[vsnet-chat 3768] Re: WX Hyi behaviour

[Taichi Kato <tkato>]

Re: [vsnet-chat 3767] WX Hyi behaviour

> WX Hyi has just shown the following sequence of events in succession
> 
> 1. normal outburst
> 2. superoutburst
> 3. another normal (?) outburst, ongoing at this moment.
> 
> Phases 1 and 2 do occur in succession with other systems too.
> However event 3 seems a bit out of phase. The going theory spells that the 
> superoutburst is the 'complete cleaning' phase, iow all H is burned 
> away.
> What happens to WX Hyi then for it still to have another outburst? Is it 
> unstable mass transfer by the secondary triggered by the past s/outburst 
> or is it due to another unrelated activity?

    The present activity of WX Hyi looks normal, looking back at the
historical light curve.  WX Hyi repeated normal outbursts with intervals
as short as 6-7 days (one of the shortest among SU UMa stars).  The normal
outburst next to the 1998 March superoutburst occurred within 5 days of
the termination of the superoutburst, which is quite similar to the
present condition.

    In the 'standard' disk instability model, the interval of normal
outbursts is the shortest just after the superoutburst.  This is because
the disk radius is the smallest (as you mentioned).  Less matter is
required for a small disk to cause disk instability (outburst).

    The increased activity in the post-superoutburst stage can be also
made possible because of the increased turbulence in the just preceding
superoutbursting disk.  If the disk viscosity is higher than usual,
even the same input from the secondary can result in a shorter outburst
cycle length.

Regards,
Taichi Kato

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