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Astron. Astrophys. 321, 452-464 (1997)

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Short-lived radionuclide production by non-exploding Wolf-Rayet stars

M. Arnould 1, G. Paulus 1 and G. Meynet 2

1 Institut d'Astronomie et d'Astrophysique, C.P. 226, Université Libre de Bruxelles, Bd. du Triomphe, B-1050 Brussels, Belgium
2 Observatoire de Genève, CH-1290 Sauverny, Switzerland

Received 11 June 1996 / Accepted 27 August 1996

Abstract

This paper presents an extension and update of previous calculations of the production by non-exploding Wolf-Rayet stars of radionuclides that could be responsible for certain isotopic anomalies discovered in meteoritic inclusions, or in meteoritic grains of probable circumstellar origin.

Quantitative predictions of the time dependence of the radionuclide composition of the wind of Wolf-Rayet stars with initial masses in the wide [FORMULA] range and for metallicities [FORMULA] are obtained from a set of revised stellar evolution models. Special emphasis is put on the radionuclides with half-lives between about [FORMULA] and [FORMULA] y that could be produced by neutron captures during central helium burning and ejected during the WC-WO evolutionary phases. We stress that the radionuclide yield predictions are much more secure for Wolf-Rayet stars than for any other potential source of these species that has been contemplated up to now. This relates directly to the simplicity of these stars compared to highly difficult to model objects like Asymptotic Giant Branch stars, novae or supernovae.

Our abundance predictions are confronted with existing observational data, or are hoped to help unravelling cases of potential interest for further laboratory quest when observations are lacking. The case of [FORMULA], of special interest for [FORMULA] -ray line astronomy as well as for cosmochemistry, is also briefly revisited. In contrast to the other considered radionuclides, [FORMULA] is produced during hydrogen burning, and is ejected at the WN evolutionary phase of the Wolf-Rayet stars. Our computed yields are also used as the basis for a qualitative discussion of the astrophysical plausibility of the contamination of the protosolar nebula with the radionuclides loading the Wolf-Rayet winds.

Our calculations indicate that [FORMULA], [FORMULA] and [FORMULA] can be produced at a level compatible with the observations from a large variety of Wolf-Rayet stars with different masses and initial compositions. Wolf-Rayet stars could also account for the very uncertain limits set on [FORMULA] and [FORMULA]. In addition, [FORMULA], [FORMULA], [FORMULA] and [FORMULA] are predicted to be produced in more or less large amounts, but the lack of secure experimental data prevents any meaningful confrontation with the observations. In contrast, the considered stars cannot explain the limits set recently on the amount [FORMULA] of [FORMULA] that was live at the start of the condensation sequence in the solar system. Other radionuclides of interest ([FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA]) cannot be produced either during the non-explosive evolution of the Wolf-Rayet stars, but could be synthesized during their eventual supernova explosion.

Key words: nuclear reactions, nucleosynthesis – stars: abundances – stars: Wolf-Rayet – solar system: meteors, meteoroids – stars: formation

Send offprint requests to: M. Arnould

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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