The High-Resolution Photospheric Soft X-Ray Spectrum of Sirius B

Abstract

The authors present the high-resolution soft X-ray spectrum of the hot white dwarf Sirius B, as measured with the 500 lines mm^-1 transmission grating spectrometer on EXOSAT. The X-rays are of purely photospheric origin. Using a large grid of model atmospheres, the authors determine the effective temperature of Sirius B with high accuracy. It is shown that a consistent description of the complete electromagnetic spectrum of Sirius B, from optical to X-ray wavelengths, is now possible. This solution requires T_e to be in the range 25,000 - 26,000K, dependent on the choice of the other parameters, and the gravity to be in the range log g = 8.5 - 8.7.