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Browsing by Author "Henning, Th."

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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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    The formation and evolution of planetary systems : Grain growth and chemical processing of dust in T Tauri systems
    (IOP Publishing, 2008-08-10) Bouwman, J.; Henning, Th.; Hillenbrand, L. A.; Meyer, M. R.; Pascucci, I.; Carpenter, J.; Hines, D.; Kim, J. S.; Silverstone, M. D.; Hollenbach, D.; Wolf, S.; Max Planck Society; California Institute of Technology; University of Arizona; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; University of Alabama Tuscaloosa
    This paper is one in a series presenting results obtained within the Formation and Evolution of Planetary Systems (FEPS) Legacy Science Program on the Spitzer Space Telescope. Here we present a study of dust processing and growth in seven protoplanetary disks. Our spectra indicate that the circumstellar silicate dust grains have grown to sizes at least 10 times larger than observed in the interstellar medium and show evidence for a non-negligible (similar to 5% in mass fractions) contribution from crystalline species. These results are similar to those of other studies of protoplanetary disks. In addition, we find a correlation between the strength of the amorphous silicate feature and the shape of the spectral energy distribution. This latter result is consistent with the growth and subsequent gravitational settling of dust grains toward the disk midplane. Furthermore, we find a change in the relative abundance of the different crystalline species: more enstatite than forsterite is observed in the inner warm dust population at similar to 1 AU, while forsterite dominates in the colder outer regions at similar to 5-15 AU. This change in the relative abundances argues for a localized crystallization process rather than a radial mixing scenario in which crystalline silicates are being transported outwards from a single formation region in the hot inner parts of the disk. Finally, we report the detection of emission from polycyclic aromatic hydrocarbon ( PAH) molecules in five out of seven sources. We find a tentative PAH band at 8.2 mu m that was previously undetected in the spectra of disks around low-mass pre-main-sequence 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.