Main Scientific Results of the OGLE-I Project

discovery of the first microlensing events toward the Galactic bulge (Udalski et al. 1993)
first determination of the optical depth for microlensing toward the Galactic bulge (Udalski et al. 1994a)
discovery of the first microlensing by a binary object - OGLE-BUL-7 (Udalski et al. 1994b)
first system of detection of microlensing events in progress ( Early Warning System, EWS, Udalski et al. 1994c)
the Galactic structure analysis - evidence for existence of a bar in the Galaxy (Stanek et al. 1996)
publication of extinction maps towards the Galactic Bulge (Stanek 1996)
variable stars search in the direction of the Galactic center: "Catalog of Periodic Variable Stars in the Galactic Center" (Udalski et al. 1997) including 2861 objects
photometry of globular clusters - discovery of numerous detached eclipsing binaries in omega Cen and 47 Tuc (Kaluzny et al. 1996)
photometry of dwarf galaxies in Sculptor (Kaluzny et al. 1995) and Sagittarius (Mateo et al. 1996)

First Phase of the Optical Gravitational Lensing Experiment - OGLE-I

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 (LCO) which is operated by the Carnegie Institution of Washington.

First part of the project, concluded in 1995, was carried out using the 1 m Swope telescope. New 1.3 m Polish telescope was built in Las Campanas Observatory by the Warsaw University. The telescope produced its first light in 1996 and regular observations started in January 1997. The telescope is dedicated for the long term, photometric surveys of the large areas of the sky.

During the first part of OGLE project nineteen 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:

OGLE #1 OGLE #2 OGLE #3 OGLE #4 OGLE #5 OGLE #6

OGLE #7 OGLE #8 OGLE #9 OGLE #10 OGLE #11 OGLE #12

OGLE-I team at Las Campanas Observatory,
Chile in June 1992

100" du Pont telescope and 24" Canadian telescope (right) at Las Campanas Observatory. Polish telescope will be located between the astrograph house (in the middle) and seeing tower.

In 1994 observing season a new feature is implemented in the OGLE data system: the Early Warning System (EWS). It allows the detection and identification of microlensing events in real time. Thus, the system makes it possible to reschedule observations to obtain the best coverage of a microlensing event while it unfolds, as well as to arrange follow-up photometric and/or spectoscopic observations from other observatories.

First ever ongoing microlensing event was caught on July 8, 1994. The EWS detected a microlens candidate in Baade's Window field BW6. The event was a low-magnification (0.3 mag) short-lasting (t0=13 days) event. First OGLE ALERT info was sent to interested astronomers for follow-up observations.

Second ongoing event was detected on August 20, 1994. The star from Baade's Window, BW5 I 83758, underwent microlensing. The time scale was about 20 days.

In 1995 season 6 more events, that is OGLE 14 - 19, have been discovered so far with the EWS system (beginning of August 1995).

The huge amount of the collected photometric data necessary for microlensing search provides also an unique observing material for conducting independent side projects. Results of the first of them on the structure of our Galaxy have already been published. The huge catalog of periodic variable stars is available from OGLE archive: anonymous ftp.

There is also a WWW interface to the Database of OGLE results:
General Catalog of Stars
Variable Stars Catalog

The observing time when the Galactic Bulge is not visible or seeing is too large for observations of the dense Bulge fields is used for additional observational side projects. In 1992 clusters of galaxies were observed for supernovae, in 1993 globular clusters and Sculptor dwarf galaxy were observed for variable stars.

Another project being pursued when the bulge is not observable is a systematic study of the newly discovered Sagittarius dwarf galaxy. Deep photometry of the galaxy and light curves for newly-discovered variables in Sgr are also available.

View of the Las Campanas Observatory from the 100'' du Pont telescope. 24'' Canadian telescope (left) and 40'' Swope telescope are seen.
In 1992-94 the OGLE project is/was conducted using the 40'' Swope telescope.

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