Structure and Evolution of Barred Spiral Galaxies, I

Some exact two-dimensional rotating non-axially symmetric collisionless self-gravitating stellar systems have been constructed. Their approximate evolution, as they lose mass and angular momentum, has been computed by using the adiabatic invariants associated with each stellar orbit. If the arms of barred spiral galaxies form from gas streaming out along the bar, the results indicate that the bar becomes more dense, more stubby, rotates more rapidly, and becomes more bound against centrifugal force. The results favour this scheme for spiral arm formation against another mechanism which has been suggested (8, 9).