Abstract
In the present paper we investigate the possible connection between s-process nucleosynthesis occurring during the asymptotic giant branch (AGB) phase of low-mass stars (LMS) and the isotopic anomalies of the “Fe-group” elements observed in several macroscopic samples of meteorites or in grains formed as circumstellar condensates (hereafter CIRCONs). The available measurements of chromium, iron, and nickel are well reproduced by stellar models, which account for the largest shifts in the heaviest isotopes of each element: in particular 54Cr, 58Fe, and 64Ni. Moreover, many circumstellar condensates reflect 50Ti excesses and some production of 46, 47, 49Ti, as predicted by slow-neutron captures in AGB stars. Nevertheless, some difficulties are found in comparing theoretical calculations of s-process nucleosynthesis with calcium, silicon, and zinc isotopic anomalies.
Highlights
The production of elements generally considered to be members of the iron-group is commonly attributed to supernovae (SNe), both core collapse and SNeIa
In order to obtain a direct comparison with the meteoritic measurements, the enrichment factors E (i, k) for isotopic abundances of the “Fe-group” elements are calculated as follow: N (i)
We computed the effects of slow neutron capture nucleosynthesis on Cr, Fe, and Ni through 1.5 M and 3 M asymptotic giant branch (AGB) models, adopting solar and 1/3 solar metallicities
Summary
The production of elements generally considered to be members of the iron-group (such as Ti, Cr, Fe, Ni, and Zn) is commonly attributed to supernovae (SNe), both core collapse and SNeIa. The isotopes of these elements can be traced in pristine meteorites with high accuracy, as in the last decades several analysis techniques have been developed allowing to measure anomalies for the abundances of elements and isotopes at the level of a few parts in ten thousand ( units) These isotopic effects are common in calcium-aluminum-rich inclusions (CAIs) in meteorites, but are wide spread at lower levels in “bulk” samples of different groups of meteorites. In this context, we suggest that slow neutron captures, the so-called s-process occurring in the asymptotic giant branch phases (AGB) low mass stars (LMS), modify the original abundance of these elements collected from the interstellar medium by the star, by adding more neutrons, altering the isotopic admixture in favour of heavier isotopes [1]. The s-process nucleosynthesis calculations suggest a large positive shift for 54Cr, 58Fe, and 64Ni (representing the heaviest stable isotope of each element), while only limited variations are expected for other nuclei and in some cases, as for 50Cr and 54Fe, even a negative shift is predicted
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