COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2826 Konkoly Observatory Budapest 27 November 1985 HU ISSN 0374 - 0676 PHOTOELECTRIC OBSERVATIONS OF EV Lac IN 1984 Photoelectric monitoring observations of the flare star EV Lac in the U bandpass have been carried out in the National Astronomical Observatory of the Bulgarian Academy of Sciences, using the 60 cm telescope and the one-channel photoelectric photometer. Table I gives the monitoring intervals in UT, number of flares observed and mean errors (sigma/Io) for the respective run. The characteristics of the individual flares observed are given in Table II: a) Date and Universal Time of maximum; b) Flare rise time; Table I. Coverage of the flare star EV Lac in 1984 Date Monitoring intervals Total monit. Number of sigma/Io UT time flares 1984 July 24/25 23h50m28s - 00h25m53s, 00 26 42 - 00 51 00. 0h59m43s 3 0.11 July 31/ 23 39 36 - 00 13 21, Aug. 1 00 14 15 - 00 35 42, 1 26 24 2 0.12 00 36 30 - 01 07 42. Aug. 29 22 06 45 - 22 24 19, 0 38 26 1 0.07 22 25 58 - 22 46 50. Aug. 30 22 45 36 - 23 08 34, 1 02 43 1 0.11 23 09 27 - 23 49 12. Oct.1 18 15 06 - 19 32 38. 1 17 32 3 0.10 Nov.23 18 34 15 - 18 48 07, 18 51 21 - 18 57 37, 1 05 33 1 0.09 18 58 37 - 19 44 02. Nov. 24 18 37 53 - 19 43 06, 1 25 44 2 0.08 19 45 43 - 20 06 14. Nov.25 16 24 16 - 16 41 15, 16 46 14 - 16 48 09, 3 08 44 1 0.09 16 49 18 - 19 00 46, 19 05 54 - 19 44 16. Nov.26 17 22 42 - 18 52 09, 18 55 43 - 19 13 38, 2 32 11 6 0.10 20 16 25 - 21 01 14. Total: 13h37m00s 20 [FIGURE 1] Table II. Characteristics of the flares observed Flare Date UT max. t(rise) t(0.5) Duration (If-Io)/Io sigma/I logE log E No. 1984 h m s sec sec sec ergs 1 25 July 00 14 25 2 3 12 0.43 0.10 29.39 2 25 July 00 24 11 71 7 300 3.10 0.11 31.13 3 25 July 00 38 26 26 10 80 0.49 0.11 30.27 4 1 Aug. 00 09 52 4 8 52 0.63 0.12 30.23 5 1 Aug. 00 32 37 7 8 80 0.88 0.13 30.36 6 29 Aug. 22 12 24 144 155 1740 3.47 0.07 32.31 7 30 Aug. 22 49 55 20 4 35 0.49 0.11 29.98 8 1 Oct. 18 53 50 13 50 163 0.55 0.11 30.67 9 1 Oct. 19 12 29 2 4 23 0.48 0.11 29.85 10 1 Oct. 19 17 21 5 1 20 0.54 0.09 29.75 11 23 Nov. 18 35 44 15 26 121 0.58 0.08 30.59 12 24 Nov. 18 42 57 4 3 8 0.23 0.07 29.07 13 24 Nov. 19 57 53 10 3 22 0.36 0.10 29.71 14 25 Nov. 17 43 56 34 44 108 0.56 0.09 30.49 15 26 Nov. 17 31 51 4 1 13 0.33 0.10 29.44 16 26 Nov. 17 46 53 36 22 643 2.91 0.09 31.37 17 26 Nov. 18 04 10 18 10 98 0.50 0.12 30.42 18 26 Nov. 18 32 59 30 21 61 0.87 0.10 30.49 19 26 Nov. 18 34 35 65 65 390 0.99 0.10 31.40 20 26 Nov. 20 35 43 23 5 160 0.92 0.08 30.61 Remark: the optical companion of EV Lac has been excluded c) Flare decline time to 0.5 of the maximum; d) Total flare duration; e) Intensity of the flare radiation at maximum, (If-Io)/Io, where If is the intensity of star plus flare (reduced for background) and Io is the quiet-state star intensity (reduced for background); f) Random noise sigma/Io; g) Total flare energy, estimated by integration of the flare intensity over the total duration of the flare. Fig. 1 shows 6 flares of EV Lac, observed on November 26, 1984 in the U- filter. During the total of 13.62 hours monitoring time 20 flares were registered. Therefore the frequency of flares for our patrol is: f = 1.47 +- .33 flares per hour. Comparing this frequency with previously reported for EV Lac by Moffett, 1974 (22 flares in 66.3 hours) we come to the conclusion, that during August-November 1984 EV Lac was in an enhanced activity state. K. P. PANOV V. PIIROLA T. KORHONEN Department of Astronomy and Observatory and Turku University National Astronomical Observatory Astrophysics Laboratory Observatory Bulgarian Academy of Sciences University of Helsinki It. Pitkakatu 1 72 Lenin Blvd Tahtitorninmaki 20520 Turku 52 1184 Sofia SF-00130 Helsinki Finland Bulgaria Finland Reference : Moffett, T.J.: 1974, Astrophys. J. Suppl. Ser. 29, No. 273. [BIBCODE 1974ApJS...29....1M ]