2.1. The surface brightness profile Photometric imaging by B89 provides azimuthally averaged surface brightness (SB) profiles in the B − and R − bands, both of which display a sharp rise within 50 pc and a Freeman (1970) Type II hump between 50 pc and ∼ 2 kpc. The SB profile is exponential beyond that. The central flattening is accompanied by a slight reddening in the B − R profile (Fig. 1). A circumnuclear H α ring is observed at R ∼ 1 . 2 kpc, indicating a star-forming region (Knapen et al. 2006). The outer exponential is remarkably straight in spite of the large error bars; a linear fit to those points yields a photometric scale length R$_{d}$ of 1 . 18 ± 0 . 04 kpc, which becomes about 1.3 kpc when corrected for inclination and scale height. Fig. 2 shows the log µ -log R plot of the surface brightness. The inner few points are almost straight, approaching a line with a slope ∼ 1, suggesting a S´ ersic index of 1. There are three possibilities for the origin of Type II profiles: first, they may be caused by dust extinction; second, they may reflect the formation of bright stars that do not trace the mass; and third, they may be intrinsic to the mass distribution of the disc. In NGC 6503, the reddening in the inner portion may support the dust extinction hypothesis (Bottema & Gerritsen 1997, hereafter BG97). BG97 adopt an exponential disc and assume that the flattening in the surface brightness is due to dust (we return to this work in § 7.1). The possibility that dust extinction causes Type II profiles is also discussed by MacArthur et al. (2003) for their sample of spiral galaxies with optical and IR imaging; these authors are unable to reliably distinguish between Type I and Type II profiles on the basis of dust extinction, however. The second possibility relates to bar formation. Baggett, Baggett & Anderson (1998) and Anderson, Baggett & Baggett (2004) show that many galaxies with Type II profiles can be fit using Kormendy’s (1977) inner truncated profile where R$_{h}$ is a turnover radius and α is a cutoff index. Most of Baggett et al.’s (1998) galaxies have a bar, but a significant minority do not. These authors also argue that such flattening is intrinsic to the galaxy rather than being caused by dust. It is known that bars can induce ring formation in galaxies, which may contribute to the Type II profile flattening, and that circumnuclear rings correlate strongly with barred galaxies (Knapen 2005). Moreover, simulations by Foyle et al. (2008) suggest that the SB flattening could also be caused by the presence of a central bar, as the resulting reorganization of light can flatten the SB profile over the bar’s extent. Furthermore, while NGC 6503 does not appear to have a bar, it is possible for bars to dissolve by gas inflow, which transfers angular momentum from the gas to the bar (Bournaud et al. 2005). The ring currently seen in NGC 6503 may 5 I ( R ) = I$_{0}$ exp[ − ( R/R$_{d}$ + ( R$_{h}$/R ) $^{α}$)] (1)