Carbon, Nitrogen and Oxygen Abundances in Atmospheres of the 5-11 M B-type Main Sequence Stars

TL;DR

This study determines the carbon, nitrogen, and oxygen abundances in 22 B-type main sequence stars, confirming their initial atmospheric compositions align with cosmic standards and previous findings.

Contribution

First detailed non-LTE analysis of C, N, O in B-type stars with a focus on their initial abundances and comparison with cosmic standards.

Findings

Mean C, N, O abundances match recent nearby B star data.

Results agree with the Cosmic Abundance Standard.

Excluding potential mixed stars yields consistent abundance values.

Abstract

Fundamental parameters and the carbon, nitrogen and oxygen abundances are determined for 22 B-type stars with distances up to 600 pc and slow rotation (vsini up to 66 km/s). The stars are selected according to their effective temperatures Teff and surface gravities log g, namely: Teff is between 15300 and 24100 K and log g is mostly greater than 3.75; therefore, stars with medium masses of 5-11 M are selected. Theory predicts for the stars with such parameters that the C, N and O abundances in their atmospheres should correspond to their initial values. Non-LTE analysis of C II, N II and O II lines is implemented. The following mean C, N and O abundances are obtained: log \epsilon(C) = 8.31+-0.13, log \epsilon(N) = 7.80+-0.12 and log \epsilon(O) = 8.73+-0.13. These values are in very good agreement with recent data on the C, N and O abundances for nearby B stars from other authors; it is important that different techniques are applied by us and other authors. When excluding for the stars HR 1810 and HR 2938, which can be mixed, we obtain the following mean abundances for the remaining 20 stars: log \epsilon(C) = 8.33+-0.11, log \epsilon(N) = 7.78+-0.09 and log \epsilon(O) = 8.72+-0.12; these values are in excellent agreement with a present-day Cosmic Abundance Standard (CAS) of Nieva & Przybilla.