Nucleosynthesis of light elements inside thermally pulsing AGB stars

I. The case of intermediate-mass stars

¹ Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, BP 53, F–38041 Grenoble Cedex 9, France
² Laboratoire d'Astrophysique de Toulouse, CNRS UMR 5572, Toulouse, France

Send offprint request to: M. Forestini

Received: 22 April 1996
Accepted: 30 July 1996

Abstract

The structural and nucleosynthetic evolution of 3, 4, 5, 6 and stars with two metallicities ( and 0.02) has been computed in detail, from the early pre-main sequence phase up to the thermally pulsing (TP) AGB phase or the onset of off-center carbon burning. Typically 10 to 20 thermal pulses have been followed for each TP-AGB object. This homogeneous and quite large set of models allows us to present an overview of the thermal pulse properties as well as of the nucleosynthesis accompanying the TP-AGB phase of intermediate-mass stars. More specifically, after a brief description of the previous evolutionary stages, predictions are given for the isotopic ratios involving C, N, O, Ne, Mg, Al and Si. Also the surface abundances of , and are reported. As the asymptotic phase of the thermal pulses has been reached for each star, we also indicate how these abundances will probably evolve until the stars completely loose their envelope, by including the evolution of the nucleosynthesis itself.