Carbon burning in intermediate-mass primordial stars

¹ Departament de Física Aplicada, Escola Politécnica Superior de Castelldefels, Universitat Politècnica de Catalunya, Avda. del Canal Olímpic s/n, 08860 Castelldefels, Spain e-mail: [pilar;garcia]@fa.upc.es
² Department of Physics, Hokkaido University, Sapporo, Hokkaido 060–0810, Japan
³ Meme Media Laboratory, Hokkaido University, Sapporo, Hokkaido 060–0813, Japan
⁴ Institute for Space Studies of Catalonia, c/Gran Capità 2–4, Edif. Nexus 104, 08034 Barcelona, Spain

Received: 29 July 2004
Accepted: 2 December 2004

Abstract

The evolution of a zero metallicity star is computed, analyzed and compared with that of a solar metallicity star of identical ZAMS mass. Our computations range from the main sequence until the formation of a massive oxygen-neon white dwarf. Special attention has been payed to carbon burning in conditions of partial degeneracy as well as to the subsequent thermally pulsing Super-AGB phase. The latter develops in a fashion very similar to that of a solar metallicity star, as a consequence of the significant enrichment in metals of the stellar envelope that ensues due to the so-called third dredge-up episode. The abundances in mass of the main isotopes in the final ONe core resulting from the evolution are O, Ne and Mg. This core is surrounded by a buffer mainly composed of carbon and oxygen, and on top of it a He envelope of mass ∼.