The rotation of horizontal-branch stars. IV. Members of the globular cluster NGC 288.

Radial velocities and line breadths are measured for seven blue horizontal-branch stars in the globular cluster NGC 288. The mean velocity is -43.2 + or - 1.5 km/s, and the intrinsic velocity dispersion is 2.6 + or - 0.3 km/s, in keeping with a solar mass-to-light ratio. Line broadening was detected in over half the stars, with a maxmimum v sin i = 22 + or - 3 km/s. This establishes a level of rotation in NGC 288 greater than that found in the globular clusters M3, M4, and M5, but not M13. Since the ranking of these clusters by the degree of rotation is the same as their ranking according to the prevalence of blue stars on the horizontal branch, the idea is strongly supported that rotation does increase the proportion of blue stars on the horizontal branch of some intermediate-metallicity clusters.