REFINED METALLICITY INDICES FOR M DWARFS USING THE SLoWPoKES CATALOG OF WIDE, LOW-MASS BINARIES

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Abstract
We report the results from spectroscopic observations of 113 ultra-wide, low-mass binary systems, largely composed of M0-M3 dwarfs, from the SLoWPoKES catalog of common proper motion pairs identified in the Sloan Digital Sky Survey. Radial velocities of each binary member were used to confirm that they are comoving and, consequently, to further validate the high fidelity of the SLoWPoKES catalog. Ten stars appear to be spectroscopic binaries based on broad or split spectral features, supporting previous findings that wide binaries are likely to be hierarchical systems. We measured the H alpha equivalent width of the stars in our sample and found that components of 81% of the observed pairs have similar H alpha levels. The difference in H alpha equivalent width among components with similar masses was smaller than the range of H alpha variability for individual objects. We confirm that the Lepine et al. zeta-index traces iso-metallicity loci for most of our sample of M dwarfs. However, we find a small systematic bias in zeta, especially in the early-type M dwarfs. We use our sample to recalibrate the definition of zeta. While representing a small change in the definition, the new zeta is a significantly better predictor of iso-metallicity for the higher-mass M dwarfs.
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