The Optical Gravitational Lensing Experiment (OGLE-II). Difference Image Analysis of the Bulge Data.

Details The Optical Gravitational Lensing Experiment (OGLE-II). Difference Image Analysis of the Bulge Data. The Optical Gravitational Lensing Experiment (OGLE-II). Difference Image Analysis of the Bulge Data.

Dec 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...197.6702w&link_type=abstract

American Astronomical Society, 197th AAS Meeting, #67.02; Bulletin of the American Astronomical Society, Vol. 32, p.1512

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During 1997-1999 observing seasons (mid March to mid December) the OGLE-II project collected more than 11,000 2Kx8K frames (over 370 GB of pixel data) of the Galactic Bulge using 1.3m Warsaw Telescope at the Las Campanas Observatory, Chile. Each of the 49 fields has roughly 200-300 measurements in I band. The fields span the range approximately from -10 to 10 deg in galactic longitude. I present a complete reanalysis of this data set using the optimal image subtraction method developed by Alard and Lupton (1998) and Alard (1999). Databases of difference measurements contain about 100,000 variable objects. This information is supplemented with colors from DoPhot photometry. Noise properties of our difference light curves are exceptionally good for this kind of massive monitoring program. The nongaussian tail in the distribution of residuals is totally negligible for usual applications. For faint stars the measurement errors are only 1.15 times photon noise. The difference photometry is always at least a factor of 2 better than results from DoPhot. Systematic effects due to blending are greatly relieved, the most important difference being the unbiased value of the variable light centroid. We discovered 512 microlensing events (compared to 214 from DoPhot photometry, Udalski et al. 2000). 305 of those were found fully algorithmically and have good quality light curves making them very well suited for optical depth determination. In the nearest future we plan to obtain an upper limit on the number of jupiters around microlenses as these should manifest themselves in the nongaussian tail of the residual distribution. Next possibilities include much better and larger extinction maps of the bulge and studies of the galactic bar. With 300-500 events we should be able to study the depth of the lens/source populations (Stanek 1996).

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