Leggett, S. K. and Saumon, D. and Albert, Loic and Cushing, Michael C. and Liu, Michael C. and Luhman, K. L. and Marley, M. S. and Kirkpatrick, J. Davy and Roellig, Thomas L. and Allers, K. N. (2008) HN Peg B: A Test of Models of the L to T Dwarf Transition. Astronomical Journal, 682 (1). pp. 1256-1263. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:LEGapj08
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Luhman and collaborators recently discovered an early-T dwarf companion to the G0 dwarf star HN Peg, using Spitzer Infrared Array Camera (IRAC) images. Companionship was established on the basis of the common proper motion inferred from 1998 Two Micron All Sky Survey images and the 2004 IRAC images. In this paper we present new near-infrared imaging data which confirm the common proper motion of the system.We also present new 3-4 μm spectroscopy of HN Peg B, which provides tighter constraints on both the bolometric luminosity determination and the comparison to synthetic spectra. New adaptive optics imaging data are also presented, which show the T dwarf to be unresolved, providing limits on the multiplicity of the object. We use the age, distance, and luminosity of the solar-metallicity T dwarf to determine its effective temperature and gravity, and compare synthetic spectra with these values, and a range of grain properties and vertical mixing, to the observed 0.8-4.0 μm spectra and mid-infrared photometry. We find that models with temperature and gravity appropriate for the older end of the age range of the system (0.5 Gyr) can do a reasonable job of fitting the data, but only if the photospheric condensate cloud deck is thin, and if there is significant vertical mixing in the atmosphere. Dwarfs such as HN Peg B, with well-determined metallicity, radius, gravity, and temperature, will allow development of dynamical atmosphere models, leading to the solution of the puzzle of the L to T dwarf transition.
|Additional Information:||© 2008. The American Astronomical Society. Received 2008 February 21; accepted 2008 April 8. Print publication: Issue 2 (2008 August 1). This work uses observations obtained at the Gemini Observatory through Program GN-2007B-Q-22. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina). We are very grateful to John Rayner for the NSFCAM2 observations. We would also like to thank the observers and queue coordinators who carried service observations at CFHT (programs 06BD94, 07AD98, and 07AD84). We gratefully acknowledge the Keck LGS AO team for their exceptional efforts in bringing the LGS AO system to fruition. It is a pleasure to thank Randy Campbell, Jim Lyke, Cindy Wilburn, Joel Aycock, and the Keck Observatory staff for assistance with the observations. This work is based and supported (in part) on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This publication makes use of data from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, and funded by the National Aeronautics and Space Administration and the National Science Foundation, the SIMBAD database, operated at CDS, Strasbourg, France, and NASA's Astrophysics Data System Bibliographic Services. S. K. L.'s research is supported by the Gemini Observatory. M. C. L. and K. L. A. acknowledge support for this work from NSF grants AST 04-07441 and AST 05-07833, and an Alfred P. Sloan Research Fellowship. Facilities: CFHT, Gemini:Gillett(NIRI), IRTF(SpeX), Keck:II. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Some data were also obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.|
|Subject Keywords:||binaries: visual — stars: individual (2MASS J21442847+1446077, HN Peg, HN Peg B) — stars: low-mass, brown dwarfs|
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|Deposited By:||Kristin Buxton|
|Deposited On:||05 Feb 2009 08:08|
|Last Modified:||26 Dec 2012 10:46|
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