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Isotope Anomalies in the Fe-group Elements in Meteorites and Connections to Nucleosynthesis in AGB Stars

Wasserburg, G. J. and Trippella, O. and Busso, M. (2015) Isotope Anomalies in the Fe-group Elements in Meteorites and Connections to Nucleosynthesis in AGB Stars. Astrophysical Journal, 805 (1). Art. No. 7. ISSN 0004-637X.

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We study the effects of neutron captures in AGB stars on "Fe-group" elements, with an emphasis on Cr, Fe, and Ni. These elements show anomalies in ^(54)Cr, ^(58)Fe, and ^(64)Ni in solar system materials, which are commonly attributed to supernovae (SNe). However, as large fractions of the interstellar medium (ISM) were reprocessed in AGB stars, these elements were reprocessed, too. We calculate the effects of such reprocessing on Cr, Fe, and Ni through 1.5 M⊙ and 3 M⊙ AGB models, adopting solar and 1/3 solar metallicities. All cases produce excesses of ^(54)Cr, ^(58)Fe, and ^(64)Ni, while the other isotopes are little altered; hence, the observations may be explained by AGB processing. The results are robust and not dependent on the detailed initial isotopic composition. Consequences for other "Fe group" elements are then explored. They include ^(50)Ti excesses and some production of ^(46,47,49)Ti. In many circumstellar condensates, Ti quantitatively reflects these effects of AGB neutron captures. Scatter in the data results from small variations (granularity) in the isotopic composition of the local ISM. For Si, the main effects are instead due to variations in the local ISM from different SN sources. The problem of Ca is discussed, particularly with regard to ^(48)Ca. The measured data are usually represented assuming terrestrial values for ^(42)Ca/^(44)Ca. Materials processed in AGB stars or sources with variable initial ^(42)Ca/^(44)Ca ratios can give apparent ^(48)Ca excesses/deficiencies, attributed to SNe. The broader issue of galactic chemical evolution is also discussed in view of the isotopic granularity in the ISM.

Item Type:Article
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URLURL TypeDescription Paper
Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 2015 American Astronomical Society. Received 2014 October 2; accepted 2015 March 6; published 2015 May 13. G.J.W. would like to acknowledge the Epsilon Foundation for continuing support and NASA (grant NNX12AJ01G to A. Krot, University of Hawaii) for partial contribution. This research was co-funded by the Italian INFN, Istituto Nazionale di Fisica Nucleare, through the ASFIN collaboration. Thanks are due to INFN also for financial support to O.T. The authors are greatly indebted to the knowledgeable and unknown reviewer who made very valuable and constructive comments that led to a much improved manuscript. These results were first reported at the R. J. O’Connell Symposium at Harvard, 2014 September. This work is dedicated to Rick.
Funding AgencyGrant Number
Epsilon FoundationUNSPECIFIED
Istituto Nazionale di Fisica Nucleare (INFN)UNSPECIFIED
Subject Keywords:ISM: abundances; meteorites; nuclear reactions, nucleosynthesis, abundances; stars: AGB and post-AGB
Issue or Number:1
Record Number:CaltechAUTHORS:20150514-073838250
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Official Citation:Isotope Anomalies in the Fe-group Elements in Meteorites and Connections to Nucleosynthesis in AGB Stars G. J. Wasserburg et al. 2015 ApJ 805 7
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57517
Deposited By: Tony Diaz
Deposited On:14 May 2015 18:51
Last Modified:03 Oct 2019 08:25

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