Mass measurement of a single unseen star and planetary detection efficiency for OGLE 2007-BLG-050

摘要

Aims. We analyze OGLE-2007-BLG-050, a high magnification microlensing event ()whose peak occurred on 2May, 2007, with pronounced finite-sourceand parallax effects. We compute planet detection efficiencies for thisevent in order to determine its sensitivity to the presence of planetsaround the lens star. Methods. Both finite-source and parallax effects permit a measurement of the angular Einstein radius mas and the parallax ,leading to an estimate of the lens mass and its distance to the observer kpc.This is only the second determination of a reasonably precise (<30%)mass estimate for an isolated unseen object, using any method. Thisallows us to calculate the planetary detection efficiency in physicalunits ,where is the projected planet-star separation andis the planet mass. Results. When computing planet detection efficiency, we did notfind any planetary signature, i.e. none of the planetary configurationsprovides a improvement higher than60, and our detection efficiency resultsreveal significant sensitivity to Neptune-mass planets, and to a lesserextent Earth-mass planets in some configurations. Indeed, Jupiter andNeptune-mass planets are excluded with a high confidence for a largeprojected separation range between the planet and the lens star,respectively [0.6-10] and [1.4-4]AU, and Earth-mass planets areexcluded with a10% confidence in the lensing zone, i.e.[1.8-3.1]AU. Key words: gravitational lensing - techniques: photometric - stars: individual: OGLE 2007-BLG-050 - planetary systems