Interloper Stars in the Large Magellanic Cloud
A recent radial-velocity study (Olsen et al. 2011) of ~5900 red giants and supergiants in the LMC has uncovered a population of a few hundred stars that have distinct kinematics from the stars of the LMC disk. Metallicities of a subsample of these stars were found to be similar to stars in the Small Magellanic Cloud. This led the authors to suggest the stars were captured from the SMC by the LMC in a previous interaction of the Clouds.
We have used SPM4 proper motions to analyze the extra two velocity dimensions of these stars. Combining the proper motions and radial velocities, we were able to determine that the SMC-captured stars rotate in the same sense as the LMC disk, but at an inclination of about 50 degrees with respect to the disk. The existence of these stars, together with other facts, point to an off-center, moderate to highly inclined collision of the SMC with the LMC disk some 100 to 200 million years ago.
Image Credits: (header) NASA, ESA, J. Hester and A. Loll (Arizona State University)