AAS 201st Meeting, January, 2003
Session 26. Galaxy Structure and Interactions
Oral, Monday, January 6, 2003, 10:00-11:30am, 616-617

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[26.01] Why Barred Galaxies do not have Inner Linblad Resonances

M. W. Regan (STScI), P. J. Teuben (University of Maryland)

Although inner Lindlbad resonances are commonly invoked to explain the formation of nuclear rings in barred spiral galaxies, these resonances do not exist in any but the most weakly barred galaxies. In this talk I quickly review the epicyclic approximation of orbits and how Linblad resonances are defined. I show that the assumptions used for the epicylic approximation of Lindblad resonances: a small non-axisymmetric component of the potential, small deviations from circular orbits, and that only the resonance orbits are closed, are all violated for a barred galaxy. Although for a weakly barred galaxy the epicylic approximation does predict the radial extent of the orbit family elongated along the minor axis of the bar (x2 orbits), even this breaks down for strongly barred galaxies. In fact, it is the x2 orbits that control the formation of nuclear rings.

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