COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 1906

                                    Konkoly Observatory
                                    Budapest
                                    1981 January 7

                                    HU ISSN 0374-0676


   PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR AD Leo IN 1976



     Continuous photoelectric monitoring of the flare star AD Leo
has been carried out at the Stephanion Observatory (lambda=-22d49'44",
phi=+37d45'15") during the year 1976, using the 30-inch Cassegrain
reflector of the Department of Geodetic Astronomy, University of
Thessaloniki. Observations have been made with a Johnson dual
channel photoelectric photometer in the B colour of the international 
UBV System. The telescope and photometer will be described 
elsewhere. Here we mention only that the transformation of our
instrumental ubv system to the international UBV system is given
by the following equations:
                 V = v_0 - 0.008(b-v)_0 + 2.292,
              (B-V)= 0.737 + 1.043(b-v)_0,
              (U-B)= -1.798 + 1.131(u-b)_0
    The monitoring intervals in UT as well as the total monitoring 
time for each night are given in Table I. Any interruption of
more than one minute has been noted.

                     Table I
             Monitoring intervals in 1976
 Date   Monitoring intervals (U.T.) Total Monitoring   sigma(U.T.)
 1976                      		  Time
May 13	19h56m-20h33m,20h36m-21h03m,             0.06(19h58m),0.09
        21 05 -21 24, 21 36 -22 10.    01h57m   (20h39m),0.09(21 09),
                                                0.11 (21 38).
    27  20 05 -20 35, 20 37 -21 02.    00 55    0.06(20 17),0.06
                                 	        (20 39).
June 2  19 38 -20 15, 20 17 -20 44,
        20 46 -21 20.         	       01 38    0.05(19 43),0.07
                                 	        (20 21),0.07(20 57).
                      Total 04h30m=4h.50
In the fourth column of Table I the standard deviation of random


                            [FIGURE 1]


noise fluctuation sigma(mag)=2.5 log(I_0 + sigma)/I_0 for different times
(UT) of the corresponding monitoring intervals is given.
     During the 4.5 hours of the monitoring time one flare was
observed the characteristics of which are given in Table II.

                    Table II
         Characteristics of the flare observed
Flare  Date  U.T.  t_b t_a  Duration      I_f-I_0 / I_0  P  Deltam sigma  Air
No.    1976  max   min min    min             max     min   mag   mag   mass
        May
 1     13 21h15m47 0.44 0.72  1.16            0.68   0.32  0.56  0.09  1.68

For this flare following characteristics (Andrews et al. 1969)
are given: a) the date and universal time of flare maximum, b)
the duration before and after the maximum (tb and ta, respectively), 
as well as the total duration of the flare, C) the value of the
ratio (I_f - I_0)/I_0 corresponding of flare maximum, where I_0 is
the intensity deflection less sky background of the quiet star
and I_f is the total intensity deflection less sky background
of the star plus flare, d) the integrated intensity of the flare
over its total duration, including pre-flares, if present,
P=Integral(I_f - I_0)/I_0 dt, e) the increase of the apparent magnitude of
the star at flare maximum Deltam(b)=2.5 log(I_f / I_0), where b is
the blue magnitude of the star in the instrumental system, f)
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 and g) the air mass at flare
maximum. The light curve of the observed flare in the b colour
is shown in Fig. 1.


Acknowledgement : The support of the National Hellenic Research
Foundation for this research is gratefully acknowledged.



            G. ASTERIADIS, F. MAHMOUD, L.N. MAVRIDIS
              Department of Geodetic Astronomy
                University of Thessaloniki

Reference:
Andrews, A.D., Chugainov, P. F. , Gershberg, R.I., and Oskanian,
   V.S.,: 1969, I.B.V.S. No. 326