Sources of carbon and the evolution of the abundance of CNO elements

Free access article

Issue		A&A Volume 374, Number 3, August II 2001


Page(s)		936 - 956
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20010801

A&A 374, 936-956 (2001)
DOI: 10.1051/0004-6361:20010801

Sources of carbon and the evolution of the abundance of CNO elements

Y. C. Liang, G. Zhao and J. R. Shi

Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, PR China National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China

(Received 29 March 2000 / Accepted 30 May 2001 )

Abstract
Using the standard infall model of Galactic chemical evolution, we explore the origin of carbon and calculate the abundance evolution of CNO elements for 8 different models of stellar nucleosynthesis yields. The results show that, in the early stage of the Galaxy, massive stars are the main producer of carbon, and that as our Galaxy evolves to the late stage, the longer lived intermediate- and low-mass stars play an increasingly important role, while at the same time, metal-rich Wolf-Rayet stars eject a significant amount of carbon into the ISM by radiative-driven stellar winds. However, from the present published nucleosynthesis yields we cannot distinguish whether the main source of carbon in the late Galactic stage is just the massive stars ( $M> 8 M_{\odot}$ ) alone, or just the intermediate-, low-mass stars and $M\leq 40 M_{\odot}$ massive stars that do not go through the Wolf-Rayet stage. The ¹²C $(\alpha,\gamma)^{16}$ O reaction rate is very important in the stellar nucleosynthesis calculations: a lower rate will give a higher yield of carbon. The contribution to nitrogen is dominated by intermediate- and low-mass stars, and the secondary source of massive stars cannot explain the observed [N/Fe] in metal-poor stars. Most of oxygen is produced by massive stars. The fact that a higher O abundance in metal-poor stars is derived from the OI 7771-7775 Å triplet than from the forbidden [OI] line at 6300 Å poses a problem.

Key words: nuclear reactions, nucleosynthesis, abundances -- stars: AGB -- stars: supernova -- stars: Wolf-Rayet -- Galaxy: abundance -- Galaxy: evolution

Offprint request: G. Zhao, zg@orion.bao.ac.cn

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