| Abstract: Understanding the demographics of white dwarf-main sequence (WDMS) binaries is crucial for constraining binary stellar evolution and the formation pathways of several exotic stellar populations. Despite extensive efforts, the census of unresolved WDMS binaries remains significantly incomplete, even within the 100 pc volume of the solar neighborhood.
We present a simple and efficient method to identify WDMS binaries that are photometrically hidden within the main-sequence of optical color-magnitude diagrams (CMDs). Applying this technique to a 100 pc volume-limited sample, we identify 347 WDMS binary candidates, of which 188 are newly reported. Our approach exploits NUV-optical CMDs to distinguish unresolved WDMS systems from single stars, combining high-precision astrometry and photometry from Gaia-DR3 with NUV data from GALEX GR6/7.
Stellar parameters (effective temperature, bolometric luminosity, and radius) are estimated using binary spectral energy distribution fitting with the Virtual Observatory SED Analyzer (VOSA). WD masses are derived using evolutionary cooling models. As we use the sources which are detected only in NUV band of GALEX, this study directly complements to majority of the previous studies. Consequently, our method preferentially identifies systems with cooler WD companions (≲10,000 K). The inferred WD masses span ~0.2-1.3 M⊙, and the majority of main-sequence companions are M-type stars.
A significant fraction of our candidates is independently supported by spectroscopic observations from Gaia, LAMOST, SDSS-V, and other archival surveys. Accounting for the incomplete sky coverage of GALEX and avoidance of the Galactic plane, we estimate a conservative lower limit of ~2% for the catalog completeness. This methodology is readily applicable to forthcoming UV missions, such as INSIST, and when combined with Gaia, it offers a powerful route toward a more complete, volume-limited census of WDMS binaries within 100 pc. |
