Spectral analysis of the hottest known helium-rich white dwarf: KPD0005+5106.
Abstract
We present a non-LTE model atmosphere analysis of the helium-rich white dwarf KPD0005+5106. The analysis is based on optical spectra obtained at the Calar Alto 3.5m telescope, ultraviolet observations retrieved from the Hubble Space Telescope data archive, and X-ray data recorded during the ROSAT all-sky survey. From the optical and ultraviolet HeII line spectrum we find that KPD0005+5106 is the hottest helium-rich white dwarf known (Teff=120000K, logg=7). The atmospheric parameters place the star within the domain of the PG1159 group, however, the metal abundances in KPD0005+5106 (C=-3.5, N=-4.0, O<=-4, logarithm of number ratio relative to helium) are significantly different from the C- and O-rich PG1159 objects. The hydrogen deficiency suggests that KPD0005+5106 is a late He-flash object. However, the C and N abundances contradict the simple interpretation that He-rich intershell matter (as a product of the CNO burning process) is exposed at the surface after removal of the H-rich envelope by mass-loss. Instead we propose that the metal abundances may result from the interplay of radiative levitation and gravitational settling. The presence of several ultrahigh-excitation features like the OVIII emission lines cannot be explained even with the high photospheric temperature encountered. Furthermore we show that the X-ray spectrum as well cannot be photospheric in origin but may be assigned to a hot corona around KPD0005+5106.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 1994
- Bibcode:
- 1994A&A...284..907W
- Keywords:
-
- Abundance;
- Helium;
- Spectrum Analysis;
- Stellar Atmospheres;
- Stellar Evolution;
- Ultraviolet Spectra;
- Visible Spectrum;
- White Dwarf Stars;
- X Ray Spectra;
- Atmospheric Models;
- Faint Object Camera;
- Hubble Space Telescope;
- Local Thermodynamic Equilibrium;
- Position Sensing;
- Proportional Counters;
- Rosat Mission;
- Spectrographs;
- Astronomy;
- STARS: INDIVIDUAL: KPD0005+5106;
- WHITE DWARFS;
- STARS: ATMOSPHERES;
- STARS: EVOLUTION;
- STARS: ABUNDANCES