Reconstructing the Evolution of HZ 9: a Post-common Envelope Binary in the Hyades Open Cluster

HZ 9 is a post-common-envelope binary consisting of a DA white dwarf and a dM main-sequence star in the Hyades star cluster. In this work, we measured precise masses of the components of HZ 9 using new ground-based radial velocity measurements and combining those with recently developed mass-luminosity relationships for M dwarfs. Using the parallax measured by ESA's Gaia Mission and infrared magnitudes from the Two Micron All Sky Survey (2MASS), we determine a precise mass of the dM component. We measured single-line radial velocities of the dM using the high-resolution infrared iSHELL spectrograph on NASA's Infrared Telescope Facility, and we measured optical double-line radial velocities of both components using the DeVeny spectrograph on the Lowell Discovery Telescope. Combining the radial velocity measurements with the measured dM mass, we measured a precise mass of the DA component. Using this measured white dwarf mass and the age of the Hyades, we reconstruct the common envelope evolution of the binary.