COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3307

                                          Konkoly Observatory
                                          Budapest
                                          17 March 1989

                                          HU ISSN 0374 - 0676


     RAPID VARIATIONS OF THE X-RAY SOURCE KR AURIGAE IN U COLOUR


It was shown that flickering in cataclysmic variables is caused by mass
transfer and accretion process (Robinson, 1976).  The absence of flickering at
minimum light observed in 1980 in MV Lyr was interpreted as cessing of the mass
transfer (Robinson et al. 1981), because flickering is typical for maximum
light in this star. With regard to explain the presence of occasional deep
minima in the light curves of some other binaries with orbital periods also
near the period gap (2-3 h) it is worthwhile more information about the
flickering activity of these stars and the changes of its rate with time to be
obtained.

KR Aur, with an orbital period of 3h54m (Shafter, 1983) is one of the stars
in this group. It was the first one, characterized according to its light
curve with the term "anti-nova" (Popova, 1974). Taking, besides, into account
the spectral features, Bond (1980) proposed this subtype of cataclysmic
variables to be named "anti-dwarf novae".

Here we present results from observations of short time-scale variations of KR
Aur at National Astronomical Observatory of Bulgarian Academy of Sciences. The
observations were made on the night 3 Nov. 1986 using a photon counting
photometer (Panov et al. 1982) attached to the 60 cm Cassegrain telescope.
The integration time was 10 sec in U. The star was in maximum light during the
observations.

Figure 1 shows the light curve beginning at UT 00h52m03s. The differences
delta u in instrumental system are obtained with respect to the comparison star
"c" from Popova's (1965) sequence. The standard deviation is +-0.06m.

The rapid variations in U colour of KR Aur are quite similar to the flickering
displayed at maximum light in MV Lyr. So, the flickering activity of KR Aur
indicates that mass transfer was taking place at the time of observations. It
is very important to follow the changes of the rate of flickering activity of
the object with the changes of the brightness, especially during the minimum
light.


                                [FIGURE 1]


If the character of the photometric behaviour of KR Aur is continuing to be the
same as in the last decades, the next deep minimum can be expected in the next
1- 2 years.


V.N. POPOV and A.P. ANTOV
Department of Astronomy with
National Astronomical Observatory
Bulgarian Academy of Sciences
Bulgaria

References:

Bond, H.E. 1980, paper presented at the Fifth Ann. Workshop on Cataclysmic
   Variables and Related Objects, Univ. of Texas (cited by Shafter, 1983).
Panov, K.P., Pamukchiev, I.Ch., Christov, P.P., Petkov, D.I., Notev, P.T.,
   Kotsev, N.G. 1982, Compt. Rend. Bulg. Acad. Sci., 35, No. 6, 717.
Popova, M.D. 1965, Perem. Zvezdy, 15, 534. [BIBCODE 1965PZ.....15..534P ]
Popova, M.D. 1974, in "Late Stages of Stellar Evolution", ed. R. Taylor, p. 192 [BIBCODE 1974IAUS...66..192P ]
Robinson, E.L. 1976, Ann. Rev. Astr. Ap., 14, 119. [BIBCODE 1976ARA&A..14..119R ]
Robinson, E.L., Barker, E.S., Cochran, A.L., Cochran, W.D., Nather, R.E. 1981,
   Astrophys. J., 251, 611. [BIBCODE 1981ApJ...251..611R ]
Shafter, A. 1983, Astrophys. J., 267, 222. [BIBCODE 1983ApJ...267..222S ]