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Gravitational Lensing and Proper Motions of Stars Surrounding the Galactic Center

100%

Jaroszyński M.

1998

tom Vol. 48, No. 3

413--429

We examine lensing by the black hole in the Galactic center. We use the new photometric data in the infrared to estimate the density of stars in the star cluster surrounding the black hole. We calculate the probability of lensing by the black hole, the rate of the new events and the influence of lensing on the velocity distribution of proper motions of stars. The relative importance of lensing has its maximum at distances ≈10 mas from the star cluster center. The measurement of the proper motion of stars on the scale of ≈3 mas would be necessary to investigate the orbits of stars at distances ≈103rg from the black hole. In principle the deformation of the projected orbit shape by lensing may serve as a way to estimate the angular momentum of the black hole.

The OGLE Collection of Variable Stars. Classical, Type II, and Anomalous Cepheids toward the Galactic Center

88%

Soszyński I. , Udalski A. , Szymański M. K. , Wyrzykowski Ł. , Ulaczyk K. , Poleski R. , Pietrukowicz P. , Kozłowski S. , Skowron D. M. , Skowron J. , Mróz P. , Pawlak M. , Rybicki K. , Jacyszyn-Dobrzeniecka A.

tom Vol. 67, No. 4

297--316

We present a collection of classical, typeII, and anomalous Cepheids detected in the OGLE fields toward the Galactic center. The sample contains 87 classical Cepheids pulsating in one, two or three radial modes, 924 type II Cepheids divided into BL Her, W Vir, peculiar W Vir, and RV Tau stars, and 20 anomalous Cepheids - first such objects found in the Galactic bulge. Additionally, we upgrade the OGLE Collection of RR Lyr stars in the Galactic bulge by adding 828 newly identified variables. For all Cepheids and RRLyr stars, we publish time-series VI photometry obtained during the OGLE-IV project, from 2010 through 2017. We discuss basic properties of our classical pulsators: their spatial distribution, light curve morphology, period-luminosity relations, and position in the Petersen diagram. We present the most interesting individual objects in our collection: a typeII Cepheid with additional eclipsing modulation, WVir stars with the period doubling effect and the RVb phenomenon, a mode-switching RR Lyr star, and a triple-mode anomalous RRd star.