Stellar differential rotation and inclination angle from spectro-interferometry

Differential interferometry (DI) is a technique that combines high spectral resolution with high spatial resolution. It is particularly suited to probe mechanisms that induce chromatic signatures, such as large scale mass motions. We thus investigate the use of DI combined with the Fourier transform method to study the stellar surface differential rotation. We show that, compared to spectroscopy, DI has the double advantage of allowing the use of all available Fourier frequencies as well as of disentangling the stellar differential rotation rate and the inclination angle. We derive some reference analytical expressions of DI observables. It is shown that the foreseen instrumental performances of the spectro-interferometer VLTI/AMBER are high enough to study the stellar differential rotation.