Daniel Schaerer 1 Grazyna Stasinska 2
1 Laboratoire d'Astrophysique de Toulouse, Observatoire Midi-Pyrenees F-31400 Toulouse, France
2 DAEC, Observatoire de Meudon, F-92195 Meudon, France
Recent developments in stellar interior and atmosphere modeling have allowed consistent predictions of stellar tracks and spectra including the effects of stellar winds, non-LTE and line blanketing for massive stars (CoStar models). The ionizing fluxes for O3-B0 stars derived from these models (Schaerer & de Koter, 1997, AA 322, 598) show important changes (particularly in the HeI and HeII continua) compared to previous models.
The implications of the CoStar models on single star HII regions
have been studied by Stasinska & Schaerer (1997, AA 322, 615).
Predictions for IR lines are particularly sensitive to differences in
the ionizing fluxes.
Comparisons with observations of ionic ratios from IR and optical line
measurements of Galactic HII regions show in particular that the new
models
naturally reproduce the observed value of
,
i.e. resolve
the
so-called [NeIII] problem (cf. Simpson et al. 1995, ApJ 444, 721).
They provide a strong support for the ionizing fluxes from our CoStar
models.
The current status and new developments of O star atmosphere models is summarized. We then present the first results from photoionization models for starburst populations calculated from our evolutionary synthesis models using the CoStar spectra, appropriate Wolf-Rayet atmosphere models and the latest Geneva stellar evolution tracks (see Schaerer & Vacca 1998, ApJ 497, 618). We show the predicted behaviour of IR fine structure lines on the atmosphere models and the other (nebular and burst) model parameters. The implications for the determination of fundamental properties of starbursts (age, duration, IMF) from ISO observations are discussed.
Our new model set including state-of-the-art combined stellar structure and atmosphere models (CoStar), up to date evolutionary synthesis models, and photoionization models provides an ideal tool to interpret a wide range of observations of Galactic and extra-galactic HII regions and starbursts. The model predictions incorporating the most recent progress in stellar physics are in particular well suited for analysis of ISO observations of IR fine structure lines.