LONG-TIMESCALE BEHAVIOR OF THE BLAZHKO EFFECT FROM RECTIFIED KEPLER DATA

Abstract

In order to benefit from the four year unprecedented precision of the Kepler data, we extracted light curves from the pixel photometric data of the Kepler space telescope for 15 Blazhko RR Lyrae stars. To collect all the flux from a given target as accurately as possible, we defined tailor-made apertures for each star and quarter. In some cases, the aperture finding process yielded sub-optimal results, because some flux have been lost even if the aperture contains all available pixels around the star. This fact stresses the importance of those methods that rely on the whole light curve instead of focusing on the extrema (O − C diagrams and other amplitude independent methods). We carried out detailed Fourier analysis of the light curves and the amplitude independent O − C diagram. We found 12 (80%) multiperiodically modulated stars in our sample. This ratio is much higher than previously found. Resonant coupling between radial modes, a recent theory for explaining the Blazhko effect, allows single, multiperiodic, or even chaotic modulations. Among the stars with two modulations, we found three stars (V355 Lyr, V366 Lyr, and V450 Lyr) where one of the periods dominates in amplitude modulation, but the other period has a larger frequency modulation amplitude. The ratio between the primary and secondary modulation periods is almost always very close to the ratios of small integer numbers. It may indicate the effect of undiscovered resonances. Furthermore, we detected the excitation of the second radial overtone mode f 2 for three stars where this feature was formerly unknown. Our data set comprises the longest continuous, most precise observations of Blazhko RR Lyrae stars ever published. These data are made publicly available and will be unrivaled for years to come.

The SERMON project: 48 new field Blazhko stars and an investigation of modulation-period distribution

“…Accurate space data helped uncover various dynamical processes present only in modulated stars (for example, period doubling Kolláth et al 2011) and additional radial and non-radial modes Benkő et al 2014;Szabó et al 2014). Data from the ground-based surveys, on the other hand, are very useful for studying large samples statistically and investigating general and common characteristics of modulated stars (e.g.…”

“…Jurcsik et al (2005a) showed that the modulation amplitude of short-pulsation-period RR Lyrae stars can be higher than for long-period stars. Benkő et al (2014) and Benkő & Szabó (2015) suggest a monotonic dependence between the strength of amplitude modulation and the period of the BL cycle (the longer the cycle, the larger the amplitude). While the upper limit of the modulation length is still unclear, the bottom limit is probably defined by the upper limit of the rotational velocity of a star.…”

Blazhko modulation in first-overtone RR Lyrae stars from the OGLE Collection

“…In the power spectrum, it manifests as signals close to half-integer frequencies. This phenomenon was detected for the first time in RR Lyr from Kepler data ( [5]), and later studies showed that it affects many modulated RRab stars (see, e.g., [2,14] , first overtone and long-periodic variability forming a period ratio 0.68 are marked with pink crosses ( [7]), RR Lyrae stars with short-period signal are marked with yellow squares ( [9]) and RRab stars with another shortperiod signal are marked with blue filled circles ( [10]). Blazhko stars with additional signals from our sample are marked with orange symbols.…”

Progress report on the K2 RR Lyrae survey

“…K2 is a bona fide community endeavour: without a central, pre-determined research plan, exoplanets, stellar (asteroseismic and other variable) sources, extragalactic objects, microlensing events, and even Solar System objects have been proposed by community members. 1 This opened up new possibilities in RR Lyrae research, too, since compared to the original Kepler field, where roughly 50 RR Lyrae stars were found ( [1,6,7]), thousands of RR Lyrae stars can be observed with K2. Members of the Kepler Asteroseismic Science Consortium (KASC) RR Lyrae and Cepheids Working Group initiated a large survey to ensure that as many RR Lyrae stars will be observed with K2 as possible.…”