The Nebular Environment and Enigmatic Hard X-Ray Emission of the Hot DO White Dwarf KPD 0005+5106
Abstract
We have detected an ionized nebula around the hot DO white dwarf KPD 0005+5106 and used the [O III]/Hα ratios and nebular velocities to separate this nebula from the background H II region of AO Cas. The angular size of the [O III] nebula of KPD 0005+5106 is ~3°. The velocity of this nebula is similar to those of the local interstellar H I gas and the interstellar/circumstellar absorption lines in the UV spectra of KPD 0005+5106 but has a large offset from those of the stellar photospheric lines. The mass of the ionized nebula, ~70 Msolar, indicates that it consists of interstellar material and that the velocity offset between the star and the ambient medium should not be interpreted as a wind outflow. We have also analyzed the ROSAT PSPC observation of KPD 0005+5106 to determine its hard X-ray luminosity. Using the LX/Lbol relation for late-type stars and the lack of obvious near-IR excess of KPD 0005+5106, we exclude the possible existence of a binary companion with coronal activity. Without a wind outflow, the presence of stellar O VIII emission requires that X-rays at energies greater than 0.871 keV are present in the vicinity of KPD 0005+5106. This hard X-ray emission is most puzzling, since neither photospheric emission at such high energies nor a high-temperature corona is expected from current stellar atmospheric models of KPD 0005+5106. X-ray observations with high angular resolution and sensitivity are needed to confirm the positional coincidence and to enable X-ray spectral analyses for constraining the physical origin of the hard X-ray emission from KPD 0005+5106.
- Publication:
-
The Astronomical Journal
- Pub Date:
- November 2004
- DOI:
- 10.1086/424942
- arXiv:
- arXiv:astro-ph/0408363
- Bibcode:
- 2004AJ....128.2357C
- Keywords:
-
- ISM: H II Regions;
- ISM: Planetary Nebulae: General;
- Stars: Individual: Alphanumeric: KPD 0005+5106;
- Stars: White Dwarfs;
- Astrophysics
- E-Print:
- LaTeX, 17 pages, 4 figures, Accepted for publication in the AJ, Nov issue