Hubble Space Telescope imaging spectrograph observations of the hot white dwarf in the close binary Feige 24

We obtained and analyzed two Hubble Space Telescope Imaging Spectrograph sp ectra of the white dwarf in the DA plus dMe binary Feige 24. The spectra, o btained at orbital quadratures, provide new estimates of the white dwarf mo tion and gravitational redshift resulting in revised white dwarf parameters . An analysis of interstellar absorption lines reveals the presence of two clouds (+3.1 km s(-1), +17.6 km s(-1)) in the line of sight toward Feige 24 ; one of these clouds (+17.6 km s(-1)) is identified with the "local cloud. " A study of the Ly alpha H I and D I interstellar medium lines shows that the deuterium-to-hydrogen abundance ratio (D/H = 1.3 x 10(-5)) is consisten t with other measurements supporting a relative constancy of this ratio thr oughout the local interstellar medium. The total hydrogen column density me asured with Ly alpha (log n(H) = 2.95 x 10(18) cm(-2)) is in agreement with EUV Lyman continuum flux measurements. Finally, we present a complete abun dance pattern for the white dwarf demonstrating the predominance of iron an d nickel over lighter elements. Residual ionization imbalance in the case o f several elements, most notably in the case of O IV/O V, which cannot be e xplained by temperature or surface gravity variations, may indicate the pre sence of other atmospheric constituents, inhomogeneous stratification of ox ygen in the photosphere, and/or remaining inaccuracies in the treatment of model atoms. The abundance patterns in Feige 24 and in the hot DA white dwa rf G191-B2B are remarkably similar, indicating that the same processes are operating equally in both stars.