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As part of an ongoing project to generate model integrated spectra for star clusters and galaxy nuclei we have calculated new isochrones which cover all phases of stellar evolution from the zero-age main sequence through the asymptotic giant branch. The ages range from 2 to 18 Gyr and the metallicities from [Fe/H] = -2.3 to +0.2. The elemental abundances are in the solar ratio.
We have computed synthetic stellar spectra at representative intervals along each of these isochrones and measured their colors via convolution with filter transmission profiles. Various spectral feature indices have been determined in a similar manner. This allows us to directly transform the isochrones into any given color-magnitude or color-color space. By combining the synthetic spectra according to the expected mass function we also produce a synthetic integrated spectrum corresponding to each age and metallicity. In addition, the effect of non-solar abundance ratios is investigated by substituting stellar spectra which have been recomputed using the desired abundances (for example, using enhanced nitrogen and depleted carbon to mimic the mixing of CN-cycled material into the atmospheres).
The color systems currently under study include UBVRI, DDO, Stromgren uvby, and Washington. Spectral feature indices such as those on the Lick system are also considered.
This work has been supported under NSF grant AST-9122361.
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