WIYN OPEN CLUSTER STUDY. XXXIX. ABUNDANCES IN NGC 6253 FROM HYDRA SPECTROSCOPY OF THE Li 6708 A REGION

摘要

High-dispersion spectra of 89 potential members of the old, super-metal-rich open cluster, NGC 6253, have beenobtained with the HYDRA multi-object spectrograph. Based upon radial-velocity measurements alone, 47 starsat the turnoff of the cluster color–magnitude diagram (CMD) and 18 giants are identified as potential members.Five turnoff stars exhibit evidence of binarity while proper-motion data eliminate two of the dwarfs as members.The mean cluster radial velocity from probable single-star members is -29.4 ± 1.3 km s-1 (sd). A discussionof the current estimates for the cluster reddening, derived independently of potential issues with the BV clusterphotometry, lead to an adopted reddening of E(B - V ) = 0.22 ± 0.04. From equivalent width analyses of 38probable single-star members near the CMD turnoff, the weighted average abundances are found to be Fe/H = +0.43 ± 0.01, Ni/H = +0.53 ± 0.02, and Si/H = +0.430.030.04, where the errors refer to the standard errors of theweighted mean.Weak evidence is found for a possible decline in metallicity with increasing luminosity among starsat the turnoff. We discuss the possibility that our turnoff stars have been affected by microscopic diffusion. For 15probable single-star members among the giants, spectrum synthesis leads to abundances of +0.460.020.03 for Fe/H.While NGC 6253 is less than half the age of NGC 6791, it is at least as metal-rich and, within the uncertainties,exhibits the same general abundance pattern as that typified by super-metal-rich dwarfs of the galactic bulge.