Two unseen massive white dwarf candidates in close binaries

Abstract

We report the discovery of two binary systems, each consisting of a slightly bloated G-type main-sequence star and an unseen companion, identified through photometric data from TESS and radial velocity variation from Gaia. High-resolution spectroscopy confirms orbital periods of 1.37 and 2 .67 d with circular orbits. The visible components have masses of $\sim$0.9--1.0$M_{\odot }$, while the minimum masses of the unseen companions are $1.078_{-0.060}^{+0.058}{M}_{\odot }$ and $0.943_{-0.049}^{+0.048}{M}_{\odot }$, respectively. Assuming tidal synchronization, we estimate the companion masses to be $1.13_{-0.08}^{+0.11}{M}_{\odot }$ and $1.05_{-0.10}^{+0.15}{M}_{\odot }$. The absence of detectable spectral features from the companions rules out main-sequence stars of these masses, suggesting that the unseen companions are likely O/Ne or C/O massive white dwarfs. The short orbital periods imply that these systems are post-common envelope binaries. Their subsequent evolution is uncertain, with possible outcomes including cataclysmic variables, Type Ia supernovae, or accretion-induced collapse, depending on the nature of future mass transfer.

This article is published in PASJ as open access, published by OUP (https://doi.org/10.1093/pasj/psaf148). 23 pages, 19 figures