S. M. Haser

O-star winds in the Magellanic Clouds and the Milky Way. A modified empirical analysis of UV P-Cygni profiles

UV P-Cygni profiles of OB-stars in the Magellanic Clouds (observed with HST), and the galaxy (observed with IUE) are analyzed empirically using a line formation procedure similar to the one described by Lamers et al. (1987). The assumption of a constant microturbulencevturb throughout the wind is dropped and replaced by a radially increasing turbulence parametervturb(v), thus improving the fit for the emission peaks substantially, and at the same time avoiding the need for a justification of extremely supersonic turbulence in the vicinity of the winds sonic point. The Sobolev optical depth is determined interatively at fixed velocities in the wind, which removes the bias introduced by the choice of a specific parameterization function. Where it was possible and necessary a full photospheric spectrum was used to illuminate the wind line. The terminal velocitiesv∞ are are found to be largest in the Galaxy, smallest in the Small Magellanic Cloud, and intermediate or similar to galactic in the Large Cloud.

Hubble space telescope spectroscopy of massive hot stars in the Magellanic Clouds and M31

Using the Hubble Space Telescope (HST) and the Faint Object Spectrograph (FOS) high signal to noise spectrograms were obtained for 15 OB stars in the Magellanic Clouds***, three of which are of spectral type O3. The data cover the spectral region from 1150 A–2300 A with a resolution of Δλ/λ ≈ 1 A. One O8.5 supergiant, OB78#231, in M31 ‡is also included in this work. These data are a substantial improvement on previous high resolution IUE observations in the Magellanic Clouds (Walborn et al. 1985 and references therein) because of the smaller aperture and the much better signal to noise ratio, while no high resolution UV spectra of O stars in M31 have been obtained before. In this paper we discuss various morphological aspects of the spectra, concerning metallicity and the stellar winds, compared to galactic analogues.