The closest extremely low-mass white dwarf to the Sun

Abstract

We present the orbit and properties of 2MASS J050051.85-093054.9, establishing it as the closest (d ≈ 71 pc) extremely low-mass white dwarf to the Sun. We find that this star is hydrogen rich with $T_\textrm {eff}\approx 10\, 500$ K, log g ≈ 5.9, and, following evolutionary models, has a mass of ≈0.17 M_⊙. Independent analysis of radial velocity and Transiting Exoplanet Survey Satellite(TESS) photometric time series reveals an orbital period of ≈9.5 h. Its high velocity amplitude ( $K\approx 144~\textrm {km}\, \textrm {s}^{-1}$ ) produces a measurable Doppler beaming effect in the TESSlight curve with an amplitude of 1 mmag. The unseen companion is most likely a faint white dwarf. J0500-0930 belongs to a class of post-common envelope systems that will most likely merge through unstable mass transfer and in specific circumstances lead to Type Ia supernova explosions.