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Anomalous Z Cam stars: a response to mass-transfer outbursts

Abstract : Context. Recent observations of two unusual Z Cam systems, V513 Cas and IW And have shown light curves that seem to contradict the disc-instability model for dwarf novae: outbursts are appearing during standstills of the system when according to the model, the disc is supposed to be in a hot quasi-equilibrium state.
Aims: We investigate what additional physical processes need to be included in the model to reconcile it with observations of such anomalous Z Cam systems.
Methods: We used our code for modeling thermal-viscous outbursts of the accretion discs and determined what types of mass-transfer variations reproduce the observed light curves.
Results: Outbursts of mass transfer (with a duration of a few days, with a short rise time and an exponential decay) from the stellar companion will account for the observed properties of V513 Cas and IW And, provided they are followed by a short but significant mass-transfer dip. The total mass involved in outbursts is of the order of 1023g.
Conclusions: We studied the possible origins of these mass transfer outbursts and showed that they most probably result from a giant flare near the secondary star surface, possibly due to the absence of star spots in the L1 region.
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Submitted on : Monday, April 25, 2022 - 10:08:31 AM
Last modification on : Friday, August 5, 2022 - 3:37:49 PM
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J. -M. Hameury, J. -P. Lasota. Anomalous Z Cam stars: a response to mass-transfer outbursts. Astronomy and Astrophysics - A&A, EDP Sciences, 2014, 569, ⟨10.1051/0004-6361/201424535⟩. ⟨insu-03645329⟩

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