[vsnet-alert 106] Re: AL Com

[tkato@kusastro.kyoto-u.ac.jp]

  Dear vsnet-alert members,

  As S. Howell has already commented, the present extremely rare outburst
of AL Com will certainly provide one of the best opportunities in revealing
the nature of WZ Sge-type dwarf novae, or TOADs, to which AL Com is
suspected to belong.  One may expect large-amplitude superhumps at the
very early phase of a superoutburst as in WZ Sge itself, which has been
a matter of debate in interpreting the WZ Sge phenomenon from the two
competing mechanisms of WZ Sge-type dwarf nova outburst: namely the disk
instability and mass-transfer instability.  Observations of superhumps or
other short-term variability (like "super-QPOs") at the earliest stage are
therefore highly recommended.

  The orbital period of AL Com is suspected to be between 87 min and 90 min,
from the high-amplitude humps observed during quiescence (Abbott et al. 1992,
Ap. J. 399, 680).  This object is also suggested to be an intermediate polar
(Szkody 1991), but with a debate concerning this classification
(Abbott et al. 1992).  Observers are strongly urged to search for any
coherent modulation expected from the intermediate polar classification.

  Concerning the 1975 outburst, the historical record tells that the outburst
lasted more than one month (Mar. 16 -- June 29), with a very deep (fainter
than 17.3) dip in the middle of the light curve.

  Unfortunately the night in Japan is already over.  Continuous observations
(longer one is of course better in determining the period, minimum a few
hours) would reveal a number of new findings about WZ Sge stars.  We are
looking forward to hearing earliest reports of successful detection of
superhumps, and possibly other phenomena, through this network.
Ouda team will also prepare observations in order to complement the suggested
international coverage of this fascinating object.

Regards,
Taichi Kato

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