ON THE POSSIBLE PREDOMINANCE OF LYNDEN-BELL BARS

It is shown that the density distribution in SB and SBO galaxies is de termined mainly by the resonant response of almost circular orbits of the disk to the slowly increasing potential of a Lynden-Bell bar. The correct ratio of the radii of the outer and inner rings in SB(r) galax ies, r2/r1 congruent-to 2.2, can be obtained only on the basis of the proposed theory. The inner ring lies at the inner Lindblad resonance ( ILR), due to the dominant angular harmonic (m=2) of the bar potential, and the outer ring lies at the ILR with the next most significant har monic (m=4). The main spiral arms in SB(s) galaxies are probably also of a resonant nature, and are determined by the same ILR (2:1) as the inner rings in SB(r) systems. We attribute the difference between SB(r ) and SB(s) galaxies mainly to the higher bar growth rates in systems of the SB(s) type, which makes the spirals more open. Correspondingly, transitional SB(rs) and SB(sr) systems are obtained with intermediate growth rates. The spiral pattern between the inner and outer rings in SB(r) galaxies (if it is observed at all) is then naturally associate d with the long-wavelength mode which is excited at the ILR (2:1) in t he self-gravitating disk by the bar and propagates outward from the ba r. The comparatively weak continuations of the main (resonance) spiral arms of SB(s) galaxies are engendered similarly.