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Astron. Astrophys. 358, L67-L70 (2000)

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1. Introduction

The most successful p-process models available to-date call for the synthesis of the stable neutron-deficient nuclides heavier than Fe in the O/Ne layers of Type II supernovae (SNII) (Rayet et al. 1995, hereafter RAHPN). In spite of their many virtues in reproducing the solar-system p-nuclide abundance distribution, they however suffer from some shortcomings. One of them concerns their persistent underproduction of the light Mo ([FORMULA], [FORMULA]) and Ru ([FORMULA], [FORMULA]) p-isotopes. Some have tried to remedy this situation with exotic solutions, calling in particular for accreting neutron stars or black holes (e.g. Schatz et al. 1998). The level of the contribution of such sites to the solar system content of the nuclides of concern here is quite impossible to assess in any reliable way. In contrast, it has been emphasized many times over the last decade that the problem might just be due to some misrepresentation of the production in the He-burning core of massive stars of the s-nuclide seeds for the p-process (e.g. Arnould et al. 1998).

The aim of this Letter is to scrutinize the latter, `non-exotic', solution in a quantitative way by duly taking into account the uncertainties that still affect the rate of the [FORMULA] reaction, as they appear in the NACRE compilation of reaction rates (Angulo et al. 1999). Clearly, these uncertainties in the key neutron producer in conditions obtained during central He burning in massive stars have a direct impact on the predicted abundances of the s-nuclide seeds for the p-process, as already analyzed quantitatively by Meynet & Arnould (1993). Another potential embarassment of the p-process predictions identified by RAHPN is a SNII overproduction of oxygen relative to the p-nuclides. We show that this problem might be cured along with the one of the underproduction of the light Mo and Ru isotopes if the [FORMULA] rate is modified adequately within a range permitted by the NACRE compilation. For the sake of illustration, we just discuss here the case of a 25 [FORMULA] solar metallicity ([FORMULA]) star. A more complete study dealing in particular with a set of stars with different masses and metallicities, and analyzing the impact of the uncertainties in the rates of a variety of reactions, is currently under way.

The adopted input physics is briefly described in Sect. 2, and some results are presented in Sect. 3. Conclusions are drawn in Sect. 4.

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© European Southern Observatory (ESO) 2000

Online publication: June 20, 2000