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Title: RELICS OF ANCIENT POST-AGB STARS IN A PRIMITIVE METEORITE

Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme isotopic anomalies in C, Ca, and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low {sup 12}C/{sup 13}C isotopic ratios in these grains are a result of abundant {sup 12}C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of ∼10{sup 15} cm{sup –3}, typical of the i-process, are achieved during this phase in post-AGB stars. The large {sup 42,43,44}Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from {sup 46,48}Ca,more » which cannot be resolved from the isobars {sup 46,48}Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a VLTP.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa, Honolulu, HI 96822 (United States)
  2. Department of Physics, University of Basel, CH-4056 Basel (Switzerland)
  3. Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada)
  4. Laboratory for Space Sciences and the Physics Department, Washington University, St. Louis, MO 63130 (United States)
  5. Dipartimento di Fisica Generale, Università di Torino and INAF, Via Pietro Giuria 1, 10125 Torino (Italy)
Publication Date:
OSTI Identifier:
22224064
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 777; Journal Issue: 2; Other Information: 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; ABUNDANCE; CALCIUM 44; CALCIUM 48; CARBON 12; CARBON 13; CONDENSATES; GRAIN DENSITY; GRAPHITE; ISOTOPE RATIO; METEORITES; NEUTRON DENSITY; NEUTRON REACTIONS; NUCLEOSYNTHESIS; PROTONS; SUPERNOVAE; TITANIUM 48