KMT-2016-BLG-1107: A New Hollywood-Planet Close/Wide Degeneracy

TL;DR

This paper identifies a new degeneracy in microlensing events where a giant-star source can produce similar light curve anomalies under different binary configurations, complicating the interpretation of planetary signals.

Contribution

The study introduces a novel degeneracy between close and wide binary microlensing events involving giant-star sources, with methods to distinguish solutions using future high-resolution imaging.

Findings

A new degeneracy between close and wide binary microlensing events was identified.

High-resolution imaging can resolve the degeneracy in future observations.

Analytic conditions for the degeneracy's occurrence are provided.

Abstract

We show that microlensing event KMT-2016-BLG-1107 displays a new type of degeneracy between wide-binary and close-binary Hollywood events in which a giant-star source envelops the planetary caustic. The planetary anomaly takes the form of a smooth, two-day "bump" far out on the falling wing of the light curve, which can be interpreted either as the source completely enveloping a minor-image caustic due to a close companion with mass ratio $q=0.036$, or partially enveloping a major-image caustic due to a wide companion with $q=0.004$. The best estimates of the companion masses are both in the planetary regime ($3.3^{+3.5}_{-1.8}\,M_{\rm jup}$ and $0.090^{+0.096}_{-0.037}\,M_{\rm jup}$) but differ by an even larger factor than the mass ratios due to different inferred host masses. We show that the two solutions can be distinguished by high-resolution imaging at first light on next-generation ("30m") telescopes. We provide analytic guidance to understand the conditions under which this new type of degeneracy can appear.