Candidates for RR Lyrae in binary systems from the OGLE Galactic bulge survey

Abstract

We present 20 newly discovered candidates for binary systems with an RR Lyrae companion. Using the photometric data from the Optical Gravitational Lensing Experiment (OGLE) and Korea Microlensing Telescope Network (KMTNet) for the Galactic bulge, we searched for binary candidates among non-modulated fundamental-mode RR Lyrae variables. We constructed and investigated over 9000 O − C diagrams for individual pulsators, in order to find signs of the light-travel time effect. We found 20 variables exhibiting cyclic variation in the O −C (time of the observed minus calculated brightness maximum) diagram, which can be associated with a second component in the system, but for confirmation of binarity, a long-term radial velocity study is necessary. The modeling of the O − C diagrams yields orbital parameters, estimates of the semi-amplitude of the radial velocity curve, and the mass function. The orbital periods of our candidates range from 3 to 15 years. Two of the binary candidates display a minimum mass higher than the assumed mass of the RR Lyrae component, which points towards an evolved companion that can under some circumstances contribute significantly to the total light of the system.

On the Use of Field RR Lyrae as Galactic Probes. III. The α-element Abundances*

“…There is evidence that some RRLs are the aftermath of close binary evolution and could be younger objects (Pietrzyński et al 2012;Karczmarek et al 2017). However, the fraction of RRLs in binary systems is of the order of a few percent (Hajdu et al 2015;Kervella et al 2019;Prudil et al 2019), and the figure for systems with mass transfer is likely to be even more modest. In all our spectroscopic investigations with the present sample, we found no evidence of binarity.…”

Evidence for Galactic disc RR Lyrae stars in the solar neighbourhood

“…Binary systems with an RR Lyrae component are very rare; to this day only TU UMa seems to be bound in a binary system (e.g., Wade et al 1999;Liška et al 2016b). Another 105 RR Lyrae stars are potential candidates for a binary system, based on the RRLyrBinCan database 11 (Hajdu et al 2015;Liska & Skarka 2016;Liška et al 2016a;Prudil et al 2019b). From our 22 RR Lyrae stars, four (RS Boo, XZ Dra, CN Lyr, DM Cyg) are considered to be binary candidates and their proper motion could have been affected by the unknown second component.…”

The age of the Milky Way inner stellar spheroid from RR Lyrae population synthesis

“…Therefore, we looked for potential binary systems in our sample by searching in the literature, and by utilizing photometric data from the OGLE database (Soszyński et al 2014;Udalski et al 2015) to construct and analyse O−C diagrams 6 for our RRL sample, according to the prescriptions of Hajdu et al (2015) and Prudil et al (2019). Searching for signs of binarity in photometric data of RRLs can be hampered by several effects that can mimic a binary in the O−C diagram, such as the Blazhko effect (quasi-periodic modulation of the light curve Blažko 1907).…”