April 29, 1999 CfA Colloquium

Title: Optical Gravitational Lensing Experiment - Present and Future Plans

Speaker: Bohdan Paczynski

Abstract: Since January 6, 1997 the Optical Gravitational Lensing Experiment begun a full skale operation at the Las Campanas Observatory in Chile with the dedicated 1.3 meter R/C telescope, belonging to the Warsaw University Observatory. The key person is Andrzej Udalski, who made the currently used 2k x 2k CCD camera with a thin SITe device with 24 micron pixels, corresponding to 0.4" in the sky. Most of observations are done in a drift scan mode, and each field covers 14' x 57' in the sky. The observations are done in standard UBVI system, with 80% of data in the I band. The data is processed in real time and the microlensing alert system is in place since the beginning of 1998. Large areas in the galactic bulge, in the LMC and in the SMC are monitored every clear night. With this instrument OGLE detected a total of about 90 events in the bulge, but none so far in the Magellanic Clouds. A major result is the `short' distance to the Magellanic Clouds obtained with the red clump giants, RR Lyrae variables, and the eclipsing binary HV 2274, with (m-M)_{LMC} = 18.2.

A major software and hardware upgrades are planned for the year 2000. Udalski will build a mosaic 8k x 8k CCD camera using thin SITe CCDs, with 15 micron pixels (0.25" in the sky). Princeton graduate student Przemek Wozniak will incorporate the image subtraction software developed by Christophe Alard and Robert Lupton in the OGLE standard data pipeline. The expected alert rate for microlensing events in the galactic bulge will reach several hundred per year, and in the Magellanic Clouds more than 10 per year.

Reference for students:

Lunch on Wednesday 4/28 at 12:30 in the classroom (A-101).