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Astron. Astrophys. 351, 21-30 (1999)

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2. Observations

Two samples of photoelectric observations of the NGC 1275 nucleus, obtained with the 1.25-m telescope of the Crimean Astrophysical Observatory were considered. The first sample consists of photoelectric narrow-slit observations of the galaxy continuum; these have been made during the period 12.11.1982-23.10.1987 using the scanned photocounting spectrometer ASP-38.

The diaphragm was 10", an entrance slit of the spectrometer [FORMULA] = 80 Å was centered at the wavelength [FORMULA] 5200 Å. During 35 nights of observations 379 flux measurements with a time resolution of 4-5 min were made. The accuracy [FORMULA] of a single flux measurement was in the range [FORMULA]4%.

The second sample consists of five observational series obtained simultaneously in five bands of the UBVRI ([FORMULA] 3700-8300 Å) photometric system from 22.12.1989 to 29.12.1994 with the use of the Double Image Chopping Photometer-Polarimeter (Piirola V., 1973). Observations were carried out with the round diaphragm 20". During 37 nights 820 estimates of the flux in each filter were made. The error [FORMULA] of a single flux measurement was in the range [FORMULA]1%, the time resolution was about 4 min.

The observations are carried out using a conventional technique. Two comparison stars are used, the second one for check purposes. Stars were taken from the list by Lyuty (1972). The telescope is fully automated, during observation the location of the object inside the diaphragm is controlled by the autoguide. The duration of one night's observations varied from 0.5 to 8.7 hours. The monitoring of the NGC 1275 nucleus was made in good atmospheric conditions; as a rule, the estimated seeing was 1-3 arcsec. The sky background has been subtracted. Details of the observational techniques, part of the observational data of nucleus of the NGC 1275 and the analysis of the errors of the measured fluxes were published in papers by Merkulova (1986), Merkulova & Pronik (1987), Merkulova et al. (1988, 1992, 1993), Merkulova & Metik (1995, 1996). Averaged values of the flux F of the nucleus of NGC 1275 for each night of observations in 1982-1987 are listed in Table 1.


Table 1. Observational data of the NGC 1275 continuum at [FORMULA]5200 Å obtained in 1982-1987

There were 6 independent series of observations: one series was obtained in 1982-1987, and 5 sets in the U, B, V, R and I bands were obtained in 1989 -1994. During some nights 40-60 measurements of the nucleus brightness were made. To keep the observational material homogeneous and to examine differences in the characteristics of the variability at different times and different wavelength regions, we examine below the variable flux of the NGC 1275 nucleus separately for each of the 6 series.

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© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999