GLOBULAR-CLUSTER ORBITS AND 2ND PARAMETER EFFECTS

Clusters that lie on retrograde orbits are found to belong preferentially to Oosterhoff class I ( >99% confidence). M3-like clusters predominantly occupy plunging orbits (98.5% confidence). Furthermore, orbit shape and Galactocentric distance are found to be correlated (99.9% confidence), with a tendency for clusters at large distances to have plunging orbits and below-average luminosities. Half of the 10 halo clusters known to be on retrograde orbits are observed to have - 1.60 <[Fe/H]< - 1.50. This strengthens and confirms a similar conclusion previously published by Rodgers & Paltoglou [ApJ, 283, L5 (1984)]. The results obtained in the present paper suggest that some second parameter effects might be due to the way in which the protoGalaxy collapsed. In particular the present work hints at the possibility that the Galactic halo might contain a population component which was derived from a massive ancestral object (or objects) with an M3-like population (Oosterhoff class I) that merged with the main body of the protoGalaxy after falling in on a plunging retrograde orbit.