COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1707

                                  Konkoly Observatory
                                  Budapest
                                  1979 November 23


           HIGH SPEED PHOTOMETRY OF U Sco


The recent outburst (I.A.U. telegram received June 27, 1979) of the recurrent
nova U Sco provided the first opportunity for photoelectric photometry of this
species with the benefit of superior time resolution (we here relegate the 1978
eruption of WZ Sge to an outburst of a dwarf nova (Warner 1976; Robinson et al.
1978)).

Announcement of this event coincided with an observing run by the writer on the
40-inch (1016 mm) telescope at the South African Astronomical Observatory. The
first occasion on which the nova could be observed was 29 June, and it was
consequently honoured with five second integrations, in white light (i.e. no
filter: photomultiplier with S11 response) starting at 18:40:47 U.T. and
lasting for nearly 5 hours. It emerged that this amount of attention was
superfluous: there was no activity on a timescale of seconds. We can
therefore exclude U Sco from the class of ultra-short orbital period,
hyper-long outburst dwarf novae personified by WZ Sge. There was, however,
activity on a timescale of 10 minutes, as is shown by the light curve (in which
we have added contiguous integrations to furnish a record with 25 seconds
resolution). In this light curve, abscissa carets mark time intervals of 0.02
days and ordinate carets are in steps of 3000 counts per second, commencing at
42,000 c.p.s. (these are rates obtained after removal of extinction). The
mean visual magnitude during the observation was about 11.5 (c.f. Bortle,
I.A.U. Circ. 3378).

                           [FIGURE 1]

As can be seen from the Figure, there was a general increase in brightness
during the observation, reaching maximum shortly before termination, on which
there were significant variations of order 10-20 minute duration.

The spectroscopic observations reported by Hill and by Pringle and Whelan
(I.A.U. Circ, 3378) are stated to indicate that U Sco was "not unlike T CrB",
which, if interpreted as meaning that U Sco resembled T CrB, agree in excluding
this object from the WZ Sge class. The timescales of the variations reported
here have considerable relevance to the processes occuring in the star a few
days after its outburst.


BRIAN WARNER
Department of Astronomy
University of Cape Town

References:

B. Warner, 1976. In I.A.U. Colloquium. No. 73, Cambridge, p. 85. [BIBCODE 1976IAUS...73...85W ]
Robinson, E.L., Nather, R.E. and Patterson, J., 1978. Astrophys. J., 219, 168. [BIBCODE 1978ApJ...219..168R ]