Spectral analysis of the OB subdwarf HD 149382.

Abstract

The ultraviolet and blue spectrum of the OB subdwarf HD 149 382 is analyzed in an investigation of the star's evolutionary status. An effective temperature of 35,000 + or - 2000 K is derived from fitting the observed continuum, hydrogen lines and helium lines to fluxes of unblanketed non-LTE models. LTE analyses of heavy-element lines yield deficiencies of carbon and oxygen and normal nitrogen abundance compared to the sun, which indicates the CNO cycle's possession of the material. Calcium is overabundant, phosphorus and sulfur are normal, and aluminum and silicon are deficient. A tentative explanation of the abundance pattern in terms of the diffusion hypothesis is proposed, and the C/N/O abundance ratios indicate that the CNO cycle operated on a mixture which originally may have been poorer in the heavier elements than the solar mixture.