A chromospheric model for FU Ori

We present medium and high-dispersion optical spectra of the FUOr variable FU Ori, demonstrating that some lines are subject to variability both on a yearly and on a daily time scale. Some raw models of accretion disk atmosph eres are presented in order to explain both qualitatively and quantitativel y the dynamics of the observed line variability. Computing synthetic profil es for the Her line by using the non-LTE MULTI code, we find that the emiss ion component of this feature is very sensitive to the temperature gradient and the maximum temperature reached in a chromospheric-like layer. Further , the blue absorption component of the Her depends only on the velocity fie ld of the wind and the transition between the absorption and emission compo nents is produced where the chromosphere ends and the wind begins. Similar chromospheric analysis is applied to the profile of the Na I D lines in pur e absorption.