COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1784 Konkoly Observatory Budapest 1980 May 12 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV Lac IN 1975 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 1975 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: for the time interval from 25-6-1975 to 30-7-1975 V=v_0+0.119(b-v)_0+2.163, (B-V)=0.819+1.047(b-v)_0, (U-B)=-1.509+1.006(u-b)_0, for the time interval from 31-7-1975 to 16-9-1975 V=v_0+0.046(b-v)_0+2.440, (B-V)=0.782+1.062(b-v)_0, (U-B)=-1.612+1.063(u-b)_0, and for the time interval from 17-9-1975 to 20-2-1976 V=v_0+0.059(b-v)_0+2.368, (B-V)=0.737+1.035(b-v)_0, (U-B)=-1.675+1.122(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. Flare Star EV Lac, 1975 Tale I Date Monitoring Intervals Total Monitoring sigma (U.T.) 1975 (U.T.) Time July 19-20 20h 48m -21h 15m, 21h 18m -21h 55m, 21h 58m -22h 27m, 0.03(21h 05m), 0.02(21h 40m), 22 42 -23 11, 23 16 -23 46, 23 52 -23 56, 0.01(22 21), 0.02(22 55), 00 00 -00 09, 00 12 -00 26, 00 44 -01 13, 0.01(23 32), 0.02(23 53), 01 18 -01 53. 4h 03m 0.01(00 57), 0.01(01 37). August 10-11 22 00 -22 31, 22 39 -23 03, 23 10 -23 36, 0.02(22 16), 0.02(22 50), 23 56 -00 20, 00 34 -00 54, 01 01 -01 16. 2 20 0.02(23 20), 0.02(00 11), 0.02(00 46), 0.02(01 09). 11-12 21 51 -22 17, 22 19 -22 50, 22 54 -23 27, 0.02(22 12), 0.02(22 35), 23 42 -00 09, 00 12 -00 45, 00 48 -01 34. 3 16 0.02(23 15), 0.03(23 59), 0.02(00 33), 0.02(01 19). 12-13 21 55 -22 24, 22 28 -22 57, 23 02 -23 31, 0.03(22 15), 0.02(22 46), 00 29 -01 03, 01 05 -01 44. 2 40 0.02(23 18), 0.03(00 46), 0.03(01 20 ). 15-16 21 15 -21 41, 21 44 -22 12, 22 14 -22 46, 0.02(21 30), 0.02(21 57), 23 00 -23 36, 00 26 -00 56, 00 58 -01 34. 3 08 0.02(22 32), 0.02(23 18), 0.02(00 46), 0.02(01 16). 18 00 15 -01 00, 01 03 -01 48. 1 30 0.03(00 45), 0.02(01 19). 19-20 19 26 -19 59, 20 02 -20 31, 20 32 -21 06, 0.06(19 44), 0.10(20 16), 21 20 -21 55, 21 58 -22 27, 22 32 -23 22, 0.07(20 55), 0.04(21 35), 00 13 -00 58, 01 01 -01 44. 4 58 0.06(22 12), 0.07(22 50), 0.05(00 34), 0.04(01 16). 27-28 19 03 -19 34, 19 38 -20 06, 20 09 -20 38, 0.02(19 25), 0.02(19 53), 20 51 -21 24, 21 30 -21 53, 21 57 -22 32, 0.02(20 21), 0.03(21 06), 23 21 -00 19, 00 21 -01 14, 01 16 -01 27. 5 01 0.03(21 42), 0.03(22 15), 0.03(23 49), 0.04(00 50), 0.03(01 20). 28-29 19 14 -19 43, 19 46 -20 22, 20 25 -21 03, 0.02(19 29), 0.02(20 01), 21 15 -21 45, 21 48 -22 21, 22 24 -23 04, 0.02(20 46), 0.03(21 30), 23 52 -00 31, 00 33 -01 04, 01 14 -01 45, 5 07 0.03(22 02), 0.02(22 41), 0.03(00 14), 0.03(00 48), 0.03(01 29). 29-30 19 13 -19 45, 19 46 -20 17, 20 20 -20 54, 0.02(19 27), 0.02(20 01), 21 04 -21 36, 21 38 -22 07, 22 09 -22 51, 0.02(20 35), 0.02(21 20), 23 47 -00 28, 00 32 -01 21, 01 24 -01 50. 5 16 0.02(21 51), 0.03(22 32), 0.03(00 04), 0.03(00 59), 0.03(01 39). 30 19 03 -19 31, 19 36 -20 08, 20 11 -20 56, 0.02(19 16), 0.03(19 49), 21 15 -21 41, 21 46 -22 19. 2 44 0.02(20 33), 0.02(21 30), 0.02(21 58). 31- 1 19 21 -20 02, 20 05 -20 41, 20 48 -21 18, 0.02(19 43), 0.02(20 29), 21 34 -22 05, 22 09 -22 35, 22 37 -23 11, 0.02(20 59), 0.02(21 46), 01 31 -02 00, 02 04 -02 34, 02 39 -03 02. 4 40 0.01(22 12), 0.02(22 53), 0.02(01 49), 0.02(02 19), 0.03(02 47), September 2- 3 21 44 -22 14, 22 17 -22 48, 22 51 -23 21, 0.02(21 58), 0.02(22 29), 23 33 -00 16, 00 17 -00 59, 01 03 -01 51. 3 44 0.02(23 08), 0.02(23 57), 0.03(00 37), 0.03(01 32). 11-12 21 48 -21 55, 21 59 -22 18, 23 04 -23 15, 0.02(22 08), 0.02(23 32), 23 19 -23 33, 23 36 -23 48, 23 50 -00 03. 1 16 0.02(00 01). 14-15 23 06 -23 24, 23 26 -23 31, 23 35 -23 55, 0.02(23 30), 0.02(24 00), 23 59 -00 03, 00 06 -00 14, 00 17 -00 26, 0.02(00 29), 0.03(00 55), 00 28 -00 31, 00 41 -01 09, 01 14 -01 20, 0.02(01 34). 01 21 -01 46. 2 06 17 19 54 -20 18, 20 21 -20 42, 20 43 -20 55, 0.02(20 02), 0.02(20 39), 20 58 -21 27, 1 26 0.03(21 09). 25-26 22 49 -23 16, 23 19 -23 46, 23 49 -00 15, 0.03(22 59), 0.03(23 29), 00 55 -01 12, 01 21 -01 25, 01 28 -01 44. 1 57 0.04(23 59), 0.06(01 23). October 1 20 55 -21 19, 21 22 -21 50, 21 53 -22 44m 0.02(21 10), 0.01(21 41), 22 47 -23 04, 23 17 -23 28, 23 31 -23 44, 0.01(22 58). 23 50 -23 55 2 29 2-3 20 32 -20 59, 21 02 -21 34, 21 36 -22 05, 0.02(20 44), 0.02(21 17), 22 19 -22 48, 22 50 -23 32, 23 35 -00 08. 3 12 0.02(21 49), 0.02(22 31) 0.02(23 09), 0.02(23 46). 3 19 34 -20 02, 20 04 -20 44, 20 46 -21 18, 0.02(19 50), 0.02(20 21), 21 29 -21 59, 22 10 -22 40, 22 43 -23 15, 0.02(20 52), 0.02(21 45), 23 17 -23 47. 3 42 0.02(22 25), 0.02(22 57), 0.02(23 30). 4 18 56 -19 31, 19 33 -19 58, 20 00 -20 36, 0.03(19 15), 0.03(19 44), 20 48 -21 10. 1 58 0.02(20 16), 0.03(20 59). 7 20 15 -20 44, 20 48 -21 09, 21 21 -21 50, 0.02(20 30), 0.02(20 58), 22 03 -22 35, 22 37 -23 05, 23 09 -23 39. 2 49 0.02(21 34), 0.02(22 18), 0.02(22 48), 0.02(23 19). 8 19 16 -19 46, 19 48 -20 18, 20 20 -20 51, 0.02(19 31), 0.02(19 58), 21 03 -21 36, 21 51 -22 16, 22 19 -22 51, 0.02(20 31), 0.02(21 18), 23 02 -23 43, 3 42 0.02(22 05), 0.02(22 35), 0.02(23 21). 10 18 41 -18 59, 19 18 -19 35. 0 35 0.03(18 51), 0.03(19 28). 11 18 33 -19 01, 19 03 -19 34, 19 38 -20 10, 0.03(18 46), 0.02(19 17), 20 24 -20 57, 21 01 -21 48, 21 52 -22 25, 0.03(19 52), 0.03(20 41), 22 49 -23 20, 23 22 -23 54. 4 27 0.03(21 20), 0.02(22 13), 0.02(23 02), 0.03(23 35). 12 18 26 -19 00, 19 03 -19 34, 19 36 -20 11 0.03(18 43), 0.03(19 18), 20 23 -20 59, 21 02 -21 39, 21 42 -21 54. 3 05 0.03(19 52), 0.03(20 41), 0.03(21 17), 0.03(21 47). 21 19 03 -19 50, 19 53 -20 25, 20 29 -20 34, 0.06(19 28), 0.05(20 12), 20 37 -20 46. 1 33 0.06(20 41). TOTAL 82^h44^m Flare Star EV Lac, 1975 Table II Characteristics of the Flares Observed Date U.T. t_b t_a Duration I_f-I_o/I_o P delta m sigma Air Flare 1975 max. min min min max. min mag. mag. mass No. Jul 00h 02.06m 0.92m 3.32m 4.24m 0.23 0.36 0.22 0.02 1.05 1a 20 00 03.93 0.28 0.27 0.02 1.05 1b 20 August 23 20.2 0.16 0.40 0.56 0.07 0.02 0.07 0.02 1.01 2 12 21 51.0 0.56 11.81 12.37 0.19 0.73 0.19 0.02 1.07 3 15 21 58.12 0.32 1.64 1.96 0.15 0.06 0.15 0.02 1.02 4 29 September 00 11.1 0.08 0.19 0.27 0.08 0.01 0.08 0.02 1.07 5 3 October 22 15.1 0.58 44.78 45.36 2.24 1.27 6.27 0.01 1.06 6 1 20 38.2 8.36 26.40 34.76 0.22 ? 0.21 0.02 1.01 7 3 22 46.2 0.56 6.94 7.50 0.11 ? 0.08 0.02 1.15 8 7 23 12.6 0.39 0.80 1.19 0.09 0.03 0.09 0.02 1.21 9 7 19 22.8 1.32 9.26 10.58 0.10 0.28 0.10 0:02 1.02 10 8 19 59.95 0.61 0.76 1.37 0.10 0.06 0.10 0.02 1.01 11 8 21 37.3 0.56 4.34 4.90 0.22 0.45 0.22 0.03 1.07 12 11 22 07.84 0.76 17.23 17.99 0.14 0.63 0.14 0.02 1.11 13 11 [FIGURE 1] [FIGURE 2] During the 82.73 hours of monitoring time 13 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 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 Figures 1-13. M.E. CONTADAKIS, F. MAHMOUD L.N. MAVRIDIS, D. STAVRIDIS Department of Geodetic Astronomy University of Thessaloniki Reference: Andrews, A.D. Chugainov, P.F., Gershberg, R.E. and Oskanian, V.S.: 1969, I.B.V.S., No. 326