1999A&A...344..930F

A time variation of the microturbulence velocity v_turb in the atmosphere of RR Lyrae is estimated from a comparison of the observed and theoretical FWHM curves of the FeII4923.921Å absorption line. The theoretical line profiles were obtained using a hydrodynamical RR Lyrae model, discussed in Fokin & Gillet (1997A&A...325.1013F). The estimated value of the v_turb varies from 2 to 7km/s, with a maximum at the phase 0.7. The dominant increase of the v_turb seems to be caused by a strong shock, propagating through the line formation region and producing compression of the turbulent gas. Indeed, according to the current theories of the shock/turbulence interaction, the mean density increases, such as revealed by the model, should lead to a certain turbulence enhancement. Yet, the detailed mechanism of such an amplification is to be clarified.