Abstract.We have analyzed the far-ultraviolet spectrum of two Galactic O4 stars, the O4If+ supergiant HD 190429A and the O4V((f)) dwarf HD 96715, using archival FUSE and IUE data. We have conducted a quantitative analysis using the two NLTE model atmosphere and wind codes,  and , which incorporate a detailed treatment of NLTE metal line blanketing. From the far-UV spectrum, we have derived the stellar and wind parameters and the surface composition of the two stars. The surface of HD 190429A has a composition typical of an evolved O supergiant (nitrogen-rich, carbon and oxygenpoor), while HD 96715 exhibits surface nitrogen enhancement similar to the enrichment found in SMC O dwarfs which has been attributed to rotationally-induced mixing. Following studies of Magellanic Cloud O stars, we find that homogeneous wind models could not match the observed profile of O λ1371 and require very low phosphorus abundance to fit the P λλ1118−1128 resonance lines. We show, on the other hand, that we are able to match the O  and P  lines using clumped wind models. In addition to these lines, we find that N λ1718 is also sensitive to wind clumping. For both stars, we have calculated clumped wind models that match well all these lines from different species and that remain consistent with Hα data. In particular, we have achieved an excellent match of the P  resonance doublet, indicating that our physical description of clumping is adequate.These fits therefore provide a coherent and thus much stronger evidence of wind clumping in O stars than earlier claims. We show that the success of the clumped wind models in matching these lines results from increased recombination in the clumps, hence from a better description of the wind ionization structure. We find that the wind of these two stars is highly clumped, as expressed by very small volume filling factors, namely f ∞ = 0.04 for HD 190429A and f ∞ = 0.02 for HD 96715. In agreement with our analysis of SMC stars, clumping starts deep in the wind, just above the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more. These lower mass loss rates will affect substantially the evolution of massive stars. Accounting for wind clumping is essential when determining the wind properties of O stars. Our study therefore calls for a fundamental revision in our understanding of mass loss and of O-type star stellar winds.

Aims. We study three Galactic H ii regions -RCW 79, RCW 82, and RCW 120 -where triggered star formation is taking place. Two stellar populations are observed: the ionizing stars of each H ii region and young stellar objects on their borders. Our goal is to show that they represent two distinct populations, as expected from successive star-forming events. Methods. We use near-infrared integral field spectroscopy obtained with SINFONI on the VLT to make a spectral classification. We derived the stellar and wind properties of the ionizing stars using atmosphere models computed with the code CMFGEN. The young stellar objects were classified according to their K-band spectra. In combination with published near and mid infrared photometry, we constrained their nature. Linemaps were constructed to study the geometry of their close environment. Results. We identify the ionizing stars of each region. RCW 79 is dominated by a cluster of a dozen O stars, identified for the first time by our observations. RCW 82 and RCW 120 are ionized by two and one O star, respectively. All ionizing stars are early-to-late O stars, close to the main sequence. The cluster ionizing RCW 79 formed 2.3 ± 0.5 Myr ago. Similar ages are estimated, albeit with a larger uncertainty, for the ionizing stars of the other two regions. The total mass-loss rate and ionizing flux is derived for each region. In RCW 79, where the richest cluster of ionizing stars is found, the mechanical wind luminosity represents only 0.1% of the ionizing luminosity, questioning the influence of stellar winds on the dynamics of these three H ii regions. The young stellar objects show four main types of spectral features: H 2 emission, Brγ emission, CO bandheads emission, and CO bandheads absorption. These features are typical of young stellar objects surrounded by disks and/or envelopes, confirming that star formation is taking place on the borders of the three H ii regions. The radial velocities of most YSOs are consistent with that of the ionized gas, firmly establishing their association with the H ii regions. Exceptions are found in RCW 120 where differences up to 50 km s −1 are observed. Outflows are detected in a few YSOs. All YSOs have moderate-to-strong near-IR excess. In the [24] versus K-[24] diagram, the majority of the sources dominated by H 2 emission lines stand out as redder and brighter than the rest of the YSOs. The quantitative analysis of their spectra indicates that, for most of them, the H 2 emission is essentially thermal and likely produced by shocks. We tentatively propose that they represent an earlier phase of evolution compared to sources dominated by Brγ and CO bandheads. We suggest that they still possess a dense envelope in which jets or winds create shocks. The other YSOs have partly lost their envelopes and show signatures of accretion disks. Overall, the YSOs show distinct spectroscopic signatures compared to the ionizing sources, confirming the presence of two stellar populations.

Abstract. Extensive photoionization model grids for single star H  regions using state-of-the-art stellar atmosphere models have been computed to test their predicted ionizing spectra against recent ISO mid-IR observations of Galactic H  regions. Particular care has been paid to examining in detail the dependences of the nebular properties on the numerous nebular parameters which are generally unconstrained. Provided the ionization parameter U is fairly constant on average and the atomic data is correct these comparisons show the following:-Both recent non-LTE codes including line blanketing and stellar winds (WM-Basic and CMFGEN) show a reasonable agreement with the observations, although non-negligible differences between their predicted ionizing spectra are found. Recurrently none of the models can be preferred over the other. -The softening of the ionizing spectra with increasing metallicity predicted by the WM-Basic models is found to be too strong. -We confirm earlier indications that the CoStar atmospheres, including an approximate treatment of line blanketing, overpredict somewhat the ionizing flux at high energies. -Both LTE and non-LTE plane parallel hydrostatic atmosphere codes predict ionizing spectra that are too soft, especially over the energy range between 27.6, 35.0, and 41.1 eV and above. The inclusion of wind effects is crucial for accurate predictions of ionizing fluxes.These conclusions are found to be robust to effects such as changes of U, stellar metallicity changes, and the inclusion of dust. Uncertainties due to atomic data (especially for Ar) are discussed. We also discuss the difficulties in estimating absolute stellar temperatures from mid-IR line ratios. Finally we have examined which parameters are chiefly responsible for the observed mid-IR excitation sequences. The galactic gradient of metallicity changing the shape of the stellar emission is found to be one of the drivers for the excitation sequence of Galactic H  regions, the actual contribution of this effect being finally atmosphere model dependent. The observed excitation scatter can be explained by effects due to statistical sampling of the IMF leading to a T eff dispersion plus additional dispersion of U.