Making 13 sigma dynamical mass measurements for the components of the HD
104304 binary system using radial velocities and direct imaging.
Combining direct imaging astrometry and long-baseline radial velocity
(RV) measurements of stellar binaries can provide precise constraints on
their 3D orbits and yield dynamical masses for both components. We
applied the combination of these methods to study HD104304, a binary
system with a decades-long orbit containing a G8IV subgiant and a
recently-discovered M dwarf companion. Using radial velocities collected
over a timespan of two decades by Keck/HIRES and astrometry calculated
from adaptive optics images taken by Keck/NIRC2, we explored models to
jointly fit the astrometric orbital motion and RV trend. Previous
studies of this system (Howard & Fulton, 2016) were unable to
distinguish between two and three body solutions using RVs alone.
However, we are able to break this degeneracy by incorporating images
into the fit. We make 13-sigma dynamical mass measurements of the
primary and secondary, and find that a slightly eccentric solution
(e=0.3) is required. However, the dynamical mass we measure for the
primary (~1.8 solar masses) is significantly higher than
its well constrained spectroscopic mass of 1.02 solar masses. This hints
at the need for a three-body solution to accurately model the observed
trend in the HD 104304 system.