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Hα Imaging of X-ray Sources in Selected Globular Clusters with the SOAR Telescope

Pietrukowicz P.

Acta Astronomica

2009

Vol. 59, No. 3

291--305

We present results of a search for objects with Hα excess, such as cataclysmic variables (CVs) and chromospherically active binaries (ABs), as counterparts to X-ray sources detected with Chandra satellite observatory in six Galactic globular clusters (GCs): M4, M28, M30, M71, M80, NGC 6752. Binary systems play a critical role in the evolution of GCs, serving as an internal energy source countering the tendency of GC cores to collapse. Theoretical studies predict dozens of CVs in the cores of some GCs (eg., 130 for M28, 40 for M30). A number of such binaries is also expected outside the core radius. However, few CVs are known so far in GCs. Using subtraction technique applied to images taken with the 4.1-m SOAR telescope we have found 27 objects with Hα excess in the field of the observed clusters, of which nine are likely associated with the clusters. Four are candidate CVs, four are candidate ABs, one could be either a CV or an AB. One Hα object seems to be a background galaxy, while other 17 detected objects are probably foreground or background stars.

CURiuos Variables Experiment (CURVE): Variable Stars in the Metal-Poor Globular Cluster M56

Pietrukowicz P., Olech A., Kędzierski P., Złoczewski K., Wiśniewski M., Mularczyk K.

Acta Astronomica

2008

Vol. 58, No. 2

121--130

We surveyed a 6.5'×6.5' field centered on the globular cluster M56 (NGC 6779) in a search for variable stars detecting seven variables, among which two objects are new identifications. One of the new variables is an RRLyrae star, the third star of that type in M56. Comparison of the new observations and old photometric data for an RV Tauri variable V6 indicates a likely period change in the star. Its slow and negative rate of -0.005±0.003 d/yr would disagree with post-AGB evolution, however this could be a result of blue-loop evolution and/or random fluctuations of the period.

CURious Variables Experiment (CURVE). CCD Photometry and Variable Stars in the Field of Open Cluster NGC 637

Pietrukowicz P., Olech A., Wiśniewski M., Kędzierski P., Mularczyk K., Złoczewski K., Starczewski S., Szaruga K.

Acta Astronomica

2006

Vol. 56, No. 3

267--275

We present VI photometry for the open cluster NGC 637 which is located in the Cassiopeia region. Morphology of cluster color-magnitude diagram indicates that it is a young object with age of a few million years. The apparent distance modulus of the cluster is 13.9<(m-M)V<14.3 mag, while reddening is 0.69