Followup observations of highmagnification 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 highmagnification events based on the realtime data from the Korea Microlensing Telescope Network (KMTNet). We started a new phase of followup observations with the help of HighMagFinder in 2021. Here we report the discovery of two planets in highmagnification microlensing events, KMT2021BLG0171 and KMT2021BLG1689, which were identified by the HighMagFinder. We find that both events suffer the ‘centralresonant’ caustic degeneracy. The planethost massratio is q ∼ 4.7 × 10−5 or q ∼ 2.2 × 10−5 for KMT2021BLG0171, and q ∼ 2.5 × 10−4 or q ∼ 1.8 × 10−4 for KMT2021BLG1689. 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 disfavoured under this consideration. This factor can be included in future statistical studies to weight degenerate solutions.
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ABSTRACT 
Abstract We report on the observations, analysis and interpretation of the microlensing event MOA2019BLG008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finitesource effects were observed. Therefore, the angular Einstein ring radius θ E cannot be measured from the light curve alone. However, the large event duration, t E ∼ 80 days, allows a precise measurement of the microlensing parallax π E . In addition to the constraints on the angular radius θ * and the apparent brightness I s of the source, we employ the Besançon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two galactic models: the companion is likely a resident of the brown dwarf desert with a mass M p ∼ 30 M Jup , and the host is a mainsequence dwarf star. The lens lies along the line of sight to the Galactic bulge, at a distance of ≤4 kpc. We estimate that in about 10 yr the lens and source will be separated by ∼55 mas, and it will be possible tomore »Free, publiclyaccessible full text available August 2, 2023

Aims. With the aim of finding shortterm planetary signals, we investigated the data collected from current highcadence microlensing surveys. Methods. From this investigation, we found four planetary systems with low planettohost mass ratios, including OGLE2017BLG1691L, KMT2021BLG0320L, KMT2021BLG1303L, and KMT2021BLG1554L. Despite the short durations, ranging from a few hours to a couple of days, the planetary signals were clearly detected by the combined data of the lensing surveys. We found that three of the planetary systems have mass ratios on the order of 10 −4 and the other has a mass ratio that is slightly greater than 10 −3 . Results. The estimated masses indicate that all discovered planets have subJovian masses. The planet masses of KMT2021BLG0320Lb, KMT2021BLG1303Lb, and KMT2021BLG1554Lb correspond to ~0.10, ~0.38, and ~0.12 times the mass of the Jupiter, and the mass of OGLE2017BLG1691Lb corresponds to that of the Uranus. The estimated mass of the planet host KMT2021BLG1554L, M host ~ 0.08 M ⊙ , corresponds to the boundary between a star and a brown dwarf. Besides this system, the host stars of the other planetary systems are lowmass stars with masses in the range of ~[0.3–0.6] M ⊙ . The discoveries of the planets fully demonstrate themore »Free, publiclyaccessible full text available August 1, 2023

Aims. The light curve of the microlensing event KMT2021BLG0240 exhibits a shortlasting anomaly with complex features near the peak at the 0.1 mag level from a singlelens singlesource model. We conducted modeling of the lensing light curve under various interpretations to reveal the nature of the anomaly. Methods. It is found that the anomaly cannot be explained with the usual model based on a binarylens (2L1S) or a binarysource (1L2S) interpretation. However, a 2L1S model with a planet companion can describe part of the anomaly, suggesting that the anomaly may be deformed by a tertiary lens component or a close companion to the source. From the additional modeling, we find that all the features of the anomaly can be explained with either a triplelens (3L1S) model or a binarylens binarysource (2L2S) model. However, it is difficult to validate the 2L2S model because the light curve does not exhibit signatures induced by the source orbital motion and the ellipsoidal variations expected by the close separation between the source stars according to the model. We, therefore, conclude that the two interpretations cannot be distinguished with the available data, and either can be correct. Results. According to the 3L1S solution, the lens ismore »Free, publiclyaccessible full text available August 1, 2023

We complete the analysis of all 2018 primefield microlensing planets identified by the Korea Microlensing Telescope Network (KMTNet) Anomaly Finder. Among the ten previously unpublished events with clear planetary solutions, eight are either unambiguously planetary or are very likely to be planetary in nature: OGLE2018BLG1126, KMT2018BLG2004, OGLE2018BLG1647, OGLE2018BLG1367, OGLE2018BLG1544, OGLE2018BLG0932, OGLE2018BLG1212, and KMT2018BLG2718. Combined with the four previously published new Anomaly Finder events and 12 previously published (or in preparation) planets that were discovered by eye, this makes a total of 24 2018 primefield planets discovered or recovered by Anomaly Finder. Together with a paper in preparation on 2018 subprime planets, this work lays the basis for the first statistical analysis of the planet massratio function based on planets identified in KMTNet data. By systematically applying the heuristic analysis to each event, we identified the small modification in their formalism that is needed to unify the socalled closewide and innerouter degeneracies.Free, publiclyaccessible full text available August 1, 2023

ABSTRACT We report the complete statistical planetary sample from the prime fields (Γ ≥ 2 h−1) of the 2019 Korea Microlensing Telescope Network (KMTNet) microlensing survey. We develop the optimized KMTNet AnomalyFinder algorithm and apply it to the 2019 KMTNet prime fields. We find a total of 13 homogeneously selected planets and report the analysis of three planetary events, KMT2019BLG(1042,1552,2974). The planet–host mass ratios, q, for the three planetary events are 6.34 × 10−4, 4.89 × 10−3, and 6.18 × 10−4, respectively. A Bayesian analysis indicates the three planets are all cold giant planets beyond the snow line of their host stars. The 13 planets are basically uniform in log q over the range −5.0 < log q < −1.5. This result suggests that the planets below qbreak = 1.7 × 10−4 proposed by the MOAII survey may be more common than previously believed. This work is an early component of a large project to determine the KMTNet massratio function, and the whole sample of 2016–2019 KMTNet events should contain about 120 planets.Free, publiclyaccessible full text available July 20, 2023

Aims. The light curve of the microlensing event KMT2021BLG1898 exhibits a shortterm central anomaly with doublebump features that cannot be explained by the usual binarylens or binarysource interpretations. With the aim of interpreting the anomaly, we analyze the lensing light curve under various sophisticated models. Methods. We find that the anomaly is explained by a model, in which both the lens and source are binaries (2L2S model). For this interpretation, the lens is a planetary system with a planet/host mass ratio of q ~ 1.5 × 10 −3 , and the source is a binary composed of a turn off or a subgiant star and a mid K dwarf. The doublebump feature of the anomaly can also be depicted by a triplelens model (3L1S model), in which the lens is a planetary system containing two planets. Among the two interpretations, the 2L2S model is favored over the 3L1S model not only because it yields a better fit to the data, by ∆ χ 2 = [14.3−18.5], but also the Einstein radii derived independently from the two stars of the binary source result in consistent values. According to the 2L2S interpretation, KMT2021BLG1898 is the third planetary lensing event occurring on amore »Free, publiclyaccessible full text available July 1, 2023

Context. Brown dwarfs are transition objects between stars and planets that are still poorly understood, for which several competing mechanisms have been proposed to describe their formation. Mass measurements are generally difficult to carry out for isolated objects as well as for brown dwarfs orbiting lowmass stars, which are often too faint for a spectroscopic followup. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here, we present an analysis of the microlensing event OGLE2019BLG0033/MOA2019BLG035, which is caused by a binary system composed of a brown dwarf orbiting a red dwarf. Methods. Thanks to extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including the parallax, source radius, and orbital motion of the binary lens. Results. Following an accurate modeling process, we found that the lens is composed of a red dwarf with a mass of M 1 = 0.149 ± 0.010 M ⊙ and a brown dwarf with a mass of M 2 = 0.0463 ± 0.0031 M ⊙ at a projected separation of a ⊥ = 0.585 au. The system has a peculiar velocity that is typical ofmore »Free, publiclyaccessible full text available July 1, 2023

Aims. The highmagnification microlensing event KMT2021BLG1077 exhibits a subtle and complex anomaly pattern in the region around the peak. We analyze the lensing light curve of the event with the aim of revealing the nature of the anomaly. Methods. We test various models in combination with several interpretations: that the lens is a binary (2L1S), the source is a binary (1L2S), both the lens and source are binaries (2L2S), or the lens is a triple system (3L1S). We search for the bestfit models under the individual interpretations of the lens and source systems. Results. We find that the anomaly cannot be explained by the usual threebody (2L1S and 1L2S) models. The 2L2S model improves the fit compared to the threebody models, but it still leaves noticeable residuals. On the other hand, the 3L1S interpretation yields a model explaining all the major anomalous features in the lensing light curve. According to the 3L1S interpretation, the estimated mass ratios of the lens companions to the primary are ~1.56 × 10 −3 and ~1.75 × 10 −3 , which correspond to ~1.6 and ~1.8 times the Jupiter/Sun mass ratio, respectively, and therefore the lens is a multiplanetary system containing two giant planets. Withmore »Free, publiclyaccessible full text available June 1, 2023

Abstract OGLE2016BLG1093 is a planetary microlensing event that is part of the statistical Spitzer microlens parallax sample. The precise measurement of the microlens parallax effect for this event, combined with the measurement of finitesource effects, leads to a direct measurement of the lens masses and system distance, M host =0.38–0.57 M ⊙ and m p = 0.59–0.87 M Jup , and the system is located at the Galactic bulge ( D L ∼ 8.1 kpc). Because this was a highmagnification event, we are also able to empirically show that the “cheapspace parallax” concept produces wellconstrained (and consistent) results for ∣ π E ∣. This demonstrates that this concept can be extended to many twobody lenses. Finally, we briefly explore systematics in the Spitzer light curve in this event and show that their potential impact is strongly mitigated by the color constraint.Free, publiclyaccessible full text available May 10, 2023