Statistics – Computation
Scientific paper
Nov 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983mnras.205..487p&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 205, Nov. 1983, p. 487-513.
Statistics
Computation
82
Accretion Disks, Dwarf Novae, Relaxation Oscillators, Stellar Models, Stellar Oscillations, Boundary Value Problems, Computational Fluid Dynamics, Hydrogen Ions, Mass Transfer, Thermal Stability, Variable Stars
Scientific paper
We examine a promising model for the outburst cycles of dwarf novae. According to this model hydrogen ionization zones of accretion discs are unstable and modulate mass transfer throughout the disc. The instability occurs when disc temperatures are sufficiently low for incomplete hydrogen ionization.
The problem is approached in two stages. In the first, a much simplified analogue treatment, we allow disc viscosity, v, to be a prescribed, multiple-valued function of the local integrated surface density, Ε. For certain ranges of mass-input rate, no steady state is possible; instead the accretion-disc flow establishes a limit cycle. This numerical experiment shows that even with a purely local prescription for viscosity, phase transitions can propagate throughout the disc collectively due to an avalanche effect.
In the second, more realistic approach, appropriate thermodynamic effects are included in a modified thin-disc α-model approximation. Radial thermal contact is also included and account is taken of energy advected between different radial positions. From these global analyses we show that the disc is indeed thermally unstable. The non-local effects and viscosity transitions are important in promoting the collective nature of the instability and its growth. The instability may be touched off at one radial position, but have its most noticeable effects at another. Our model reproduces the basic outburst cycles of dwarf novae.
Faulkner John
Lin Doug N. C.
Papaloizou John
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