Search for: All records

Abstract The current studies of microlensing planets are limited by small number statistics. Follow-up observations of high-magnification microlensing events can efficiently form a statistical planetary sample. Since 2020, the Korea Microlensing Telescope Network (KMTNet) and the Las Cumbres Observatory (LCO) global network have been conducting a follow-up program for high-magnification KMTNet events. Here, we report the detection and analysis of a microlensing planetary event, KMT-2023-BLG-1431, for which the subtle (0.05 mag) and short-lived (5 hr) planetary signature was characterized by the follow-up from KMTNet and LCO. A binary-lens single-source (2L1S) analysis reveals a planet/host mass ratio ofq= (0.72 ± 0.07) × 10⁻⁴, and the single-lens binary-source (1L2S) model is excluded by Δχ²= 80. A Bayesian analysis using a Galactic model yields estimates of the host star mass of $M_{\mathrm{host}}={0.57}_{-0.29}^{+0.33}{M}_{\odot }$, the planetary mass of $M_{\mathrm{planet}}={13.5}_{-6.8}^{+8.1}{M}_{\oplus }$, and the lens distance of $D_{\mathrm{L}}={6.9}_{-1.7}^{+0.8}$kpc. The projected planet-host separation of $a_{\perp }={2.3}_{-0.5}^{+0.5}$au or $a_{\perp }={3.2}_{-0.8}^{+0.7}$au, subject to the close/wide degeneracy. We also find that without the follow-up data, the survey-only data cannot break the degeneracy of central/resonant caustics and the degeneracy of 2L1S/1L2S models, showing the importance of follow-up observations for current microlensing surveys. 

Abstract We present the analysis of seven microlensing planetary events with planet/host mass ratios q < 10 −4 : KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016–2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with q < 10 −4 from 2016–2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals ( A ≳ 65), and a follow-up project for KMTNet high-magnification events could detect at least two more q < 10 −4 planets per year and form an independent statistical sample. 

Abstract We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary-lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near ( M 1 = 170 − 50 + 40 M J and M 2 = 110 − 30 + 20 M J ), or well below ( M 1 = 22.5 − 0.4 + 0.7 M J and M 2 = 13.3 − 0.3 + 0.4 M J ) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown-dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next 10 years through infrared adaptive-optics imaging with a 40 m class telescope. 

ABSTRACT We report the discovery and analysis of a candidate triple-lens single-source (3L1S) microlensing event, OGLE-2019-BLG-1470. This event was first classified as a normal binary-lens single-source (2L1S) event, but a careful 2L1S modelling showed that it needs an additional lens or source to fit the observed data. It is found that the 3L1S model provides the best fit, but the binary-lens binary-source (2L2S) model is only disfavoured by Δχ2 ≃ 18. All of the feasible models include a planet with planet-to-host mass-ratios 10−3 ≲ q ≲ 10−2. A Bayesian analysis based on a Galactic model indicates that the planet is super-Jovian, and the projected host-planet separation is about 3 au. Specifically, for the best-fitting 3L1S model, the two stars have masses of $$M_1=0.57^{+0.43}_{-0.32}{\rm M}_{\odot}$$, and $$M_2=0.18^{+0.15}_{-0.10}\mathrm{M}_{\odot}$$ with projected separation of $$1.3^{+0.5}_{-0.5}$$ au, and the planetary mass is $$M_3=2.2^{+1.8}_{-1.3}M_{\rm {Jupiter}}$$. For the 2L2S model, the masses of the host star and the planet are $$0.55^{+0.44}_{-0.31}\mathrm{M}_{\odot }$$ and $$4.6^{+3.7}_{-2.6}M_{\rm {Jupiter}}$$, respectively. By investigating the properties of all known microlensing planets in binary systems, we find that all planets in binary systems published by the KMTNet survey are located inside the resonant caustics range with q ≳ 2 × 10−3, indicating the incompleteness of the KMTNet sample for planets in binary systems. Thus, planets in binary systems cannot be included in the current study of the KMTNet mass-ratio function, and a systematic search for planetary anomalies in KMTNet microlensing light curves of binary systems is needed. 

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, KMT-2019-BLG-(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 MOA-II survey may be more common than previously believed. This work is an early component of a large project to determine the KMTNet mass-ratio function, and the whole sample of 2016–2019 KMTNet events should contain about 120 planets. 

ABSTRACT Only a few wide-orbit planets around old stars have been detected, which limits our statistical understanding of this planet population. Following the systematic search for planetary anomalies in microlensing events found by the Korea Microlensing Telescope Network, we present the discovery and analysis of three events that were initially thought to contain wide-orbit planets. The anomalous feature in the light curve of OGLE-2018-BLG-0383 is caused by a planet with mass ratio q = 2.1 × 10−4 and a projected separation s = 2.45. This makes it the lowest mass-ratio microlensing planet at such wide orbits. The other two events, KMT-2018-BLG-0998 and OGLE-2018-BLG-0271, are shown to be stellar binaries (q > 0.1) with rather close (s < 1) separations. We briefly discuss the properties of known wide-orbit microlensing planets and show that the survey observations are crucial in discovering and further statistically constraining such a planet population. 

ABSTRACT We report the discovery and analysis of a planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is q = (2.65 ± 0.16) × 10−3. The ground-based observations yield a constraint on the angular Einstein radius θE, and the microlensing parallax vector $$\boldsymbol{{\pi} }_{\rm E}$$, is strongly constrained by the Spitzer data. However, the 2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so there is ambiguity in the magnitude of the parallax. In our preferred interpretation, a full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $$M_{\rm planet} = 0.26_{-0.11}^{+0.22}M_{\rm J}$$ planet orbiting an $$M_{\rm host} = 0.093_{-0.038}^{+0.082}~\mathrm{M}_{\odot }$$, at a distance of $$D_{\rm L} = 3.71_{-1.70}^{+3.24}$$ kpc. An alternate interpretation of the data shifts the localization of the minima along the arc-shaped microlens parallax constraints. This, in turn, yields a more massive host with median mass of $$0.13 {\, \mathrm{M}_{\odot }}$$ at a distance of 6.3 kpc. This analysis demonstrates the robustness of the osculating circles formalism, but shows that further investigation is needed to assess how systematics affect the specific localization of the microlens parallax vector and, consequently, the inferred physical parameters.