V. Neves, X. Bonfils, N. C. Santos, X. Delfosse, T. Forveille, F. Allard, C. Natário, C. S. Fernandes, S. Udry

Abstract
Stellar parameters are not easily derived from M dwarf spectra, which are dominated by complex bands of diatomic and triatomic molecules and do not agree well with the individual line predictions of 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 K_s band absolute magnitude and its V - K_s color, but disagree at the ±0.1 dex level. We compared these calibrations using a sample of 23 M dwarfs, which we selected 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 ∼0.03 magnitude. We find that the Schlaufman & Laughlin (2010, A&A, 519, A105) calibration has the lowest offsets and residuals against our sample, and used 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.

Keywords
stars: late-type – stars: fundamental parameters – binaries: general – planetary systems – stars: atmospheres

Notes
Based on observations collected with the FEROS spectrograph at la Silla observatory under ESO programs 073.D-0802(A), 074.D-0670(A), 078.D-0760(A), and with the ELODIE and SOPHIE spectrographs at the Observatoire de Haute Provence.

Astronomy & Astrophysics
Volume 538, Number of pages A25_1
2012 February

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