An Analysis of STIS HST UV Spectra of M33 early B Supergiants

Abstract

We present terminal velocities of M33 B-supergiants, obtained from STIS HST spectra as part of our programme to investigate the Wind Momentum -- Luminosity Relationship (WLR) in the Local Group. Terminal velocities are derived from their NV, CIV, and SiIV resonance lines in UV spectra. Comparing with IUE spectra of Galactic B-supergiants we found evidence of low metallicity in three of our objects. %%The terminal velocities are found to be consistent with the %%values found for Galactic stars, except for B-133. For this The terminal velocities are consistent with the corresponding values of Galactic stars, except for B-133. For this star we find a very large vterm and a red SiIV component deeper than the blue one, that might be an indication of binarity. The average ratio between terminal and turbulent wind velocities is 0.25, well above the value found for Galactic stars.