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AH Herculis

 AH Her is a Z Cam type dwarf nova. Dwarf novae are extremely close binaries typically consisting of a white dwarf primary and a red dwarf secondary that has filled its Roche lobe and is spilling material onto the white dwarf via an accretion disk. These systems are prone to "outbursts", where copious amounts of energy are released, causing the systems to brighten suddenly by several magnitudes. AH Her  typically goes into outburst every 17-21 days, so it is very active and interesting to follow. Z Cam type dwarf novae, like AH Her, also exhibit a behavior known as "standstills". These occur when the system has begun to fade from outburst to quiescence. For some reason the drop in brightness halts well above quiescent levels and the Z Cam may stay at this intermediate level for days to months at a time before finally fading to minimum.

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