The MACHO Collaboration Microlensing Survey:\\Results Toward the LMC and the Bulge

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Session 33 -- Relativistic Astrophysics
Display presentation, Tuesday, 31, 1994, 9:20-6:30

[33.01] The MACHO Collaboration Microlensing Survey:\\Results Toward the LMC and the Bulge

K.Cook, C.Alcock, R.Allsman, T.Axelrod (LLNL), D.Bennett, S.Perlmutter (UCB), S.Marshall, M.Pratt, C.Stubbs (UCSB), K.Griest (UCSD), W. Sutherland (Oxford), K.Freeman, P.Quinn, B.Peterson, A.Rodgers (MSSSO)

The MACHO Collaboration uses a dedicated 1.27-m telescope (The Great Melbourne Telescope) at Mount Stromlo to make photometric measurements of millions of stars per night searching for the gravitational microlensing signature of massive compact objects in the halo and disk of the Milky Way. A prime focus corrector and dichroic beamsplitter provide red (6300--8000 \AA) and blue (4500--6300 \AA) foci with 1 degree fields of view. A 2x2 mosaic of 2048x2048 pixel CCDs in each focal plane yields simultaneous images of 0.5 square degrees. By June of 1994, we will have collected more than 17,000 images of fields in the Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC) and the bulge of the Milky Way. We have recently implemented an online analysis system which yields photometric reductions of a night's data (5 Gbyte of images) within 24 hours. This system will allow us to identify and follow interesting events in real-time in order to better sample potential microlensing events. We will present the design and our first experiences with this system.

We will also present recent results from observations of the LMC and the Bulge. We have previously reported 4 candidate microlensing events toward the LMC obtained from the analysis of light curves of 8.3 x $10^6$ stars. We will show spectra of 2 of the source stars obtained at the CTIO 4-m, and also spectra from 8 of our 'bumpers'. These 'bumpers' stars exhibit long periods without photometric variation, then occasionally brighten for a short period of time by about 25 \% in a slightly asymmetric and chromatic fashion. These stars appear to be related to Be stars. We will also present analysis results of observations toward the bulge of the Milky Way. In just one field toward the bulge, we have observed 4 candidate microlensing events, one of which has a peak amplification of a factor of 18!

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