COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2618

                                   Konkoly Observatory
                                   Budapest
                                   1 November 1984

                                   HU ISSN 0374 - 0676




           PHOTOELECTRIC OBSERVATIONS OF AD LEONIS



  Continuous photoelectric monitoring of the flare star AD Leo was carried
out at the Stephanion Observatory and the National Astronomical Observatory
at Rozhen during 1980 - 1984 within the framework of the Program for Scientific
and Technical Co-operation between the Department of Geodetic Astronomy,
University of Thessaloniki, Greece and the Department of Astronomy and
National Astronomical Observatory, Bulgarian Academy of Sciences, Bulgaria.
  Observations were made with the 30 inch Cassegrain reflector at the
Stephanion Observatory equipped with a Johnson dual channel photoelectric
photometer, in the B colour and with the 60 cm Cassegrain reflector at Rozhen
equipped with an EF-1 one channel photoelectric photometer, in the U colour of
the international UBV system. The telescopes and the photometers used have
been described elsewhere (Mavridis et al., 1982; Panov et al., 1982). The
transformations of our instrumental ubv systems to the international UBV
system for the period of 1980 - 1984 is given by the following equations:

          V = v_0 - 0.011(b-v)_0 + 3.191
      B - V = 0.569 + 1.022(b-v)_0  (1980, Stephanion)
      U - B = -1.858 + 0.962(u-b)_0
     DeltaV = Deltav - 0.12(b-v)
Delta(B - V)= 1.14 Delta(b-v)       (1982- 1984, Rozhen)
Delta(U - B)= 1.08 Delta(u-b)

The monitoring intervals in U.T., as well as the total monitoring time
for each night are given in Table I. The standard deviation of random noise
fluctuation (sigma_mag=2.5 log (I_0 + sigma)/I_0) for different times (U.T.) of the
corresponding monitoring intervals is given in the fourth column of Table I.
During the 5.9 hours of monitoring time one flare was observed,   the
characteristics of which are given in Table II. The following characteristics
(Andrews et al., 1969) for the flare are given:
a. the date and universal time of the maximum;
b. the duration before and after the maximum (t_b and t_a, respectively),


                          Table I
            Monitoring intervals in 1980 - 1984
----------------------------------------------------------------------
Date       Monitoring intervals (U.T.)  Total    sigma(U.T.)
           (at Stephanion)             Mon.Time
-----------------------------------------------------------------------
1980
March       20h34m-20h58m, 21h04m-21h49m,       0.03(20h42m), 0.03(21h40m),
20/21       21 58 -22 15 , 22 16 -22 56         0.03(22 05 ), 0.03(22 29),
            22 57 -00 31.                3h40m  0.03(00 00).
            (at Rozhen)
1982
Feb.21/22   23h47m14s-00h07m38s          20m24s 0.04(23h55m).
Oct.27      01 57 18 -02 03 27,                 0.04(02 00 ),
            02 06 33 -02 19 19,                 0.03(02 13 ),
            02 23 46 -02 27 37,                 0.04(02 25 ),
            02 33 22 -02 52 18,                 0.03(02 41 ),
            02 56 21 -03 05 33,                 0.04(02 59 ),
            03 06 42 -03 09 10,                 0.03(03 07 ),
            03 10 12 -03 12 52,                 0.04(03 11 ),
            03 13 42 -03 16 03,                 0.03(03 14 ),
            03 16 43 -03 20 57.          60m37s 0.03(03 18).
1984
March 28    21 18 37 -21 32 55,                 0.05(21 25 ),
            21 41 26 -21 48 09,                 0.05(21 44 ),
            21 53 43 -22 11 29,                 0.04(22 05 ),
            22 16 01 -22 26 29,                 0.04(22 20 ),
            22 29 38 -22 32 25.          50m02s 0.04(22 30).
                                  Total =5h53m03s




                             Table II
                 Characteristics of the observed flare
-----------------------------------------------------------------------
Date  U.T.       t_b   t_a   dura-  I_f-I_0   P   Deltam  sigma   Air
      max.       min.  min.  tion     I_0    min    mag    mag    mass
-----------------------------------------------------------------------
Mar.28 22h21.4m  0.9   4.0   4.9     0.274   0.330  0.26   0.04   1.217




as well as the total duration of the flare;
 c. the value of the ratio (I_f - I_0 )/I_0 corresponding the flare maximum,
where I_0 is the intensity deflection of the quiet star lessened with sky
background and I_f is the total intensity deflection of the star plus flare
lessened with sky background;
 d. the integrated intensity of the flare over its total duration, including
pre-flares, if present: P = Intergal(I_f-I_0)/I_0 dt ;
 e. the increase of the apparent magnitude of the star at flare maximum
Deltam(u) = 2.5 log (I_f/I_0), where u is the ultraviolet magnitude of the star in
the instrumental system;

                          [FIGURE 1]

 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;
  g. the air mass at the flare maximum.
  The light curve of the observed flare in the u-colour is shown in Figure 1.
  The authors would like to express their gratitude to the relevant 
authorities of the respective countries for their support.




M.K. TSVETKOV, A.P. ANTOV          I.N. MAVRIDIS, G.A. ASTERIADIS
Department of Astronomy and        Department of Geodetic Astronomy
National Astronomical Observatory  University of Thessaloniki
Bulgarian Academy of Sciences      Thessaloniki, Greece
Sofia, Bulgaria




References:

Andrews, A.D., Chugainov, P.F., Gershberg, R.E., and Oskanian, V.S. 1969:
   Inf. Bull. Var. Stars, No. 326.
Mavridis, L.N., Asteriadis, G.A., and Mahmoud, F.M.  1982: In: Compendium in
   Astronomy, D.Reidel, Dordrecht, Holland, p. 245. [BIBCODE 1982coas.conf..253M ]
Panov, K.P., Pamukchiev, I.Ch., Christov, P.P., Petkov, D.I., Notev, P.T.,
   and Kotsev, N.G. 1982: Comptes rendus of the Bulgarian Academy of
   Sciences, 35, No. 6, p. 717.