Radial velocities of red giants in NGC 1817

In addition, we have used radial velocities and new UBVR photoelectric photometry to investigate the membership of 59 new candidates located in an outer corona surrounding NGC 1817, identified from the POSS plates. We have confirmed 18 new members out to a distance of 27' from the centre, thus doubling the previous cluster radius.

Ten definite spectroscopic-binary members have been discovered, corresponding to a binary frequency of 25.6% and four orbits have been determined so far. Three additional stars have been identified as possible spectroscopic-binary members. We derive a cluster mean velocity of +65.33+/-0.09 (0.52 s.e.) km/s based on 29 members with no detected velocity variations plus the 3 binary members with orbital solutions.