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1 Acta Astronomica

1 1999

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Variable Stars in the Field of the Open Cluster NGC 7789

Mochejska B. J., Kaluzny J.

Acta Astronomica

1999

Vol. 49, No. 3

351--370

We present the results of our search for variable stars in the intermediate-age open cluster NGC 7789. We have found 45 variable stars: 35 eclipsing binaries, five pulsating variables and five miscellaneous variables. Most of the eclipsing binaries show W UMa type of variability, with periods shorter than one day. Four systems exhibit unusual behavior: two, V8 and V32, are probably RS CVn stars, another, V9, is a possible cataclysmic binary. The nature of the fourth binary, V4, is unclear: the system exhibits asymmetric maxima. Among the pulsating variables two, V44 and V45 are background RR Lyrae stars and one, V10, is a δ Sct variable which is a blue straggler belonging to the cluster. Some of the miscellaneous variables may have periods longer than the five day timespan of our observations. We also present a color-magnitude diagram for the NGC 7789 open cluster, fairly complete down to V≈20. The relatively large number of variables found in the comparison field (14 compared to 31 in the cluster field) implies that objects not associated physically with the cluster can account for a significant number of variables identified in the cluster field, as well as in other globular and open clusters observed on a dense background/foreground of disk stars.