Physics
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........21m&link_type=abstract
Thesis(PhD). UNIVERSITE PAUL SABATIER, TOULOUSE (FRANCE). 290 pages.
Physics
8
Massive Stars, Stellar Atmospheres, Line-Blanketing, Winds
Scientific paper
Atmosphere models for massive stars have become very realistic since the recent inclusion of line-blanketing. In the first part of this thesis we have studied quantitatively the effects of metals on the atmospheric structure and emergent spectrum of models computed with the code CMFGEN. We have first shown that the effective temperature scale of O dwarfs was cooler than previous calibrations based on H He models. We have also shown that line-blanketing modifies the spectral energy distribution of O stars: the flux below ~ 500 A is reduced due to the inclusion of bound-free opacities. Finally, we have tested these new SEDs in a study of nebular lines emitted in compact Galactic HII regions and observed by ISO and we have found that the inclusion of line-blanketing leads to significant improvement, although the agreement with the observations is still not perfect. In the second part of this thesis, we have studied the stellar and wind properties of O dwarfs in order to quantify their mass loss rates and modified wind momenta and their dependence on metallicity and luminosity. We have been especially interested in stars with weak winds since they have never been analysed through quantitative spectroscopy before. We have shown thar both the stellar component of the High Excitation Blob N81 in the Small Magellanic Cloud (O stars possibly members of the Vz class) and faint Galactic O dwarfs display very weak winds with mass loss rates of the order of 1e-9 Msol/yr. Such mass loss rates are lower than ever observed and lower than predicted by hydrodynamical simulations. The same can be said about modified wind momenta so that the modified wind momentum - luminosity relation displays a break-down around log L/Lsol = 5.2. Several possibilities to explain such weak winds are investigated, but the exact physical reason remains unknown.
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