The chemical compositions of four B-type stars in the Small Magellanic Cloud.

Abstract

High-resolution echelle spectra of three main-sequence B-type stars and one B-type giant in the Small Magellanic Cloud (SMC) have been obtained using the 3.9 m Anglo-Australian Telescope. These spectra have been analyzed in conjunction with IUE low-resolution spectra by using LTE model atmosphere techniques, to derive the stellar atmospheric parameters and photospheric chemical compositions; the latter should reflect that of the current interstellar medium within the SMC. From a differential analysis performed relative to the Galactic B-type stars τ Sco and 67 Oph, the SMC stars appear to have a mild helium deficiency (of 0.1-0.2 dex), and a general heavy element depletion of approximately -0.8 dex. Nitrogen is found to be significantly more underabundant (< -1.1 dex) and oxygen is possibly less depleted (-0.5 dex) than the average. There is also marginal evidence for variations in the chemical compositions derived for different stars, suggesting that the interstellar medium of the SMC may not be homogeneous.