Space distribution and orbits of globular clusters of the galaxy

Abstract

For 29 globular clusters of the Galaxy with integrated spectral type F, we have calculated their orbits from their radial velocity and proper motion data using three different galactic potential models. The results show: (1) Most of the sample clusters are distributed in the region 5 kpc–10 kpc from the Galactic center, in a spherically symmetrical distribution about the center, and their space velocities follow an ellipsoidal distribution; (2) The clusters can be classified by metallicity into the HB and MP subsystems, and their number density peaks at [ Fe H ]=−1.6 ; (3) The clusters follow periodic but not closed orbits with maximum galactocentric distances generally less than 40 kpc. Using the different potential models makes little difference in the orbital morphology. When an orbit passes within about 1 kpc of the galactic centre, “chaotic” behavior may take place. The orbital morphology is not obviously correlated with metallicity. (4) The orbital semi-major axis, apogalactic distance and azimuthal period vary in similar ways with the metallicity, and the correlation between the orbital eccentricity and the metallicity is obvious. About 24% of the sample clusters have orbital eccentricities less than 0.4. The effect of different potential models is not obvious in the perigalactic distance, eccentricity and the uncertainties of the orbital parameters, but is more obvious in the other orbital parameters, including the apogalactic distance, semi-major axis, radial period, and azimuthal period.