The rotation curves and orientation parameters of the spiral galaxies NGC 2715, 5033 and 5055.

We present observations of the velocity fields in the inner parts of the spiral galaxies NGC 5033 and 5055 obtained from measurements of the optical emission lines (mainly H ) in 12 position angles from the nucleus. These and similar observations in 14 position angles of NGC 2715 (van der Kruit 1976a) are analysed in order to obtain the rotation curves, position angles of the lines of nodes, inclinations and systemic velocities. These data are to be used later in combination with Westerbork HI-observations. No evidence for large-scale non-circular motions is found in the inner parts of these three systems down to about 14 kms-' (1 ) in the line of sight. The rotation curves out to about 1 arcmin from the centre (respectively 9, 5 and 3 kpc for NGC 2715, 5033 and 5055 for a distance scale based on H=55 kms-' Mpc-1) are derived with rms error of 5/sin i kms-' (1 G) at 4" intervals. The position angles of the lines of nodes and the inclinations are derived accurate to within a few degrees. The rotation curve of NGC 5055 derived by Burbidge, Burbidge and Prendergast (1960) is shown to be somewhat too high. Key words: Spiral galaxies - rotation curves - orientation parameters