The Open Cluster NGC 7789. I. Radial Velocities for Giant Stars

摘要

A total of 597 radial velocity observations for 112 stars in the ～1.6 Gyr old open cluster NGC 7789 have been obtained since 1979 with the radial velocity spectrometer at the Dominion Astrophysical Observatory. 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 proper motion study of McNamara & Solomon. Twenty-five stars (32%) among 78 members are possible radial velocity variable stars, but no orbits are determined because of the sparse sampling. Seventeen stars are radial velocity nonmembers, while the membership estimates of six stars are uncertain. There is a hint that the observed velocity dispersion falls off at large radius. This may due to the inclusion of long-period binaries preferentially in the central area of the cluster. The known radial velocity variables also seem to be more concentrated toward the center than members with constant velocity. Although this is significant at only the 85% level, when combined with the similar result of Raboud & Mermilliod for three other clusters, the data strongly support the conclusion that mass segregation is being detected.