Peculiar double-periodic pulsation in RR Lyrae stars of the OGLE collection – I. Long-period stars with dominant radial fundamental mode

• DOI: 10.1093/mnras/stw1519
• Publication Date: 2016-06-29T11:37:38Z
• Authors: R. Smolec; Z. Prudil; M. Skarka; K. Bakowska
• Keywords: RR Lyrae variable; Overtone; Variable star

We present the discovery of a new, peculiar form double-periodic pulsation in RR Lyrae stars. In four, long-period (P > 0.6 d) stars observed by Optical Gravitational Lensing Experiment, and classified as fundamental mode pulsators (RRab), we detect additional, low-amplitude variability, with period shorter than period. The ratios fall range similar to double-mode first overtone (RRd), exception one star, which ratio is significantly lower nearly exactly equals 0.7. Although are fairly different for four stars, light-curve shapes corresponding dominant, very similar. peak-to-peak amplitudes amplitude (Fourier parameters R21 R31) among highest RRab period, while Fourier phases (φ21 φ31) lowest If additional variability interpreted due radial overtone, then, most extreme RRd variables longest periods known. Indeed, can be well modelled high-metallicity models. However, at such long periods, typically damped. Five other candidates, weak signature sharing same characteristics, were also detected briefly discussed.