Abstract details

Evolved stars on the TP-AGB dominate the infrared spectra of intermediate age populations (e.g. Bruzual \& Charlot 2003 MNRAS 344 1000, Maraston 2005 MNRAS 362, 799), but the AGB stars are usually not included in published synthetic spectral libraries. On the AGB, stars may evolve from spectral type M to spectral type C. In this transition the chemistry in the relatively cool atmospheres change from oxygen rich to carbon rich and the resulting spectra change dramatically. The fraction of AGB stars that will become carbon stars increases with decreasing metallicity. A low metallicity grid of spherically symmetric hydrodynamic carbon star model atmospheres is under construction. We present here a first subset of moderate resolution synthetic spectra computed from this grid. The spectra are computed from models including opacities from atoms, small molecules and dust with selfconsistently modelled dust formation. The grid will cover a range of metallicity, C/O ratio, carbon isotopic ratio, effective temperature, mass and luminosity including the superwind phase.