[vsnet-chat 567] Re: Dwarf nova vs. nova outbursts -- a question

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

Dear Bob,

   Welcome to vsnet-chat!

> .. what the origin of the light outburst is in a typical cataclysmic like SS 
> Cygni or U Geminorum. Is the accretion disk the key source for the 
> great magnitude change in dwarf novae? Or does it  burn hydrogen on 
> the surface of the white dwarf star as in a nova?

  I believe a good consensus has been reached on this problem.  Dwarf novae
(SS Cyg or U Gem) are considered to be accretion-disk phenomenon, i.e.
the release of gravitational potential energy via accretion to the white
dwarf.  Accretion proceeds through the accretion disk by the help of
viscosity, which also heats the gas in the accretion disk to result
brightening: outburst.  Canonically dwarf novae do not burn hydrogen
during their usual outburst-quiescence cycle, at least to a level of
thermonuclear flash or runaway to be observed.

  Of course, the nova phenomenon (thermonuclear runaway on the white dwarf)
is independent from the accretion disk phenonenon.  Classical novae may
become dwarf novae after the nova eruption (like GK Per or V446 Her),
and dwarf novae may in future accumulate enough hydrogen on the white
dwarf to result nova explosions (probably not observed yet).

Regards,
Taichi Kato

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