Upper panel: our surface-brightness profile in the R-band. The solid line is the beta-model. Open circles denote the surface brightness with spherical isophotes. Open triangles denote the surface brightness with elliptical isophotes (ellipticity 0.3, position angle 50°). This profile was shifted by −0.5 mag for better visibility. Lower panel: residuals in mag between our measurements (upper panel) and the photometric model in the sense: observations-model.