Program: GN-2017A-C-4

Magnetic field has a crucial role in the formation and evolution of fully convective object like mid-Mdwarfs. Since the last five years, mid-M dwarfs are key targets to find Habitable Earth-like planets orbiting them. The simulated occurrence rate of planets is based on our current knowledge of their fundamental properties (luminosity, temperature, gravity, metallicity, age and magnetic field). Most of the fundamental properties are well determined, except the magnetic field strength, which is required to predict accurately the expected activity radial velocity jitter of the star. We propose to determine precisely the relation between activity proxy and the small-scale magnetic field strength based on a sample of 15 bright mid-M dwarfs.