Carbon and Oxygen Galactic Abundance Gradients: A Comparative Study of Stellar Yields

Abstract

Chemical evolution models for the Galactic disk are presented for seven sets of stellar yields. In particular, the effects of stellar yields on the C/O chemical history of the solar neighborhood and on abundance gradients are discussed. In the solar vicinity, the increase of C/O with Z is due to massive stars alone. Models with yields by Maeder (1992) or by Portinari, Chiosi, & Bressan (1998) reproduce the observed C/O increase with Z, while models assuming yields by Woosley & Weaver (1995) and Woosley, Langer, & Weaver (1993) do not. Models based on yields by Maeder (1992) are in agreement with the C/O gradient, while those based on yields by Portinari et al. (1998) or by Woosley & Weaver (1995) and Woosley et al. (1993) are not. Models call for: i) yields that take into account metal-dependent stellar winds; and ii) for massive stars, a mass-loss rate with a metallicity dependence not as simple as Z^0.5. C/O abundance ratios predicted with yields by Marigo, Bressan, & Chiosi (1996, 1998) are higher than those with yields by Renzini & Voli (1981), which in turn are higher than those with yields by the van den Hoek & Groenewegen (1997).