Other stellar sources

Aluminum-26 is produced by stellar nucleosynthesis in a wide variety of stellar sites. Its abundance relative to other short-lived nuclides provides information about the stellar source(s) for short-lived nuclides and the environment in which the Sun formed. Aluminum-26 is also produced by interactions between heavier nuclei such as silicon atoms and cosmic rays. Aluminum-26 is one of several nuclides used to estimate the cosmic-ray exposure ages of meteorites as they traveled from their parent asteroids to the solar system. 

Cameron (1973) speculated that grains from stellar sources survive in the interstellar medium, become incorporated into bodies of the Solar System, and may be found in meteorites, because some meteorites represent nearly unprocessed material from the time of Solar System formation. These grains may be identified by unusual isotopic abundance ratios of some elements, since material from nuclear burning zones is mixed at the end of the life of stars into the matter from which dust is formed. Indeed, these presolar dust grains3 were found in the late 1980s in meteorites (and later also in other types of primitive Solar System matter) and they contain rich information on their formation conditions and on nucleosynthetic processes in stars (see Section 2.2). By identifying such grains in primitive Solar System matter it is possible to study the nature and composition of at least some components of the interstellar dust mixture in the laboratory. 

Laboratory studies of presolar dust grains also show that dust is formed in the mass ejected after an SN explosion, as will also be discussed in Section 2.2. Observations show that the ejected mass shells occasionally do form dust some time after the SN explosions (e.g. Bianchi Schneider 2007), but generally the efficiency of dust production seems to be rather low (Bianchi Schneider 2007 Zhukovska et al. 2008). Other important sources of stardust are red supergiants (mostly silicate dust). Most of the dust from red supergiants, however, is not expected to survive the shock wave from the subsequent SN explosion of the star (Zhukovska et al. 2008). Some dust is also formed by novae (Amari et al. 2001b), Wolf-Rayet stars (WRs, Crowther 2007), and luminous blue variables (LBVs, Voors et al. 2000), but the dust quantities formed by these are very small. Stardust - i.e. dust that is formed in stellar outflows or ejecta - in the interstellar medium is dominated by dust from AGB stars. 

Trends observed in noble gas isotopic patterns are, however, contrary to the trends observed in other elements, such as, e.g., Ba (Gallino et al. 1993 Lewis et al. 1994). In addition, the noble gas G component appears little/not elementally fractionated relative to its stellar source, while the N component is [especially within the heavy noble gases and in the ratio of the heavy noble gases relative to He and Ne (cf. Fig. 2 Lewis et al. 1990,... 

Helium, plentiful in the cosmos, is a product of the nuclear fusion reactions that are the prime source of stellar energy. The other members of the hehum-group gases are thought to have been created like other heavier elements by further nuclear condensation reactions occurring at the extreme temperatures and densities found deep within stars and in supernovas. 

Nowadays it is widely accepted that the 13C(a, n)160 reaction is the main source or neutrons of the s-process in AGB stars. Comparison between the s-element abundance patterns found in AGB stars of different classes and metallicity with theoretical predictions show a nice agreement (see e.g. Busso et al. 2001 and references therein). This comparison would indicate also that, at a given stellar metallicity, a dispersion in the quantity of 13C burnt may exists as one would expect, on the other hand. In fact, s-element patterns for individual stars can be fitted assuming that the amount of 13C burnt ranges from 10 7 to almost 10-5 Mq. However, the large error bar in the abundances precludes to put more... 

In recent years, a new source of information about stellar nucleosynthesis and the history of the elements between their ejection from stars and their incorporation into the solar system has become available. This source is the tiny dust grains that condensed from gas ejected from stars at the end of their lives and that survived unaltered to be incorporated into solar system materials. These presolar grains (Fig. 5.1) originated before the solar system formed and were part of the raw materials for the Sun, the planets, and other solar-system objects. They survived the collapse of the Sun s parent molecular cloud and the formation of the accretion disk and were incorporated essentially unchanged into the parent bodies of the chondritic meteorites. They are found in the fine-grained matrix of the least metamorphosed chondrites and in interplanetary dust particles (IDPs), materials that were not processed by high-temperature events in the solar system. 

Stellar nucleosynthesis No production of 6Li seems possible in stars, other than a very small surface abundance that can be established by nuclear reactions in solar flares. Even with that small production, stars are net destroyers of 6Li, so when their ejecta return to the interstellar material it is 6Li-poor. So stars are not its source. 

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