Discovery, TESS Characterization, and Modeling of Pulsations in the Extremely Low Mass White Dwarf GD 278

ISACC D. LOPEZ; J. J. HERMES; LEILA M. CALCAFERRO; KEATON J. BELL; ADAM SAMUELS; ZACHARY P. VANDERBOSCH; ALEJANDRO H. CÓRSICO; ALINA G. ISTRATE

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2021

0004-637X

We report the discovery of pulsations in the extremely low mass (ELM), likely helium-core white dwarf GD 278 via ground- and space-based photometry. GD 278 was observed by the Transiting Exoplanet Survey Satellite (TESS) in Sector 18 at a 2-min cadence for roughly 24 d. The TESS data reveal at least 19 significant periodicities between 2447 − 6729 s, one of which is the longest pulsation period ever detected in a white dwarf. Previous spectroscopy found that this white dwarf is in a 4.61 hr orbit with an unseen >0.4 M⊙ companion and has T eff = 9230 ± 100 K and log g = 6.627 ± 0.056, which corresponds to a mass of 0.191 ± 0.013 M⊙ . Patterns in the TESS pulsation frequencies from rotational splittings appear to reveal a stellar rotation period of roughly 10 hr, making GD 278 the first ELM white dwarf with a measured rotation rate. The patterns inform our mode identification for asteroseismic fits, which unfortunately do not reveal a global best-fit solution. Asteroseismology reveals two main solutions roughly consistent with the spectroscopic parameters of this ELM white dwarf, but with vastly different hydrogen-layer masses; future seismic fits could be further improved by using the stellar parallax. GD 278 is now the tenth known pulsating ELM white dwarf; it is only the fifth known to be in a short-period binary, but is the first with extended, space-based photometry.