Study by MOA of extrasolar planets in gravitational microlensing events of high magnification

Abstract

A search for extrasolar planets was carried out in three gravitational microlensing events of high magnification, MACHO 98–BLG–35, MACHO 99–LMC–2 and OGLE 00–BUL–12. Photometry was derived from observational images by the MOA and OGLE groups using an image subtraction technique. For MACHO 98–BLG–35, additional photometry derived from the MPS and PLANET groups was included. Planetary modelling of the three events was carried out in a supercluster computing environment. The estimated probability for explaining the data on MACHO 98–BLG–35 without a planet is <1 per cent. The best planetary model has a planet of mass ~(0.4–1.5)×MEarth at a projected radius of either ~1.5 or ~2.3 au. We show how multiplanet models can be applied to the data. We calculate exclusion regions for the three events and find that Jupiter-mass planets can be excluded with projected radii from as wide as about 30 au to as close as around 0.5 au for MACHO 98–BLG–35 and OGLE 00–BUL–12. For MACHO 99–LMC–2, the exclusion region extends out to around 10 au and constitutes the first limit placed on a planetary companion to an extragalactic star. We derive a particularly high peak magnification of ~160 for OGLE 00–BUL–12. We discuss the detectability of planets with masses as low as Mercury in this and similar events.