Fig. 3.— Rotation curve data for NGC 6503. The H β data are filled red circles, the stellar rotation data are filled blue triangles (Bottema 1989) and the H I data are hollow purple squares (Begeman 1987). The black curve shows the fit using Eq. 2 to the gas data and the green curve shows the fit to the stellar data. The fitting parameters are: for the black curve, v$_{0}$ = 117 ± 1 km s − $^{1}$, R$_{c}$ = 0 . 88 ± 0 . 03 kpc and ζ = 2 . 1 ± 0 . 1; and for the green curve, v$_{0}$ = 108 ± 4 km s − $^{1}$, R$_{c}$ = 0 . 95 ± 0 . 04 kpc and ζ = 3 . 2 ± 0 . 6. The data have not been corrected for inclination. 37