[vsnet-chat 2892] Brief IP outbursts

[Alon Retter <ar@astro.keele.ac.uk>]

> Are all intermediate polars candidates for such outbursts? Or can some
> systems be ruled out?

As I said all CVs (including all intermediate polar and intermediate polar 
candidates) might have this property. 
 
> I wouldn't call the brightenings of the IP candidate HT Cam (= RX J0757...)
> 'mini-outbursts'. The outburst that I observed on 1999 May 23 (vsnet-alert
> 3014, 3025) had an amplitude of more than 4 magnitudes. One day later the  
> variable was back at quiescence. Such a rapid fading has never been
> observed during normal outbursts of SU UMa-type dwarf novae (outside
> eclipses ;-)). However, Taichi Kato commented that on the other hand such 
> large-amplitude outbursts had never been observed in intermediate polars
> (although I would say that the outburst amplitude of HT Cam is not so much
> larger than that of EX Hya). So how can this below-the-orbital-period-gap
> system be classified? 

Obviously some intermediate polars have normal dwarf nova outbursts. GK
Per is an example. Others (with short orbital periods) should have
superoutbursts as well. The mini/brief outbursts in certain CVs (but not
in TV Col) might be explained by attempts to form dwarf nova outburst that
fail (according to Osaki).

> I think the intermediate polar DO Dra should also have been included in
> Alon's list. Or doesn't he count the brightenings to mag 10 of this variable
> as 'mini'-outbursts? They have about the same outburst amplitude as those of
> EX Hya and HT Cam (remark: the (bright) outbursts of DO Dra and EX Hya last
> longer than one day). 

I'm not familiar with the outbursts in this object. Any references?
Anyway, I'm sure that there are much more reported and unreported cases.

> Several years ago Stefan Korth and I observed independently the reverse(?) 
> phenomenon. During a standstill (mag about 11.7) the brightness of RX And
> dropped for one day by about 1 magnitude. 

Interesting!

> What kind of observations should be made during IP outbursts? Time-resolved
> photometry? Spectroscopy? 

If they have short orbital periods, then photometry might reveal
superhumps confirming the suggestion of dwarf nova outbursts.
Detecting superhumps during quiescence in a CV that has these brief
outbursts will tell us that the outbursts cannot be dwarf nova outbursts
(this is the case in TV Col). Detailed spectroscopy can reveal the secrets
of the outbursts. See Hellier & Buckley (1993) for example.

Cheers,
Alon

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