Department of Physics & Astronomy

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Browsing Department of Physics & Astronomy by Subject "2-DIMENSIONAL RADIATIVE-TRANSFER"

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    The disk and environment of a young Vega analog: HD 169142
    (IOP Publishing, 2007-08-20) Grady, C. A.; Schneider, G.; Hamaguchi, K.; Sitko, M. L.; Carpenter, W. J.; Hines, D.; Collins, K. A.; Williger, G. M.; Woodgate, B. E.; Henning, Th.; Menard, F.; Wilner, D.; Petre, R.; Palunas, P.; Quirrenbach, A.; Nuth, J. A., III; Silverstone, M. D.; Kim, J. S.; Eureka Scientific; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University of Arizona; Universities Space Research Association (USRA); University System of Ohio; University of Cincinnati; University of Louisville; Johns Hopkins University; Max Planck Society; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Communaute Universite Grenoble Alpes; Universite Grenoble Alpes (UGA); Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of Texas System; University of Texas Austin; Ruprecht Karls University Heidelberg; University of Alabama Tuscaloosa
    We trace the disk of HD169142 (A8 Ve) from 0.57" to 1.4" (approximate to 80-200 AU projected distance) in 1.1 mu m scattered light with HST NICMOS coronagraphy. The azimuthally symmetric disk has a peak azimuthally medianed surface brightness (SB) of approximate to 5 mJy arcsec(-2) at 0.57" from the star, and drops alpha r(-3). This radial SB profile is consistent with the presence of spatially resolved PAH emission and a Meeus group I IR SED only if the inner disk is either substantially flatter than the outer disk or partially devoid of material. Analysis of new HST ACS FUV imagery in tandem with archival IUE data indicates. M-acc <= 10(-9) M circle dot yr(-1). We estimate the age of HD 169142 to be 6(-3)(+6) Myr by identifying 2MASS 18242929-2946559, located 9.3" to the southwest, as a 130 mas separation weak-line T Tauri binary that is comoving with HD 169142 at the 4 sigma confidence level. We find no evidence for any additional stellar companion in either the ACS or Chandra ACIS-S data at r <= 1". HD 169142 has previously been interpreted as a slowly rotating, chemically peculiar star. However, by combining the disk inclination and v sin i from the literature, we find that the star has upsilon(equatorial) approximate to 240 km s(-1), making it a rapid rotator, similar to Altair or Vega. The UV data for HD 169142 are consistent with gravity darkening, while the X-ray luminosity and spectrum resembles early F stars at the age of the beta Pictoris moving group, rather than mid-A stars. In this context, spectral features previously interpreted as evidence for chemical peculiarity are more likely to reflect the presence of a strong photospheric latitudinal temperature gradient. With such a gradient, HD 169142 should closely resemble Vega at the epoch of central disk clearing.
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    LOCATING THE ACCRETION FOOTPRINT ON A HERBIG Ae STAR: MWC 480
    (IOP Publishing, 2010-08-20) Grady, C. A.; Hamaguchi, K.; Schneider, G.; Stecklum, B.; Woodgate, B. E.; McCleary, J. E.; Williger, G. M.; Sitko, M. L.; Menard, F.; Henning, Th; Brittain, S.; Troutmann, M.; Donehew, B.; Hines, D.; Wisniewski, J. P.; Lynch, D. K.; Russell, R. W.; Rudy, R. J.; Day, A. N.; Shenoy, A.; Wilner, D.; Silverstone, M.; Bouret, J. -C.; Meusinger, H.; Clampin, M.; Kim, S.; Petre, R.; Sahu, M.; Endres, M.; Collins, K. A.; Eureka Scientific; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University System of Maryland; University of Maryland Baltimore; University of Arizona; New Mexico State University; University of Louisville; Johns Hopkins University; UDICE-French Research Universities; Universite Cote d'Azur; Observatoire de la Cote d'Azur; University System of Ohio; University of Cincinnati; Centre National de la Recherche Scientifique (CNRS); Communaute Universite Grenoble Alpes; Universite Grenoble Alpes (UGA); Max Planck Society; Clemson University; University of Washington; University of Washington Seattle; Aerospace Corporation - USA; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Aix-Marseille Universite; University of Alabama Tuscaloosa
    Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-chromatic data for the Herbig Ae star MWC 480 to address whether similar processes occur in intermediate-mass stars. MWC 480 has X-ray emission typical of actively accreting Herbig Ae stars, but with similar to 10x more photoelectric absorption than expected from optical and FUV data. We consider three sources for the absorption: the disk, absorption in a wind or jet, and accretion. While we detect the disk in scattered light in a re-analysis of archival Hubble Space Telescope data, the data are consistent with grazing illumination of the dust disk. We find that MWC 480's disk is stratified, geometrically thin, and is not responsible for the observed photoelectric absorption. MWC 480 drives a bipolar jet, but with a mass-loss rate that is low compared to other Herbig Ae stars, where the outflow is more favorably oriented and enhanced photoelectric absorption is not seen. This excludes a jet or wind origin for the enhanced photoelectric absorption. We compare MWC 480's OVI emission with other Herbig Ae stars. The distribution of the emission in inclination, and lack of a correlation of profile shape and system inclination excludes equatorially confined accretion for the FUSE Herbig Ae stars. The photoelectric absorption data further suggest that the accretion footprint on MWC 480 and other Herbig Ae stars is located at high-temperate, rather than polar, latitudes. These findings support the presence of funneled accretion in MWC 480 and Herbig Ae stars, strengthening the parallel to T Tauri stars.
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    REVEALING THE STRUCTURE OF A PRE-TRANSITIONAL DISK: THE CASE OF THE HERBIG F STAR SAO 206462 (HD 135344B)
    (IOP Publishing, 2009-07-10) Grady, C. A.; Schneider, G.; Sitko, M. L.; Williger, G. M.; Hamaguchi, K.; Brittain, S. D.; Ablordeppey, K.; Apai, D.; Beerman, L.; Carpenter, W. J.; Collins, K. A.; Fukagawa, M.; Hammel, H. B.; Henning, Th.; Hines, D.; Kimes, R.; Lynch, D. K.; Menard, F.; Pearson, R.; Russell, R. W.; Silverstone, M.; Smith, P. S.; Troutman, M.; Wilner, D.; Woodgate, B.; Clampin, M.; Eureka Scientific; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University of Arizona; University System of Ohio; University of Cincinnati; University of Louisville; Johns Hopkins University; Catholic University of America; University System of Maryland; University of Maryland Baltimore County; Clemson University; Osaka University; Max Planck Society; Aerospace Corporation - USA; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Communaute Universite Grenoble Alpes; Universite Grenoble Alpes (UGA); Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; University of Alabama Tuscaloosa
    SAO 206462 (HD 135344B) has previously been identified as a Herbig F star with a circumstellar disk with a dip in its infrared excess near 10 mu m. In combination with a low accretion rate estimated from Br gamma, it may represent a gapped, but otherwise primordial or "pre-transitional" disk. We test this hypothesis with Hubble Space Telescope coronagraphic imagery, FUV spectroscopy and imagery and archival X-ray data, and spectral energy distribution (SED) modeling constrained by the observed system inclination, disk outer radius, and outer disk radial surface brightness (SB) profile using the Whitney Monte Carlo Radiative Transfer Code. The essentially face-on (i less than or similar to 20 degrees) disk is detected in scattered light from 0 ''.4 to 1 ''.15 (56-160 AU), with a steep (r(-9.6)) radial SB profile from 0.'' 6 to 0.'' 93. Fitting the SB data requires a concave upward or anti-flared outer disk, indicating substantial dust grain growth and settling by 8 +/- 4 Myr. The warm dust component is significantly variable in near to mid-IR excess and in temperature. At its warmest, it appears confined to a narrow belt from 0.08 to 0.2 AU. The steep SED for this dust component is consistent with grains with a <= 2.5 mu m. For cosmic carbon to silicate dust composition, conspicuous 10 mu m silicate emission would be expected and is not observed. This may indicate an elevated carbon to silicate ratio for the warm dust, which is not required to fit the outer disk. At its coolest, the warm dust can be fit with a disk from 0.14 to 0.31 AU, but with a higher inclination than either the outer disk or the gaseous disk, providing confirmation of the high inclination inferred from mid-IR interferometry. In tandem, the compositional and inclination difference between the warm dust and the outer dust disk suggests that the warm dust may be of second-generation origin, rather than a remnant of a primordial disk component. With its near face-on inclination, SAO 206462's disk is a prime location for planet searches.
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    STRUCTURE AND COMPOSITION OF TWO TRANSITIONAL CIRCUMSTELLAR DISKS IN CORONA AUSTRALIS
    (IOP Publishing, 2010-08-13) Hughes, A. M.; Andrews, S. M.; Wilner, D. J.; Meyer, M. R.; Carpenter, J. M.; Qi, C.; Hales, A. S.; Casassus, S.; Hogerheijde, M. R.; Mamajek, E. E.; Wolf, S.; Henning, T.; Silverstone, M. D.; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Swiss Federal Institutes of Technology Domain; ETH Zurich; California Institute of Technology; National Radio Astronomy Observatory (NRAO); Universidad de Chile; Leiden University; Leiden University - Excl LUMC; University of Rochester; University of Kiel; Max Planck Society; Eureka Scientific; University of Alabama Tuscaloosa
    The late stages of evolution of the primordial circumstellar disks surrounding young stars are poorly understood, yet vital to constraining theories of planet formation. We consider basic structural models for the disks around two similar to 10 Myr old members of the nearby RCrA association: RX J1842.9-3532 and RX J1852.3-3700. We present new arc second-resolution maps of their 230 GHz continuum emission from the Submillimeter Array and unresolved CO(3-2) spectra from the Atacama Submillimeter Telescope Experiment. By combining these data with broadband fluxes from the literature and infrared fluxes and spectra from the catalog of the Formation and Evolution of Planetary Systems Legacy program on the Spitzer Space Telescope, we assemble a multiwavelength data set probing the gas and dust disks. Using the Monte Carlo radiative transfer code RADMC to model simultaneously the spectral energy distribution and millimeter continuum visibilities, we derive basic dust disk properties and identify an inner cavity of radius 16 AU in the disk around RX J1852.3-3700. We also identify an optically thin 5 AU cavity in the disk around RX J1842.9-3532, with a small amount of optically thick material close to the star. The molecular line observations suggest an intermediate disk inclination in RX J1842.9-3532, consistent with the continuum emission. In combination with the dust models, the molecular data allow us to derive a lower CO content than expected, suggesting that the process of gas clearing is likely underway in both systems, perhaps simultaneously with planet formation.