Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Youn Kil Jung
Weicheng Zang
Hanyue Wang
Cheongho Han
Andrew Gould
Andrzej Udalski
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Hongjing Yang
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Chung-Uk Lee
Dong-Joo Lee
Yongseok Lee
Abstract： We complete the publication of all microlensing planets (and ``possible planets'') identified by the uniform approach of the KMT AnomalyFinder system in the 21 KMT subprime fields during the 2019 observing season, namely KMT-2019-BLG-0298, KMT-2019-BLG-1216, KMT-2019-BLG-2783, OGLE-2019-BLG-0249, and OGLE-2019-BLG-0679 (planets), as well as OGLE-2019-BLG-0344, and KMT-2019-BLG-0304 (possible planets). The five planets have mean log mass-ratio measurements of $(-2.6,-3.6,-2.5,-2.2,-2.3)$, median mass estimates of $(1.81,0.094,1.16,7.12,3.34)\, M_{\rm Jup}$, and median distance estimates of $(6.7,2.7,5.9,6.4,5.6)\, {\rm kpc}$, respectively. The main scientific interest of these planets is that they complete the AnomalyFinder sample for 2019, which has a total of 25 planets that are likely to enter the statistical sample. We find statistical consistency with the previously published 33 planets from the 2018 AnomalyFinder analysis according to an ensemble of five tests. Of the 58 planets from 2018-2019, 23 were newly discovered by AnomalyFinder. Within statistical precision, half of all the planets have caustic crossings while half do not (as predicted by Zhu et al. 2014), an equal number of detected planets result from major-image and minor-image light-curve perturbations, and an equal number come from KMT prime fields versus subprime fields.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Andrew Gould
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Youn Kil Jung
Doeon Kim
Chung-Uk Lee
Shude Mao
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Dong-Joo Lee
Yongseok Lee
Abstract： We reexamine high-magnification microlensing events in the previous data collected by the KMTNet survey with the aim of finding planetary signals that were not noticed before. In this work, we report the planetary system KMT-2018-BLG-1988L that was found from this investigation. The planetary signal appears as a deviation with $\lesssim 0.2$~mag from a single-lens light curve and lasted for about 6 hours. The deviation exhibits a pattern of a dip surrounded by weak bumps on both sides of the dip. The analysis of the lensing light curve indicates that the signal is produced by a low mass-ratio ($q\sim 4\times 10^{-5}$) planetary companion located near the Einstein ring of the host star. The mass of the planet, $M_{\rm planet}=6.8^{+4.7}_{-3.5}~M_\oplus$ and $5.6^{+3.8}_{-2.8}~M_\oplus$ for the two possible solutions, estimated from the Bayesian analysis indicates that the planet is in the regime of a super-Earth. The host of the planet is a disk star with a mass of $M_{\rm host} = 0.47^{+0.33}_{-0.25}~M_\odot$ and a distance of $D_{\rm L}= 4.2^{+1.8}_{-.14}$~kpc. KMT-2018-BLG-1988Lb is the seventeenth microlensing planet with a mass below the upper limit of a super-Earth. The fact that 14 out of 17 microlensing planets with masses $\lesssim 10~M_\oplus$ were detected during the last 5 years since the full operation of the KMTNet survey indicates that the KMTNet database is an important reservoir of very low-mass planets.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Greg Olmschenk
David P. Bennett
Ian A. Bond
Weicheng Zang
Youn Kil Jung
Jennifer C. Yee
Etienne Bachelet
Fumio Abe
Richard K. Barry
Aparna Bhattacharya
Hirosane Fujii
Akihiko Fukui
Yuki Hirao
Stela Ishitani Silva
Yoshitaka Itow
Rintaro Kirikawa
Iona Kondo
Naoki Koshimoto
Yutaka Matsubara
Sho Matsumoto
Abstract： We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet with an estimated sub-Saturn mass. With a mass ratio $q = 3.17^{+0.28}_{-0.26} \times 10^{-4}$ and a separation $s = 1.3807^{+0.0018}_{-0.0018}$, the planet lies near the peak of the mass-ratio function derived by the MOA collaboration (Suzuki et al. 2016), 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 $m_\mathrm{planet} = 46^{+42}_{-24} \; M_\oplus$ and a host star of mass $M_\mathrm{host} = 0.43^{+0.39}_{-0.23} \; M_\odot$, located at a distance $D_L = 7.49^{+0.99}_{-1.13} \; \mathrm{kpc}$. For the second scenario, we estimate $m_\mathrm{planet} = 69^{+37}_{-34} \; M_\oplus$, $M_\mathrm{host} = 0.66^{+0.35}_{-0.32} \; M_\odot$, and $D_L = 7.81^{+0.93}_{-0.93} \; \mathrm{kpc}$. As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models and qualifies for inclusion in the extended MOA-II exoplanet microlensing sample.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Renkun Kuang
Weicheng Zang
Youn Kil Jung
Andrzej Udalski
Hongjing Yang
Shude Mao
Michael D. Albrow
Sun-Ju Chung
Andrew Gould
Cheongho Han
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung- Lee Kim
Chung-Uk Lee
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 $\Delta\chi^2 \simeq 18$. All of the feasible models include a planet with planet-to-host mass-ratios $10^{-3} \lesssim q \lesssim 10^{-2}$. A Bayesian analysis based on a Galactic model indicates that the planet is super-Jovian, and the projected host-planet separation is about 3 $\mathrm{au}$. Specifically, for the best-fit 3L1S model, the two stars have masses of $M_1=0.57^{+0.43}_{-0.32}M_{\odot}$, and $M_2=0.18^{+0.15}_{-0.10}M_{\odot}$, with projected separation of $1.3^{+0.5}_{-0.5}$ $\mathrm{au}$, 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 $0.55^{+0.44}_{-0.31}M_{\odot}$ 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 $q \gtrsim 2 \times 10^{-3}$, 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Chung-Uk Lee
Andrew Gould
Youn Kil Jung
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Doeon Kim
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Hongjing Yang
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Dong-Joo Lee
Yongseok Lee
Byeong-Gon Park
Abstract： 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. We first sort out lensing events with weak short-term anomalies in the lensing light curves from the visual inspection of all non-prime-field events, and then test various interpretations of the anomalies. From this procedure, we find two previously unidentified candidate planetary lensing events KMT-2017-BLG-0673 and KMT-2019-BLG-0414. It is found that the planetary signal of KMT-2017-BLG-0673 was produced by the source crossing over a planet-induced caustic, but it was previously missed because of the sparse coverage of the signal. On the other hand, the possibly planetary signal of KMT-2019-BLG-0414 was generated without caustic crossing, and it was previously missed due to the weakness of the signal. We identify a unique planetary solution for KMT-2017-BLG-0673. However, for KMT-2019-BLG-0414, we identify two pairs of planetary solutions, for each of which there are two solutions caused by the close-wide degeneracy, and a slightly less favored binary-source solution, in which a single lens mass gravitationally magnified a rapidly orbiting binary source with a faint companion (xallarap). From Bayesian analyses, it is estimated that the planet KMT-2017-BLG-0673Lb has a mass of $3.7^{+2.2}_{-2.1}~M_{\rm J}$, and it is orbiting a late K-type host star with a mass of $0.63^{+0.37}_{-0.35}~M_\odot$. Under the planetary interpretation of KMT-2010-BLG-0414L, a star with a mass of $0.74^{+0.43}_{-0.38}~M_\odot$ hosts a planet with a mass of $\sim 3.2$--3.6~$M_{\rm J}$ depending on the solution. We discuss the possible resolution of the planet-xallarap degeneracy of KMT-2019-BLG-0414 by future adaptive-optics observations on 30~m class telescopes.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
In-Gu Shin
Jennifer C. Yee
Andrew Gould
Kyu-Ha Hwang
Hongjing Yang
Ian A. Bond
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Youn Kil Jung
Yoon-Hyun Ryu
Yossi Shvartzvald
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Chung-Uk Lee
Dong-Joo Lee
Yongseok Lee
Byeong-Gon Park
Abstract： We present the analysis of three more planets from the KMTNet 2021 microlensing season. KMT-2021-BLG-0119Lb is a $\sim 6\, M_{\rm Jup}$ planet orbiting an early M-dwarf or a K-dwarf, KMT-2021-BLG-0192Lb is a $\sim 2\, M_{\rm Nep}$ planet orbiting an M-dwarf, and KMT-2021-BLG-0192Lb is a $\sim 1.25\, M_{\rm Nep}$ planet orbiting a very--low-mass M dwarf or a brown dwarf. These by-eye planet detections provide an important comparison sample to the sample selected with the AnomalyFinder algorithm, and in particular, KMT-2021-BLG-2294, is a case of a planet detected by-eye but not by-algorithm. KMT-2021-BLG-2294Lb is part of a population of microlensing planets around very-low-mass host stars that spans the full range of planet masses, in contrast to the planet population at $\lesssim 0.1\, $ au, which shows a strong preference for small planets.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Xiangyu Zhang
Andrzej Udalski
Jennifer C. Yee
Andrew Gould
Shude Mao
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Chung-Uk Lee
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 ($A \gtrsim 65$), 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Andrzej Udalski
Doeon Kim
Chung-Uk Lee
Michael D. Albrow
Sun-Ju Chung
Andrew Gould
Kyu-Ha Hwang
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Dong-Joo Lee
Yongseok Lee
Abstract： We search for microlensing planets with signals exhibiting no caustic-crossing features, considering the possibility that such signals may be missed due to their weak and featureless nature. For this purpose, we reexamine the lensing events found by the KMTNet survey before the 2019 season. From this investigation, we find two new planetary lensing events, KMT-2018-BLG-1976 and KMT-2018-BLG-1996. We also present the analysis of the planetary event OGLE-2019-BLG-0954, for which the planetary signal was known, but no detailed analysis has been presented before. We identify the genuineness of the planetary signals by checking various interpretations that can generate short-term anomalies in lensing light curves. From Bayesian analyses conducted with the constraint from available observables, we find that the host and planet masses are $(M_1, M_2)\sim (0.65~M_\odot, 2~M_{\rm J})$ for KMT-2018-BLG-1976L, $\sim (0.69~M_\odot, 1~M_{\rm J})$ for KMT-2018-BLG-1996L, and $\sim (0.80~M_\odot, 14~M_{\rm J})$ for OGLE-2019-BLG-0954L. The estimated distance to OGLE-2019-BLG-0954L, $3.63^{+1.22}_{-1.64}$~kpc, indicates that it is located in the disk, and the brightness expected from the mass and distance matches well the brightness of the blend, indicating that the lens accounts for most of the blended flux. The lens of OGLE-2019-BLG-0954 could be resolved from the source by conducting high-resolution follow-up observations in and after 2024.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hongjing Yang
Weicheng Zang
Andrew Gould
Jennifer C. Yee
Kyu-Ha Hwang
Grant Christie
Takahiro Sumi
Jiyuan Zhang
Shude Mao
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Abstract： Follow-up observations of high-magnification gravitational microlensing events can fully exploit their intrinsic sensitivity to detect extrasolar planets, especially those with small mass ratios. To make followup more uniform and efficient, we develop a system, HighMagFinder, based on the real-time data from the Korean Microlensing Telescope Network (KMTNet) to automatically alert possible ongoing high-magnification events. We started a new phase of follow-up observations with the help of HighMagFinder in 2021. Here we report the discovery of two planets in high-magnification microlensing events, KMT-2021-BLG-0171 and KMT-2021-BLG-1689, which were identified by the HighMagFinder. We find that both events suffer the ``central-resonant'' caustic degeneracy. The planet-host mass-ratio is $q\sim4.7\times10^{-5}$ or $q\sim 2.2\times10^{-5}$ for KMT-2021-BLG-0171, and $q\sim2.5\times10^{-4}$ or $q\sim 1.8\times10^{-4}$ for KMT-2021-BLG-1689. Together with two events reported by Ryu et al. (2022), 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 new factor for weighting the probability of each solution from the phase-space. The resonant interpretations for the two events are disfavored under this consideration. This factor can be included in future statistical studies to weight degenerate solutions.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Weicheng Zang
Kyu-Ha Hwang
Andrzej Udalski
Tianshu Wang
Wei Zhu
Takahiro Sumi
Jennifer C. Yee
Andrew Gould
Shude Mao
Xiangyu Zhang
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Abstract： In order to exhume the buried signatures of "missing planetary caustics" in the KMTNet data, we conducted a systematic anomaly search to the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search reveals the lowest mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet-host mass ratio of $q = (1.25 \pm 0.13) \times 10^{-5}$. A Bayesian analysis yields estimates of the mass of the host star, $M_{\rm host} = 0.61_{-0.24}^{+0.29}~M_\odot$, the mass of its planet, $M_{\rm planet} = 2.48_{-0.98}^{+1.19}~M_{\oplus}$, the projected planet-host separation, $a_\perp = 3.4_{-0.5}^{+0.5}$ au, and the lens distance of $D_{\rm L} = 6.8_{-0.9}^{+0.6}$ kpc. The discovery of this very low mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet-host mass-ratio function down to $q \sim 10^{-5}$.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Youn Kil Jung
Andrew Gould
Doeon Kim
Chung-Uk Lee
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Hyoun-Woo Kim
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Hongjing Yang
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Dong-Joo Lee
Yongseok Lee
Abstract： We systematically inspect 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 binary-lens or binary-source interpretations. From the inspection, we find that interpreting the three lensing events OGLE-2018-BLG-0584, KMT-2018-BLG-2119, and KMT-2021-BLG-1122 requires four-body (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 \citet{Han2023}, here we present the 3L1S analysis of the KMT-2021-BLG-1122. It is found that the lens of the event KMT-2021-BLG-1122 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 $(s_2, q_2)\sim (1.4, 0.53)$ and $(s_3, q_3) \sim (1.6, 0.24)$. By conducting a Bayesian analysis, we estimate that the masses of the individual lens components are $(M_1, M_2, M_3)\sim (0.47\,M_\odot, 0.24\,M_\odot, 0.11\,M_\odot)$. The companions are separated in projection from the primary by $(a_{\perp,2}, a_{\perp,3})\sim (3.5, 4.0)$~AU. The lens of KMT-2018-BLG-2119 is the first triple stellar system detected via microlensing.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Weicheng Zang
Hongjing Yang
Cheongho Han
Chung-Uk Lee
Andrzej Udalski
Andrew Gould
Shude Mao
Xiangyu Zhang
Wei Zhu
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Abstract： We report the complete statistical planetary sample from the prime fields ($\Gamma \geq 2~{\rm hr}^{-1}$) 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 14 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 $6.34 \times 10^{-4}, 4.89 \times 10^{-3}$ and $6.18 \times 10^{-4}$, 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 $q_{\rm break} = 1.7 \times 10^{-4}$ 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Andrew Gould
Doeon Kim
Youn Kil Jung
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Chung-Uk Lee
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Dong-Joo Lee
Yongseok Lee
Byeong-Gon Park
Richard W. Pogge
Abstract： The light curve of the microlensing event KMT-2021-BLG-1898 exhibits a short-term central anomaly with double-bump features that cannot be explained by the usual binary-lens or binary-source interpretations. With the aim of interpreting the anomaly, we analyze the lensing light curve under various sophisticated models. 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 $q\sim 1.5\times 10^{-3}$, and the source is a binary composed of a turn off or a subgiant star and a mid K dwarf. The double-bump feature of the anomaly can also be depicted by a triple-lens 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 $\Delta\chi^2=[14.3$--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, KMT-2021-BLG-1898 is the third planetary lensing event occurring on a binary stellar system, following MOA-2010-BLG-117 and KMT-2018-BLG-1743. Under the 2L2S interpretation, we identify two solutions resulting from the close-wide degeneracy in determining the planet-host separation. From a Bayesian analysis, we estimate that the planet has a mass of $\sim 0.7$--0.8~$M_{\rm J}$, and it orbits an early M dwarf host with a mass of $\sim 0.5~M_\odot$. The projected planet-host separation is $\sim 1.9$~AU and $\sim 3.0$~AU according to the close and wide solutions, respectively.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Amber Malpas
Michael D. Albrow
Jennifer C. Yee
Andrew Gould
Andrzej Udalski
Antonio Herrera Martin
Spitzer Team
Charles A. Beichman
Geoffery Bryden
Sebastiano Calchi Novati
Sean Carey
Calen B. Henderson
B. Scott Gaudi
Yossi Shvartzvald
Wei Zhu
KMTNet Collaboration
Sang-Mok Cha
Sun-Ju Chung
Cheongho Han
Kyu-Ha Hwang
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 ($M_1 = 170^{+40}_{-50} M_J$ and $M_2 = 110^{+20}_{-30} M_J$), or well below ($M_1 = 22.5^{+0.7}_{-0.4} M_J$ and $M_2 = 13.3^{+0.4}_{-0.3} M_J$) 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 ten years through infrared adaptive-optics imaging with a 40 m class telescope.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Andrzej Udalski
Youn Kil Jung
Doeon Kim
Hongjing Yang
Michael D. Albrow
Sun-Ju Chung
Andrew Gould
Kyu-Ha Hwang
Hyoun-Woo Kim
Chung-Uk Lee
Yoon-Hyun Ryu
Yossi Shvartzvald
In-Gu Shin
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Dong-Joo Lee
Abstract： We conduct a systematic investigation of the microlensing data collected during the previous observation seasons for the purpose of reanalyzing anomalous lensing events with no suggested plausible models. We find that two anomalous lensing events OGLE-2018-BLG-0584 and KMT-2018-BLG-2119 cannot be explained with the usual models based on either a binary-lens single-source (2L1S) or a single-lens binary-source (1L2S) interpretation. We test the feasibility of explaining the light curves with more sophisticated models by adding an extra lens (3L1S model) or a source (2L2S model) component to the 2L1S lens-system configuration. We find that a 2L2S interpretation well explains the light curves of both events, for each of which there are a pair of solutions resulting from the close and wide degeneracy. For the event OGLE-2018-BLG-0584, the source is a binary composed of two K-type stars, and the lens is a binary composed of two M dwarfs. For KMT-2018-BLG-2119, the source is a binary composed of two dwarfs of G and K spectral types, and the lens is a binary composed of a low-mass M dwarf and a brown dwarf.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Weicheng Zang
Yossi Shvartzvald
Andrzej Udalski
Jennifer C. Yee
Chung-Uk Lee
Takahiro Sumi
Xiangyu Zhang
Hongjing Yang
Shude Mao
Sebastiano Calchi Novati
Andrew Gould
Wei Zhu
Charles A. Beichman
Geoffery Bryden
Sean Carey
B. Scott Gaudi
Calen B. Henderson
Przemek Mróz
Jan Skowron
Radoslaw Poleski
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 $q = (2.65 \pm 0.16) \times 10^{-3}$. The ground-based observations yield a constraint on the angular Einstein radius $\theta_{\rm E}$, and the microlensing parallax vector $\vec{\pi}_{\rm E}$, 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 $M_{\rm planet} = 0.26_{-0.11}^{+0.22}~M_{J}$ planet orbiting an $M_{\rm host} = 0.093_{-0.038}^{+0.082}~M_{\odot}$, 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 $0.13 {M_{\odot}}$ 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
D. Specht
R. Poleski
M. T. Penny
E. Kerins
I. McDonald
Chung-Uk Lee
A. Udalski
I. A. Bond
Y. Shvartzvald
Weicheng Zang
R. A. Street
D. W. Hogg
B. S. Gaudi
T. Barclay
G. Barentsen
S. B. Howell
F. Mullally
C. B. Henderson
S. T. Bryson
D. A. Caldwell
Abstract： We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens--source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data, and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass--position--velocity degeneracy and measure the planet's mass directly. We find a host mass of $0.58\pm0.04 ~{\rm M}_\odot$ and a planetary mass of $1.1\pm0.1 ~{\rm M_J}$. The system lies at a distance of $5.2\pm0.2~$kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be $4.2\pm0.3~$au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}~$au and orbital period $P = 13^{+9}_{-2}~$yr. This makes K2-2016-BLG-0005Lb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA's Nancy Grace Roman Space Telescope and, possibly, ESA's Euclid mission, will provide demanding tests of current planet formation models.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Cheongho Han
Doeon Kim
Andrew Gould
Andrzej Udalski
Ian A. Bond
Valerio Bozza
Youn Kil Jung
Michael D. Albrow
Sun-Ju Chung
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Weicheng Zang
Sang-Mok Cha
Dong-Jin Kim
Seung-Lee Kim
Chung-Uk Lee
Dong-Joo Lee
Abstract： With the aim of finding short-term planetary signals, we investigated the data collected from the high-cadence microlensing surveys. 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. It is found that three of the planetary systems have mass ratios of the order of $10^{-4}$ and the other has a mass ratio slightly greater than $10^{-3}$. 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 $\sim 0.10$, $\sim 0.38$, and $\sim 0.12$ times of 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, $M_{\rm host}\sim 0.08~M_\odot$, 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 $\sim [0.3$--$0.6]~M_\odot$. The discoveries of the planets well demonstrate the capability of the current high-cadence microlensing surveys in detecting low-mass planets.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hanyue Wang
Weicheng Zang
Wei Zhu
Kyu-Ha Hwang
Andrzej Udalski
Andrew Gould
Cheongho Han
Michael D. Albrow
Sun-Ju Chung
Youn Kil Jung
Doeon Kim
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Chung-Uk Lee
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 (KMTNet), 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 $q=2.1\times 10^{-4}$ 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.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jiyuan Zhang
Weicheng Zang
Youn Kil Jung
Hongjing Yang
Andrew Gould
Takahiro Sumi
Shude Mao
Subo Dong
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Kyu-Ha Hwang
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Jennifer C. Yee
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Abstract： We present the observations and analysis of a high-magnification microlensing planetary event, KMT-2022-BLG-0440, for which the weak and short-lived planetary signal was covered by both the KMTNet survey and follow-up observations. The binary-lens models with a central caustic provide the best fits, with a planet/host mass ratio, $q = 0.75$--$1.00 \times 10^{-4}$ at $1\sigma$. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by $\Delta\chi^2 > 70$. The binary-source model can fit the anomaly well but is rejected by the ``color argument'' on the second source. From Bayesian analyses, it is estimated that the host star is likely a K or M dwarf located in the Galactic disk, the planet probably has a Neptune-mass, and the projected planet-host separation is $1.9^{+0.6}_{-0.7}$ or $4.6^{+1.4}_{-1.7}$ au, subject to the close/wide degeneracy. This is the third $q < 10^{-4}$ planet from a high-magnification planetary signal ($A \gtrsim 65$). Together with another such planet, KMT-2021-BLG-0171Lb, the ongoing follow-up program for the KMTNet high-magnification events has demonstrated its ability in detecting high-magnification planetary signals for $q < 10^{-4}$ planets, which are challenging for the current microlensing surveys.
Peer Review Status:Awaiting Review
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