Rotation of the Andromeda Nebula from a Spectroscopic Survey of Emission Regions

Spectia of sixty-seven H Ir regions from 3 to 24 kpc from the nucleus of M31 have been obtained with the DTM image-tube spectrograph at a dispersion of 135 A mm '. Radial velocities, principally from Ha, have been determined with an accuracy of 10 km sec ' for most regions. Rotational velocities have been calculated under the assumption of circular motions only. For the region interior to 3 kpc where no emission regions have been identified, a narrow N 13 x6583 emission line is observed. Velocities from this line indicate a rapid rotation in the nucleus, rising to a maximum circular velocity of V = 225 km at R = 400 pc, and falling to a deep minimum near R = 2 kpc. From the rotation curve for R 3 kpc, agree with the 21-cm observations, although the maximum rotational velocity, V = 270 t 10 km sec ', is slightly higher than that obtained from 21-cm observations.