Sirius – Like Systems in the Gaia DR3

Evidence of hot white dwarf (WD) components in 722 binary stars with main sequence (MS) primaries was examined by calculating an absolute magnitude excess in the Galaxy Evolution Explorer (GALEX) far-UV (FUV) band. The binary stars selected for this study were characterized by the Gaia Data Processing and Analysis Consortium (DPAC) as having a faint and compact companion in accordance with the Astrometric Mass Ratio Function (AMRF) algorithm of Shahaf et al (2019). The excess calculation was taken as the difference between the absolute FUV magnitude of the collective binary system, and a calculation of the absolute FUV magnitude of the MS component. The former quantity was calculated from the GALEX GR6+7 release of the photometric data, and was scaled to an absolute context using parallax data from the Gaia Data Release 3 (DR3). The MS component FUV magnitudes were calculated from Kurucz (2003) stellar models. For 16 of the binary systems, the astrophysical parameters that characterize the Kurucz models were taken as the results from the Gaia DR3 Astrophysical Parameters Inference System (APSIS). For 13 of the binary systems, astrophysical parameters were obtained from a chi square best of Kurucz stellar models to spectral energy distributions (SEDs), that were constructed from Gaia synthetic optical photometry bands. For these 13systems, the effective temperature, surface gravity, stellar radius and metallicity of the MS component was estimated. In total, 28 binary systems were found to have an FUV excess greater than zero, with 24/28 having an excess of >10 and a maximum FUV excess of ~23. From the FUV excess results, the absolute FUV magnitudes of the possible WD components and the corresponding effective temperatures were estimated from a linear interpolation of WD photometry tables of the state-of-the-art Montréal white dwarf models.