Catalog of fundamental mode RR Lyrae stars in the Galactic bulge from the Optical Gravitational Lensing Experiment

We present a catalog of 1888 distinct fundamental-mode RR Lyrae stars detected in the Galactic bulge fields of the second phase of the Optical Gravitational Lensing Experiment (OGLE), covering an area near 11 deg. These stars were selected primarily according to their light curve morphologies. The catalog includes basic parameters of the light curves, significant frequencies detected close to the main pulsation frequencies (characteristic of the Blazhko effect), V − I colors at minimum light (for most stars), and information useful for assessing the quality of the data for each star. We detect a high rate of incidence of the Blazhko phenomenon (at least 27.6%), including an unprecedentedly large proportion of stars with symmetrical frequency triplets, which we attribute to the new and sensitive method we employ to search for them. We find that the minimum light V −I color (useful as a reddening indicator) grows slowly redder with increasing period and exhibits an unexpectedly large star-to-star scatter of approximately 0.07 mag. We use this color to evaluate the zero-point accuracy of the reddening map of the Galactic bulge derived from OGLE data, and find that in addition to probable low-level random errors or resolution effects (responsible for much of the scatter), the map may systematically over-represent E(V −I) by approximately 0.05 mag in most fields. While the conclusion about the reddening zero points is somewhat tentative, we have reasonably robust evidence that the RR Lyrae-to-red clump color separation is larger by 0.05–0.08 mag in the bulge than locally; at a minimum this sounds a cautionary note about the use of these stars for reddening determinations until the effect is better constrained. We consider the RR Lyrae constraint on the Galactocentric distance, but our uncertainty about the absolute magnitude calibration and possible errors in the extinction determinations leave significant flexibility in the result. However, in contrast to previous results, we robustly detect the signature of the Galactic bar in the RR Lyrae population within the inner ±3◦ of longitude, and we highlight the apparent differences between the structures traced by the red clump giants and the more metal-poor RR Lyrae stars. Princeton University Observatory, Princeton, New Jersey 08544, USA