Historical vanishing of the Blazhko effect of RR Lyr from the GEOS and Kepler surveys

Abstract

RR Lyr is one of the most studied variable stars. Its light curve has been\nregularly monitored since the discovery of the periodic variability in 1899.\nAnalysis of all observed maxima allows us to identify two primary pulsation\nstates defined as pulsation over a long (P0 longer than 0.56684 d) and a short\n(P0 shorter than 0.56682 d) primary pulsation period. These states alternate\nwith intervals of 13-16 yr, and are well defined after 1943. The 40.8 d\nperiodical modulations of the amplitude and the period (i.e. Blazhko effect)\nwere noticed in 1916. We provide homogeneous determinations of the Blazhko\nperiod in the different primary pulsation states. The Blazhko period does not\nfollow the variations of P0 and suddenly diminished from 40.8 d to around 39.0\nd in 1975. The monitoring of these periodicities deserved and deserves a\ncontinuous and intensive observational effort. For this purpose we have built\ndedicated, transportable and autonomous small instruments, Very Tiny Telescopes\n(VTTs), to observe the times of maximum brightness of RR Lyr. As immediate\nresults the VTTs recorded the last change of P0 state in mid-2009 and extended\nthe time coverage of the Kepler observations, thus recording a maximum O-C\namplitude of the Blazhko effect at the end of 2008, followed by the\nhistorically smallest O-C amplitude in late 2013. This decrease is still\nongoing and VTT instruments are ready to monitor the expected increase in the\nnext few years.\n