Title: "Nucleosynthesis in the Hyades Open Cluster- Evidence for the Enhanced Depletion of 12C"

Abstract: The CNO bi-cycle is the dominant set of H burning reactions powering the cores of stars more massive than the Sun. The cycle results in no net loss of the CNO nuclei, but due to different lifetimes to proton capture, the relative numbers of each do change: 12C is depleted, 14N is enhanced, and 16O, if the ON cycle is active, is depleted. At the end of core H burning, stars experience the first dredge-up, and material processed by the CN and possibly ON cycles are mixed to the surface layers where the products of these core nuclear processes can be observed. Here I present the results of our observational program designed to test standard stellar evolution models and our understanding of core nuclear processes on the main sequence (MS). We have derived CNNO abundances of three giants and three solar-type MS dwarfs in the Hyades open cluster and used the abundances of the dwarfs as a proxy for the initial composition of the giants.  The observed N and O abundances are found to match well a stellar evolution model tailored to the Hyades giants, but the observed C abundance is a factor of 1.5 lower than the model prediction. Put another way, the observed C+N+O abundance of the dwarfs does not equal the C+N+O abundance of the giants, as would be expected from the CNO bi-cycle. I describe our efforts to account for the missing 12C and the possibility that a heretofore unknown nucleosynthetic process may be active in the cores of near-solar metallicity 2.5 M_solar stars.