Discovery and Characterization of White Dwarf-FGK Main-Sequence Binaries within the Optical Main-Sequence Locus

TL;DR

This study identifies and characterizes 654 white dwarf-main sequence binaries with FGK companions using multi-source data, revealing their properties and binary nature, and providing a valuable, well-defined sample for binary evolution research.

Contribution

The paper presents a new, large catalog of FGK+white dwarf binaries identified through ultraviolet excess and refined with Gaia and LAMOST data, including detailed component characterization.

Findings

Majority of MS companions are G-type stars (~52%)

Most WDs are low-mass and hot, with many extremely low-mass WDs

Radial velocity variations support close-binary status

Abstract

White dwarf main-sequence (WDMS) binaries provide important laboratories for studying binary evolution and the formation of low-mass white dwarfs. In this work, we identify 654 reliable WDMS candidates with FGK-type companions from an initial set of 772 ultraviolet-excess sources, selected using stellar atmospheric parameters from LAMOST spectroscopy and subsequently refined with \textit{Gaia} DR3 astrometry and photometry together with ultraviolet data from \textit{GALEX}. Candidates were selected based on ultraviolet excess relative to the \textit{Gaia} main-sequence locus and refined using isochrone constraints to exclude systems inconsistent with MS companions. Binary spectral energy distribution fitting yields effective temperatures and radii for both components, as well as distance and extinction estimates. The MS companions are dominated by G-type stars (\(\sim52\%\)), with comparable fractions of F- and K-type companions, and no A-type primaries. Using white-dwarf evolutionary cooling models, we find that the WD components are predominantly low-mass (\(M_{\rm WD}\,\sim\,0.2\text{--}0.4\,M_\odot\)), including a substantial population of extremely low-mass (\(<0.3\,M_\odot\)) WDs likely produced through binary interaction. The WDs are generally hot (\(\sim1.5\times10^4\,\mathrm{K}\)), consistent with the ultraviolet selection bias favoring luminous, large-radius WDs. Multi-epoch LAMOST radial velocities show larger amplitudes than those of a comparison sample of MS stars, supporting the close-binary nature of these systems. Although subject to strong selection effects, the catalog offers a clean and well-characterized sample of FGK+WD binaries.