Studies of Hot B Subdwarfs. V. Continuing Investigation of the C, N, and SI Abundance Patterns in the Atmospheres of sdB Stars

Abstract

High-dispersion ultraviolet observations of two hot, hydrogen-rich subdwarfs have been obtained with the IUE observatory and are presented. These data are analyzed with model atmosphere techniques, and element abundances for C, N, and Si are derived. Both PG 0342 + 026 (Te = 21,800 K) and PG 1104 + 243 (Te = 27,200 K) display abundances of these ions consistent with trends observed previously in generally hotter sdB and sdOB stars. In particular, the strong silicon underabundance observed in those is also seen in PG 1104 + 243. These results provide additional constraints on current models invoking element diffusion - with or without competing particle transport processes - as the source of the abundance peculiarities observed in hot, hydrogen-rich subdwarfs.