[vsnet-alert 24714] Re: DDE 72 anomalous outburst pattern

[Taichi Kato]

Re: DDE 72 anomalous outburst pattern

> At the first glance this looks like the interchanging superoutbursts
> and normal outbursts (1SO-1NO-1SO-1NO and so on). But a pattern like
> this is not normally observed in SU UMa-type stars (please correct me
> if there are such examples). Yet there are no quiescent states between
> the outbursts.
>
> On the other hand, a pattern like this is not normally observed in Z
> Cam-type stars either. Z Cam outbursts are saw-toothed with sharp
> peaks of the nearly same rise and fall time. During the long outbursts
> DDE 72 is spending about 10 days above the normal outburst peak,
> fading at 0.1 mag/day rate.
>
> This behavior is very similar to that of anomalous Z Cam-type star IW
> And in July 2010 - March 2011, as can be seen in AAVSO database. IW
> And has shown at least three cycles of "one long-one short" outbursts
> in August-September 2010 followed by a standstill in October 2010 and
> then again at least four "one long-one short" cycles in November 2010
> - January 2011.

   This pattern of alternating short and long outbursts is
no unusual.  There are many examples in SS Cyg stars.
Two short and one long is also often observed.

   During short outbursts of SS Cyg (or Z Cam) stars,
the mass (and the angular momentum) in the disk does not
accrete sufficiently.  After this, the next outburst
starts when the angular momentum and the mass are higher,
resulting in a larger outburst.  In such an outburst,
the disk reaches the tidal truncation radius
(not in short outbursts) and the angular momentum the disk
mass is efficiently removed due to the tidal torque
(but not causing the 3:1 resonance as in SU UMa stars).