225 Circumstellar Disks Poster Session
225.01
Resolved Images of Large Cavities in Protoplanetary Transition Disks
Sean M. Andrews1, D. J. Wilner1, C. Espaillat1, M. Hughes2, K. Dullemond3, M. K. McClure4, C. Qi1, J. M. Brown1
1Harvard-Smithsonian Center for Astrophysics, 2University of California, Berkeley, 3Universitat Heidelberg, Germany, 4University of Michigan.
8:00 AM - 7:00 PM
Essex Ballroom
We present new and archival high angular resolution Submillimeter Array (SMA) observations of the 880 micron dust continuum emission from 12 transition disks in nearby star-forming regions. In each case, we directly resolve a dust-depleted cavity around the central star. Using two-dimensional Monte Carlo radiative transfer calculations, we interrpret these dust disk structures in a homogeneous, parametric model framework by reproducing their SMA continuum visibilities and spectral energy distributions. The cavities in these disks are large (R = 15-73 AU) and substantially depleted of small (micron-sized) dust grains, although their mass contents are still uncertain. The structures of the remnant material at larger radii are comparable to normal disks. We demonstrate that these large cavities are common among the millimeter-bright disk population, comprising at least 20% of the disks in the bright half of the millimeter luminosity distribution. We suggest that these observations are most commensurate with dynamical clearing due to tidal interactions with low-mass companions - young brown dwarfs of giant planets on long-period orbits.
225.02
Modeling Morphological Structures Observed in Spatially Resolved Scattered Light Images of Protoplanetary Disks
John P. Wisniewski1, B. Whitney2, SEEDS Team
1University of Washington, 2University of Wisconsin.
8:00 AM - 7:00 PM
Essex Ballroom
New near-IR scattered light imagery of young protoplanetary disk systems, imaged by the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey and other facilities, reveal a wealth of morphological features. We explore the origin of these features using 2D and 3D Monte Carlo radiative transfer simulations, which have been modified to include the effects of inner disk warps, inner disk holes, and spiral structures. Initial comparisons between model runs and observational data will be presented.
We acknowledge funding from NSF AST 0802230, NSF AST 1009314, and a Chretien International Research Grant.
225.03
Unraveling the Accretion Disk Spectrum in the Symbiotic Binary R Aquarii
Edwin M. Kellogg1, J. DePasquale1, J. Nichols1
1Harvard/Smithsonian CfA.
8:00 AM - 7:00 PM
Essex Ballroom
R Aquarii is a symbiotic binary with jets and outer thermal lobes. It is known to contain a Mira red giant and its companion is generally believed to be a white dwarf. Here, we analyze the X-ray spectrum of the central binary. We observe several components: a soft thermal source, T ~ 5e6 K, a hard heavily obscured thermal source, T ~ 1.4e8 K, and apparently a complex series of fluorescence lines dominated by Fe Kalpha, but including a series of lines from even Z elements down to C. We compare relative intensities with models of collisional and photo excitation in cool gas. The shape of the Fe Kalpha line may give information on the compactness of the companion.
225.04
Discovery Of Strong Helium 10830A Absorption In The Mid-eclipse Disk Of Epsilon Aurigae
Robert E. Stencel1, B. Kloppenborg1, M. Sitko2, J. Rayner3, A. Tokunaga3
1Univ. of Denver, 2Univ. of Cincinnati, 3NASA IRTF.
8:00 AM - 7:00 PM
Essex Ballroom
During the 2010 eclipse of the enigmatic binary, epsilon Aurigae (F0p + B5?), we obtained a series of near-infrared spectra with the SpeX instrument at NASA's IRTF, primarily to detect the re-appearance of CO (2-0) at 2.29 microns after nominal mid-eclipse, 2010 August 4 (JD 2,454,000). To our surprise, the well-known He I 10830A line appeared in absorption, in the spectrum closest to mid-eclipse (Aug.24, RJD 55433), persisting in spectra Sep.27 (55467), Oct.24 and 29 (55494, 55499). The line weakened by Nov.12 (55513), and was gone Dec.7 (55537) and 2011 Jan.7 (55569). The extra absorption, up to 6A equivalent width, appeared atop a weaker, persistent 1A equivalent width feature. With Van de Kamp's distance (580 pc) and orbital velocities during eclipse phase, the duration of the extra absorption implies a region 1.0 +/- 0.2 AU in radial extent, in the middle of the eclipse-causing dark disk with its 3.8 +/- 0.2 AU radius. He I 10830 arises from a metastable triplet from a lower level at 19.82 volts, representing plasma in excess of 25,000K. If the disk-center star were B5V type and experiencing a modest amount of accretion, it would create a 1 AU Stromgren He+ sphere. This assumes a mean gas density of 10$^{10}$ cm$^{-3}$, which is the lower limit to the column density established by non-detection of soft Xrays. This heated region could represent the presence of an upper main sequence object and accretion onto the hidden star inside the disk, in analogy to Be stars, symbiotics, zeta Aurs and YSOs. This work was supported in part by the bequest of William Herschel Womble in support of astronomy at the University of Denver, by NSF grant 1016678 and JPL RSA 1414715 to the University of Denver, and by NASA ADP grant NNX09AC73G to the University of Cincinnati.
225.05
Accretion in the Disk of epsilon Aurigae: Results of Monte Carlo Radiative Transfer Modelling
Naomi Pequette1, R. Stencel1, B. Whitney2
1University of Denver, 2Space Science Institute.
8:00 AM - 7:00 PM
Essex Ballroom
Epsilon Aurigae is a mysterious eclipsing binary system that has been observed for more than 175 years. Current theory remains undecided whether the system is made up of a massive F-supergiant star and an equally massive, but hidden, companion, or a post-AGB F-star and a binary companion made up of a B5V which is surrounded by a transitional or debris disk. We used a Monte Carlo Radiative Transfer Model (MCRTM, written by Barbra Whitney of the Space Sciences Institute) to model the B-star and surrounding disk. By using this model, our goal was to reproduce the observed Spectral Energy Distribution (SED, Hoard, Howell and Stencel, HHS, 2010) of the B-star and disk components of the epsilon Aurigae System. Our initial parameters utilized the results of HHS. The initial run of MCRTM did not result in matching the observed SED. Subsequently, we explored previously unknown disk parameters, most importantly disk mass and accretion rate. We found that to reproduce the observed 10:1 ratio of IR to Far-UV flux, we must have a non-zero rate of accretion occuring in the disk. To avoid depleting the disk too quickly, our simulations find that a more massive disk becomes too opaque due to increased scattering and does not reproduce the observed SED. Thus, we propose the extra mass might be in the form of planetesimals. The high accretion rate also implies dust mass replinishment, possibly due to a high rate of collisional interaction among planetesimals embedded in the disk. This work was supported in part by the bequest of William Herschel Womble in support of astronomy at the University of Denver, by NSF grant 1016678 and JPL RSA 1414715 to the University of Denver.
225.06
Hydrodynamic Simulations of Algol Systems with Tilted Accretion Disks
Eric Raymer1, J. Blondin1
1North Carolina State University.
8:00 AM - 7:00 PM
Essex Ballroom
Recent observational data has shown that the Algol-type binary system RS Vul possesses an accretion disk tilted out of the orbital plane. Magnetic effects in the surface of the donor star could produce a nontrivial effect in the flow of the accretion stream as it travels through the L1 Lagrange point. Such a deflection could introduce angular momentum with a non-z component that could propagate toward the primary and lead to a tilted accretion disk. We use three-dimensional hydrodynamic simulations of the mass transfer and accretion disk in RS Vul to investigate this hypothesis.
225.07
Dynamics and Evolution of Self-Gravitating Circumstellar Disks on a Moving Mesh
Diego Munoz1, L. Hernquist1
1Harvard University.
8:00 AM - 7:00 PM
Essex Ballroom
We present a novel approach to the numerical study of gas disks around young stars using the Voronoi-tessellation cosmological code AREPO (Springel,2010).
This finite-volume code is shock-capturing and second-order-accurate in time and space. Its moving mesh makes it a Lagrangian/Eulerian code that satisfies Galilean invariance and has a very low diffusivity due to its unbiased unstructured grid. Its pseudo-Lagrangian nature makes it ideal for problems that show large dynamical range in density, such as gravitationally unstable systems with clustering and collapse. The self-gravity solver is implemented consistently for collisionless particles as well as for gas ``particles" (Voronoi cells) in an N-body fashion using a tree algorithm.
The hydrodynamics+N-body approach of AREPO is unparalleled in its ability to treat self-gravitating systems that lack of a symmetric configuration while retaining the resolution and accuracy of conventional grid codes. Thus, it combines the benefits of both particle- and mesh-based codes. Precisely, these two approaches are used in numerical studies of circumstellar disks depending on the physical process of interest. For example, those studies that choose particle based codes -- such as SPH -- focus on gravitationally unstable disks or the tidal interaction of disks. On the other hand, grid codes are preferred in studies of planet-disk interaction, where proper treatment of shocks, wakes and gaps requires an accurate shock-capturing method. We present examples of how the flexible approach of AREPO can be used to simulate these and other types of problems.
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