Characterization of a Sample of Southern M Dwarfs Using Harps and X-shooter Spectra

We present the homogeneous analysis of a sample of Southern early-type M dwarfs in the solar neighborhood (d < 60 pc). We used the MCAL technique to derive the effective temperature T-eff, metallicity [Fe/H], and activity index i(a)(H-alpha) of 420 M stars using HARPS spectra. The effective temperature T-eff, surface gravity log g, metallicity [Fe/H], and projected rotational velocity V(rot)sini of 153 M0-M6 dwarfs were determined by fitting the observed intermediate-resolution spectra from the VIS arm of VLT/X-shooter with a grid of BT-Settl stellar atmosphere models. We estimated the typical uncertainties of the fit with X-shooter spectra by varying region-to-region results by sigma T-eff similar to 50 K, sigma log g similar to 0.2, and sigma[Fe/H] similar to 0.2 dex. Photometric verification of T-eff for the 295 stars from the HARPS sample and the 61 stars from the X-shooter sample is also provided. We compared our results from different methods to estimate absolute uncertainty in determining the physical properties of M dwarfs.