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J. J. Drake (Smithsonian Astrophysical Observatory), K. Werner (Institut für Astronomie und Astrophysik, Universität Tübingen)
The soft X-ray emission from non-interacting hot white dwarfs (WDs) is the manifestation of the Wein tail of their photospheric spectra. In this context, the ROSAT PSPC pulse height spectrum of the peculiar He-rich hot WD KPD~0005+5106 provided a great surprise when first analysed. It exhibited more short wavelength flux than expected, and defied the best non-LTE modelling attempts in terms of photospheric emission. Instead, Fleming, Werner & Barstow found that a thermal plasma model with a temperature of 2-3\times 105~K provided a much better match to the data. KPD~0005+5106 then appeared to be a unique object: it was the only known WD with a corona. However, a high resolution Chandra LETG+HRC-S spectrum of KPD~0005+5106 lacks the spectral shape of thermal bremsstrahlung and narrow lines of H-like and He-like C expected from a coronal plasma. Instead, there is a more continuous broad peak in emission between 40 and 50~Å, in addition to the expected photospheric emission toward longer wavelengths. We show here that the former component does not come from a corona, but arises from photospheric layers that become more transparent at those wavelengths. This flux is highly sensitive to the adopted Fe abundance and provides a rough Fe abundance diagnostic for KPD~005+5106.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.