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Searching for Variable Stars in the Central Part of the Globular Cluster M22

100%

Pietrukowicz P. , Kaluzny J.

tom Vol. 56, No. 4

371-378

Time-series data taken with the Hubble Space Telescope of three fields covering the central part of the globular cluster M22 have been analyzed in search of variable objects. We report identification of eleven periodic variables of which eight are new discoveries. The sample includes five certain contact binaries as well as one SX Phe star. Two objects with periods longer than 1 day are preliminarily classified as either spotted variables of BY Dra type or ellipsoidal variables. The most unusual of the identified variables, M22_V11, has IC≈19.9 and is located far to the red of the main sequence in the cluster color-magnitude diagram. It shows variability with a period as short as P≈0.066 days or alternatively with P≈0.132 days. We propose that it may be an ellipsoidal variable harboring a degenerate component.

The Cluster AgeS Experiment (CASE). Detecting Aperiodic Photometric Variability with the Friends of Friends Algorithm

75%

Rozyczka M. , Narloch W. , Pietrukowicz P. , Thompson I. B. , Pych W. , Poleski R.

tom Vol. 68, No. 1

63--78

We adapt the friends of friends algorithm to the analysis of light curves, and show that it can be succesfully applied to searches for transient phenomena in large photometric databases. As a test case we search OGLE-III light curves for known dwarf novae. A single combination of control parameters allows us to narrow the search to 1% of the data while reaching a ≈90% detection efficiency. A search involving ≈2% of the data and three combinations of control parameters can be significantly more effective - in our case a 100% efficiency is reached. The method can also quite efficiently detect semi-regular variability. In particular, 28 new semi-regular variables have been found in the field of the globular cluster M22, which was examined earlier with the help of periodicity-searching algorithms.