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We report the identification of 19 presolar oxide grains from the Orgueil CImeteorite with substantial enrichments in $^{54}$Cr, with $^{54}$Cr/$^{52}$Crratios ranging from 1.2 to 56 times the solar value. The most enriched grainsalso exhibit enrichments at mass 50, most likely due in part to $^{50}$Ti, butclose-to-normal or depleted $^{53}$Cr/$^{52}$Cr ratios. There is a stronginverse relationship between $^{54}$Cr enrichment and grain size; the mostextreme grains are all <80 nm in diameter. Comparison of the isotopic data withpredictions of nucleosynthesis calculations indicate that these grains mostlikely originated in either rare, high-density Type Ia supernovae (SNIa), or inelectron-capture supernovae (ECSN) which may occur as the end stage ofevolution for stars of mass 8-10 M$_\odot$. This is the first evidence forpreserved presolar grains from either type of supernova. An ECSN origin isattractive since these likely occur much more frequently than high-densitySNIa, and their evolutionary timescales ($\sim$20 Myr) are comparable to thoseof molecular clouds. Self-pollution of the Sun's parent cloud from an ECSN mayexplain the heterogeneous distribution of n-rich isotopic anomalies inplanetary materials, including a recently reported dichotomy in Mo isotopes inthe solar system. The stellar origins of three grains with solar$^{54}$Cr/$^{52}$Cr, but anomalies in $^{50}$Cr or $^{53}$Cr, as well as of agrain enriched in $^{57}$Fe, are unclear.

the astrophysical journal. letters

Extremely $^{54}$Cr- and $^{50}$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