COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3577 Konkoly Observatory Budapest 14 March 1991 HU ISSN 0374 - 0676 SIMULTANEOUS PHOTOELECTRIC OBSERVATIONS OF AD LEONIS As a part of the programme for investigation of fast (several seconds) flares and short time-scale variations on late spectral classes stars (flare stars, cataclysmic variables, red giants et al.) at the Department of Astronomy of the Bulgarian Academy of Sciences, simultaneous photometric monitoring of the flare star AD Leo was carried out on February 3, 1990. The observations were made in U-colour of the standard UBV system using two identical single channel photon-counting photoelectric photometers, attached to 60 cm Cassegrain telescopes in the National Astronomical Observatory Rozhen and in the Belogradchik Astronomical Observatory. The photometers used have been described by Panov et al. (1982) and Antov et al. (1991). The altitude above the sea level is 1750 m at Rozhen and 630 m at Belogradchik. The distance between them is 270 km. The accuracy in the time synchronization between the two observatories was approximately 2 sec. The star with coordinates alpha_1950=10h16m48s, delta_1950=20d8.5' was used as a comparison star for the observations made at Belogradchik and for the observations made at Rozhen. du(mag) is the difference between AD Leo and the comparison star in the instrumental system. The amplitude of the flares Delta m_u was calculated regarding the quiet state phase of the star AD Leo immediately before flare. The data processing has been made by Kirov, Antov and Genkov's program system (Kirov et al. (1990)). The integration time was 1 sec. The monitoring intervals in U.T., as well as the total monitoring time for the night are given in Table 1. The standard deviation of random noise fluctuation sigma_mag was calculated when the intensity in impulses was lessened with the sky background. They are sigma_mag <= 0.06 for the observations at Rozhen and sigma_mag <= 0.09 for the observations at Belogradchik. Table 1 Monitoring intervals (U.T.) in 3/4 Feb 1990 Monitoring intervals (U.T.) sigma (U.T.) (at Rozhen) 19h37m18s-19h52m23s, 19h54m07s-20h13m41s 007(19h44m), 006(20h04m) 20 15 49-20 37 41, 20 39 12-21 06 00 007(20 26), 005(20 52) 21 08 19-21 30 23, 21 33 38-21 54 53 005(21 19), 005(21 44) 21 56 50-22 18 45, 22 26 12-22 50 59 004(22 07), 004(22 36) 22 52 27-23 22 38, 23 24 58-23 43 15 004(23 07), 005(23 35) 23 45 55-00 11 14, 00 27 50-00 36 31 004(23 58), 005(00 32) Total monitoring time 4h15m38s. (at Belogradchik) 21h04m35s-21h06m16s, 21h08m02s-21h17m56s 010(21h05m), 009(21h12m) 21 18 12-21 29 15, 21 30 30-21 40 08 010(21 23), 009(21 35) 21 40 25-21 50 57, 21 51 58-22 01 53 010(21 44), 009(21 55) 22 02 05-22 10 52, 22 11 58-22 26 03 011(22 05), 009(22 18) 22 27 02-22 41 29, 22 42 32-22 55 22 010(22 33), 009(22 48) 22 55 39-23 09 36, 23 19 05-23 31 45 010(23 02), 008(23 29) 23 31 58-23 39 32, 23 40 30-23 51 56 007(23 35), 008(23 45) 23 52 13-00 03 32, 00 04 41-00 18 50 008(23 57), 006(00 11) 00 19 07-00 30 22, 00 31 20-00 45 04 009(00 25), 009(00 38) 00 45 18-00 54 37, 00 55 56-01 05 35 008(00 49), 005(01 00) 10 05 50-01 15 35, 01 16 45-01 28 03 008(01 10), 008(01 22) 01 28 19-01 39 15, 01 40 15-01 49 49 006(01 33), 008(01 45) 01 50 07-01 54 50 007(01 52) Total monitoring time 4h28m17s. Table 2 Flare U.T. t_b t_a Duration (I_f-I_0)/ Delta m_u sigma_mag Date no. max min min min I_0 3/4 1 R. 21h09m44s 0.07 0.12 0.19 0.37 0.34 0.07 Feb B. 21 09 47 0.07 0.12 0.19 0.47 0.42 0.10 1990 2 R. 21 46 35 0.5 14.0 14.5 1.11 0.81 0.05 B. 21 46 36 0.5 14.0 14.5 1.16 0.84 0.10 2a R. 21 48 58 0.07 0.10 0.17 0.19 0.19 0.05 B. 21 48 59 0.07 0.10 0.17 0.16 0.16 0.06 3 R. 23 33 26 0.3 1.5 1.8 0.96 0.73 0.05 B. 23 33 28 0.3 1.5 1.8 1.18 0.84 0.08 R. - Rozhen, B. - Belogradchik [FIGURE 1] [FIGURE 2] [FIGURE 3] Three flares were observed during the 4.26 hours total monitoring time at Rozhen and 4.47 hours at Belogradchik. The data for these flares are given in Table 2 in the following form: - date; - number of the flare; - U.T. of the maximum; - the duration before and after the maximum (t_b and t_a respectively), as well as the total duration of the flare; - the value of the ratio (I_f I_0)/I_0 corresponding to the flare maximum, where I_0 is the intensity in impulses of the quiet star lessened with sky background and if is the total intensity in impulses of the star plus flare lessened with the sky background. - the increase of the stellar brightness of the star at flare maximum Delta m_u, where m_u is the ultraviolet magnitude of the star in the instrumental system; - 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. The light curves of the observed flares are shown in Fig. 1-3. Some small details from the light curves obtained at Rozhen and Belogradchik with a good coincidence are seen. A detail is pointed out with the small letter 'a'. Data for the flares and the detail are given in Table 2. There are indications for decreasing of the brightness just before the flare no. 2. A. P. Antov, V. V. Genkov, R. Konstantinova-Antova Bulgarian Academy of Sciences Department of Astronomy bul. Lenin 72 1784 Sofia, BULGARIA N. K. Kirov Bulgarian Academy of Sciences Institute of Mathematics ul. Acad. G. Bonchev, bl. 8 1113 Sofia, BULGARIA References: Panov K.P., Pamukchiev I.Ch., Christov P.P., Petkov D.I., Notev P.T., Kotsev N.G., 1982: Compt. Rend. Bulg. Acad. Sci. 35, no. 6., p. 717. Kirov N.K., Antov A.P., Genkov V.V., 1990: in preparation. Antov A.P., Genkov V.V., Kirov N.K., Konstantinova-Antova R.K., Staikov Yu., Nikov Ch.N., Sediankov S.S., Yaramov K.; Pamukchiev I.Ch., Notev P.T., Kotsev N.G., 1991: in preparation.