Carbon, nitrogen, and oxygen abundances in early B-type stars

Abstract

A survey of the C, N, and O abundances in a sample of early B-type stars which was undertaken to test the hypothesis of Liubimkov (1984) that CN-cycled material is mixed to the surfaces of these stars during their core hydrogen-burning phase. Equivalent widths of generally weak lines are obtained using high-signal-to-noise Reticon spectra of 39 stars in four spectral regions. Effective temperatures and gravities for these stars are derived. Projected rotational velocities are measured using a cross-correlation technique. Abundances are derived using LTE methods and non-LTE equivalent width calculations. He, C, N, and O abundances of the nonsupergiant stars in the sample are found to be very close to the values found for the Orion Nebula, with the notable exception of a few stars which show enhanced N, a signature of CN-cycled material. No compelling evidence for a systematic increase in N abundance with evolutonary age was found; thus Liubimkov's claim that mixing occurs generally in main-sequence B stars cannot be confirmed.