Unveiling subarcsecond multiplicity in the Pleiades with Gaia multicolor photometry

Abstract

The list of 409 probable cluster members down to $G=15^{\rm mag}$ ($m \gtrsim 0.5M_\odot$) is compiled for the two degree radius of the Pleiades, based on astrometric data from Gaia DR3 and the PPMXL catalog, along with several radial velocity surveys, including APOGEE and LAMOST. This approach allows for the inclusion of binary stars with unreliable Gaia solutions, thereby eliminating associated bias. Thus, the often-neglected 14 sources with Gaia two-parameter solutions are included. The subsequent analysis of color-magnitude and color-color diagrams exploits artifacts in Gaia photometric data, caused by the different field sizes used to measure fluxes in the $G$, $B_p$, and $R_p$ passbands, to reveal binary stars with subarcsecond angular separation. The findings are validated with prior high-resolution observations. Overall, $24 \pm 3$ cluster members with angular separation between 0.1 and 1 arcsec (13.5 to 135 AU projected distance) and mass ratio $q>0.5$ are deemed binary, indicating a binarity fraction of $6 \pm 1$\%.