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Astron. Astrophys. 345, 505-513 (1999)

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2. Observations and reductions

As mentioned above, the CCD observations of h Persei started at the Mt. Suhora Observatory in 1994 and were continued until 1997 using mainly Johnson [FORMULA] and [FORMULA] bands. In addition, observations in the [FORMULA] and [FORMULA] bands were obtained from time to time. In 1997, [FORMULA] observations of this cluster were also collected at the Bial ków Observatory. At both sites, 60-cm Cassegrain-type telescopes equipped with Photometrics Star I CCD cameras were used. This equipment gives us a 4[FORMULA] 6´ field of view. The observed field covered the central region of h Persei. Owing to the different orientations of the CCD cameras at both sites and the fact that the observed field was changed slightly several times during the run, the total field covered by our observations was larger than that of a single field. This can be seen in Fig. 1, where all 311 stars we detected are shown.

[FIGURE] Fig. 1. A schematic view of the observed field in h Persei. Except for W 49, the variables are labeled with their Oosterhoff (1937) numbers. Note that only these stars which we detected are plotted. North is up, east to the left.

During four seasons between October 18, 1994 and January 1, 1998 we acquired 24, 57, 103, and 10 hours of observations in the U, B, V, and [FORMULA] bands, respectively. All these data were corrected for bias, dark and flat-fields in the usual way and then reduced with the DAOPHOT II package (Stetson 1987). In order to improve the signal-to-noise, some consecutive frames in the [FORMULA] and [FORMULA] bands were summed prior to reduction. Next, because of variable quality from night to night, some data were binned, so that each point on the light curve has approximately the same weight.

[FORMULA] light curves were obtained for all stars with reasonable photometry with respect to the nearby comparison stars. At this stage of reduction, the data were corrected for second-order extinction effects. Then, they were analyzed for variability using error and periodogram analysis in addition to visual inspection of the light curves. Out of 311 stars detected in the field, 10 were found to be variable. They are listed in Table 1. The light curves of all the variables are available in electronic form from CDS in Strasbourg via anonymous ftp to


Table 1. Variable stars in the central region of h Persei. W 49 stands for the star number 49 of Wildey (1964).

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© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999