The observation presented here were carried out with the one-meter telescope
of Yunnan Observatory during November 1996 to January 1997. The telescope is
equipped with a direct CCD (10241024 pixels) camera at the Cassergrain
focus. The CCD was bought from Princeton Instruments Company, U.S.A.
The field is about 6.56.5.
The filters are standard Johnson broadband filters as:
B - GG385(2 mm) + BG12(1 mm) + BG18(2 mm)
V - GG495(2 mm) + BG18(2 mm)
R - RG610(3 mm) + 66.2500(1 mm)
I - RG715(3 mm) + 60.5050(1 mm).
The exposure time is 300 - 400 seconds for B and V filters, 100 - 200 seconds for R and I filters. The sources we observed are listed in Table 1. They are selected arbitrarily. The standard stars in the field are taken from Smith et al. (1985, 1991) (see Table 1).
The results are given in Table 2. The first column is the observing date, the
second the Julian date, the third the magnitude, the fourth the observational
1 uncertainty level and the last the filter used. All observing
data were processed using the photometric tool, APPHOT, in IRAF software
package. The flat field images were taken at dusk and dawn when possible.
The bias (taken at least 15 images each night) were taken at the beginning
of the observation and the end. The source magnitude is given as the average
of those derived with respect to the two brightest standard stars in the
image frame containing the source which present the smallest variations in
their differential magnitudes. The errors quoted in Table 2 are calculated
from the two standard stars, star 1 and star 2, in the usual way,
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