IW And-Type State in IM Eridani

Abstract

IW And stars are a recently recognized group of dwarf novae which are characterized by a repeated sequence of brightening from a standstill-like phase with damping oscillations followed by a deep dip. Kimura et al. (2019) recently proposed a model based on thermal-viscous disk instability in a tilted disk to reproduce the IW And-type characteristics. IM Eri experienced the IW And-type phase in 2018 and we recorded three cycles of the (damping) oscillation phase terminated by brightening. We identified two periods during the IW And-type state: 4-5 d small-amplitude (often damping) oscillations and a 34-43 d long cycle. This behavior is typical for an IW And-type star. The object gradually brightened within the long cycle before the next brightening which terminated the (damping) oscillation phase. This observation agrees with the increasing disk mass during the long cycle predicted by a model of thermal-viscous disk instability in a tilted disk (Kimura et al. 2019). We, however, did not succeed in detecting negative superhumps, which are considered to be the signature of a tilted disk.

arXiv comment6 pages, 3 figures, si.pdf (supporting information), accepted for publication in PASJ

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Cited by in corpus (4)

• KIC 9406652: A laboratory of the tilted disk in cataclysmic variable stars
• A MeerKAT Survey of Nearby Novalike Cataclysmic Variables
• A New IW And-Type Star: Karachurin 12 with Tilted Disks and Diverse cycles
• BC Cassiopeiae: First Detection of IW And-Type Phenomenon Among Post-Eruption Novae