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 observations more uniform and efficient, we develop a system, HighMagFinder, to automatically alert possible ongoing high-magnification events based on the real-time data from the Korea Microlensing Telescope Network (KMTNet). 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 ∼ 4.7 × 10−5 or q ∼ 2.2 × 10−5 for KMT-2021-BLG-0171, and q ∼ 2.5 × 10−4 or q ∼ 1.8 × 10−4 for KMT-2021-BLG-1689. Together with two other events, 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 quantitative factor to weight 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.

Mass Production of 2021 KMTNet Microlensing Planets. I

“…Pending the development of a more systematic approach, we would advocate running hot chains on all resonant-and near-resonantcaustic solutions. See Yang et al (2022) for a complementary approach.…”

Systematic KMTNet Planetary Anomaly Search. VII. Complete Sample of q < 10−4 Planets from the First 4 yr Survey

“…For degenerate solutions, Yang et al (2022) suggested that the phase-space factors can be used to weight the probability of each solution. We follow the procedures of Yang et al (2022) and first calculate the covariance matrix, C, of ( a s q log , log , ) from the MCMC chain. Then, the phase-space factor is…”

Mass Production of 2021 KMTNet Microlensing Planets. III. Analysis of Three Giant Planets

“…This paper is the third in our series that aims to publish all by-eye planet detections from the 2021 Korea Microlensing Telescope Network (KMTNet; Kim et al 2016) observing season. Previously, in Ryu et al (2022a) and Ryu et al (2022b), we published eight planet detections; 10 other planets from the 2021 season have been published in other work (Han et al 2022a(Han et al , 2022b(Han et al , 2022c(Han et al , 2022dYang et al 2022).…”

“…In addition to the s † (or offset) degeneracy, 2L1S models may be subject to a degeneracy in ρ * , which may affect the value of q (Ryu et al 2022a;Yang et al 2022). Typically, the degeneracy between the two solutions arises because the observed duration of a "bump" anomaly may be controlled either by the width of the caustic (so ρ * is small in comparison) or the size of the source (so ρ * is  the width of the caustic).…”