Three-dimensional gas-dynamical modeling of changes in the flow structure during the transition from the quiescent to the active state in symbiotic stars

Abstract

The results of 3D modelling 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 able to sufficiently increase the accretion rate on a time scale typical to the duration of outburst development.Our calculations have confirmed the transition mechanism from quiescence to outburst in classic symbiotic systems suggested earlier on the basis of 2D calculations (Bisikalo et al, 2002). The analysis of our results have shown that for wind velocity of 20 km/s an accretion disc forms in the system. The accretion rate for the solution with 1 2 the disc is ∼ 22.5 − 25% of the mass loss rate of the donor, that is, ∼ 4.5 − 5 · 10 −8 M ⊙ /yr for Z And. This value is in agreement with the steady burning range for white dwarf masses typically accepted for this system. When the wind velocity increases from 20 to 30 km/s the accretion disc is destroyed and the matter of the disc falls onto the accretor's surface. This process is followed by an approximately twofold accretion rate jump. The resulting accretion rate growth is sufficient for passing the upper limit of the steady burning range, thereby bringing the system into an active state. The time during which the accretion rate is above the steady burning value is in a very good agreement with observations.The analysis of the results presented here allows us to conclude that small variations in the donor's wind velocity can lead to the transition from the disc accretion to the wind accretion and, as a consequence, to the transition from quiescent to active state in classic symbiotic stars.

Mass-loss rates of “hot-Jupiter” exoplanets with various types of gaseous envelopes

“…The potential forces acting in the system were defined using the Roche potential, modified (in a way similar to (Mitsumoto et al, 2005)) to take into account the acceleration of the stellar wind by introducing the parameter Γ, which is equal to zero in regions filled with stellar wind and unity in all other regions:…”

Chemical Abundances in Symbiotic Stars

“…During the quiescent phase, SSs are undergoing stable hydrogen burning on the surfaces of the WD accretors. The outbursts may be due to either the thermonuclear outbursts on the surfaces of accreting WDs, which are called as symbiotic novae ( Tutukov & Yungelson 1976;Paczyński & Rudak 1980), or accretion-disk instabilities around a nearly steady burning WDs, which are called as multiple outbursts (Mitsumoto et al 2005;Mikoyajewska 2007). Recent reviews of the properties of SSs can be found in Mürset & Schmid (1999) and Mikoyajewska ( , 2007.…”

Colliding winds in symbiotics

“…Results of our 3D calculations described in Mitsumoto et al (2005) winds collision) and there should be areas observable in UV and X-rays. The configuration of a symbiotic system (winds of a symbiotic system have very different characteristics and can be isolated spectroscopically) allows us to estimate parameters of the winds.…”