Sulfur Abundances in the Orion Association B Stars

TL;DR

This study measures sulfur abundances in ten Orion B stars using LTE and non-LTE models, finding a homogeneous abundance consistent with solar values and minimal sulfur depletion, supporting a shallow galactic abundance gradient.

Contribution

First detailed sulfur abundance analysis of Orion B stars using self-consistent LTE and non-LTE spectrum synthesis methods.

Findings

Sulfur abundance in Orion B stars is homogeneous with A(S)=7.15+/-0.05.

Sulfur abundances agree with solar values and show little depletion onto grains.

Results support a shallow sulfur abundance gradient in the Galaxy.

Abstract

Sulfur abundances are derived for a sample of ten B main-sequence star members of the Orion association. The analysis is based on LTE plane-parallel model atmospheres and non-LTE line formation theory by means of a self-consistent spectrum synthesis analysis of lines from two ionization states of sulfur, SII and SIII. The observations are high-resolution spectra obtained with the ARCES spectrograph at the Apache Point Observatory. The abundance distribution obtained for the Orion targets is homogeneous within the expected errors in the analysis: A(S)=7.15+/-0.05. This average abundance result is in agreement with the recommended solar value (both from modelling of the photospheres in 1-D and 3-D, and meteorites) and indicates that little, if any, chemical evolution of sulfur has taken place in the last ~4.5 billion years. The sulfur abundances of the young stars in Orion are found to agree well with results for the Orion nebulae, and place strong constraints on the amount of sulfur depletion onto grains as being very modest or nonexistent. The sulfur abundances for Orion are consistent with other measurements at a similar galactocentric radius: combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of -0.037+/-0.012 dex/kpc.