The gravitational microlensing technique is most sensitive to planets in a Jupiterlike orbit and has detected more than 200 planets. However, only a few wideorbit (
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Abstract s > 2) microlensing planets have been discovered, wheres is the planettohost separation normalized to the angular Einstein ring radius,θ _{E}. Here, we present the discovery and analysis of a strong candidate wideorbit microlensing planet in the event OGLE2017BLG0448. The whole light curve exhibits longterm residuals to the static binarylens singlesource model, so we investigate the residuals by adding the microlensing parallax, microlensing xallarap, an additional lens, or an additional source. For the first time, we observe a complex degeneracy between all four effects. The wideorbit models withs ∼ 2.5 and a planettohost mass ratio ofq ∼ 10^{−4}are significantly preferred, but we cannot rule out the close models withs ∼ 0.35 andq ∼ 10^{−3}. A Bayesian analysis based on a Galactic model indicates that, despite the complicated degeneracy, the surviving wideorbit models all contain a superEarthmass to Neptunemass planet at a projected planethost separation of ∼6 au and the surviving closeorbit models all consist of a Jovianmass planet at ∼1 au. The host star is probably an M or K dwarf. We discuss the implications of this dimensiondegeneracy disaster on microlensing lightcurve analysis and its potential impact on statistical studies. 
Abstract Following Shin et al. (2023b), which is a part of the “Systematic KMTNet Planetary Anomaly Search” series (i.e., a search for planets in the 2016 KMTNet prime fields), we conduct a systematic search of the 2016 KMTNet subprime fields using a semimachinebased algorithm to identify hidden anomalous events missed by the conventional byeye search. We find four new planets and seven planet candidates that were buried in the KMTNet archive. The new planets are OGLE2016BLG1598Lb, OGLE2016BLG1800Lb, MOA2016BLG526Lb, and KMT2016BLG2321Lb, which show typical properties of microlensing planets, i.e., giant planets orbit Mdwarf host stars beyond their snow lines. For the planet candidates, we find planet/binary or 2L1S/1L2S degeneracies, which are an obstacle to firmly claiming planet detections. By combining the results of Shin et al. (2023b) and this work, we find a total of nine hidden planets, which is about half the number of planets discovered by eye in 2016. With this work, we have met the goal of the systematic search series for 2016, which is to build a complete microlensing planet sample. We also show that our systematic searches significantly contribute to completing the planet sample, especially for planet/host mass ratios smaller than 10^{−3}, which were incomplete in previous byeye searches of the KMTNet archive.

Abstract We measure the Einstein radius of the singlelens microlensing event KMT2022BLG2397 to be
θ _{E}= 24.8 ± 3.6μ as, placing it at the upper shore of the Einstein Desert, 9 ≲θ _{E}/μ as ≲ 25, between freefloating planets (FFPs) and bulge brown dwarfs (BDs). In contrast to the six BD (25 ≲θ _{E}≲ 50) events presented by Gould et al. (2022), which all had giantstar source stars, KMT2022BLG2397 has a dwarfstar source, with angular radiusθ _{ast}∼ 0.9μ as. This prompts us to study the relative utility of dwarf and giant sources for characterizing FFPs and BDs from finitesource pointlens (FSPL) microlensing events. We find “dwarfs” (including mainsequence stars and subgiants) are likely to yield twice as manyθ _{E}measurements for BDs and a comparable (but more difficult to quantify) improvement for FFPs. We show that neither current nor planned experiments will yield complete mass measurements of isolated bulge BDs, nor will any other planned experiment yield as manyθ _{E}measurements for these objects as the Korea Microlensing Telescope (KMT). Thus, the currently anticipated 10 yr KMT survey will remain the best way to study bulge BDs for several decades to come. 
Aims. We systematically inspected the microlensing data acquired by the KMTNet survey during the previous seasons in order to find anomalous lensing events for which the anomalies in the lensing light curves cannot be explained by the usual binarylens or binarysource interpretations. Methods. From the inspection, we find that interpreting the three lensing events OGLE2018BLG0584, KMT2018BLG2119, and KMT2021BLG1122 requires fourbody (lens+source) models, in which either both the lens and source are binaries (2L2S event) or the lens is a triple system (3L1S event). Following the analyses of the 2L2S events presented in our previous work, here we present the 3L1S analysis of the KMT2021BLG1122. Results. It is found that the lens of the event KMT2021BLG1122 is composed of three masses, in which the projected separations (normalized to the angular Einstein radius) and mass ratios between the lens companions and the primary are ( s 2 , q 2 )∼(1.4, 0.53) and ( s 3 , q 3 )∼(1.6, 0.24). By conducting a Bayesian analysis, we estimate that the masses of the individual lens components are ( M 1 , M 2 , M 3 )∼(0.47 M ⊙ , 0.24 M ⊙ , 0.11 M ⊙ ). The companions are separated in projection from the primary by ( a ⊥, 2 , a ⊥, 3 )∼(3.5, 4.0) AU. The lens of KMT2018BLG2119 is the first triple stellar system detected via microlensing.more » « less

Aims. We inspect the four microlensing events KMT2021BLG1968, KMT2021BLG2010, KMT2022BLG0371, and KMT2022BLG1013, for which the light curves exhibit partially covered shortterm central anomalies. We conduct detailed analyses of the events with the aim of revealing the nature of the anomalies. Methods. We tested various models that can explain the anomalies of the individual events, including the binarylens (2L1S) and binarysource (1L2S) interpretations. Under the 2L1S interpretation, we thoroughly inspected the parameter space to determine the existence of degenerate solutions, and if they existed, we tested whether the degeneracy could be resolved. Results. We find that the anomalies in KMT2021BLG2010 and KMT2022BLG1013 are uniquely defined by planetarylens interpretations with planettohost mass ratios of q ~ 2.8 × 10 −3 and ~1.6 × 10 −3 , respectively. For KMT2022BLG0371, a planetary solution with a mass ratio q ~ 4 × 10 −4 is strongly favored over the other three degenerate 2L1S solutions with different mass ratios based on the χ 2 and relative proper motion arguments, and a 1L2S solution is clearly ruled out. For KMT2021BLG1968, on the other hand, we find that the anomaly can be explained either by a planetary or a binarysource interpretation, making it difficult to firmly identify the nature of the anomaly. From the Bayesian analyses of the identified planetary events, we estimate that the masses of the planet and host are ( M p / M J , M h / M ⊙ ) = (1.07 −0.68 +1.15 , 0.37 −0.23 +0.40 ), (0.26 −0.11 +0.13 , 0.63 −0.28 +0.32 ), and (0.31 −0.16 +0.46 , 0.18 −0.10 +0.28 ) for KMT2021BLG2010L, KMT2022BLG0371L, and KMT2022BLG1013L, respectively.more » « lessFree, publiclyaccessible full text available June 1, 2024

Abstract We continue our program of publishing all planets (and possible planets) found by eye in 2021 Korea Microlensing Telescope Network (KMTNet) online data. We present four planets (KMT2021BLG0712Lb, KMT2021BLG0909Lb, KMT2021BLG2478Lb, and KMT2021BLG1105Lb), with planettohost mass ratios in the range − 3.3 ≲ log q ≲ − 2.2 . This brings the total of secure, byeye, 2021 KMTNet planets to 16, including 8 in this series. The byeye sample is an important check of the completeness of semiautomated detections, which are the basis for statistical analyses. One of the planets, KMT2021BLG1105Lb, is blended with a relatively bright ( I , V ) ∼ (18.9, 21.6) star that may be the host. This could be verified immediately by highresolution imaging. If so, the host is an early G dwarf, and the planet could be characterized by radial velocity observations on 30 m class telescopes.more » « less

Abstract We report on the discovery and analysis of the planetary microlensing event OGLE2019BLG1180 with a planettostar mass ratio
q ∼ 0.003. The event OGLE2019BLG1180 has unambiguous cusppassing and causticcrossing anomalies, which were caused by a wide planetary caustic withs ≃ 2, wheres is the star–planet separation in units of the angular Einstein radiusθ _{E}. Thanks to wellcovered anomalies by the Korea Micorolensing Telescope Network (KMTNet), we measure both the angular Einstein radius and the microlens parallax in spite of a relatively short event timescale oft _{E}= 28 days. However, because of a weak constraint on the parallax, we conduct a Bayesian analysis to estimate the physical lens parameters. We find that the lens system is a superJupitermass planet of orbiting a latetype star of ${M}_{\mathrm{p}}={1.75}_{0.51}^{+0.53}\phantom{\rule{0.25em}{0ex}}{M}_{\mathrm{J}}$ at a distance ${M}_{\mathrm{h}}={0.55}_{0.26}^{+0.27}\phantom{\rule{0.25em}{0ex}}{M}_{\odot}$ . The projected star–planet separation is ${D}_{\mathrm{L}}={6.1}_{1.3}^{+0.9}\phantom{\rule{0.25em}{0ex}}\mathrm{kpc}$ , which means that the planet orbits at about four times the snow line of the host star. Considering the relative lens–source proper motion of ${a}_{\perp}={5.19}_{1.23}^{+0.90}\phantom{\rule{0.25em}{0ex}}\mathrm{au}$μ _{rel}= 6 mas yr^{−1}, the lens will be separated from the source by 60 mas in 2029. At that time one can measure the lens flux from adaptive optics imaging of Keck or a nextgeneration 30 m class telescope. OGLE2019BLG1180Lb represents a growing population of wideorbit planets detected by KMTNet, so we also present a general investigation into prospects for further expanding the sample of such planets. 
ABSTRACT In this work, we update and develop algorithms for KMTNet tenderlove care (TLC) photometry in order to create a new, mostly automated, TLC pipeline. We then start a project to systematically apply the new TLC pipeline to the historic KMTNet microlensing events, and search for buried planetary signals. We report the discovery of such a planet candidate in the microlensing event MOA2019BLG421/KMT2019BLG2991. The anomalous signal can be explained by either a planet around the lens star or the orbital motion of the source star. For the planetary interpretation, despite many degenerate solutions, the planet is most likely to be a Jovian planet orbiting an M or K dwarf, which is a typical microlensing planet. The discovery proves that the project can indeed increase the sensitivity of historic events and find previously undiscovered signals.

Abstract We inaugurate a program of “mass production” of microlensing planets discovered in 2021 KMTNet data, with the aim of laying the basis for future statistical studies. While we ultimately plan to quickly publish all 2021 planets meeting some minimal criteria, the current sample of four was chosen simply on the basis of having low initial estimates of the planet–host mass ratio, q . It is therefore notable that two members of this sample suffer from a degeneracy in the normalized source radius ρ that arises from different morphologies of closely spaced caustics. All four planets (KMT2021BLG1391, KMT2021BLG1253, KMT2021BLG1372, KMT2021BLG0748) have wellcharacterized mass ratios, q , and therefore are suitable for massratio frequency studies. Both of the ρ degeneracies can be resolved by future adaptive optics (AO) observations on 30 m class telescopes. We provide general guidance for such AO observations for all events in anticipation of the prospect that they will revolutionize the field of microlensing planets.more » « less

Aims. We investigate the microlensing data collected during the 2017–2019 seasons in the peripheral Galactic bulge fields with the aim of finding planetary signals in microlensing light curves observed with relatively sparse coverage. Methods. We first sort out lensing events with weak shortterm anomalies in the lensing light curves from the visual inspection of all nonprimefield events, and then test various interpretations of the anomalies. From this procedure, we find two previously unidentified candidate planetary lensing events KMT2017BLG0673 and KMT2019BLG0414. It is found that the planetary signal of KMT2017BLG0673 was produced by the source crossing over a planetinduced caustic, but it was previously missed because of the sparse coverage of the signal. On the other hand, the possibly planetary signal of KMT2019BLG0414 was generated without caustic crossing, and it was previously missed due to the weakness of the signal. We identify a unique planetary solution for KMT2017BLG0673. However, for KMT2019BLG0414, we identify two pairs of planetary solutions, for each of which there are two solutions caused by the closewide degeneracy, and a slightly less favored binarysource solution, in which a single lens mass gravitationally magnified a rapidly orbiting binary source with a faint companion (xallarap). Results. From Bayesian analyses, it is estimated that the planet KMT2017BLG0673Lb has a mass of 3.7 −2.1 +2.2 M J , and it is orbiting a late Ktype host star with a mass of 0.63 −0.35 +0.37 M ⊙ . Under the planetary interpretation of KMT2010BLG0414L, a star with a mass of 0.74 −0.38 +0.43 M ⊙ hosts a planet with a mass of ~3.2–3.6 M J depending on the solution. We discuss the possible resolution of the planetxallarap degeneracy of KMT2019BLG0414 by future adaptiveoptics observations on 30 m class telescopes. The detections of the planets indicate the need for thorough investigations of nonprimefield lensing events for the complete census of microlensing planet samples.more » « less