Browsing by Author "Kim H-W"

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    Brown dwarf companions in microlensing binaries detected during the 2016-2018 seasons
    (EDP Sciences on behalf of the European Southern Observatory, 2022-11-08) Han C; Ryu Y-H; Shin I-G; Jung YK; Kim D; Hirao Y; Bozza V; Albrow MD; Zang W; Udalski A; Bond IA; Chung S-J; Gould A; Hwang K-H; Shvartzvald Y; Yang H; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Yee JC; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Silva SI; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Itow Y
    Aims. With the aim of finding microlensing binaries containing brown dwarf (BD) companions, we investigate the microlensing survey data collected during the 2016 2018 seasons. Methods. For this purpose, we first modeled lensing events with light curves exhibiting anomaly features that are likely to be produced by binary lenses. We then sorted out BD companion binary-lens events by applying the criterion that the companion-to-primary mass ratio is q 0.1. With this procedure, we identify six binaries with candidate BD companions: OGLE-2016-BLG-0890L, MOA-2017-BLG-477L, OGLE-2017-BLG-0614L, KMT-2018-BLG-0357L, OGLE-2018-BLG-1489L, and OGLE-2018-BLG-0360L. Results. We estimated the masses of the binary companions by conducting Bayesian analyses using the observables of the individual lensing events. According to the Bayesian estimation of the lens masses, the probabilities for the lens companions of the events OGLE-2016-BLG-0890, OGLE-2017-BLG-0614, OGLE-2018-BLG-1489, and OGLE-2018-BLG-0360 to be in the BD mass regime are very high with PBD > 80%. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with PBD = 61% and 69%, respectively.
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    KMT-2019-BLG-1715: Planetary microlensing event with three lens masses and two source stars
    (IOP Publishing on behalf of the American Astronomical Society, 2021-06-01) Han C; Udalski A; Kim D; Jung YK; Lee C-U; Bond IA; Albrow MD; Chung S-J; Gould A; Hwang K-H; Kim H-W; Ryu Y-H; Shin I-G; Shvartzvald Y; Zang W; Yee JC; Cha S-M; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Kim C-H; Kim W-T; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki M; Abe F; Barry R; Bennett DP; Bhattacharya A; Donachie M; Fujii H; Fukui A; Itow Y; Hirao Y; Kirikawa R; Kondo I; Li MCA; Matsubara Y; Muraki Y; Miyazaki S; Ranc C; Rattenbury NJ; Satoh Y; Shoji H; Suematsu H; Sumi T; Suzuki D; Tanaka Y; Tristram PJ; Yamakawa T; Yamawaki T; Yonehara A
    We investigate the gravitational microlensing event KMT-2019-BLG-1715, the light curve of which shows two short-term anomalies from a caustic-crossing binary-lensing light curve: one with a large deviation and the other with a small deviation. We identify five pairs of solutions, in which the anomalies are explained by adding an extra lens or source component in addition to the base binary-lens model. We resolve the degeneracies by applying a method in which the measured flux ratio between the first and second source stars is compared with the flux ratio deduced from the ratio of the source radii. Applying this method leaves a single pair of viable solutions, in both of which the major anomaly is generated by a planetary-mass third body of the lens, and the minor anomaly is generated by a faint second source. A Bayesian analysis indicates that the lens comprises three masses: a planet-mass object with ∼2.6 MJ and binary stars of K and M dwarfs lying in the galactic disk. We point out the possibility that the lens is the blend, and this can be verified by conducting high-resolution follow-up imaging for the resolution of the lens from the source.
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    MOA-2020-BLG-208Lb: Cool Sub-Saturn-mass Planet within Predicted Desert
    (American Astronomical Society, 2023-03) Olmschenk G; Bennett DP; Bond IA; Zang W; Jung YK; Yee JC; Bachelet E; Abe F; Barry RK; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Silva SI; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Munford B; Muraki Y; Okamura A; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Albrow MD; Cha S-M; Chung S-J; Gould A; Han C; Hwang K-H; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Ryu Y-H; Shin I-G; Shvartzvald Y; Christie G; Cooper T; Drummond J; Green J; Hennerley S; McCormick J; Monard LAG; Natusch T; Porritt I; Tan T-G; Mao S; Maoz D; Penny MT; Zhu W; Bozza V; Cassan A; Dominik M; Hundertmark M; Jaimes RF; Kruszyńska K; Rybicki KA; Street RA; Tsapras Y; Wambsganss J; Wyrzykowski L; Zieliński P; Rau G
    We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet, MOA-2020-BLG-208Lb, with an estimated sub-Saturn mass. With a mass ratio q=3.17-0.26+0.28×10-4, the planet lies near the peak of the mass-ratio function derived by the MOA collaboration and near the edge of expected sample sensitivity. For these estimates we provide results using two mass-law priors: one assuming that all stars have an equal planet-hosting probability, and the other assuming that planets are more likely to orbit around more massive stars. In the first scenario, we estimate that the lens system is likely to be a planet of mass mplanet=46-24+42M⊕ and a host star of mass Mhost=0.43-0.23+0.39M⊙, located at a distance DL=7.49-1.13+0.99kpc . For the second scenario, we estimate mplanet=69-34+37M⊕, Mhost=0.66-0.32+0.35M⊙, and DL=7.81-0.93+0.93kpc . The planet has a projected separation as a fraction of the Einstein ring radius s=1.3807-0.0018+0.0018 . As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models
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    OGLE-2017-BLG-1049: Another giant planet microlensing event
    (Korean Astronomical Society, 2020-12-31) Kim YH; Chung S-J; Udalski A; Bond IA; Jung YK; Gould A; Albrow MD; Han C; Hwang K-H; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Zang W; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Poleski R; Mróz P; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Abe F; Barry R; Bennett DP; Bhattacharya A; Donachie M; Fujii H; Fukui A; Itow Y; Hirao Y; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Muraki Y; Miyazaki S; Ranc C; Rattenbury NJ; Satoh Y; Shoji H; Sumi T; Suzuki D; Tristram PJ; Tanaka Y; Yamawaki T; Yonehara A
    We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet–host star mass ratio of q = 9.53 ± 0.39 × 10−3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36−0.29M⊙ hosting a giant planet with Mp = 5.53+3.62 −2.87MJup, at a distance of DL = 5.67+1.11−1.52 kpc. The projected star–planet separation is a⊥ = 3.92+1.10−1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens–source proper motion is µrel ∼ 7 mas yr−1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.
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    OGLE-2018-BLG-0971, MOA-2023-BLG-065, and OGLE-2023-BLG-0136: Microlensing events with prominent orbital effects
    (EDP Sciences, 2024-06-14) Han C; Udalski A; Bond IA; Lee C-U; Gould A; Albrow MD; Chung S-J; Hwang K-H; Jung YK; Kim H-W; Ryu Y-H; Shvartzvald Y; Shin I-G; Yee JC; Yang H; Zang W; Cha S-M; Kim D; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Rybicki KA; Iwanek P; Ulaczyk K; Wrona M; Gromadzki M; Mróz MJ; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    Aims. We undertake a project to reexamine microlensing data gathered from high-cadence surveys. The aim of the project is to reinvestigate lensing events whose light curves exhibit intricate anomaly features that are associated with caustics, but lack prior proposed models that would explain these features. Methods. Through detailed reanalyses considering higher-order effects, we determined that it is vital to account for the orbital motions of lenses to accurately explain the anomaly features observed in the light curves of the lensing events OGLE-2018-BLG-0971, MOA-2023-BLG-065, and OGLE-2023-BLG-0136. Results. We estimated the masses and distances to the lenses by conducting Bayesian analyses using the lensing parameters of the newly found lensing solutions. These analyses showed that the lenses of the events OGLE-2018-BLG-0971 and MOA-2023-BLG-065 are binaries composed of M dwarfs, while the lens of OGLE-2023-BLG-0136 likely is a binary composed of an early K-dwarf primary and a late M-dwarf companion. For all lensing events, the probability that the lens resides in the bulge is considerably higher than that it is located in the disk.
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    Probable brown dwarf companions detected in binary microlensing events during the 2018- 2020 seasons of the KMTNet survey
    (EDP Sciences, 2023-07-04) Han C; Jung YK; Kim D; Gould A; Bozza V; Bond IA; Chung S-J; Albrow MD; Hwang K-H; Ryu Y-H; Shin I-G; Shvartzvald Y; Yang H; Zang W; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Yee JC; Lee Y; Park B-G; Pogge RW; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Silva SI; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Itow Y
    Aims. We inspect the microlensing data of the KMTNet survey collected during the 2018-2020 seasons in order to find lensing events produced by binaries with brown dwarf (BD) companions. Methods. In order to pick out binary-lens events with candidate BD lens companions, we conducted systematic analyses of all anomalous lensing events observed during the seasons from 2018 to 2020. By applying a selection criterion of mass ratio between the lens components of 0.03 q 0.1, we identify four binary-lens events with candidate BD companions, namely KMT-2018-BLG-0321, KMT-2018-BLG-0885, KMT-2019-BLG-0297, and KMT-2019-BLG-0335. For the individual events, we present interpretations of the lens systems and measure the observables that can be used to constrain the physical lens parameters. Results. The masses of the lens companions estimated from the Bayesian analyses based on the measured observables indicate high probabilities that the lens companions are in the BD mass regime; that is, 59%, 68%, 66%, and 66% for the four respective events.
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    Systematic KMTNet Planetary Anomaly Search. II. Six New q < 2 × 10−4 Mass-ratio Planets
    (IOP Publishing on behalf of the American Astronomical Society, 2022-02-01) Hwang K-H; Zang W; Gould A; Udalski A; Bond IA; Yang H; Mao S; Albrow MD; Chung S-J; Han C; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge R; Mróz P; Poleski R; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Munford B; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh YK; Shoji H; Silva SI; Sumi T; Suzuki D; Tristram PJ; Yonehara A; Zhang X; Zhu W; Penny MT; Fouqué P
    We apply the automated AnomalyFinder algorithm of Paper I to 2018-2019 light curves from the ≃13 deg2 covered by the six KMTNet prime fields, with cadences Γ ≥ 2 hr-1. We find a total of 11 planets with mass ratios q < 2 × 10-4, including 6 newly discovered planets, 1 planet that was reported in Paper I, and recovery of 4 previously discovered planets. One of the new planets, OGLE-2018-BLG-0977Lb, is in a planetary caustic event, while the other five (OGLE-2018-BLG-0506Lb, OGLE-2018-BLG-0516Lb, OGLE-2019-BLG-1492Lb, KMT-2019-BLG-0253, and KMT-2019-BLG-0953) are revealed by a "dip"in the light curve as the source crosses the host-planet axis on the opposite side of the planet. These subtle signals were missed in previous by-eye searches. The planet-host separations (scaled to the Einstein radius), s, and planet-host mass ratios, q, are, respectively, (s, q × 105) = (0.88, 4.1), (0.96 ± 0.10, 8.3), (0.94 ± 0.07, 13), (0.97 ± 0.07, 18), (0.97 ± 0.04, 4.1), and (0.74, 18), where the "± "indicates a discrete degeneracy. The 11 planets are spread out over the range . Together with the two planets previously reported with q ∼ 10-5 from the 2018-2019 nonprime KMT fields, this result suggests that planets toward the bottom of this mass-ratio range may be more common than previously believed.
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    Systematic KMTNet Planetary Anomaly Search. XI. Complete Sample of 2016 Subprime Field Planets
    (American Astronomical Society, 2024-06-03) Shin I-G; Yee JC; Zang W; Han C; Yang H; Gould A; Lee C-U; Udalski A; Sumi T; Albrow MD; Chung S-J; Hwang K-H; Jung YK; Ryu Y-H; Shvartzvald Y; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Rybicki KA; Iwanek P; Ulaczyk K; Wrona M; Gromadzki M; Abe F; Bando K; Barry R; Bennett DP; Bhattacharya A; Bond IA; Fujii H; Fukui A; Hamada R; Hamada S; Hamasaki N; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Nagai T; Nunota K; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    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 semi-machine-based algorithm to identify hidden anomalous events missed by the conventional by-eye search. We find four new planets and seven planet candidates that were buried in the KMTNet archive. The new planets are OGLE-2016-BLG-1598Lb, OGLE-2016-BLG-1800Lb, MOA-2016-BLG-526Lb, and KMT-2016-BLG-2321Lb, which show typical properties of microlensing planets, i.e., giant planets orbit M-dwarf 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 by-eye searches of the KMTNet archive.
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    Systematic KMTNet planetary anomaly search: V. Complete sample of 2018 prime-field
    (EDP Sciences, 2022-08-08) Gould A; Han C; Zang W; Yang H; Hwang K-H; Udalski A; Bond IA; Albrow MD; Chung S-J; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymanski MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Silva SI; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Beichman C; Bryden G; Novati SC; Gaudi BS; Henderson CB; Penny MT; Jacklin S; Stassun KG
    We complete the analysis of all 2018 prime-field 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: OGLE-2018-BLG-1126, KMT-2018-BLG-2004, OGLE-2018-BLG-1647, OGLE-2018-BLG-1367, OGLE-2018-BLG-1544, OGLE-2018-BLG-0932, OGLE-2018-BLG-1212, and KMT-2018-BLG-2718. 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 prime-field 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 mass-ratio 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 so-called close-wide and inner-outer degeneracies.
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    Systematic reanalysis of KMTNet microlensing events, paper I: Updates of the photometry pipeline and a new planet candidate
    (Oxford University Press on behalf of the Royal Astronomical Society., 2024-02-01) Yang H; Yee JC; Hwang K-H; Qian Q; Bond IA; Gould A; Hu Z; Zhang J; Mao S; Zhu W; Albrow MD; Chung S-J; Kim S-L; Park B-G; Han C; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Cha S-M; Kim D-J; Kim H-W; Lee C-U; Lee D-J; Lee Y; Pogge RW; Zang W; Abe F; Barry R; Bennett DP; Bhattacharya A; Donachie M; Fujii H; Fukui A; Hirao Y; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Silva SI; Li MCA; Matsubara Y; Muraki Y; Suzuki D; Tristram PJ; Yonehara A; Ranc C; Miyazaki S; Olmschenk G; Rattenbury NJ; Satoh Y; Shoji H; Sumi T; Tanaka Y; Yamawaki T
    In this work, we update and develop algorithms for KMTNet tender-love 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 MOA-2019-BLG-421/KMT-2019-BLG-2991. 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.