OGLE Study of the Sagittarius Dwarf Spheroidal Galaxy and its M54 Globular Cluster

We use the fundamental-mode RR Lyr-type variable stars (RRab) from OGLE-IV to draw a 3D picture of the central part of the tidally disrupted Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy in the background of the Galactic bulge. We estimate the line-of-sight thickness of the Sgr dSph stream to be FWHMcen=2.42 kpc.

Based on OGLE-IV observations collected in seasons 2011-2014 we have conducted a comprehensive study of stellar variability in the field of the globular cluster M54 (NGC 6715) residing in the core of this dwarf galaxy. We report the identification of 174 RR Lyr stars, four Type II Cepheids (I-band light curves presented below), 51 semi-regular variable red giants, three SX Phe-type stars, eighteen eclipsing binary systems. Eighty-three variables are new discoveries.

The distance to M54 determined from RRab stars is 26.7±0.03stat±1.3sys kpc. We confirm the presence of two old populations in the dwarf galaxy as well as in the globular cluster.

Details on the detected variables, V- and I-band photometry, and finding charts are available to the astronomical community from the OGLE Internet archive.

Please cite the following paper when using the data or referring to these OGLE results: Hamanowicz et al. 2016, Acta Astron, 66, 197. (arXiv:1605.04906)

Any comments about the data and the form of their presentation are welcome. Send your messages to this adress.