[vsnet-campaign 919] (fwd) AL Com: strange behavior of the extremely rare superoutburst!

[Taichi Kato <tkato>]

(fwd) AL Com: strange behavior of the extremely rare superoutburst!

   This is a copy of the news posted to AstroAlert.  Detailed analysis
will be separatedly issued by Ishioka-san et al.

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        Strange Behavior Observed in Extremely Rare Superoutburst of
                          AL Comae Berenices
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   We notifed in our earlier notice issued on 2001 May 19, the WZ Sge-type
dwarf nova AL Com is undergoing an extremely rare superoutburst!
The international photometric campaign led by the VSNET Collaboration
team is in progress very successfully, as already quickly informed in
News from VSNET, on May 21.

   A quick analysis of the data received up to now (the Kyoto team;
Gary W. Billings; Rudolf Novak and Petr Sobotka) has shown that AL Com
has apparently brightened further, associated with intermittent appearance
of large-amplitude superhumps.  Superhumps in WZ Sge-type dwarf novae
are usually classified into two categories: early superhumps seen in
the earliest stage of superoutburst, and common superhumps which are
equivalent to superhumps in all SU UMa-type dwarf novae.  Early superhumps
have a period almost identical to the orbital period of the system,
and they usually quickly decay within several days of the start of
superoutburst.  However, the present AL Com superburst seems to have
behaved differently!  Early superhumps had a singly-peaked profile,
which is unlike other early superhumps ever observed in WZ Sge-type
systems, but has a period identical to the orbital period.

   More strangely, these humps sometimes appear with a large amplitude
and sometimes disappear from time to time!  Such behavior has never been
observed in past AL Com outbursts, nor in other WZ Sge-type systems.
The analysis and observations are being intensively undertaken by
the VSNET Collaboration team, and more detailed analysis will be
issued via VSNET mailing lists and regular "News from VSNET".
The evolution of these early superhumps (and possibly some hint of
common superhumps), and the outburst itself, being very quick and
totally unexpected, we would like to emergently call for more and urgent
observations of this dramatic superoutburst!

   The VSNET AL Com 2001 page:
   http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/DNe/alcom0105.html

(footnote)
CCD observations of such targets are a relatively easy task for a 20-40cm
telescope; simply take as many CCD frames (with exposure times 10-30 sec)
as possible, spanning several hours per night.  The only requirements are
the weather and your patience!  If you need more help on the observing
technique, please feel free to ask on the vsnet-campaign list.

   We would sincerely appreciate volunteers who would join the VSNET
Collaboration team to study the wonders of these exotic variable stars.

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