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Description
We present the discovery of a white dwarf companion to the G1 V star 12Psc found as part of a Keck adaptive optics imaging survey of long-term accelerating stars from the McDonald Observatory Planet Search Program. Twenty years of precise radial-velocity monitoring of 12Psc with the Tull Spectrograph at the Harlan J. Smith telescope reveals a moderate radial acceleration (~10m/s/yr), which together with relative astrometry from Keck/NIRC2 and the astrometric acceleration between Hipparcos and Gaia DR2 yields a dynamical mass of M_B_=0.605_-0.022_^+0.021^M{sun} for 12PscB, a semimajor axis of 40_-4_^+2^au, and an eccentricity of 0.84{+/-}0.08. We also report an updated orbital fit of the white dwarf companion to the metal-poor (but barium-rich) G9 V dwarf HD159062 based on new radial velocity observations from the High-Resolution Spectrograph at the Hobby-Eberly Telescope and astrometry from Keck/NIRC2. A joint fit of the available relative astrometry, radial velocities, and tangential astrometric acceleration yields a dynamical mass of M_B_=0.609_-0.011_^+0.010^M{sun} for HD159062B, a semimajor axis of 60_-7_^+5^au, and preference for circular orbits (e<0.42 at 95% confidence). 12PscB and HD159062B join a small list of resolved Sirius-like benchmark white dwarfs with precise dynamical mass measurements which serve as valuable tests of white dwarf mass-radius cooling models and probes of AGB wind accretion onto their main-sequence companions.
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