Volume 569, September 2014
|Number of page(s)||5|
|Section||Stellar structure and evolution|
|Published online||18 September 2014|
Anomalous Z Cam stars: a response to mass-transfer outbursts
Observatoire Astronomique de Strasbourg, CNRS UMR 7550,
2 CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
3 Nicolaus Copernicus Astronomical Center, Bartycka 18, 00716 Warsaw, Poland
4 Sorbonne Universités, UPMC Univ. Paris 06, UMR 7095, 98bis Bd Arago, 75014 Paris, France
Accepted: 21 July 2014
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.
Key words: accretion, accretion disks / stars: dwarf novae / instabilities
© ESO, 2014
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