Microlensing Optical Depth toward the Galactic Bulge Using Clump Giants from the MACHO Survey
Popowski, P; Griest, K; Thomas, C L; Cook, Kem H; Bennett, D P; Becker, Andrew C; Alves, David R; Minniti, Dante; Drake, Andrew J; Alcock, Charles; Allsman, Robyn A; Axelrod, Tim S; Freeman, Kenneth; Geha, M; Lehner, M J; Marshall, S L; Nelson, C A; Peterson, Bruce; Quinn, Peter J; Stubbs, Christopher W; Sutherland, William J; Vandehei, T; Welch, D L
Using 7 yr of MACHO survey data, we present a new determination of the optical depth to microlensing toward the Galactic bulge. We select the sample of 62 microlensing events (60 unique) on clump giant sources and perform a detailed efficiency analysis. We use only the clump giant sources because these are bright bulge stars and are not as strongly affected by blending as other events. Using a subsample of 42 clump events concentrated in an area of 4.5 deg2 with 739,000 clump giant stars, we...[Show more]
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