  For stars between 0.8-8.0 solar masses, nucleosynthesis enters its final
phase during the asymptotic giant branch (AGB) stage. During this evolutionary
period, grain condensation occurs in the stellar atmosphere, and the star
experiences significant mass loss. The production of presolar grains can often
be attributed to this unique stellar environment. A subset of presolar oxide
grains features dramatic 18O depletion that cannot be explained by the standard
AGB star burning stages and dredge-up models. An extra mixing process, referred
to as "cool bottom processing" (CBP), was proposed for low-mass AGB stars. The
18O depletion observed within certain stellar environments and within presolar
grain samples may result from the 18O+p processes during CBP. We report here on
a study of the 18O(p,gamma)19F reaction at low energies. Based on our new
results, we found that the resonance at Er = 95 keV (lab) has a negligible
affect on the reaction rate at the temperatures associated with CBP. We also
determined that the direct capture S-factor is almost a factor of 2 lower than
the previously recommended value at low energies. An improved thermonuclear
reaction rate for 18O(p,gamma)19F is presented.
