A Soft X-Ray Survey of Hot White Dwarfs with EXOSAT
Abstract
Broadband multicolor soft X-ray photometry of 34 hot white dwarfs is presented, obtained with the Low Energy Imaging Telescopes on Exosat. By combining the soft X-ray fluxes with measurements of the stellar parameters in the UV and optical bands, photospheric He abundances for 16 of the 21 hot DA white dwarfs are derived. Supplemented by five stars previously observed with Einstein, a total of 21 helium abundances is compiled which span a range between He/H less than 10 to the minus 5 and He/H = 1/100, for effective temperatures (Te) between 25,000 and 65,000 K. For the cooler DAs in the sample (Te less than 45,000 K) evidence is found that accretion from the interstellar medium is the dominant mechanism determining the photospheric He content. For the six stars at higher Te, no compelling evidence for a positive correlation between Te and He/H is found.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1989
- DOI:
- 10.1086/167354
- Bibcode:
- 1989ApJ...339.1000P
- Keywords:
-
- Astronomical Photometry;
- White Dwarf Stars;
- X Ray Astronomy;
- Abundance;
- Exosat Satellite;
- Helium;
- Stellar Mass Accretion;
- Stellar Temperature;
- Astrophysics;
- STARS: ABUNDANCES;
- STARS: ATMOSPHERES;
- STARS: WHITE DWARFS;
- STARS: X-RAYS