Results for "Cheongho Han"

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Probing the Spatial Distribution of Extrasolar Planets with Gravitational MicrolensingMar 14 2003Under the current microlensing planet search strategy of monitoring events caused by stellar-mass lenses, only planets located within a narrow region of separations from central stars can be effectively detected. However, with the dramatic increase of ... More
Color-Shift Measurement in Microlensing-Induced Stellar Variation from Future Space-Based SurveysJan 31 2008If a microlensing event is caused by a star, the event can exhibit change in color due to the light from the lens. In the previous and current lensing surveys, the color shift could not be used to constrain the lens population because the blended light ... More
Astrometric Detection of Double Gravitational Microlensing EventsDec 05 2001If a gravitational microlensing event is caused by a widely separated binary lens and the source approaches both lens components, the source flux is successively magnified by the individual lenses: double microlensing events. If events are observed astrometrically, ... More
Distinguishing between Planetary and Binary Interpretations of Microlensing Central Perturbations under Severe Finite-Source EffectDec 08 2008In the current strategy of microlensing planet searches focusing on high-magnification events, wide and close binaries pose important sources of contamination that imitates planetary signals. For the purpose of finding systematic differences, we compare ... More
Galactic Bulge Pixel Lensing EventsMar 28 2001Gould & DePoy proposed a pixel lensing survey towards the Galactic bulge using a small aperture (~65 mm) camera with a large pixel size (10") detector and deliberately degraded optics achieving 30" PSF. In this paper, we estimate the event rate of this ... More
Unique Determination of the Physical Parameters of Individual MACHOs from Astrometric Parallax MeasurementsFeb 04 1999Feb 05 1999The Einstein time scale, which is the only information obtained from current microlensing experiments, results from a complicated combination of the lens parameters that we want to determine. Of the methods for breaking the lens parameter degeneracy, ... More
On the Astrometric Behavior of Binary Microlensing EventsOct 27 2000Nov 07 2000Despite the suspected binarity for a significant fraction of Galactic lenses, the current photometric surveys detected binary microlensing events only for a small fraction of the total events. The detection efficiency is especially low for non-caustic ... More
Correction for Blending Problem in Gravitational Microlensing Events by Using Hubble Space TelescopeApr 22 1997The biggest uncertainty in determining microlensing parameters comes from the blending of source star images because the current experiments are being carried out toward very dense star fields: the Galactic bulge and Magellanic Clouds. The experiments ... More
Expansion of the Planet Detection Channels in Next-Generation Microlensing SurveysJul 28 2007We classify various types of planetary lensing signals and the channels of detecting them. We estimate the relative frequencies of planet detections through the individual channels with special emphasis on the new channels to be additionally provided ... More
Effect of Binary Source Companions on the Microlensing Optical Depth Determination toward the Galactic Bulge FieldJul 04 2005Currently, gravitational microlensing survey experiments toward the Galactic bulge field utilize two different methods of minimizing blending effect for the accurate determination of the optical depth \tau. One is measuring \tau based on clump giant (CG) ... More
Criteria in the Selection of Target Events for Planetary Microlensing Follow-Up ObservationApr 07 2007To provide criteria in the selection of target events preferable for planetary lensing follow-up observations, we investigate the variation of the probability of detecting planetary signals depending on the observables of the lensing magnification and ... More
Secure Identification of Free-Floating PlanetsMar 02 2006Among the methods proposed to detect extrasolar planets, microlensing is the only technique that can detect free-floating planets. Free-floating planets are detected through the channel of short-duration isolated lensing events. However, if a seemingly ... More
Microlensing Zone of Planets Detectable through the Channel of High-Magnification EventsAug 22 2008A microlensing lensing zone refers to the range of planet-star separations where the probability of detecting a planetary signal is high. Its conventional definition as the range between $\sim 0.6$ and 1.6 Einstein radii of the primary lens is based on ... More
Astrometric Microlensing: A Channel to Detect Multiple Lens SystemsApr 08 2002If a source star is gravitationally microlensed by a multiple lens system, the resulting light curve can have significant deviations from the standard form of a single lens event. The chance to produce significant deviations becomes important when the ... More
On the Baseline Flux Determination of Microlensing Events Detectable with the Difference Image Analysis MethodOct 12 1999To improve photometric precision by removing blending effect, a newly developed technique of difference image analysis (DIA) is adopted by several gravitational microlensing experiment groups. However, the principal problem of the DIA method is that, ... More
The Effect of a Binary Source Companion on the Astrometric Microlensing BehaviorJul 28 2001If gravitational microlensing occurs in a binary-source system, both source components are magnified, and the resulting light curve deviates from the standard one of a single source event. However, in most cases only one source component is highly magnified ... More
Characterization of Microlensing Planets with Moderately Wide SeparationsMay 21 2009In future high-cadence microlensing surveys, planets can be detected through a new channel of an independent event produced by the planet itself. The two populations of planets to be detected through this channel are wide-separation planets and free-floating ... More
Microlensing Search for Planets with Two Simultaneously Rising SunsJan 31 2008Among more than 200 extrasolar planet candidates discovered to date, there is no known planet orbiting around normal binary stars. In this paper, we demonstrate that microlensing is a technique that can detect such planets. Microlensing discoveries of ... More
Investigating Binary Properties with Next-Generation Microlensing SurveysJan 04 2007We explore the usefulness of future gravitational microlensing surveys in the study of binary properties such as the binary fraction and the distributions of binary separation and mass ratio by using the binary sample detectable through a channel of repeating ... More
On the Feasibility of Characterizing Lens Stars in Future Space-Based Microlensing SurveysJul 04 2005If a light-emitting star is responsible for a gravitational microlensing event, the lens can be characterized by analyzing the blended light from the lens. In this paper, we investigate the feasibility of characterizing lenses by using this method in ... More
Better Astrometric Deblending of Gravitional Microlensing Events by Using the Difference Image Analysis MethodJan 27 2000Due to the choice of very dense star fields for a higher event rate, the current microlensing searches suffer from large uncertainties caused by blending effect. To measure light variations of microlensing events free from the effect of blending, a newly ... More
Astrometric Method to Break the Photometric Degeneracy between Binary-source and Planetary Microlensing PerturbationsJul 27 2001An extra-solar planet can be detected by microlensing because the planet can perturb the smooth lensing light curve created by the primary lens. However, it was shown by Gaudi that a subset of binary-source events can produce light curves that closely ... More
Additional Information from Astrometric Gravitational Microlensing ObservationsMar 24 2000Astrometric observations of microlensing events were originally proposed to determine the lens proper motion with which the physical parameters of lenses can be better constrained. In this proceeding, we demonstrate that besides this original usage astrometric ... More
Analytic Relations between the Observed Gravitational Microlensing Parameters With and Without the Effect of BlendingOct 25 1998Jun 07 1999When a microlensing light curve is contaminated by blended light from unresolved stars near the line of sight to the lensed star, the light curve shape and corresponding parameterization for the event will differ from the values expected when the event ... More
The Effects of Amplification Bias in Gravitational Microlensing ExperimentsAug 01 1996Although a source star is fainter than the detection limit imposed by crowding, it is still possible to detect an event if the star is located in the seeing disk of a bright star is and gravitationally amplified: amplification bias. Using a well-constrained ... More
Pixel Lensing Experiment toward the M31 BulgeNov 01 1995Jun 26 1996I demonstrate that one can detect pixel gravitational microlensing events at the rate $\sim 180\ {\rm events}\ {\rm yr}^{-1}$ and that some fraction of events ($\sim 15$) will be good enough to measure time scales at the $20\%$ level if the experiment ... More
The Orientation of Spin Vectors of Galaxies in the Ursa Major FilamentAug 06 1994Spin vectors of 60 galaxies in the ``Ursa Major Filament'' are obtained from CCD images and spectroscopic determinations of the directions of rotation. These data are used to remove the four-fold degeneracy introduced by the project ed images of galaxies, ... More
Microlensing Detections of Moons of ExoplanetsMay 17 2008We investigate the characteristic of microlensing signals of Earth-like moons orbiting ice-giant planets. From this, we find that non-negligible satellite signals occur when the planet-moon separation is similar to or greater than the Einstein radius ... More
Near-Field Microlensing from Wide-Field SurveysAug 09 2007We estimate the rate of near-field microlensing events expected from all-sky surveys and investigate the properties of these events. Under the assumption that all lenses are composed of stars, our estimation of the event rate ranges from \Gamma_{tot}~0.2 ... More
Properties of Planetary Caustics in Gravitational MicrolensingOct 07 2005Although some of the properties of the caustics in planetary microlensing have been known, our understanding of them is mostly from scattered information based on numerical approaches. In this paper, we conduct a comprehensive and analytic analysis of ... More
Analysis of Microlensing Light Curves Induced by Multiple-Planet SystemsMar 31 2005To maximize the number of planet detections by increasing efficiency, current microlensing follow-up observation experiments are focusing on high-magnification events to search for planet-induced perturbations near the peak of lensing light curves. It ... More
On the Intrinsic Bias in detecting Caustic Crossings between Galactic Halo and Self-lensing Events in the Magellanic CloudsMay 12 1999In this paper, we investigate the intrinsic bias in detecting caustic crossings between Galactic halo and self-lensing events in the Magellanic Clouds. For this, we determine the region for optimal caustic-crossing detection in the parameter space of ... More
Degeneracy between Lensing and Occultation in the Analysis of Self-lensing PhenomenaMar 11 2016More than 40 years after the first discussion, it was recently reported the detection of a self-lensing phenomenon within a binary system where the brightness of a background star is magnified by its foreground companion. It is expected that the number ... More
Angular Radii of Stars via MicrolensingAug 09 2002Nov 27 2002We outline a method by which the angular radii of giant and main sequence stars in the Galactic bulge can be measured to a few percent accuracy. The method combines ground-based photometry of caustic-crossing bulge microlensing events, with a handful ... More
Blending in Future Space-based Microlensing SurveysSep 05 2006We investigate the effect of blending in future gravitational microlensing surveys by carrying out simulation of Galactic bulge microlensing events to be detected from a proposed space-based lensing survey. From this simulation, we find that the contribution ... More
On the Feasibility of Detecting Satellites of Extrasolar Planets via MicrolensingJul 17 2002Although many methods of detecting extra-solar planets have been proposed and successful implementation of some of these methods enabled a rapidly increasing number of exoplanet detections, little has been discussed about the method of detecting satellites ... More
The Effect of Luminous Lens Blending in Gravitational Microlensing ExperimentsJul 16 1997The most important uncertainty in the results of gravitational microlensing experiments comes from the difficulties of photometry caused by blending of source stars. Recently Nemiroff (1997) pointed out that the results of microlensing experiments can ... More
Astrometric Resolution of Severely Degenerate Binary Microlensing EventsJan 11 2000We investigate whether the "close/wide" class of degeneracies in caustic-crossing binary microlensing events can be broken astrometrically. Dominik showed that these degeneracies are particularly severe because they arise from a degeneracy in the lens ... More
Einstein Radii from Binary Lensing EventsApr 05 1996Jun 26 1996We show that the Einstein ring radius and transverse speed of a lens projected on the source plane, $\hat{r}_{\rm e}$ and $\hat{v}$, can be determined from the light curve of a binary-source event, followed by the spectroscopic determination of the orbital ... More
Galactic versus Extragalactic Pixel Lensing Events toward M31Feb 19 1996Jun 26 1996A new type of gravitational microlensing experiment toward a field where stars are not resolved is being developed observationally and theoretically: pixel lensing. When the experiment is carried out toward the M31 bulge area, events may be produced both ... More
The Applicability of the Astrometric Method in Determining the Physical Parameters of Gravitational MicrolensesAug 26 1998In this paper, we investigate the applicability of the astrometric method to the determination of the lens parameters for gravitational microlensing events toward both the LMC and the Galactic bulge. For this analysis, we investigate the dependency of ... More
Identification of Bright Lenses from the Astrometric Observations of Gravitational Microlensing EventsJun 09 1999When a source star is gravitationally microlensed by a dark lens, the centroid of the source star image is displaced relative to the position of the unlensed source star with an elliptical trajectory. Recently, routine astrometric follow-up measurements ... More
Reevaluating of the feasibility of ground-based earth-mass microlensing planet detectionsMar 05 2014One important strength of the microlensing method in detecting extrasolar planets is its high sensitivity to low-mass planets. However, it is often believed that microlensing detections of Earth-mass planets from ground-based observation would be difficult ... More
The Mass Spectrum Of Machos From Parallax MeasurementsSep 14 1994We demonstrate that by making satellite-based parallax measurements of Macho events, it is possible to distinguish disk from bulge Machos and to determine individual masses of disk Machos to an accuracy of $0.2$ in the log. This is at least a 3-fold improvement ... More
Where Are the Binary Source Gravitational Microlensing Events? IIApr 26 1998Currently, 6 candidate binary lens events have been reported, while only a single candidate binary source event has been reported. To account for the rarity of binary source events, Dominik pointed out that for a typical binary source event the separation ... More
Statistical Determination of the MACHO Mass SpectrumApr 22 1995Jan 16 1996The mass function of 51 Massive Compact Objects (MACHOs) detected toward the Galactic bulge is statistically estimated from Einstein ring crossing times $t_{\rm e}$. For a Gaussian mass function, the best fitting parameters are $\langle \log (m/M_{\odot}) ... More
Statistics Of Microlensing Optical DepthOct 18 1994We show that the statistical error, $\sigma_{\tau}$, in estimating the optical depth, $\tau$, due to microlensing is substantially higher than the naive Poisson estimate: $\sigma_{\tau} = \sqrt{\eta / N} \tau$, where $N$ is the number of detections and ... More
Signs of Planetary Microlensing SignalsJul 21 2003An extrasolar planet can be detected via microlensing from the perturbation it makes in the smooth lensing light curve of the primary. In addition to the conventional photometric microlensing, astrometric observation of the center-of-light motion of the ... More
Properties of Planet-induced Deviations in the Astrometric Microlensing Centroid Shift TrajectoryAug 09 2001In this paper, we investigate the properties of the planet-induced deviations in the trajectory of the microlensed source star centroid motion (astrometric curve) and the correlations between the astrometric and photometric deviations. For this, we construct ... More
Inventory of Gravitational Microlenses toward the Galactic BulgeMay 19 1997We determine the microlensing event rate distribution, $\Gamma(t_{E})$, that is properly normalized by the first year MACHO group observations (Alcock et al. 1997). By comparing the determined $\Gamma(t_{E})$ with various MF models of lens populations ... More
Improved Detection Rates for Close Binaries Via Astrometric Observations of Gravitational Microlensing EventsJan 15 1999Jun 25 1999In addition to constructing a Galactic matter mass function free from the bias induced by the hydrogen-burning limit, gravitational microlensing allows one to construct a mass function which is less affected by the problem of unresolved binaries (Gaudi ... More
Observational Evidence for the Effect of Amplification Bias in Gravitational Microlensing ExperimentsApr 26 1998Recently Alard\markcite{alard1996} proposed to detect the shift of a star's image centroid, $\delta x$, as a method to identify the lensed source among blended stars. Goldberg & Wo\'zniak\markcite{goldberg1997} actually applied this method to the OGLE-1 ... More
Planetary Lensing Signals of High-Magnification Events under Severe Finite-Source EffectSep 24 2008We investigate the effect of a finite source on the planetary-lensing signals of high-magnification events. From this, we find that the dependency of the finite-source effect on the caustic shape is weak and perturbations survive even when the source ... More
Stellar Contribution to the Galactic Bulge Microlensing Optical DepthMar 13 2003We estimate the optical depth to self-lensing by stars in the Galactic bulge using the HST star counts of Holtzman et al and Zoccali et al as extrapolated by Gould into the brown-dwarf and remnant regimes and deprojected along the line of sight using ... More
Detectability of the Parallax-induced Deviations in the Astrometric Centroid Shift Trajectories of Gravitational Microlensing EventsNov 04 2000The uncertainty of the lens mass can be substantially reduced if it is determined from the lens proper motion obtained from astrometric measurements of the source image centroid shifts, $\vdelta\vtheta_c$, by using high precision interferometers. However, ... More
Microlensing Sensitivity to Earth-mass Planets in the Habitable ZoneJan 31 2006Microlensing is one of the most powerful methods that can detect extrasolar planets and a future space-based survey with a high monitoring frequency is proposed to detect a large sample of Earth-mass planets. In this paper, we examine the sensitivity ... More
The Many Possible Interpretations of Microlensing Event OGLE-2002-BLG-055Feb 17 2004Apr 20 2004Microlensing event OGLE-2002-BLG-055 is characterized by a smooth, slightly asymmetric single-lens curve with an isolated, secure data point that is ~0.6 magnitudes brighter than neighboring points separated by a few days. It was previously suggested ... More
Effect of a wide binary companion to the lens on the astrometric behavior of gravitational microlensing eventsMar 01 2002In this paper, we investigate the effect of a wide binary companion of the lens on the astrometric behavior of Galactic gravitational microlensing events and compare it to the effect on the photometric behavior. We find that the wide binary companion ... More
A New Channel to Search for Extra-solar Systems with Multiple Planets via Gravitational MicrolensingFeb 03 2002Gaudi, Naber & Sackett pointed out that if an event is caused by a lens system containing more than two planets, all planets will affect the central region of the magnification pattern, and thus the existence of the multiple planets can be inferred by ... More
Comparison of the Two Followup Observation Strategies for Gravitational Microlensing Planet SearchesAug 22 2000There are two different strategies of followup observations for the detection of planets by using microlensing. One is detecting the light curve anomalies affected by the planetary caustic from continuous monitoring of all events detected by microlensing ... More
Characterization of Stellar Spots in Next-Generation Microlensing SurveysDec 03 2009One of the important microlensing applications to stellar atmospheres is the study of spots on stellar surface provided by the high resolution of caustic-crossing binary-lens events. In this paper, we investigate the characteristics of spot-induced perturbations ... More
Determination of Stellar Ellipticities in Future Microlensing SurveysFeb 03 2006We propose a method that can determine the ellipticities of source stars of microlensing events produced by binary lenses. The method is based on the fact that the products of the caustic-crossing timescale, $\Delta t$, and the cosine of the caustic incidence ... More
Variation of Spot-induced Anomalies in Caustic-crossing Binary Microlensing Event Light CurvesJan 09 2002We investigate the pattern of anomalies in the light curves of caustic-crossing binary microlensing events induced by spot(s) on the lensed source star. For this purpose, we perform simulations of events with various models of spots. From these simulations, ... More
A Characteristic Planetary Feature in Double-Peaked, High-Magnification Microlensing EventsMay 08 2008A significant fraction of microlensing planets have been discovered in high-magnification events, and a significant fraction of these events exhibit a double-peak structure at their peak. However, very wide or very close binaries can also produce double-peaked ... More
The Importance of Binary Gravitational Microlensing Events Through High-Magnification ChannelNov 30 2009We estimate the detection efficiency of binary gravitational lensing events through the channel of high-magnification events. From this estimation, we find that binaries in the separations ranges of 0.1 < s < 10, 0.2 < s < 5, and 0.3 < s < 3 can be detected ... More
An Additional Application of the Space Interferometry Mission to Gravitational Microlensing ExperimentsOct 20 1998Jan 15 1999Despite the detection of a large number of gravitational microlensing events, the nature of Galactic dark matter remains very uncertain. This uncertainty is due to two major reasons: the lens parameter degeneracy in the measured Einstein timescale and ... More
Colour Change Measurements of Gravitational Microlensing Events by Using the Difference Image Analysis MethodJan 27 2000Aug 07 2000Detecting colour changes of a gravitational microlensing event induced by the limb-darkened extended source effect is important to obtain useful information both about the lens and source star. However, precise measurements of the colour changes are hampered ... More
Direct Lens Imaging of Galactic Bulge Microlensing EventsSep 18 2002Recently, from the Hubble Space Telescope (HST) images of one of the Large Magellanic Cloud (LMC) events taken 6.3 years after the original lensing measurement, Alcock et al. were able to directly image the lens. Although the first resolved lens was identified ... More
Another Channel to detect Close-in Binary Companions via Gravitational MicrolensingMay 11 2001Gaudi & Gould (1997) showed that close companions of remote binary systems can be efficiently detected by using gravitational microlensing via the deviations in the lensing light curves induced by the existence of the lens companions. In this paper, we ... More
Astrometric Properties of Gravitational Binary-Microlens Events and Their ApplicationsJun 14 1999In this paper, we study the astrometric properties of gravitational microlensing events caused by binary lenses. By investigating the centroid shifts for various types of binary-lens events, we find that the deviations of the centroid shift trajectories ... More
Lunar Occultation of MACHOsMay 30 1995Lunar occultation can be used to measure the proper motions of some of the long time scale microlensing events, $t_{e} \gsim 70$ days, now being detected toward the Galactic bulge. The long events are difficult to explain within the context of standard ... More
Prospects for the Detection of Earth-Mass PlanetsMay 11 2004We compare potential state-of-the-art experiments for detecting Earth-mass planets around main-sequence stars using radial velocities, transits, astrometry, and microlensing. For conventionally-discussed signal-to-noise ratio (S/N) thresholds, S/N ~ 8, ... More
Resolving the Microlens Mass Degeneracy for Earth-Mass PlanetsApr 16 2003May 23 2003Of all planet-finding techniques, microlensing is potentially the most sensitive to Earth-mass planets. However, microlensing lightcurves generically yield only the planet-star mass ratio: the mass itself is uncertain to a factor of a few. To determine ... More
The Effect of Bright Lenses in the Astrometric Measurements of MACHO Proper MotionJul 16 1998In current microlensing experiments, the information about the physical parameters of individual lenses are obtained from the Einstein timescales. However, the nature of MACHOs is still very uncertain despite the large number of detected events. This ... More
Detection of Stellar Spots from the Observations of Caustic-Crossing Binary-Lens Gravitational Microlensing EventsJan 27 2000Recently, Heyrovsk\'y & Sasselov (1999) investigated the sensitivity of {\it single-lens} gravitational microlensing event light curves to small spots and found that during source transit events spots can cause deviations in amplification larger than ... More
Correlations Between Planetary Microlensing ParametersSep 02 2010Characterization of microlensing planets requires modeling of observed light curves including many parameters. Studying the dependency of the pattern of light curves on the lensing parameters and the correlations between the parameters is important to ... More
Probing Structures of Distant Extrasolar Planets with MicrolensingSep 25 2002Jan 14 2003Planetary companions to the source stars of a caustic-crossing binary microlensing events can be detected via the deviation from the parent light curves created when the caustic magnifies the star light reflecting off the atmosphere or surface of the ... More
Microlensing Characterization of Wide-Separation PlanetsSep 24 2004With their excellent photometric precision and dramatic increase in monitoring frequency, future microlensing survey experiments are expected to be sensitive to very short time-scale, isolated events caused by free-floating and wide-separation planets ... More
Chromaticity of Gravitational Microlensing EventsNov 19 1999In this paper, we investigate the color changes of gravitational microlensing events caused by the two different mechanisms of differential amplification for a limb-darkened extended source and blending. From this investigation, we find that the color ... More
Properties of Microlensing Light Curve Anomalies Induced by Multiple PlanetsJul 27 2001In this paper, we show that the pattern of microlensing light curve anomalies induced by multiple planets are well described by the superposition of those of the single-planet systems where the individual planet-primary binary pairs act as independent ... More
A New Non-Planetary Interpretation of the Microlensing Event OGLE-2013-BLG-0723Apr 22 2016Recently, the discovery of a Venus-mass planet orbiting a brown-dwarf host in a binary system was reported from the analysis of the microlensing event OGLE-2013-BLG-0723. We reanalyze the event considering the possibility of other interpretations. From ... More
Distribution of Caustic-Crossing Intervals for Galactic Binary-Lens Microlensing EventsNov 15 1999Detection of caustic crossings of binary-lens gravitational microlensing events is important because by detecting them one can obtain useful information both about the lens and source star. In this paper, we compute the distribution of the intervals between ... More
Reanalysis of the Gravitational Microlensing Event MACHO-97-BLG-41 based on Combined DataMar 05 2013Mar 25 2013MACHO-97-BLG-41 is a gravitational microlensing event produced by a lens composed of multiple masses detected by the first-generation lensing experiment. For the event, there exist two different interpretations of the lens from independent analyses based ... More
OGLE-2011-BLG-0417: A Radial Velocity Testbed for MicrolensingFeb 04 2013Microlensing experiments are returning increasingly detailed information about the planetary and binary systems that are being detected, far beyond what was originally expected. In several cases the lens mass and distance are measured, and a few very ... More
A Comparison of the Intrinsic Shapes of Two Different Types of Dwarf Galaxies: Blues Compact Dwarfs and Dwarf EllipticalsSep 19 1997We measure the apparent shapes for a sample of 62 blue compact dwarf galaxies (BCDs), and compare them with the apparent shapes for a sample of 80 dwarf elliptical galaxies (dEs). The BCDs are flatter, on average, than the dEs, but the difference is only ... More
Effects of Gas on Formation and Evolution of Stellar Bars and Nuclear Rings in Disk GalaxiesJan 07 2019We run self-consistent simulations of Milky Way-sized, isolated disk galaxies to study formation and evolution of a stellar bar as well as a nuclear ring in the presence of gas. We consider two sets of models with cold or warm disks that differ in the ... More
Optimal Survey Strategies and Predicted Planet Yields for the Korean Microlensing Telescope NetworkJun 09 2014The Korean Microlensing Telescope Network (KMTNet) will consist of three 1.6m telescopes each with a 4 deg^{2} field of view (FoV) and will be dedicated to monitoring the Galactic Bulge to detect exoplanets via gravitational microlensing. KMTNet's combination ... More
Gravitational Microlensing: A Tool for Detecting and Characterizing Free-Floating PlanetsNov 18 2003Various methods have been proposed to search for extrasolar planets. Compared to the other methods, microlensing has unique applicabilities to the detections of Earth-mass and free-floating planets. However, the microlensing method is seriously flawed ... More
Microlensing Detections of Planets in Binary Stellar SystemsSep 13 2007We demonstrate that microlensing can be used for detecting planets in binary stellar systems. This is possible because in the geometry of planetary binary systems where the planet orbits one of the binary component and the other binary star is located ... More
A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291Jun 15 2018We present the analysis of planetary microlensing event MOA-2011-BLG-291, which has a mass ratio of $q=(3.8\pm0.7)\times10^{-4}$ and a source star that is redder (or brighter) than the bulge main sequence. This event is located at a low Galactic latitude ... More
Limits of Binaries That Can Be Characterized by Gravitational MicrolensingAug 15 2008Due to the high efficiency of planet detections, current microlensing planet searches focus on high-magnification events. High-magnification events are sensitive to remote binary companions as well and thus a sample of wide-separation binaries are expected ... More
The Demographics of Extrasolar Planets Beyond the Snow Line with Ground-based Microlensing SurveysMar 04 2009In the currently-favored paradigm of planet formation, the location of the snow line in the protoplanetary disk plays a crucial role. Determining the demographics of planets beyond the snow line of stars of various masses is thus essential for testing ... More
The Intrinsic Shapes of Low-Surface-Brightness Dwarf Irregular Galaxies and Comparison to Other Types of Dwarf GalaxiesMar 04 1998In this paper, we measure the ellipticities of 30 LSB dI galaxies and compare the ellipticity distribution with that of 80 dEs (Ryden & Terndrup 1994; Ryden et al. 1998) and 62 BCDs (Sung et al. 1998). We find that the ellipticity distribution of LSB ... More
On Bayes' theorem for improper mixturesDec 14 2011Although Bayes's theorem demands a prior that is a probability distribution on the parameter space, the calculus associated with Bayes's theorem sometimes generates sensible procedures from improper priors, Pitman's estimator being a good example. However, ... More
Statistical analysis of latent generalized correlation matrix estimation in transelliptical distributionMay 29 2013Sep 28 2016Correlation matrices play a key role in many multivariate methods (e.g., graphical model estimation and factor analysis). The current state-of-the-art in estimating large correlation matrices focuses on the use of Pearson's sample correlation matrix. ... More
Decoding spectral energy distributions of dust-obscured starburst-AGNFeb 28 2012We present BayeSED, a general purpose tool for doing Bayesian analysis of SEDs by using whatever pre-existing model SED libraries or their linear combinations. The artificial neural networks (ANNs), principal component analysis (PCA) and multimodal nested ... More
Triple Microlens OGLE-2008-BLG-092L: Binary Stellar System with a Circumprimary Uranus-type PlanetAug 26 2014Jun 25 2015We present the gravitational microlensing discovery of a 4 M_Uranus planet that orbits a 0.7 M_Sun star at ~18 AU. This is the first known analog of Uranus. Similar planets, i.e., cold ice-giants, are inaccessible to either radial velocity or transit ... More
Spitzer Microlensing of MOA-2016-BLG-231L : A Counter-Rotating Brown Dwarf Binary in the Galactic DiskFeb 08 2019Feb 12 2019We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very low-mass brown dwarfs (BDs) with $M_1 = 21^{+12}_{-5} \ M_J$ and $M_2 = 9^{+5}_{-2}\ M_J$, and it is located in ... More
High Dimensional Semiparametric Scale-Invariant Principal Component AnalysisFeb 18 2014We propose a new high dimensional semiparametric principal component analysis (PCA) method, named Copula Component Analysis (COCA). The semiparametric model assumes that, after unspecified marginally monotone transformations, the distributions are multivariate ... More
ECA: High Dimensional Elliptical Component Analysis in non-Gaussian DistributionsOct 14 2013Oct 03 2016We present a robust alternative to principal component analysis (PCA) --- called elliptical component analysis (ECA) --- for analyzing high dimensional, elliptically distributed data. ECA estimates the eigenspace of the covariance matrix of the elliptical ... More