ORCID Profile
0000-0003-0043-3925
Current Organisation
Korea Astronomy and Space Science Institute
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: American Astronomical Society
Date: 23-11-2015
Publisher: American Astronomical Society
Date: 17-08-2010
Publisher: American Astronomical Society
Date: 08-2012
Publisher: American Astronomical Society
Date: 26-03-2010
Publisher: American Astronomical Society
Date: 16-08-2011
Publisher: American Astronomical Society
Date: 19-10-2009
Publisher: American Astronomical Society
Date: 02-02-2010
Publisher: American Astronomical Society
Date: 07-10-2010
Publisher: American Astronomical Society
Date: 07-04-2014
Publisher: American Astronomical Society
Date: 16-10-2015
Publisher: American Astronomical Society
Date: 11-2013
Publisher: American Astronomical Society
Date: 13-08-2012
Publisher: American Astronomical Society
Date: 27-06-2202
Publisher: American Astronomical Society
Date: 02-2012
Publisher: American Astronomical Society
Date: 16-09-2009
DOI: 10.1088/0004-637X/703/2/2082
Abstract: We analyze the extreme high-magnification microlensing event OGLE-2008-BLG-279, which peaked at a maximum magnification of A ∼ 1600 on 2008 May 30. The peak of this event exhibits both finite-source effects and terrestrial parallax, from which we determine the mass of the lens, M l = 0.64 ± 0.10 M ☉ , and its distance, D l = 4.0 ± 0.6 kpc. We rule out Jupiter-mass planetary companions to the lens star for projected separations in the range 0.5–20 AU. More generally, we find that this event was sensitive to planets with masses as small as with projected separations near the Einstein ring (∼3 AU).
Publisher: American Astronomical Society
Date: 02-08-2022
Abstract: 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 θ E cannot be measured from the light curve alone. However, the large event duration, t E ∼ 80 days, allows a precise measurement of the microlensing parallax π E . In addition to the constraints on the angular radius θ * and the apparent brightness I s of the source, we employ the Besançon 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 M p ∼ 30 M Jup , 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 ≤4 kpc. We estimate that in about 10 yr 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.
Publisher: American Astronomical Society
Date: 30-05-2012
Publisher: American Astronomical Society
Date: 11-02-2019
Publisher: American Astronomical Society
Date: 12-11-2013
Publisher: American Astronomical Society
Date: 20-06-2011
Publisher: American Astronomical Society
Date: 28-04-2015
Publisher: American Astronomical Society
Date: 06-07-2012
Publisher: EDP Sciences
Date: 07-2010
Publisher: American Astronomical Society
Date: 10-05-0010
Abstract: OGLE-2016-BLG-1093 is a planetary microlensing event that is part of the statistical Spitzer microlens parallax s le. The precise measurement of the microlens parallax effect for this event, combined with the measurement of finite-source effects, leads to a direct measurement of the lens masses and system distance, M host =0.38–0.57 M ⊙ and m p = 0.59–0.87 M Jup , and the system is located at the Galactic bulge ( D L ∼ 8.1 kpc). Because this was a high-magnification event, we are also able to empirically show that the “cheap-space parallax” concept produces well-constrained (and consistent) results for ∣ π E ∣. This demonstrates that this concept can be extended to many two-body lenses. Finally, we briefly explore systematics in the Spitzer light curve in this event and show that their potential impact is strongly mitigated by the color constraint.
Publisher: American Astronomical Society
Date: 27-04-2015
Publisher: American Astronomical Society
Date: 31-07-2012
Publisher: EDP Sciences
Date: 12-04-2011
Publisher: American Astronomical Society
Date: 18-02-2010
Publisher: Oxford University Press (OUP)
Date: 02-07-2012
Publisher: American Astronomical Society
Date: 07-07-2016
Publisher: American Astronomical Society
Date: 27-01-2014
Publisher: Springer Science and Business Media LLC
Date: 16-10-2017
DOI: 10.1038/NATURE24290
Publisher: EDP Sciences
Date: 08-10-2009
Publisher: American Astronomical Society
Date: 03-11-2017
Publisher: American Astronomical Society
Date: 28-12-2017
Publisher: American Astronomical Society
Date: 18-08-2023
Abstract: We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ 2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q , and separation, s , cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ∼ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters.
Publisher: Oxford University Press (OUP)
Date: 10-07-2019
Abstract: We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing c aign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average time-scale of ∼9 d. The asteroseismic analysis also provides us source properties including the source angular size (∼27 $\\mu$as) and distance (∼11.5 kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional χ2 minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a ∼0.045 M⊙ brown dwarf at distance ∼9.0 kpc, or a ∼0.073 M⊙ ultracool dwarf at distance ∼9.8 kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\\sim 35{{\\ \\rm per\\ cent}}$ probability for the lens to be a bulge object and $\\sim 65{{\\ \\rm per\\ cent}}$ to be a background disc object.
Publisher: American Astronomical Society
Date: 05-05-2014
Publisher: American Astronomical Society
Date: 11-08-2015
Publisher: American Astronomical Society
Date: 27-02-2017
Publisher: American Astronomical Society
Date: 08-01-2015
Publisher: EDP Sciences
Date: 05-2014
Publisher: EDP Sciences
Date: 25-10-2012
Publisher: American Astronomical Society
Date: 12-10-2011
Publisher: American Astronomical Society
Date: 22-03-2016
Publisher: American Astronomical Society
Date: 23-04-2013
Publisher: American Astronomical Society
Date: 28-06-2016
Publisher: American Astronomical Society
Date: 14-11-2012
Publisher: EDP Sciences
Date: 27-03-2013
Publisher: American Association for the Advancement of Science (AAAS)
Date: 04-07-2014
Abstract: Many known exoplanets (planets outside our own solar system) are hosted by binary systems that contain two stars. These planets normally circle around both of their stars. Using microlensing data taken with a worldwide network of telescopes, Gould et al. found a planet twice the mass of Earth that circles just one of a pair of stars. The same approach has the potential to uncover other similar star systems and help to illuminate some of the mysteries of planet formation. Science , this issue p. 46
Publisher: American Astronomical Society
Date: 19-12-2012
Publisher: American Astronomical Society
Date: 27-11-2013
Publisher: American Astronomical Society
Date: 04-06-2009
Publisher: EDP Sciences
Date: 08-2015
Publisher: American Astronomical Society
Date: 24-09-2014
Publisher: Oxford University Press (OUP)
Date: 11-05-2007
Publisher: American Astronomical Society
Date: 28-01-2011
Publisher: American Astronomical Society
Date: 17-01-2013
Publisher: American Astronomical Society
Date: 06-05-2013
Publisher: American Astronomical Society
Date: 18-08-2017
Publisher: Oxford University Press (OUP)
Date: 11-07-2007
Publisher: American Astronomical Society
Date: 07-2022
Abstract: We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration ( t E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of 6 yr, reveals a clear relativistic astrometric deflection of the background star’s apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of Earth’s motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 ± 1.3 M ⊙ and a distance of 1.58 ± 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic disk stars at similar distances by an amount corresponding to a transverse space velocity of ∼45 km s −1 , suggesting that the BH received a “natal kick” from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial velocity measurements of Galactic X-ray binaries and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.
Publisher: American Astronomical Society
Date: 07-09-2030
Publisher: American Astronomical Society
Date: 02-05-2012
Publisher: American Astronomical Society
Date: 05-04-2017
Publisher: American Astronomical Society
Date: 23-07-2020
Publisher: Oxford University Press (OUP)
Date: 13-11-2006
Publisher: American Association for the Advancement of Science (AAAS)
Date: 15-02-2008
Abstract: Searches for extrasolar planets have uncovered an astonishing ersity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of ∼0.71 and ∼0.27 times the mass of Jupiter and orbital separations of ∼2.3 and ∼4.6 astronomical units orbiting a primary star of mass ∼0.50 solar mass at a distance of ∼1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
Publisher: American Astronomical Society
Date: 14-10-2010
Publisher: American Astronomical Society
Date: 03-07-2017
Publisher: American Astronomical Society
Date: 08-01-2013
Publisher: American Astronomical Society
Date: 24-03-2023
Abstract: We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet, MOA-2020-BLG-208Lb, with an estimated sub-Saturn mass. With a mass ratio q = 3.17 − 0.26 + 0.28 × 10 − 4 , the planet lies near the peak of the mass-ratio function derived by the MOA collaboration and near the edge of expected s le 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 planet = 46 − 24 + 42 M ⊕ and a host star of mass M host = 0.43 − 0.23 + 0.39 M ⊙ , located at a distance D L = 7.49 − 1.13 + 0.99 kpc . For the second scenario, we estimate m planet = 69 − 34 + 37 M ⊕ , M host = 0.66 − 0.32 + 0.35 M ⊙ , and D L = 7.81 − 0.93 + 0.93 kpc . The planet has a projected separation as a fraction of the Einstein ring radius s = 1.3807 − 0.0018 + 0.0018 . As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models.
Location: Korea, Republic of
No related grants have been discovered for Chung-Uk Lee.