2004A&A...415..349R

We have re-analyzed the Galactic O-star sample from Puls (1996A&A...305..171P) by means of line-blanketed NLTE model atmospheres in order to investigate the influence of line-blocking/blanketing on the derived parameters. The analysis has been carried out by fitting the photospheric and wind lines from H and He. In most cases we obtained a good fit, but we have also found certain inconsistencies which are probably related to a still inadequate treatment of the wind structure. These inconsistencies comprise the line cores of H_γ and H_β in supergiants (the synthetic profiles are too weak when the mass-loss rate is determined by matching H_α) and the ``generalized dilution effect'' (cf. Voels, 1989ApJ...340.1073V) which is still present in HeI 4471 of cooler supergiants and giants. Compared to pure H/He plane-parallel models we found a decrease in effective temperatures which is largest at earliest spectral types and for supergiants (with a maximum shift of roughly 8000K). This finding is explained by the fact that line-blanketed models of hot stars have photospheric He ionization fractions similar to those from unblanketed models at higher T<sub>eff</sub> and higher logg. Consequently, any line-blanketed analysis based on the He ionization equilibrium results in lower T<sub>eff</sub>-values along with a reduction of either logg or helium abundance (if the reduction of logg is prohibited by the Balmer line wings). Stellar radii and mass-loss rates, on the other hand, remain more or less unaffected by line-blanketing. We have calculated ``new'' spectroscopic masses and compared them with previous results. Although the former mass discrepancy Herrero et al. (1992A&A...261..209H) becomes significantly reduced, a systematic trend for masses below 50M_☉ seems to remain: The spectroscopically derived values are smaller than the ``evolutionary masses'' by roughly 10M<sub>☉</sub>. Additionally, a significant fraction of our sample stars stays over-abundant in He, although the actual values were found to be lower than previously determined. Also the wind-momentum luminosity relation (WLR) changes because of lower luminosities and almost unmodified wind-momentum rates. Compared to previous results, the separation of the WLR as a function of luminosity class is still present but now the WLR for giants/dwarfs is consistent with theoretical predictions. We argue that the derived mass-loss rates of stars with H<sub>α</sub> in emission are affected by clumping in the lower wind region. If the predictions from different and independent theoretical simulations (Vink et al., 2000A&A...362..295V; Pauldrach et al., 2003, in Proc. IAU Symp., 209, in press; 03, Puls et al., 2003, in Proc. IAU Symp., 212, 61) that the WLR should be independent of luminosity class were correct, a typical clumping factor <ρ<sup>2</sup>>/<ρ><sup>2</sup>≃5 should be derived by ``unifying'' the different WLRs.