Assessing Spectroscopic Binary Multiplicity Properties Using Robo-AO Imaging

Abstract

Abstract We present higher-order multiplicity results for 60 solar-type spectroscopic binaries based on 0.75 μm imaging data taken by the robotic adaptive optics (Robo-AO) system at the Kitt Peak 2.1 m telescope. Our contrast curves show sensitivity up to ∼5 mag at ∼1″ separation; at very small separations, we identify candidate companions from image deviations relative to the point spread function. We find candidate tertiary companions for 62% of our binaries overall, but we find that this fraction is a strong function of the inner binary orbital period; it ranges from ∼47% for P bin > 30 days to as high as ∼90% for P bin ≲ 5 days. We similarly find an increasing tertiary companion frequency for shorter-period binaries in a secondary sample of Kepler eclipsing binaries observed by Robo-AO. Using Gaia distances, we estimate an upper limit orbital period for each tertiary candidate and compare the tertiary-to-binary period ratios for systems in the field versus those in star-forming regions. Taken all together, these results provide further evidence for angular momentum transfer from three-body interactions, resulting in tight binaries with tertiaries that widen from pre-main-sequence to field ages.