The Ultraviolet and Optical Spectra of Luminous B-Type Stars in the Small Magellanic Cloud

Abstract

We present ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) of 12 early B-type stars in the Small Magellanic Cloud (SMC), composed of nine supergiants and three giants. A morphological comparison with Galactic analogs is made using archival data from the International Ultraviolet Explorer (IUE). In general, the intensity of the P Cygni emission in the UV resonance lines is greater and is seen to later spectral types in the Galactic spectra than in their metal-deficient SMC counterparts. We attribute these effects as most likely arising from weaker stellar winds in the SMC targets, as predicted by radiatively driven wind theory. We also include unpublished STIS observations of two late O-type stars in the SMC. In combination with published O-type STIS data, we now have an extensive ultraviolet spectral library of metal-deficient stars to use in the study of unresolved starbursts and high-redshift star-forming galaxies. In this context, we present empirical measurements for the B-type spectra of the new ``1978 index'' suggested by Rix et al. as a probe of metallicity in such systems.