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E. Sandquist (San Diego State U.), M Shetrone (U. Texas / McDonald Obs.)
We have analyzed high-resolution spectroscopy of relatively cool blue stragglers as well as main sequence turnoff stars in the old open cluster M67. With some exceptions, we find the metallicity and abundance ratios of the blue stragglers to be identical to those of the turnoff stars, although binary companions complicate the analysis of several of the stragglers. We assert that the current upper limits on lithium abundances of all blue stragglers observed in M67 (by us and others) are consistent with no mixing during the formation process, assuming pre-main sequence and main sequence depletion patterns observed for M67 main sequence stars. We discuss composition signatures that would more definitively distinguish between blue straggler formation mechanisms in cluster stars.
We confirm the spectroscopic detection of a binary companion to the straggler S 1082. From our spectra, we find that the secondary is the cooler component (by 200 K), that the secondary has a projected rotational speed of 90±20 km s-1 for the secondary, and that its radial velocity varies with a peak-to-peak amplitude of 25 km s-1. If this secondary is associated with the 5.5 km s-1 peak-to-peak amplitude of the primary the mass ratio would be 5.