Other
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.3003s&link_type=abstract
American Astronomical Society, DPS meeting #40, #30.03; Bulletin of the American Astronomical Society, Vol. 40, p.445
Other
Scientific paper
The viscous overstability of dense collisional rings offers a promising explanation for the small scale radial density variations in the B and the inner A ring of Saturn. Viscous overstability, in the form of spontaneous growth of axisymmetric oscillations, was first directly demonstrated in the selfgravitating N-body simulations (Salo etal. 2001). In contrast to previous isothermal hydrodynamical analysis (Schmit & Tscharnuter 1995), which suggested that practically any dense ring should be overstable, our N-body simulations indicated that a steep rise of viscosity with optical depth was required. In particular, a selfgravitating system of identical particles following the Bridges etal. (1984) elasticity formula was found to become overstable for optical depths τ > 1., forming oscillations in about 100 meter scale. In these simulations the axisymmetric oscillations were found to coexist with the inclined selfgravity wake structures. In addition, a basically similar overstability was seen in nongravitating simulations, but shifted to very high optical depths, or in simulations were just the vertical selfgravity was included, leading to an enhanced impact frequency and viscosity. Although an improved non-isothermal hydrodynamical analysis (Spahn et al. 2000, Schmidt et al. 2001) was able to describe quantitatively these non-selfgravitating cases, even in the weakly nonlinear regime (Schmidt & Salo, 2003), a reliable study of realistic selfgravitating rings must rely on numerical experiments.
We report the results of a new N-body survey of viscous overstability. For example, we study the optical depth and gravity strength regimes which lead to the excitation of overstability, co-existence of overstabilities and gravity wakes, or to the suppression of overstability in the case of very strong wakes. Also the effects of various factors (particle elasticity, surface friction and adhesion, size distribution) on the threshold density required for the triggering of overstability are investigated This study is supported by the Academy of Finland
Miodrag Sremčević
Salo Heikki J.
Schmidt Jonas
Spahn Frank
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