Population synthesis models that follow in detail the chemical and spectral
evolution of stellar systems are needed in order to interpret observational
data on both distant galaxies (blue systems seen early on in their chemical
history) and nearby ones (either ellipticals or spiral bulges containing
stars of metallicity higher than solar or dwarf blue galaxies which are
currently forming stars at metallicities considerably lower than solar).
The possibility of building detailed spectro-chemical evolution models
of stellar populations using evolutionary synthesis techniques is limited
by the inexistence of a comprehensive library of stellar spectra comprising
stars in a wide metallicity range, from well below solar ([Fe/H] from
-2 to -1) to above solar metallicities ([Fe/H]>0).
Current evolutionary synthesis models follow the evolution
of stars of solar metallicity and in the visible range are largely based on
the Gunn and Stryker spectral atlas or Kurucz model stellar atmospheres.
The use of theoretical model atmospheres is quite permissible in evolutionary
population synthesis. However, in general, the resulting synthetic spectra do
not reproduce the spectral features observed in composite stellar populations
with the same degree of accuracy as models based solely on observed stellar
spectra. One of the weakest points in using theoretical model atmospheres
is the fact that the spectra for the coolest stars in some of the most
relevant regions in the HR diagram (giants) are not contained in Kurucz atlas.
The Kurucz atlas does not contain model atmospheres for stars cooler
than 3500 K and one use of some rudimentary approximations to
construct the missing spectra.
The main objective of our Stellar Library is to build a homogeneous library
of stellar spectra in the visible range (3200 to 9500A), including
stars of all spectral types and luminosity classes that can be observed from the
ground with the current instrumentation. Most of the stars in our sample have
already well determined metallicities.
It is worth mentioning that the Gunn and Stryker atlas, so useful in
this kind of studies, was not compiled as part of a specific observing
project, but the spectra were obtained during different circumstances.
The spectral resolution of our Stellar Library is about 3A FWHM, compared to
10 to 20 for Gunn and Stryker atlas.
Send Comments to: Jean-Francois Le Borgne
