Variable stars in galactic globular clusters. I. The population of RR Lyrae stars

Abstract

We present a comprehensive catalog of $2824$ RR Lyrae stars (RRLs) residing in $115$ Galactic globular clusters (GCs). Our catalog includes 1594 fundamental-mode (RRab), 824 first-overtone (RRc), and 28 double-mode (RRd) RRLs, as well as 378 RRLs of an unknown pulsation mode. We cross-matched 481\,349 RRLs reported in the third data release (DR3) of the ESA mission and the literature to 170 known GCs. Membership probabilities were computed as the products of a position and shape-dependent prior and a likelihood was computed using parallaxes, proper motions, and, where available, radial velocities from Membership likelihoods of RRLs were computed by comparing cluster average parameters based on known member stars and the cross-matched RRLs. We determined empirical RRL instability strip (IS) boundaries based on our catalog and detected three new cluster RRLs inside this region via their excess $G-$band photometric uncertainties. We find that $77<!PCT!>$ of RRLs in GCs are included in the DR3 Specific Object Study, and $82<!PCT!>$ were classified as RRLs by the DR3 classifier, with the majority of the missing sources being located at the crowded GC centers. Surprisingly, we find that $25<!PCT!>$ of cluster member stars located within the empirical IS are not RRLs and appear to be non-variable. Additionally, we find that $80<!PCT!>$ of RRab, $84<!PCT!>$ of RRc, and $100<!PCT!>$ of the RRd stars are located within theoretical IS boundaries predicted using MESA models with $Z=0.0003$, $M=0.7$ \(M_ and $Y=0.290$. Unexpectedly, a higher $Y=0.357$ is required to fully match the location of RRc stars, and lower $Y=0.220$ is needed to match the location of RRab stars. Lastly, our catalog does not exhibit an Oosterhoff dichotomy, with at least 22 GCs located inside the Oosterhoff "gap," which is close to the mode of the distribution of mean RRL periods in GCs.