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P. Popowski, K.H. Cook, A.J. Drake, S.L. Marshall, C.A. Nelson (IGPP/LLNL), C. Alcock (UPenn), R.A. Allsman, T.S. Axelrod, K.C. Freeman, B.A. Peterson (ANU), D.R. Alves (STScI), A.C. Becker, C.W. Stubbs, A.B. Tomaney (Washington), D.P. Bennett (Notre Dame), M. Geha (UC Santa Cruz), K. Griest, T. Vandehei (UC San Diego), M.J. Lehner (Sheffield), D. Minniti (Catolica), M.R. Pratt (CSR/MIT), P.J. Quinn (ESO), W. Sutherland (Oxford), D. Welch (McMaster), MACHO Collaboration
We present preliminary results of the analysis of 5 years of MACHO data on the Galactic bulge microlensing events with clump giants as sources. This class of events allows one to obtain robust conclusions because relatively bright clump stars are not strongly affected by blending effects. We discuss: 1) the selection of `giant' events, 2) the distribution of impact parameters as a measure of the quality of our sample, 3) the distribution of event durations in comparison with the expectations from Galactic models, 4) the competing interpretations of the concentration of long duration events in MACHO field 104 centered on (l,b) = (3 \fdg 1, -3 \fdg 0). We report the preliminary average optical depth of \tau = (2.0 ±0.4) \times 10-6 \;\;({\rm internal}) at (l,b) = (3\fdg 9, -3 \fdg 8). We describe the spatial distribution of the optical depth and discuss future work aimed at the determination of the mass function of the lensing objects.
The author(s) of this abstract have provided an email address for comments about the abstract: popowski@igpp.ucllnl.org