Two Low Mass-Ratio Microlensing Planets and Two Types of Central-Resonant Degeneracy
Westlake University（西湖大学）；Korea Astronomy and Space Science Institute（韩国天体物理与空间科学研究所）；Astronomical Observatory, University of Warsaw（华沙大学天文台）；Westlake Institute for Advanced Study（西湖高等研究院）；University of Canterbury, School of Physical and Chemical Sciences（坎特伯雷大学物理与化学科学学院）；Max-Planck-Institute for Astronomy（马克斯·普朗克天文学研究所）；Department of Astronomy, Ohio State University（俄亥俄州立大学天文学系）；Department of Physics, Chungbuk National University（忠北国立大学物理系）；National University of S（国立S大学）
Yuchen Tang, Weicheng Zang, Yoon-Hyun Ryu, Andrzej Udalski, Hongjing Yang, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Cheongho Han, Kyu-Ha Hwang, Youn Kil J… 展开作者
Yuchen Tang, Weicheng Zang, Yoon-Hyun Ryu, Andrzej Udalski, Hongjing Yang, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Cheongho Han, Kyu-Ha Hwang, Youn Kil Jung, In-Gu Shin, Yossi Shvartzvald, Jennifer C. Yee, Dong-Jin Kim, Chung-Uk Lee, Byeong-Gon Park, Leandro de Almeida, Yunyi Tang, Zhixing Li, Jiyuan Zhang, Hongyu Li, Shude Mao, Qiyue Qian, Dan Maoz, Christian Elias Borges, Fabrício Santos Kalaki, Altair Ramos Gomes Júnior, Wei Zhu, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radosław Poleski, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof A. Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz
We present observations and analysis of two low planet/host mass-ratio ($q$) microlensing planets discovered in high-magnification events. KMT-2025-BLG-0811Lb has $q \sim 4.5 \times 10^{-5}$, and a Bayesian analysis favors a super-Earth/mini-Neptune orbiting an M- or K-dwarf host at a projected separation of $\sim 3$ au. KMT-2025-BLG-0912Lb has $q = 2.6 \times 10^{-4}$ and likely hosts a super-Earth/mini-Neptune around either a low-mass M dwarf or a brown dwarf at $\sim 1$ au. Even with an observing cadence of $Γ> 30~{\rm hr}^{-1}$ during the planetary signal, KMT-2025-BLG-0811 still exhibits the "central-resonant" degeneracy. Reviewing nine such events, we find that the "central-resonant" degeneracy can be divided into two distinct types that occupy separate regions in the plane of $q$ and normalized source radius ($ρ$). Type~I events have similar $q$ but substantially different $ρ$ and are more difficult to resolve from the light curves. For Type~II events, the "resonant" solutions have relatively lower $q$ and larger $ρ$. Our review provides guidance for searching for the alternative solution once one solution has been identified.
We report two microlensing planet candidates discovered by the KMTNet survey in $2017$. However, both events have the 2L1S/1L2S degeneracy, which is an obstacle to claiming the discovery of the planets with certainty unless the degeneracy can be resolved. For KMT-2017-BLG-0962, the degeneracy cannot be resolved. If the 2L1S solution is correct, KMT-2017-BLG-0962 might be produced by a super Jupiter-mass planet orbiting a mid-M dwarf host star. For KMT-2017-BLG-1119, the light curve modeling favors the 2L1S solution but higher-resolution observations of the baseline object tend to support the 1…
We report the discovery of microlensing planet OGLE-2017-BLG-0373Lb. We show that while the planet-host system has an unambiguous microlens topology, there are two geometries within this topology that fit the data equally well, which leads to a factor 2.5 difference in planet-host mass ratio, i.e., $q=1.5\times 10^{-3}$ vs. $q=0.6\times 10^{-3}$. We show that this is an "accidental degeneracy" in the sense that it is due to a gap in the data. We dub it "the caustic-chirality degeneracy". We trace the mathematical origins of this degeneracy, which should enable similar degenerate solutions to b…
It is shown that the linear approximation of the central caustic for the planetary ($q\ll1$) microlensing is valid if $|1-s|\gg q^{1/3}$ (where $q$ is the mass ratio and $s$ is the projected separation in the unit of the Einstein ring radius of the primary). The condition is also consistent with the requirement that the binary separation is far from those in the resonant binary regime resulting in a single six-cusp caustic. Given that the linear approximation of the caustic is invariant under $s\leftrightarrow s^{-1}$, the close/wide binary degeneracy observed under the same condition may be u…
The offset microlensing degeneracy, recently proposed by Zhang et al. (2022), has been shown to generalize the close-wide and inner-outer caustic degeneracies into a unified regime of magnification degeneracy in the interpretation of 2-body planetary microlensing observations. While the inner-outer degeneracy expects the source trajectory to pass equidistant to the planetary caustics of the degenerate lens configurations, the offset degeneracy states that the same mathematical expression applies to any combination of the close, wide, and resonant caustic topologies, where the projected star-pl…
University of California, Berkeley（加州大学伯克利分校）；The Ohio State University（俄亥俄州立大学）
While gravitational microlensing by planetary systems provides unique vistas on the properties of exoplanets, observations of a given 2-body microlensing event can often be interpreted with multiple distinct physical configurations. Such ambiguities are typically attributed to the close-wide and inner-outer types of degeneracies that arise from transformation invariances and symmetries of microlensing caustics. However, there remain unexplained inconsistencies between aforementioned theories and observations. Here, leveraging a fast machine learning inference framework, we present the discover…
We present the analysis of the planetary microlensing event MOA-2016-BLG-319. The event light curve is characterized by a brief ($\sim 3$ days) anomaly near the peak produced by minor-image perturbations. From modeling, we find two distinct solutions that describe the observed light curve almost equally well. From the investigation of the lens-system configurations, we find that the confusion in the lensing solution is caused by the degeneracy between the two solutions resulting from the source passages on different sides of the planetary caustic. These degeneracies can be severe for major-ima…
We report new results for the gravitational microlensing target OGLE-2011-BLG-0950 from adaptive optics (AO) images using the Keck observatory. The original analysis by Choi et al. 2012 reports degenerate solutions between planetary and stellar binary lens systems. This is due to a degeneracy in high magnification events where the shape of the light curve peak can be explained by a source approach to two different cusp geometries with different source radius crossing times. This particular case is the most important type of degeneracy for exoplanet demographics, because the distinction between…
For microlenses with sufficiently low mass, the angular radius of the source star can be much larger than the angular Einstein ring radius of the lens. For such extreme finite source effect (EFSE) events, finite source effects dominate throughout the duration of the event. Here, we demonstrate and explore a continuous degeneracy between multiple parameters of such EFSE events. The first component in the degeneracy arises from the fact that the directly-observable peak change of the flux depends on both the ratio of the angular source radius to the angular Einstein ring radius and the fraction …
We report the discovery of a sub-Jupiter mass planet orbiting beyond the snow line of an M-dwarf most likely in the Galactic disk as part of the joint Spitzer and ground-based monitoring of microlensing planetary anomalies toward the Galactic bulge. The microlensing parameters are strongly constrained by the light curve modeling and in particular by the Spitzer-based measurement of the microlens parallax, $π_\mathrm{E}$. However, in contrast to many planetary microlensing events, there are no caustic crossings, so the angular Einstein radius, $θ_\mathrm{E}$ has only an upper limit based on the…
We analyze the combined Spitzer and ground-based data for OGLE-2017-BLG-1140 and show that the event was generated by a Jupiter-class $(m_p\simeq 1.6\,M_{\rm jup})$ planet orbiting a mid-late M dwarf $(M\simeq 0.2\,M_\odot)$ that lies $D_{LS}\simeq 1.0\,\mathrm{kpc}$ in the foreground of the microlensed, Galactic-bar, source star. The planet-host projected separation is $a_\perp \simeq 1.0\,\mathrm{au}$, i.e., well-beyond the snow line. By measuring the source proper motion ${\mathbfμ}_s$ from ongoing, long-term OGLE imaging, and combining this with the lens-source relative proper motion ${\ma…
K2 Campaign 9 (K2C9) was the first space-based microlensing parallax survey capable of measuring microlensing parallaxes of free-floating planet candidate microlensing events. Simultaneous to K2C9 observations we conducted the K2C9 Canada-France-Hawaii Telescope Multi-Color Microlensing Survey (K2C9-CFHT MCMS) in order to measure the colors of microlensing source stars to improve the accuracy of K2C9's parallax measurements. We describe the difference imaging photometry analysis of the K2C9-CFHT MCMS observations, and present the project's first data release. This includes instrumental differe…
We conducted a project of reinvestigating the 2017--2019 microlensing data collected by the high-cadence surveys with the aim of finding planets that were missed due to the deviations of planetary signals from the typical form of short-term anomalies. The project led us to find three planets including KMT-2017-BLG-2509Lb, OGLE-2017-BLG-1099Lb, and OGLE-2019-BLG-0299Lb. The lensing light curves of the events have a common characteristic that the planetary signals were produced by the crossings of faint source stars over the resonant caustics formed by giant planets located near the Einstein rin…
Current microlensing surveys are sensitive to free-floating planets down to Earth-mass objects. All published microlensing events attributed to unbound planets were identified based on their short timescale (below two days), but lacked an angular Einstein radius measurement (and hence lacked a significant constraint on the lens mass). Here, we present the discovery of a Neptune-mass free-floating planet candidate in the ultrashort ($t_{\rm E}=0.320\pm0.003$ days) microlensing event OGLE-2016-BLG-1540. The event exhibited strong finite-source effects, which allowed us to measure its angular Ein…
We report the discovery of a sub-Jovian-mass planet, OGLE-2014-BLG-0319Lb. The characteristics of this planet will be added into a future extended statistical analysis of the Microlensing Observations in Astrophysics (MOA) collaboration. The planetary anomaly of the light curve is characterized by MOA and OGLE survey observations and results in three degenerate models with different planetary mass-ratios of $q=(10.3,6.6,4.5)\times10^{-4}$, respectively. We find that the last two models require unreasonably small lens-source relative proper motions of $μ_{\rm rel}\sim1\;{\rm mas/yr}$. Consideri…
KMT-2025-BLG-1314 and KMT-2025-BLG-1392: two microlensing planetary/brown-dwarf candidates analyzed with differentiable code
Tsinghua University（清华大学）；Westlake University（西湖大学）；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究院）；University of Canterbury（坎特伯雷大学）；Max-Planck-Institute for Astronomy（马克斯·普朗克天文学研究所）；Ohio State University（俄亥俄州立大学）；Chungbuk National University（忠北国立大学）；National University of Science and Technology (UST)（韩国科学技术院）
A Newly Identified Degeneracy Keeps the Planetary Interpretation Viable for OGLE-2011-BLG-0950
Tsinghua University（清华大学）；Westlake University（西湖大学）；University of Warsaw（华沙大学）；Westlake Institute for Advanced Study（西湖高等研究院）；University of Warwick（华威大学）
We show that microlensing event KMT-2016-BLG-1107 displays a new type of degeneracy between wide-binary and close-binary Hollywood events in which a giant-star source envelops the planetary caustic. The planetary anomaly takes the form of a smooth, two-day "bump" far out on the falling wing of the light curve, which can be interpreted either as the source completely enveloping a minor-image caustic due to a close companion with mass ratio $q=0.036$, or partially enveloping a major-image caustic due to a wide companion with $q=0.004$. The best estimates of the companion masses are both in the p…
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…
We report the discovery of the microlensing planet OGLE-2018-BLG-0740Lb. The planet is detected with a very strong signal of $Δχ^2\sim 4630$, but the interpretation of the signal suffers from two types of degeneracies. One type is caused by the previously known close/wide degeneracy, and the other is caused by an ambiguity between two solutions, in which one solution requires to incorporate finite-source effects, while the other solution is consistent with a point-source interpretation. Although difficult to be firmly resolved based on only the photometric data, the degeneracy is resolved in s…
We analyze the binary gravitational microlensing event OGLE-2017-BLG-1130 (mass ratio q~0.45), the first published case in which the binary anomaly was only detected by the Spitzer Space Telescope. This event provides strong evidence that some binary signals can be missed by observations from the ground alone but detected by Spitzer. We therefore invert the normal procedure, first finding the lens parameters by fitting the space-based data and then measuring the microlensing parallax using ground-based observations. We also show that the normal four-fold space-based degeneracy in the single-le…
We report on the analysis of a microlensing event OGLE-2014-BLG-1722 that showed two distinct short term anomalies. The best fit model to the observed light curves shows that the two anomalies are explained with two planetary mass ratio companions to the primary lens. Although a binary source model is also able to explain the second anomaly, it is marginally ruled out by 3.1 $σ$. The 2-planet model indicates that the first anomaly was caused by planet "b" with a mass ratio of $q = (4.5_{-0.6}^{+0.7}) \times 10^{-4}$ and projected separation in unit of the Einstein radius, $s = 0.753 \pm 0.004$…
We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data. For this purpose, we conduct a systematic inspection of high-magnification microlensing events, with peak magnifications $A_{\rm peak}\gtrsim 30$, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identify an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens. We identify three degenerate solutions, i…
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 2 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 [KMT-2021-BLG-…
Mass Production of 2023 KMTNet Microlensing Planets. II: Two Planets and A Brown Dwarf
Westlake University（西湖大学）；Tsinghua University（清华大学）；Korea Astronomy and Space Science Institute（韩国天体宇宙科学研究所）；Astronomical Observatory, University of Warsaw（华沙大学天文台）；Department of Earth and Space Science, Graduate School of Science, Osaka University（大阪大学理学研究科地球・宇宙科学系）；University of Canterbury, School of Physical and Chemical Sciences（坎特伯雷大学物理与化学科学学院）
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 …
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 even…
A free-floating-planet microlensing event caused by a Saturn-mass object
Department of Astronomy, School of Physics, Peking University（北京大学物理学院天文学系）；Kavli Institute of Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究所）；Astronomical Observatory University of Warsaw（华沙大学天文台）；Department of Particle Physics and Astrophysics, Weizmann Institute of Science（魏茨曼科学研究所粒子物理与天体物理系）；Institute of Astronomy, University of Cambridge（剑桥大学天文研究所）；Department of Astronomy, University of Geneva（日内瓦大学天文学系）；Division of Astrophysics, Department of Physics, Lund University（隆德大学物理系天体物理分部）；Institute for Advanced Study in Physics, Zhejiang University（浙江大学物理学高等研究院）；Institute for Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；Department of Astronomy, Tsinghua University（清华大学天文学系）；Max-Planck-Institute for Astronomy（马克斯·普朗克天文学研究所）
Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. V. Detection Rates of Multiplanetary Systems in High Magnification Microlensing Events
The Astrometric Resoeccentric Degeneracy: Eccentric Single Planets Mimic 2:1 Resonant Planet Pairs in Astrometry
Center for Computational Astrophysics, Flatiron Institute（计算天体物理学中心，平顿研究所）；Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（卡弗里天体物理与空间研究所，麻省理工学院）；Department of Physics and Astronomy, Stony Brook University（物理与天文系，石溪大学）；School of Physics & Astronomy, Monash University（物理与天文学院，蒙纳士大学）
We present the analysis of the microlensing event OGLE-2015-BLG-1670, detected in a high-extinction field, very close to the Galactic plane. Due to the dust extinction along the line of sight, this event was too faint to be detected before it reached the peak of magnification. The microlensing light-curve models indicate a high-magnification event with a maximum of $A_\mathrm{max}\gtrsim200$, very sensitive to planetary deviations. An anomaly in the light curve has been densely observed by the microlensing surveys MOA, KMTNet, and OGLE. From the light-curve modeling, we find a planetary anomal…
We present the analysis of the microlensing event KMT-2018-BLG-1743. The light curve of the event, with a peak magnification $A_{\rm peak}\sim 800$, exhibits two anomaly features, one around the peak and the other on the falling side of the light curve. An interpretation with a binary lens and a single source (2L1S) cannot describe the anomalies. By conducting additional modeling that includes an extra lens (3L1S) or an extra source (2L2S) relative to a 2L1S interpretation, we find that 2L2S interpretations with a planetary lens system and a binary source best explain the observed light curve …
As the Kepler mission has done for hot exoplanets, the ESA Euclid and NASA Roman missions have the potential to create a breakthrough in our understanding of the demographics of cool exoplanets, including unbound, or "free-floating", planets (FFPs). In this study, we demonstrate the complementarity of the two missions and propose two joint-surveys to better constrain the mass and distance of microlensing events. We first demonstrate that an early brief Euclid survey (7 h) of the Roman microlensing fields will allow the measurement of a large fraction of events relative proper motions and lens …
