Irregularities in atmospheric pulsations of RR Lyrae stars

From high spectral resolution observations of the Fe II line at 4923.921 An gstrom, it is shown that the star RRLyrae shows significant differences, bo th in radial velocity and in line FWHM, from one pulsation cycle to the nex t. Two explanations are discussed. The first one is the multiperiodic chara cter of the pulsation (Blazhko effect) which was recently detected (Chadid et al. 1999). In this case, the investigated variations would not be irregu lar but multiperiodic. Nevertheless, the intensity of the multiplet compone nts seem too weak to fully reproduce the amplitude of the observed "irregul arities''. The second mechanism is a dynamical interaction between the high est atmospheric layers and the deepest ones, which are traversed by strong outward shock waves. Nevertheless, because it is known that the shock wave intensities are modulated by the Blazhko effect, it is not excluded that th e multiperiodic behavior of the pulsation can be in part at the origin of t he observed variations. New observations an required to determine the exact intensity value of all components. A comparison with a non-Blazhko star wo uld be helpful.