COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1271

                                                    Konkoly Observatory
                                                    Budapest
                                                    1977 April 25

    A FLARE EVENT ON THE dM0e VARIABLE BY DRACONIS

As part on an ongoing program to obtain a body of
high quality photometric data on the flare star BY Draconis,
a series of observations was undertaken during the past year
(1976) in order to time-resolve the reported light variations.
The behavior of BY Dra has been interpreted in terms of a 
binary system (non-eclipsing) wherein an apparent rotational
modulation of the integrated luminosity has been attributed to
the existence of starspots on one of the components, after
Vogt (1975). Thus, it is of considerable interest to determine
whether further observations support such a hypothesis and 
indeed verify the existence of starspots. During the course of
obtaining additional observations, a prominent flare was 
observed on BY Dra, the characteristics of which are described
below.
   The flare was observed while using the 91-cm telescope
of the McDonald Observatory in conjunction with an uncooled 56
DVP photomultiplier operating in a pulse counting mode. Using
the B filter of the standard Johnson UBV system, the method of
collecting the data followed the conventions suggested by 
Andrews et al. (1969). Residual magnitudes (Delta B) were 
determined with respect to the mean of two established comparison
stars (C1 = BD +51d2410; C2 = BD +51d2408 ) with consecutive
measures being taken on each star and then the sky background.
The observations, corrected for extinction, are shown in 
Figure 1, where the flare data is displaced above that of the two
comparison stars for clarity of illustration. The sky 
backgrounds (in counts per sec) are also shown beneath the 
comparison stars. Each data point represents an average of three

                         [FIGURE 1]

15-sec integrations which was formed upon removing the appropriate 
sky background measure and the dark current of the photometer. 
The accuracy per data point is determined to be .002
mag. as estimated from the scatter in the residuals of, the two
comparison stars. A slight increase in the mean light of BY
Dra is evident in the Figure as it was observed on the rising
portion of its light curve. Other relevant data pertaining
to the flare.event is collected in Table I.


                     Table I

         Summary of Flare Characteristics

Quantity              Value        Comments
  (1)                  (2)           (3)

Date (1976)           June 30
U.T.(max.)            08h36m    Flare maximum
Duration (minutes)     ~23
P+ (minutes)          0.285
Delta m++ (mag.)      0.031    Maximum amplitude
sigma (mag.)          0.002
Airmass, X            1.13     At flare maximum
                	         Andrews et al.
                                    (1969)
Notes: + p= Integral(Delta m d tau)

       ++ Delta m is the instrumental b magnitude

   Although the time resolution of the flare is rather
coarse, evidence for multiple structure can be seen in examining 
Figure 1. It is also of interest to note the possible 
precursor to the main flare which occurred some 51 minutes earlier
and attained an amplitude of ~0.007 mag. above the quiescent
level.


                                  MARK H. SLOVAK

                              Department of Astronomy
                                University of Texas



References:

Andrews, A.D., Chugainov, P.F., Gershberg, R.E., and Oskanian, V.S. 1969,
   I.B.V.S. No. 326.
Vogt, S.S. 1975, Ap.J., 199, 418. [BIBCODE 1975ApJ...199..418V ]