Chemical Abundances for a Sample of Southern OB Stars

Abstract

Chemical abundances are presented for carbon, nitrogen, oxygen, magnesium, aluminum, silicon, and sulfur in a sample of 25 OB stars that are members of open clusters, OB associations, and H II regions having Galactocentric distances that lie inside the solar Galactic orbit. The elemental abundances are derived from fits of observed high-resolution spectra to non-LTE synthetic line profiles. Our effective temperature scale is based on calibrations of the Stromgren photometric indices coupled to Hγ line profiles. For stars without Stromgren indices, the reddening-free Q-parameter, defined from UBV photometry is used, with the Q-parameter calibrated against Teff for stars that have Stromgren photometry. We also investigated other effective temperature scales from the literature and conclude that adoption of these other Teff scales, which typically result in lower temperatures, produces dependences of the derived abundances with Teff. Our non-LTE abundances reveal dispersions that are very similar to those expected from the analysis uncertainties. The solar abundances, some of which have been recently revised, fall within the abundance distributions defined by this sample of inner disk OB stars for all seven studied elements.