Terminal velocities of luminous, early-type stars in the Small Magellanic Cloud

Ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) are used to determine terminal velocities for 11 O and B-type giants and supergiants in the Small Magellanic Cloud (SMC) from the Si iv and C iv resonance lines. Using archival data from observations with the Goddard High-Resolution Spectrograph and the International Ultraviolet Explorer telescope, terminal velocities are obtained for a further five B-type supergiants. We discuss the metallicity dependence of stellar terminal velocities for supergiants, finding no evidence for a significant scaling between Galactic and SMC metallicities for T-eff < 30,000 K, consistent with the predictions of radiation-driven wind theory. A comparison of the v(∞)/v(esc) ratio between the SMC and Galactic samples, while consistent with the above statement, emphasizes that the uncertainties in the distances to galactic OB-type stars are a serious obstacle to a detailed comparison with theory. For the SMC sample there is considerable scatter in v(∞)/v(esc) at a given effective temperature, perhaps indicative of uncertainties in stellar masses.