[vsnet-alert 3996] Re: RXJ0640-24 outburst update

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

Greetings,

Last night was cloudy but tonight - Jan 10 - I have been measuring
RXJ0640-24 since 0845UT.
It's quite faint, unfiltered about the same as the ~14.8 star 60" to the
NE. As
my telescope is set up in the bright star configuration at the moment
reductions will be difficult. My main experience of SU UMa stars is with VW
Hydri, WX Hyi, Z Cha. None of these have ever shown superhumps during the
precursor, although VW has shown orbital phase humps (about 30x normal
level) immediately prior to going into the superoutburst stage. Since
there's still a possibility that the present event could trigger an SO I'll
have another look later in the night if possible.

Postscript to this message - the star is definitely brighter than it was at
the beginning of the run ~40 minutes ago, although still faint. I'll watch
a little longer.

Regards,
Stan 

----------
> From: Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>
> To: vsnet-alert@kusastro.kyoto-u.ac.jp
> Subject: [vsnet-alert 3980] RXJ0640-24 outburst update
> Date: Saturday, January 08, 2000 11:59 PM
> 
> RXJ0640-24 outburst update
> 
> Dear Colleagues,
> 
>     As notified by Uemura-san, RX J0640-24 is apparently quickly fading
> from outburst.  The possible superhump-like feature observed in the Jan.
7
> data seems to have decayed on Jan. 8 data.  However, there looks like
> some evidence of modulations with a likely period less than an hour.
> During the 3.4-hour run, the object showed little trend of the continuing
> rapid fading.  This precludes the possible explanation of the Jan. 7
> variation as the effect of extinction.  The rapid rate of decline (~1
mag/day
> between Jan. 6 and 8) suggests that the object can be a short-period
system
> (e.g. SU UMa stars).  It is not surprizing such a system may show
transient
> superhump activities during a short outburst, or a precursor to a
> superoutburst (the good example is the superoutburst of SU UMa in 1998
> December).  Observers are strongly requested to continue monitoring the
> activity of the object for short-term variations on coming nights, and
> to look for a possible (immediate or future) superoutburst.  The campaign
> is still ongoing, and please keep us in touch.
> 
> Regards,
> Taichi Kato and Makoto Uemura
>

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