Gaia vbroad. Spectral-line Broadening, and binarity

The Gaia DR3 catalogue includes line-broadening measurements (vbroad) for 3524677 stars. We concentrate here on the low-mass main-sequence sub-sample of the catalogue, with BP-RP in the range 1-1.6, which includes 81371 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.