Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sf2a.conf..246g&link_type=abstract
SF2A-2007: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics held in Grenoble, France, July
Astronomy and Astrophysics
Astrophysics
Scientific paper
Primitive meteorites contain presolar grains that originated in stellar outflows and supernovae ejecta prior to the formation of the solar system. These grains represent a unique means to access interstellar matter within the framework of dust evolution. Laboratory measurements of the noble gas abundances trapped into a large sample of presolar SiC grains recovered from the Murchison meteorite showed a strong enrichment of the heavier gases (Xe, Kr) compared to the lighter ones (He, Ne, Ar) for both solar (so-called N) and Asymptotic Giant Branch (AGB)-star (so-called G) isotopic components isolated from SiC. This cannot possibly be due to nuclear processes, but requires some fractionation process. We have developed a simple atom implantation and grain erosion model which allows us to better understand this mass-fractionation of the elemental abundances and which provides new insights on both the physical conditions of grain formation and implantation around evolved stars and the processing of dust in circumstellar and interstellar environments. We argue in favor of an implantation at constant gas-grain velocity so that heavier elements are implanted more deeply, and thus are more susceptible to be conserved during erosion in the interstellar medium (ISM). We show that the N-component has been implanted in supernova-generated shock waves in the ISM, at a relatively low velocity (120 ± 40 km s-1) and high equivalent hydrogen-fluences (1018 to 1019 cm-2) in a so-called steady-state regime where implantation is accompanied by erosion. On the other hand, the G-component is consistent with implantation in the fast (220 ± 20 km s-1) wind of the planetary nebulae (PN) phase, at low H-fluences (1017 to 1018 cm-2) so that one can ignore erosion at this stage. In both cases, the mass-driven fractionation of the observed elemental abundances is a result of implantation in different astrophysical sites and subsequent erosion mainly in the ISM.
Guillard Pierre
Jones Adrian P.
Tielens Alexander G. G. M.
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