2006CoAst.148...21G

High-precision multisite photometry was used to investigate the bump occurring before minimum light in the light curves of the two RRab Blazhko stars RR Lyr and SS For. For both stars the phase of the bump was found to be variable with a period equal to the Blazhko period. There seems to be a direct connection between the behavior of the bump and the Blazhko effect. As most models connect the phase of the bump to the stellar radius, a variable bump phase may provide constraints to the models for explaining the bump.