Deposing the Cool Corona of KPD 0005+5106

The ROSAT PSPC pulse height spectrum of the peculiar He-rich hot white dwarfKPD 0005+5106 provided a great surprise when first analysed by Fleming, Werner& Barstow (1993). It defied the best non-LTE modelling attempts in terms ofphotospheric emission from He-dominated atmospheres including C, N and O andwas instead interpreted as the first evidence for a coronal plasma around awhite dwarf. We show here that a recent high resolution Chandra LETGS spectrumhas more structure than expected from a thermal bremsstrahlung continuum andlacks the narrow lines of H-like and He-like C expected from a coronal plasma.Moreover, a coronal model requires a total luminosity more than two orders ofmagnitude larger than that of the star itself. Instead, the observed 20-80 AAflux is consistent with photospheric models containing trace amounts of heavierelements such as Fe. The soft X-ray flux is highly sensitive to the adoptedmetal abundance and provides a metal abundance diagnostic. The weak X-rayemission at 1 keV announced by O'Dwyer et al (2003) instead cannot arise fromthe photosphere and requires alternative explanations. We echo earlierspeculation that such emission arises in a shocked wind. Despite the presenceof UV-optical O VIII lines from transitions between levels n=7-10, no X-ray OVIII Ly alpha flux is detected. We show that O VIII Lyman photons can betrapped by resonant scattering within the emitting plasma and destroyed byphotoelectric absorption.Comment: 15 Pages, 4 figures. Accepted for the Astrophysical Journa