Rare outburst of EX Hya (1998)

(vsnet-alert 2017)

EX Hya is in outburst, visual observations.

 Star      Date      UT     mag.
EX Hya    980808    9:14    13.5
          980809    9:03     9.6
          980809    9:20     9.5
          980809    9:56     9.5

Rod Stubbings
Drouin, Vic.

(vsnet-alert 2028)

Dear Colleagues,

We have been informed that EX Hya is being observed with the RXTE. The target is first time observed during outburst in X-rays (Koji Mukai, mukai@lheavx.gsfc.nasa.gov). Coordinated optical observations are strongly recommended.

Taichi Kato

Previous outbursts

(vsnet-chat 1129) Hi,

If my memory is correct, I have monitored EX Hya since 1992 and have not experienced an outburst so far. I will be more than happy to monitor this rare event, weather allowing...

Good luck to Rod for this one again!


Berto Monard

(vsnet-chat 1138)

According to my archives, there has been at least 1 more outburst since 1987 :

1994.1225 at mag 9.4; observed by A. Jones; ref : The Astronomer Elec. Circ. 910

There have been quite a few 'brightenings' of this object too. The most recent, I could trace back, is :

1995.0527 at mag 12.7; observed by Koshiro, Takahashi; ref : FSPACE 05-1995

Tonny Vanmunster
CBA Belgium Observatory


(vsnet-chat 1131)

Rod Stubbing's observations (vsnet-obs 13673):

>  Star          Date      UT      mag.
> EX HYA        980808     9:14    13.5
>               980809     9:03     9.6
>               980809     9:20     9.5  (*)
>               980809     9:31     9.5
>               980809     9:42     9.4
>               980809     9:56     9.5
>               980809    10:52     9.4  (*)

  The epochs of observations (*) are close to predicted eclipses.

  YYMMDD hh:mm:ss
  980809 09:13:36 
  980809 10:51:52 

The latter observation done at expected mid-eclipse. This observation very likely suggests that eclipses become shallower during outbursts.

We observed during the 1987 outburst (during the fading branch) several eclipses, which were seen as broad, shallow features (published in VSOLJ Variable Star Bulletin). The full data are available from


Hope this information helps.

Taichi Kato

(vsnet-chat 1140)


Bill Allen and I have been CCD monitoring EX Hydrae along with other DN during the last few months. The eclipse events measured (20 to 30) are close to the predicted times. However the 67 minute cycle which is visible as a sinusoidal wave with an amplitude of ~0.5 to 0.7 magnitudes is rather different to the GCVS ephemeris - which dates back to 1979 - and we'd be interested in any more recent information on this.

Incidentally, the last outbust we measured at Auckland was in the mid-eighties and may well have been in 1987. From memory this event was double with a week or so between outbursts. Unfortunately the records are not immediately accessible to me in Kaitaia but it would be worthwhile keeping a watch out for a similar occurrence. And the storm which hit New South Wales last week has now made it to northern New Zealand. Beautiful lightning display at the moment but very non-astronomical!


(vsnet-chat 1145)

In IBVS 3724, C. Hellier and L. N. Sproats give the following ephemerides:

  TDB_eclipse = 2437699.94179 + 0.068233846 E
   (with a sinusoidal term of 0.00028 d)

  TDB_67_max = 2437699.8914(5) + 0.046546504(9) E - 7.9(4)x10^-13 E^2
  (spin maximum)
Please note the time is expressed in TDB.

Taichi Kato

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