Issue |
A&A
Volume 487, Number 2, August IV 2008
|
|
---|---|---|
Page(s) | 671 - 687 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:200809953 | |
Published online | 24 June 2008 |
Simulations of eccentric disks in close binary systems
1
Institut für Astronomie & Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany e-mail: wilhelm.kley@uni-tuebingen.de; kley@tat.physik.uni-tuebingen.de
2
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge, CB3 0WA, UK
Received:
11
April
2008
Accepted:
23
June
2008
Context. Eccentric accretion disks in superoutbursting cataclysmic and other binary systems.
Aims. We study the development of finite eccentricity in accretion disks in close binary systems using a grid-based numerical scheme. We perform detailed parameter studies to explore the dependence on viscosity, disk aspect ratio, the inclusion of a mass-transfer stream and the role of the boundary conditions.
Methods.
Using a two-dimensional grid-based scheme we study the instability
of accretion disks in close binary systems that causes them to attain
a quasi-steady state with finite eccentricity. Mass ratios
appropriate to superoutbursting cataclysmic binary systems are considered.
Results.
Our grid-based scheme enables us to study the development of eccentric disks
for disk aspect ratio h in the range and
dimensionless kinematic viscosity ν in the range
. Previous studies using particle-based methods
were limited to the largest values for these parameters on account of their diffusive
nature. Instability to the formation of a precessing eccentric disk
that attains a quasi-steady state with mean eccentricity
in the range
occurs readily. The shortest growth times
are ~15 binary orbits for the largest viscosities and the instability
mechanism is for the most part
consistent with the mode-coupling mechanism associated with the 3:1 resonance
proposed by Lubow.
However, the results
are sensitive to the treatment of the inner boundary and to the incorporation
of the mass-transfer stream. In the presence of a stream we found a critical viscosity
below which the disk remains circular.
Conclusions. Eccentric disks readily develop in close binary systems with
Incorporation of a mass-transfer stream tends to impart stability for small
enough viscosity (or, equivalently, mass-transfer rate through the disk) and to
assist in obtaining a prograde precession rate that is
in agreement with observations.
For the larger q the location of the 3:1 resonance is pushed outwards towards
the Roche lobe where higher-order mode couplings and nonlinearity occur.
It is likely that three-dimensional simulations that properly resolve the disk's vertical structure are required to make significant progress in this case.
Key words: accretion, accretion disks / stars: binaries: close / novae, cataclysmic variables
© ESO, 2008
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