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arXiv · 2210.13614

An Atmospheric Retrieval of the Brown Dwarf Gliese 229B

Emily Calamari·Jacqueline K. Faherty·Ben Burningham·Eileen Gonzales·Daniella Bardalez-Gagliuffi·Johanna M. Vos·Marina Gemma·Niall Whiteford·Josefine Gaarn
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Abstract

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. 2017, Zalesky et al. 2022 and Gonzales et al. 2020. Fundamental parameters (mass, radius, log(L_{Bol}/L_{Sun}), log(g)) determined from our model agree within 1\sigma 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^{+12}_{-9} 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 H_2O, CO, CH_4, NH_3, 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, internal physical processes as well as model biases.

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Emily Calamari, Jacqueline K. Faherty, Ben Burningham, Eileen Gonzales, Daniella Bardalez-Gagliuffi, Johanna M. Vos, Marina Gemma, Niall Whiteford, Josefine Gaarn. 2022-10-24. An Atmospheric Retrieval of the Brown Dwarf Gliese 229B. https://doi.org/10.3847/1538-4357/ac9cc9

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