FREQUENTLY ASKED QUESTIONS for BaSTI
last modification: 22 Jun 2010
Why integrated colours, spectra and M/L ratios of some
metallicities are missing ?
The `missing' files are a result of the low-[Fe/H] limits on
various of the spectral libraries we used.
The low resolution spectra all have a lower limit at [Fe/H]=-2.0
because the Basel 3.1 spectral library (Westera et al. 2002) we used
for non carbon-stars with Teff < 3500 K has this [Fe/H] limit
(the Castelli & Kurucz (2003) spectra go down to [Fe/H]=-2.5, but we
can't produce a full integrated SED for
any of the SSPs without using the Basel spectra in addition). This
means that for scaled solar abundances Z=0.0001 is missing, whilst
for alpha-anhanced, both Z=0.0001 and 0.0003 are missing. We
decided to only produce Integrated colours and ML ratio files for SSPs for
which we were able to create the full SED.
At high resolution, the spectral library (Munari et al. 2005) goes down
to [Fe/H]=-2.5 for scaled solar abundances, but only [Fe/H]=-2.0
for alpha-enhanced, hence the Z=0.0001 and 0.0003 SEDs are
missing. Also note that the high resolution spectral library
doesn't quite cover all the log(g)-Teff parameter space required to
cover the youngest age SSPs (the lower age limit is slightly
different for each value of Z), so there are different numbers of
spectra files (i.e. a different number of ages covered) for each
There is only one set of cooling tracks and oxygen profiles, but WD isochrones
are available for each metallicity in the database. Why ?
The cooling tracks employed in all our WD isochrones
are the same, irrespective of the progenitor initial chemical composition.
When we compute WD isochrones
for a stellar population of a given initial composition --
only as far as the WD initial chemical stratification is concerned -- we are
neglecting the effect of the progenitor metallicity
and we are assuming an initial-final mass relationship given by the core masses at
the first thermal pulse of solar metallicity progenitors, including core
overshooting during the main sequence.
The tests discussed in in our paper (Salaris et al. 2010, ApJ 716, 1241)
demonstrate that this choice does not introduce
major uncertainties in the cooling times of models at fixed mass.
The BaSTI Team