COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2408 Konkoly Observatory Budapest 6 October 1983 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV Lac IN 1980 Continuous photoelectric monitoring of the flare star EV Lac has been carried out at the Stephanion Observatory during the year 1980 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, the photometer and the observational procedure have been described elsewhere (Mavridis et al., 1982). 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 - 0.177(b-v)_0 + 2.648, B-V = 0.549 + 0.964(b-v)_0, U-B = -1.596 + 1.140(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. During the 66.56 hours of monitoring time 2 flares were observed the characteristics of which are given in Table II, For each flare following characteristics (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 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 preflares if resent, 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 Table I Monitoring intervals in 1980 Date Monitoring intervals (U.T.) Total monitoring 1980 time July 24 21h30m-21h57m, 22h02m-22h34m, 22h37m-23h15m. 01h37m 26 20 34 -21 11 , 21 13 -21 48 , 21 50 -22 31 , 22 41 -23 33. 02 45 28 21 06 -21 40 , 21 43 -22 16 , 22 19 -22 50 , 23 01 -23 42. 02 19 29 20 02 -20 35 , 20 38 -21 09 , 21 12 -21 48 , 21 59 -22 26, 22 29 -23 00 , 23 02 -23 35. 03 11 30 21 03 -21 41 , 21 43 -22 19 , 22 21 -23 06 , 23 15 -23 39. 02 23 31 20 00 -20 37 , 20 39 -21 17 , 21 27 -21 54 August 14 00 10 -00 32 , 00 36 -01 04 , 01 08 -01 34 . 01 16 14-15 21 44 -22 11 , 22 41 -22 46 , 22 46 -23 13 , 23 17 -23 42, 23 56 -00 24 , 00 28 -00 36. 02 20 16 00 25 -00 51 , 00 54 -01 39. 01 11 16-17 21 20 -21 48 , 21 52 -22 20 , 22 24 -22 53 , 23 08 -23 37, 23 40 -00 13 , 00 17 -00 48 , 01 02 -01 48. 03 44 17-18 23 36 -00 14 , 00 17 -00 53 , 00 57 -01 37. 01 54 21-22 23 12 -23 46 , 00 04 -00 51 , 00 57 -01 16. 04 40 25 00 17 -00 52 , 00 57 -01 19. 01 17 26-27 22 49 -23 28 , 23 33 -00 02 , 00 20 -00 29. 01 17 27-28 23 40 -00 13 , 00 17 -00 49 , 00 52 -00 58 , 01 02 -01 26. 01 35 30-31 20 54 -21 24 , 21 29 -22 02 , 22 07 -22 42 , 23 02 -23 34, 23 38 -23 57 , 00 02 -00 45 , 00 58 -01 36. 03 50 Aug.-Sept. 31- 1 23 42 -00 10 , 00 14 -00 54 , 00 58 -01 34. 01 44 16-17 23 14 -23 43 , 23 57 -00 26 , 00 29 -01 03 , 01 06 -01 29. 01 55 17 19 16 -19 47 , 19 50 -20 23 , 20 32 -20 51 , 22 28 -22 56, 23 00 -23 43. 02 34 18 19 06 -19 37 , 19 41 -20 07 , 20 19 -20 49 , 20 53 -21 16, 21 35 -22 05 , 22 08 -22 39 , 22 51 -23 28. 03 28 19 18 37 -19 02 , 19 04 -19 33 , 19 44 -20 14 , 20 16 -20 45, 20 56 -21 27 , 21 44 -22 13 , 22 26 -22 51 , 22 54 -23 33. 03 47 21-22 19 57 -20 26 , 20 29 -21 01 , 21 11 -21 41 , 21 45 -22 13, 22 32 -23 04 , 23 08 -23 44 , 23 56 -00 26 , 00 30 -00 59, 01 03 -01 21 , 01 21 -01 26. 04 26 23-24 18 33 -19 00 , 19 04 -19 32 , 19 46 -19 59 , 20 03 -20 35, 00 15 -00 45 , 00 50 -01 15 , 01 18 -01 35. 02 54 28-29 21 14 -21 43 , 21 46 -22 16 , 22 20 -22 54 , 23 06 -23 24, 23 28 -23 40 , 23 43 -00 14 , 00 17 -00 47 , 01 01 -01 39. 03 42 Octob. 2- 3 18 59 -19 29 , 19 32 -20 00 , 20 04 -20 36 , 20 52 -21 39, 21 41 -22 20 , 22 23 -22 54 , 23 07 -23 37 , 23 39 -00 04, 00 07 -00 29. 04 44 3- 4 21 02 -21 31 , 21 33 -22 06 , 22 10 -22 40 , 22 51 -23 19, 23 22 -23 53 , 23 56 -00 23 , 00 34 -01 14. 03 38 --------------- TOTAL 66 33 Table II Characteristics of the flares observed Flare Date U.T. tb ta Dura- If-I0/I0 P Deltam sigma Air No. max min min tion max min mag mag mass min 1980 Aug. 1 16 22 27.27 0.44 1.64 2.08 0.38 0.34 0.35 0.03 1.008 2 21 23 24.13 0.56 4.11 4.67 0.74 0.64 0.60 0.03 1.014 [FIGURE 1] [FIGURE 2] 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 Figures 1-2. Acknowledgements: The support of the National Hellenic Research Foundation for this research is gratefully acknowledged. G. ASTERIADIS ^1 S. AVGOLOUPIS ^2 L.N. MAVRIDIS ^1 P. VARVOGLIS ^3 1 Department of Geodesy and Surveying, University of Thessaloniki 2 Department of Astronomy, University of Thessaloniki 3 Department of Mathematics, University of Thrace References: Andrews, A.D., Chugainov, P.F., Gershberg, R.E. and Oskanian, V.S.: 1969 Inf. Bull. Var. Stars No. 326 Mavridis, L.N., Asteriadis, G. and Mahmoud, F.M.: 1982, in E.G. Mariopoulos, P.S. Theocaris and L.N. Mavridis (Eds.) Compendium in Astronomy, D. Reidel, Dordrecht-Holland, p. 253 [BIBCODE 1982coas.conf..253M ]