ISOTOPE ANOMALIES IN THE FE-GROUP ELEMENTS IN METEORITES AND CONNECTIONS TO NUCLEOSYNTHESIS IN AGB STARS

ABSTRACT 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 54Cr, 58Fe, and 64Ni in solar system materials, which are commonly attributed to supernovae (SNe). However, as large fractions of the...

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Bibliographic Details
Published in:The Astrophysical journal 2015-05, Vol.805 (1), p.1-18
Main Authors: Wasserburg, G. J., Trippella, O., Busso, M.
Format: Article
Language:English
Subjects:
Anomalies
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Asymptotic giant branch stars
CALCIUM 42
CALCIUM 44
CALCIUM 48
Capture (nuclear)
Chemical evolution
Chromium
CHROMIUM 54
ELEMENT ABUNDANCE
IRON 58
ISM: abundances
ISOTOPE RATIO
Isotopes
Mathematical models
METALLICITY
METEORITES
Nickel
NICKEL 64
nuclear reactions, nucleosynthesis, abundances
NUCLEOSYNTHESIS
SOLAR SYSTEM
stars: AGB and post-AGB
SUPERNOVAE
TITANIUM 50
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Summary:ABSTRACT 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 54Cr, 58Fe, and 64Ni 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 and 3 AGB models, adopting solar and 1/3 solar metallicities. All cases produce excesses of 54Cr, 58Fe, and 64Ni, 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 50Ti excesses and some production of 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 48Ca. The measured data are usually represented assuming terrestrial values for 42Ca/44Ca. Materials processed in AGB stars or sources with variable initial 42Ca/44Ca ratios can give apparent 48Ca excesses/deficiencies, attributed to SNe. The broader issue of galactic chemical evolution is also discussed in view of the isotopic granularity in the ISM.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/805/1/7