CFHT adaptive optics observations of M15

An average seeing of 0.15'' FWHM, with the best-seeing image having 0.09'', allowed us to measure accurately the velocities for five stars within 1'' of the center of M15. Our estimate of the second moment of the velocity distribution (i.e., the dispersion, ignoring rotation) inside a radius of 2'' is 11.5 km.s^-1^, the same value we find out to a radius of about 6''.

However, the projected net rotation does increase dramatically at small radii, as our previous observations led us to suspect. The rotation amplitude inside a radius of 3.4'' is v=10.4+/-2.7 km.s^-1^ and the dispersion after removing the rotation is {sigma}=10.3+/-1.4 km.s^-1^, so v/{sigma} {~} 1 in this region. In addition, the position angle of the projected rotation axis differs by 100 degrees from that of the net cluster rotation at larger radii.