Discovery of highly ionized species in the ultraviolet spectrum of Feige 24.

Abstract

A high-resolution ultraviolet spectrum of the nearby (90 pc) white dwarf binary Feige 24 (DA + M1-2 V) obtained with the International Ultraviolet Explorer satellite (IUE) reveals two sets of absorption features in the species C IV, Si IV, and N V. The low-velocity component (V approximately 1 km/s) arises from the local interstellar gas apparently ionized by the white dwarf. The second component, at high velocities (V approximately +83 km/s), arises in the atmosphere of the white dwarf in the Feige 24 system. The presence of this large velocity shift supplies the first strong evidence for narrow absorption cores due to high-temperature species in a white dwarf atmosphere. Observations around the orbital period will provide a direct measurement of the gravitational redshift and the mass of the white dwarf. The inferred hydrogen density is 0.008 per cu cm toward this source.