Revealing unresolved white dwarf-main sequence binaries using Gaia DR3 and GALEX

I. A Volume limited study of 100 pc

Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña MacKenna 4860, 7820436 Santiago, Chile

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Received: 9 November 2024
Accepted: 20 March 2026

Abstract

Context. Understanding the demographics of white dwarf-main sequence (WDMS) binaries is key to uncovering the formation of various stellar exotica and refining the details of binary stellar evolution. Despite several dedicated efforts to identify unresolved WDMS binaries, their population remains incomplete, even within a 100 pc volume-limited sample.

Aims. This study aims to identify WDMS binaries hidden within the MS of the optical color-magnitude diagram (CMD), improving the completeness of WDMS binaries within a volume-limited sample of 100 pc.

Methods. We used near-ultraviolet (NUV)-optical CMDs to distinguish unresolved WDMS binaries from the rest of the populations. High-precision astrometric and photometric data from Gaia DR3 and NUV data from GALEX GR6/7 were combined to construct CMDs. Using the binary spectral energy distribution (SED) fitting algorithm within the Virtual Observatory SED Analyzer (VOSA) tool, we estimated stellar parameters such as effective temperature, bolometric luminosity, and radii. The WD masses were determined using WD evolutionary models. As we used the sources that were only detected in the NUV band of GALEX, this study directly complements the majority of the previous studies.

Results. We identify 347 WDMS binary candidates within 100 pc, with 188 being newly reported. Our method predominantly identifies binaries with cooler WDs (≤10 000 K) compared to previous studies. The WD masses range from ∼0.2 and 1.3 M_⊙, and most MS companions are of M spectral type.