NLTE analysis of the unique pre-white dwarf H 1504+65.

Abstract

High S/N optical spectra and line profile fits with line-blanketed non-LTE model atmospheres show that H 1504 + 65 is the hottest star ever analyzed by model atmosphere methods. It is also noted that the atmospheric composition of this prewhite dwarf is almost entirely carbon and oxygen by equal parts, and that it is virtually devoid of H and He. These findings imply that this dwarf is an extreme PG 1159 star, which has lost its entire H and He envelopes as a result of a late He shell flash; its mass, however, is considerably higher than the mean mass of white dwarfs and the PG 1159 stars. It accordingly represents the naked core of a former ABG red giant, allowing further research to probe the thermonuclear C-12(alpha, gamma)O-16 reaction rate.