1997A&A...325.1013F

A series of nonlinear nonadiabatic models for the variable star RR Lyrae are calculated and FeII and BaII line profiles are reconstructed in order to study the recently detected line doubling phenomenon. We found the doubling in both absorption lines, which is proved to be a result of a shock passage through the line formation region (LFR), in agreement with the Schwarzschild (1952) mechanism. It is shown that a number of shock waves of different amplitudes and different physical origins form in the RR Lyrae atmosphere, but only the most strong one is responsible for the observed line doubling. In the FeII and BaII LFR, the associated shock undergoes a very rapid acceleration, which provokes a sudden appearance of a new absorption component near zero velocity. It is found that the shock is first receding for the observer, then becomes almost stationary during the doubling phenomenon, and then advances. These three phases of the shock evolution are well confirmed by recent high resolution observations (Chadid and Gillet, 1996A&A...308..481C), showing a similar complex doubling evolution of the line profile.