The chemical compositions of three main-sequence B-type stars in the Large Magellanic Cloud.

Abstract

High-resolution observations of three B-type main-sequence stars in the Large Magellanic Cloud (LMC) have been obtained with the UCL echelle spectrograph on the 3.9-m Anglo-Australian Telescope. These spectra and IUE low-resolution spectroscopic data have been analysed using LTE model-atmosphere techniques, to derive stellar atmospheric parameters and chemical compositions. As these stars lie on the hydrogen burning main-sequence, their surface abundances should reflect those of the present-day interstellar medium. From a differential analysis of LH 104-24 and PS 34-16 performed relative to the Galactic B-type stars τ Sco and γ Peg, we conclude that there exists a general heavy-element underabundance of ~0.3dex within the LMC, but there is some evidence to suggest that these stars possess different oxygen and silicon abundances. The third star, PS 34-144, exhibits chemical anomalies, with a helium underabundance of 0.5dex and a mean metal deficiency of approximately 0.8dex. We classify this object as a Helium-weak star that is a member of the LMC. However, as additional processes such as diffusion may have occurred in its atmosphere, we do not believe that element abundances derived for PS 34-144 to be representative of the progenitor interstellar material.