Using Optical and Near‐Infrared Photometry to Test MACHO Lens Candidates

We obtained new VLT/ISAAC H-band observations for five MACHO LMC source starsand adjacent LMC field regions. After combining our near-IR photometry withHST/PC BVRI optical photometry, we compared the MACHO objects to the adjacentfield stars in a variety of color-magnitude and color-color diagrams. Thesediagnostic diagrams were chosen to be sensitive to our hypothesis that at leastsome of the MACHO lenses were foreground Galactic disk or thick disk M dwarfs.For the five lensed objects we studied, our hypothesis could be ruled out formain sequence lens masses >= 0.1 Mo for distances out to 4 kpc. On the otherhand, the fact that LMC-MACHO-5, an object not in our study, has been recentlyfound to have just such a foreground lens, highlights that the remainder of theLMC MACHO objects should be searched for the signature of their lenses usingour photometric technique, or via near-IR spectroscopy. We also constructeddiagnostic color-color diagrams sensitive to determining reddening for theindividual MACHO source stars and found that these five objects did not showevidence for significant additional reddening. At least these five MACHOobjects are thus also inconsistent with the LMC self-lensing hypothesis.Comment: 28 pages, 8 figures, ApJ, accepted for Oct 1 issu