THE OPEN CLUSTER NGC-7789 - I - RADIAL-VELOCITIES FOR GIANT STARS

A total of 597 radial velocity observations for 112 stars in the simil ar to 1.6 Gyr old open cluster NGC 7789 have been obtained since 1979 with the radial velocity spectrometer at the Dominion astrophysical Ob servatory. The mean cluster radial velocity is -54.9 +/- 0.12 km s(-1) and the dispersion is 0.86 km s(-1), from 50 constant velocity stars selected as members from this radial velocity study and the 1981 prope r motion study of McNamara & Solomon. Twenty-five stars (32%) among 78 members are possible radial velocity variable stars, but no orbits ar e determined because of the sparse sampling. Seventeen stars are radia l velocity nonmembers, while the membership estimates of six stars are uncertain. There is a hint that the observed velocity dispersion fall s off at large radius. This may due to the inclusion of long-period bi naries preferentially in the central area of the cluster The known rad ial velocity variables also seem to be more concentrated toward the ce nter than members with constant velocity. Although this is significant at only the 85% level, when combined with the similar result of Rabou d & Mermilliod for three other clusters, the data strongly support the conclusion that mass segregation is being detected.