COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1943 Konkoly Observatory Budapest 1981 March 30 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF EV Lac Between 1972 and 1976 a series of photoelectric observations was made on the flare star EV Lac at the Stephanion Observatory by the staff of the Department of Geodetic Astronomy, University of Thessaloniki, with a 30 inch reflector equipped with a cooled Johnson dual channel photometer (RCA 1P21 multiplier) and Johnson standard UBV filters. The measurements were secured by a Hewlett- Packard 7100 B chart recorder. The data of the comparison stars are given in Table I, the observations of the variable (nightly means) in Table II. The tie- in observations were also made at Stephanion Observatory. Table I Comparison V B a = BD +43d4299 9.16 10.33 b = BD +43d4296 9.97 10.83 The characteristics of the flares observed during the period 1971-1975 and 1978 have been already published (Contadakis, Mavridis 1972; Asteriadis, Mavridis, Stavridis 1973; Arabelos, Kareklidis, Mavridis, Stavridis 1978; Contadakis, Kareklidis, Tsioumis 1979; Contadakis, Mahmoud, Mavridis, Stavridis 1980; Avgouloupis, Kareklidis, Mavridis, Phylactopoulos, Varvoglis 1980). Mahmoud (1978) determined the quiet state magnitudes of the flare star EV Lac corresponding to the period 1972-1976 for a discussion of the photoelectric behaviour of the star during quiescent state. His material has been used in this present paper for the purpose of periodicities detection in the variation of the quiet state luminosity of the star. In order to find any periodic variation in the star's brightness during quiescent light, Fourier analyses of the observed data Table II Photoelectric yellow and blue observations of EV Lac J.D. V J.D. V J.D. V J.D. V 2440000+ 2440000+ 244000+ 2440000+ 1545.414 10.08 1950.386 9.97 2306.419 10.07 3026.445 10.05 1547.476 10.01 1952.392 10.01 2308.411 10.09 3033.419 9.97 1569.524 9.91 2269.515 10.08 2310.407 10.05 3034.423 9.97 1570.437 10.02 2271.494 10.05 2637.502 10.23 3035.422 9.98 1572.412 10.11 2273.502 10.08 2642.490 10.19 3036.420 9.95 1929.435 10.04 2282.474 10.08 2644.490 10.20 3037.413 9.97 1931.463 10.00 2283.485 10.09 2652.463 10.22 3038.408 9.95 1933.428 10.02 2284.485 10.07 2653.470 10.24 3039.406 9.99 1934.443 10.03 2285.488 10.03 2656.475 10.24 3040.406 9.96 1935.440 10.05 2291.517 10.20 2996.537 9.95 3041.396 10.00 1941.419 9.90 2293.481 10.07 2999.523 9.87 3047.394 9.95 1942.406 9.98 2295.475 10.05 3009.487 9.98 3048.378 9.98 1943.391 10.04 2296.459 10.06 3021.478 9.95 3050.369 9.99 1944.427 9.87 2297.459 10.06 3024.443 9.96 3051.370 9.95 1946.400 10.01 2300.428 10.10 3025.438 9.97 3052.370 10.01 1948.395 9.99 2305.417 10.15 J.D. B J.D. B J.D. B J.D. B 1545.414 11.55 2274.363 11.47 2654.348 11.58 3018.486 11.42 1547.476 11.42 2282.446 11.44 2655.332 11.60 3019.448 11.46 1569.524 11.47 2283.449 11.46 2656.419 11.61 3020.451 11.42 1570.437 11.46 2284.413 11.45 2658.488 11.59 3021.469 11.41 1572.412 11.53 2285.457 11.41 2688.429 11.66 3022.502 11.43 1929.435 11.42 2291.464 11.54 2689.397 11.57 3023.451 11.42 1931.463 11.38 2293.426 11.42 2690.337 11.59 3024.473 11.42 1933.428 11.43 2294.468 11.35 2693.415 11.63 3025.459 11.41 1934.443 11.39 2295.474 11.47 2694.392 11.57 3026.443 11.46 1935.440 11.46 2296.426 11.37 2696.276 11.63 3027.429 11.46 1941.419 11.32 2297.461 11.40 2697.349 11.66 3033.459 11.42 1942.406 11.38 2300.444 11.47 2707.289 11.66 3034.452 11.46 1943.391 11.39 2305.420 11.50 2981.521 11.37 3035.444 11.44 1944.427 11.29 2306.419 11.46 2982.488 11.39 3036.430 11.40 1946.400 11.41 2308.398 11.46 2983.531 11.36 3037.435 11.40 1948.398 11.39 2310.365 11.36 2996.531 11.40 3038.454 11.41 1950.386 11.36 2324.478 11.60 2998.421 11.39 3039.385 11.43 1952.392 11.41 2327.436 11.46 2999.529 11.39 3040.454 11.38 2239.514 11.41 2329.454 11.45 3003.458 11.39 3041.438 11.48 2240.514 11.48 2613.458 11.64 3005.456 11.41 3047.438 11.38 2241.543 11.44 2615.430 11.73 3007.457 11.41 3048.400 11.43 2245.513 11.46 2635.479 11.61 3008.475 11.41 3050.405 11.42 2247.477 11.43 2636.487 11.65 3009.491 11.41 3051.411 11.41 2247.560 11.49 2637.455 11.56 3010.403 11.42 3052.400 11.46 2248.435 11.51 2640.465 11.66 3011.444 11.46 3054.436 11.44 2267.496 11.46 2642.535 11.62 3012.503 11.44 3055.407 11.12 2269.479 11.47 2644.466 11.61 3013.500 11.44 3062.320 11.31 2270.506 11.51 2652.402 11.61 3016.447 11.43 3063.438 11.46 2271.462 11.43 2653.440 11.63 3017.464 11.44 3064.453 11.10 2273.465 11.45 [FIGURE 1] [Figs. 1-3] were made. Since the dMe stars show slow, small amplitude light variations with periods of the order of some days, the period search was made between 0.1 and 1 cycle/day (1 and 10 days) for each year's observations, separately. The calculations were carried out with the TPAi computer of Konkoly Observatory. A light variation of 4.378d period and about 0.07m amplitude was detected by Pettersen (1980) concerning his 1979 observations. Figures 1, 2 and 3 display the periodograms of EV Lac. Although there are some peaks in the graphs, all of them are under the significance level. The arrows indicate the value where Pettersen's period was found. It is mentioned that the average brightness of EV Lac in 1975 seems to be about 0.2 magnitude fainter (both in V and B), and also the flare activity of the star was weaker than in the other years (see Mahmoud, 1980). In this star during the observed time intervals no periodic light variations have been found. This result means that either the star had constant brightness during the time of observations, or the amplitude of the possible light variations are less than the observational error. The authors wish to express their thanks to G. Kovacs for kindly placing his period analysis program at their disposal. F.M. MAHMOUD Helwan Insitute of Astronomy and Geophysics Cairo-Egypt K. OLAH Konkoly Observatory References: Arabelos, D., Kareklidis, G., Mavridis, L.N., Stavridis, D., 1978, I.B.V.S. No. 1505 Asteriadis, G., Mavridis,L.N., Stavridis, D., 1973, I.B.V.S. No. 809 Avgoloupis, S., Kareklidis, G., Mavridis, L.N., Phylactopoulos, P., Varvoglis, P., 1980, I.B.V.S. No. 1793 Contadakis, M.E., Kareklidis, G., Mavridis, L.N., Tsioumis, A.C., 1979, I.B.V.S. No. 1653 Contadakis, M.E., Mahmoud, F., Mavridis, L.N., Stavridis, D., 1980, I.B.V.S. No. 1784 Contadakis, M.E., Mavridis, L.N., 1972, I.B.V.S. No. 669 Mahmoud, F.M., 1978, Contribution in the study of the flare star EV Lac, Thesis, Aristoteleion University of Thessaloniki, Greece Pettersen, B.R., 1980, Astron. J. 85, 871 [BIBCODE 1980AJ.....85..871P ]