[vsnet-chat 87] Re: EG Cnc - first one?

[Daisaku Nogami <nogami@kusastro.kyoto-u.ac.jp>]

 Taichi Kato wrote:
 > Fraser Farrell wrote:
 > > I speculate that EG Cnc may represent an extreme example - decades of
 > > inactivity, then months (years??) of vigorous activity, then inactivity
 > > again.  Perhaps this should be part of the definition of ER UMa stars?
 > > I await discussion from our professional readers!
 >     I believe the ER UMa stars are defined by their short supercycle
 > lengths, and not by activity/inactivity cycles.  ER UMa stars are assumed
 > to have exceptionally high mass-transfer rates among SU UMa-type dwarf
 > novae, in contrast to EG Cnc or WZ Sge-stars.  However, it is still
 > under investigation whether secular changes exist in ER UMa stars.

The original definitions of ER UMa stars given by Nogami et al.
(1995, PASJ 47, 897) are: 1) the extremely short supercycle,
2) the extraordinary long duty cycle, 3) the normal outbursts
repeating with a very short cycle length, and 4) the small
amplitude of a superoutburst ($\sim3$ mag).  All of these are
concerned with CURRENT activities.  However, the secular change
of the activity and the mass transfer rate is one of the hottest
topics in observational and theoretical studies of CVs.  Close
monitoring ER UMa stars (though RZ LMi and DI UMa might be too
faint for visual observers) is highly encouraged!

As for EG Cnc, it is disappointing that the spectacular show
seems to have ended (though EG Cnc has stayed slightly brighter
than its genuin quiescence).  However, an interesting problem
is left:  what's the mechanism for the show?
1) purely disk-originated phenomena
2) ER UMa-like behavior caused by temporarily enhanced mass transfer
      from the secondary star heated by the superoutburst
3) others
Which do you bet?

Regards,
Daisaku Nogami

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