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.
Astronomy and Astrophysics
- Pub Date:
- September 2014
- accretion disks;
- stars: dwarf novae;
- Astrophysics - Solar and Stellar Astrophysics
- 5 pages, 2 figures. Misprints corrected, in particular "inside-out" should have read "outside-in"