The kinematics of an old stellar population in the Large Magellanic Cloud - The CH stars

We have obtained radial velocities for 39 CH stars in the LMC for the purpose of identifying a possible extended halo component. The stars were selected from a catalog of ~200 candidates found on thin-prism Schmidt plates. The stars were chosen as potential halo tracers in the LMC because Galactic CH stars show a high velocity dispersion perpendicular to the plane indicating an old population. Using all the LMC CH stars as a group, we obtain kinematic solutions similar to those found earlier by Freeman, Illingworth, and Oemler for the old LMC clusters (i.e., a relatively high rotational velocity and a line of nodes considerably displaced from that for H I). However, our data suggest that it is reasonable to interpret the CH star velocities in terms of two kinematical components-a component with kinematics similar to those of the LMC planetaries (i.e., a rotating, flattened distribution which resembles the Galactic thick disk), and another component with lower systematic velocity which may be related in some way to the bar of the LMC. Neither the H I gas nor the H II regions apparently shows the relatively low velocities which we attribute to the second component, although such low velocities appear in the planetary nebulae and old cluster data.