Journal
ASTROPHYSICAL JOURNAL
Volume 647, Issue 1, Pages 552-557Publisher
UNIV CHICAGO PRESS
DOI: 10.1086/505419
Keywords
stars : abundances; stars : atmospheres; stars : individual (Gliese 570D); stars : low-mass, brown dwarfs
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We present the first analysis of an optical to mid-infrared spectrum of the T7.5 dwarf Gliese 570D with model atmospheres, synthetic spectra, and brown dwarf evolution sequences. We obtain precise values for the basic parameters of G1 570D: T-eff = 800-820 K, log g (cm s(-2)) 5.09-5.23, and log (L/L-circle dot) = -5.525 to -5.551. The Spitzer Infrared Spectrograph (IRS) spectrum shows prominent features of ammonia (NH3) that can only be fitted by reducing the abundance of NH3 by about 1 order of magnitude from the value obtained with chemical-equilibrium models. We model departures from chemical equilibrium in the atmosphere of Gl 570D by considering the kinetics of nitrogen and carbon chemistry in the presence of vertical mixing. The resulting model spectrum reproduces the data very well.
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