A Dynamical Mass of $70 pm 5$ Jupiter Masses for Gliese 229B, the First Imaged T Dwarf. (arXiv:1910.01652v1 [astro-ph.SR])

A Dynamical Mass of $70 pm 5$ Jupiter Masses for Gliese 229B, the First Imaged T Dwarf. (arXiv:1910.01652v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_T/0/1/0/all/0/1">Timothy D. Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dupuy_T/0/1/0/all/0/1">Trent J. Dupuy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bowler_B/0/1/0/all/0/1">Brendan P. Bowler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gagliuffi_D/0/1/0/all/0/1">Daniella C. Bardalez Gagliuffi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Faherty_J/0/1/0/all/0/1">Jacqueline Faherty</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brandt_G/0/1/0/all/0/1">G. Mirek Brandt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Michalik_D/0/1/0/all/0/1">Daniel Michalik</a>

We combine Keck/HIRES radial velocities, imaging with HiCIAO/Subaru and the
Hubble Space Telescope, and absolute astrometry from Hipparcos and Gaia to
measure a dynamical mass of $70 pm 5$ $M_{rm Jup}$ for the brown dwarf
companion to Gl 229. Gl 229B was the first imaged brown dwarf to show clear
signs of methane in its atmosphere. Cooling models have been used to estimate a
mass in the range of 20-55 $M_{rm Jup}$, much lower than our measured value.
We argue that our high dynamical mass is unlikely to be due to perturbations
from additional unseen companions or to Gl 229B being itself a binary, and we
find no evidence of a previously claimed radial velocity planet around Gl 229A.
Future Gaia data releases will confirm the reliability of the absolute
astrometry, though the data pass all quality checks in both Hipparcos and Gaia.
Our dynamical mass implies a very old age for Gl 229, in some tension with
kinematic and activity age indicators, and/or shortcomings in brown dwarf
cooling models. Gl 229B joins a small but growing list of T dwarfs with masses
approaching the minimum mass for core hydrogen ignition.

We combine Keck/HIRES radial velocities, imaging with HiCIAO/Subaru and the
Hubble Space Telescope, and absolute astrometry from Hipparcos and Gaia to
measure a dynamical mass of $70 pm 5$ $M_{rm Jup}$ for the brown dwarf
companion to Gl 229. Gl 229B was the first imaged brown dwarf to show clear
signs of methane in its atmosphere. Cooling models have been used to estimate a
mass in the range of 20-55 $M_{rm Jup}$, much lower than our measured value.
We argue that our high dynamical mass is unlikely to be due to perturbations
from additional unseen companions or to Gl 229B being itself a binary, and we
find no evidence of a previously claimed radial velocity planet around Gl 229A.
Future Gaia data releases will confirm the reliability of the absolute
astrometry, though the data pass all quality checks in both Hipparcos and Gaia.
Our dynamical mass implies a very old age for Gl 229, in some tension with
kinematic and activity age indicators, and/or shortcomings in brown dwarf
cooling models. Gl 229B joins a small but growing list of T dwarfs with masses
approaching the minimum mass for core hydrogen ignition.

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