A Singular Presolar S[CLC]i[/CLC]C Grain with Extreme [TSUP]29[/TSUP]S[CLC]i[/CLC] and [TSUP]30[/TSUP]S[CLC]i[/CLC] Excesses

An ion-imaging search of presolar SiC grains from the Murchison meteorite revealed one grain whose isotopic ratios are highly unusual: 12 C/ 13 C = 844±34, 14 N/ 15 N = 213±21, 29 Si/ 28 Si = (3.68±0.02) times solar, and 30 Si/ 28 Si = (4.29±0.04) times solar. Although several populations of presolar SiC grains have been identified, most of which originate in low-mass asymptotic giant branch stars, this is the first grain of its kind among ~20,000 SiC grains analyzed to date. Type II supernovae and Wolf-Rayet O binary systems are possible stellar sources.