[vsnet-gcvs 220] Re: [AAVSO-DIS] GP Com

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

Re: [AAVSO-DIS] GP Com

> I'm not sure GP Com is classified as a 'cataclysmic binary' since
> to the best of my knowledge, it has never been seen in outburst.
> The Downes et al. catalog classifies it as an 'interacting binary
> white dwarf.'

    The existence of outbursts is not a necessary condition of a CV
(cataclysmic variable).  For example, GD 552 = NSV 25966, which is
naturally included as a CV in almost all(?) catalogs, has not been yet
seen in outburst.  In addition, UX UMa and other NL-type CVs are classified
as such because of the lack of dwarf-nova outbursts.

    Interacting binary white dwarfs (IBWDs), also known as AM CVn stars,
are ultrashort-period binaries which contain a mass-accreting white dwarf
and a helium white dwarf.  The accreted matter usually forms an accretion
disk as in other hydrogen-rich CVs.  The only difference is the composition
of the transferred matter (hydrogen-rich in usual CVs and helium-rich in
IBWDs).  From this point, many authors consider these IBWDs as a helium
variery of CVs.  Some objects (CR Boo, V803 Cen, CP Eri, KL Dra) show
outbursts just as in hydrogen-rich dwarf novae.  Some authors regard
GP Com as a helium analog of WZ Sge, which only very infrequently shows
outbursts.  There may have been "missed" outbursts in GP Com, since this
stars has been regularly monitored only recently.

Regards,
Taichi Kato

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