Stellar activity and magnetism studied by optical interferometry

By means of numerical simulations, we investigate the ability of optical interferometry, via the fringe phase observ- able, to address stellar activity and magnetism. To derive abundance maps and stellar rotation axes, we use color differential interferometry which couples high angular resolution to high spectral resolution. To constrain magnetic field topologies, we add to this spectro-interferometer a polarimetric mode. Two cases of well-known Chemically Peculiar (CP) stars (βCrB and α 2 CVn) are simulated to derive instrumental requirements to obtain 2D-maps of abundance inhomogeneities and magnetic fields. We conclude that the near-infrared instrument AMBER of the VLTI will allow us to locate abundance inhomogeneities of CP stars larger than a fraction of milliarcsecond whereas the polarimetric mode of the French GI2T/REGAIN interferometer would permit one to disentangle various magnetic field topologies on CP stars. We emphasize the crucial need for developing and validating inversion algorithms so that future instruments on optical aperture synthesis arrays can be optimally used.