arXiv subjects

In-Gu Shin

Publications and source records attributed to In-Gu Shin.

At least 91 records · Page 5Linked to original sources

arXiv2023

Systematic KMTNet Planetary Anomaly Search, Paper VII: Complete Sample of $q < 10^{-4}$ Planets from the First Four-Year Survey

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.

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arXiv2022

OGLE-2018-BLG-0584 and KMT-2018-BLG-2119: two microlensing events with two lens masses and two source stars

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.

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arXiv2022

Mass Production of 2021 KMTNet Microlensing Planets III: Analysis of Three Giant Planets

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.

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arXiv2022

Brown-dwarf companions in microlensing binaries detected during the 2016--2018 seasons

With the aim of finding microlensing binaries containing brown-dwarf (BD) companions, we investigate the microlensing survey data collected during the 2016--2018 seasons. For this purpose, we first conducted modeling of 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 $q \lesssim 0.1$. From this procedure, we identify 6 binaries with candidate BD companions, including 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. We estimate 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 $P_{\rm BD}> 80\%$. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with $P_{\rm BD}=61\%$ and 69\%, respectively.

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arXiv2022

OGLE-2019-BLG-1470LABc: Another Microlensing Giant Planet in a Binary System?

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 $Δχ^2 \simeq 18$. 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.

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arXiv2022

KMT-2017-BLG-0673Lb and KMT-2019-BLG-0414Lb: Two microlensing planets detected in peripheral fields of KMTNet survey

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.

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arXiv2022

OGLE-2019-BLG-0362Lb: A super-Jovian-mass planet around a low-mass star

We present the analysis of a planetary microlensing event OGLE-2019-BLG-0362 with a short-duration anomaly $(\sim 0.4\, \rm days)$ near the peak of the light curve, which is caused by the resonant caustic. The event has a severe degeneracy with $Δχ^2 = 0.9$ between the close and the wide binary lens models both with planet-host mass ratio $q \simeq 0.007$. We measure the angular Einstein radius but not the microlens parallax, and thus we perform a Bayesian analysis to estimate the physical parameters of the lens. We find that the OGLE-2019-BLG-0362L system is a super-Jovian-mass planet $M_{\rm p}=3.26^{+0.83}_{-0.58}\, M_{\rm J}$ orbiting an M dwarf $M_{\rm h}=0.42^{+0.34}_{-0.23}\, M_\odot$ at a distance $D_{\rm L} =5.83^{+1.04}_{-1.55}\, \rm kpc$. The projected star-planet separation is $a_{\perp} = 2.18^{+0.58}_{-0.72}\, \rm AU$, which indicates that the planet lies beyond the snow line of the host star.

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arXiv2022

OGLE-2018-BLG-0799Lb: a $q \sim 2.7 \times 10^{-3}$ Planet with Spitzer Parallax

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 $θ_{\rm E}$, and the microlensing parallax vector $\vecπ_{\rm E}$, 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.

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arXiv2022

Systematic KMTNet Planetary Anomaly Search. IV. Complete Sample of 2019 Prime-Field

We report the complete statistical planetary sample from the prime fields ($Γ\geq 2~{\rm hr}^{-1}$) 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.

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arXiv2022

Mass Production of 2021 KMTNet Microlensing Planets II

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 4 planets, (KMT-2021-BLG-0712Lb, KMT-2021-BLG-0909Lb, KMT-2021-BLG-2478Lb, and KMT-2021-BLG-1105Lb), with planet-host mass ratios in the range -3.3 < log q < -2.2. This brings the total of secure, by-eye, 2021 KMTNet planets to 16, including 8 in this series. The by-eye sample is an important check of the completeness of semi-automated detections, which are the basis for statistical analyses. One of the planets, KMT-2021-BLG-1105Lb, is blended with a relatively bright $(I,V)\sim (18.9,21.6)$ star that may be the host. This could be verified immediately by high-resolution imaging. If so, the host is an early G dwarf, and the planet could be characterized by radial-velocity observations on 30m class telescopes.

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arXiv2022

Systematic KMTNet Planetary Anomaly Search. VI. Complete Sample of 2018 Sub-Prime-Field Planets

We complete the analysis of all 2018 sub-prime-field microlensing planets identified by the KMTNet AnomalyFinder. Among the 9 previously unpublished events with clear planetary solutions, 6 are clearly planetary (KMT-2018-BLG-0030, KMT-2018-BLG-0087, KMT-2018-BLG-0247, OGLE-2018-BLG-0298, KMT-2018-BLG-2602, and OGLE-2018-BLG-1119), while the remaining 3 are ambiguous in nature. In addition, there are 8 previously published sub-prime field planets that were selected by the AnomalyFinder algorithm. Together with a companion paper (Gould et al. 2022) on 2018 prime-field planets, this work lays the basis for the first statistical analysis of the planet mass-ratio function based on planets identified in KMTNet data. As expected (Zhu et al. 2014), half (17/33) of the 2018 planets likely to enter the mass-ratio analysis have non-caustic-crossing anomalies. However, only 1 of the 5 non-caustic anomalies with planet-host mass ratio $q<10^{-3}$ was discovered by eye (compared to 7 of the 12 with $q>10^{-3}$), showing the importance of the semi-automated AnomalyFinder search.

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arXiv2022

Systematic KMTNet Planetary Anomaly Search, Paper I: OGLE-2019-BLG-1053Lb, A Buried Terrestrial Planet

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 $q \sim 10^{-5}$.

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arXiv2022

KMT-2021-BLG-0171Lb and KMT-2021-BLG-1689Lb: Two Microlensing Planets in the KMTNet High-cadence Fields with Followup Observations

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.

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arXiv2022

Four sub-Jovian-mass planets detected by high-cadence microlensing surveys

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.

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arXiv2022

MOA-2019-BLG-008Lb: a new microlensing detection of an object at the planet/brown dwarf boundary

We report on the observations, analysis and interpretation of the microlensing event MOA-2019- BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite source effects were observed. Therefore the angular Einstein ring radius cannot be measured from the light curve alone. However, the large event duration, t E about 80 days, allows a precise measurement of the microlensing parallax. In addition to the constraints on the angular radius and the apparent brightness I s of the source, we employ the Besancon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two Galactic models: the companion is likely a resident of the brown dwarf desert with a mass Mp about 30 MJup and the host is a main sequence dwarf star. The lens lies along the line of sight to the Galactic Bulge, at a distance of less then4 kpc. We estimate that in about 10 years, the lens and source will be separated by 55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground or space-based observatories.

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arXiv2022

KMT-2021-BLG-0240: Microlensing event with a deformed planetary signal

The light curve of the microlensing event KMT-2021-BLG-0240 exhibits a short-lasting anomaly with complex features near the peak at the 0.1~mag level from a single-lens single-source model. We conducted modeling of the lensing light curve under various interpretations to reveal the nature of the anomaly. It is found that the anomaly cannot be explained with the usual model based on a binary-lens (2L1S) or a binary-source (1L2S) interpretation. However, a 2L1S model with a planet companion can describe part of the anomaly, suggesting that the anomaly may be deformed by a tertiary lens component or a close companion to the source. From the additional modeling, we find that all the features of the anomaly can be explained with either a triple-lens (3L1S) model or a binary-lens binary-source (2L2S) model obtained under the 3L1S interpretation. However, it is difficult to validate the 2L2S model because the light curve does not exhibit signatures induced by the source orbital motion and the ellipsoidal variations expected by the close separation between the source stars according to the model. We, therefore, conclude that the two interpretations cannot be distinguished with the available data, and either can be correct. According to the 3L1S solution, the lens is a planetary system with two sub-Jovian-mass planets in which the planets have masses of 0.32--0.47~$M_{\rm J}$ and 0.44--0.93~$M_{\rm J}$, and they orbit an M dwarf host. According to the 2L2S solution, on the other hand, the lens is a single planet system with a mass of $\sim 0.21~M_{\rm J}$ orbiting a late K-dwarf host, and the source is a binary composed of a primary of a subgiant or a turnoff star and a secondary of a late G dwarf. The distance to the planetary system varies depending on the solution: $\sim 7.0$~kpc according to the 3L1S solution and $\sim 6.6$~kpc according to the 2L2S solution.

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arXiv2022

KMT-2021-BLG-1898: Planetary microlensing event involved with binary source stars

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 $Δχ^2=[14.3$--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.

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arXiv2022

Systematic KMTNet Planetary Anomaly Search. V. Complete Sample of 2018 Prime-Field

We complete the analysis of all 2018 prime-field microlensing planets identified by the KMTNet AnomalyFinder. Among the 10 previously unpublished events with clear planetary solutions, 8 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 4 previously published new AnomalyFinder events and 12 previously published (or in preparation) planets that were discovered by eye, thismakes a total of 24 2018 prime-field planets discovered or recovered by AnomalyFinder. Together with a paper in preparation on 2018 sub-prime 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 of Hwang et al. (2022) to each event, we identify the small modification in their formalism that is needed to unify the so-called close/wide and inner/outer degeneracies, as conjectured by

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