Presolar Graphite: Noble Gases and their Origins

Presolar graphite contains a ²²Ne-rich component called Ne-E(L). Noble gas studies on graphite aggregates and single grains have shown that although a dominant source of the ²²Ne is ²²Na, ²²Ne in the He-shell of asymptotic giant branch stars have also contributed to the Ne-E(L). In addition to novae that have been considered to be a possible source of ²²Na, supernovae are a likely source as well. Krypton isotopic ratios of the separates indicate that part of graphite formed in low-mass (<=3M_solar) asymptotic giant branch stars of low metallicity (Z<=0.006).