Journal Articles

Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915

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    KMT-2021-BLG-1150Lb: Microlensing planet detected through a densely covered planetary-caustic signal
    (EDP Sciences, France, 2023-07) Han CH; Jung YK; Bond IA; Gould A; Chung S-J; Albrow MD; Hwang K-H; Ryu Y-H; Shin I-G; Shvartzvald Y; Yang H; Yee JC; Zang W; Cha S-M; Kim D; Kim D-J; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Ishitani Silva S; Itow Y; 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; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    Aims. Recently, there have been reports of various types of degeneracies in the interpretation of planetary signals induced by planetary caustics. In this work we check whether such degeneracies persist in the case of well-covered signals by analyzing the lensing event KMT-2021-BLG-1150, the light curve of which exhibits a densely and continuously covered short-term anomaly. Methods. In order to identify degenerate solutions, we thoroughly investigated the parameter space by conducting dense grid searches for the lensing parameters. We then checked the severity of the degeneracy among the identified solutions. Results. We identify a pair of planetary solutions resulting from the well-known inner-outer degeneracy, and find that interpreting the anomaly is not subject to any degeneracy other than the inner-outer degeneracy. The measured parameters of the planet separation (normalized to the Einstein radius) and mass ratio between the lens components are (s, q)in ∼ (1.297, 1.10 - 10-3) for the inner solution and (s, q)out ∼ (1.242, 1.15 - 10-3) for the outer solution. According to a Bayesian estimation, the lens is a planetary system consisting of a planet with a mass Mp = 0.88-0.36+0.38 Mj and its host with a mass Mh = 0.73-0.30+0.32 M· lying toward the Galactic center at a distance DL = 3.8-1.2+1.3 kpc. By conducting analyses using mock data sets prepared to mimic those obtained with data gaps and under various observational cadences, we find that gaps in data can result in various degenerate solutions, while the observational cadence does not pose a serious degeneracy problem as long as the anomaly feature can be delineated.
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    KMT-2021-BLG-0284, KMT-2022-BLG-2480, and KMT-2024-BLG-0412: Three microlensing events involving two lens masses and two source stars
    (EDP Sciences for The European Southern Observatory, 2024-12) Han C; Udalski A; Bond IA; Lee C-U; Gould A; Albrow MD; Chung S-J; Hwang K-H; Jung YK; 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; Szymanski MK; Skowron J; Poleski R; Soszynski 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; Ishitani Silva S; 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 carried out a project involving the systematic analysis of microlensing data from the Korea Microlensing Telescope Network survey. The aim of this project is to identify lensing events with complex anomaly features that are difficult to explain using standard binary-lens or binary-source models. Methods. Our investigation reveals that the light curves of microlensing events KMT-2021-BLG-0284, KMT-2022-BLG-2480, and KMT-2024BLG-0412 display highly complex patterns with three or more anomaly features. These features cannot be adequately explained by a binary-lens (2L1S) model alone. However, the 2L1S model can effectively describe certain segments of the light curve. By incorporating an additional source into the modeling, we identified a comprehensive model that accounts for all the observed anomaly features. Results. Bayesian analysis, based on constraints provided by lensing observables, indicates that the lenses of KMT-2021-BLG-0284 and KMT-2024-BLG-0412 are binary systems composed of M dwarfs. For KMT-2022-BLG-2480, the primary lens is an early K-type main-sequence star with an M dwarf companion. The lenses of KMT-2021-BLG-0284 and KMT-2024-BLG-0412 are likely located in the bulge, whereas the lens of KMT-2022-BLG-2480 is more likely situated in the disk. In all events, the binary stars of the sources have similar magnitudes due to a detection bias favoring binary source events with a relatively bright secondary source star, which increases detection efficiency.
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    KMT-2022-BLG-0475Lb and KMT-2022-BLG-1480Lb: Microlensing ice giants detected via the non-caustic-crossing channel
    (EDP Sciences, France, 2023-08) Han C; Lee C-U; Bond IA; Zang W; Chung S-J; Albrow MD; Gould A; Hwang K-H; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Yang H; Yee JC; Cha S-M; Kim D; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Mao S; Zhu W; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Ishitani Silva S; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    Aims. We investigate the microlensing data collected in the 2022 season from high-cadence microlensing surveys in order to find weak signals produced by planetary companions to lenses. Methods. From these searches, we find that two lensing events, KMT-2022-BLG-0475 and KMT-2022-BLG-1480, exhibit weak short-term anomalies. From a detailed modeling of the lensing light curves, we determine that the anomalies are produced by planetary companions with a mass ratio to the primary of q 1.8 A-104 for KMT-2022-BLG-0475L and q 4.3 A-104 for KMT-2022-BLG-1480L. Results. We estimate that the host and planet masses and the projected planet-host separation are (Mh/M, Mp/MU, a/au) = (0.430.23+0.35, 1.730.92+1.42, 2.030.38+0.25) for KMT-2022-BLG-0475L and (0.180.09+0.16, 1.820.92+1.60, 1.220.14+0.15) for KMT-2022-BLG-1480L, where MU denotes the mass of Uranus. The two planetary systems have some characteristics in common: the primaries of the lenses are early-mid M dwarfs that lie in the Galactic bulge, and the companions are ice giants that lie beyond the snow lines of the planetary systems.
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    Brown dwarf companions in binaries detected in the 2021 season high-cadence microlensing surveys
    (EDP Sciences on behalf of The European Southern Observatory, 2023-10) Han C; Jung YK; Bond IA; Chung S-J; Albrow MD; Gould A; Hwang K-H; Lee C-U; Ryu Y-H; Shin I-G; Shvartzvald Y; Yang H; Yee JC; Zang W; Cha S-M; Kim D-J; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Ishitani Silva S; 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. As a part of the project aiming to build a homogeneous sample of binary-lens (2L1S) events containing brown dwarf (BD) companions, we investigate the 2021 season microlensing data collected by the Korea Microlensing Telescope Network (KMTNet) survey. Methods. For this purpose, we first identified 2L1S events by conducting systematic analyses of anomalous lensing events. We then selected candidate BD companion events by applying the criterion that the mass ratio of the lens components is lower than qth∼ 0.1. Results. From this procedure, we find four events including KMT-2021-BLG-0588, KMT-2021-BLG-1110, KMT-2021-BLG-1643, and KMT-2021-BLG-1770, for which the estimated mass ratios are q∼ 0.10, 0.07, 0.08, and 0.15, respectively. Event KMT-2021-BLG-1770 was selected as a candidate even though the mass ratio is slightly greater than qth because the lens mass expected from the measured short timescale of the event, tE∼ 7.6 days, is low. From the Bayesian analyses, we estimate that the primary and companion masses are (M1/M⊙,M2/M⊙) = (0.54- 0.24+0.31, 0.053- 0.023+0.031) for KMT-2021-BLG-0588L, (0.74- 0.35+0.27, 0.055- 0.026+0.020) for KMT-2021-BLG-1110L, (0.73- 0.17+0.24,0.061- 0.014+0.020) for KMT-2021-BLG-1643L, and (0.13- 0.07+0.18, 0.020- 0.011+0.028) for KMT-2021-BLG-1770L. It is estimated that the probabilities that the lens companions are in the BD mass range are 82%, 85%, 91%, and 59% for the individual events. To confirm the BD nature of the lens companions found in this and previous works by directly imaging the lenses from future high-resolution adaptive-optics (AO) followup observations, we provide the lens-source separations expected in 2030, which is the approximate year of the first AO light on 30 m class telescopes
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    Four sub-Jovian-mass planets detected by high-cadence microlensing surveys
    (EDP Sciences on behalf of the European Southern Observatory, 2022-08-05) Han C; Kim D; Gould A; Udalski A; Bond IA; Bozza V; Jung YK; Albrow MD; Chung S-J; Hwang K-H; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Zang W; Cha S-M; Kim D-J; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozaowski S; Ulaczyk K; Rybicki KA; Iwanek P; Abe F; Barry RK; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Itow Y; Kirikawa R; Koshimoto N; Kondo I; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Olmschenk G; Okamura A; Ranc C; Rattenbury NJ; Satoh Y; Silva SI; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H
    Aims. With the aim of finding short-term planetary signals, we investigated the data collected from current high-cadence microlensing surveys. Methods. From this investigation, we found four planetary systems with low planet-to-host mass ratios, including OGLE-2017-BLG-1691L, KMT-2021-BLG-0320L, KMT-2021-BLG-1303L, and KMT-2021-BLG-1554L. 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 sub-Jovian masses. The planet masses of KMT-2021-BLG-0320Lb, KMT-2021-BLG-1303Lb, and KMT-2021-BLG-1554Lb correspond to ∼0.10, ∼0.38, and ∼0.12 times the mass of the Jupiter, and the mass of OGLE-2017-BLG-1691Lb corresponds to that of the Uranus. The estimated mass of the planet host KMT-2021-BLG-1554L, Mhost ∼ 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 low-mass stars with masses in the range of ∼[0.3-0.6] M⊙. The discoveries of the planets fully demonstrate the capability of the current high-cadence microlensing surveys in detecting low-mass planets.
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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.