COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2022 Konkoly Observatory Budapest 1981 October 1 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV Lac IN 1980 Photoelectric monitoring of the flare star EV Lac has been carried out in September and October 1980 using the 60 cm Cassegrain reflector of the National Astronomical Observatory of the Bulgarian Academy of Sciences. Observations have been made with a one channel photoelectric photometer (Tomov, 1977) using an EMI 9789QB photomultiplier and a photoncounting system. The observations have been made in the "b" colour with an integration time of 1 sec. The transformation of our instrumental ubv system to the international UBV system is given by the following equations: DeltaV = Deltav - 0.12 Delta(b-v), Delta(B-V) = 1.14 Delta(b-v), Delta(U-B) = 1.08 Delta(u-b); 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 15.4 hours of monitoring time 5 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 flare 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_0 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 integrated 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 at 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)- 2.5 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 1-5. Table I Monitoring intervals in 1980 Date Monitoring intervals(U.T.) Total Monitoring sigma(U.T.) 1980 Time Sept. ------------------------------------------------------------------------------ 21 19h02m-19h31m,19h33m 20h00m,20h16m-20h46m, 0.03(19h04m),0.04(19h35m), 20 48 -21 17 ,21 36 -21 55 ,21 59 -22 40, 0.04(20 19 ),0.04(20 50 ), 22 48 -23 38. 3h45m 0.04(21 38 ),0.04(22 11 ), 0.03(22 50 ),0.03(23 21 ), 22-23 18 44 -19 37 ,20 02 -20 35 ,20 37 -21 21, 0.04(18 45 ),0.06(19 20 ), 21 27 -21 51 ,21 53 -22 36 ,22 47 -23 29, 0.05(20 03 ),0.04(20 31 ), 23 30 -00 13 ,00 15 -00 19. 4 51 0.06(21 04 ),0.03(21 36 ), 0.03(22 19 ),0.05(22 50 ), 0.06(23 31 ),0.04(00 11 ), 28 19 12 -19 36. 24 0.04(19 14 ). 29-30 20 40 -20 53 ,20 54 -21 40 ,21 46 -22 03, 0.02(20 41 ),0.03(21 13 ), 22 06 -00 12 ,00 15 -00 20. 3 27 0.03(21 47 ),0.03(22 16 ), 0.03(22 37 ),0.03(23 07 ), 0.04(23 37 ). 30 20 57 -21 47 ,21 52 -22 33 ,22 44 -23 05, 0.03(20 58 ),0.03(21 28 ), 23 06 -24 00. 2 46 0.02(21 53 ),0.02(22 24 ), 0.02(23 07 ),0.02(23 32 ), Oct. 1 00 00 -00 11. 11 0.02(00 01 ). Total = 15h24m = 15h.40 ------------------------------------------------------------------------------- [FIGURE 1] [FIGURE 2] [FIGURE 3] [Figs 1-5.] Table II Characteristics of the Flares Observed Flare Date U.T. t_b t_a Duration (I_f-I_0)/I_0 P Deltam sigma Air No. max min min min max min mag mag mass 1980 Sept. ------------------------------------------------------------------------------- 1 28 19h22.33m 2.50 2.67 5.17 0.382 0.850 0.351 0.04 1.044 2 28 19 28.67 2.55 1.60 4.15 0.452 0.962 0.405 0.04 1.038 3 30 00 10.43 2.40 2.10 4.50 1.346 2.326 0.926 0.06 1.286 4 30 21 24.70 1.00 2.35 3.35 0.543 0.906 0.471 0.03 1.020 5 30 21 31.65 1.90 2.67 4.57 0.206 0.387 0.203 0.03 1.024 ------------------------------------------------------------------------------- Acknowledgements The observations reported in this paper are part of the joint research project under the title "Studies on Variable Stars" carried out, by the Department of Astronomy with National Observatory, Bulgarian Academy of Sciences and the Department of Geodetic Astronomy, University of Thessaloniki, Greece in the framework of the Program for Scientific and Technical Co-operation between Greece and Bulgaria. The authors would like to express their gratitude to the relevant authorities of the respective countries for their support. L.N. MAVRIDIS, G. ASTERIADIS K.P. PANOV, M.K. TSVETKOV Department of Geodetic Astronomy Department of Astronomy with University of Thessaloniki, Greece National Astronomical Observatory Bulgarian Academy of Sciences, Sofia Bulgaria References: Andrews, A.D., Chugainov, P.F., Gershberg, R.E. and Oskanian, V.S.: 1969, I.B.V.S. No. 326 Tomov, A.: 1977, Dissertation, Bulgarian Academy of Sciences Sofia