Metallicity of M dwarfs I. A photometric calibration and impact on the mass-luminosity relation at the bottom of the main sequence

Abstract

We obtained high resolution ELODIE and CORALIE spectra for both components of 20 wide visual binaries composed of an F-, G- or K-dwarf primary and an M-dwarf secondary. We analyse the well understood spectra of the primaries to determine metallicities ([Fe/H]) for these 20 systems, and hence for their M dwarf components. We pool these metallicities with determinations from the literature to obtain a precise (+- 0.2 dex) photometric calibration of M dwarf metallicities. This calibration represents a breakthrough in a field where discussions have had to remain largely qualitative, and it helps us demonstrate that metallicity explains most of the large dispersion in the empirical V-band mass-luminosity relation. We examine the metallicity of the two known M-dwarf planet-host stars, Gl 876 (+0.02 dex) and Gl 436 (-0.03 dex), in the context of preferential planet formation around metal-rich stars. We finally determine the metallicity of the 47 brightest single M dwarfs in a volume limited sample, and compare the metallicity distributions of solar-type and M-dwarf stars in the solar neighbourhood.

arXiv commentfinal version, accepted for publication (A&A)

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• Homogeneous studies of transiting extrasolar planets. II. Physical properties
• The M Dwarf GJ 436 and its Neptune-Mass Planet
• A Long-Period Jupiter-Mass Planet Orbiting the Nearby M Dwarf GJ849
• The very nearby M/T dwarf binary SCR 1845-6357
• Spectroscopic distances of 28 nearby star candidates
• Exoplanetary Interiors