COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2705


                                       Konkoly Observatory
                                       Budapest
                                       9 April 1985

                                       HU ISSN 0374 - 0676


             A FLARE ON THE CONTACT BINARY CN And


  About twenty years ago a large flare event was observed on the prototype
contact binary W UMa by Kuhi (1964). Similar events have been reported on
44i Boo (Eggen, 1948), U Peg (Huruhata, 1952) and VW Cep (Egge and Pettersen,
1982). This is the first event of this kind to be reported for CN And. This
star is an eclipsing binary, classified to be in contact, showing asymmetric
light curve (Kaluzny, 1983). The orbital period is 11h06m. The absolute
magnitude is about 3.41m at maximum light (Dworak, 1975).
  The photoelectric observations were made with the 106 cm telescope at
Yunnan Observatory using an integrating photometer on the night 25/26 November, 
1981. Data were taken through a yellow filter with the effective wavelength
5420 angstrom. BD+39deg0069 and BD+39deg0076 were used as the comparison star and the
check star, respectively. The sequence of the observation was: sky-background-
comparison star-variable star- sky-background. Integration time of each
measure is 16 seconds. The check star was measured at intervals of 30 minutes.
The possible error of the magnitude difference between the check star and the
comparison star is +/- 0.007 mag. The magnitude differences between the variable star
and the comparison star were corrected for differential extinction and were
transformed to the standard UBV system.

  Figure 1 shows portions of the light curve, observed in the V filter. The
light curve of the flare itself, corrected for the effects of eclipses is shown
in Figure 2. The flare is detected from about phase 0.21 to about phase 0.24.
The total duration of the flare is about 22 minutes. The flare rises to half
of the peak value in 4 minutes, and decays to one half of the peak value in
14 minutes. The magnitude of the peak value of the flare is about 0.11 mag. The
obvious dispersion of the light curve from phase 0.18 to 0.30 seems to show
that also some activity on CN And occurs before and after the flare.


                               [FIGURE 1]

    Figure 1: a portion of light curve on CN And displaying a flare

                               [FIGURE 2]

            Figure 2: a flare on CN And at V wavelength





 Adopting the absolute magnitude of 3.41m for CN And (Dworak, 1975), we
estimate 1.5x10^33 erg/s(V) for the peak fluxes of the flare. Integrating 
numerically under the light curve we obtain for the total energy during the flare
8.8x10^35 erg(V).





                      YANG YU-LAN and LIU QING-YAO
                      Yunnan Observatory, Academy Sinica
                      Kunming, P.O. Box 110
                      People's Republic of China




References:

Dworak T.Z.: 1975 Acta Astron. 25, 383 [BIBCODE 1975AcA....25..383D ]
Egge, K.E. and Pettersen, B.R.: 1982, in IAU Colloquium 71,"Activity in
       Red-Dwarf Stars", ed. P.B. Byrne and M. Rodono, p. 481 [BIBCODE 1983ASSL..102..481E ]
Eggen, O.J.: 1948 Ap.J., 108, 15 [BIBCODE 1948ApJ...108...15E ]
Huruhata, M.: 1952, Publ.Astron.Soc.Pacific, 64, 200 [BIBCODE 1952PASP...64..200H ]
Kaluzny, J.: 1983, Acta Astron., 33, 345 [BIBCODE 1983AcA....33..345K ]
Kuhi, L.V.: 1964, Publ.Astron.Soc.Pacific, 76, 430 [BIBCODE 1964PASP...76..430K ]