The APO-K2 Catalog. III. Exploring the Multiplicity of 7,673 Evolved Stars from the APO-K2 Catalog.

We present an exploration of the multiplicity in 7,673 evolved stars, searching for visually resolved and unresolvable companions using stellar parameters from the APO-K2 survey along with Gaia parameters and spatial searches. First, we investigate the distribution of binaries in this evolved sample in angular resolution. We then consider how the distance to companions on the Red Giant Branch differs from the Main Sequence and how this may result from binary interaction and mass loss. Second, we use Gaia to characterize the companion stars we find, investigating how mass transfer plays a role in the whole sample. Finally, we use the well-understood selection function provided with the APO-K2 catalog to determine a statistical distribution of companions in evolved star samples throughout the Milky Way.