COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2183 Konkoly Observatory Budapest 1982 August 2 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV Lac IN 1976 Continuous photoelectric monitoring of the flare star EV Lac has been carried out at the Stephanion Observatory (lambda=-22d49'44", phi =+37d45'15") 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 color 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 + 0.042(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. During the 198.37 hours of monitoring time 17 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. is the intensity deflection less sky background of the quiet star and I_f is the total intensity deflection less sky background of the Table I Monitoring Intervals in 1976 Date Monitoring Intervals Total 1976 (U.T.) Monitoring July Time 21-22 23h52m -00h37m,00h39m -01h11m. 01h 17m 22-23 22 23 -23 01 ,23 04 -23 45 ,23 48 -00 31,00 34 -01 05. 02 33 23-24 22 24 -23 13 ,23 16 -00 00 ,00 03 -01 07. 02 37 August 5-6 23 00 -23 29 ,23 32 -00 02 ,00 05 -00 35,01 16 -01 36. 01 49 7-8 19 57 -20 26 ,20 28 -21 00 ,21 02 -21 31,21 43 -22 13, 22 15 -22 48 ,22 50 -23 23 ,23 34 -23 51,23 53 -00 36, 00 39 -01 06 ,01 08 -01 43 . 05 08 8-9 20 02 -20 27 ,20 29 -20 58 ,21 00 -21 31,21 49 -22 19, 22 22 -22 49 ,22 51 -23 25 ,23 35 -00 01,00 55 -01 40. 04 07 12-13 20 03 -20 35 ,20 38 -21 06 ,21 09 -21 35,21 45 -22 14, 22 16 -22 45 ,22 47 -23 14 ,23 36 -23 54,23 58 -00 26, 00 29 -01 00 ,01 14 -01 49 . 04 43 14-15 20 16 -20 44 ,20 47 -21 16 ,21 18 -21 46,21 58 -22 28, 22 31 -23 01 ,23 26 -00 00 ,00 11 -00 41,00 44 -01 13, 01 16 -01 41 . 04 23 16-17 20 02 -20 32 ,20 36 -21 03 ,21 05 -21 37,21 40 -22 10, 22 19 -22 46 ,22 49 -23 20 ,23 24 -23 44,23 55 -0031, 00 33 -01 12 ,01 14 -01 45 . 05 03 17-18 21 28 -21 56 ,21 59 -22 33 ,22 36 -23 01,23 11 -23 39, 23 42 -00 07 ,00 09 -00 40 ,00 53 -01 24,01 26 -02 00. 03 56 18-19 21 19 -21 50 ,21 53 -22 23 ,22 25 -23 13,00 56 -01 36, 01 38 -02 02 . 02 53 19-20 19 47 -20 20 ,20 23 -20 56 ,20 59 -21 37,21 52 -22 28, 22 30 -23 04 ,23 06 -23 33 ,23 51 -00 42,00 43 -01 22, 01 24 -02 11 . 05 38 20-21 19 42 -19 59 ,20 28 -20 54 ,21 01 -21 20,21 54 -22 04, 22 06 -22 34 ,22 36 -23 00 ,23 11 -23 45,23 48 -00 05, 00 18 -00 29 ,00 32 -00 54 ,01 17 -02 13. 04 24 21-22 20 36 -21 04 ,21 06 -21 29 ,21 31 -21 38,29 46 -22 92, 22 14 -22 32 ,22 44 -22 57 ,23 00 -23 14,23 17 -23 48, 23 51 -00 25 ,00 38 -00 41 ,00 44 -01 31,01 33 -02 11. 04 42 22-23 23 04 -23 40 ,23 42 -00 15 ,00 18 -00 59,01 08 -01 44, 01 45 -02 24 . 03 05 25-26 21 35 -21 58 ,22 01 -22 36 ,22 39 -23 14,23 27 -23 58, 00 01 -00 31 ,00 33 -01 01 . 03 02 26-27 20 33 -21 02 ,21 04 -21 32 ,21 33 -22 00,22 10 -22 43, 22 46 -23 24 ,23 26 -00 03 ,00 13 -00 57,01 01 -01 33, 10 35 -02 05 . 04 58 27-28 20 48 -21 27 ,21 29 -21 59 ,22 02 -22 33,23 13 -23 49, 23 52 -00 32 ,00 34 -01 15 ,01 31 -02 31. 04 37 28-29 20 34 -21 10 ,21 11 -21 40 ,21 43 -22 18,22 30 -23 06, 23 09 -23 36 ,23 38 -00 09 ,00 22 -00 59,01 02 -01 46, 01 49 -02 20 . 05 06 29-30 19 42 -20 16 ,20 18 -20 47 ,20 50 -21 18,21 30 -22 00, 22 02 -22 34 ,22 36 -23 05 ,23 18 -00 00,00 02 -00 43, 00 46 -01 30 ,01 39 -02 28 . 05 58 30-31 20 00 -20 31 ,20 34 -21 08 ,21 11 -21 37,21 48 -22 23, 22 25 -22 53 ,23 40 -00 14 ,00 16 -00 55,00 58 -01 37, 01 46 -02 31 . 05 11 31 22 07 -22 39 ,22 41 -23 23 ,23 25-00 00. 01 49 Table I (Continued) September 1 00h10m -00h50m, 00h53m -01h03m, 01h06m -01h59m. 01h 43m 1-2 19 55 -20 25 , 20 35 -21 18 , 21 21 -21 54 ,21 57 -22 27 , 23 10 -23 28 , 23 41 -00 01 , 00 04 -00 32 ,00 34 -01 01 , 01 12 -01 58 . 04 35 2-3 20 39 -21 12 , 21 15 -21 51 , 21 54 -22 27 ,23 04 -23 43 , 23 46 -00 04 , 00 20 -00 59 , 01 10 -01 59 . 04 07 3-4 19 57 -20 35 , 20 39 -21 19 , 21 21 -22 10 ,22 52 -23 35 , 23 39 -00 13 , 00 16 -00 51 , 01 02 -01 28 ,01 31 -01 57 . 04 51 4-5 20 16 -21 02 , 21 05 -21 42 , 21 46 -22 22 ,22 59 -23 29 , 23 36 -00 02 , 00 04 -00 44 , 00 55 -01 26 ,01 29 -02 02 . 04 39 5-6 19 55 -20 43 , 20 47 -21 14 , 21 17 -21 48 ,21 59 -22 36 , 22 38 -23 14 , 23 16 -23 54 , 00 10 -00 42 ,00 44 -01 17 , 01 20 -01 59 . 05 21 11-12 19 36 -20 12 , 20 13 -20 56 , 20 58 -21 46 ,22 26 -23 02 , 23 04 -23 38 , 23 40 -00 03 , 00 14 -01 03 ,01 05 -01 27 , 01 29 -02 01 . 05 23 12-13 20 16 -20 49 , 20 51 -21 50 , 22 32 -23 18 ,23 23 -23 53 , 23 55 -00 48 , 00 58 -01 29 , 01 31 -02 00 . 04 41 13-14 20 00 -20 35 , 20 39 -21 14 , 21 15 -21 47 ,22 28 -23 10 , 23 13 -23 37 , 23 44 -00 26 , 00 36 -01 01 ,01 03 -01 30 , 01 33 -01 57 . 04 46 14-15 19 35 -20 16 , 20 27 -20 41 , 20 49 -21 41 ,22 16 -22 49 , 22 52 -23 38 , 23 50 -00 38 , 00 48 -01 23 ,01 25 -02 00 . 05 04 15-16 19 41 -20 19 , 20 22 -20 59 , 21 01 -21 38 ,22 14 -22 56 , 23 11 -23 40 , 23 43 -00 03 , 00 12 -00 52 ,00 55 -01 28 , 01 31 -02 01 . 05 06 16-17 19 24 -20 03 , 20 05 -20 55 , 20 59 -21 31 ,22 06 -22 37 , 22 54 -23 28 , 23 31 -23 58 , 00 00 -00 39 ,00 50 -01 21 , 01 24 -01 58 . 05 17 17 19 36 -20 03 , 20 07 -21 28 , 22 02 -22 41 ,22 45 -23 00 . 02 42 18-19 20 26 -21 29 , 22 01 -22 37 , 22 38 -23 05 ,23 12 -23 43 , 23 53 -00 36 , 00 40 -01 14 , 01 16 -02 02 . 04 40 19-20 20 06 -20 37 , 20 39 -21 14 , 21 46 -22 05 ,22 15 -22 46 , 22 49 -23 18 , 23 20 -23 43 , 23 54 -00 24 ,00 27 -00 56 . 03 47 25-26 20 09 -21 07 , 21 43 -22 10 , 22 13 -22 46 ,22 48 -23 19 , 23 31 -00 05 , 00 08 -00 31 , 00 34 -00 58 ,01 13 -01 56 . 04 13 26-27 19 59 -20 46 , 21 21 -21 49 , 21 51 -22 22 ,22 25 -22 52 , 23 02 -23 35 , 23 38 -00 09 , 00 18 -01 00 . 03 59 28-29 19 19 -20 02 , 20 04 -20 36 , 21 09 -21 45 ,21 47 -22 17 , 22 20 -22 56 , 23 06 -23 26 , 23 37 -23 42 ,23 50 -00 21 , 00 23 -00 50 , 00 52 -01 14 , 01 26 -02 13 . 05 29 29-30 19 36 -20 07 , 20 09 -20 37 , 21 10 -21 43 ,21 45 -22 15 , 22 19 -22 57 , 23 08 -23 37 , 23 40 -00 10 ,00 20 -00 45 , 00 55 -01 19 , 01 24 -01 39 , 01 49 -02 15 . 05 08 30 19 34 -20 01 , 20 04 -20 36 , 21 10 -21 47 ,21 52 -22 22 , 22 25 -22 52 , 23 02 -23 33 , 23 47 -00 00 . 03 17 October 1 00 00 -00 32 , 00 35 -01 03 , 01 14 -01 57 . 01 43 2-3 20 01 -20 27 , 20 29 -21 13 , 21 15 -21 53 ,22 01 -22 34 , 22 38 -23 05 , 23 08 -23 33 , 23 44 -00 26 ,00 28 -00 52 , 01 02 -02 02. 05 19 3-4 19 22 -19 49 , 19 51 -20 20 , 20 22 -20 48 ,21 00 -21 33 , 21 35 -22 09 , 22 10 -22 40 , 22 53 -23 27 ,23 39 -00 08 , 00 11 -00 44 , 00 58 -01 31 , 01 33 -02 02 . 05 37 Table I (Continued) October 10 19h42m -20h15m, 20h17m -20h50m, 20h52m -21h23m,21h34m-22h03m, 20 05 -22 31 , 22 33 -23 01 . 03h 00m 11-12 19 25 -19 57 , 19 59 -20 30 , 20 32 -21 05 ,21 16 -21 49 , 21 51 -22 23 , 22 25 -23 07 , 23 20 -23 25 ,23 28 -00 07,, 00 09 -00 38 , 00 50 -01 12 . 04 58 12-13 22 55 -23 28 , 23 31 -00 04 , 00 07 -00 52 ,01 05 -01 12 . 01 58 Total 198h 22m 198h37 Table II Characteristics of the Flares Observed Flare Date U.T. t_b t_a Dura- I_f-I_0/I_0 P Deltam sigma Air No. 1976 tion July max min min min max min mag mag mass 1 23 22h24m54 0.33 0.62 0.95 0.22 0.04 0.22 0.06 1.02 Aug. 2 7 23 38.04 0.78 6.20 6.98 0.68 1.30 0.56 0.09 1.01 3 20 02 01.08 0.74 3.14 3.88 0.33 0.38 0.31 0.06 1.16 4 27 01 40.20 0.96 2.12 3.08 0.18 0.11 0.18 0.06 1.18 5 29 02 05.04 0.72 3.72 4.44 0.22 0.19 0.22 0.05 1.26 6 31 02 08.22 0.84 8.28 9.12 0.61 0.79 0.52 0.07 1.30 Sept. 7a 1 19 57.66 0.24 26.78 27.02 1.57 5.71 1.02 0.06 1.14 7b 1 0.93 0.71 8 3 01 31.68 0.30 0.56 0.86 0.17 0.03 0.17 0.05 1.23 9 15 22 34.14 1.06 11.42 12.48 3.54 5.35 1.64 0.04 1.03 10 15 23 43.92 0.48 9.46 9.94 2.38 3.58 1.32 0.07 1.10 11 16 22 15.86 1.08 15.16 16.24 0.51 3.16 0.45 0.06 1.02 12 19 21 50.82 0.12 1.48 1.60 0.37 0.06 0.34 0.06 1.01 13 25 20 12.84 0.96 14.24 15.20 0.21 1.57 0.21 0.05 1.02 14 28 23 12.18 0.54 0.86 1.40 0.19 0.05 0.19 0.05 1.14 15 30 01 24.36 0.24 3.40 3.64 0.69 0.60 0.57 0.06 1.64 Oct. 16 3 23 40.66 0.36 1.98 2.34 0.36 0.15 0.33 0.08 1.26 17 11 20 40.20 0.36 2.42 2.78 0.48 0.25 0.43 0.08 1.02 star plus Flare, d) the integrated intensity of the flare over its total duration, including preflares, 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 flare maximum. The light curves of the observed flares in the b Color are shown in Figs. 1-17. [FIGURE 1] [FIGURE 2] [FIGURE 3] [FIGURE 4] [FIGURE 5] [FIGURE 6] [FIGURE 7] [FIGURE 8] [FIGURE 9] [FIGURE 10] [FIGURE 11] [FIGURE 12] [FIGURE 13] [FIGURE 14] [FIGURE 15] [FIGURE 16] [FIGURE 17] G. ASTERIADIS, M.E. CONTADAKIS, F. MAHMOUD, L.N. MAVRIDIS, D. STAVRIDIS, P. VARVOGLIS Department of Geodetic Astronomy University of Thessaloniki 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., and Mahmoud, F.M.: 1982, in: Compendium in Astronomy (Eds.: E.G. Mariolopoulos, P.S. Theocaris, and L.N. Mavridis) D. Reidel, Dordrecht-Holland, p. 253 [BIBCODE 1982coas.conf..253M ]