FREQUENTLY ASKED QUESTIONS for BaSTI

last modification: 22 Jun 2010

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• Why integrated colours, spectra and M/L ratios of some metallicities are missing ?

• There is only one set of cooling tracks and oxygen profiles, but WD isochrones are available for each metallicity in the database. Why ?

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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 T_eff < 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)-T_eff 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 metallicity 'set'.

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.