The Velocity Dispersion of Old Stars in the Large Magellanic Cloud

Radial velocities have been obtained for a group of the oldest long-period variables (LPVs) in the Large Magellanic Cloud. The LPVs have periods in the range 150 to 250 days, and they are similar to the Mira variables in 47 Tuc and the Galactic center; in particular, they have ages more than 10 billion yr. The old LPVs belong to a kinematic system which has a systemic velocity that is indistinguishable from that of the H I gas. The intrinsic line-of-sight dispersion of the LPV velocities about their systemic velocity mean is 30 km/s. Such a velocity dispersion is consistent with that expected for stars belonging to a flattened disk with a scale height of about 0.3 kpc. There is marginal evidence that the kinematic system to which the old LPVs belong rotates.