COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2340 Konkoly Observatory Budapest 25 May 1983 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV Lac IN 1982 Continuous photoelectric monitoring of the flare star EV Lac has been carried out at Stephanion Observatory during the autumn 1982 in the framework of the Program for Scientific and Technical Co-operation between the Department of Geodetic Astronomy, University of Thessaloniki - Greece and the Department of Astronomy with National Astronomical Observatory, Bulgarian Academy of Sciences - Bulgaria. Observations have been made with the 30-inch Cassegrain reflector at Stephanion Observatory with a Johnson dual channel photoelectric photometer in B colour of the international UBV system. The telescope and the photometer have been described elsewhere (Mavridis et al., 1982). The -transformation of our instrumental ubv system to the international UBV system for the year 1982 is given by the following equations: V = v_0 - 0.011 (b-v)_0 + 3.288 B - V = 0.597+ 1.010 (b-v)_0 U - B = -1.899+ 1.031 (u-b)_0 The monitoring intervals in U.T. as well as 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 (U.T.) of the corresponding monitoring intervals is given. During the 11.15 hours of monitoring time 6 flares were observed the characteristics of which are given in Table II. For each flare the following characteristics (Andrews et al., 1969) are given: a. the date and universal time of maximum, b. the duration before and after 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_o is the intensity deflection less sky background of the quiet star and I_f is the total intensity deflection less sky background of the star plus flare. d. the integral intensity of the flare over 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 of flare maximum -Deltam(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)=2.5log(I_0 +sigma)/I_0, during the quiet-state phase immediately preceding the beginning of the flare. g. the air mass at flare maximum. Table I Monitoring intervals in 1982 -------------------------------------------------------------------------- Date Monitoring intervals (U.T.) Total sigma_mag(U.T.) 1982 Monitoring Time -------------------------------------------------------------------------- Oct.13 19h06m-19h49m,19h52m-20h27m, 4h02m 0.02(19h24m),0.02(20h18m), 20 30 -21 09 ,21 28 -21 42 , 0.03(21 05) ,0.03(21 33 ), 21 43 -22 12 ,22 15 -22 57 , 0.03(22 06) ,0.03(22 55 ), 22 59 -23 39. 0.02(23 31). 14 20 21 -20 49 ,20 51 -21 00 , 2 10 0.03(20 36) ,0.03(20 55 ), 21 03 -21 23 ,21 26 -21 52 , 0.03(21 10) ,0.03(21 40 ), 21 53 -22 36 ,22 39 -22 43. 0.03(22 13) ,0.07(22 40). 15 19 11 -19 31 ,19 35 -19 56 , 2 00 0.02(19 18) ,0.03(19 53 ), 19 59 -20 26 ,20 29 -20 44 , 0.03(20 20) ,0.03(20 34 ), 21 52 -22 01 ,22 03 -22 31. 0.03(21 57) ,0.03(22 27 ). 17 18 27 -19 25 ,19 26 -19 52 , 2 57 0.02(19 00) ,0.02(19 46 ), 19 54 -20 33 ,20 35 -21 29. 0.02(20 18) ,0.03(21 20 ). Total =11h09m -------------------------------------------------------------------------- Table II Characteristics of the Flares Observed ------------------------------------------------------------------------------- Flare Date U.T. t_b t_a I_f-I_0/ P Deltam sigma Air No. 1982 Duration I_0 min mag mag mass max min min min max ------------------------------------------------------------------------------- 1. Oct.13 22h33.4m 1.06 1.34 2.40 0.127 0.092 0.13 0.02 1.320 2. 14 20 40.1 0.30 5.90 6.20 0.857 1.389 0.67 0.03 1.025 3. 14 21 42.6 0.60 4.60 5.20 0.311 0.347 0.29 0.03 1.090 4. 15 20 22.4 0.42 1.90 2.32 0.181 0.107 0.18 0.03 1.019 5. 17 19 47.8 0.52 2.32 2.84 0.190 0.110 0.19 0.02 1.008 6. 17 21 22.4 0.60 0.77 1.37 0.155 0.078 0.16 0.03 1.078 ----------------------------------------------------------------------------------- The light curves of the observed flares in the b colour are shown in Figs. 1-6. [FIGURE 1] [FIGURE 2] The authors would like to express their gratitude to the relevant authorities of the respective countries for their support. M.K. TSVETKOV Department of Astronomy with National Astronomical Observatory Bulgarian Academy of Sciences, Bulgaria L.N. MAVRIDIS, G.A. ASTERIADIS Department of Geodetic Astronomy University of Thessaloniki Greece References: Andrews A.D., Chugainov P.F., Gershberg R.E. and Oskanian V.S., 1969, I.B.V.S. No. 326 Mavridis L.N., Asteriadis G.A. and Mahmoud F.M., 1982, In: Compendium in Astronomy, D. Reidel, Dordrecht, Holland, p. 245 [BIBCODE 1982coas.conf..253M ]