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), comprising 9 supergiants and 3 giants. A morphological comparison with Galactic analogues 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 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 We also include unpublished STIS observations of two late O-type stars in the SMC.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 the B-type observations, and published O-type data, we now have an extensive ultraviolet spectral library of metal-deficient stars, of 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.