Photometric determination of main-sequence binaries with Gaia

Abstract

ABSTRACT Since its launch in 2013, the Gaia space telescope has provided precise measurements of the positions and magnitudes of over 1 billion stars. This has enabled extensive searches for stellar and substellar companions through astrometric and radial velocity measurements. However, these surveys require a prior knowledge of any unresolved companion affecting the results which can be identified using photometry. In this work, Gaia’s magnitude measurements are combined with near-infrared observations from the Two Micron All Sky Survey (2MASS) and Wide-field Infrared Survey Explorer (WISE) catalogues and simulation-based inference is applied to constrain astrophysical parameters and search for hidden companions. This method is first tested on simulated sets of binary stars before expanding to Gaia’s non-single star catalogue. Using this test, a region is identified on the H–R diagram in which the method is the most accurate and all Gaia sources within that region are analysed. This analysis reproduces a known anticorrelation between metallicity and binary fraction. Finally, the method is applied to the nearby star cluster M67 and, using previous studies of the metallicity distribution, it is possible to improve constraints on binary fraction. From this the binary fraction in the cluster is calculated to vary from 30 per cent in the outer cluster to 45 per cent near the core. This is found to be significantly higher the 23 per cent binary fraction calculated for the wider stellar neighbourhood.