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K.A. Venn, M. Dieng (Macalester College), D.J. Lennon (ING-La Palma), R.P. Kudritzki (USM-MPIA)
The wind momentum-luminosity relationship (WLR) is a purely spectroscopic method to determine the intrinsic luminosity of OBA-type supergiants. Given that these are the most luminous stars in a galaxy, then the WLR is a new and independent distance indicator. The stellar wind parameters required by the WLR are currently not well understood though, e.g., mass loss rates (dM/dt) are known to be metallicity dependent, and yet the uncertainties in the simple functional form of dM(z)/dt versus the actual value for an individual star can be substantial. The effects of metallicity on the terminal velocities of stellar winds (Vt),another parameter that is needed for application of the WLR, is currently unknown. In this poster, we will present new terminal velocities of A-type supergiants in the Magellanic Clouds from HST GHRS data. We do find evidence for a metallicity effect on the maximum Vt values, although star-to-star variations in Vt (per spectral type and luminosity) are more substantial. In the WLR, large variations in Vt correspond to smaller uncertainties in luminosity, yielding a preliminary estimate of the uncertainty in distance due our observed variations in Vt as only ~15
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