The main result of this paper is the demonstration that it is feasible to survey NGC 6397 for eclipsing binaries using the 1-m class telescope under mediocre weather conditions. Detection of detached eclipsing binaries among upper main-sequence stars in NGC 6397 would be of great interests. By combining radial velocity curves with photometry one would be able to determine absolute parameters for components of such binaries. This in turn would provide information about age of the cluster.
The periods of two SX Phe stars identified in NGC 6397 confirm the correlation noted by McNamara (1995). He noted that the shortest period variables are found preferably in the most metal-poor clusters. In fact star V10 has the shortest period among all known SX Phe stars.
We identified six close binaries in the surveyed field. Four of them are probable cluster members and one is most probably a field object. The membership status and type of the sixth variable cannot be determined based on our photometry.
As a by product of our mini-survey we obtained two sets of BV photometry for stars from the central part of the cluster. The more extended set contains data for 13028 stars. The second set includes 9852 stars but the reduced number of objects is compensated by the relatively higher quality of the photometry. Although the derived photometry is not very deep as for temporary standards it does cover much larger area than any other CCD based study published so far for NGC 6397.
This project was supported by the Polish KBN grant 2P03D00808 to JK and
by NSF grant AST 93-13620 to Bohdan Paczynski.
Thanks are due to Kazik Stepien for comments on the draft version
of this paper.