COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1151

                                Konkoly Observatory
                                Budapest
                                1976 July 12

    ON THE DECREASE OF THE ULTRAVIOLET FLICKERING
            OF T CORONAE BOREALIS


   We have observed the recurrent Nova T CrB in the ultraviolet 
using pulse counting photometers and the instrumentation
at the 122 cm telescope of Asiago (see Bernacca et al., 1973).
We have six nights of observations in May and June 1975 and June
1976 (three nights each year, a total of 11 hours of observation).
This year's data, taken with the two channel photometer, show
a marked lack of the flickering reported earlier by Walker (1957)
and seen also from Asiago in 1975.
   The table below lists the observers' name, dates, Julian
Days, orbital phases phi (according to Kraft, 1958), rough estimates 
of the average amplitude a of the flickering (in magnitudes),
the maximum variation A (in magnitudes), the average interval t
between maxima and the duration T of each night's observation.

Observer         Date       J.D.     phi     a       A     t       T

Walker       29 May 1954  2434893   0.51   0.106   0.49   3.5     106

Walker        1 Jun 1954  2434895   0.52   0.072   0.28   4.0     100

Bianchini    16 May 1975  2442549   0.14   0.1     0.35   3.5     100

Bianchini    30 May 1975  2442563   0.21   0.1     0.42   3.5     100

Bianchini     4 Jun 1975  2442568   0.23   0.089   0.30   3.75    137

Middleditch- 18 Jun 1976  2442948   0.90   0.05    0.10   3.5      68
Bianchini                                                (6.7)

Middleditch- 20 Jun 1976  2442950   0.91   0.05    0.10~4         171
Bianchini

Middleditch  21 Jun 1976  2442951   0.91   0.030   0.10~4         137

   Fourier analysis of the last five nights data reveals no
consistent periodicities to below 0.005 magnitudes, although the
data taken on 4 June 1975 and 18 June 1976 tend to indicate 3.6-
minute and 6.7-minute components. Kraft's epoch for phi=0 (J.D.
2432046.0) corresponds to the blue star being nearer to the Earth.
The lack of flickering at phase 0.9 can be explained in two 
different ways. The first explanation has the blue star itself with
a hot variable spot on its surface which is visible at phi=0.14
and phi=0.5 but occulted by the star at phi=0.9, contrary to the
currently accepted theory fixing the flickering at the stream-
disk intersection which should be visible at phi=0.9 according to
Kraft's inclination of 68deg.
    The second hypothesis considers the red giant star not
filling, at present, its Roche-lobe. Each of these two explanations 
would naively predict a decrease in the average U light of
at least 0.2 magnitudes which has not been observed. Further
U observations should help.


                          ANTONIO BIANCHIINI
                           JOHN MIDDLEDITCH

                     Asiago Astrophysical Observatory
                       of the University of Padua


References:
Bernacca, P.L., et al.: 1973, Asiago Scientific and Technical
                Report No. 1
Kraft, R.P.: 1958, Astrophysical Journal 127, 625 [BIBCODE 1958ApJ...127..625K ]
Walker, M.F.: 1957, IAU Symposium No. 3, 46 [BIBCODE 1957IAUS....3...46W ]