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 0. 9–1. 0\, M_, while the minimum masses of the unseen companions are 1. 078^+0. 058-₀. ₀₆₀\, M_ and 0. 943^+0. 048-₀. ₀₄₉\, M_, respectively. Assuming tidal synchronization, we estimate the companion masses to be 1. 13^+0. 11-₀. ₀₈\, M_ and 1. 05^+0. 15-₀. ₁₀\, M_. 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.
Shiraishi et al. (Mon,) studied this question.