2000A&A...356..888D

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 atmospheres are presented in order to explain both qualitatively and quantitatively the dynamics of the observed line variability. Computing synthetic profiles for the Hα line by using the non-LTE MULTI code, we find that the emission 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 Hα depends only on the velocity field of the wind and the transition between the absorption and emission components is produced where the chromosphere ends and the wind begins. Similar chromospheric analysis is applied to the profile of the NaI D lines in pure absorption.