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Issue A&A Volume 411, Number 3, December I 2003 Page(s) L473 - L476 Section Letters DOI 10.1051/0004-6361:20031299

A&A 411, L473-L476 (2003)
DOI: 10.1051/0004-6361:20031299

Letter

A new model for brown dwarf spectra including accurate unified line shape theory for the Na I and K I resonance line profiles

N. F. Allard^{1, 2}, F. Allard³, P. H. Hauschildt⁴, J. F. Kielkopf⁵ and L. Machin<sup>1, 3

1</sup>  Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, 75014 Paris, France
²  Observatoire de Paris-Meudon, LERMA, 92195 Meudon Principal Cedex, France
³  Centre de Recherche Astronomique de Lyon, École Normale Supérieure, 69364 Lyon Cedex 07, France
⁴  Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁵  Department of Physics, University of Louisville, Louisville, KY 40292, USA

(Received 28 July 2003 / Accepted 26 August 2003)

Abstract
We present the first brown dwarf atmosphere models based on theoretical calculations of absorption profiles of sodium and potassium perturbed by helium and molecular hydrogen. The synthetic spectra have been compared to previous calculations with Lorentz profiles and the classic van der Waals approximation, and to the observed spectrum of the T dwarf SDSS 1624. The new profiles provide increased opacities in the optical spectra of methane brown dwarfs. However, the potassium and sodium far wings alone cannot explain the missing opacity in the 0.85 to 1.1  m range.

Key words: brown dwarfs -- line: profiles -- radiation mechanisms: general -- stars: atmospheres

Offprint request: N. F. Allard, allard@iap.fr

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