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Session 77 - Structures of Galaxies.
Display session, Friday, January 09
Most SB galaxies show rings of gas clouds and young stars thought to be in orbits near the inner Lindblad (ILR), four-fold ultraharmonic (UHR), and outer Lindblad resonances (OLR) with the bar. These are presumed to be associated with nuclear, inner, and outer rings, respectively. To confirm and extend numerical simulations by Schwarz(1981) and by Byrd et al. (1994) which duplicated observed ring morphology, we present an analytical formulation of the rings which includes dissipative damping of gas cloud oscillations. For a given rotation curve plus correct choices of the bar pattern speed and strength, the analytic rings match the observed rings' sizes and morphologies. The rings are plots of periodic orbit groups in which star formation is promoted by cloud number density enhancement but strong collisions do not occur. For flat rotation curves, we find a pair of two-fold orbits which bracket the ILR. The smaller ring can be identified with a ``nuclear ring." The larger ILR ring and its narrow pointy
Ousley was supported by a McWane Undergraduate Research Fellowship, Dalla Piazza was supported by NSF REU grant AST-9424226. We thank R. Buta and D. Crocker for allowing us to duplicate Figures from their 1991 paper. We also thank Tarsh Freeman for checking the formulae although any errors remain our responsibility.
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