OGLE-2012-BLG-0563: Relative Proper Motion Constraint from Keck Follow-up Finds the Correct Lens

Abstract We present Keck/NIRC2 adaptive optics imaging results of planetary microlensing event OGLE-2012-BLG-0563. We find that the OGLE-2012-BLG-0563L planetary system consists of a 1.12 ± 0.09 M Jup planet orbiting a 0.81 ± 0.04 M ⊙ host star at a distance of 5.49 ± 0.56 kpc from the Sun. This event has a lens-source separation of 23.28 ± 0.48 mas, which is the smallest lens-source separation measured to date with Keck AO data. We find that the incorrect solution—which identifies the northeast (NE) star as the source star—is favored if one only considers the discovery paper, the A. Fukui et al. (2015) solution, or an unconstrained model. However, by performing an image-constrained light-curve model fit using the relative proper-motion direction constraint from the Keck follow-up data, we demonstrate that the correct solution identifies the NE star as the lens star. The discrepancy in the unconstrained models is driven by systematics in the Faulkes Telescope South (FTS) and ​​​Microlensing Observations in Astrophysics (MOA) B and C data, alongside the impact of the relative proper-motion direction constraints. This outcome offers two important lessons for future Roman data analysis: (1) thoroughly verify systematics across all passbands and identify the precise origin of χ 2 differences, and (2) utilize image-constrained light-curve modeling incorporating relative proper-motion direction constraints to identify the correct lens.