Three-dimensional gas-dynamical modeling of changes in the flow structure during the transition from the quiescent to the active state in symbiotic stars |
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| Authors: | M Mitsumoto B Jahanara T Matsuda K Oka D V Bisikalo E Yu Kilpio H M J Boffin A A Boyarchuk O A Kuznetsov |
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| Institution: | (1) Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan;(2) Misuho Research Institute, Tokyo 101-8443, Japan;(3) Institute of Astronomy, Moscow, Russia;(4) European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85738 Garching, Germany;(5) Keldysh Institute for Applied Mathematics, Moscow, Russia |
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| Abstract: | The results of three-dimensional modeling of the flow structure in the classical symbiotic system Z Andromedae are presented. Outbursts in systems of this type occur when the accretion rate exceeds the upper limit of the steady-burning range. Therefore, in order to realize the transition from a quiescent to an active state, it is necessary to find a mechanism capable of sufficiently increasing the accretion rate on the time scales typical for outburst development. Our calculations provide support for a mechanism for the transition from quiescence to outburst in classical symbiotic systems suggested earlier based on two-dimensional calculations (Bisikalo et al., 2002). Our results show that an accretion disk forms in the system for a wind velocity of 20 km s?1. The accretion rate for the solution with the disk is ～22.5–25% of the mass-loss rate of the donor, which is ～4.5?5 × 10?8M⊙ yr?1 for Z And. This value is in agreement with the steady-burning range for the white-dwarf masses usually accepted for this system. When the wind velocity increases from 20 to 30 km s?1, the accretion disk is destroyed and the disk material falls onto the accretor surface. This process is followed by an approximately twofold jump in the accretion rate. The resulting growth in the accretion rate is sufficient so as to exceed the upper limit of the steady-burning range, thus bringing the system into an active state. The time during which the accretion rate is above the steady-burning value is in very good agreement with observations. Our analysis leads us to conclude that small variations in the donor wind velocity can lead to the transition from disk accretion to wind accretion and, as a consequence, to the transition from a quiescent to an active state in classical symbiotic stars. |
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