Parallax microlensing events in the OGLE II data base toward the Galactic bulge |
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| Authors: | Martin C Smith Shude Mao P Woz´niak |
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| Institution: | University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL,; Princeton University Observatory, Princeton, NJ 08544-1001, USA and; Los Alamos National Laboratory, MS D436, Los Alamos, NM 87545, USA |
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| Abstract: | We present a systematic search for parallax microlensing events among a total of 512 microlensing candidates in the OGLE II data base for the 1997–1999 seasons. We fit each microlensing candidate with both the standard microlensing model and a parallax model that accounts for the Earth's motion around the Sun. We then search for the parallax signature by comparing the χ 2 of the standard and parallax models. For the events which show a significant improvement, we further use the 'duration' of the event and the signal-to-noise ratio as criteria to separate true parallax events from other noisy microlensing events. We have discovered one convincing new candidate, sc33_4505, and seven other marginal cases. The convincing candidate (sc33_4505) is caused by a slow-moving, and likely low-mass, object, similar to other known parallax events. We found that irregular sampling and gaps between observing seasons hamper the recovery of parallax events. We have also searched for long-duration events that do not show parallax signatures. The lack of parallax effects in a microlensing event puts a lower limit on the Einstein radius projected on to the observer plane, which in turn imposes a lower limit on the lens mass divided by the relative lens–source parallax. Most of the constraints are however quite weak. |
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| Keywords: | gravitational lensing Galaxy: bulge Galaxy: centre |
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