Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........12l&link_type=abstract
Ph.D. Thesis Queens Univ., Kingston (Ontario). Dept. of Physics.
Astronomy and Astrophysics
Astrophysics
2
Accretion Disks, Astronomical Models, Interstellar Gas, Molecular Clouds, Spiral Galaxies, Astrophysics, Disks (Shapes), Star Formation
Scientific paper
A self-similar formalism is presented for studying spiral structure in gas disks. The equations are applicable to molecular clouds and accretion disks and perhaps even galactic disks. In the most general case the two-dimensional formulation is time dependent, the gas is self-gravitating and non-ideal physical processes such as viscosity, heat conduction and radiative losses are incorporated. When the gas is taken to be ideal, it is shown that the effects of a passive halo may be included; further restricting the problem to be time independent allows inclusion of a central point-mass as well. For a steady-state, ideal gas analytic and uniform flow solutions are found for zero temperature disks controlled by a central mass and by a passive halo. Accretion solutions containing spiral-shaped shocks are found numerically for the case of a steady-state, ideal gas disk in a central potential. For these solutions, it is shown that increasing the adiabatic index results in more and weaker shocks. For the full time-dependent, viscous gas case periodic outflow solutions are found for which the derivative of the temperature is discontinuous at a spiral arm. The solutions with small pitch angles have pattern speeds greater than the gas speed and display relatively small, smooth variations. In the case of larger pitch angles, the gas flows more rapidly than the pattern and solutions reminiscent of shocks are found. It is argued that star formation near the density peak in these solutions will provide a heat source which can be made consistent with the jump in the temperature derivative.
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