COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1891

                                   Konkoly Observatory
                                   Budapest
                                   1980 December 17

                                   HU ISSN 0374-0676


  PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR BY Dra IN 1975


   Continuous photoelectric monitoring of the flare star BY Dra
has been carried out at the Stephanion Observatory (lambda=-22d49'44",
phi=+37d45'15") during the year 1975, 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:

       for the time interval from 5-2-1975 to 24-6-1975
       V=v_0+0.001(b-v)_0+2.278
       (B-V)=0.908+1.037(b-v)_0
       (U-B)=-1.895+1.031(u-b)_0 ,
       for the time interval from 25-6-1975 to 30-7-1975
       V=v_0+0.119(b-v)_0+2.163
       (B-V)=0.819+1.047(b-v)_0
       (U-B)=-1.509+1.006(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. In the fourth column of
Table I the standard deviation of random 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 22.27 hours of monitoring time one flare was observed 
the characteristics of which are given in Table II. 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 (t_b and t_a, respectively),

                           Table I
               Monitoring intervals in 1975
Date    Monitoring intervals (UT)      Total              sigma(UT)
                                    monitoring
1975                                   time
June
20      21h59m-22h28m,22h32m-23h01m                0.01(22h15m),0.002(22h51m).
        23 05 -23 11.                 1h04m
21-22   23 44 -23 55, 00 04 -00 18,                0.01(23 46), 0.01 (00 25),
        00 22 -00 57, 01 01 -01 25.   1 24         0.01(01 03).
26-27   23 36 -00 02, 00 06 -00 40,                0.01(23 38), 0.01 (00 08),
        00 44 -01 18.                 1 34,        0.01(00 46).
29-30   19 56 -20 23, 20 26 -20 44,                0.01(19 59), 0.01 (20 29),
        20 57 -21 30, 23 05 -23 34,                0.01(20 59), 0.002(23 08),
        23 37 -24 00, 00 04 -00 29,                0.01(23 40), 0.01 (00 08),
        00 43 -01 07, 01 10 -01 37.   3 26         0.01(01 00), 0.01 (01 12).
June-July
30-1    20 26 -20 57, 21 00 -21 27,                0.01(20 27), 0.01 (21 03),
        21 30 -22 02, 23 27 -00 01,                0.01(21 33), 0.01 (23 30),
        00 04 -00 36, 00 39 -01 25.   3 22         0.01(00 05), 0.01 (00 41).
July
1-2     21 32 -22 00, 22 04 -22 34,                0.02(21 41), 0.01 (22 30),
        22 37 -22 48, 22 51 -23 07,                0.02(22 58), 0.01 (23 37),
        23 21 -23 50, 23 54 -00 26,                0.01(00 10), 0.01 (00 32),
        00 30 -00 50, 01 04 -01 24.   3 06         0.01(01 17).
3-4     20 30 -20 57, 21 16 -21 38,                0.01(20 33), 0.01 (21 19),
        21 42 -22 15, 22 30 -22 58,                0.01(21 45), 0.01 (22 32),
        23 02 -23 12, 23 19 -23 23,                0.01(23 41), 0.01 (00 26),
        23 26 -23 59, 00 21 -00 48,                0.01(01 10).
        00 51 -01 24.                 3 37
6-7     20 59 -21 28, 21 34 -22 01,                0.01(21 00),0.003 (21 38),
        22 04 -22 35, 23 49 -00 24,                0.003(22 23),0.01 (23 54),
        00 28 -00 57, 01 00 -01 21.   2 52         0.01 (00 30),0.01 (01 15).
7       21 33 -21 59, 22 14 -22 43,                0.01 (21 50),0.01 (22 20),
        22 47 -23 11, 23 14 -23 46.   1 51         0.01 (23 05),0.01 (23 23).
                             Total: 22h16m=22.27h

                             Table II
          Characteristics of the flare observed
                             I -I
Flare Date    U.T.    t_b   t_a   Duration  I_f-I_0/I_0  P  Delta m  sigma   Air
No            max     min            min        max     min   mag     mag   mass
         1975                         
1     July  22h38.92m 0.51  3.89    4.40      0.19    0.21    0.19    0.01  1.92
        1

as well as the total duration of the flare, c/ the value of the
ratio (I_f-I_0)/I_0 corresponding to flare maximum, where I_0 is the
intensity deflection less sky background of the quiet star and
If 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,

                       [FIGURE 1]

e/ the increase of the apparent magnitude of the star at flare
maximum Delta m(b)=2.5log(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)=2.5log(I_0+sigma)/I_0 during the quietstate 
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.



                            L.N. MAVRIDIS
                      Department of Geodetic Astronomy
                        University of Thessaloniki
                             Greece

                             P. VARVOGLIS
                         Department of Mathematics
                          University of Thrace
                              Greece


Reference:
Andrews, A.D., Chugainov, P.F., Gershberg, R.I., Oskanian, V.S.
   1969, Inf. Bull. var. Stars, No. 326.