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IW And stars are a subgroup of dwarf novae characterized by repetitive lightvariations of the intermediate-brightness state with oscillations, which isterminated by brightening. This group of dwarf novae is also known to exhibit awide variety even within one system in long-term light curves including usualdwarf-nova outbursts, Z Cam-type standstills, and so on, besides the typical IWAnd-type variations mentioned above. Following the recent observationssuggesting that some IW And stars seem to have tilted disks, we haveinvestigated how the thermal-viscous instability works in tilted accretiondisks in dwarf novae and whether it could reproduce the essential features ofthe light curves in IW And stars. By adopting various simplifying assumptionsfor tilted disks, we have performed time-dependent one-dimensional numericalsimulations of a viscous disk by taking into account various mass supplypatterns to the disk; that is, the gas stream from the secondary star flows notonly to the outer edge of the disk but also to the inner portions of the disk.We find that tilted disks can achieve a new kind of accretion cycle, in whichthe inner disk almost always stays in the hot state while the outer diskrepeats outbursts, thereby reproducing alternating mid-brightness intervalsometimes with dips and brightening, which are quite reminiscent of the mostcharacteristic observational light variations of IW And stars. Further, we havefound that our simulations produce diverse light variations, depending ondifferent mass supply patterns even without time variations in mass transferrates. This could explain the wide variety in long-term light curves of IW Andstars.

Thermal-viscous instability in tilted accretion disks: a possible application to IW And-type dwarf novae