Astron. Astrophys. 357, 669-676 (2000)

Improved isotopic ratio determinations in IRC+10216, the progenitor mass and the s process

C. Kahane ¹, E. Dufour ¹, M. Busso ², R. Gallino ³, M. Lugaro ⁴, M. Forestini ¹ and O. Straniero <sup>5

1</sup> Laboratoire d'Astrophysique de l'Observatoire de Grenoble B.P. 53, 38041 Grenoble Cedex 9, France
² Osservatorio Astronomico di Torino, 10025 Torino, Italy
³ Dipartimento di Fisica Generale, Universitá di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁴ Department of Mathematics, Monash University, Clayton 3168, Victoria, Australia
⁵ Osservatorio Astronomico di Collurania, 64100 Teramo, Italy

Received 17 December 1999 / Accepted 2 March 2000

Abstract

We present an improved determination of the chlorine isotopic ratio in the circumstellar envelope IRC+10216. This determination is the first clear evidence that in this circumstellar envelope elements heavier than the CNO do show deviations from the solar isotopic ratios, thus allowing a detailed comparison with quantitative model predictions. We have compared these data, together with other measurements for Mg and CNO isotopes, with predictions of AGB stellar models of solar metallicity and initial masses 1.5, 3 and 5 computed with the FRANEC evolutionary code. The comparison shows excellent agreement for the results of a low mass AGB model and remarkable disagreement for those of the 5 star. We briefly discuss the impact that model uncertainties can have on our conclusions.

Key words: nuclear reactions, nucleosynthesis, abundances stars: AGB and post-AGB stars: individual: IRC+10216 stars: circumstellar matter radio lines: stars

Send offprint requests to: C. Kahane (claudine.kahane@obs.ujf-grenoble.fr)

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000

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