Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time e
ffect in so-called observed minus calculated ($O-C$) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide $O-C$ diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that $gtrsim 4$ per cent of the RRL reside in binary systems.
In an extended photometric campaign of RR Lyrae variables of the globular cluster M3, an aberrant light-curve, non-Blazhko RRab star, V123, was detected. Based on its brightness, colors and radial velocity curve, V123 is a bona fide member of M3. The
light curve of V123 exhibits neither a bump preceding light minimum, nor a hump on the rising branch, and has a longer than normal rise time, with a convex shape. Similar shape characterizes the mean light curves of some large-modulation-amplitude Blazhko stars, but none of the regular RRab variables with similar pulsation periods. This peculiar object thus mimics Blazhko variables without showing any evidence of periodic amplitude and/or phase modulation. We cannot find any fully convincing answer to the peculiar behavior of V123, however, the phenomenon raises again the possibility that rotation and aspect angle might play a role in the explanation of the Blazhko phenomenon, and some source of inhomogeneity acts (magnetic field, chemical inhomogeneity) that deforms the radial pulsation of Blazhko stars during the modulation.
