Refined Metallicity Indices for M Dwarfs Using the SLoWPoKES Catalog of Wide, Low-mass Binaries

TL;DR

This study uses spectroscopic data from wide, low-mass binary systems to validate and improve metallicity indices for M dwarfs, enhancing the accuracy of metallicity estimation in these stars.

Contribution

The paper introduces a recalibration of the {ta} metallicity index, improving its predictive power for higher mass M dwarfs based on spectroscopic observations.

Findings

Confirmed co-moving status of binary components via radial velocities.

Identified a small systematic bias in the {ta} index for early-type M dwarfs.

Recalibrated the {ta} index, making it a better predictor of metallicity.

Abstract

We report the results from spectroscopic observations of 113 ultra-wide, low-mass binary systems, composed largely 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 co-moving 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 has similar H{\alpha} levels. The difference in H{\alpha} equivalent width amongst components with similar masses was smaller than the range of H{\alpha} variability for individual objects. We confirm that the Lepine et al. {\zeta}(CaH2+CaH3, TiO5) 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.