COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 791 Konkoly Observatory Budapest 1973 May 21 CONTINUOUS PHOTOELECTRIC PHOTOMETRY OF AD LEO DURING THE 1973 INTERNATIONAL PATROL The flare star AD Leo was observed photoelectrically with the 30cm Cassegrain reflector at Oslo Solar Observatory (lambda=0h43m02s, phi= =+60d12'30", h= 585 m) which is operated by the Institute of Theoretical Astrophysics, University of Oslo. The observing session lasted January 27 - February 9, 1973, according to the program of the IAU Working Group on Flare Stars (1). The monitoring was performed with a filter combination (1 mm Schott BG 12 + 2 mm Schott GG 385) which gives a bandpass equal to the B-band in Johnson's photometric system. The applied diaphragm has a diameter of 1 mm, corresponding to a field of 57.8 seconds of arc. The observations in intervals 4 and 5 on February 8 were performed with a 1/2 mm diaphragm (28.9 seconds of arc). The photomultiplier is a RCA 1P21, working at air temperature. All nights except February 2-3 the air temperature was well below 0dC, and it never changed more than 2dC during a night. Using a paper speed equal to 240 cm/hour, the time resolution on the recording paper is better than the time constant of the equipment, which is 1 second. The photometer system is described by Sivertsen (2). A detailed presentation of the monitoring intervals is found in Table 1, noting all interruptions exceeding 1 minute. The last column contains weighted mean values with respect to time of sigma/I_0. A total coverage of 20.8 hours resulted in 2 observed flares, the physical characteristics of which are presented in Table 2, according to Andrews et. al. (3). U-band (2mm Schott UG 2) observations of flare no. 1 4m20s after maximum give Delta m(u)= 0.7 +- 0.2 magnitudes, compared to Delta m(b)= 0.09 magnitudes 15 seconds earlier. Flare no. 2 was observed in the B-band only. This flare should be recorded as "suspected". Some minutes after the flare had ended. we discovered that the recorder pen was out of position, and this could have caused a spurious flare. However, there are no unusual recording preceding the flare. For flare no. 1 the points of the rising and declining branch of the light curve was determined by taking 15 seconds and 60 seconds means of the intensity, respectively. For flare no. 2 both rising and declining branch was constructed from 5 seconds means. As light curve was taken the best fit to the points, and the smoothed curves are presented in the figures. [FIGURE 1] [FIGURE 2] We thank observator R. Brahde for giving us the opportunity to use the equipment at the observatory. Institute of Theoretical Astrophysics University of Oslo P.O. Box 1029, Blindern, Oslo 3. Norway. Oslo, May 14, 1973. B. R. PETTERSEN B. N. ANDERSEN Table 1 Monitoring Intervals ----------------------------------------------------------------------- Date Monitoring 1973 Monitoring Intervals UT Time ----------------------------------------------------------------------- Jan. 27 18h45m-19h05m,19 11- 19 23, 22 36- 23 14, 23 17- 23 27, 23 31- 24 00, 1h49m 0.10 28 00 00- 00 57, 01 00- 01 15, 01 20- 01 28, 01 31- 02 19, 02 24- 03 44, 03 48- 03 58, 04 01- 04 10, 04 12- 04 21, 04 25- 04 54, 05 00- 05 21, 05 23- 05 43, 05 43- 05 51, 05 52- 05 59. 5 21 0.09 Feb. 2 21 30- 21 43, 21 46- 22 13, 22 27- 22 36, 22 38- 22 55, 22 57- 23 00, 23 04- 23 10, 23 12- 23 25, 23 36- 23 49, 23 54- 24 00. 1 47 0.10 3 00 04- 01 12, 01 17- 02 02, 02 52- 03 08. 2 09 0.08 4 13 19- 18 28, 18 31- 18 42, 18 45- 18 56, 18 58- 19 00, 21 37- 21 43, 21 45- 21 51, 21 53- 22 00, 22 02- 22 23, 22 27- 22 50, 22 52- 23 35, 23 37- 24 00. 2 09 0.07 5 00 00- 00 08, 00 10- 01 08. 1 06 0.08 7 23 21- 23 25, 23 26- 23 31, 23 36- 24 00. 33 0.08 8 00 00- 00 16, 00 18- 00 28, 01 22- 01 49, 01 52- 02 00, 02 12- 02 23, 02 27- 04 03, 04 17- 05 00, 05 02- 05 25, 05 27- 05 30, 05 31- 05 33. 3 59 0.06 9 18 00- 18 21, 18 55- 19 09, 19 12- 19 14, 19 27- 19 41, 19 50- 20 20. 1 21 0.14 ----------------------------------------------------------------------- Total coverage: 20h47m Table 2 Physical Characteristics of the Observed Flares --------------------------------------------------------------------------------------- Flare Date t_max Duration. Maximum Intensity Stand. Equiv. Air No 1973 UT tau_b tau_a (I_0+f - I_0)/I_0 Delta m(b) dev. Energy mass (mag) sigma(b) P(min.) X --------------------------------------------------------------------------------------- 1 Jan.28 00h55m10s 1m21s 18m50s 0.24 0.21 0.07 1.45 1.31 2 Feb. 2 21 58 45 15 1 30 0.29 0.28 0.08 0.15 1.43 --------------------------------------------------------------------------------------- References: 1; Chugainov, P.F. Comm. 27 IAU, I.B.V.S. No. 744, 1972. 2; Sivertsen, S. Institute of Theoretical Astrophysics, Blindern-Oslo. Report No. 34, 1972. 3; Andrews, A.D., Chugainov, P.F., Gershberg, R.F., and Oskanian, V.S. Comm. 27 IAU, I.B.V.S. No. 326, 1969. ERRATA TO I.B.V.S. No. 723. The UT times for EV Lac flare no. 2 presented in I.B.V.S. no. 723 are 5 minutes wrong. The time interval on the light curve should run from 24h47m to 49m. In table 2 the time of maximum, Max UT, should be 21h46.5m. B.N. ANDERSEN, B.R. PETTERSEN