paper

Extremely Cr- and Ti-rich presolar oxide grains in a primitive meteorite: Formation in rare types of supernovae and implications for the astrophysical context of solar system birth

arXiv:1803.04286 · doi:10.3847/2041-8213/aab61f

Abstract

We report the identification of 19 presolar oxide grains from the Orgueil CI meteorite with substantial enrichments in Cr, with Cr/Cr ratios ranging from 1.2 to 56 times the solar value. The most enriched grains also exhibit enrichments at mass 50, most likely due in part to Ti, but close-to-normal or depleted Cr/Cr ratios. There is a strong inverse relationship between Cr enrichment and grain size; the most extreme grains are all <80 nm in diameter. Comparison of the isotopic data with predictions of nucleosynthesis calculations indicate that these grains most likely originated in either rare, high-density Type Ia supernovae (SNIa), or in electron-capture supernovae (ECSN) which may occur as the end stage of evolution for stars of mass 8-10 M. This is the first evidence for preserved presolar grains from either type of supernova. An ECSN origin is attractive since these likely occur much more frequently than high-density SNIa, and their evolutionary timescales (20 Myr) are comparable to those of molecular clouds. Self-pollution of the Sun's parent cloud from an ECSN may explain the heterogeneous distribution of n-rich isotopic anomalies in planetary materials, including a recently reported dichotomy in Mo isotopes in the solar system. The stellar origins of three grains with solar Cr/Cr, but anomalies in Cr or Cr, as well as of a grain enriched in Fe, are unclear.

Accepted for publication in The Astrophysical Journal Letters; 14 pp, including 1 table and 4 figures

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