The observations presented in this paper clearly indicate that important irregularities occur during successive pulsation cycles. In the framework of available observations, which reveal the multiperiodic behavior of the pulsation closely related to the Blazhko effect, it is not yet possible to fully explain the observed "irregularities". In this case, these variations should not be irregular but multiperiodic. New observations are required to confirm that this mechanism is not sufficient. Because there are two strong outward shock waves together with an infalling shock per pulsation period, we suggest that the observed "irregularities" could be also due in part to nonlinear dynamical processes between the motion of the highest and deepest metallic layers when strong shock waves traverse them, which occurs during the bump or the hump. In these conditions, the motion of these layers can be out of synchronization with respect to the photosphere during a small part of the pulsation period. These two mechanisms perharps combine together to produce the observed variations. New high quality observations of a non-Blazhko RR Lyrae star would be helpful to check if these "irregularities" can occur without the presence of the Blazhko effect.
© European Southern Observatory (ESO) 2000
Online publication: July 13, 2000