Hot DA white dwarfs seen with Einstein, an ultrahot H- and HE-poor white dwarf and Zanstra temperatures of planetary nebula nuclei.
Abstract
Einstein observations of hot DA white dwarfs are analyzed using model atmospheres. It is found that, for a relatively limited sample of stars, that hot He-poor stars like HZ 43 are indeed the exception, and that there is an apparent correlation between He/H ratio and increasing temperature. The seventh brightest soft X-ray source in the HEAO-A1 catalog, H1504+65, turns out to be an ultrahot white dwarf star, with a temperature of approximately 160,000 K, showing spectral features of the Zanstra method for determining the temperatures of central stars of planetary nebulae demonstrates that the H I Zanstra temperatures are indeed reliable and suggests that a substantial fraction of these central stars have He/H ratios which are considerably less than the solar value.
- Publication:
-
Memorie della Societa Astronomica Italiana
- Pub Date:
- 1987
- Bibcode:
- 1987MmSAI..58...49S
- Keywords:
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- Abundance;
- Planetary Nebulae;
- Spaceborne Astronomy;
- Stellar Spectrophotometry;
- Stellar Temperature;
- White Dwarf Stars;
- Emission Spectra;
- Heao 2;
- Helium;
- Hot Stars;
- Hydrogen;
- Line Spectra;
- Astrophysics