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We compute surface brightness profiles of galactic disks for outwardlypropagating waves of star formation with a view to investigate the stellarpopulations in ring galaxies. We consider two mechanisms which can createoutwardly propagating star forming rings in a purely gaseous disk --- aself-induced wave and a density wave. We show that the surface brightnessprofiles produced by both scenarios of ring formation are similar and arestrongly sensitive to the velocity of the wave. The results of our computationsare compared with the observational quantities sensitive to the young and oldstellar populations in the ring galaxies A0035-335 (the Cartwheel galaxy) andVIIZw466. The best fit to the observed radial H_alpha surface brightnessdistribution in the Cartwheel galaxy is obtained for a wave velocity of about90 km/s. The red continuum brightness of the ring can be fully explained by theevolving stars present in the trailing part of the wave. However the redcontinuum brightness in regions internal to the ring indicates that the wave ofstar formation propagates in a pre-existing stellar disk in the Cartwheel. TheH_alpha and K-band surface brightness profiles in VIIZw466 match the valuesexpected from stellar populations produced by a wave of star formationpropagating in a purely gaseous disk very well. We conclude that VIIZw466 isprobably experiencing the first event of star formation in the disk.Comment: Uses aas2pp4.sty and epsfig.sty, 15 pages To appear in Astrophysical  Journal, March 10, 199

Surface Brightness Gradients Produced by the Ring Waves of Star Formation