MOA-2008-BLG-379Lb: A massive planet from a high magnification event with a faint source

Abstract

We report on the analysis of the high microlensing event MOA-2008-BLG-379, which has a strong microlensing anomaly at its peak due to a massive planet with a mass ratio of q = 6.9 × 10-3. Because the faint source star crosses the large resonant caustic, the planetary signal dominates the light curve. This is unusual for planetary microlensing events, and as a result, the planetary nature of this light curve was not immediately noticed. The planetary nature of the event was found when the Microlensing Observations in Astrophysics (MOA) Collaboration conducted a systematic study of binary microlensing events previously identified by the MOA alert system. We have conducted a Bayesian analysis based on a standard Galactic model to estimate the physical parameters of the lens system. This yields a host star mass of orbited by a planet of mass at an orbital separation of AU at a distance of kpc. The faint source magnitude of I S = 21.30 and relatively high lens-source relative proper motion of μrel = 7.6 ± 1.6 mas yr-1 imply that high angular resolution adaptive optics or Hubble Space Telescope observations are likely to be able to detect the source star, which would determine the masses and distance of the planet and its host star. © 2014. The American Astronomical Society. All rights reserved..