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Session 61 - Russell Prize Lecture.
Invited session, Tuesday, January 16
1st Floor, La Villita Assembly Building
Stars within a given "monometallic" globular cluster often exhibit wide variations in the abundances of C,N, and O as well as certain light metals, particularly Mg, Na and Al. Such variations are generally less pronounced as cluster metallicity increases, and are also less pronounced at a given metallicity in field halo giants. In general, these variations tend to be of two types: those related to evolutionary state and (2) variations among stars in the same evolutionary state. The abundances of C and N and of O and N often prove to be anticorrelated, and most recently it has been found that there exists a "universal" anticorrelation between O and Na, as well as a correlation between Al and Na. These results are discussed in terms of competing scenarios, one in which the anomalies are driven by deep mixing associated with stellar evolution as opposed to another picture in which the variations reflect the primordial state of the cluster gas.
Recent observations of r-process species in omega Cen (Smith et al 1996) and Na abundances among giants in M13 and the halo field (Pilachowski et al 1996) are discussed in connection with these hypotheses.
