We present results from an atmospheric retrieval analysis of Gl 229B using the Brewster retrieval code. We find the best fit model to be cloud-free, consistent with the T dwarf retrieval work of Line et al.; Zalesky et al. and Gonzales et al. Fundamental parameters (mass, radius, log(L Bol /L Sun), log(g)) determined from our model agree within 1σ to SED-derived values, except for T eff where our retrieved T eff is approximately 100 K cooler than the evolutionary model-based SED value. We find a retrieved mass of 50−9+12 M Jup, however, we also find that the observables of Gl 229B can be explained by a cloud-free model with a prior on mass at the dynamical value, 70 M Jup . We are able to constrain abundances for H2O, CO, CH4, NH3, Na and K and find a supersolar C/O ratio as compared to its primary, Gl 229A. We report an overall subsolar metallicity due to atmospheric oxygen depletion, but find a solar [C/H], which matches that of the primary. We find that this work contributes to a growing trend in retrieval-based studies, particularly for brown dwarfs, toward supersolar C/O ratios and discuss the implications of this result on formation mechanisms and internal physical processes, as well as model biases.
- Stars and Stellar Physics