KMT-2022-BLG-0440Lb: A New $q<10^{-4}$ Microlensing Planet with the Central-Resonant Caustic Degeneracy Broken

Abstract

We present the observations and analysis of a high-magnification microlensing planetary event, KMT-2022-BLG-0440, for which the weak and short-lived planetary signal was covered by both the KMTNet survey and follow-up observations. The binary-lens models with a central caustic provide the best fits, with a planet/host mass ratio, $q=0.75$--$1.00\times 10^{-4}$ at $1\sigma$. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by $\Delta {\chi }^2>70$. The binary-source model can fit the anomaly well but is rejected by the ``color argument'' on the second source. From Bayesian analyses, it is estimated that the host star is likely a K or M dwarf located in the Galactic disk, the planet probably has a Neptune-mass, and the projected planet-host separation is $1.9_{-0.7}^{+0.6}$ or $4.6_{-1.7}^{+1.4}$ au, subject to the close/wide degeneracy. This is the third $q<10^{-4}$ planet from a high-magnification planetary signal ($A\gtrsim 65$). Together with another such planet, KMT-2021-BLG-0171Lb, the ongoing follow-up program for the KMTNet high-magnification events has demonstrated its ability in detecting high-magnification planetary signals for $q<10^{-4}$ planets, which are challenging for the current microlensing surveys.

arXiv commentMNRAS accepted

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