A Newly Identified Degeneracy Keeps the Planetary Interpretation Viable for OGLE-2011-BLG-0950

TL;DR

This paper reveals a new degeneracy in the microlensing event OGLE-2011-BLG-0950 that allows for a planetary interpretation consistent with high-resolution imaging, refining the understanding of the lens system and emphasizing the importance of accounting for source companions.

Contribution

It introduces a newly identified degeneracy that supports a planetary model for OGLE-2011-BLG-0950, reconciling light curve data with proper motion measurements and highlighting complexities in lens characterization.

Findings

A new planetary model consistent with observations was identified.

Source star has unresolved companions affecting light measurements.

Single mass-luminosity relations underestimate uncertainties in lens properties.

Abstract

The microlensing event OGLE-2011-BLG-0950 exhibits the well-known ``Planet/Binary'' degeneracy, in which distinct lens configurations produce similar light curves but imply substantially different mass ratios between the lens components. A previous study suggested that high-resolution imaging could break this degeneracy through differences in the lens-source relative proper motion. In this work, we identify a new planetary model for this event that arises from a newly identified degeneracy, simultaneously reproducing the observed light curve and remaining consistent with the relative proper motion measured from high-resolution imaging. By combining constraints from the light-curve modeling and high-resolution observations, we infer a lens system consisting of a $\sim 1~M_{\odot}$ host star orbited by a $\sim 1.5~M_{\rm Jup}$ planet, with a projected separation of about 2 or 8 au, subject to the ``Close/Wide'' degeneracy. Our reanalysis of the color-magnitude diagram further indicates that the source star has unresolved companions that contribute non-negligible blended light, highlighting the importance of carefully accounting for source and lens companions in future Roman microlensing analyses. Finally, we show that adopting a single mass--luminosity relation significantly underestimates the uncertainties in the inferred lens properties for host masses $\gtrsim 1~M_{\odot}$.