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Session 19 - Source Surveys, Galaxy Surveys, Distance Scale II.
Display session, Wednesday, January 07
Exhibit Hall,

[19.10] The MACHO Bulge Database: Microlensing and Galactic Structure

D. Minniti, C. Alcock, D. Alves, K. Cook, S. Marshall (LLNL), R. Allsman, T. Axelrod, K. Freeman, B. Peterson, A. Rodgers (MSSSO), K. Griest, T. Vandehei (UCSD), A. Becker, M. Pratt, C. Stubbs, A. Tomaney (UW), D. Bennett (ND), M. Lehner (Sheffield), P. Quinn (ESO), W. Sutherland (Oxford), D. Welch (McMaster)

The MACHO Collaboration has detected about 200 possible microlensing events in the Galactic bulge fields to date. The interpretation of these events strongly depends on the structure of the inner Galaxy. We use different distance indicators to trace the three main components in these fields: bulge, disk and inner halo. The density distribution of these components is probed as follows:

The bulge is studied using \delta Scuti variable stars, clump giants, semiregular and long period variables. These tracers show a clear barred distribution, with the near side of the bar located at positive longitudes, confirming the results of previous studies.

(2) The inner disk is studied using short period contact binaries. The distribution of these binary stars is consistent with an exponential disk density distribution, showing no cutoff or hole in the inner regions.

(3) The inner halo is studied using RR Lyrae variable stars. The RR Lyrae show a density law that is very well fit by the extension of the power law that describes the metal-poor halo in the outer regions of the Milky Way. In particular, there is no cutoff or core seen in the RR Lyrae distribution, the power law continues to the innermost fields at R=0.3 kpc.

Since the bulge, disk, and halo components have different kinematics in these inner fields (Minniti 1996, ApJ, 459, 175), microlensing events in these components would have different distributions of observed parameters. The present results are compared with the observed color-magnitude diagrams and timescales of the MACHO events. \bigskip

This work is dedicated to the memory of Alex Rodgers.

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