A Multisite UBV Photometric Campaign on 53 Persei in 1991 January

New UBV observations of 53 Persei obtained during an international photometric campaign in 1991 January are presented. Techniques of observation and data reduction employed at each of the four participating observatories are described in detail, followed by a discussion of the observational uncertainties and systematic errors. The formal standard deviations determined from check-star measurements are 0.011, 0.012, and 0.020 mag for V, B, and U, respectively. Multiple frequency analysis shows that the light variations of 53 Persei during the campaign can be fitted very well by two sinusoids of frequencies 0.462 and 0.603 cycles per day (c/d) which are practically identical to those found by others from 1977-1983 photometric and spectroscopic data. The detection of the same frequencies in the data obtained more than 10 yr apart has convincingly confirmed the stable multiperiodicity in 53 Persei and extended the stability duration from 5.5 yr reported in an earlier investigation to about 13 yr. This pivotal result strongly supports the nonradial pulsation as the physical cause responsible for light and line-profile variations in this prototype star. Definite changes have been detected in amplitudes and amplitude ratios of the light variations. Since 1981, the amplitude ratio of the two modes mentioned above has increased from approximately 0.9 to greater than 2.5. The single mode of 0.462 c/d has become the dominant component in the two-mode pulsation of 53 Persei. The deviations of data from the two-frequency fits may imp ly the existence of additional frequencies. But we cannot prove this inference with present data.