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Missing Red Dwarfs: Caption, Credits and Copyright

MACHO Observation (OGLE microlensing event)

This pair of images presents two 30 by 30 arcsec subframes centered on the OGLE (Optical Gravitational Lensing Experiment) event #2, taken at minimum (left) and maximum (right) brightness. Time scale for the observations is 45 days.

The Optical Gravitational Lensing Experiment (OGLE) is a long term observational program with the main goal to search for dark, unseen matter using the microlensing phenomena. The idea of employing microlensing for that purpose was originally proposed by Paczynski (ApJ, 304, 1; ApJ Letters, 371, L63). The Magellanic Clouds and the Galactic Bulge are the most natural locations to conduct such search due to a large number of background stars that are potential targets for microlensing. The LMC and SMC stars may be lensed mostly by the Galactic halo objects, in case of the Galactic Bulge stars one expects an additional component -- microlensing by low-mass disk stars. In both cases the optical depth for microlensing is very small -- about 10^-6. Therefore a massive, long term survey must be conducted to a) detect and b) collect statistatically significant sample of microlensing events to draw any conclusion about the nature of dark matter. The OGLE project started in 1992 and the Galactic Bulge has been selected as the first target. Observations are carried out at the Las Campanas Observatory, Chile which is operated by the Carnegie Institution of Washington. So far twelve microlensing events have been found in the direction of the Galactic Bulge including one event most likely caused by a binary lens. You can find more info about these events here:

You can find more about OGLE at:

Courtesy of Bohdan Paczynski, Princeton University; Andrzej Udalski, Warsaw University.

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Copyright, (c) 1995: Board of Trustees, University of Illinois

NCSA. Last modified 11/2/95.