COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3037


                                        Konkoly Observatory
                                        Budapest
                                        24 June 1987

                                        HU ISSN 0374-0676




       PHOTOELECTRIC OBSERVATIONS OF EX HYDRAE DURING THE
               1986 JULY-AUGUST OUTBURST

   EX Hydrae was monitored photoelectrically in July and August 1986
during one of its rare outbursts. As far as the authors are aware this
outburst is the first eruption of EX Hydrae to be measured by photoelectric
means. Ten second integrations were made predominantly in white light
using the photon counting system attached to the 50 cm Zeiss Cassegrain
reflector at the Auckland Observatory. Star '96' on AAVSO chart 24728(e)
was used as a comparison star with V=9.62, B-V=0.48 and U-B=0.08.
   Occasional Johnson U, B and V readings were also taken and the
nightly means of three are given in Table I. The existence of two rises in
brightness above the normal quiescent level is confirmed by the visual
observations of Jones (1986) as can be seen in Figure 1.

Table I: Three colour observations during the 1986 July-August outburst
of EX Hydrae

Date                         Number of VBU         Mean    Values
1986              JD-2446000 Observations         V       B-V     U-B

July 30            641.91       15              12.46    0.18   -0.91
July 31            642.89       20              13.39   -0.09   -1.10
August 4           646.83        1              12.68    0.09   -0.72
August 5           647.83       16              10.43    0.00   -0.91
August 6           648.86        5              11.13    0.08   -0.73
August 10          652.81        2              13.46    0.04   -1.11


                                [FIGURE 1]

 Figure 1. Overall light curve of the 1986 July-August outburst of EX
 Hydrae. The data shown are the photoelectric V magnitudes (+) and the
 visual estimates of Jones, 1986.


  Continuous monitoring of EX Hydrae on August 6 revealed three hump
like features similar to those that characterise the well known 67 minute
cycle present in the quiescent state light curve (Vogt et al. 1980, Sterken
et al. 1983). However the outburst features are considerably enhanced in
intensity compared to the quiescent state features. A graph of the white
light magnitude difference from the comparison star clearly shows three
features in Figure 2. The heliocentric times of the maxima were found to
be HJD 2446648.8037, 2446648.8471 and 2446648.8905.
  The light curve shown in Figure 2 indicates that no obvious eclipse-
like features occur close to the eclipse times predicted by the ephemeris
of Sterken et al. (1983). Dips do appear in the light curve but these may
be due to the particularly high level of flickering always present.
   Extensive long period monitoring was prevented by inclement weather
and the unfavourable position of EX Hydrae at that particular time of year.
Further analysis of the data is underway at present and the authors therefore 
invite others with photoelectric data covering the event to contact
them.


                             [FIGURE 2]

 Figure 2. EX Hydrae light curve obtained on August 6. Each point
 corresponds to one 10 second integration in white light. The timing marks
 below the data correspond to the eclipse times predicted by the ephemeris
 of Sterken et al. (1983).




    I. BOND, R.V. FREETH - Physics Department, University of Auckland
    B.F. MARINO, W.S.G. WALKER - Auckland Observatory


References:

Jones, A., 1986, Private communication.
Sterken, C., Vogt, N., Freeth, R., Kennedy, H.D., Marino, B.F., Page, A.A.,
   and Walker, W.S.G., 1983, Astron. Astrophys. 118, 325. [BIBCODE 1983A&A...118..325S ]
Vogt, N., Krzeminski, W., and Sterken, C., 1980, Astron. Astrophys. 85,
   106. [BIBCODE 1980A&A....85..106V ]