Large scale structure and kinematics of the LMC from a study of long-period variable stars

Abstract

A recently completed study of the kinematics of Long-Period (or red) Variables (LPVs) in the LMC by Hughes et al. (1990) has shown that those with short periods (100 to 225 days) have spheroidal kinematics (high velocity dispersion and low rotational velocity about the LMC). This is the first evidence of the LMC's possessing a spheroidal population. The spheroid is flattened (with axial ratio c/a ˜0.3 to 0.5), and is not much thicker than the intermediate age disk. The velocity distribution of the old LPVs indicates that the mass of the LMC is ˜ 6.2 ± 1.5 × 109M, and that of the spheroid represented by the old LPVs is ˜2 % of the LMC's total mass. If these old LPVs are members of the LMC's disk, then their velocity dispersion implies that they have an age of ˜10 Gyr. The LPVs with intermediate periods (225 to 450 days) are members of the LMC's rotating disk population, with an age ˜4 Gyr derived from their velocity dispersion, and similar to that of the planetary nebulae, CH stars and old cluster populations.