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Title: AGB stars and presolar grains

Among presolar materials recovered in meteorites, abundant SiC and Al{sub 2}O{sub 3} grains of AGB origins were found. They showed records of C, N, O, {sup 26}Al and s-element isotopic ratios that proved invaluable in constraining the nucleosynthesis models for AGB stars [1, 2]. In particular, when these ratios are measured in SiC grains, they clearly reveal their prevalent origin in cool AGB circumstellar envelopes and provide information on both the local physics and the conditions at the nucleosynthesis site (the H- and He-burning layers deep inside the structure). Among the properties ascertained for the main part of the SiC data (the so-called mainstream ones), we mention a large range of {sup 14}N/{sup 15}N ratios, extending below the solar value [3], and {sup 12}C/{sup 13}C ratios ≳ 30. Other classes of grains, instead, display low carbon isotopic ratios (≳ 10) and a huge dispersion for N isotopes, with cases of large {sup 15}N excess. In the same grains, isotopes currently feeded by slow neutron captures reveal the characteristic pattern expected from this process at an efficiency slightly lower than necessary to explain the solar main s-process component. Complementary constraints can be found in oxide grains, especially Al{sub 2}O{sub 3} crystals.more » Here, the oxygen isotopes and the content in {sup 26}Al are of a special importance for clarifying the partial mixing processes that are known to affect evolved low-mass stars. Successes in modeling the data, as well as problems in explaining some of the mentioned isotopic ratios through current nucleosynthesis models are briefly outlined.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. INFN and University of Perugia, Perugia (Italy)
  2. INAF - Arcetri Astrophysical Observatory, Firenze, Italy and INFN - Section of Perugia, Perugia (Italy)
  3. Departamento de Fìsica Teòrica y del Cosmsos, Universidad de Granada, Granada (Spain)
Publication Date:
OSTI Identifier:
22280410
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1595; Journal Issue: 1; Conference: 7. European summer school on experimental nuclear astrophysics, Santa Tecla, Sicily (Italy), 15-17 Sep 2013; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALUMINIUM 26; ALUMINIUM OXIDES; ASTROPHYSICS; CAPTURE; CARBON 12; CARBON 13; COSMOLOGY; DWARF STARS; ELEMENT ABUNDANCE; ISOTOPE RATIO; METEORITES; NITROGEN 14; NITROGEN 15; NUCLEOSYNTHESIS; OXYGEN ISOTOPES; S PROCESS; SILICON CARBIDES