Flux-calibrated stellar population models of Lick absorption-line
  indices with variable element abundance ratios
  We present new stellar population models of Lick absorption-line indices with
variable element abundance ratios. The models are based on our new calibrations
of absorption-line indices with stellar parameters derived from the MILES
stellar library. The key novelty compared to our previous models is that they
are now available at the higher spectral resolution of MILES (~2.7A FWHM) and
flux-calibrated, hence not tied anymore to the Lick/IDS system. This is
essential for the interpretation of galaxy spectra where calibration stars are
not available, such as large galaxy redshift surveys or other high-redshift
observations. We note that the MILES resolution appears to be comparable to
SDSS resolution, so that our models can be applied to SDSS data without any
corrections for instrumental spectral resolution. For the first time we provide
random errors for the model predictions based on the uncertainties in the
calibration functions and the underlying stellar parameter estimates. We show
that random errors are small except at the edges of the parameter space
(high/low metallicities and young ages <1 Gyr) where the stellar library is
under-sampled. We calibrate the base model for the parameters age, metallicity
and alpha/Fe ratio with galactic globular cluster and galaxy gradient data. We
discuss two model flavours with different input stellar evolutionary tracks
from the Frascati and Padova groups. The new model release now includes
abundance variations of the elements C, N, Mg, Na, Si, Ca, Ti, Cr, and Fe. The
individual elements that are best accessible with these models and the standard
set of Lick absorption features are C, N, Mg, Ca, Ti, and Fe. The model data is
available at www.icg.port.ac.uk/~thomasd.
