[vsnet-alert 9306] GW Lib: decaying stage of early superhumps?

[Taichi Kato]

Dear all,

   Berto Monard has kindly reported three nights of observations
(14.0 - 16.0 UT).

   On the first night, the object showed clear hump signature
with an amplitude of 0.04 mag.  On the second night (just following
Japanese observations), the amplitude decreased to 0.02-0.03 mag.
On the third night, the light curve was dominated by several
small-amplitude peaks within an orbital period.
Although the analysis is still very preliminary, the behavior
of hump amplitude is consistent with the well-known rapid decay
of early superhumps.  However, the hump (esp. at around the outburst
maximum) was singly peaked rather than double humps as in usual
early superhumps.  The rapid decay of the amplitude and slight
irregularity in the light curve makes unique determination of the
period difficult.  The observed periodicity is consistent with
signatures either from orbital period or from superhumps.
During the observation, the object faded more rapidly (~0.3 mag/d)
than in superoutbursts of usual SU UMa-type dwarf novae.

   Combining all the features, we have likely observed the rapidly
decaying stage of early superhumps as well as rapid, viscous decay
stage of a WZ Sge-type superoutburst.  The difference (low amplitude
and single peak) from other well-observed WZ Sge-type stars may have
been a result of a low orbital inclination.  Other possibilities
(transient appearance of growing superhumps etc.) may remain valid,
which need to be clarified by further observations.