COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3338

                                            Konkoly Observatory
                                            Budapest
                                            13 June 1989

                                            HU ISSN 0374 - 0676


                FLARE OBSERVATIONS OF UV CETI


In order to study the structure of the flare light curves, synchronous
photoelectric observations were made on UV Ceti at Maydanak high-mountain
station of Tashkent Astronomical Institute, using two 60-cm telescopes.
During 12 hours of observations 15 flares were detected in U-band, in
October and November 1987. The synchronization of the two telescopes was as
precise as 0.001 sec. The measurements were made by the photon counting
method. The duration of each measurement was 2 seconds, and the time interval
between two measurements was 0.4 s.

The results of the observations are presented in Table I: number of flare,
date of flare in UT, the beginning moment of the flare (in UT), the rise time
and the decay time (in seconds), and the amplitudes of the flares as measured
with the two telescopes (delta U_1 and delta U_2, respectively) are given. The
light curves of the flares No. 14 and No. 15 are presented in Figure 1 for the
illustration, where I_0 is the stellar intensity in normal state, and I_f is
the additional intensity.

                                 Table I

N     Date of      Beginning of    Rise time   Decay time     Delta     Delta
     flare (UT)    the flare (UT)   (s)         (s)             U_1       U_2
1    18 Oct.1987   21h08m21s        3           51             0.80m     1.00m
2    19 Oct.1987   17 58 24         6          120             0.78      0.80
3    19 Oct.1987   18 27 57         21         354             1.04      1.10
4    19 Oct.1987   18 47 09         6           51             1.06      1.16
5    19 Oct.1987   19 47 48         3           36             2.35      2.35
6    19 Oct.1987   19 53 00         -          420             2.05      2.19
7    16 Nov.1987   16 04 54         15         144             1.38      1.53
8    16 Nov.1987   16 21 12         30         135             1.34      1.19
9    16 Nov.1987   16 49 30         48         465             2.91      2.86
10   16 Nov.1987   18 25 09         33         198             1.26      1.16
11   16 Nov.1987   18 30 15         27         255             1.70      1.63
12   16 Nov.1987   18 36 33         9          198             3.04      2.94
13   16 Nov.1987   18 56 00         15         105             1.75      1.79
14   16 Nov.1987   19 05 21         30         187             1.66      1.70
15   17 Nov.1987   16 25 03         12         435             1.68      1.66


                                [FIGURE 1]


In addition to these 15 flares, four "spike-shaped" increases of the light were
observed, duration of each one being less than or equal to two seconds. These
four cases are illustrated in Figure 2. In all cases the "spike-shaped"
increase of the brightness is registered only with one telescope. Such
"spike-shaped" increases of the light were already detected during the EV Lac
flare observations (Tovmasian and Zalinian, 1988; Tsvetkov et al., 1986a,b; and
Zalinian and Tovmasian, 1986). Unlike the results for EV Lac, it seems to us
that this kind of increase can be explained by the Poissonian distribution of
the observational errors (the number of the points on our registrograms is more
than 20000 on each telescope).

The authors are indebted to Prof. L.V. Mirzoyan for suggesting these
observations.

                                [FIGURE 2]




N.D. MELIKIAN                           N.N. KILJACHKOV, V.S. SHEVCHENKO,
Byurakan Astrophysical Observatory      A.V. CHERNISHEV, D.L. PORTNOV
                                        Tashkent Astronomical Institute

References:

Tovmasian, H.M., and Zalinian, V.P. 1988, Astrofizika, 28, 131. [BIBCODE 1988Afz....28..131T ]
Tsvetkov, M.K., Antov, A.P., Tsvetkova, A.G. 1986a, In: Eruptive Phenomena in
   Stars; Comm. Konkoly Obs., Budapest, No. 86, p. 423.
                                                      [BIBCODE 1986CoKon..86..423T ]
Tsvetkov, M.K., Tsvetkova, K.P., Melikian, N.D. 1986b, IBVS, No. 2954.
Zalinian, V.P., and Tovmasian, H.M. 1986, IBVS, No. 2992.