[vsnet-chat 1544] Re: How fast is a Fast Nova?

[Taichi Kato <tkato>]

Re: [vsnet-chat 1540] Re: How fast is a Fast Nova?

Dr. Henden wrote:

> My understanding (from Brian Warner's book) is that classical novae
> have to (a) not repeat, and (b) have amplitudes greater than 6 magnitudes.

    Classical novae can repeat nova explosions.  Novae with repeated
explosions are called recurrent novae.  Theoretical predictions tell
all classical novae are essentially recurrent, but the expected intervals
(100 to 10000 yrs) are too long for the human being to confirm the
prediction.  The distinguishing essence of classical novae from dwarf novae,
regardless of outburst amplitudes, is in the thermonuclear runaway process
(explosive nuclear buring on the white dwarf), which causes mass ejection.

    I think the borderline is more ambiguous between classical novae
and symbiotic novae (it may be a meaningful question whether symbiotic
novae are novae, since this criterion strongly affects the "nova awards"),
and other nuclear flash objects (like Sakurai's object).

> So yes, I'd think some objects classified as novae could actually be exotic
> dwarf novae.

    PQ And (Nova And 1988) may be an example.  This object was discovered
as a potential nova, and at least one spectroscopic confirmation appeared
in IAUCs.  The object was later found to be recurrent in nature, bursting
every ten years or so.  This is more remniscent of infrequently outbursting
dwarf novae.  I wonder whether the object actually showed emission lines
characteristic of a classical nova.

    Another different sort of object may be X-ray novae.  V404 Cyg was
originally discovered and cataloged as a nova, but the recurrence was
caught by the X-ray satellite.  This object is now considered as a
black-hole binary with infrequent X-ray and optical outbursts.  It may
be difficult to exactly tell from the presence of broad H-alpha emission
whether the object is a classical nova or a X-ray nova.

Regards,
Taichi Kato

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