Searching for Unresolved Companions to Galactic Halo Stars

We present the initial results of a multiplicity survey of nearby Galactic halo stars using the ‘Alopeke and Zorro speckle instruments at Gemini Observatory. Currently, the overall multiplicity fraction and binary distribution of the nearby Galactic halo star population is not well known with estimates varying between 12%-35%. Part of the reason for this has been the lack of easily observable stars. However, using Gaia Data Release 3, we determine a sample of 1149 halo and high velocity thick disk stars within 100 pc using a tangential velocity cut at 150 km/s and G magnitudes above 18. We observe 128 of these stars using ‘Alopeke and Zorro and find 6 candidate binaries. Our raw result represents a value much lower than previous results. We combine this result with a crossmatch with the SUPERWIDE wide binary catalog to effectively search these stars for possible companions down to 2.5 au. We present the contrast curves and reconstructed images of the detected binaries and compare our initial results to previous surveys.