COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1989

                                   Konkoly Observatory
                                   Budapest
                                   1981 July 8

                                   HU ISSN 0374-0676



OBSERVATIONS OF SU UMa BEFORE AND DURING A SUPEROUTBURST +


SU UMa stars have recently been defined by Vogt (1980) as dwarf
novae that show two distinct properties: short and long lasting
eruptions (superoutbursts) and periodic light variations 
(superhumps) during a superoutburst. The prototype SU UMa itself,
though being fairly bright, apparently was never observed in
detail during a superoutburst. Therefore its membership to this
subgroup of dwarf novae still needs to be confirmed.

SU UMa was observed with a 2-channel highspeed photometer 
attached to the 1.23 m telescope of the Calar Alto Observatory in
Spain (Table I gives the observational data). During two nights
the object was measured in minimum light, during the third
night SU UMa was in outburst (Barwig et al., 1980). Using data
from the AAVSO (1981) it could be confirmed that the star
started a superoutburst just before our last run. A lightcurve
of this eruption, derived from the AAVSO data, is shown in
Fig. 1.

To demonstrate the short time variations in the lightcurve, two
examples of our measurements in minimum and maximum light are
shown in Fig. 2 and 3 respectively. The amplitude of the flickering 
in minimum light is comparable to that of WX Hyi and V436
Cen and increases in intensity by a factor of two during 
outburst. No pronounced periodic features were found which could
be attributed to orbital motion, but an analysis of periodic

+ Based on observations collected at the MPIA Heidelberg Observatory, 
Calar Alto, Spain.

variations in our measurements before the outburst yielded a
period of 120 min +- 10% with a relative amplitude of a few 
percent and a significance of 3 - 4 sigma. Interpreted as an orbital
phenomenon SU UMa would belong to the long period members of
this special group. The chance, however, that this result is
accidentally is large.
Periodogram and autocorrelation function revealed a period of
13 min, which is most clearly seen in channel R of run 2
(Fig.4) and less pronounced in run 3. Similar periodic variations 
have already been reported by Mumford (1964).



                 Table I

                   Start    End
     Date     Run
              No.   HJD    2444300+
1980-03-10/11 1    09.570   09.694  Wavelength region:
1980-03-12/13 2    11.529   11.694  Channel B : lambda_eff = 400 nm
                                    Channel R : lambda_eff = 590 nm
1980-03-15/16 3    14.331   14.626
                           Integration time: 3s


                          [FIGURE 1]

 Fig.1  Lightcurve of SU UMa from AAVSO (1980, Mar.2 - Apr.6).
        The times of our runs are indicated by arrows 1 - 3.
        The point in brackets means "fainter than".

                          [FIGURE 2]

 Fig.2  Photometry of SU UMa in minimum light (run 2,channel B)

                          [FIGURE 3]

 Fig.3  Photometry of SU UMa during superoutburst (run 3, chan. B)

                          [FIGURE 4]

 Fig.4  Autocorrelation function of SU UMa (run 2, channel B)


It is important to know whether SU UMa exhibits superhumps or
not.
According to the AAVSO data our last run covers the time interval 
between 15 and 22 hours after start of eruption (T_0). As
can be seen in Fig. 3, during that time the brightness of the
star increased by less than 0.1m if one disregards light
changes due to flickering. A similar result can be derived from
AAVSO data received near the time of our measurements: 4 out
of 6 values indicate constant luminosity (11.6m). That means,
the brightness of SU UMa reached a standstill at the time of
our observations.

A thorough investigation of our data by means of normal periodogram 
technique did not reveal any periodic features with
significant amplitudes for any superhumps. The AAVSO data from
the time interval between 2 and 6 days after T_0 clearly show a
further increase in brightness. With regard to the small sample 
and large scatter in these data, periodic light variations
cannot be excluded but cannot be proved either.

In other SU UMa stars superhumps evolved one or two days after
beginning of outburst. Marino et al. (1979) and Vogt (1981)
already proposed that each superoutburst starts with a normal
eruption, and after a short standstill the characteristic
supermaximum emerges.

Under this respect it may still be possible that SU UMa is the
prototype of its group.


                          H. BARWIG
                          R. SCHOEMBS
                          Universitats-Sternwarte
                          Scheinerstr. 1
                          D-8000 Munchen 80
                          Germany

References

AAVSO, 1981, private communication
Barwig, H., Schoembs, R., 1981, Mitt. Astron. Ges. 52, 17 [BIBCODE 1981MitAG..52...17B ]
Marino, B.F., Walker, W.S.G., 1979, IAU Coll. 46, 29 [BIBCODE 1979ctvs.conf...29M ]
Mumford, G.S., 1964, AJ 69, 270 [BIBCODE 1964AJ.....69..262M ]
Vogt, N., 1980, Astron.Astrophys. 88, 66 [BIBCODE 1980A&A....88...66V ]
Vogt, N., 1981, Habilitationsschrift am Institut fur Physik
                u. Astronomie der Ruhr-Universitat Bochum