We calculate the numbers of O and WR stars produced during a starburst and
provide detailed predictions of UV and optical emission line strengths for
both the WR stellar lines and the major nebular hydrogen and helium emission
lines, as a function of several input parameters related to the starburst
episode. We also derive the theoretical frequency of WR-rich starbursts.

Our models predict that nebular He II
4686 emission from a
low-metallicity starburst should be associated with the presence of WC/WO
stars and/or hot WN stars evolving to become WC/WO stars. In addition,
WR starts contribute to broad components beneath the nebular Balmer lines;
the broad WR component may constitute several percent of the total flux in the
line.

We review the various techniques used to derive the WR and O star content from
integrated spectra, assess their accuracy, and propose two new formulae to
estimate the WR/O number ratio from the UV or optical spectra.

We also explore the implications of the formation of WR stars through mass
transfer in close binary systems in instantaneous bursts. While the formation
of WR stars through Roche lobe overflow prolongs the WR dominated phase,
there are clear observational signatures which allow the phases in which
WR stars are formed predominantly through the single or the binary star
channels to be distinguished. In particular at low metallicities, when
massive close binaries contribute significantly to the formation of WR stars,
the binary-dominated phase is expected to occur at ages corresponding to
relatively low H
equivalent widths.

The observational features predicted by our models allow a detailed
quantitative determination of the massive star population in a starburst
region (particularly in so-called "WR-galaxies") from its integrated spectrum
and provide a means of deriving the burst properties (e.g., duration, age) and
the parameters of the initial mass function of young starbursts. The model
predictions should provide the most reliable determination to date. They
can also be used to test the current theories of massive star evolution
and atmospheres and investigate the variation in stellar properties with
metallicity.

END:: epreps.stsci//prep1193