1996A&A...314..448L

A photometric search for variable stars among the blue stragglers (BS) in southern open clusters of old and intermediate age led to the discovery of one eclipsing binary BS in NGC 2354. The star D266 is 1.5 magnitudes brighter than the cluster turn-off while its angular distance to the cluster center is about seven tenths of the estimated cluster radius. This star was observed for several nights and a total of 422 UBV measurements were obtained. The coverage of the orbital cycle was almost completed, a period of 0.6388228 days was determined, and finally the first light curves of this eclipsing variable star were obtained. They show the typical characteristics of an EB-class close binary with minima about 0.4 and 0.1 magnitudes deep. The photometric analysis by means of the Wilson-Devinney code allowed to define a set of ten possible solutions for assumed values of the mass-ratio between 0.2 and 5.0. Two minima of the quality-of-fit function for q=0.30 and q=3.0 indicate the best solutions we could obtain. Regardless of the value of q, the following features could be established: a) both components are very close to the critical contact lobes and both detached or semidetached configurations fit the light curves in an acceptable way; b) the temperature difference between the components is one of the highest among this type of stars; c) the primary component always remains in the BS zone of the cluster colour-magnitude diagram. If we assume that D266 is a member of NGC 2354, we may conclude that mass-exchange between the components of this system is the most probable cause of its present BS state.