Sang-Mok Cha
A5002320920- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Astronomical Observations and Instrumentation
- Galaxies: Formation, Evolution, Phenomena
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Atmospheric Ozone and Climate
- History and Developments in Astronomy
- Calibration and Measurement Techniques
- Spacecraft Design and Technology
- Optical Systems and Laser Technology
- Astrophysical Phenomena and Observations
- CCD and CMOS Imaging Sensors
- Astrophysics and Cosmic Phenomena
- Space Exploration and Technology
- Advanced Frequency and Time Standards
- solar cell performance optimization
- Infrared Target Detection Methodologies
- Particle accelerators and beam dynamics
- Isotope Analysis in Ecology
- Advanced Thermodynamic Systems and Engines
Kyung Hee University
2014-2024
Korea Astronomy and Space Science Institute
2014-2024
Pukyong National University
2024
Max Planck Society
1989-2018
Max Planck Institute for Astronomy
2018
Korea University of Science and Technology
2016
Chungbuk National University
2006-2008
Max Planck Institute for Plasma Physics
1989
The Korea Microlensing Telescope Network (KMTNet) is a wide-field photometric system installed by the Astronomy and Space Science Institute (KASI). Here, we present overall technical specifications of KMTNet observation system, test results, data transfer image processing procedure, finally, science programs. consists three 1.6 m optical telescopes equipped with mosaic CCD cameras 18k pixels. Each telescope provides 2.0 square degree field view. We have finished installing all sequentially...
We analyze an ensemble of microlensing events from the 2015 Spitzer campaign, all which were densely monitored by ground-based high-cadence survey teams. The simultaneous observations and ground yield measurements parallax vector $\pi_{\rm E}$, compact constraints on microlens properties are derived, including $\lesssim$25\% uncertainties lens mass distance. With current sample, we demonstrate that majority microlenses indeed in range M dwarfs. planet sensitivities 41 sample calculated,...
Abstract We report the discovery of a giant planet in OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite relatively short event timescale t E ∼ 7.5 days. Einstein radius is unusually small, θ = 0.065 mas, implying that lens system either has very low mass or lies much closer to microlensed source than Sun, both. A Bayesian analysis yields component masses and source-lens distance , this brown-dwarf/Jupiter...
Some low-mass planets are expected to be ejected from their parent planetary systems during early stages of system formation. According planet-formation theories, such as the core accretion theory, typical masses should between 0.3 and 1.0 $M_{\oplus}$. Although in practice objects do not emit any light, they may detected using gravitational microlensing via light-bending gravity. Microlensing events due terrestrial-mass rogue have extremely small angular Einstein radii (< 1 uas) short...
Abstract We apply the automated AnomalyFinder algorithm of Paper I to 2018–2019 light curves from ≃13 deg 2 covered by six KMTNet prime fields, with cadences Γ ≥ hr −1 . find a total 11 planets mass ratios q < × 10 −4 , including 6 newly discovered planets, 1 planet that was reported in I, and recovery 4 previously planets. One new OGLE-2018-BLG-0977Lb, is planetary caustic event, while other five (OGLE-2018-BLG-0506Lb, OGLE-2018-BLG-0516Lb, OGLE-2019-BLG-1492Lb, KMT-2019-BLG-0253,...
ABSTRACT We report the complete statistical planetary sample from prime fields (Γ ≥ 2 h−1) of 2019 Korea Microlensing Telescope Network (KMTNet) microlensing survey. develop optimized KMTNet AnomalyFinder algorithm and apply it to fields. find a total 13 homogeneously selected planets analysis three events, KMT-2019-BLG-(1042,1552,2974). The planet–host mass ratios, q, for events are 6.34 × 10−4, 4.89 10−3, 6.18 respectively. A Bayesian indicates all cold giant beyond snow line their host...
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 Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016–2019 KMTNet events. A Bayesian indicates that all lens systems consist a cold super-Earth orbiting an M or K dwarf. Together 17...
SN~2018aoz is a Type Ia SN with $B$-band plateau and excess emission in the infant-phase light curves $\lesssim$ 1 day after first light, evidencing an over-density of surface iron-peak elements as shown our previous study. Here, we advance constraints on nature origin based its evolution until nebular phase. Near-peak spectroscopic features show intermediate between two subtypes normal Ia: Core-Normal Broad-Line. The could have contributions from radioactive decay well ejecta interaction...
We report the discovery of OGLE-2016-BLG-1190Lb, which is likely to be first Spitzer microlensing planet in Galactic bulge/bar, an assignation that can confirmed by two epochs high-resolution imaging combined source-lens baseline object. The planet's mass M_p= 13.4+-0.9 M_J places it right at deuterium burning limit, i.e., conventional boundary between "planets" and "brown dwarfs". Its existence raises question whether such objects are really (formed within disks their hosts) or "failed...
We present microlensing planet OGLE-2017-BLG-0173Lb, with planet-host mass ratio either $q\simeq 2.5\times 10^{-5}$ or 6.5\times 10^{-5}$, the lowest among ever detected. The planetary perturbation is strongly detected, $\Delta\chi^2\sim 10,000$, because it arises from a bright (therefore, large) source passing over and enveloping caustic: so-called "Hollywood" event. factor $\sim 2.5$ offset in $q$ of previously unrecognized discrete degeneracy between Hollywood events which caustic fully...
High-cadence observations of the Galactic bulge by microlensing surveys led to discovery a handful extremely short-timescale events that can be attributed free-floating or wide-orbit planets. Here, we report another strong planet candidate, which was found from analysis gravitational event OGLE-2019-BLG-0551. The light curve is characterized very short duration (<3 d) and small amplitude (< 0.1 mag). From modeling curve, find Einstein timescale, tE = 0.381 +/- 0.017 d, much shorter, angular...
Abstract In order to exhume the buried signatures of “missing planetary caustics” in Korea Microlensing Telescope Network (KMTNet) data, we conducted a systematic anomaly search residuals from point-source point-lens fits, based on modified version KMTNet EventFinder algorithm. This revealed lowest-mass-ratio caustic date microlensing event OGLE-2019-BLG-1053, for which signal had not been noticed before. The system has planet–host mass ratio q = (1.25 ± 0.13) × 10 −5 . A Bayesian analysis...
Abstract We present the analyses of two microlensing events, OGLE-2018-BLG-0567 and OGLE-2018-BLG-0962. In both short-lasting anomalies were densely continuously covered by high-cadence surveys. The light-curve modeling indicates that are generated source crossings over planetary caustics induced companions to hosts. estimated planet/host separation (scaled angular Einstein radius θ E ) mass ratio ( s , q × 10 3 = (1.81 ± 0.02, 1.24 0.07) (1.25 0.03, 2.38 0.08), respectively. From Bayesian...
Abstract We report the analysis of OGLE-2019-BLG-0960, which contains smallest mass-ratio microlensing planet found to date ( q = 1.2–1.6 × 10 −5 at 1 σ ). Although there is substantial uncertainty in satellite parallax measured by Spitzer, measurement annual effect combined with finite source allows us determine mass host star M L 0.3–0.6 ⊙ ), its m p 1.4–3.1 ⊕ projected separation between and a ⊥ 1.2–2.3 au), distance lens system D 0.6–1.2 kpc). The plausibly blend, could be checked...
We complete the analysis of all 2018 prime-field microlensing planets identified by Korea Microlensing Telescope Network (KMTNet) Anomaly Finder. Among ten previously unpublished events with clear planetary solutions, eight are either unambiguously or very likely to be 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 four published new Finder 12 (or...
ABSTRACT In this work, we update and develop algorithms for KMTNet tender-love care (TLC) photometry in order to create a new, mostly automated, TLC pipeline. We then start project systematically apply the new pipeline historic microlensing events, search buried planetary signals. report discovery of such planet candidate event MOA-2019-BLG-421/KMT-2019-BLG-2991. The anomalous signal can be explained by either around lens star or orbital motion source star. For interpretation, despite many...
Abstract We complete the analysis of planetary candidates found by KMT AnomalyFinder for 2017 prime fields that cover ∼13 deg 2 . report three unambiguous planets: OGLE-2017-BLG-0640, OGLE-2017-BLG-1275, and OGLE-2017-BLG-1237. The first two these were not previously identified, while last was published due to technical complications induced a nearby variable. further fourth anomalous event, recognized OGLE-2017-BLG-1777, is very likely be planetary, although its light curve requires...
Current microlensing surveys are sensitive to free-floating planets down Earth-mass objects. All published events attributed unbound were identified based on their short timescale (below two days), but lacked an angular Einstein radius measurement (and hence a significant constraint the lens mass). Here, we present discovery of Neptune-mass planet candidate in ultrashort ($t_{\rm E}=0.320\pm0.003$ days) event OGLE-2016-BLG-1540. The exhibited strong finite-source effects, which allowed us...
An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb, Weicheng Zang, Cheongho Han, Iona Kondo, Jennifer C. Yee, Chung-Uk Lee, Andrew Gould, Shude Mao, Leandro de Almeida, Yossi Shvartzvald, Xiangyu Zhang, Michael D. Albrow, Sun-Ju Chung, Kyu-Ha Hwang, Youn Kil Jung, Yoon-Hyun Ryu, In-Gu Shin, Sang-Mok Cha, Dong-Jin Kim, Hyoun-Woo Seung-Lee Dong-Joo Yongseok Byeong-Gon Park, Richard W. Pogge, John Drummond, Thiam-Guan Tan, José Dias do Nascimento Júnior, Dan Maoz, Matthew T. Penny,...
Abstract We complete the analysis of all 2018 sub-prime-field microlensing planets identified by KMTNet AnomalyFinder. Among 9 previously unpublished events with clear planetary solutions, 6 are clearly (OGLE-2018-BLG-0298, KMT-2018-BLG-0087, KMT-2018-BLG-0247, KMT-2018-BLG-0030, OGLE-2018-BLG-1119, and KMT-2018-BLG-2602), while remaining 3 ambiguous in nature. The above ordering these is made to facilitate grouping their Bayesian estimates: first two lower-mass gas giants last four...
We complete the survey for finite-source/point-lens (FSPL) giant-source events in 2016-2019 KMTNet microlensing data. The 30 FSPL show a clear gap Einstein radius, $9\,\mu{\rm as}<\theta_{\rm E} <26\,\mu{\rm as}$, which is consistent with timescales near $t_{\rm E}\sim 0.5\,$days found by Mroz et al. (2017) an independent sample of point-source/point-lens (PSPL) events. demonstrate that two surveys are consistent. estimate 4 below this due to power-law distribution free-floating planet...
We complete the publication of all microlensing planets (and ``possible planets'') identified by uniform approach KMT AnomalyFinder system in 21 subprime fields during 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 OGLE-2019-BLG-0344, KMT-2019-BLG-0304 (possible planets). The five have mean log mass-ratio measurements $(-2.6,-3.6,-2.5,-2.2,-2.3)$, median mass estimates...
We examined the anomalies in light curves of lensing events MOA-2022-BLG-033, KMT-2023-BLG-0119, and KMT-2023-BLG-1896. conducted detailed modeling to uncover nature anomalies. This revealed that all signals originated from planetary companions primary lens. The planet-to-host mass ratios are very low: $q\sim 7.5\times 10^{-5}$ for 3.6\times 10^{-4}$ 6.9\times occurred as source passed through negative deviation region behind central caustic along planet-host axis. solutions subject a common...
We examined the anomalies in light curves of lensing events MOA-2022-BLG-033, KMT-2023-BLG-0119, and KMT-2023-BLG-1896. These share similar traits: they occur near peak moderately to highly magnified display a distinct short-term dip feature. conducted detailed modeling uncover nature anomalies. This revealed that all signals originated from planetary companions primary lens. The planet-to-host mass ratios are very low: q∼ 7.5 for $q∼ 3.6 $ 6.9 occurred as source passed through negative...