Issue |
A&A
Volume 453, Number 3, July III 2006
|
|
---|---|---|
Page(s) | 1027 - 1036 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20054225 | |
Published online | 28 June 2006 |
Low compressibility accretion disc formation in close binaries: the role of physical viscosity
1
INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: glanzafame@oact.inaf.it
2
Dipartimento di Fisica e Astronomia dell'Universitá - Sezione Astrofisica, via S. Sofia 78, 95123 Catania, Italy
3
Dipartimento di Fisica e Tecnologie Relative, Universitá di Palermo, Viale delle Scienze, 90128 Palermo, Italy
Received:
19
September
2005
Accepted:
9
March
2006
Aims.Physical viscosity naturally hampers gas dynamics (rarefaction or compression). Such a role should support accretion disc development inside the primary gravitation potential well in a close binary system, even for low compressibility modelling. Therefore, from the astrophysical point of view, highly viscous accretion discs could exist even in the low compressibility regime showing strong thermal differences to high compressibility ones
Methods.We performed simulations of stationary Smooth Particle Hydrodynamics (SPH) low compressibility
accretion disc models for the same close binary system. Artificial viscosity operates in all models. The
absence of physical viscosity and a supersonic high mass transfer characterize the first model. Physical
viscosity and the same supersonic high mass transfer characterize the second model, whilst physical
viscosity and a subsonic low mass transfer characterize the third model. The same binary system
parameters, such as stellar masses and their separation, have been adopted, as well as the same
polytropic index . Thus we investigated the role of physical viscosity in mass and angular
momentum transport in the two viscid models and compare them to the inviscid model. An initial value of
the parameter
has been considered for the physically viscous models, according to the
well-known Shakura and Sunjaev formulation, but simulations were carried out also for
and
in the case of a supersonic mass transfer. Physical viscosity is represented by the
viscous force contribution expressed by the divergence of the symmetric viscous stress tensor in the
Navier-Stokes equation, while the viscous energy contribution is given by a symmetric combination of the
symmetric shear tensor times the particle velocity.
Results.The results show that physical viscosity supports and favours accretion disc formation despite the very low compressibility assumed. On the contrary, in the inviscid case no evident disc structure appears. In all models neither shock fronts nor extended clear spirals in the radial flow develop.
Key words: accretion, accretion discs / stars: binaries: close / stars: dwarf novae, white dwarfs / methods: numerical / methods: N-body simulations
© ESO, 2006
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