RR Lyrae stars and the Blazhko effect

Abstract

A survey of RR Lyrae stars in the observations of the PLANET collaboration between the years 1995 and 2005 is presented. An exhaustive search of the data has identified 87 RR Lyrae stars and 10 of them exhibit a detectable Blazhko modulation. Lightcurves of the stars are produced through combining data from all the telescopes contributing to PLANET and the stars are well described in a catalogue format. Attempts to constrain models for the Blazhko effect lead to a comparison of the PLANET data to OGLE microlensing survey observations. It is established that the methods used for identifying the RR Lyrae stars in the PLANET data produce a complete detection of these stars in the areas that were observed. Further, the use of the OGLE data produced results supporting magnetic models for the Blazhko effect. New equidistant frequency quintuplets have been discovered in the lightcurves of two Blazhko stars. Such frequency quintuplets are a requirement of the magnetic models attempting to explain the Blazhko effect. The Blazhko effect has remained unexplained for over 100 years and represents a well known and persistent puzzle in variable star research. Competing models for explaining this effect have been developed but all lack conclusive support from observations. In recent years only six other detections of a frequency quintuplet in a Blazhko star have been published (Hurta et al 2008, Jurcsik et al 2008, Kolenberg et al 2009, Jurcsik et al 2009, Chadid et al 2010, Kolenberg et al 2011). This work provides additional support for the magnetic model explanation of the Blazhko effect by showing that frequency quintuplets in Blazhko stars are relatively common and are not an analysis or data artefact. Error and significance analysis shows that the detected frequency quintuplets have small amplitudes but are significant and occur very close to the positions required by the magnetic models.