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The OGLE Collection of Variable Stars: Over 18 000 Rotating Variables toward the Galactic Bulge

Iwanek P., Soszyński I., Stępień K., Kozłowski S., Skowron J., Udalski A., Szymański M. K., Wrona M., Pietrukowicz P., Poleski R., Mróz P., Ulaczyk K., Skowron D. M., Gromadzki M., Rybicki K., Mróz M. J., Ratajczak M.

Acta Astronomica

2024

Vol. 74, No. 1

1--25

Stellar rotation, a key factor influencing stellar structure and evolution, also drives magnetic activity, which is manifested as spots or flares on stellar surface. Here, we present a collection of 18 443 rotating variables located toward the Galactic bulge, identified in the photometric database of the Optical Gravitational Lensing Experiment (OGLE) project. These stars exhibit distinct magnetic activity, including starspots and flares. With this collection, we provide long-term, time-series photometry in Cousins I- and Johnson V-band obtained by OGLE since 1997, and basic observational parameters, i.e., equatorial coordinates, rotation periods, mean brightness, and brightness amplitudes in both bands. This is a unique dataset for studying stellar magnetic activity, including activity cycles.

Blue Large-Amplitude Pulsators and Other Short-Period Variable Stars in OGLE-IV Fields of the Outer Galactic Bulge

Borowicz J., Pietrukowicz P., Skowron J., Soszyński I., Udalski A., Szymański M. K., Ulaczyk K., Poleski R., Kozłowski S., Mróz P., Skowron D. M., Rybicki K., Iwanek P., Wrona M., Gromadzki M., Mróz M. J.

Acta Astronomica

2023

Vol. 73, No. 4

265--290

In this work, we search the OGLE-IV outer Galactic bulge fields for short-period variable objects. The investigation focuses on unexplored timescales roughly below one hour in an area containing about 700 million stellar sources down to I≈20 mag. We concentrate mainly on Blue Large-Amplitude Pulsators (BLAPs), which represent a recently discovered enigmatic class of short-period hot subluminous stars. We find 33 BLAPs in the period range from 7.5 min to 66.5 min. Thirty-one of them are new discoveries, which increases the number of known stars of this class to over one hundred. Additional eighteen objects with pulsation-like light curve shapes and periods ranging from 17.3 min to 53.7 min are presented. Very likely, these are δSct/SX Phe-type stars, but some of them could be pulsating hot subdwarfs or BLAPs. We also report on the detection of five eclipsing binary systems with orbital periods between 61.2 min and 121.9 min and three mysterious variable objects with I-band amplitudes larger than 0.9 mag. A spectroscopic follow-up would help in the final classification of the variables.