COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3142



                                       Konkoly Observatory
                                       Budapest
                                       2 February 1988

                                       HU ISSN 0374-0676


          SIMULTANEOUS TWO-COLOUR OBSERVATION OF THE
             FLARE STAR EV Lac IN SEPTEMBER 1987

  Photoelectric monitoring of the flare star EV Lac has been carried out
with the help of two-channel photoelectric photometer attached to the 40 cm
Cassegrain reflector of the Byurakan Astrophysical Observatory. The 
photometer gives us the possibility to record flares in both U and B colours
simultaneously with time resolution equal to 0.01 sec (Zalinian and Tovmassian, 
1987).
  On 15 September 1987 a flare of 40 min duration was recorded with time
resolution of 0.1 sec. The light curve and colours of the flare are given
in Figures 1 and 2, In Fig. 2 the light curve of the flare is averaged over
5 points.


                              [FIGURE 1]
                              [FIGURE 2]


   The light curve shows, that the flare obviously consists of two maxima
"b" and "c", and that the flare is preceded by a faint precursor of 2 s
duration. A similar preflare of 1.5 s duration and deltamU = 1.1 was recorded
on 8 August 1985 at 5 s before the beginning of the main flare with an amplitude
of DeltamU = 2.2 (Zalinian and Tovmassian, 1986).
   The durations of preflares in both cases are small (in both cases < 3 s).
If such preflares really occur before each large flare they could not be
recorded in observations with larger integration time.

                   Table I

     max  T   DeltamU   Deltams   U-B   Duration
         (sec)                           (min)
      a        1.2        0.4     0.3
          63
      b        2.6        1.1    -0.4
          27
      c        3.1        1.6    -0.5     40

   The main characteristic features of the observed flare are given in
Table I in which T is the time interval between maxima "a" and "b",and "b"
and "c"; DeltamU, DeltamB, amplitudes of flares in U and B colours; U-B: colour
of the star during the flare.


                              V.P. ZALINIAN
                        Byurakan Astrophysical Observatory
                           Byurakan, Armenia, USSR

References:
Zalinian V.P., Tovmassian H.M., 1986, Soobshch.Byurakan Obs., 58. [BIBCODE 1986SoByu..58...87Z ]
Zalinian V.P., Tovmassian H.M., 1987, IBVS, No. 2992.