  We have obtained high-spatial resolution ultraviolet and optical STIS
spectroscopy and imaging of the metal-rich nuclear starburst in NGC3049. The
stellar continuum and the absorption line spectrum in the ultraviolet are used
to constrain the massive stellar population. The strong, blueshifted stellar
lines of CIV and SiIV detected in the UV spectra indicate a metal-rich,
compact, massive (1E6 Msol) cluster of age 3--4 Myr emitting the UV-optical
continuum. We find strong evidence against a depletion of massive stars in this
metal-rich cluster. The derived age and the upper mass-limit cut-off of the
initial mass function are also consistent with the detection of Wolf-Rayet (WR)
features at optical wavelengths. As a second independentconstraint on the
massive stellar content, the nebular emission-line spectrum is modeled with
photoionization codes using stellar spectra from evolutionary synthesis models.
However, the nebular lines are badly reproduced by 3--4 Myr instantaneous
bursts, as required by the UV line spectrum, when unblanketed WR and/or Kurucz
stellar atmospheres are used. The corresponding number of photons above 24 and
54 eV in the synthetic models is too high in comparison with values suggested
by the observed line ratios. Since the ionizing spectrum in this regime is
dominated by emission from WR stars, this discrepancy between observations and
models is most likely the result of incorrect assumptions about the WR stars.
Thus we conclude that the nebular spectrum of high-metallicity starbursts is
poorly reproduced by models for WR dominated populations. However, the new
model set of Smith et al. (2002) with blanketed WR and O atmospheres and
adjusted WR temperatures predicts a softer far-UV radiation field, providing a
better match to the data.
