2015AJ....150...53N

Recently Tsuji & Nakajima and Tsuji et al. have developed a method of molecular line spectroscopy of M dwarfs with which carbon and oxygen abundances are derived respectively from CO and H₂ O lines in the K band. They applied this method to Gliese 229A(Gl 229A), the primary star of the brown dwarf companion, Gliese 229B(Gl 229B). The derived abundances of Gl 229A are log A_C = -3.27 ± 0.07 and log A₀ = -3.10 ± 0.02, which are close to the classical values of the solar abundances of carbon and oxygen. We generate model spectra of Gl 229B for the metallicity of Gl 229A as well as for the classical solar metallicity (log A_C = -3.40 and A₀ = -3.08). We find that the differences in the resulting spectra are not so large for differences in metallicity of 0.1 dex or so, but we now discuss the spectrum of Gl 229B on the basis of reliable metallicity. From the literature, the lower limit to the age of Gl 229A is found to be 0.3 Gyr. From the kinematics of Gl 229A, we evaluate the upper limit to the age of Gl 229A to be 3.0 Gyr. The observed and model spectra are compared and the goodness of fit is obtained in the range of model parameters 750 ≤ T_eff ≤ 1000 K and 4.5 ≤ log g ≤ 5.5. Among the candidates that satisfy the age constraint, the best combinations of model parameters are (T_eff, log g) = (800 K, 4.75) and (850 K, 5.0), while acceptable combinations are (750 K, 4.75), (850 K, 4.75) and (900 K, 5.0).