GJ 229B: Solving the Puzzle of the First Known T Dwarf with the APOLLO Retrieval Code

GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynam...

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Bibliographic Details
Published in:The Astrophysical journal 2022-08, Vol.935 (2), p.107
Main Authors: Howe, Alex R., McElwain, Michael W., Mandell, Avi M.
Format: Article
Language:English
Subjects:
Abundance
Astrochemistry
Astrophysics
Atmosphere
Atmospheric models
Brown dwarf stars
Celestial bodies
Exoplanet atmospheres
Extrasolar planets
Planets
Retrieval
Source code
Space Sciences (General)
Spectroscopic analysis
Spectroscopy
Substellar companion stars
T dwarfs
Telescopes
Wavelengths
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Summary:GJ 229B was the first T dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than that of most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B’s mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of astronomical units from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5–5.1 μm) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of 41.6 ± 3.3MJ and an effective temperature estimate of 869 +5 −7 K, which are more consistent with evolutionary models for brown dwarfs and suggest an older age for the system of >1.0 Gyr. We also present retrieved molecular abundances for the atmosphere, including replicating the previously observed high CO abundance, and discuss their implications for the formation and evolution of this object. This retrieval effort will give us insight into how to study other brown dwarfs and directly imaged planets, including those observed with JWST and other next-generation telescopes.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ac5590