Bright Blazhko RRab Lyrae stars observed by ASAS and the SuperWASP surveys ^⋆

Department of Theoretical Physics and AstrophysicsFaculty of science, Masaryk University, Kotlářská 2, 611-37 Brno, Czech Republic
e-mail: maska@physics.muni.cz

Received: 15 August 2013
Accepted: 4 December 2013

Abstract

Aims. Period study of 321 fundamental mode RR Lyrae type stars (RRab), which had appropriate data in ASAS and SuperWASP surveys, was performed to complement and extend the list of known Blazhko stars in galactic field with bright stars up to 12.5 mag in maximum light.

Methods. An individual approach was applied to each studied star. Permanent visual supervision was maintained to each procedure in data analysis (data cleaning, frequency spectra examination) to avoid missing any possible sign of the Blazhko effect. Period analysis was performed using Period04 software.

Results. We found 100 stars to be definitely modulated. In 25 cases, previously unknown modulation was revealed and 8 new candidates for Blazhko stars were identified. Their modulation needs to be confirmed. In 18 previously found Blazhko stars, no modulation was detectable. Multiple modulation was revealed for eight stars that were previously proposed to show simple modulation. In total, there were twelve stars with some peculiarity in their modulation in the sample. This brings the incidence rate of multiple/irregularly-modulated stars to 12%. The ratio of the modulation periods of five of the double-modulated stars was within the ratios of small integers. One of stars studied, IK Hya, showed a very interesting frequency spectrum, which we interpret as changing Blazhko period between 71.81 and 75.57 days and an additional 1403-day-long cycle analogous to a four-year cycle of the prototype RR Lyr. The limits of the shorter period produce a beating period that is approximately twice as big as a 1403-day period. The newly revealed Blazhko star RZ CVn seems to undergo changes in the amplitude of the modulation, as well as in the basic pulsation and Blazhko periods. We found that the incidence rate of the Blazhko RR Lyraes is at least 31%, more likely even higher. It was also found that the majority of the Blazhko variables show triplet structures in their frequency spectra and that in 89% of these cases, the peak with larger amplitude is on the right-hand side of the main pulsation component.