Constraints on intervening stellar populations toward the Large MagellanicCloud

The suggestion by Zaritsky & Lin (ZL) that a vertical extension of the red clump feature (the VRC) in color-magnitude diagrams (CMDs) of the Large Mag ellanic Cloud is consistent with a significant population of foreground sta rs to the LMC that could account for the observed microlensing optical dept h has been challenged by various investigators. We respond by (1) examining each of the challenges presented, to determine whether any or all of those arguments invalidate the claims made by ZL, and (2) presenting new photome tric and spectroscopic data obtained in an attempt to resolve this issue. W e systematically discuss why the objections raised so far do not unequivoca lly refute ZL's claim. We conclude that although the CMD data do not mandat e the existence of a foreground population, they are entirely consistent wi th a foreground population associated with the LMC that contributes signifi cantly (similar to 50%) to the observed microlensing optical depth. From ou r new data, we conclude that less than or similar to 40% of the VRC stars a re young, massive red clump stars, because (1) synthetic CMDs created using the star formation history derived independently from Hubble Space Telesco pe data suggest that fewer than 50% of the VRC stars are young, massive red clump stars, (2) the angular distribution of the VRC stars is more uniform than that of the young (<1 Gyr) main-sequence stars, and (3) the velocity dispersion of the VRC stars in the region of the LMC examined by ZL, 18.4 /- 2.8 km s(-1) (95% confidence limits), is inconsistent with the expectati on for a young disk population. Each of these arguments is predicated on as sumptions, and the conclusions are uncertain. Therefore, an exact determina tion of the contribution to the microlensing optical depth by the various h ypothesized foreground populations, and the subsequent conclusions regardin g the existence of halo MACHOs, requires a detailed knowledge of many compl ex astrophysical issues, such as the initial mass function, star formation history, and post-main-sequence stellar evolution.