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 × 10−4 at 1σ. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by Δχ2 > 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 $1.9^{+0.6}_{-0.7}$ or $4.6^{+1.4}_{-1.7}$ au, subject to the close/wide degeneracy. This is the third q < 10−4 planet from a high-magnification planetary signal (A ≳ 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.

OGLE-2017-BLG-0448Lb: A Low Mass–Ratio Wide-orbit Microlensing Planet?

“…According to the CMD analysis in Section 4, the second source has a color of (V − I) = 1.95 ± 0.12. Applying the blue boundary of the bulge main-sequence stars derived by Zhang et al (2023), a source star with I ∼ 24.8 should be redder than (V − I) = 2.9 (see Figure 6). Therefore, the 1L2S parallax model can also be excluded by ∼8σ based on the color argument.…”

KMT-2023-BLG-1431Lb: A New q < 10−4 Microlensing Planet from a Subtle Signature

“…For the present case, θ E is measured but π E is not constraint, so we estimate the physical parameters of the lens system by a Bayesian analysis based on a Galactic model. The Galactic model is the same as used in Zhang et al (2023), in which we adopt initial mass function from Kroupa (2001), with a 1.3M e and 1.1M e cutoff for the disk and the bulge lenses, respectively (Zhu et al 2017), the stellar number density profile is depicted in Yang et al (2021), and the dynamical distributions of the bulge and disk lenses are described by the Zhu et al (2017) and Yang et al (2021) model, respectively. We generate a sample of 10 7 simulated events from prior functions of the Galactic model above by conducting a Monte Carlo simulation. For each simulated event i of solution k with parameters t E,i,k , μ rel,i,k , and θ E,i,k , we weight it by…”