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WZ Sagittae

WZ Sge is the prototype of an exceptional class of dwarf novae with large amplitudes, long recurrence times, low mass-transfer rates, and very short orbital periods.  They're cataclysmic variables consisting of a white dwarf and a low-mass companion object locked in close orbit about one another.  Their orbital periods are very short, typically less than 90 minutes.  Despite being close to one another, there's only a trickle of mass transfer from the secondary to the white dwarf, and so their quiescent luminosities are very small compared to those of other dwarf novae.  However, when they go into outburst, they really outburst!  Some have amplitudes of eight magnitudes or more.

WZ Sge's last outburst in 2001 showed many of the hallmarks of this class: a large amplitude, "superhumps" (periodic variations caused by precession in the outbursting accretion disk), and a slow decline to quiescence interrupted several times by alternating rapid fadings and rebrightenings.  WZ Sge has a recurrence time around 33 years, with prior outbursts in 1913, 1946, and 1978.  It's an interesting star to observe at any time, but keep your eyes peeled when it's next expected to go off... around 2034!

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484