Relics of ancient post-AGB stars in a primitive meteorite

Jadhav, M.; Pignatari, M.; Herwig, F.; Zinner, E.; Gallino, R.; Huss, G. R.

Abstract

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 ¹²C/¹³C isotopic ratios in these grains are a result of abundant ¹²C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of ∼10 15 cm -3 , typical of the i-process, are achieved during this phase in post-AGB stars. The large 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 ⁴⁶, ⁴⁸ Ca, which cannot be resolved from the isobars 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. © 2013. The American Astronomical Society. All rights reserved.

Citation

Jadhav, M., Pignatari, M., Herwig, F., Zinner, E., Gallino, R., & Huss, G. R. (2013). Relics of ancient post-AGB stars in a primitive meteorite. Astrophysical journal. Letters, 777(2), L27. https://doi.org/10.1088/2041-8205/777/2/l27

• Journal Article Type: Article
• Acceptance Date: Oct 4, 2013
• Online Publication Date: Oct 23, 2013
• Publication Date: Nov 10, 2013
• Deposit Date: Jun 29, 2018
• Publicly Available Date: Jul 24, 2018
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Electronic ISSN: 2041-8213
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 777
• Issue: 2
• Article Number: L27
• Pages: L27
• DOI: https://doi.org/10.1088/2041-8205/777/2/l27
• Keywords: Astrochemistry; Circumstellar matter; Meteorites, meteors, meteoroids; Nuclear reactions, nucleosynthesis, abundances; Stars: abundances; Stars: AGB and post-AGB
• Public URL: https://hull-repository.worktribe.com/output/561751
• Publisher URL: http://iopscience.iop.org/article/10.1088/2041-8205/777/2/L27