COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2358 Konkoly Observatory Budapest 23 June 1983 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR EV Lac IN 1982 Photoelectric observations of flare stars have been continued at the National Astronomical Observatory of the Bulgarian Academy of Sciences and the Stephanion Observatory, Greece. In this paper we report about joint observations of the flare star EV Lac in 1982. At the National Astronomical Observatory the observations were made with the 60 cm Cassegrain telescope and the UBV one-channel photometer. A photon counting system with an integration time of 1 sec was used. Details of the photometric equipment at NAO are published by Panov et al. (1982). The transformation of the instrumental ubv system at NAO to the international UBV system for the time under consideration is given by the equations: DeltaV = Deltav + 0.08 Delta(b-v) Delta(B-V) = 1.12 Delta(b-v) Delta(U-B) = 0.84 Delta(u-b) At the Stephanion Observatory the observations were carried out with the 30-inch Cassegrain reflector of the Department of Geodesy and Surveying, University of Thessaloniki, and a Johnson dual channel photoelectric photometer. The transformation of the Stephanion ubv system to the international UBV system for the period under consideration is given by the 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 Table I contains, for each night, the monitoring intervals in UT, the colour in which observations were made, the number of flares observed, the standard deviation of random noise fluctuations in mag for those nights, in which no flare was observed, and the total monitoring time. Designation NAO or Steph.O. stands for the National Astronomical Observatory or Stephanion Table I Flare star EV Lac, 1982 ----------------------------------------------------------------------------- ' Date Monitoring intervals Total Number Colour NAO/ (UT) monit. of flares Steph.O. time ----------------------------------------------------------------------------- 1982 Aug. 19/20 23h51m34s-23h57m30s 23 58 41 -00 48 36 , 00 49 25 -00 58 50 . 1h05m16s 2 U NAO 20/21 22 45 14 -00 20 18 , 00 21 44 -00 38 15 , 00 39 31 -00 51 35 , 00 52 41 -01 05 41 , 01 06 37 -01 33 56 , 01 35 08 -01 49 51 , 01 52 26 -01 58 01 . 3 04 16 3 U NAO Sep. 2/3 22 16 39 -22 4302 , 22 43 58 -23 3026 , 0 23 31 22 -01 0924 . 2 50 53 sigma=0.16 U NAO Oct. 8 20 11 12 -22 36 41 , 22 37 53 -22 56 04 , 0 22 57 16 -23 14 46 . 3 01 10 sigma=0.05 U NAO 23 19 14 00 -19 24 12 , 19 32 22 -20 00 31 , 20 02 24 -21 27 53 , 21 31 00 -23 00 00 , 23 02 36 -23 20 55 . 3 51 09 2 B Steph.O. 24 19 15 34 -20 40 00 , 20 41 24 -21 06 30 , 0 21 10 30 -22 29 38 . 3 08 40 sima=0.02 B Steph.O. 25 18 21 00 -18 44 14 , 18 47 22 -20 19 43 , 20 22 00 -21 12 30 . 2 46 05 1 B Steph.O. Nov. 8 19 11 09 -20 43 33 , 20 44 40 -21 06 11 . 1 53 55 2 U NAO 13 17 03 15 -17 11 56 , 17 15 01 -18 57 24 , 19 20 47 -20 03 29 . 2 33 46 2 U NAO Total: 24h15m10s ------------------------------------------------------------------------------ Observatory, respectively. During the total of 14h29m16s monitoring time in "u" colour (NAO) 9 flares were observed. During the total of 9h45m54s monitoring time in "b" colour (Steph.O.) 3 flares were observed. All observations of EV Lac. (at NAO and Steph.O.) include also the optical companion. The characteristics of the observed flares are given in Table II. Table II Characteristics of the flares observed ----------------------------------------------------------------------------- Flare Date U.T. t_b t_a Duration I_f/I_0 Deltam sigma p Air No. 1982 max min min min max mag mag min mass ----------------------------------------------------------------------------- N A O August 1 20d 0h20m16s 0.1 0.6 0.7 1.38 0.35 0.08 0.13 1.021 2 20 02 50 08 0.4 0.9 1.3 1.70 0.57 0.08 0.46 1.025 3 20 23 31 25 0.25 0.58 0.83 1.24 0.23 0.06 0.10 1.003 4 21 01 27 47 0.05 0.22 0.27 1.55 0.48 0.06 0.07 1.104 5 21 01 28 57 0.28 1.0 1.3 1.51 0.45 0.06 0.26 1.105 November 6 8 19 40 29 0.23 0.52 0.75 1.20 0.19 0.04 0.06 1.058 7 8 19 47 10 0.17 2.8 3.0 1.22 0.22 0.04 0.33 1.067 8 13 17 59 10 0.58 1.9 2.5 1.19 0.19 0.05 0.17 1.004 9 13 19 58 45 0.17 0.8 1.0 1.51 0.45 0.05 0.17 1.112 Stephanion Observatory October 1 23 21 21 26 0.55 1.23 1.8 1.20 0.20 0.02 0.18 1.117 2 23 22 56 48 0.2 0.8 1.0 1.17 0.17 0.03 0.08 1.380 3 25 18 34 50 1.95 0.83 2.8 1.83 0.66 0.07 0.76 1.007 ----------------------------------------------------------------------------- For each flare 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), c. the total duration of the flare, d. the value of the ratio I_f /I_0, corresponding to flare maximum, where I_f is the total intensity of the star plus flare less sky background, and I_0 is the quiet state intensity less sky background, e. the increase of star's brightness in magnitudes at flare maximum: Deltam=2.5 log(I_f/I_0) Delta m = 2.5 log(If/I0) f. the standard deviation of random noise fluctuations in mag: I_0+sigma sigma(mag)=2.5 log --------- I_0 g. the integrated intensity of the flare over its total duration: p = Integral (I_f-I_0)/I_0 dt, h. the air mass. The light curves of the observed flares in colours "u" (NAO) and "b" (Steph.O.) are shown in Figures 1-12. [FIGURE 1] [FIGURE 2] Acknowledgements The observations reported in this paper are part of the joint research project under the title "Study of variable stars", carried out by the Department of Astronomy with National Astronomical Observatory, Bulgarian Academy of Sciences, and the Department of Geodesy and Surveying (former Department of Geodetic Astronomy), University of Thessaloniki, Greece. This project is part of the Program for Scientific and Technical Co-operation between Bulgaria and Greece. The authors would like to express their gratitude to the relevant authorities of the respective countries for their support. K.P. PANOV G. ASTERIADIS Department of Astronomy with L.N. MAVRIDIS National Astronomical Observatory Bulgarian Academy of Sciences Department of Geodesy and Surveying Sofia-1000, 7th November Str. No. 1 University of Thessaloniki Bulgaria Thessaloniki, Greece References: Andrews, A.D., Chugainov, P.F., Gershberg, R.E., and Oskanian, V.S., 1969, I.B.V.S. No. 326 Panov, K.P., Pamukchiev, I.Ch., Christov, P.P., Petkov, D.I., Notev, P.T., Kotsev, N.G., 1982, Comptes rendus of the Bulgarian Acad. of Sciences, 35, No. 6, 717