SDSS J184037.78+642312.3: The First Pulsating Extremely Low Mass White Dwarf
Abstract
We report the discovery of the first pulsating extremely low mass (ELM) white dwarf (WD), SDSS J184037.78+642312.3 (hereafter J1840). This DA (hydrogen-atmosphere) WD is by far the coolest and the lowest-mass pulsating WD, with T eff = 9100 ± 170 K and log g = 6.22 ± 0.06, which corresponds to a mass of ~0.17 M ☉. This low-mass pulsating WD greatly extends the DAV (or ZZ Ceti) instability strip, effectively bridging the log g gap between WDs and main-sequence stars. We detect high-amplitude variability in J1840 on timescales exceeding 4000 s, with a non-sinusoidal pulse shape. Our observations also suggest that the variability is multi-periodic. The star is in a 4.6 hr binary with another compact object, most likely another WD. Future, more extensive time-series photometry of this ELM WD offers the first opportunity to probe the interior of a low-mass, presumably He-core WD using the tools of asteroseismology.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2012
- DOI:
- 10.1088/2041-8205/750/2/L28
- arXiv:
- arXiv:1204.1338
- Bibcode:
- 2012ApJ...750L..28H
- Keywords:
-
- binaries: close;
- Galaxy: stellar content;
- stars: individual: SDSS J184037.78+642312.3;
- stars: variables: general;
- white dwarfs;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 5 pages, 3 figures, accepted to ApJ Letters