasis, while aberrant cell migration is found in various pathologies. Indeed, as our knowledge of migration increases, we can look forward to, for example, abating the spread of highly malignant cancer cells, retarding the invasion of white cells in the inflammatory process, or enhancing the healing of wounds. This article is organized in two main sections. The first section is devoted to the single-cell migrating in isolation such as occurs when leukocytes migrate during the immune response or when fibroblasts squeeze through connective tissue. The second section is devoted to cells collectively migrating as part of multicellular clusters or sheets. This second type of migration is prevalent in development, wound healing, and in some forms of cancer metastasis. PMID:23720251

  12. THE LONG-LIVED DISKS IN THE {eta} CHAMAELEONTIS CLUSTER

    SciTech Connect

    Sicilia-Aguilar, Aurora; Bouwman, Jeroen; Juhasz, Attila; Henning, Thomas; Roccatagliata, Veronica; Lawson, Warrick A.; Acke, Bram; Decin, Leen; Feigelson, Eric D.; Tielens, A. G. G. M.; Meeus, Gwendolyn

    2009-08-20

    We present Infrared Spectrograph spectra and revised Multiband Imaging Photometer photometry for the 18 members of the {eta} Chamaeleontis cluster. Aged 8 Myr, the {eta} Cha cluster is one of the few nearby regions within the 5-10 Myr age range, during which the disk fraction decreases dramatically and giant planet formation must come to an end. For the 15 low-mass members, we measure a disk fraction {approx}50%, high for their 8 Myr age, and four of the eight disks lack near-IR excesses, consistent with the empirical definition of 'transition' disks. Most of the disks are comparable to geometrically flat disks. The comparison with regions of different ages suggests that at least some of the 'transition' disks may represent the normal type of disk around low-mass stars. Therefore, their flattened structure and inner holes may be related to other factors (initial masses of the disk and the star, environment, binarity), rather than to pure time evolution. We analyze the silicate dust in the disk atmosphere, finding moderate crystalline fractions ({approx}10%-30%) and typical grain sizes {approx}1-3 {mu}m, without any characteristic trend in the composition. These results are common to other regions of different ages, suggesting that the initial grain processing occurs very early in the disk lifetime (<1 Myr). Large grain sizes in the disk atmosphere cannot be used as a proxy for age, but are likely related to higher disk turbulence. The dust mineralogy varies between the 8-12 {mu}m and the 20-30 {mu}m features, suggesting high temperature dust processing and little radial mixing. Finally, the analysis of IR and optical data on the B9 star {eta} Cha reveals that it is probably surrounded by a young debris disk with a large inner hole, instead of being a classical Be star.

  13. Age and speciation of iodine in groundwater and mudstones of the Horonobe area, Hokkaido, Japan: Implications for the origin and migration of iodine during basin evolution

    NASA Astrophysics Data System (ADS)

    Togo, Yoko S.; Takahashi, Yoshio; Amano, Yuki; Matsuzaki, Hiroyuki; Suzuki, Yohey; Terada, Yasuko; Muramatsu, Yasuyuki; Ito, Kazumasa; Iwatsuki, Teruki

    2016-10-01

    This paper reports the concentration, speciation and isotope ratio (129I/127I) of iodine from both groundwater and host rocks in the Horonobe area, northern Hokkaido, Japan, to clarify the origin and migration of iodine in sedimentary rocks. Cretaceous to Quaternary sedimentary rocks deposited nearly horizontally in Tenpoku Basin and in the Horonobe area were uplifted above sea level during active tectonics to form folds and faults in the Quaternary. Samples were collected from the Pliocene Koetoi and late Miocene Wakkanai formations (Fms), which include diatomaceous and siliceous mudstones. The iodine concentration in groundwater, up to 270 μmol/L, is significantly higher than that of seawater, with the iodine enrichment factor relative to seawater reaching 800-1500. The iodine concentration in the rocks decreases from the Koetoi to Wakkanai Fms, suggesting that iodine was released into the water from the rocks of deeper formations. The iodine concentration in the rocks is sufficiently high for forming iodine-rich groundwater as found in this area. X-ray absorption near edge structure (XANES) analysis shows that iodine exists as organic iodine and iodide (I-) in host rocks, whereas it exists mainly as I- in groundwater. The isotope ratio is nearly constant for iodine in the groundwater, at [0.11-0.23] × 10-12, and it is higher for iodine in rocks, at [0.29-1.1] × 10-12, giving iodine ages of 42-60 Ma and 7-38 Ma, respectively. Some iodine in groundwater must have originated from Paleogene and even late Cretaceous Fms, which are also considered as possible sources of oil and gas, in view of the old iodine ages of the groundwater. The iodine ages of the rocks are older than the depositional ages, implying that the rocks adsorbed some iodine from groundwater, which was sourced from greater depths. The iodine concentration in groundwater decreases with decreasing chlorine concentration due to mixing of iodine-rich connate water and meteoric water. A likely scenario

  14. A Dwarf Transitional Protoplanetary Disk around XZ Tau B

    NASA Astrophysics Data System (ADS)

    Osorio, Mayra; Macías, Enrique; Anglada, Guillem; Carrasco-González, Carlos; Galván-Madrid, Roberto; Zapata, Luis; Calvet, Nuria; Gómez, José F.; Nagel, Erick; Rodríguez, Luis F.; Torrelles, José M.; Zhu, Zhaohuan

    2016-07-01

    We report the discovery of a dwarf protoplanetary disk around the star XZ Tau B that shows all the features of a classical transitional disk but on a much smaller scale. The disk has been imaged with the Atacama Large Millimeter/submillimeter Array (ALMA), revealing that its dust emission has a quite small radius of ˜3.4 au and presents a central cavity of ˜1.3 au in radius that we attribute to clearing by a compact system of orbiting (proto)planets. Given the very small radii involved, evolution is expected to be much faster in this disk (observable changes in a few months) than in classical disks (observable changes requiring decades) and easy to monitor with observations in the near future. From our modeling we estimate that the mass of the disk is large enough to form a compact planetary system.

  15. Dynamo magnetic-field generation in turbulent accretion disks

    NASA Technical Reports Server (NTRS)

    Stepinski, T. F.

    1991-01-01

    Magnetic fields can play important roles in the dynamics and evolution of accretion disks. The presence of strong differential rotation and vertical density gradients in turbulent disks allows the alpha-omega dynamo mechanism to offset the turbulent dissipation and maintain strong magnetic fields. It is found that MHD dynamo magnetic-field normal modes in an accretion disk are highly localized to restricted regions of a disk. Implications for the character of real, dynamically constrained magnetic fields in accretion disks are discussed. The magnetic stress due to the mean magnetic field is found to be of the order of a viscous stress. The dominant stress, however, is likely to come from small-scale fluctuating magnetic fields. These fields may also give rise to energetic flares above the disk surface, providing a possible explanation for the highly variable hard X-ray emission from objects like Cyg X-l.

  16. Warm Disks from Giant Impacts

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    In the process of searching for exoplanetary systems, weve discovered tens of debris disks close around distant stars that are especially bright in infrared wavelengths. New research suggests that we might be looking at the late stages of terrestrial planet formation in these systems.Forming Terrestrial PlanetsAccording to the widely-accepted formation model for our solar-system, protoplanets the size of Mars formed within a protoplanetary disk around our Sun. Eventually, the depletion of the gas in the disk led the orbits of these protoplanets to become chaotically unstable. Finally, in the giant impact stage, many of the protoplanets collided with each other ultimately leading to the formation of the terrestrial planets and their moons as we know them today.If giant impact stages occur in exoplanetary systems, too leading to the formation of terrestrial exoplanets how would we detect this process? According to a study led by Hidenori Genda of the Tokyo Institute of Technology, we might be already be witnessing this stage in observations of warm debris disks around other stars. To test this, Genda and collaborators model giant impact stages and determine what we would expect to see from a system undergoing this violent evolution.Modeling CollisionsSnapshots of a giant impact in one of the authors simulations. The collision causes roughly 0.05 Earth masses of protoplanetary material to be ejected from the system. Click for a closer look! [Genda et al. 2015]The collaborators run a series of simulations evolving protoplanetary bodies in a solar system. The simulations begin 10 Myr into the lifetime of the solar system, i.e., after the gas from the protoplanetary disk has had time to be cleared and the protoplanetary orbits begin to destabilize. The simulations end when the protoplanets are done smashing into each other and have again settled into stable orbits, typically after ~100 Myr.The authors find that, over an average giant impact stage, the total amount of

  17. Reprocessing in Luminous Disks

    NASA Astrophysics Data System (ADS)

    Bell, K. R.

    1999-11-01

    We develop and investigate a procedure that accounts for disk reprocessing of photons that originate in the disk itself. Surface temperatures and simple, blackbody spectral energy distributions (SEDs) of protostellar disks are calculated. In disks that flare with radius, reprocessing of stellar photons results in temperature profiles that are not power-law at all radii but are consistently shallower than r-3/4. Including the disk as a radiation source (as in the case of active accretion) along with the stellar source further flattens the temperature profile. Disks that flare strongly near the star and then smoothly curve over and become shadowed at some distance (``decreasing curvature'' disks) exhibit nearly power-law temperature profiles that result in power-law infrared SEDs with slopes in agreement with typical observations of young stellar objects. Disk models in which the photospheric thickness is controlled by the local opacity and in which the temperature decreases with radius naturally have this shape. Uniformly flaring models do not match observations as well; progressively stronger reprocessing at larger radii leads to SEDs that flatten toward the infrared or even have a second peak at the wavelength corresponding (through the Wien law) to the temperature of the outer edge of the disk. In FU Orionis outbursting systems, the dominant source of energy is the inner disk. Reprocessing throughout the disk depends sensitively on the inner disk shape and emitted temperature profile. We show that the thermal instability outburst models of Bell & Lin reproduce trends in the observed SEDs of FU Ori systems with T~r-3/4 in the inner disk (r<~0.25 AU corresponding to λ<~10 μm) and T~r-1/2 in the outer disk. Surface irradiation during outburst and quiescence is compared in the region of planet formation (1-10 AU). The contrast between the two phases is diminished by the importance of the reprocessing of photons from the relatively high mass flux, outer disk (Ṁ=10

  18. LATE ORBITAL INSTABILITIES IN THE OUTER PLANETS INDUCED BY INTERACTION WITH A SELF-GRAVITATING PLANETESIMAL DISK

    SciTech Connect

    Levison, Harold F.; Nesvorny, David; Morbidelli, Alessandro; Tsiganis, Kleomenis; Gomes, Rodney

    2011-11-15

    We revisit the issue of the cause of the dynamical instability during the so-called Nice model, which describes the early dynamical evolution of the giant planets. In particular, we address the problem of the interaction of planets with a distant planetesimal disk in the time interval between the dispersal of the proto-solar nebula and the instability. In contrast to previous works, we assume that the inner edge of the planetesimal disk is several AUs beyond the orbit of the outermost planet, so that no close encounters between planets and planetesimals occur. Moreover, we model the disk's viscous stirring, induced by the presence of embedded Pluto-sized objects. The four outer planets are assumed to be initially locked in a multi-resonant state that most likely resulted from a preceding phase of gas-driven migration. We show that viscous stirring leads to an irreversible exchange of energy between a planet and a planetesimal disk even in the absence of close encounters between the planet and disk particles. The process is mainly driven by the most eccentric planet, which is the inner ice giant in the case studied here. In isolation, this would cause this ice giant to migrate inward. However, because it is locked in resonance with Saturn, its eccentricity increases due to adiabatic invariance. During this process, the system crosses many weak secular resonances-many of which can disrupt the mean motion resonance and make the planetary system unstable. We argue that this basic dynamical process would work in many generic multi-resonant systems-forcing a good fraction of them to become unstable. Because the energy exchange proceeds at a very slow pace, the instability manifests itself late, on a timescale consistent with the epoch of the late heavy bombardment ({approx}700 Myr). In the migration mechanism presented here, the instability time is much less sensitive to the properties of the planetesimal disk (particularly the location of its inner edge) than in the

  19. Outward Migration of Giant Planets in Orbital Resonance

    NASA Astrophysics Data System (ADS)

    D'Angelo, G.; Marzari, F.

    2013-05-01

    A pair of giant planets interacting with a gaseous disk may be subject to convergent orbital migration and become locked into a mean motion resonance. If the orbits are close enough, the tidal gaps produced by the planets in the disk may overlap. This represents a necessary condition to activate the outward migration of the pair. However, a number of other conditions must also be realized in order for this mechanism to operate. We have studied how disk properties, such as turbulence viscosity, temperature, surface density gradient, mass, and age, may affect the outcome of the outward migration process. We have also investigated the implications on this mechanism of the planets' gas accretion. If the pair resembles Jupiter and Saturn, the 3:2 orbital resonance may drive them outward until they reach stalling radii for migration, which are within ~10 AU of the star for disks representative of the early proto-solar nebula. However, planet post-formation conditions in the disk indicate that such planets become typically locked in the 1:2 orbital resonance, which does not lead to outward migration. Planet growth via gas accretion tends to alter the planets' mass-ratio and/or the disk accretion rate toward the star, reducing or inhibiting outward migration. Support from NASA Outer Planets Research Program and NASA Origins of Solar Systems Program is gratefully acknowledged.

  20. Deep MIPS Observations of the IC 348 Nebula: Constraints on the Evolutionary State of Anemic Circumstellar Disks and the Primordial-to-Debris Disk Transition

    NASA Astrophysics Data System (ADS)

    Currie, Thayne; Kenyon, Scott J.

    2009-09-01

    We describe new, deep MIPS photometry and new high signal-to-noise optical spectroscopy of the 2.5 Myr old IC 348 Nebula. To probe the properties of the IC 348 disk population, we combine these data with previous optical/infrared photometry and spectroscopy to identify stars with gas accretion, to examine their mid-IR colors, and to model their spectral energy distributions. IC 348 contains many sources in different evolutionary states, including protostars and stars surrounded by primordial disks, two kinds of transitional disks, and debris disks. Most disks surrounding early/intermediate spectral-type stars (>1.4 M sun at 2.5 Myr) are debris disks; most disks surrounding solar and subsolar-mass stars are primordial disks. At the 1-2 σ level, more massive stars also have a smaller frequency of gas accretion and smaller mid-IR luminosities than lower-mass stars. These trends are suggestive of a stellar mass-dependent evolution of disks, where most disks around high/intermediate-mass stars shed their primordial disks on rapid, 2.5 Myr timescales. The frequency of MIPS-detected transitional disks is ≈15%-35% for stars plausibly more massive than 0.5 M sun. The relative frequency of transitional disks in IC 348 compared to that for 1 Myr old Taurus and 5 Myr old NGC 2362 is consistent with a transition timescale that is a significant fraction of the total primordial disk lifetime.

  1. DEEP MIPS OBSERVATIONS OF THE IC 348 NEBULA: CONSTRAINTS ON THE EVOLUTIONARY STATE OF ANEMIC CIRCUMSTELLAR DISKS AND THE PRIMORDIAL-TO-DEBRIS DISK TRANSITION

    SciTech Connect

    Currie, Thayne; Kenyon, Scott J. E-mail: skenyon@cfa.harvard.edu

    2009-09-15

    We describe new, deep MIPS photometry and new high signal-to-noise optical spectroscopy of the 2.5 Myr old IC 348 Nebula. To probe the properties of the IC 348 disk population, we combine these data with previous optical/infrared photometry and spectroscopy to identify stars with gas accretion, to examine their mid-IR colors, and to model their spectral energy distributions. IC 348 contains many sources in different evolutionary states, including protostars and stars surrounded by primordial disks, two kinds of transitional disks, and debris disks. Most disks surrounding early/intermediate spectral-type stars (>1.4 M {sub sun} at 2.5 Myr) are debris disks; most disks surrounding solar and subsolar-mass stars are primordial disks. At the 1-2 {sigma} level, more massive stars also have a smaller frequency of gas accretion and smaller mid-IR luminosities than lower-mass stars. These trends are suggestive of a stellar mass-dependent evolution of disks, where most disks around high/intermediate-mass stars shed their primordial disks on rapid, 2.5 Myr timescales. The frequency of MIPS-detected transitional disks is {approx}15%-35% for stars plausibly more massive than 0.5 M {sub sun}. The relative frequency of transitional disks in IC 348 compared to that for 1 Myr old Taurus and 5 Myr old NGC 2362 is consistent with a transition timescale that is a significant fraction of the total primordial disk lifetime.

  2. DISPERSAL OF PROTOPLANETARY DISKS BY CENTRAL WIND STRIPPING

    SciTech Connect

    Matsuyama, I.; Johnstone, D.; Hollenbach, D.

    2009-07-20

    We present a model for the dispersal of protoplanetary disks by winds from either the central star or the inner disk. These winds obliquely strike the flaring disk surface and strip away disk material by entraining it in an outward radial-moving flow at the wind-disk interface, which lies several disk scale heights above the midplane. The disk dispersal time depends on the entrainment velocity, v{sub d} = {epsilon}c{sub s} , at which disk material flows into this turbulent shear layer interface, where {epsilon} is a scale factor and c{sub s} is the local sound speed in the disk surface just below the entrainment layer. If {epsilon} {approx} 0.1, a likely upper limit, the dispersal time at 1 AU is {approx}6 Myr for a disk with a surface density of 10{sup 3} g cm{sup -2}, a solar mass central star, and a wind with an outflow rate M-dot{sub w}=10{sup -8}M{sub odot}yr{sup -1} and terminal velocity v{sub w} = 200kms{sup -1}. When compared with photoevaporation and viscous evolution, wind stripping can be a dominant mechanism only for the combination of low accretion rates ({approx}<10{sup -8} M{sub sun} yr{sup -1}) and wind outflow rates approaching these accretion rates. This case is unusual since generally outflow rates are {approx}<0.1 of accretion rates.

  3. Accreting planets as dust dams in 'transition' disks

    SciTech Connect

    Owen, James E.

    2014-07-01

    We investigate under what circumstances an embedded planet in a protoplanetary disk may sculpt the dust distribution such that it observationally presents as a 'transition' disk. We concern ourselves with 'transition' disks that have large holes (≳ 10 AU) and high accretion rates (∼10{sup –9}-10{sup –8} M {sub ☉} yr{sup –1}), particularly, those disks which photoevaporative models struggle to explain. Adopting the observed accretion rates in 'transition' disks, we find that the accretion luminosity from the forming planet is significant, and can dominate over the stellar luminosity at the gap edge. This planetary accretion luminosity can apply a significant radiation pressure to small (s ≲ 1 μm) dust particles provided they are suitably decoupled from the gas. Secular evolution calculations that account for the evolution of the gas and dust components in a disk with an embedded, accreting planet, show that only with the addition of the radiation pressure can we explain the full observed characteristics of a 'transition' disk (NIR dip in the spectral energy distribution (SED), millimeter cavity, and high accretion rate). At suitably high planet masses (≳ 3-4 M{sub J} ), radiation pressure from the accreting planet is able to hold back the small dust particles, producing a heavily dust-depleted inner disk that is optically thin to infrared radiation. The planet-disk system will present as a 'transition' disk with a dip in the SED only when the planet mass and planetary accretion rate are high enough. At other times, it will present as a disk with a primordial SED, but with a cavity in the millimeter, as observed in a handful of protoplanetary disks.

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

    NASA Astrophysics Data System (ADS)

    Johnstone, Douglas Ian

    1995-01-01

    Newly formed stars produce sufficient Lyman continuum luminosity phi to significantly alter the structure and evolution of the accretion disk surrounding them. In the absence of a stellar wind, a nearly static, photoionized, 10^4 K, disk atmosphere, with a scale height that increases with disk radius varpi as varpi^{3/2 }, forms inside the gravitational radius varpig ~ 1014(M_*/ M_odot) cm where M _* is the mass of the central star. This ionized atmosphere is maintained by both the direct radiation from the central star and the diffuse field produced in the disk atmosphere by the significant fraction of hydrogen recombinations directly to the ground state. Beyond varpig the material evaporated from the disk is capable of escaping from the system and produces an ionized disk wind. The mass-loss due to this disk wind peaks at varpig . The inclusion of a stellar wind into the basic picture reduces the height of the inner disk atmosphere and introduces a new scale radius varpi_ {w} where the thermal pressure of the material evaporated from the disk balances the ram pressure in the wind. In this case the mass-loss due to the disk wind peaks at varpiw and is enhanced over the no-wind case. The photoevaporation of disks around newly formed stars has significance to both ultracompact HII regions and the dispersal of solar-type nebulae. High mass stars are intrinsically hot and thus yield sufficient Lyman luminosity to create, even without a stellar wind, disk mass-loss rates of order 2 times 10 ^{-5}phi_sp{49} {1/2} M_odotyr ^{-1}, where phi 49 = phi/(10 49 Lyman continuum photons s^{-1}). This wind, which will last until the disk is dispersed, ~ 10^5 yrs if the disk mass is M_ {d}~0.3M_*, yields sizes, emission measures and ages consistent with observations of ultracompact HII regions. The well-observed high mass star MWC 349 may be the best example to date of an evaporating disk around a high mass star. On the other end of the stellar scale, many newly formed low

  5. Planetary Dynamics and Evolution in Evolved Binary Systems

    NASA Astrophysics Data System (ADS)

    Perets, Hagai; Kratter, K.; Kenyon, S.

    2011-09-01

    Exo-planets typically form in protoplanetary disks left over from the formation of their host star. We discuss additional evolutionary routes which may may exist in old evolved binary systems. Stellar evolution in binaries could lead to the formation of symbiotic stars, where mass is lost from one star and (partially) transferred to its binary companion, forming an accretion disk. Planetary orbits around the mass losing star can expand and destabilize, and may result in chaotic evolution. Possible outcomes include exchange of the planet to the companion star, ejection, collision, or tidal capture by one of the binary components. We show that the conditions in the newly formed accretion disk could be very similar to protoplanetary disks. Planets around the accreting companion may interact with the disk, leading to (re)growth and (re)migration of the planets. The disk may also provide the necessary environment for the formation of a new, second generation of planets in both circumstellar or circumbinary configurations. Pre-existing planets and/or planetesimals may serve as seeds for the formation of the second generation planets. Such systems should be found in white dwarf binary systems, and may show various unique observational signatures. Most notably, second generation planets could form in environments which are unfavorable for first generation planets. The phase space available for these planets could be forbidden (unstable) to first generation planets in the pre-evolved progenitor binaries. Planets may also form in double compact object binaries and in metal poor environments. Observations of exo-planets in such unfavorable regions could possibly serve to uniquely identify their second generation character. Finally, we point out a few observed candidate second generation planetary systems (Gl 86, HD 27442 and observed circumbinary planet candidates). A second generation origin for these systems could explain their unique configurations.

  6. New Approach to Diagnosing Properties of Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Stepinski, Tomasz F.

    1998-01-01

    In this paper we suggest that subjecting the observationally derived properties of protoplanetary disks to the evolutionary interpretation yields new insights into the working of those disks, and offers valuable constraints on their models. We propose that the global properties of individual disks, such as their accretion rates and disk masses, sorted by the mass of the central star, can be indexed by the age of the star to simulate the evolution of a single disk. Using data from published surveys of T Tauri stars, we show that accretion rate data, and disk mass data for the lowest mass stars, form well-defined evolutionary tracks. The higher mass stars show a definitive negative correlation between accretion rates and star ages. We use the time-dependent alpha-disk model of the viscous protoplanetary disk to link the theory to observations. The data are consistent with the standard theoretical paradigm, but not with the layered accretion model. The best fits to the data are obtained for the standard models that start with disks that are about one-third of the mass of the central star and have their angular momenta, j, and alpha-coefficients linked by the relationship j varies as Solar mass(exp 3/2)alpha(exp 1/3). The proportionality constant in this relationship, when derived from the accretion rate data, differs from the constant derived from the disk mass data. We argue that the accretion rate data are more reliable. Taking into account typical values of the specific angular momentum of disk-forming matter, we obtain alpha is greater than or equal to 10(exp -2). A complete time-dependent standard disk model, built on the parameters determined from the best-fit procedure, is presented. Such a model constitutes a good point of departure for various theoretical studies aimed at the issue of formation of planetary systems and the character of protoplanetary disks.

  7. Database Reorganization in Parallel Disk Arrays with I/O Service Stealing

    NASA Technical Reports Server (NTRS)

    Zabback, Peter; Onyuksel, Ibrahim; Scheuermann, Peter; Weikum, Gerhard

    1996-01-01

    We present a model for data reorganization in parallel disk systems that is geared towards load balancing in an environment with periodic access patterns. Data reorganization is performed by disk cooling, i.e. migrating files or extents from the hottest disks to the coldest ones. We develop an approximate queueing model for determining the effective arrival rates of cooling requests and discuss its use in assessing the costs versus benefits of cooling.

  8. 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

  9. Subaru SEEDS Survey of Exoplanets and Disks

    NASA Technical Reports Server (NTRS)

    McElwain, Michael W.

    2012-01-01

    The Strategic Exploration of Exoplanets and Disks at Subaru (SEEDS) is the first strategic observing program (SSOPs) awarded by the National Astronomical Observatory of Japan (NAOJ). SEEDS targets a broad sample of stars that span a wide range of masses and ages to explore the formation and evolution of planetary systems. This survey has been awarded 120 nights over five years time to observe nearly 500 stars. Currently in the second year, SEEDS has already produced exciting new results for the protoplanetary disk AB Aur, transitional disk LkCa15, and nearby companion to GJ 758. We present the survey architecture, performance, recent results, and the projected sample. Finally, we will discuss planned upgrades to the high contrast instrumentation at the Subaru Telescope

  10. Tidal dissipation and obliquity evolution in hot Jupiter systems

    SciTech Connect

    Valsecchi, Francesca; Rasio, Frederic A.

    2014-05-10

    Two formation scenarios have been proposed to explain the tight orbits of hot Jupiters. They could be formed in orbits with a small inclination (with respect to the stellar spin) via disk migration, or in more highly inclined orbits via high-eccentricity migration, where gravitational interactions with a companion and tidal dissipation are at play. Here we target hot Jupiter systems where the misalignment λ has been inferred observationally and we investigate whether their properties are consistent with high-eccentricity migration. Specifically, we study whether stellar tides can be responsible for the observed distribution of λ and orbital separations. Improving on previous studies, we use detailed models for each star, thus accounting for how convection (and tidal dissipation) depends on stellar properties. In line with observations suggesting that hotter stars have higher λ, we find that λ increases as the amount of stellar surface convection decreases. This trend supports the hypothesis that tides are the mechanism shaping the observed distribution of λ. Furthermore, we study the past orbital evolution of five representative systems, chosen to cover a variety of temperatures and misalignments. We consider various initial orbital configurations and integrate the equations describing the coupled evolution of the orbital separation, stellar spin, and misalignment. We account for stellar tides and wind mass loss, stellar evolution, and magnetic braking. We show that the current properties of these five representative systems can be explained naturally, given our current understanding of tidal dissipation and with physically motivated assumptions for the effects driving the orbital evolution.

  11. Freddi: Fast Rise Exponential Decay accretion Disk model Implementation

    NASA Astrophysics Data System (ADS)

    Lipunova, G. V.; Malanchev, K. L.

    2016-10-01

    Freddi (Fast Rise Exponential Decay: accretion Disk model Implementation) solves 1-D evolution equations of the Shakura-Sunyaev accretion disk. It simulates fast rise exponential decay (FRED) light curves of low mass X-ray binaries (LMXBs). The basic equation of the viscous evolution relates the surface density and viscous stresses and is of diffusion type; evolution of the accretion rate can be found on solving the equation. The distribution of viscous stresses defines the emission from the source. The standard model for the accretion disk is implied; the inner boundary of the disk is at the ISCO or can be explicitely set. The boundary conditions in the disk are the zero stress at the inner boundary and the zero accretion rate at the outer boundary. The conditions are suitable during the outbursts in X-ray binary transients with black holes. In a binary system, the accretion disk is radially confined. In Freddi, the outer radius of the disk can be set explicitely or calculated as the position of the tidal truncation radius.

  12. Studies of Disks Around the Sun and Other Stars

    NASA Technical Reports Server (NTRS)

    Stern, S. Alan (Principal Investigator)

    1996-01-01

    We are conducting research designed to enhance our understanding of the evolution and detectability of comet clouds and disks. This area holds promise for also improving our understanding of outer solar system formation, the bombardment history of the planets, the transport of volatiles and organics from the outer solar system to the inner planets, and to the ultimate fate of comet clouds around the Sun and other stars. According to 'standard' theory, both the Kuiper Disk and the Oort Cloud are (at least in part) natural products of the planetary accumulation stage of solar system formation. One expects such assemblages to be a common attribute of other solar systems. Therefore, searches for comet disks and clouds orbiting other stars offer a new method for inferring the presence of planetary systems. This two-element program consists modeling collisions in the Kuiper Disk and the dust disks around other stars. The modeling effort focuses on moving from our simple, first-generation, Kuiper disk collision rate model, to a time-dependent, second-generation model that incorporates physical collisions, velocity evolution, dynamical erosion, and various dust transport mechanisms. This second generation model will be used to study the evolution of surface mass density and the object-size spectrum in the disk. The observational effort focuses on obtaining submm/mm-wave flux density measurements of 25-30 IR excess stars in order to better constrain the masses, spatial extents and structure of their dust ensembles.

  13. The Red and Featureless Outer Disks of Nearby Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Watkins, Aaron E.; Mihos, J. Christopher; Harding, Paul

    2016-07-01

    We present results from deep, wide-field surface photometry of three nearby (D = 4-7 Mpc) spiral galaxies: M94 (NGC 4736), M64 (NGC 4826), and M106 (NGC 4258). Our imaging reaches a limiting surface brightness of {μ }B ˜ 28-30 mag arcsec-2 and probes colors down to {μ }B ˜ 27.5 mag arcsec-2. We compare our broadband optical data to available ultraviolet and high column density H i data to better constrain the star-forming history and stellar populations of the outermost parts of each galaxy’s disk. Each galaxy has a well-defined radius beyond which little star formation occurs and the disk light appears both azimuthally smooth and red in color, suggestive of old, well-mixed stellar populations. Given the lack of ongoing star formation or blue stellar populations in these galaxies’ outer disks, the most likely mechanisms for their formation are dynamical processes such as disk heating or radial migration, rather than inside-out growth of the disks. This is also implied by the similarity in outer disk properties despite each galaxy showing distinct levels of environmental influence, from a purely isolated galaxy (M94) to one experiencing weak tidal perturbations from its satellite galaxies (M106) to a galaxy recovering from a recent merger (M64), suggesting that a variety of evolutionary histories can yield similar outer disk structure. While this suggests a common secular mechanism for outer disk formation, the large extent of these smooth, red stellar populations—which reach several disk scale lengths beyond the galaxies’ spiral structure—may challenge models of radial migration given the lack of any nonaxisymmetric forcing at such large radii.

  14. Resolved imaging of the HR 8799 Debris disk with Herschel

    SciTech Connect

    Matthews, Brenda; Booth, Mark; Broekhoven-Fiene, Hannah; Marois, Christian; Kennedy, Grant; Wyatt, Mark; Sibthorpe, Bruce; Macintosh, Bruce

    2014-01-01

    We present Herschel far-infrared and submillimeter maps of the debris disk associated with the HR 8799 planetary system. We resolve the outer disk emission at 70, 100, 160, and 250 μm and detect the disk at 350 and 500 μm. A smooth model explains the observed disk emission well. We observe no obvious clumps or asymmetries associated with the trapping of planetesimals that is a potential consequence of planetary migration in the system. We estimate that the disk eccentricity must be <0.1. As in previous work by Su et al., we find a disk with three components: a warm inner component and two outer components, a planetesimal belt extending from 100 to 310 AU, with some flexibility (±10 AU) on the inner edge, and the external halo that extends to ∼2000 AU. We measure the disk inclination to be 26° ± 3° from face-on at a position angle of 64° E of N, establishing that the disk is coplanar with the star and planets. The spectral energy distribution of the disk is well fit by blackbody grains whose semi-major axes lie within the planetesimal belt, suggesting an absence of small grains. The wavelength at which the spectrum steepens from blackbody, 47 ± 30 μm, however, is short compared with other A star debris disks, suggesting that there are atypically small grains likely populating the halo. The PACS longer wavelength data yield a lower disk color temperature than do MIPS data (24 and 70 μm), implying two distinct halo dust-grain populations.

  15. TIDAL AND MAGNETIC INTERACTIONS BETWEEN A HOT JUPITER AND ITS HOST STAR IN THE MAGNETOSPHERIC CAVITY OF A PROTOPLANETARY DISK

    SciTech Connect

    Chang, S.-H.; Gu, P.-G.; Bodenheimer, P. H.

    2010-01-10

    We present a simplified model to study the orbital evolution of a young hot Jupiter inside the magnetospheric cavity of a proto-planetary disk. The model takes into account the disk locking of stellar spin as well as the tidal and magnetic interactions between the star and the planet. We focus on the orbital evolution starting from the orbit in 2:1 resonance with the inner edge of the disk, followed by the inward and then outward orbital migration driven by the tidal and magnetic torques as well as the Roche-lobe overflow of the tidally inflated planet. The goal in this paper is to study how the orbital evolution inside the magnetospheric cavity depends on the cavity size, planet mass, and orbital eccentricity. In the present work, we only target the mass range from 0.7 to 2 Jupiter masses. In the case of the large cavity corresponding to the rotational period approx7 days, the planet of mass >1 Jupiter mass with moderate initial eccentricities (approx>0.3) can move to the region <0.03 AU from its central star in 10{sup 7} yr, while the planet of mass <1 Jupiter mass cannot. We estimate the critical eccentricity beyond which the planet of a given mass will overflow its Roche radius and finally lose all of its gas onto the star due to runaway mass loss. In the case of the small cavity corresponding to the rotational period approx3 days, all of the simulated planets lose all of their gas even in circular orbits. Our results for the orbital evolution of young hot Jupiters may have the potential to explain the absence of low-mass giant planets inside approx0.03 AU from their dwarf stars revealed by transit surveys.

  16. Modelling circumbinary protoplanetary disks. I. Fluid simulations of the Kepler-16 and 34 systems

    NASA Astrophysics Data System (ADS)

    Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.

    2015-10-01

    Context. The Kepler mission's discovery of a number of circumbinary planets orbiting close (ap< 1.1 au) to the stellar binary raises questions as to how these planets could have formed given the intense gravitational perturbations the dual stars impart on the disk. The gas component of circumbinary protoplanetary disks is perturbed in a similar manner to the solid, planetesimal dominated counterpart, although the mechanism by which disk eccentricity originates differs. Aims: This is the first work of a series that aims to investigate the conditions for planet formation in circumbinary protoplanetary disks. Methods: We present a number of hydrodynamical simulations that explore the response of gas disks around two observed binary systems: Kepler-16 and Kepler-34. We probe the importance of disk viscosity, aspect-ratio, inner boundary condition, initial surface density gradient, and self-gravity on the dynamical evolution of the disk, as well as its quasi-steady-state profile. Results: We find there is a strong influence of binary type on the mean disk eccentricity, e̅d, leading to e̅d = 0.02 - 0.08 for Kepler-16 and e̅d = 0.10 - 0.15 in Kepler-34. The value of α-viscosity has little influence on the disk, but we find a strong increase in mean disk eccentricity with increasing aspect-ratio due to wave propagation effects. The choice of inner boundary condition only has a small effect on the surface density and eccentricity of the disk. Our primary finding is that including disk self-gravity has little impact on the evolution or final state of the disk for disks with masses less than 12.5 times that of the minimum-mass solar nebula. This finding contrasts with the results of self-gravity relevance in circumprimary disks, where its inclusion is found to be an important factor in describing the disk evolution.

  17. Giant Planet Accretion And Migration: Surviving The Type I Regime

    NASA Astrophysics Data System (ADS)

    Thommes, Edward; Murray, N.

    2006-06-01

    In the core accretion model of gas giant planet formation, a large solid core about 10X the Earth's mass forms first, then accumulates its massive envelope ( 100 or more Earth masses) of gas. However, inward planet migration due to gravitational interaction with the proto-stellar gas disk poses a big hazard in this model. Core-sized bodies undergo rapid "type I" migration; for typical parameters their migration timescale is much shorter than their accretion timescale. How, then, do growing cores avoid spiraling into the central star before they ever get the chance to become gas giants? I will present a simple model of core formation in a gas disk which is viscously evolving. It turns out that as the disk accretes onto the star, a window of opportunity for successful core growth may open. I will discuss what implications this model has for the link between disk properties and the likelihood of forming gas giants.

  18. Using magnetic tape technology for data migration

    NASA Technical Reports Server (NTRS)

    Therrien, David; Cheung, Yim-Ling

    1993-01-01

    Magnetic tape and optical disk library units (jukeboxes) are satisfying the demand for high-capacity cost-effective storage. The choice between optical disk and magnetic tape technology must take into account the cost limitations as well as the performance and reliability requirements of the user environment. Library units require data management software in order to function in an automated and user-transparent way. The most common data management applications are backup and recovery, data migration, and archiving. The medium access patterns that these applications create will be described. Since the most user visible application is data migration, a queue simulator was developed to model its performance against a variety of library units. The major subject of this paper is the design and implementation of this simulator as well as some simulation results. The relative cost and reliability of magnetic tape versus optical disk library units is presented for completeness.

  19. Resolving the Dusty Debris Disk of 49 Ceti

    NASA Astrophysics Data System (ADS)

    Lieman-Sifry, Jesse; Hughes, A. Meredith

    2015-01-01

    Understanding the dispersal of primordial gas and dust from circumstellar disks is necessary for determining the timeline for giant planet formation. While the current assumption is that the gas and dust evolve simultaneously, there are a few systems that defy this paradigm. The nearby A star 49 Ceti, at a distance of 61 pc, hosts one of only a few known circumstellar disks that exhibits the dust qualities of an older debris disk but still displays a substantial mass of molecular gas, a characteristic normally associated with youth. We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations at 850μm and a spatial resolution of 0.47x0.39 arcsec that resolve emission from the dust disk for the first time. To investigate the properties of the dust grains and the morphology of the disk, we simultaneously model the high-resolution ALMA data and the unresolved spectral energy distribution (SED). The detected emission reveals a disk that extends from 1.16±0.12AU to 286±7AU with an increase in surface density at 113±2AU that is viewed at an inclination of 79.6±.4°. The increase in surface density corresponds to the inner radius of the gas disk, hinting that similar mechanisms may be responsible for sculpting the gas and dust disks at this late stage of disk evolution.

  20. The Correlation between Metallicity and Debris Disk Mass

    NASA Astrophysics Data System (ADS)

    Gáspár, András; Rieke, George H.; Ballering, Nicholas

    2016-08-01

    We find that the initial dust masses in planetary debris disks are correlated with the metallicities of their central stars. We compiled a large sample of systems, including Spitzer, the Herschel DUNES and DEBRIS surveys, and WISE debris disk candidates. We also merged 33 metallicity catalogs to provide homogeneous [Fe/H] and {σ }[{Fe/{{H}}]} values. We analyzed this merged sample, including 222 detected disks (74 warm and 148 cold) around a total of 187 systems (some with multiple components) and 440 disks with only upper limits (125 warm and 315 cold) around a total of 360 systems. The disk dust masses at a common early evolutionary point in time were determined using our numerical disk evolutionary code, evolving a unique model for each of the 662 disks backward to an age of 1 Myr. We find that disk-bearing stars seldom have metallicities less than {{[Fe/H]}}=-0.2 and that the distribution of warm component masses lacks examples with large mass around stars of low metallicity ({{[Fe/H]}}\\lt -0.085). Previous efforts to find a correlation have been largely unsuccessful; the primary improvements supporting our result are (1) basing the study on dust masses, not just infrared excess detections; (2) including upper limits on dust mass in a quantitative way; (3) accounting for the evolution of debris disk excesses as systems age; (4) accounting fully for the range of uncertainties in metallicity measurements; and (5) having a statistically large enough sample.

  1. Stellar perturbations on the scattered disk

    NASA Astrophysics Data System (ADS)

    Rickman, H.; Froeschlé, Ch.; Froeschlé, Cl.; Valsecchi, G. B.

    2004-12-01

    We present a statistical model for estimating the effects of stellar encounters on orbits in the outer Solar System, focussing on the scattered disk at ⪉103 AU from the Sun. We describe a Monte Carlo simulation using those results and apply it to the evolution of the scattered disk over 4 Gyr, finding that a final perihelion distance distribution with an extended tail reaching to very large values is to be expected. This would likely result from a single close stellar encounter, in agreement with the conclusion by Morbidelli & Levison (\\cite{Morbidelli04}). We estimate that the newly discovered minor planet (90377) Sedna may be a typical representative of such an extended scattered disk and that a few more objects of the same size may reside at similar heliocentric distances. There is a possibility that the bulk of the population, which should have smaller perihelion distances, contains some very large objects that may have contributed to sculpting the Kuiper Belt. We also find that the creation of an extended scattered disk by a stellar encounter should have been accompanied by a huge influx of large objects into the inner Solar System, but the timing of the encounter is constrained by the fact that the scattered disk must still have been quite massive. Thus it likely happened long before the purported late heavy bombardment of the terrestrial planets.

  2. Photoevaporation of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; Morrison, David (Technical Monitor)

    1994-01-01

    Young massive stars produce sufficient Lyman continuum luminosity phi to have a significant effect on the structure and evolution of the accretion disks surrounding diem. We show that inside a critical disk radius r(sub g), an isothermal 10(exp 4) K atmosphere forms with a scale height that increases with r(sup3/2) for r less than or equal to r(sub g). For r less than or equal to r(sub g), the diffuse field caused by hydrogen recombinations to the ground state in the atmosphere produces a steadily evaporating disk. The mass loss from this outer region of the disk is of order 10(exp -5) Mo/yr phi(sub 49)1/2, where phi(sub 49) is defined as phi/10(exp 49) photons/s. The mass loss has two important consequences. First, the slow (10-50 km/s) wind that results may explain the long life of unresolved ultracompact HII regions. Secondly, the dependence on phi implies that accretion through the disk onto the star will be quenched once the photoevaporation rate exceeds the accretion rate. This may act to limit the mass of the forming star.

  3. Hydraulic jumps in 'viscous' accretion disks

    NASA Astrophysics Data System (ADS)

    Michel, F. C.

    1984-04-01

    It is proposed that the dissipative process necessary for rapid accretion disk evolution is driven by hydraulic jump waves on the surface of the disk. These waves are excited by the asymmetric nature of the central rotator (e.g., neutron star magnetosphere) and spiral out into the disk to form a pattern corotating with the central object. Disk matter in turn is slowed slightly at each encounter with the jump and spirals inward. In this process, the disk is heated by true turbulence produced in the jumps. Additional effects, such as a systematic misalignment of the magnetic moment of the neutron star until it is nearly orthogonal, and systematic distortion of the magnetosphere in such a way as to form an even more asymmetric central 'paddle wheel', may enhance the interaction with inflowing matter. The application to X-ray sources corresponds to the 'slow' solutions of Ghosh and Lamb, and therefore to rms magnetic fields of about 4 x 10 to the 10th gauss. Analogous phenomena have been proposed to act in the formation of galactic spiral structure.

  4. Searching For Planets in "Holey Debris Disks"

    NASA Astrophysics Data System (ADS)

    Meshkat, Tiffany; Bailey, Vanessa P.; Su, Kate Y. L.; Kenworthy, Matthew A.; Mamajek, Eric E.; Hinz, Philip; Smith, Paul S.

    2015-01-01

    Directly imaging planets provides a unique opportunity to study young planets in the context of their formation and evolution. It examines the underlying semi-major axis exoplanet distribution and enables the characterization of the planet itself with spectroscopic examination of its emergent flux. However, only a handful of planets have been directly imaged, and thus the stars best suited for planet imaging are still a subject of debate. The "Holey Debris Disk" project was created in order to help determine if debris disks with gaps are signposts for planets. These gaps may be dynamically caused by planets accreting the debris material as they form. We present the results from our survey with VLT/NACO and the apodized phase plate coronagraph. We demonstrate that these disks with holes are good targets for directly detecting planets with the discovery of a planet around two of our targets, HD 95086 and HD 106906, at L'-band. Our non-detection of HD 95086 b in H-band demonstrates the importance of thermal infrared observations. The detected planets shepherd the outer cool debris belt. The relatively dust-free gap in these disks implies the presence of one or more closer-in planets. We discuss our new constraints on planets around other targets in our survey as well as disk properties of these targets and describe how future instruments will find the inner planets.

  5. Numerical Simulations of Disk-Planet Interactions

    NASA Astrophysics Data System (ADS)

    D'Angelo, Gennaro

    2003-06-01

    The aim of this thesis is the study the dynamical interactions occurring between a forming planet and its surrounding protostellar environment. This task is accomplished by means of both 2D and 3D numerical simulations. The first part of this work concerned global simulations in 3D. These were intended to investigate large-scale effects caused by a Jupiter-size body still in the process of accreting matter from its surroundings. Simulations show that, despite a density gap forms along the orbital path, Jupiter-mass protoplanets still accrete at a rate on the order of 0.01 Earth's masses per year when they are embedded in a minimum-mass Solar nebula. In the same conditions, the migration time scale due to gravitational torques by the disk is around 100000 years. The second part of the work was dedicated to perform 2D calculations, by employing a nested-grid technique. This method allows to carry out global simulations of planets orbiting in disks and, at the same time, to resolve in great detail the dynamics of the flow inside the Roche lobe of both massive and low-mass planets. Regardless of the planet mass, the high resolution supplied by the nested-grid technique permits an evaluation of the torques, resulting from short and very short range gravitational interactions, more reliable than the one previously estimated with the aid of numerical methods. Likewise, the mass flow onto the planet is computed in a more accurate fashion. Resulting migration time scales are in the range from 20000 years, for intermediate-mass planets, to 1000000 years, for very low-mass as well as high-mass planets. Circumplanetary disks form inside of the Roche lobe of Jupiter-size secondaries. In order to evaluate the consequences of the flat geometry on the local flow structure around planets, 3D nested-grid simulations were carried out to investigate a range of planetary masses spanning from 1.5 Earth's masses to one Jupiter's mass. Outcomes show that migration rates are relatively

  6. Ripples in disk galaxies

    NASA Astrophysics Data System (ADS)

    Schweizer, Francois; Seitzer, Patrick

    1988-05-01

    The authors present evidence that ripples ("shells") occur not only in ellipticals, as hitherto believed, but also in disk galaxies of Hubble types S0, S0/Sa, and Sa, and probably even in the Sbc galaxy NGC 3310. This evidence includes the discovery of ripples in the northern disk galaxies NGC 3032, 3619, 4382, 5548 (a Seyfert), and 5739, and in the "diskless S0" NGC 7600. It is argued that these ripples cannot usually have resulted form transient spiral waves or other forced vibrations in the existing disks, but instead consist of extraneous sheet-like 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.

  7. Hot Accretion Disks Revisited

    NASA Astrophysics Data System (ADS)

    Bjoernsson, Gunnlaugur; Abramowicz, Marek A.; Chen, Xingming; Lasota, Jean-Pierre

    1996-08-01

    All previous studies of hot (Tp 1010-1012 K), optically thin accretion disks have neglected either the presence of e+ e- pairs or advective cooling. Thus all hot disk models constructed previously have not been self-consistent. In this paper we calculate local disk models including pair physics, relevant radiative processes in the hot plasma, and the effect of advective cooling. We use a modification of the Björnsson & Svensson mapping method. We find that the role of e+ e- pairs in the structure of hot, optically thin accretion disks is far less significant than was previously thought. The improved description of the radiation-matter interactions provided in the present paper modify the previously obtained values of the critical parameters characterizing advectively dominated flows.

  8. 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)

  9. Viscosity Prescription for Gravitationally Unstable Accretion Disks

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2015-05-01

    Gravitationally unstable accretion disks emerge in a variety of astrophysical contexts—giant planet formation, FU Orioni outbursts, feeding of active galactic nuclei, and the origin of Pop III stars. When a gravitationally unstable disk is unable to cool rapidly, it settles into a quasi-stationary, fluctuating gravitoturbulent state, in which its Toomre Q remains close to a constant value {{Q}0}∼ 1. Here we develop an analytical formalism describing the evolution of such a disk, which is based on the assumptions of Q={{Q}0} and local thermal equilibrium. Our approach works in the presence of additional sources of angular momentum transport (e.g., MRI), as well as external irradiation. Thermal balance dictates a unique value of the gravitoturbulent stress {{α }gt} driving disk evolution, which is a function of the local surface density and angular frequency. We compare this approach with other commonly used gravitoturbulent viscosity prescriptions, which specify the explicit dependence of stress {{α }gt} on Toomre Q in an ad hoc fashion, and identify the ones that provide consistent results. We nevertheless argue that our Q={{Q}0} approach is more flexible, robust, and straightforward and should be given preference in applications. We illustrate this with a couple of analytical calculations—locations of the snow line and of the outer edge of the dead zone in a gravitoturbulent protoplanetary disk—which clearly show the simplicity and versatility of the Q={{Q}0} approach.

  10. 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

  11. 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.

  12. 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.

  13. [Internal migration].

    PubMed

    Borisovna, L

    1991-06-01

    Very few studies have been conducted that truly permit explanation of internal migration and it repercussions on social and economic structure. It is clear however that a profound knowledge of the determinants and consequences of internal migration will be required as a basis for economic policy decisions that advance the goal of improving the level of living of the population. the basic supposition of most studies of the relationship of population and development is that socioeconomic development conditions demographic dynamics. The process of development in Mexico, which can be characterized by great heterogeneity, consequently produces great regional disparities. At the national level various studies have estimated the volume of internal migration in Mexico, but they have usually been limited to interstate migration because the main source of data, the census, is classified by states. But given the great heterogeneity within states in all the elements related to internal migration, it is clear that studies of internal migration within states are also needed. Such studies are almost nonexistent because of their technical difficulty. National level studies show that interstate migration increased significantly between 1940-80. The proportion of Mexicans living outside their states of birth increased by 558% in those years, compared to the 342% increase in the total Mexican population. Although Puebla has a high rate of increase, migration has kept it below Mexico's national growth rate. Migration between Puebla and other states and within Puebla has led to an increasing unevenness of spatial distribution. Between 1970-80, 57 of Puebla's municipios had growth rates above the state average of 2.8%/year, 6 had growth rates equal to the average, and 129 had growth rates that were below the average but not negative. 25 states with negative growth rates that were considered strongly expulsive. In 1980, 51.7% of the population was concentrated in the 57 municipios

  14. Zodiac II: Debris Disk Science from a Balloon

    NASA Technical Reports Server (NTRS)

    Bryden, Geoffrey; Traub, Wesley; Roberts, Lewis C., Jr.; Bruno, Robin; Unwin, Stephen; Backovsky, Stan; Brugarolas, Paul; Chakrabarti, Supriya; Chen, Pin; Hillenbrand, Lynne; Krist, John; Lillie, Charles; Macintosh, Bruce; Mawet, Dimitri; Mennesson, Bertrand; Moody, Dwight; Rey, Justin; Stapelfeldt, Karl; Stuchlik, David; Trauger, John; Vasisht, Gautam

    2011-01-01

    Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity. The Zodiac II instrument is a 1.1-m diameter SiC (Silicone carbide) telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visible-wavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights in the US followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

  15. Zodiac II: Debris Disk Science from a Balloon

    NASA Technical Reports Server (NTRS)

    Bryden, Geoffrey; Traub, Wesley; Roberts, Lewis C., Jr.; Bruno, Robin; Unwin, Stephen; Backovsky, Stan; Brugarolas, Paul; Chakrabarti, Supriya; Chen, Pin; Hillenbrand, Lynne; Krist, John; Lillie, Charles; Macintosh, Bruce; Mawet, Dimitri; Mennesson, Bertrand; Moody, Dwight; Rahman, Zahidul; Rey, Justin; Stapelfeldt, Karl; Stuchlik, David; Trauger, John; Vasisht, Gautam

    2011-01-01

    Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make sa they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity. The Zodiac II instrument is a 1.1-m diameter SiC telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visible wavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights within the United States followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

  16. Childhood to adolescence: dust and gas clearing in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Brown, Joanna Margaret

    Disks are ubiquitous around young stars. Over time, disks dissipate, revealing planets that formed hidden by their natal dust. Since direct detection of young planets at small orbital radii is currently impossible, other tracers of planet formation must be found. One sign of disk evolution, potentially linked to planet formation, is the opening of a gap or inner hole in the disk. In this thesis, I have identified and characterized several cold disks with large inner gaps but retaining massive primordial outer disks. While cold disks are not common, with ~5% of disks showing signs of inner gaps, they provide proof that at least some disks evolve from the inside-out. These large gaps are equivalent to dust clearing from inside the Earth's orbit to Neptune's orbit or even the inner Kuiper belt. Unlike more evolved systems like our own, the central star is often still accreting and a large outer disk remains. I identified four cold disks in Spitzer 5-40 μm spectra and modeled these disks using a 2-D radiative transfer code to determine the gap properties. Outer gap radii of 20-45 AU were derived. However, spectrophotometric identification is indirect and model-dependent. To validate this interpretation, I observed three disks with a submillimeter interferometer and obtained the first direct images of the central holes. The images agree well with the gap sizes derived from the spectrophotometry. One system, LkH&alpha 330, has a very steep outer gap edge which seems more consistent with gravitational perturbation rather than gradual processes, such as grain growth and settling. Roughly 70% of cold disks show CO v=1&rarr 0 gas emission from the inner 1 AU and therefore are unlikely to have evolved due to photoevaporation. The derived rotation temperatures are significantly lower for the cold disks than disks without gaps. Unresolved (sub)millimeter photometry shows that cold disks have steeper colors, indicating that they are optically thin at these wavelengths, unlike

  17. Planetary System Formation in the Protoplanetary Disk around HL Tauri

    NASA Astrophysics Data System (ADS)

    Akiyama, Eiji; Hasegawa, Yasuhiro; Hayashi, Masahiko; Iguchi, Satoru

    2016-02-01

    We reprocess the Atacama Large Millimeter/Submillimeter Array (ALMA) long-baseline science verification data taken toward HL Tauri. Assuming the observed gaps are opened up by currently forming, unseen bodies, we estimate the mass of such hypothetical bodies based on the following two approaches: the Hill radius analysis and a more elaborate approach developed from the angular momentum transfer analysis in gas disks. For the former, the measured gap widths are used for estimating the mass of the bodies, while for the latter, the measured gap depths are utilized. We show that their masses are comparable to or less than the mass of Jovian planets. By evaluating Toomre’s gravitational instability (GI) condition and cooling effect, we find that the GI might be a mechanism to form the bodies in the outer region of the disk. As the disk might be gravitationally unstable only in the outer region of the disk, inward planetary migration would be needed to construct the current architecture of the observed disk. We estimate the gap-opening mass and show that type II migration might be able to play such a role. Combining GIs with inward migration, we conjecture that all of the observed gaps may be a consequence of bodies that might have originally formed at the outer part of the disk, and have subsequently migrated to the current locations. While ALMA’s unprecedented high spatial resolution observations can revolutionize our picture of planet formation, more dedicated observational and theoretical studies are needed to fully understand the HL Tauri images.

  18. 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.

  19. The Gaia-ESO Survey: Probes of the inner disk abundance gradient

    NASA Astrophysics Data System (ADS)

    Jacobson, H. R.; Friel, E. D.; Jílková, L.; Magrini, L.; Bragaglia, A.; Vallenari, A.; Tosi, M.; Randich, S.; Donati, P.; Cantat-Gaudin, T.; Sordo, R.; Smiljanic, R.; Overbeek, J. C.; Carraro, G.; Tautvaišienė, G.; San Roman, I.; Villanova, S.; Geisler, D.; Muñoz, C.; Jiménez-Esteban, F.; Tang, B.; Gilmore, G.; Alfaro, E. J.; Bensby, T.; Flaccomio, E.; Koposov, S. E.; Korn, A. J.; Pancino, E.; Recio-Blanco, A.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Heiter, U.; Hill, V.; Hourihane, A.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

    2016-06-01

    Context. The nature of the metallicity gradient inside the solar circle (RGC < 8 kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. Aims: We investigate the metallicity gradient of the inner disk using a sample of inner disk open clusters that is three times larger than has previously been studied in the literature to better characterize the gradient in this part of the disk. Methods: We used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H] values were determined based on a membership analysis for each cluster. Where necessary, distances and ages to clusters were determined via comparison to theoretical isochrones. Results: The GES open clusters exhibit a radial metallicity gradient of -0.10 ± 0.02 dex kpc-1, consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range RGC ~ 6-12 kpc. We also measure a trend of increasing [Fe/H] with increasing cluster age, as has also been found in the literature. Conclusions: We find no evidence for a steepening of the inner disk metallicity gradient inside the solar circle as earlier studies indicated. The age-metallicity relation shown by the clusters is consistent with that predicted by chemical evolution models that include the effects of radial migration, but a more detailed comparison between cluster observations and models would be premature. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002 and 193.B-0936. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive

  20. The inner disks of EXor-type eruptive stars

    NASA Astrophysics Data System (ADS)

    Sipos, Nikoletta; Kóspál, Ágnes

    2014-01-01

    EX Lupi-type young stars (EXors) show sporadic brightenings of several magnitudes, caused by the episodic increase in the accretion rate of the circumstellar matter onto the young star. As the inner disk plays a crucial role during the onset of the outburst, we examined the quiescent properties of the circumstellar environment of EXors, focusing on the inner regions. We found that in case of three EXors (VY Tau, V1143 Ori and EX Lup) the spectral energy distributions show no or weak excess above the stellar photosphere at NIR-MIR wavelengths, indicative of inner disk clearing. A detailed radiative transfer modeling of the sources revealed that the inner regions of these disks had to go through significant evolution, either the inner radius of the dusty disk is beyond the sublimation radius and/or the inner disks are flattened.

  1. Gas in Protoplanetary and Debris Disks: Insights from UV Spectroscopy

    NASA Technical Reports Server (NTRS)

    Roberge, Aki

    2008-01-01

    Over the last two decades, observations of protoplanetary and debris disks have played an important role in the new field of extrasolar planetary studies. Many are familiar with the extensive work on the cold circumstellar dust present in these disks done using infrared and sub-millimeter photometry and spectroscopy. However. UV spectroscopy has made some unique contributions by probing the elusive but vital gas component in protoplanetary and debris disks. In this talk, I will outline our picture of the evolution of protoplanetary disks and discuss the importance of the gas component. New insights obtained from UV spectroscopy will be highlighted, as well as some new puzzles. Finally, I will touch on upcoming studies of gas in protoplanetary and debris disks, some at UV wavelengths, some at far-IR and sub-mm wavelengths.