Metallicity calibration of metal poor M subdwarfs stars based on binary companions.

The aim of this work is to obtain metallicity calibration for a sample of M dwarfs stars through spectroscopic studies. The low-mass M stars are the most numerous objects in the Galaxy and their main sequence lifetimes exceed the current age of the Universe. Thus, they reveal themselves as large laboratories for studying the structure and evolution of the Galaxy. The efforts of this work are focused in the construction of relations between the strengths of some molecular bands and metallicities for M stars. For that, methodologies in the literature were followed. The motivation of this work was to continue a study initiated by Lépine et al. (2007) using for the first time a sample of M dwarf from southern hemisphere. Besides that, there is yet no definitive metallicity calibration for M dwarfs. Goodman spectrograph at SOAR was used to obtain the stellar spectra. Metallicities estimates for the sample were obtained from an adapted version of the Segue Stellar Parameters Pipeline (sspp), the SDSS\'s pipeline. The studied objects are binary systems consisting of a F or G spectral type star and a M stars. The primary star (F or G) is used to estimate the metallicity of the M star (secondary), since it is assumed that the system is formed from the same parent cloud. Despite all efforts made in this work, it was not possible to refine the metallicities calibration for the analyzed sample. The index originally developed by Lépine et al. (2007) proved to be a poor metallicity indicator, as already documented by them in 2012. Thus, metallicity calibration studies for M dwarf stars should be encouraged. (AU)