Spectral fine analysis of the extreme helium star BD +10 2179.

Abstract

Line blanketed linear transfer of energy (LTE) model atmospheres were used to analyze UV and visual spectra of the extreme He star BD +10.2179. Model inputs included a temperature within 600 K of 16,000 K, an He component totaling 0.989, and a microturbulent velocity within 1.5 km/sec of 7 km/sec. Hydrogen abundance was calculated to be 0.1% by number, and the star displayed metal abundances very different from that of the sun. C and Mg were found to be overabundant, nitrogen content is close to that of the sun, and an oxygen shortage was projected. A less than one solar mass is indicated, together with a radius within 1.7 solar radius of 6.6 solar radii, and a process of evolution toward white dwarf star is indicated. Finally, the evolutionary directions of other He stars are discussed.