FUSE Observations of Heavy Elements in the Photospheres of Cool DB White Dwarfs
Abstract
We present a comprehensive analysis of the far-ultraviolet spectra of five DB white dwarfs spanning the effective temperature range between 14,700 and 20,800 K. The FUSE line analysis shows that carbon features, previously observed in several hot DB stars at or above 22,000 K, are present in the two coolest (GD 408 and GD 378) and in the hottest (G270-124) target. The observed carbon abundances range from log N(C)/N(He) ~ - 6.9 to ~ - 8.8. In addition, four of the five objects display photospheric lines of silicon. Other elements such as oxygen, iron, and sulfur are also observed in some objects. The variations of the abundances of heavy elements as a function of effective temperature in DB stars are discussed in terms of a competition between a stellar wind, gravitational settling, accretion from interstellar (and circumstellar) matter, and convective dredge-up.
FUSE is operated by the Johns Hopkins University under NASA contract NAS5-32985.- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2008
- DOI:
- 10.1086/523699
- Bibcode:
- 2008ApJ...672..540D
- Keywords:
-
- ultraviolet: stars;
- white dwarfs