[vsnet-chat 2903] Re: Brief IP outbursts

["William S G Walker" <astroman@voyager.co.nz>]

Hi All,

I've been away for a few days and noted the discussions on TV Col amongst
all the hype on CI Aql - which I must observe if the weather ever improves.

I wondered if the visual observers ever followed these IPs through one of
the rotation cycles. I see that TV Col is listed as about 32 minutes by
Warner. I've got CCD measures of both EX Hydrae and FO Aquarii in 1999 and
the rotational amplitudes can be as much as 0.8 magnitudes in the former
and are usually 0.5 in the latter. They could be a little more visually as
I've noticed that the orbital humps in the ST6 CCD response are much less
than using a pm tube.

I'm not suggesting a programme of this but it's as well to be aware that
there is a significant difference between the peaks and troughs of the IP
rotation cycle!

I and others in Auckland have always been a little dubious about the
mini-outbursts of EX Hydrae, mainly because we've observed through one or
two of these and noted nothing unusual. EX varies in its quiescent
magnitude in a random manner over more than 0.5 magnitudes and the low
amplitude attributed to the mini-outbursts hardly exceeded this. But the
measures of TV Col and Patrick's comments are convincing me. 

Rod's and Berto's measures of TV Col made interesting reading, particularly
as with Prot at 0.022 days the 5 significant measures covered most phases
of the cycle. Either the rotational signal is low or it disappears during
outburst. I'll try to catch up on this star before it disappears. But if it
does do anything unusual I'd welcome a direct email which I'll pass on to
other CCD observers here.

Regards,
Stan

----------
> From: Alon Retter <ar@astro.keele.ac.uk>
> To: Patrick Schmeer <p.schmeer@mx.uni-saarland.de>
> Cc: vsnet-chat@kusastro.kyoto-u.ac.jp; Patrick Schmeer
<extpasc@rz.uni-sb.de>
> Subject: [vsnet-chat 2892] Brief IP outbursts
> Date: Thursday, May 04, 2000 7:30 AM
> 
> > 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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