Metallicity of M dwarfs II. A comparative study of photometric metallicity scales

TL;DR

This study compares various photometric metallicity calibrations for M dwarfs using a sample of wide companions with known metallicities, finding that the Schlaufman & Laughlin (2010) calibration performs best and that intrinsic astrophysical factors contribute to residual uncertainties.

Contribution

The paper provides a comparative analysis of existing photometric metallicity calibrations for M dwarfs and refines the best calibration based on a carefully selected sample.

Findings

Schlaufman & Laughlin (2010) calibration shows lowest residuals.

Residual dispersion exceeds measurement uncertainties.

Astrophysical factors likely cause remaining scatter.

Abstract

Stellar parameters are not easily derived from M dwarf spectra, which are dominated by complex bands of diatomic and triatomic molecules and not well described at the line by line level by atmospheric models. M dwarf metallicities are therefore most commonly derived through less direct techniques. Several recent publications propose calibrations that provide the metallicity of an M dwarf from its Ks band absolute magnitude and its V-Ks color, but disagree at the \pm0.1 dex level. We compare these calibrations on a sample of 23 M dwarfs, which we select as wide (> 5 arcsec) companions of F-, G- or K- dwarfs with metallicities measured on a homogeneous scale, and which we require to have V band photometry measured to better than \sim0.03 magnitude. We find that the Schlaufman & Laughlin (2010) calibration has lowest offsets and residuals against our sample, and use our improved statistics to marginally refine that calibration. With more strictly selected photometry than in previous studies, the dispersion around the calibration is well in excess of the [Fe/H] and photometric uncertainties. This suggests that the origin of the remaining dispersion is astrophysical rather than observational.