KMT-2021-BLG-0171Lb and KMT-2021-BLG-1689Lb: Two Microlensing Planets in the KMTNet High-cadence Fields with Followup Observations

Abstract

Follow-up observations of high-magnification gravitational microlensing events can fully exploit their intrinsic sensitivity to detect extrasolar planets, especially those with small mass ratios. To make followup more uniform and efficient, we develop a system, HighMagFinder, based on the real-time data from the Korean Microlensing Telescope Network (KMTNet) to automatically alert possible ongoing high-magnification events. We started a new phase of follow-up observations with the help of HighMagFinder in 2021. Here we report the discovery of two planets in high-magnification microlensing events, KMT-2021-BLG-0171 and KMT-2021-BLG-1689, which were identified by the HighMagFinder. We find that both events suffer the ``central-resonant'' caustic degeneracy. The planet-host mass-ratio is $q\sim 4.7\times 10^{-5}$ or $q\sim 2.2\times 10^{-5}$ for KMT-2021-BLG-0171, and $q\sim 2.5\times 10^{-4}$ or $q\sim 1.8\times 10^{-4}$ for KMT-2021-BLG-1689. Together with two events reported by Ryu et al. (2022), four cases that suffer such degeneracy have been discovered in the 2021 season alone, indicating that the degenerate solutions may have been missed in some previous studies. We also propose a new factor for weighting the probability of each solution from the phase-space. The resonant interpretations for the two events are disfavored under this consideration. This factor can be included in future statistical studies to weight degenerate solutions.

18 pages, 15 figures, 10 tabels; submitted to MNRAS

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• Mass Production of 2021 KMTNet Microlensing Planets I
• An Earth-Mass Planet and a Brown Dwarf in Orbit Around a White Dwarf
• KMT-2022-BLG-0440Lb: A New $q<10^{-4}$ Microlensing Planet with the Central-Resonant Caustic Degeneracy Broken
• Mass Production of 2021 KMTNet Microlensing Planets III: Analysis of Three Giant Planets
• Systematic Reanalysis of KMTNet Microlensing Events, Paper II: Two New Planets in Giant-Source Events
• Mass Production of 2021 KMTNet Microlensing Planets II
• KMT-2025-BLG-1616Lb: First Microlensing Bound Planet From DREAMS
• Earth-like planet predictor: A machine learning approach
• A New Parameterization for Finding Solutions for Microlensing Exoplanet Light Curves
• Binary-lens Microlensing Degeneracy: Impact on Planetary Sensitivity and Mass-ratio Function
• KMT-2025-BLG-1314 and KMT-2025-BLG-1392: two microlensing planetary/brown-dwarf candidates analyzed with differentiable code
• MOA-2020-BLG-135Lb: A New Neptune-class Planet for the Extended MOA-II Exoplanet Microlens Statistical Analysis