Stellar lifetimes and abundance ratios in chemical evolution.

The frequency of Type I supernovae (SN I) in galaxies with unusual star-formation activity, as well as the large envelopes of SN I, is regarded as almost conclusive evidence that the precursors of SN I belong to a young stellar population. It is assumed that white dwarfs, SN I, and SN II represent the deaths of stars in the mutually exclusive mass ranges below 4 solar masses, from 4 to 6.5 solar masses, and above 6.5 solar masses, respectively. Consequences of tentative assumptions based partly on empirical evidence for iron production by SN I and carbon production by low-mass stars are tested against published stellar abundances. From a variety of models for chemical abundances, it is found that the relative abundances of primary elements are essentially functions of time, determined by progenitor stellar lifetimes, although the absolute abundance levels depend mainly on the model parameters.