Evidence for an intervening stellar population toward the large magellanic cloud

We identify a vertical extension of the red clump stars in the color magnitude diagram (CMD) of a section of the Large Magellanic Cloud (LMC). The distribution of stars in this extension is indistinguishable in the U, B, V, and I bands - confirming that the detection is real and placing a strong constraint on models of this stellar population. After subtracting the principal red clump component, we find a peak in the residual stellar distribution that is ∼ 0.9 mag brighter than the peak of the principal red clump distribution. We consider and reject the following possible explanations for this population: inhomogeneous reddening, Galactic disk stars, random blends of red clump stars, correlated blends of red clump stars (binaries), evolution of the red clump stars, and red clump stars from a younger LMC stellar population. Combinations of these effects cannot be ruled out as the origin of this stellar population A natural interpretation of this new population is that it consists of red clump stars that are closer to us than those in the LMC. We derive a distance for this population of ∼ 33 to 35 kpc, although the measurement is sensitive to the modeling of the LMC red clump component. We find corroborating evidence for this interpretation in Holtzman et al. s (1997, AJ, 113, 656) Hubble Space Telescope CMD of the LMC field stars. The derived distance and projected angular surface density of these stars relative to the LMC stars (≲ 5 to 7%) are consistent with (1) models that attribute the observed microlensing lensing optical depth (Alcock et al. 1997, ApJ, 486, 697) to a distinct foreground stellar population (Zhao 1997, preprint, astro-ph/9703097) and (2) tidal models of the interaction between the LMC and the Milky Way (Lin et al. 1995, ApJ, 439, 652). The first result suggests that the Galactic halo may contain few, if any, purely halo MACHO objects. The second result suggests that this new population may be evidence of a tidal tail from the interaction between the LMC and the Galaxy (although other interpretations, such as debris from the LMC-SMC interaction, are possible). We conclude that the standard assumption of a smoothly distributed halo population out to the LMC cannot be substantiated without at least a detailed understanding of several of the following: red clump stellar evolution, binary fractions, binary mass ratios, the spatial correlation of stars within the LMC, possible variations in the stellar populations of satellite galaxies, and differential reddening - all of which are highly complex.