A hidden population of massive white dwarfs: two spotted K + WD binaries
Lu, Jessica R.; Fulton, Benjamin J.; Kochanek, Christopher S.; Thompson, Todd A.; Isaacson, Howard; Ilyin, Ilya; Jayasinghe, Tharindu; Martin, David V.; Tucker, Michael A.; Nicholson, Belinda; Abrams, Natasha S.; Lam, Casey Y.; Rowan, Dominick M.
United States, Germany, Australia, United Kingdom
Abstract
The identification and characterization of massive (≳ 0.8 M⊙) white dwarfs is challenging in part due to their low luminosity. Here, we present two candidate single-lined spectroscopic binaries, Gaia DR3 4014708864481651840 and 5811237403155163520, with K-dwarf primaries and optically dark companions. Both have orbital periods of P ~ 0.45 d and show rotational variability, ellipsoidal modulations, and high-amplitude radial velocity variations. Using light curves from the Transiting Exoplanet Survey Satellite (TESS), radial velocities from ground-based spectrographs, and spectral energy distributions, we characterize these binaries to describe the nature of the unseen companion. We find that both systems are consistent with a massive white dwarf companion. Unlike simple ellipsoidal variables, star-spots cause the light-curve morphology to change between TESS sectors. We attempt to constrain the orbital inclination using PHOEBE binary light-curve models, but degeneracies in the light curves of spotted stars prevent a precise determination. Finally, we search for similar objects using Gaia DR3 and TESS, and comment on these systems in the context of recently claimed compact object binaries.