COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1804 Konkoly Observatory Budapest 1980 June 16 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR UV Cet IN 1976 Continuous photoelectric monitoring of the flare star UV Cet has been carried out at the Stephanion Observatory (lambda=-22deg49'44" phi=+37deg45'15") during the year 1976, using the 30-inch Cassegrain reflector of the Department of Geodetic Astronomy, University of Thessaloniki. Observations have been made with a Johnson dual channel photoelectric photometer in the B colour of the international UBV System. The telescope and photometer will be described elsewhere. Here we mention only that the transformation of our instrumental ubv system to the international UBV system is given by the following equations: V = v_0 + 0.042(b-v)_0 + 2.278, (B-V)= 0.706 + 1.043(b-v)_0, (U-B)=-2.550 + 1.490(u-b)_0. The monitoring intervals in UT as well as the total monitoring time for each night are given in Table I. Any interruption of more than one minute has been noted. In the fourth column of Table I the standard deviation of random noise fluctuation sigma(mag)=2..5 log(I_0+sigma)/I_0 for different times (UT) of the corresponding monitoring intervals is given. During the 6.20 hours of the monitoring time 2 flares were observed the characteristics of which are given in Table II.For each flare following characteristics l Andrews et al. 1969) are given: a) the date and universal time of flare maximum, b) the duration before and after the maximum (t_b and t_a, respectively), as well as the total duration of the flare, c) the value of the ratio (I_f-I_0)/I_0 corresponding to flare maximum, where I_0 is the intensity deflection less sky background of the quiet star and If is the total intensity deflection less sky background of the star plus flare, d) the integrated intensity of the flare over T A B L E I Monitoring intervals in 1976 Date Monitoring intervals (U.T.) Total Monitoring 1976 sigma( U.T.) Nov. Time 21 18h44m-19h21m 19h23m-20h02m 20h05m-20h36m, 0.13(19h03m),0,13(19h42m), 20 47 -21 08, 21 15 -21 46, 21 52 -22 12, 0.13(20 15 ),0.14(20 59 ), 22 14 -22 27. 3h12m 0.14(21 33 ),0.16(22 02 ). 27 19 28 -20 00, 20 02 -20 32, 20 35 -21 09, 0.20(19 42 ),0.18(20 19 ), 21 11 -21 31, 21 35 -21 43, 21 45 -22 03, 0.13(20 50 ),0.16(21 16 ), 22 14 -22 26, 22 27 -22 38, 22 44 -22 55, 0.09(21 51 ),0.12(22 30 ). 22 59 -23 03. 3h00m TOTAL 6h12m T A B L E II Characteristics of the Flares Observed Flare Date U.T. t_b t_a Duration I_f -I_0 /I_0 P Delta m sigma Air 1976 No max. min min min max min mag mag mass Nov. 1 27 20h52.29m 0.48 16.92 17.40 13.40 15.30 2.90 0.13 1.91 20h53.89m 4.39 1.83 1.91 2 27 21h52.36m 0.07 1.73 1.80 1.16 0.39 0.84 0.09 2.28 [FIGURE 1] [FIGURE 2] its total duration, including pre-flares, if present, p=integral ((I_f-I_0)/I_0) dt, e) the increase of the apparent magnitude of the star at flare maximum Delta m(b)=2.5 log(I_f/I_0), where b is the blue magnitude of the star in the instrumental system, f) the standard deviation of random noise fluctuation sigma(mag) = 2.5 log(I_0+sigma)/I_0 during the quiet-state phase immediately preceding the beginning of the flare and g) the air mass at flare maximum. The light curves of the observed flares in the b colour are shown in Figs. 1-2. Acknowledgements: The support of the National Hellenic Research Foundation for this research is gratefully acknowledged. G.ASTERIADIS, G.KAREKLIDIS, L.N.MAVRIDIS Department of Geodetic Astronomy, University of Thessaloniki. P. VARVOGLIS Department of Mathematics, University of Thrace Reference; Andrews, A.D., Chugainov, P.F., Gershberg, R.I. and Oskanian, V.S.: 1969, I.B.V.S. No. 326