COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1185

                               Konkoly Observatory
                               Budapest
                               1976 October 11




            PERIODIC SUPERHUMPS ON WX HYDRI

   In I.B.V.S. No. 864 we drew attention to the occurence
of "humps" on the supermaximum outburst light-curve of the dwarf
nova VW Hydri. These "superhumps" were displaced in phase from
the normal humps which occur at minimum and appeared variable
from cycle to cycle. The normal humps provided direct data for
determination of the orbital period of the system.
   Vogt (1974) and Warner (1975a) subsequently analysed the
observations to show the superhumps were repetitive with a period 
approximately 3% greater than the orbital period. Warner (1975b)
has drawn attention to a similar phenomenon on V436 Centauri. We
report here the observation of superhumps on another dwarf nova,
WX Hydri. We deduce a preliminary orbital period for the system
from the superhump period and from a few observations when the
star was at minimum.
   WX Hydri was observed photo-electrically at Auckland 
Observatory on 1976 September 21 and September 22 with the Zeiss
500 mm Cassegrain telescope and an EMI 9502 photomultiplier. The
observations cover an interval of six hours on September 21 and
just under an hour on September 22 (when cloud cut short the
programme). The star was monitored in white light but five sets
of three colour UBV observations were obtained during the runs.
The peak V magnitude of WX Hydri (V~11.35) indicated that a 
supermaximum was in progress.
   The observations are presented in Figure 1. These show
three peaks on the first night and part of a peak on the following 
night. From these we have derived a period of 1 hour 52.7
minutes (0.0783 days). The peaks are similar in nature to those
on VW Hydri.
   We have also measured WX Hydri in December 1973 when it
was not in outburst. The light-curve showed quasi-periodic

variations with indications of shallow eclipse-like features having
a period of 0.14989 days. The star at V~14.7 is near our observing 
limit and so no further observations were obtained at minimum 
in the following two seasons. A period of half of this value,
i.e. 0.0749 days, is ~4% less than the superhump period, compared 
with the 3% for VW Hydri, and appears probable as the orbital
period of the system.
     There are some peculiar indentations in the light-curve
on 1976 September 21 which resemble shallow partial eclipses.
These, together with the behaviour at minimum and the amplitude
of the superhumps, indicate that WX Hydri may have a high 
inclination. Should these indentations be partial obscurations of the
source of the superhumps further observations of the feature may
provide a means of determining the nature of the superhump and
its location in the system.
     We acknowledge with thanks to the use of the Auckland
Observatory telescope and photoelectric accessories. We would
also thank Graham Blow for the use of observing time at short
notice.

                          W.S.G. WALKER,
                          BRIAN F. MARINO,
                          G. FREETH

                       Auckland Observatory
                   of the Auckland Astronomical Society
                   P.O. Box 2858, Auckland, 1. New Zealand


References:

Brian F. Marino, W.S.G. Walker, 1974, I.B.V.S. No. 864
Vogt, N. 1974, Astronomy and Astrophysics 36, 369 [BIBCODE 1974A&A....36..369V ]
Warner, B. 1975a MNRAS 170, 219 [BIBCODE 1975MNRAS.170..219W ]
Warner, B. 1975b MNRAS 173, 37p [BIBCODE 1975MNRAS.173P..37W ]


                            [FIGURE 1]