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On the Outburst Recurrence Time for the Accretion Disk Limit Cycle Mechanish in Dwarf Novae

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John K. Cannizzo

Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138

Alan W. Shafter

John C. Wheeler

Department of Astronomy, University of Texas at Austin, Austin, TX 78712

Abstract

Cataclysmic variables are binary star systems consisting of a white dwarf primary and a late-type secondary overflowing its Roche lobe and depositing material into an accretion disk surrounding the primary. Dwarf novae are a class of cataclysmic variables exhibiting outbursts of several magnitudes which last for days to weeks and recur on time-scales of months to years. One theory for these semi-oeriodic eruptions posits that the material in the accretion disk becomes unstable when a certain "critical mass" is reached. Hence, there should exist two distinct stages in the outburst cycle: first, a quiescent period when matter is being stored up, and then an outburst period as material is accreted onto the white dwarf. The amount of matter stored up in the quiescent stage depends on how big the accretion disk is and hence on theorbital period and component masses. These quantities can be related through considering the conservation of angular momentum and the Roche geometry.