We report preliminary results of a radial velocity study of the old open cluster NGC 752 using an ensemble mean approach with Hydra multi-fiber spectroscopy on the 3.5-m WIYN telescope. The goal is to detect the higher amplitude extra-solar planetary systems and brown dwarf binaries that might reside in the cluster. The oscillation modes of mid-F stars at the redward edge of the instability strip can also be observed. The observation of NGC 752 is the first step in an ongoing study of a variety of clusters with different ages and metallicities.

In 1979 a disturbing controversy arose in the field of globular cluster research when Cohen (1980) and Pilachowski, Canterna, and Wallerstein (1980) announced the results of the first high dispersion studies of the composition of giants in the globular clusters M 71 and 47 Tucanae. In contrast to earlier studies, which found metallicities of typically −0.3 and −0.5 dex, these investigators obtained values of −1.3 and −1.1. Since then, many have attempted to redetermine the abundances of M 71 and 47 Tuc to explain the discrepant results. These efforts have all suffered from the absence of high signal-to-noise, high resolution spectra of stars with temperatures above 4300 K.

Nature has filled the upper right quadrant of the Hertzsprung-Russell diagram with more varieties of peculiar stars and odd chemical compositions than even our most speculative observers and theorists could dream up. To bring some structure to this vast subject I will categorize the phenomena we observe according to our model of stellar evolution, dividing the stars among the first ascent of the giant branch and the core-helium burning phase, the asymptotic giant branch (double shell-burning) phase, and the post-AGB and pre-planetary nebula stars. The types of stars found in these three groups are summarized below.

Studies of the carbon and nitrogen abundances in metal poor giants have generally supported the models of Sweigart and Mengel (1979) which indicate the action of meridional circulation in CN-processing metal poor red giant envelopes. Carbon et al. (1982) find the trends in the carbon and nitrogen abundances in M 92 stars to be at least qualitatively consistent with CN-cycle processing of the envelope, but stars at all phases of giant branch evolution have unusual, and unexplained, carbon and nitrogen abundances. The oxygen abundance is the missing piece of information which may explain what’s going on. Sweigart and Mengel’s models suggest that ON-processing might also occur in the most metal poor giants. The sample of giants in M 92 for which Carbon et al. have provided carbon and nitrogen abundances is ideal for the determination of oxygen abundances to look for the effects of ON-processing. Once the oxygen abundances are known, the sum C+N+0 can be computed to see if it is constant along the giant branch or varies from star to star.

The metallicities of the globular clusters 47 Tucanae, NGC3201, and NGC6752 have been determined from high dispersion spectra obtained with the echelle spectrograph at CTIO. The mean iron deficiencies of NGC3201 and NGC6752 are −1.0 and −1.3, respectively. Oxygen is enriched by a factor of two in NGC3201; no oxygen data are available in NGC6752 due to the small radial velocity of this cluster. The atmospheric parameters and the abundances, relative to the Sun, of individual elements for two stars in 47 Tuc are tabulated below. Star identifications are taken from Hesser and Hartwick (1977). The stellar effective temperatures were established from the spectroscopic data; the data do not permit temperatures much in excess of those quoted. Surface gravities were calculated from the cluster's distance modulus and other reasonably well-known quantities, with the assumption that the mass of a cluster giant is 0.8 M⊙.

The clump giants in old and middle-aged open clusters provide a sample of stars whose evolutionary state can be clearly identified as core helium burning (Cannon 1970). The evolutionary state of the Ba II stars, on the other hand, is at present undetermined. The enrichment of s-process elements in the atmospheres of these peculiar stars suggests that the stars have at least passed through double shell burning, where the heavy elements may be produced and mixed to the surface. The Ba II stars are, however, too faint to be associated with this phase of stellar evolution; the absolute magnitudes and temperatures are consistent with the core helium burning phase. The barium stars should then occur in the clumps of Population I clusters in similar proportion to their numbers among the field giants.

During the past decade it has been evident that the morphologies of globular cluster color-magnitude diagrams cannot be described by only two parameters, age and metal abundance (Sandage and Wildey 1967, Hartwick 1968). The third parameter is unlikely to be helium because a normal helium abundance is needed to explain the pulsation of RR Lyrae stars (Deupree 1977) and because the helium abundance of the planetary nebula in the metal-poor cluster M15 is normal (O'Dell et al. 1964).