A multi-method Galactic halo binary survey using high-angular resolution images and light curves

Stellar multiplicity properties, including binary frequency and orbital period distributions, provide
direct insight into the initial star-forming environment as they are thought to be largely dependent
on fragmentation processes in the original Giant Molecular Cloud. Ancient stars of the Galactic
halo are more challenging to study in large numbers than the Galactic disk as they are, on average,
more distant and thus faint low-mass stars. While the multiplicity statistics of the disk-dominated
field population can be inferred from volume-limited surveys of the Solar Neighborhood, uncertainty remains in the multiplicity properties of the Galactic halo, with a wide range of multiplicity fractions (i.e. 12.5-33%) reported in the literature. With Gaia DR3, large catalogs ( 0.5 million stars) of local (d<2kpc) low-mass halo stars can now be assembled, allowing for more statistically significant surveys of Galactic halo binaries. Using a range of techniques, we conduct a multi-method multiplicity survey of Galactic halo stars using a combination of: astrometric data (Gaia), high-angular resolution ( 0.1”) images (archival HST/JWST data and ground-based AO data from LICK Observatory) for hundreds of halo stars to resolve visual binaries, and 6000 archival light curves (Kepler K2) to find eclipsing binaries and old rotators (old Galactic halo stars spun-up by a close companion). These techniques probe systems at all orbital separations, allowing for a more comprehensive examination of the orbital period distribution of binaries in the Galactic halo. This will contribute to our understanding of the preferred close binary formation mechanism(s) in the halo and the role of age and metallicity in these processes. Furthermore, we expect this survey to aid in attempts to characterize how stellar multiplicity properties vary throughout the Galaxy by parent population.