Gaia vbroad: Spectral-line broadening and binarity

Abstract

The Gaia DR3 catalogue includes line-broadening measurements (vbroad) for 3 524 677 stars. We concentrate here on the low-mass main-sequence (MS) sub-sample of the catalogue, with (G_BP ‑ G_RP)₀ in the range of 1–1.6, which includes 81 371 sources. The colour-magnitude diagram of the sample displays two distinct strips, the brighter of which is probably mostly composed of unresolved binaries, with mass ratios close to unity. We show that the suspected binary sub-sample displays a larger vbroad distribution, which we attribute to the unresolved absorption lines of the two components of each binary. A similar effect is seen in the GALAH data.