Mass-dependent multiplicity fraction in low-mass stars revealed by astrometry Gaia

Abstract

Stellar multiplicity at different orbital periods is probed by different techniques: radial velocities at the shortest periods, direct imaging at the longest, and astrometry in between. DR3 provides unprecedented astrometric information to constrain binary populations with periods of tens to thousands of days. Beyond the small fraction of direct orbit solutions, publishes coarser astrometric diagnostics for all objects, such as on-sky accelerations, jerks, or the single-star goodness-of-fit measure, RUWE. We show that these diagnostics together are sensitive to a far wider range of orbital periods than orbit solutions alone. Built on the Gaia Gaia Gaiamock emulator, we developed a forward-modelling framework to constrain rates of multiplicity from data, using all astrometric solution types. We applied this framework to 366 027 primaries of 0.20--0.75,M_⊙ between 50 and 200,pc, including vastly more M-type stars than previous multiplicity studies. For fiducial models of the period and mass-ratio distributions, the inferred multiplicity fraction is approximately constant at ∼45% from the solar-type regime down to 0.40,M_⊙, only then dropping to ∼15% by 0.20,M_⊙. This mass-multiplicity relationship revises the conventional picture of a monotonically rising mass--multiplicity relation, and aligns the upper M-type regime with solar-type stars rather than placing it on a continuous decline. Gaia