COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2220 Konkoly Observatory Budapest 1982 November 2 HU ISSN 0374-0676 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR AD Leo IN 1982 Photoelectric observations of flare stars have been continued at the National Astronomical Observatory of the Bulgarian Academy of Sciences. In this paper we report about our observations of the flare star AD Leo in 1982. The observations were carried out with the 60 cm Cassegrain reflector and the one channel U,B,V photoelectric photometer. A photon counting system with an integration time of 1 sec was used. Details of this equipment are published by Panov et al. (1982). Here we give the transformation of the instrumental u,b,v system to the international U,B,V system for the period under consideration: DeltaV= Deltav + 0.10 Delta(b-v) Delta(B-V)= 1.13 Delta(b-v) Delta(U-B)= 0.84 Delta(u-b) Monitoring observations were carried out on 6 nights in February and March 1982 in colour "u". Table I contains, for each night, the monitoring intervals in UT, the number of flares observed, as well as the total monitoring time. During the total of 17h57m monitoring time 23 flares were observed, the characteristics of which are given in Tables II-VII. For each flare the following characteristics (Andrews et al., 1969) are given: a. the date and universal time of maximum. b. the duration before and after maximum (tb and ta, respectively. c. the total duration of the flare. Table I Flare star AD Leo, 1982 Date Monitoring intervals Total monit. Number of flares (U.T.) time 1982 Febr. 16/17 21h 12m01s -23h 11m 24s, 23 15 17 -00 18 58. 3h 03m 04s 5 18 20 32 13 -21 55 24, 21 56 19 -22 19 56, 22 21 18 -23 38 09. 3 03 39 5 March 18 20 50 14 -23 00 18. 2 10 04 1 25 19 10 54 -19 27 55, 19 29 58 -22 58 22. 3 45 25 7 26 18 49 50 -19 22 19, 19 24 07 -20 56 19, 20 57 55 -21 19 55, 21 29 31 -22 31 46. 3 28 56 3 27 19 00 52 -20 13 25, 20 28 14 -20 55 36, 21 57 46 -22 43 25. 2 25 34 2 Total: 17h56m42s 23 Table II Characteristics of the flares observed on February 16, 1982 Flare U.T. tb ta Duration If/I0 Deltam sigma P Air No max min min min mag mag min mass 1 21h46m27s 0.18 1.1 1.3 1.18 0.18 0.03 0.07 1.108 2 21 59 26 0.13 2.0 2.1 1.48 0.42 0.03 0.22 1.095 3 22 58 31 0.38 1.5 1.9 1.25 0.24 0.03 0.16 1.074 4 23 37 55 0.67 0.7 1.4 1.20 0.20 0.03 0.10 1.090 5 23 57 00 0.30 4.0 4.3 1.66 0.55 0.03 1.09 1.107 Table III Characteristics of the flares observed on February 18, 1982 Flare U.T. tp ta Duration If/I0 Deltam sigma P Air No max min min min mag mag mag min mass 1 21h15m20s 0.33 4.7 5.0 2.81 1.12 0.03 1.33 1.139 2 22 07 15 0.42 0.8 1.2 1.19 0.19 0.03 0.09 1.085 3 22 09 24 1.0 1.0 2.0 1.22 0.21 0.03 0.13 1.084 4 22 21 44 0.27 2.3 2.6 1.38 0.35 0.03 0.17 1.078 5 22 51 52 0.57 1.1 1.7 1.17 0.17 0.03 0.11 1.074 Table IV Characteristics of the flare observed on March 18, 1982 Flare U.T. tb ta Duration If/I0 Deltam sigma P Air No max min min min max mag mag min mass 1 20h53m00s 0.28 1.5 1.8 1.29 0.28 0.03 0.19 1.074 Table V Characteristics of the flares observed on March 25, 1982 Flare U.T. tb ta Duration If/I0 Deltam sigma P Air No max min min min max mag mag min mass 1 19h34m55s 0.82 10.0 11.0 2.79 1.12 0.03 3.81 1.095 2 20 14 50 1.00 6.0 7.0 1.74 0.60 0.03 2.09 1.075 3 21 31 00 0.67 1.5 2.2 1.46 0.41 0.03 0.33 1.106 4 21 41 56 0.10 2.0 2.1 1.41 0.37 0.03 0.23 1.118 5 21 54 58 2.63 14.0 16.6 2.18 0.85 0.03 8.75 1.136 6 22 26 58 0.55 2.0 2.6 1.94 0.40 0.03 0.39 1.194 7 22 51 52 Duration = 2 sec 1.47 0.42 0.03 0.01 1.256 Table VI Characteristics of the flares observed on March 26, 1982 Flare U.T. tb ta Duration If /I0 Deltam sigma P Air No max min min min max mag mag min mass 1 19h11m30s 1.5 23.0 24.5 2.93 1.17 0.03 21.05 1.115 2 20 47 13 0.80 9.0 9.8 5.33 1.82 0.03 7.61 1.078 3 22 27 34 0.12 0.4 0.5 1.36 0.33 0.03 0.06 1.203 Table VII Characteristics of the flares observed on March 27, 1982 Flare U.T. tb ta Duration If/ I0 Deltam sigma P Air No max min min min max mag mag min mass 1 19h38m35s 0.42 1.5 1.9 1.71 0.58 0.03 0.19 1.092 2 22 30 08 0.13 0.7 0.8 1.61 0.52 0.03 0.05 1.198 d. The value of ratio If/I0, corresponding to flare maximum, where If is the total intensity of the star plus flare less sky background and I0 is the quiet state intensity of the star less sky background. e. the increase of star's brightness in magnitudes at flare maximum: Deltam(u) = 2.5 log If/I0 where "u" is the instrumental ultraviolet magnitude. f. the standard deviation of random noise fluctuations in mag: sigma(mag) = 2.5 log((I0+sigma)/I0) g. the integrated intensity of the flare over its total duration: P = Integrate(If-I0)/I0 dt h. the air mass. The light curves in colour "u" are shown in Figures 1-23. Every point on the figures represents 1 sec integration of intensity. The distribution of amplitudes of the observed flares is shown in Table VIII. Table VIII Distribution of the amplitudes of the flares observed Amplitudes Deltam 0.15m-0.5m 0.5m-1.0m 1.0m-1.5m 1.5m< Number of flares 14 5 3 1 Previous observations of AD Leo by other observers (Moffett, 1974) revealed a frequency of flare occuring of about 1 flare per 3 hours monitoring time (in colour "u"). In the period under consideration we observed about 3 times higher frequency of flare occuring, which means that in that period AD Leo was in a state of enhanced flare activity. Comparison with observations of the star by other observers during the same time would be most desirable. We observed pre-flare decrease of brightness only in two cases. Flare No. 1 of 18.3.1982 has a pre-flare decrease of 0.07 mag and duration of 5 sec, and flare No. 4 of 25.3.1982 has a pre-flare decrease of 0.10 mag and duration of 20 sec. It should be stressed, however, that pre-flare decreases of brightness can only be secured by synchronous observations by two or more telescopes. The comparison star BD+20deg2464 was observed on each night listed in Table I, several times in U,B,V, in order to search for long-term brightness variability of AD Leo. For the period [FIGURE 1] [FIGURE 2] [FIGURE 3] [FIGURE 4] under consideration, no significant changes in the quiet state U,B,V, brightness of AD Leo were found. Thus, the remarkable flare activity of AD Leo in 1982 was not connected with quiet state brightness variability. K.P. PANOV M. GRIGOROVA A. TSINTSAROVA Department of Astronomy with National Astronomical Observatory Bulgarian Academy of Sciences Sofia, 7 November str. No. 1 Bulgaria References: Andrews, A.D., Chugainov, P.F., Gershberg, R.E., Oskanian, V.S., 1969, I.B.V.S. No. 326 Moffet, T.J., 1974, Astrophys. J. Suppl. 29, 1 [BIBCODE 1974ApJS...29....1M ] 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