LIGHT-ELEMENT ABUNDANCE INHOMOGENEITIES IN GLOBULAR-CLUSTERS - PROBING STAR-FORMATION AND EVOLUTION IN THE EARLY MILKY-WAY

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the n ature of the observed distribution of these elements is key to constra ining protogalactic star formation history. Patterns deduced from low- resolution spectroscopy of the CN, CH, NH, and CO molecules for low-ma ss stars in their core-hydrogen or first shell-hydrogen burning phases in the oldest ensembles known, the Galactic globular star clusters, a re reviewed. New results for faint stars in NGC 104 (47 Tuc, C0021-723 ) reveal that the bimodal, anticorrelated pattern of CN and CH strengt hs found among luminous evolved stars is also present in stars nearing the end of their main-sequence lifetimes. In the absence of known mec hanisms to mix newly synthesized elements from the interior to the obs ervable surface layers of such unevolved stars, those particular inhom ogeneities imply that the original material from which the stars forme d some 15 billion years ago was chemically inhomogeneous in the C and N elements, However, in other clusters, observations of abundance rati os and C isotope ratios suggest that alterations to surface chemical c ompositions are produced as stars evolve from the main sequence throug h the red giant branch. Thus, the current observed distributions of C, N, and O among the brightest stars (those also observed most often) m ay not reflect the true distribution from which the protocluster cloud formed. The picture that is emerging of the C, N, and O abundance pat terns within globular clusters may be one which requires a complicated combination of stellar evolutionary and primordial effects for its ex planation.