Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3. (arXiv:2109.07525v2 [astro-ph.SR] UPDATED)

Improved Dynamical Masses for Six Brown Dwarf Companions Using Hipparcos and Gaia EDR3. (arXiv:2109.07525v2 [astro-ph.SR] UPDATED)
<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:+Dupuy_T/0/1/0/all/0/1">Trent J. Dupuy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_Y/0/1/0/all/0/1">Yiting Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chen_M/0/1/0/all/0/1">Minghan Chen</a>, <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:+Wong_T/0/1/0/all/0/1">Tin Long Sunny Wong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Currie_T/0/1/0/all/0/1">Thayne Currie</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:+Liu_M/0/1/0/all/0/1">Michael C. Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Best_W/0/1/0/all/0/1">William M. J. Best</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Phillips_M/0/1/0/all/0/1">Mark W. Phillips</a>

We present comprehensive orbital analyses and dynamical masses for the
substellar companions Gl~229~B, Gl~758~B, HD~13724~B, HD~19467~B, HD~33632~Ab,
and HD~72946~B. Our dynamical fits incorporate radial velocities, relative
astrometry, and most importantly calibrated Hipparcos-Gaia EDR3 accelerations.
For HD~33632~A and HD~72946 we perform three-body fits that account for their
outer stellar companions. We present new relative astrometry of Gl~229~B with
Keck/NIRC2, extending its observed baseline to 25 years. We obtain a $<$1%
mass measurement of $71.4 pm 0.6,M_{rm Jup}$ for the first T dwarf Gl~229~B
and a 1.2% mass measurement of its host star ($0.579 pm 0.007,M_{odot}$)
that agrees with the high-mass-end of the M dwarf mass-luminosity relation. We
perform a homogeneous analysis of the host stars’ ages and use them, along with
the companions’ measured masses and luminosities, to test substellar
evolutionary models. Gl~229~B is the most discrepant, as models predict that an
object this massive cannot cool to such a low luminosity within a Hubble time,
implying that it may be an unresolved binary. The other companions are
generally consistent with models, except for HD~13724~B that has a host-star
activity age 3.8$sigma$ older than its substellar cooling age. Examining our
results in context with other mass-age-luminosity benchmarks, we find no trend
with spectral type but instead note that younger or lower-mass brown dwarfs are
over-luminous compared to models, while older or higher-mass brown dwarfs are
under-luminous. The presented mass measurements for some companions are so
precise that the stellar host ages, not the masses, limit the analysis.

We present comprehensive orbital analyses and dynamical masses for the
substellar companions Gl~229~B, Gl~758~B, HD~13724~B, HD~19467~B, HD~33632~Ab,
and HD~72946~B. Our dynamical fits incorporate radial velocities, relative
astrometry, and most importantly calibrated Hipparcos-Gaia EDR3 accelerations.
For HD~33632~A and HD~72946 we perform three-body fits that account for their
outer stellar companions. We present new relative astrometry of Gl~229~B with
Keck/NIRC2, extending its observed baseline to 25 years. We obtain a $<$1%
mass measurement of $71.4 pm 0.6,M_{rm Jup}$ for the first T dwarf Gl~229~B
and a 1.2% mass measurement of its host star ($0.579 pm 0.007,M_{odot}$)
that agrees with the high-mass-end of the M dwarf mass-luminosity relation. We
perform a homogeneous analysis of the host stars’ ages and use them, along with
the companions’ measured masses and luminosities, to test substellar
evolutionary models. Gl~229~B is the most discrepant, as models predict that an
object this massive cannot cool to such a low luminosity within a Hubble time,
implying that it may be an unresolved binary. The other companions are
generally consistent with models, except for HD~13724~B that has a host-star
activity age 3.8$sigma$ older than its substellar cooling age. Examining our
results in context with other mass-age-luminosity benchmarks, we find no trend
with spectral type but instead note that younger or lower-mass brown dwarfs are
over-luminous compared to models, while older or higher-mass brown dwarfs are
under-luminous. The presented mass measurements for some companions are so
precise that the stellar host ages, not the masses, limit the analysis.

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