J.-Y. Choi
A5001798269- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- History and Developments in Astronomy
- Pulsars and Gravitational Waves Research
- Solar and Space Plasma Dynamics
- Astrophysical Phenomena and Observations
- Coral and Marine Ecosystems Studies
- Astrophysics and Cosmic Phenomena
- Astronomical Observations and Instrumentation
Chungbuk National University
2012-2016
University of Warsaw
2014
Because of the development large-format, wide-field cameras, microlensing surveys are now able to monitor millions stars with sufficient cadence detect planets. These new discoveries will span full range significance levels including planetary signals too small be distinguished from noise. At present, we do not understand where threshold is for detecting MOA-2011-BLG-293Lb first planet published surveys, and it also has substantial follow-up observations. This robustly detected in...
Impolite planet ignores host's partner 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 Using microlensing data taken with a worldwide network telescopes, Gould et al. found twice the mass Earth circles just one pair The same approach has potential to uncover other similar star and help illuminate some mysteries formation. Science , this issue p. 46
We report the discovery of a planetary system from observation high-magnification microlensing event OGLE-2012-BLG-0026. The lensing light curve exhibits complex central perturbation with multiple features. find that was produced by two planets located near Einstein ring planet host star. identify four possible solutions resulting well-known close/wide degeneracy. By measuring both lens parallax and radius, we estimate physical parameters system. According to best-fit model, masses are ∼0.11...
Observations of accretion disks around young brown dwarfs (BDs) have led to the speculation that they may form planetary systems similar normal stars. While there been several detections planetary-mass objects BDs (2MASS 1207-3932 and 2MASS 0441-2301), these companions relatively large mass ratios projected separations, suggesting formed in a manner analogous stellar binaries. We present discovery object orbiting field BD via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is...
We report the first mass and distance measurement of a caustic-crossing binary system OGLE-2014-BLG-1050L using space-based microlens parallax method. \emph{Spitzer} captured second event, which occurred $\sim$10 days before that seen from Earth. Due to coincidence source-lens relative motion was almost parallel direction binary-lens axis, four-fold degeneracy, known only occur in single-lens events, persists this case, leading either lower-mass (0.2 $M_\odot$ 0.07 $M_\odot$) at $\sim$1.1...
We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with planet–star mass ratio . Intensive photometric observations high-magnification event allow us to detect clear signal planet. Although no parallax is detected in light curve, we instead succeed at detecting flux from host star high-resolution JHK'-band images obtained by Subaru/AO188 and Infrared Camera Spectrograph instruments, allowing constrain absolute physical parameters planetary system. With help...
Although many models have been proposed, the physical mechanisms responsible for formation of low-mass brown dwarfs are poorly understood. The multiplicity properties and minimum mass brown-dwarf function provide critical empirical diagnostics these mechanisms. We present discovery via gravitational microlensing two very low-mass, tight binary systems. These binaries directly precisely measured total system masses 0.025 Msun 0.034 Msun, projected separations 0.31 AU 0.19 AU, making them...
We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because source previously known to be photometrically variable. Analyzing pre-event light curve, we demonstrate that it is irregular variable over timescales >200 days. Its dereddened color, (V − I)S, 0, 1.221 ± 0.051 mag, and from our lens model derive a radius 14.7 1.3 R☉, suggesting red giant star. initially...
We present the analysis of gravitational microlensing event OGLE-2013-BLG-0102. The light curve is characterized by a strong short-term anomaly superposed on smoothly varying lensing with moderate magnification $A_{\rm max}\sim 1.5$. It found that was produced binary lens mass ratio between components $q = 0.13$ and caused passage source trajectory over caustic located away from barycenter binary. From effects due to finite size parallactic motion Earth, physical parameters system are...
We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to microlensing event OGLE-2011-BLG-0265. Such system is very rare among known planetary systems and thus important for theoretical studies formation evolution. High-cadence temporal coverage signal combined with extended observations throughout allows us accurately model observed light curve. The final solution remains, however, degenerate yielding two possible configurations host star. In case...
We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and masses of Mh = 0.11+/-0.01 M_{sun} Mp 9.2+/-2.2M_Earth, corresponding to a very late M dwarf sub-Neptune-mass planet, respectively. system lies at DL 0.81 +/- 0.10 kpc with projected separation r 0.92 0.16 AU. Because host's a-priori-unlikely close distance, as well unusual nature system, we consider possibility that microlens parallax signal, which determines mass is actually due xallarap (source...
We present a detailed analysis of survey and follow-up observations microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage the lightcurve, especially perturbation part, allowed us to accurately measure parallax effect lens orbital motion. Combining our measurement with angular Einstein radius determined finite-source effects, we estimate physical parameters system. find that was caused by $2.73\pm 0.43\ M_{\rm J}$ planet orbiting...
Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions found by analyzing binary microlensing events discovered during 2004–2011 observation seasons. Based on low mass ratio criterion of q < 0.2, seven events: OGLE-2004-BLG-035, OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334,...
We report on the mass and distance measurements of two single-lens events from 2015 \emph{Spitzer} microlensing campaign. With both finite-source effect microlens parallax measurements, we find that lens OGLE-2015-BLG-1268 is very likely a brown dwarf. Assuming source star lies behind same amount dust as Bulge red clump, $45\pm7$ $M_{\rm J}$ dwarf at $5.9\pm1.0$ kpc. The second event, OGLE-2015-BLG-0763, $0.50\pm0.04$ $M_\odot$ $6.9\pm1.0$ show probability to definitively measure isolated...
We report the characterization of a massive (m p = 3:9±1:4M jup ) microlensing planet (OGLE-2015-BLG-0954Lb) orbiting an M dwarf host (M 0:33 0:12M ⊙ at distance toward Galactic bulge 0:6 +0.4 -0.2 kpc, which is extremely nearby by standards. The planet-host projected separation a⊥~ 1.2AU. was made possible wide-feld (4 deg 2 high cadence(Ґ 6 hr -1 monitoring Korea Microlensing Telescope Network (KMTNet), had two its three telescopes in commissioning operations time planetary anomaly. source...
We present the analysis of gravitational microlensing event OGLE-2011-BLG-0251. This anomalous was observed by several survey and follow-up collaborations conducting observations towards Galactic Bulge. Based on detailed modelling light curve, we find that lens is composed two masses with a mass ratio q=1.9 x 10^-3. Thanks to our detection higher-order effects curve due Earth's orbital motion finite size source, are able measure distance unambiguously. made up planet 0.53 +- 0.21,M_Jup...
We report the detection and mass measurement of a binary lens OGLE-2015-BLG-1285La,b, with more massive component having $M_1>1.35\,M_\odot$ (80% probability). A main-sequence star in this range is ruled out by limits on blue light, meaning that primary must be neutron or black hole. The system has projected separation $r_\perp= 6.1\pm 0.4\,{\rm AU}$ lies Galactic bulge. These measurements are based "microlens parallax" effect, i.e., comparing microlensing light curve as seen from $Spitzer$,...
Despite the astrophysical importance of binary star systems, detections are limited to those located in small ranges separations, distances, and masses thus it is necessary use a variety observational techniques for complete view stellar multiplicity across broad range physical parameters. In this paper, we report measurements two binaries discovered from observations microlensing events MOA-2011-BLG-090 OGLE-2011-BLG-0417. Determinations possible by simultaneously measuring Einstein radius...
We present the analysis of light curves 9 high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all events, we measure linear limb-darkening coefficients surface brightness profile stars by measuring deviation...
The co-planarity of solar-system planets led Kant to suggest that they formed from an accretion disk, and the discovery hundreds such disks around young stars as well co-planar planetary systems by Kepler satellite demonstrate this formation mechanism is extremely widespread. Many moons in solar system, Galilean Jupiter, also out coalesced into giant planets. We report here intermediate system OGLE-2013-BLG-0723LB/Bb composed a Venus-mass planet orbiting brown dwarf, which may be viewed...
High-magnification gravitational microlensing events provide an important channel of detecting planetary systems with multiple giants located at their birth places. In order to investigate the potential existence additional planets, we reanalyze light curves eight high-magnification for each which a single planet was previously detected. The analyzed include OGLE-2005-BLG-071, OGLE-2005-BLG-169, MOA-2007-BLG-400, MOA-2008-BLG-310, MOA-2009-BLG-319, MOA-2009-BLG-387, MOA-2010-BLG-477, and...
An important strength of the microlensing method to detect extrasolar planets is its high sensitivity low-mass planets. However, many believe that detections Earth-mass from ground-based observation would be difficult because limits set by finite-source effects. This view comes previous estimation planet detection probability based on fractional deviation planetary signals; however, a proper required when considering source brightness, which directly related photometric precision. In this...
Gravitational microlensing events produced by lenses composed of binary masses are important because they provide a major channel for determining physical parameters lenses. In this work, we analyze the light curves two binary-lens events, OGLE-2006-BLG-277 and OGLE-2012-BLG-0031, which exhibit strong deviations from standard models. From modeling considering various second-order effects, find that mostly explained effect lens orbital motion. We also parallax effects can mimic to some...
High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by planet or binary companion. It is known that central perturbations induced both types companions generally distinguished due essentially different magnification pattern around caustics. In this paper, we present case for which it difficult distinguish planetary and interpretations. The lensing light curve affected...
Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively breaks a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out an initial set 32 local minima in the parameter space. These clearly indicate lens stellar system possibly located within bulge our Galaxy, ruling alternative. We argue several types discrete degeneracies can be broken via such space-based observations.