Exploring Thousands of Nearby Hierarchical Systems with Gaia and Speckle Interferometry

Abstract

There should be about 10,000 stellar hierarchical systems within 100 pc with primary stars more massive than 0.5 M ⊙, and a similar amount of less-massive hierarchies. A list of 8000 candidate multiples is derived from wide binaries found in the Gaia Catalog of Nearby Stars where one or both components have excessive astrometric noise or other indicators of inner subsystems. A subset of 1243 southern candidates were observed with high angular resolution at the 4.1 m Southern Astrophysical Research Telescope, and 503 new pairs with separations from 0.″03 to 1″ were resolved. These data allow estimation of the inner mass ratios and periods, and help to quantify the ability of Gaia to detect close pairs. Another 621 hierarchies with known inner periods come from the Gaia catalog of astrometric and spectroscopic orbits. These two nonoverlapping groups, combined with existing ground-based data, bring the total number of known nearby hierarchies to 2754, reaching a completeness of ∼22% for stars above 0.5 M ⊙. Distributions of their periods and mass ratios are briefly discussed, and the prospects of further observations are outlined.