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Session 38 - Dwarf Galaxies.
Display session, Tuesday, January 14
Metropolitan Ballroom,
We have computed closed chemical evolution models to fit O/H, C/O, N/O, Ne/O, Si/O, S/O, Ar/O, Fe/O. Models have the following properties: a) Yields by Woosley amp; Weaver (1995) and Renzini amp; Voli (1991); b) Star Formation Rate proportional to the gas mass; and c) Initial Mass Function for M\> 0.5M_ødot given by Kroupa, Tout amp; Gilmore (1993), and normalized to yield various M_gas/M_total ratios at the observed O/H value. While the C/O, N/O and Fe/O values imply that the ``age'' of IZw18 is smaller than 3x10^8 years, the Ar/O value implies that it is older than that. We find that in general for very metal poor galaxies the N/O, Si/O, S/O, Ar/O, and Fe/O ratios are sensitive age indicators for objects younger than 10^8 years
