PopStar Evolutionary Synthesis Models II: Optical emission-line spectra
  from Giant H{\sc ii} regions
  This is the second paper of a series reporting the results from the PopStar
evolutionary synthesis models. Here we present synthetic emission line spectra
of H{\sc ii} regions photoionized by young star clusters, for seven values of
cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing Spectral
Energy Distributions (SEDs) are those obtained by the PopStar code
\citep*{mgb09} for six different metallicities, with a very low metallicity
set, Z=0.0001, not included in previous similar works. We assume that the
radius of the H{\sc ii} region is the distance at which the ionized gas is
deposited by the action of the mechanical energy of the winds and supernovae
from the central ionizing young cluster. In this way the ionization parameter
is eliminated as free argument, since now its value is obtained from the
cluster physical properties (mass, age and metallicity) and from the gaseous
medium characteristics (density and abundances). We discuss our results and
compare them with those from previous models and also with a large and data set
of giant H{\sc ii} regions for which abundances have been derived in a
homogeneous manner. The values of the [OIII] lines (at $\lambda\lambda$ 4363,
4959, 5007\AA) in the lowest metallicity nebulae are found to be very weak and
similar to those coming from very high metallicity regions (solar or
over-solar). Thus, the sole use of the oxygen lines is not enough to
distinguish between very low and very high metallicity regions. In these cases
we emphasize the need of the additional support of alternative metallicity
tracers, like the [SIII] lines in the near-\textit{IR}.
