# The 2L1S/1L2S Degeneracy for Two Microlensing Planet Candidates Discovered by the KMTNet Survey in 2017

## TL;DR

This paper discusses the challenge of distinguishing between two microlensing models in two planetary candidate events discovered by KMTNet in 2017, highlighting the importance of resolving degeneracies for confirming exoplanet discoveries.

## Contribution

It demonstrates the prevalence of the 2L1S/1L2S degeneracy in microlensing events and emphasizes the need for future proper motion measurements to resolve such ambiguities.

## Key findings

- Degeneracy cannot be resolved for KMT-2017-BLG-0962.
- Light curve modeling favors 2L1S for KMT-2017-BLG-1119.
- Higher-resolution observations support 1L2S interpretation for KMT-2017-BLG-1119.

## Abstract

We report two microlensing planet candidates discovered by the KMTNet survey in $2017$. However, both events have the 2L1S/1L2S degeneracy, which is an obstacle to claiming the discovery of the planets with certainty unless the degeneracy can be resolved. For KMT-2017-BLG-0962, the degeneracy cannot be resolved. If the 2L1S solution is correct, KMT-2017-BLG-0962 might be produced by a super Jupiter-mass planet orbiting a mid-M dwarf host star. For KMT-2017-BLG-1119, the light curve modeling favors the 2L1S solution but higher-resolution observations of the baseline object tend to support the 1L2S interpretation rather than the planetary interpretation. This degeneracy might be resolved by a future measurement of the lens-source relative proper motion. This study shows the problem of resolving 2L1S/1L2S degeneracy exists over a much wider range of conditions than those considered by the theoretical study of Gaudi (1998).