COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                              Number 2960

                                                         Konkoly Observatory
                                                         Budapest
                                                         27 November 1986

                                                         HU ISSN 0374 - 0676


               UBV OBSERVATIONS OF T CORONAE BOREALIS

The cataclysmic variables exhibit light variations on different time
scales. At Rojen observatory a program has been initiated for searching for
relatively long-time variations of the brightest old novae and recurrent novae.
In this paper the photoelectric observations of T CrB, carried out with the
60-cm telescope in 1985 are presented. The star A of SA 60 has been used as
a standard (Priser, 1974),
   A continuous 2.5 hour observation of T CrB in B band on 14/15 May 1985
showed the presence of short-time variations of amplitude <= 0.07m on a time
scale of 6 - 10 min. In Fig. 1 the differences delta m = m_var - m_std are given
foe 10 second integration time of the photon counting. The values of V, B-V and
U-B during the whole night are presented in Figure 2.
   In the observations for long-time variability when they last 10 minutes or 
more, the small range short-time variations are averaged. Shorter observations 
are less representative. In Table I the values of V, B-V and U-B are given 
for 1985. The accuracy of the data has been estimated from the observations 
of the standard star on good photometric nights. The mean error sigma is
less than +- 0.02 for V and B-V values and +-0.05 for U-B. We point out two
cases of rapid variations: (i) on 16 July (J.D. 2446263..) U-B exhibits two
jumps in 35 minutes by 0.32 mag. and 0.11 mag. respectively, V and B-V being
constant within the error: (ii) on 20 July (J.D. 2446267..) B-V and U-B change
by 0.1m, V being constant. On both nights the atmospheric conditions are
referred as good ones.


                          [FIGURE 1]
                          [FIGURE 2]


                         Table I

J.D.              V      B-V      U-B     Duration of
                                          observation
2446200.370      9.92   +1.29    +0.37       100m
    200.524      9.93   +1.32    +0.43        60
    203.833      9.91   +1.33    +0.52        15
    209.510      9.89   +1.37    +0.66        55
    210.493      9.88   +1.34    +0.52        15
    227.452      9.92   +1.28    +0.47        35
    230.451     10.01   +1.50    +0.56        10
    263.403     10.16   +1.20    -0.16        10
    263.408     10.19   +1.18    +0.16        10
    263.416     10.17   +1.16    +0.05        15
    267.381     10.11   +1.06    -0.13        15
    267.388     10.09   +1.15    -0.03        15
    290.454      9.91   +1.34    -0.32        10
    302.338     10.12   +1.20    +0.09        45
    324.341      9.93   +1.34    +0.62        45
    329.292      9.94   +1.33    +0.57        30


                       D. RAIKOVA
                        A. ANTOV

              Department of Astronomy, Bulgarian
                    Academy of Sciences
                      Sofia, Bulgaria



Reference:

Priser, J.B., 1974, Publ. US Naval Obs., Sec. ser., XX [BIBCODE 1974PUSNO..20....1P ]