Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations. (arXiv:1811.07285v1 [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 Dupuy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bowler_B/0/1/0/all/0/1">Brendan P. Bowler</a>
We measure dynamical masses for five objects–three ultracool dwarfs, one
low-mass star, and one white dwarf–by fitting orbits to a combination of the
Hipparcos-Gaia Catalog of Accelerations, literature radial velocities, and
relative astrometry. Our approach provides precise masses without any
assumptions about the primary star, even though the observations typically
cover only a small fraction of an orbit. We also perform a uniform re-analysis
of the host stars’ ages. Two of our objects, HD 4747B and HR 7672B, already
have precise dynamical masses near the stellar/substellar boundary and are used
to validate our approach. For Gl 758B, we obtain a mass of $38.1_{-1.5}^{+1.7}$
$M_{Jup}$, the most precise mass measurement of this companion to date. Gl 758B
is the coldest brown dwarf with a dynamical mass, and the combination of our
low mass and slightly older host-star age resolves its previously noted
discrepancy with substellar evolutionary models. HD 68017B, a late-M dwarf, has
a mass of $0.147pm 0.003$ $M_odot$, consistent with stellar theory and
previous empirical estimates based on its absolute magnitude. The progenitor of
the white dwarf Gl 86B has been debated in the literature, and our dynamical
measurement of $0.595 pm 0.010$ $M_odot$ is consistent with a higher
progenitor mass and younger age for this planet-hosting binary system. Overall,
these case studies represent only five of the thousands of accelerating systems
identified by combining Hipparcos and Gaia. Our analysis could be repeated for
many of them to build a large sample of companions with dynamical masses.
We measure dynamical masses for five objects–three ultracool dwarfs, one
low-mass star, and one white dwarf–by fitting orbits to a combination of the
Hipparcos-Gaia Catalog of Accelerations, literature radial velocities, and
relative astrometry. Our approach provides precise masses without any
assumptions about the primary star, even though the observations typically
cover only a small fraction of an orbit. We also perform a uniform re-analysis
of the host stars’ ages. Two of our objects, HD 4747B and HR 7672B, already
have precise dynamical masses near the stellar/substellar boundary and are used
to validate our approach. For Gl 758B, we obtain a mass of $38.1_{-1.5}^{+1.7}$
$M_{Jup}$, the most precise mass measurement of this companion to date. Gl 758B
is the coldest brown dwarf with a dynamical mass, and the combination of our
low mass and slightly older host-star age resolves its previously noted
discrepancy with substellar evolutionary models. HD 68017B, a late-M dwarf, has
a mass of $0.147pm 0.003$ $M_odot$, consistent with stellar theory and
previous empirical estimates based on its absolute magnitude. The progenitor of
the white dwarf Gl 86B has been debated in the literature, and our dynamical
measurement of $0.595 pm 0.010$ $M_odot$ is consistent with a higher
progenitor mass and younger age for this planet-hosting binary system. Overall,
these case studies represent only five of the thousands of accelerating systems
identified by combining Hipparcos and Gaia. Our analysis could be repeated for
many of them to build a large sample of companions with dynamical masses.
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