Discovery of an Ultramassive Pulsating White Dwarf
Abstract
We announce the discovery of the most massive pulsating hydrogen-atmosphere white dwarf (WD) ever discovered, GD 518. Model atmosphere fits to the optical spectrum of this star show it is a 12, 030 ± 210 K WD with a log g =9.08 ± 0.06, which corresponds to a mass of 1.20 ± 0.03 M ⊙. Stellar evolution models indicate that the progenitor of such a high-mass WD endured a stable carbon-burning phase, producing an oxygen-neon-core WD. The discovery of pulsations in GD 518 thus offers the first opportunity to probe the interior of a WD with a possible oxygen-neon core. Such a massive WD should also be significantly crystallized at this temperature. The star exhibits multi-periodic luminosity variations at timescales ranging from roughly 425 to 595 s and amplitudes up to 0.7%, consistent in period and amplitude with the observed variability of typical ZZ Ceti stars, which exhibit non-radial g-mode pulsations driven by a hydrogen partial ionization zone. Successfully unraveling both the total mass and core composition of GD 518 provides a unique opportunity to investigate intermediate-mass stellar evolution, and can possibly place an upper limit to the mass of a carbon-oxygen-core WD, which in turn constrains Type Ia supernovae progenitor systems.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2013
- DOI:
- 10.1088/2041-8205/771/1/L2
- arXiv:
- arXiv:1306.4024
- Bibcode:
- 2013ApJ...771L...2H
- Keywords:
-
- stars: evolution;
- stars: individual: GD 518;
- stars: oscillations;
- stars: variables: general;
- supernovae: general;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 5 pages, 3 figures, Astrophysical Journal Letters, 771, L2 (2013)