  We report Mo isotopic data of 27 new presolar SiC grains, including 12
14N-rich AB (14N/15N>440, AB2) and 15 mainstream (MS) grains, and their
correlated Sr and Ba isotope ratios when available. Direct comparison of the
data for the MS grains, which came from low-mass asymptotic giant branch (AGB)
stars with large s-process isotope enhancements, with the AB2 grain data
demonstrates that AB2 grains show near-solar isotopic compositions and lack
s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of
AB2 grains clearly exclude born-again AGB stars, where the intermediate
neutron-capture process (i-process) takes place, as their stellar source. On
the other hand, low-mass CO novae, and early R- and J-type carbon stars show
13C and 14N excesses but no s-process enhancements and are thus potential
stellar sources of AB2 grains. Since both early R-type carbon stars and CO
novae are rare objects, the abundant J-type carbon stars (10-15% of all carbon
stars) are thus likely to be a dominant source of AB2 grains.
