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Browsing by Author "Grady, C. A."

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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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    Probing dust grain evolution in IM Lupi's circumstellar disc - Multi-wavelength observations and modelling of the dust disc
    (EDP Sciences, 2008-08-08) Pinte, C.; Padgett, D. L.; Menard, F.; Stapelfeldt, K. R.; Schneider, G.; Olofsson, J.; Panic, O.; Augereau, J. C.; Duchene, G.; Krist, J.; Pontoppidan, K.; Perrin, M. D.; Grady, C. A.; Kessler-Silacci, J.; van Dishoeck, E. F.; Lommen, D.; Silverstone, M.; Hines, D. C.; Wolf, S.; Blake, G. A.; Henning, T.; Stecklum, B.; University of Exeter; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Communaute Universite Grenoble Alpes; Universite Grenoble Alpes (UGA); California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); University of Arizona; Leiden University; Leiden University - Excl LUMC; University of California System; University of California Berkeley; University of California Los Angeles; University of Texas System; University of Texas Austin; Max Planck Society; Eureka Scientific; University of Kiel; University of Alabama Tuscaloosa
    Aims. We present a panchromatic study, involving a multiple technique approach, of the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). Methods. We have undertaken a comprehensive observational study of IM Lupi using photometry, spectroscopy, millimetre interferometry and multi-wavelength imaging. For the first time, the disc is resolved from optical and near-infrared wavelengths in scattered light, to the millimetre regime in thermal emission. Our data-set, in conjunction with existing photometric data, provides an extensive coverage of the spectral energy distribution, including a detailed spectrum of the silicate emission bands. We have performed a simultaneous modelling of the various observations, using the radiative transfer code MCFOST, and analysed a grid of models over a large fraction of the parameter space via Bayesian inference. Results. We have constructed a model that can reproduce all of the observations of the disc. Our analysis illustrates the importance of combining a wide range of observations in order to fully constrain the disc model, with each observation providing a strong constraint only on some aspects of the disc structure and dust content. Quantitative evidence of dust evolution in the disc is obtained: grain growth up to millimetre-sized particles, vertical stratification of dust grains with micrometric grains close to the disc surface and larger grains which have settled towards the disc midplane, and possibly the formation of fluffy aggregates and/ or ice mantles around grains.
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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.