  We report C, N, and Si isotopic data for 59 highly 13C-enriched presolar
submicron- to micron-sized SiC grains from the Murchison meteorite, including
eight putative nova grains (PNGs) and 29 15N-rich (14N/15N<=solar) AB grains,
and their Mg-Al, S, and Ca-Ti isotope data when available. These 37 grains are
enriched in 13C, 15N and 26Al with the PNGs showing more extreme enhancements.
The 15N-rich AB grains show systematically higher 26Al and 30Si excesses than
the 14N-rich AB grains. Thus, we propose to divide the AB grains into groups 1
(14N/15N<solar) and 2 (14N/15N>=solar). For the first time, we have obtained
both S and Ti isotopic data for five AB1 grains and one PNG, and found 32S
and/or 50Ti enhancements. Interestingly, one AB1 grain had the largest 32S and
50Ti excesses, strongly suggesting a neutron-capture nucleosynthetic origin of
the 32S excess and thus the initial presence of radiogenic 32Si (t1/2=153 yr).
More importantly, we found that the 15N and 26Al excesses of AB1 grains form a
trend that extends to the region in the N-Al isotope plot occupied by C2
grains, strongly indicating a common stellar origin for both AB1 and C2 grains.
Comparison of supernova models with the AB1 and C2 grain data indicates that
these grains came from SNe that experienced H ingestion into the He/C zones of
their progenitors.
