Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-05-22
Astrophys.J.647:552-557,2006
Astronomy and Astrophysics
Astrophysics
Accepted for publication in the ApJ. 10 pages, including 3 figures
Scientific paper
10.1086/505419
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 Gl 570D: Teff=800 - 820K, log g (cm/s^2)=5.09 - 5.23, and log L/Lsun= -5.525 to -5.551. The Spitzer IRS spectrum shows prominent features of ammonia (NH3) that can only be fitted by reducing the abundance of NH3 by about one 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.
Cushing Michael. C.
Freedman Richard Stuart
Leggett Sandy K.
Lodders Katharina
Marley Mark S.
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