Hyun-Il Sung
A5002554891- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Pulsars and Gravitational Waves Research
- Calibration and Measurement Techniques
- Innovation in Digital Healthcare Systems
- Marine and Coastal Research
- Medical Imaging Techniques and Applications
- Spectroscopy and Laser Applications
- Radio Astronomy Observations and Technology
- Diverse Approaches in Healthcare and Education Studies
- Optical Systems and Laser Technology
- CCD and CMOS Imaging Sensors
- Science Education and Pedagogy
- Particle Accelerators and Free-Electron Lasers
- Technology and Data Analysis
- Optical Wireless Communication Technologies
- Impact of Light on Environment and Health
Korea Astronomy and Space Science Institute
2012-2024
Tokyo Institute of Technology
2011
Seoul National University
2002
ABSTRACT We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters ( BVRI and ugriz ). Combined with ultraviolet the Hubble Space Telescope Swift , we confirm significant time delays between continuum bands as a function wavelength, extending wavelength coverage 1158 Å z band (~9160 Å). find that lags at wavelengths longer...
Abstract We present the main results from a long-term reverberation mapping campaign carried out for Seoul National University AGN Monitoring Project (SAMP). High-quality data were obtained during 2015–2021 32 luminous active galactic nuclei (AGNs; i.e., continuum luminosity in range of 10 44–46 erg s −1 ) at regular cadence, 20–30 days spectroscopy and 3–5 photometry. obtain time lag measurements between variability H β emission AGNs; 25 those have best based on our quality assessment,...
Abstract One of the keys to success multimessenger astronomy is rapid identification electromagnetic wave counterpart, kilonova (KN), gravitational-wave (GW) event. Despite its importance, it hard find a KN associated with GW event, due poorly constrained localization map and numerous signals that could be confused as KN. Here, we present Gravitational-wave Electromagnetic Counterpart Korean Observatory (GECKO) project, GECKO observation GW190425, prospects in fourth observing run (O4)...
ABSTRACT During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert 1 galaxy NGC 5548 performed from 2014 February to July, normally highly correlated far continuum and broad emission line variations decorrelated for ∼60–70 days, starting ∼75 days after first HST /COS observation. Following this anomalous state, flux variability lines returned a more normal state. This transient behavior, characterized by significant deficits in...
Abstract How the environment of host galaxy affects formation multiple populations (MPs) in globular clusters (GCs) is one outstanding questions near-field cosmology. To understand true nature old GC MPs Large Magellanic Cloud (LMC), we study Ca–CN–CH photometry metal-poor LMC NGC 2257. We find predominantly first-generation-dominated populational number ratio n (FG): (SG) = 61:39(±4), where FG and SG denote first second generations, respectively. Both have similar cumulative radial...
We conduct a multiwavelength continuum variability study of the Seyfert 1 galaxy NGC 5548 to investigate temperature structure its accretion disk. The 19 overlapping light curves (1158 9157 angstroms) combine simultaneous HST , Swift and ground-based observations over 180 day period from 2014 January July. Light-curve is interpreted as reverberation response disk irradiation by central time-varying point source. Our model yields inclination, i, T1 at black hole, temperature-radius slope,...
Abstract The broad-line region (BLR) size–luminosity relation has paramount importance for estimating the mass of black holes in active galactic nuclei (AGNs). Traditionally, size H β BLR is often estimated from optical continuum luminosity at 5100 Å, while α and its correlation with much less constrained. As a part Seoul National University AGN Monitoring Project, which provides 6 yr photometric spectroscopic monitoring data, we present our measurements lags high-luminosity AGNs. Combined...
On 2005 December 30, Y.-J. Choi and P. R. Weissman discovered that the formerly dormant Centaur 2000 EC98 was in strong outburst. Previous observations by Rousselot et al. spanning a 3-year period indicated lack of coma down to 27 mag arcsec-2 level. We present Spitzer Space Telescope MIPS this newly active Centaur—now known as 174P/Echeclus (2000 EC98)—or 60558 Echeclus—taken 2006 late February. The images show signal at both 24 70 μm bands reveal an extended about 2' diameter. Analyses...
Context. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is a variability survey of Milky Way bulge and an adjacent section disk carried out from 2010 on Visible Infrared Telescope for Astronomy (VISTA). VVV will eventually deliver deep near-IR atlas with photometry positions five passbands (ZYJHKS) catalogue 1−10 million variable point sources – mostly unknown that require classifications.
The main progenitor candidates of Type Ia supernovae (SNe Ia) are white dwarfs in binary systems where the companion star is another dwarf (double degenerate (DD) system) or a less-evolved, non-degenerate with R* ≳ 0.1 R⊙ (single system). However, no direct observational evidence exists to tell us which system more common. Recent studies suggest that light curve supernova shortly after its explosion can be used set limit on size, R*. Here, we report high-cadence monitoring observations SN...
Abstract The progenitor system of Type Ia supernovae (SNe Ia) is expected to be a close binary consisting carbon/oxygen white dwarf (WD) and nondegenerate star or another WD. Here, we present results from high-cadence monitoring observations SN 2021hpr in spiral galaxy, NGC 3147, constraints on the based its early multicolor light-curve data. First, classify as normal long-term photometric spectroscopic More interestingly, found significant “early excess” light curve over simple power-law ∼...
Abstract The nuclear transient AT2019cuk/Tick Tock/SDSS J1430+2303 has been suggested to harbor a supermassive black hole (SMBH) binary near coalescence. We report results from high-cadence NICER X-ray monitoring with multiple visits per day 2022 January August, as well continued optical during the same time period. find no evidence of periodic/quasiperiodic modulation in X-ray, UV, or bands; however, we do observe exotic hard variability that is unusual for typical active galactic nuclei...
We present the results of high-resolution (R $\ge$ 30,000) optical and near-infrared spectroscopic monitoring observations a FU Orionis-type object, V960 Mon, which underwent an outburst in 2014 November. have monitored this object with Bohyunsan Optical Echelle Spectrograph (BOES) Immersion GRating INfrared (IGRINS) since December. Various features produced by wind, disk, outflow/jet were detected. The wind varied over time continually weakened after outburst. detected double-peaked line...
Abstract We present the results of a high-cadence spectroscopic and imaging monitoring campaign active galactic nucleus (AGN) NGC 4395. High signal-to-noise-ratio spectra were obtained at Gemini-N 8 m telescope using GMOS integral field spectrograph (IFS) on 2019 March 7 Keck I 10 Low-Resolution Imaging Spectrometer with slit masks 3 April 2. Photometric data number 1 m-class telescopes during same nights. The narrow-line region (NLR) is spatially resolved; therefore, its variable...
We present the variability and time lag measurements of PG 0934+013 based on a photometric spectroscopic monitoring campaign over two year period. obtained 46 epochs data from campaign, which was carried out using Southern African Large Telescope with $\sim$1 week cadence sets 4 month-long observing period, while we 80 \textit{B}-band imaging few 1-m class telescopes. Due to seven month gap between periods, separately measured lags broad emission lines including H$\beta$, by comparing line...
We present optical follow-up observation results of three binary black hole merger (BBH) events, GW190408_181802, GW190412, and GW190503_185404, which were detected by the Advanced LIGO Virgo gravitational wave (GW) detectors. Electromagnetic (EM) counterparts are generally not expected for BBH events. However, some theoretical models suggest that EM can possibly arise in special environments, prompting motivation to search such observed high-credibility regions sky events with telescopes...
Time-series CCD photometric observations of an intermediate age open cluster NGC 2301 were performed to search for variable stars, particularly γ Dor stars and δ Sct stars. We also carried out UBVI photometry study physical properties in the cluster. derived observational parameters from results. The best fit empirical ZAMS a color-color diagram gives reddening value . estimated distance modulus , isochrone fitting color-magnitude diagram. Using V time-series data, we carefully examined...
We report the results of our high resolution optical spectroscopic monitoring campaign (<TEX>${\lambda}$</TEX> = 3800 ~ 8800 <TEX>${\AA}$</TEX>, R 30000 - 45000) new FU Orionis-type object HBC 722. observed 722 with BOES 1.8-m telescope between November 26 and December 29, 2010, Orionis itself on January 26, 2011. detect a number previously unreported high-resolution K I Ca II lines beyond 7500 <TEX>${\AA}$</TEX>. resolve H<TEX>${\alpha}$</TEX> line profiles into three velocity components,...
We present the variability study of lowest-luminosity Seyfert 1 galaxy NGC 4395 based on photometric monitoring campaigns in 2017 and 2018. Using 22 ground-based space telescopes, we monitored with a $\sim$5 minute cadence during period 10 days obtained light curves UV, V, J, H, K/Ks bands as well H$\alpha$ narrow-band. The RMS is $\sim$0.13 mag \emph{Swift}-UVM2 V filter curves, decreasing down to $\sim$0.01 K filter. After correcting for continuum contribution narrow-band, measured time...
Even in an era where 8-meter class telescopes are common, small considered very valuable research facilities since they available for rapid follow-up or long term monitoring observations. To maximize the usefulness of Korea, we established SomangNet, a network 0.4-1.0 m optical operated by Korean institutions, 2020. Here, give overview project, describing current participating telescopes, its scientific scope and operation mode, prospects future activities. SomangNet currently includes 10...
Active galactic nuclei (AGNs) show a correlation between the size of broad line region (BLR) and monochromatic continuum luminosity at 5100 \AA, allowing black hole mass estimation based on single-epoch spectra. However, validity is yet to be clearly tested for high-luminosity AGNs. We present first reverberation-mapping results Seoul National University AGN monitoring program (SAMP), which designed focus luminous AGNs probing high end size-luminosity relation. report time lag measurements...
While the reverberation mapping technique is best available method for measuring black hole mass in active galactic nuclei (AGN) beyond local volume, this has been mainly applied to relatively low-to-moderate luminosity AGNs at low redshift. We present strategy of Seoul National University AGN Monitoring Project, which aims time delay \Hb\ line emission with respect continuum, using a sample high out z $\sim$0.5. simulated cross correlation results based on number mock light curves, order...