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Over 38 000 RR Lyrae Stars in the OGLE Galactic Bulge Fields

Soszyński I., Udalski A., Szymański M. K., Pietrukowicz P., Mróz P., Skowron J., Kozłowski S., Poleski R., Skowron D., Pietrzyński G., Wyrzykowski L., Ulaczyk K., Kubiak M.

Acta Astronomica

2014

Vol. 64, No. 3

177--196

We present the most comprehensive picture ever obtained of the central parts of the Milky Way probed with RR Lyr variable stars. This is a collection of 38 257 RR Lyr stars detected over 182 square degrees monitored photometrically by the Optical Gravitational Lensing Experiment (OGLE) in the most central regions of the Galactic bulge. The sample consists of 16 804 variables found and published by the OGLE collaboration in 2011 and 21 453 RR Lyr stars newly detected in the photometric databases of the fourth phase of the OGLE survey (OGLE-IV). 93% of the OGLE-IV variables were previously unknown. The total sample consists of 27 258 RRab, 10 825 RRc, and 174 RRd stars. We provide OGLE-IV I- and V-band light curves of the variables along with their basic parameters. About 300 RR Lyr stars in our collection are plausible members of 15 globular clusters. Among others, we found the first pulsating variables that may belong to the globular cluster Terzan 1 and the first RRd star in the globular cluster M54. Our survey also covers the center and outskirts of the Sagittarius Dwarf Spheroidal Galaxy enabling studies of the spatial distribution of the old stellar population from this galaxy. A group of double-mode RR Lyr stars with period ratios around 0.740 forms a stream in the sky that may be a relic of a cluster or a dwarf galaxy tidally disrupted by the Milky Way. Three of our RR Lyr stars experienced a pulsation mode switching from double-mode to single fundamental mode or vice versa. We also present the first known RRd stars with large-amplitude Blazhko effect.

The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XI. RR Lyrae Stars in the Galactic Bulge

Soszyński I., Dziembowski W. A., Udalski A., Poleski R., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Kozłowski S., Pietrukowicz P.

Acta Astronomica

2011

Vol. 61, No. 1

1--23

The eleventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 16 836 RR Lyr stars detected in the OGLE fields toward the Galactic bulge. The total sample is composed of 11 756 RR Lyr stars pulsating in the fundamental mode (RRab), 4989 overtone pulsators (RRc), and 91 double-mode (RRd) stars. About 400 RR Lyr stars are members of the Sagittarius Dwarf Spheroidal Galaxy. The catalog includes the time-series photometry collected in the course of the OGLE survey, basic parameters of the stars, finding charts, and cross-identifications with other catalogs of RR Lyr stars toward the Milky Way center. We notice that some RRd stars in the Galactic bulge show unusually short periods and small ratio of periods, down to PF≈0.35 days and P1O/PF≈0.726. In the Petersen diagram double-mode RRLyr stars form a parabola-like structure, which connects shorter- and longer-period RRd stars. We show that the unique properties of the bulge RRd stars may be explained by allowing for the wide range of the metal abundance extending up to [Fe/H]≈-0.36. We report the discovery of an RR Lyr star with additional eclipsing variability with the orbital period of 15.2447 days. Some statistical features of the RRLyr sample are presented. We discuss potential applications of our catalog in studying the structure and history of the central region of the Galaxy, mapping the interstellar extinction toward the bulge, studying globular clusters and the Sagittarius Dwarf Galaxy.