Measurement of the EUV Spectrum of the Hot White Dwarf Feige 24

Abstract

A high-resolution EUV spectrum of the hot white dwarf Feige 24 in the 190-350 A range is presented. It is demonstrated that, in this region, the measured spectrum deviates strongly from energy distributions calculated from LTE homogeneous model atmospheres for hot DA white dwarfs. The data cannot be fitted with a pure hydrogen spectrum nor with a spectrum for a homogeneous mixture of H, traces of He, and metals, at parameter values derived from the optical and UV spectrum. Some suggestions for more refined model atmospheres are briefly discussed.