The Atmosphere of the Helium-Carbon Star BD+10°2179

A fine analysis of the helium-carbon star BD+1O°2179 has been performed by using a grid of con- stant flux models. Opacities considered are: H i, if, He i, He ii, He, C ii, and electron scattering. The C ii opacities are taken from quantum-defect calculations of Peach. The parameters of the models are: Teff = 160000, 180000 K; log g = 2.5, 3.0; X (mass fraction of hydrogen) = 1O3; Z~ (mass fraction of carbon) = 0.035, 0.152, 0.52. The following quantities are computed: He i line profiles, equivalent widths of twenty C ii lines, ionization equilibria of Si li/Si iii and S u/S iii, Dx34~ (He i discontinuity 2aP0~~k) , emergent flux, UBV colors, and bolometric corrections. The model that best represents the observed data is Teff = 160000 K, logg = 2.8, V = 0.45, X = 0.0001, Z~ = 0.55, and vt = 0 km sec1. Great care was taken to include line broadening and turbulent velocity properly. Abundances of thirteen elements are derived and compared with previous analyses. The mass of BD+1O°2179 is estimated to »=O.5 Mo. A preliminary analysis of Popper's star, HD 124448, yields a carbon abundance of Zc = 0 17. On the basis of the high carbon content, the helium stars BD+1O°2179 and HD 124448 are considered to be hot carbon stars. I. INTRODUCTIO