Chemical Homogeneity in the Orion Association: Oxygen Abundances of B Stars

TL;DR

This study determines that B stars in the Orion association have a uniform oxygen abundance of approximately 8.78, indicating chemical homogeneity consistent with previous findings and comparable to solar neighborhood values.

Contribution

It provides non-LTE oxygen abundance measurements for Orion B stars using fully blanketed models, demonstrating chemical homogeneity with improved precision over earlier LTE-based studies.

Findings

Oxygen abundance in Orion B stars is uniform with a small dispersion.

The average oxygen abundance aligns with previous studies but with reduced scatter.

Results support chemical homogeneity in the Orion association.

Abstract

We present non-LTE oxygen abundances for a sample of B stars in the Orion association. The abundance calculations included non-LTE line formation and used fully blanketed non-LTE model atmospheres. The stellar parameters were the same as adopted in the previous study by Cunha & Lambert (1994). We find that the young Orion stars in this sample of 10 stars are described by a single oxygen abundance with an average value of A(O)=8.78 and a small dispersion of +/- 0.05 dex, which is of the order of the uncertainties in the analysis. This average oxygen abundance compares well with the average oxygen abundance obtained previously in Cunha & Lambert (1994): A(O) = 8.72 +/- 0.13 although this earlier study, based upon non-blanketed model atmospheres in LTE, displayed larger scatter. Small scatter of chemical abundances in Orion B stars had also been found in our previous studies for neon and argon; all based on the same effective temperature scale. The derived oxygen abundance distribution for the Orion association compares well with other results for the oxygen abundance in the solar neighborhood.