Abstract.We have re-analyzed the Galactic O-star sample from Puls et al. (1996) 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 et al. 1989) which is still present in He  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 8000 K). 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 eff and higher log g. Consequently, any line-blanketed analysis based on the He ionization equilibrium results in lower T eff -values along with a reduction of either log g or helium abundance (if the reduction of log g 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. 1992) becomes significantly reduced, a systematic trend for masses below 50 M seems to remain: The spectroscopically derived values are smaller than the "evolutionary masses" by roughly 10 M . 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 windmomentum 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 α in emission are affected by clumping in the lower wind region. If the predictions from different and independent theoretical simulations (Vink et al. 2000;Pauldrach et al. 2003; Puls et al. 2003a) that the WLR should be independent of luminosity class were correct, a typical clumping factor < ρ 2 > / < ρ > 2 ≈ 5 should be derived by "unifying" the different WLRs.

Abstract. We present new or improved methods for calculating NLTE, line-blanketed model atmospheres for hot stars with winds (spectral types A to O), with particular emphasis on fast performance. These methods have been implemented into a previous, more simple version of the model atmosphere code F (Santolaya-Rey et al. 1997) and allow us to spectroscopically analyze large samples of massive stars in a reasonable time-scale, using state-of-the-art physics. Although this updated version of the code has already been used in a number of recent investigations, the corresponding methods have not been explained in detail so far, and no rigorous comparison with results from alternative codes has been performed. This paper intends to address both topics. In particular, we describe our (partly approximate) approach to solve the equations of statistical equilibrium for those elements that are primarily responsible for line-blocking and blanketing, as well as an approximate treatment of the line-blocking itself, which is based on a simple statistical approach using suitable means of line opacities and emissivities. Both methods are validated by specific tests. Furthermore, we comment on our implementation of a consistent temperature structure. In the second part, we concentrate on a detailed comparison with results from two codes used in alternative spectroscopical investigations, namely  (Hillier & Miller 1998) and -Basic (Pauldrach et al. 2001). All three codes predict almost identical temperature structures and fluxes for λ > 400 Å, whereas at lower wavelengths a number of discrepancies are found. Particularly in the He continua, where fluxes and corresponding numbers of ionizing photons react extremely sensitively to subtle differences in the models, we consider any uncritical use of these quantities (e.g., in the context of nebula diagnostics) as unreliable. Optical H/He lines as synthesized by  are compared with results from , obtaining a remarkable coincidence, except for the He singlets in the temperature range between 36 000 to 41 000 K for dwarfs and between 31 000 to 35 000 K for supergiants, where  predicts much weaker lines. Consequences of these discrepancies are discussed.Finally, suggestions are presented as to adequately parameterize model-grids for hot stars with winds, with only one additional parameter compared to standard grids from plane-parallel, hydrostatic models.

Abstract. We study mass-loss and wind momentum rates of 29 Galactic O-type stars with luminosity classes I, III and V by means of a pure Hα profile analysis and investigate to what extent the results compare to those originating from a state-ofthe-art, complete spectral analysis. Our investigation relies on the approximate method developed by Puls et al. (1996) which we have modified to account for the effects of line-blanketing. Effective temperatures and gravities needed to obtain quantitative results from such a simplified approach have been derived by means of calibrations based on most recent spectroscopic NLTE analyses and models of Galactic stars by Repolust et al. (2003) and Martins et al. (2002). Comparing (i) the derived winddensities to those determined by Repolust et al. (2003) for eleven stars in common and (ii) the Wind-momentum Luminosity Relationship (WLR) for our sample stars to those derived by other investigations, we conclude that our approximate approach is actually able to provide consistent results. Additionally, we studied the consequences of "fine tuning" some of the direct and indirect parameters entering the WLR, especially by accounting for different possible values of stellar reddening and distances. Combining our data set with the corresponding data provided by Herrero et al. (2002) and Repolust et al. (2003) we finally study the WLR for the largest sample of Galactic O-type stars gathered so far, including an elaborate error treatment. The established disagreement between the theoretical predictions and the "observed" WLRs being a function of luminosity class is suggested to be a result of wind clumping. Different strategies to check this hypothesis are discussed, particularly by comparing the Hα mass-loss rates with the ones derived from radio observations.

Abstract. In this paper we have analyzed 25 Galactic O and early B-stars by means of H and K band spectroscopy, with the primary goal to investigate to what extent a lone near-IR spectroscopy is able to recover stellar and wind parameters derived in the optical. Most of the spectra have been taken with -, at an intermediate resolution of 12 000, and with a very high S/N, mostly on the order of 200 or better. In order to synthesize the strategic H/He lines, we have used our recent, line-blanketed version of  (Puls et al. 2005, A&A, 435, 669). In total, seven lines have been investigated, where for two stars we could make additional use of the He2.05 singlet which has been observed with -. Apart from Br γ and He2.18, the other lines are predominately formed in the stellar photosphere, and thus remain fairly uncontaminated from more complex physical processes, particularly clumping. First we investigated the predicted behaviour of the strategic lines. In contradiction to what one expects from the optical in the O-star regime, almost all photospheric H/He/He H/K band lines become stronger if the gravity decreases. Concerning H and He, this finding is related to the behaviour of Stark broadening as a function of electron density, which in the line cores is different for members of lower (optical) and higher (IR) series. Regarding He, the predicted behaviour is due to some subtle NLTE effects resulting in a stronger overpopulation of the lower level when the gravity decreases.We have compared our calculations with results from the alternative NLTE model atmosphere code  (Hillier & Miller 1998, ApJ, 496, 407). In most cases, we found reasonable or nearly perfect agreement. Only the He2.05 singlet for mid O-types suffers from some discrepancy, analogous with findings for the optical He singlets. For most of our objects, we obtained good fits, except for the line cores of Br γ in early O-stars with significant mass-loss. Whereas the observations show Br γ mostly as rather symmetric emission lines, the models predict a P Cygni type profile with strong absorption. This discrepancy (which also appears in lines synthesized by ) might be an indirect effect of clumping. After having derived the stellar and wind parameters from the IR, we have compared them to results from previous optical analyses. Overall, the IR results coincide in most cases with the optical ones within the typical errors usually quoted for the corresponding parameters, i.e., an uncertainty in T eff of 5%, in log g of 0.1 dex and inṀ of 0.2 dex, with lower errors at higher wind densities. Outliers above the 1-σ level where found in four cases with respect to log g and in two cases forṀ.

Abstract. We report on a re-analysis of the Galactic a-type star sample presented by Puls et ale (1996) by means of non-LTE model atmospheres including line-blocking and line-blanketing. In particular, we concentrate on the question concerning the dependence of the wind-momentum luminosity relation (WLR) on luminosity class. Owing to the line-blanketing, the derived effective temperatures become significantly lower when compared to previous results, whereas the so-called 'modified wind-momentum rates' remain roughly at their former values. Therefore, we obtain a new WLR for a-type stars. By comparing these 'observational' results with new theoretical predictions and simulations, we conclude that the Ho forming region for objects with Ho in emission might be considerably clumped and thus a larger mass-loss rate than actually present is mimicked. We suggest that the previously found dependence of the WLR on luminosity class is an artefact.