Barred Galaxies ASP Conference Series, Vol. 91, 1996 R. Buta, D. A. Crocker, and B. G. Elmegreen, eds. The Corotation Radius and Other Resonances in NGC 7479 J. A. L. Aguerri, C. Munoz-Tunon, and A. M. Varela Institute) de Astrofisica de Canarias, Tenerife, Spain. M. Prieto Department of Astronomy, University of Florida, P. 0. Box 112055, Gainesville, FL 32611-2055, USA. 1. Introduction The luminosity profiles perpendicular to the bar of the galaxy NGC 7479 display "shoulders", which are observationally identified as an increase in the brightness profile (see Figure 1, right). In the literature (see e.g. Buta 1986), the presence of these features in other barred spirals has been reported. The "shoulders" have been attributed to annular structures resulting from the presence of a bar (Schwarz 1981, 1984, 1985), appearing at the OLR. Their stability and the precise modelling depends on the structural parameters of the bar. We attempt to test the plausibility of this theoretical interpretation using 2D photometry of the barred galaxy NGC 7479. The key parameter is the corotation radius (CR), defined as the galactocentric distance at which the gas and the shock wave corotate. From the CR all other Lindblad resonances can be obtained. Some of the techniques used to derive the CR are: 1. The CR is obtained assuming that the surface brightness of some tracers (stars or neutral hydrogen) obeys the continuity equation (Tremaine & Weinberg 1984). 2. The CR is determined by the arm-interarm ratio of the efficiency of massive star formation (Cepa & Beckman 1990) 3. The CR and other resonances are determined from a study of optical symmetries (Elmegreen & Elmegreen 1990; Elmegreen et al. 1992). 2. The Method and Results A description of observations and reduction of data presented here is given in Varela et al. (these proceedings). In this work we propose to determine the CR of NGC 7479 from the surface photometry by: 1. Color indices: The color index B — I shows a minimum of star formation at a galactocentric distance of 60". 2. Bar morphology: The end of the bar is located at 60" from the center (see Varela et al. these proceedings). 557 terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100050430 Downloaded from https://www.cambridge.org/core. IP address: 173.234.59.138, on 24 Apr 2020 at 15:13:55, subject to the Cambridge Core