IAU Symposium Abstract S186-090P

New models for Wolf-Rayet and O star populations in young starbursts

Daniel Schaerer1 and William D. Vacca2
1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA < schaerer@stsci.edu >
2 Institute for Astronomy, Honolulu, HI 96822, USA < vacca@athena.ifa.hawaii.edu >

We present new evolutionary synthesis models for young starbursts in order to derive more accurately the O and Wolf-Rayet (WR) star populations from observed spectra of starburst galaxies. The models include 1 evolutionary tracks which have extensively been tested against local populations, 2 the most recent sets of line blanketed spherically expanding non-LTE atmospheres, and 3 empirical WR line fluxes. The metallicity values covered ranges from the lowest values typical of Blue Compact Dwarf Galaxies to greater than solar. The synthesized quantities (nebular H and He lines, WR emission lines, SED etc.) allow accurate determinations of the total number of O stars and Wolf-Rayet stars present, as well as the number of the various WR subtypes. We examine the importance of WR stars on the ionizing spectrum of starbursts. Our results yield important contraints on the age, duration, intensity and IMF of the burst episode in a starburst region. The theoretical frequency of the WR phenomenon in starburst and the impact of this phase in the evolution of starburst is also discussed.