Induk Lee

SEOUL NATIONAL UNIVERSITY 4K × 4K CAMERA (SNUCAM) FOR MAIDANAK OBSERVATORY

We present the characteristics of the Seoul National University 4k Camera (SNUCAM) and report its performance on the 1.5m telescope at the Maidanak observatory in Uzbekistan. SNUCAM is a CCD camera with a pixel scale of 0.266” in 4096 × 4096 format, covering 18.1’×18.1’ field of view on the 1.5m. The camera is currently equipped with Bessell UBVRI, Hα, SDSS ugriz, and Y-band filters, allowing us to carry out a variety of scientific programs ranging from exoplanet studies to survey of quasars at high redshift. We examine properties of SNUCAM such as the bias level and its temporal variation, the dark current, the readout noise, the gain, the linearity, the fringe patterns, the amplifier bias, and the bad pixels. From our observations, we also constructed the master fringe frames in I-, z-, and Y-band. We outline some of the current scientific programs being carried out with SNUCAM, and demonstrate that SNUCAM on the 1.5m can deliver excellent images that reach to the 5-σ detection limits of R ~ 25.5 mag and z ~ 22.7 mag in 1 hour total integration.

OPTICAL IMAGES AND SOURCE CATALOG OF AKARI NORTH ECLIPTIC POLE WIDE SURVEY FIELD

We present the source catalog and the properties of the B-, R-, and I-band images obtained to support the AKARI North Ecliptic Pole Wide (NEP-Wide) survey. The NEP-Wide is an AKARI infrared imaging survey of the north ecliptic pole covering a 5.8 deg2 area over 2.5-6 μm wavelengths. The optical imaging data were obtained at the Maidanak Observatory in Uzbekistan using the Seoul National University 4k × 4k Camera on the 1.5 m telescope. These images cover 4.9 deg2 where no deep optical imaging data are available. Our B-, R-, and I-band data reach the depths of ~23.4, ~23.1, and ~22.3 mag (AB) at 5σ, respectively. The source catalog contains 96,460 objects in the R band, and the astrometric accuracy is about 015 at 1σ in each R.A. and decl. direction. These photometric data will be useful for many studies including identification of optical counterparts of the infrared sources detected by AKARI, analysis of their spectral energy distributions from optical through infrared, and the selection of interesting objects to understand the obscured galaxy evolution.

Seoul National University Bright Quasar Survey in Optical (SNUQSO). II. Discovery of 40 Bright Quasars Near the Galactic Plane

We report the discovery of 40 bright quasars and active galactic nuclei (AGNs) at low Galactic latitude (b < ). The low Galactic latitude region has been considered a place to avoid when searching for extragalactic sources, because of the high Galactic extinction, as well as a large number of stars contaminating the sample selection. Bright quasars (R 17) suffer more from such difficulties because they look like bright stars, which are numerous at low b, yet their surface number density is very low. In order to find quasars in this region of the sky less explored for extragalactic sources, we have started a survey of low Galactic latitude bright quasars as a part of the Seoul National University Quasar Survey in Optical (SNUQSO). Quasar candidates have been selected from radio and near-infrared (NIR) data. Out of 88 targets, we identify 29 bright quasars/AGNs around the antigalactic center, and 11 bright quasars/AGNs in the outskirts of the Galactic center, from two observing runs in 2006 at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea. Our finding demonstrates that quasars/AGNs can be discovered effectively, even at low Galactic latitude, using multiwavelength data.

FIRST KOREAN OBSERVATIONS OF GAMMA-RAY BURST AFTERGLOWS AT MT. LEMMON OPTICAL ASTRONOMY OBSERVATORY (LOAO)

We outline our GRB afterglow observation program using the 1-m telescope at Mt. Lemmon Optical Astronomy Observatory (LOAO), and report the first observations of the GRB afterglows. During the 2007B semester, we performed follow-up imaging obsrevations of 6 GRBs, and succeeded in detecting four GRB afterglows (GRB 071010B, GRB 071018, GRB 071020, and GRB 071025) while placing useful upper limits on the light curves of the other GRBs. Among the observed events, we find that three events are special and interesting. GRB 071010B has a light curve which has an unusually long jet break time of U.8 days. For GRB 071025, its red R - I (~ 2) color suggests that it is likely to be at z ~ 5. GRB 071020 has a light curve which shows a clear brightening at 0.3-1 days after the burst, where our LOAO data playa crucial role by providing an unambiguous evidence for the brightening. These are the first successful detections of GRB afterglows by a facility owned and operated by a Korean institution, demonstrating the usefulness of the 1-m telescope for transient phenomena such as GRBs up to very high redshift.

Seoul National University Bright Quasar Survey in Optical (SNUQSO). I. First Phase Observations and Results

We present results from the first phase of the Seoul National University Bright Quasar Survey in Optical (SNUQSO) as well as its basic observational setup. Previous and current large-area surveys have been successful in identifying many quasars, but they could have missed bright quasars due to their survey design. In order to help complete the census of bright quasars, we have performed spectroscopic observations of new bright quasar candidates selected from various methods based on optical colors, near-infrared colors, radio, and X-ray data. In 2005/2006, we observed 55 bright quasar candidates using the Bohyunsan Optical Echelle Spectrograph (BOES) on the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea. We identify 14 quasars/Seyferts from our observation, including an optically bright quasar with i = 14.98 mag at z = 0.092 (SDSS J003236.59–091026.2). Non-quasar/Seyfert objects are found to be mostly stars, among which there are five M-type stars and one cataclysmic variable. Our result shows that there still exist bright quasars to be discovered. However, at the same time, we conclude that finding new bright quasars in high Galactic latitude regions is very challenging and that the existing compilation of optically bright quasars is nearly complete in the northern hemisphere.

Dust Properties in the Afterglow of GRB 071025 at z ~ 5

At high redshift, the universe is so young that core-collapse supernovae (SNe) are suspected to be the dominant source of dust production. However, some observations indicate that the dust production by SNe is an inefficient process, casting doubts on the existence of abundant SNe-dust in the early universe. Recently, Perley et al. reported that the afterglow of GRB 071025—an unusually red gamma-ray burst (GRB) at z ~ 5—shows evidence for SNe-produced dust. Since this is perhaps the only high-redshift GRB exhibiting compelling evidence for SNe-dust but the result could easily be affected by small systematics in photometry, we re-examined the extinction properties of GRB 071025 using our own optical/near-infrared data at a different epoch. In addition, we tested SNe-dust models with different progenitor masses and dust destruction efficiencies to constrain the dust formation mechanisms. By searching for the best-fit model of the afterglow spectral energy distribution, we confirm the previous claim that the dust in GRB 071025 is most likely to originate from SNe. We also find that the SNe-dust model of 13 or 25 M ☉ without dust destruction fits the extinction property of GRB 071025 best, while pair-instability SNe models with a 170 M ☉ progenitor poorly fit the data. Our results indicate that, at least in some systems at high redshift, SNe with intermediate initial masses within 10-30 M ☉ were the main contributors for the dust enrichment, and the dust destruction effect due to reverse shock was negligible.

DUST PROPERTIES IN THE AFTERGLOW OF GRB 071025 AT z {approx} 5

At high redshift, the universe is so young that core-collapse supernovae (SNe) are suspected to be the dominant source of dust production. However, some observations indicate that the dust production by SNe is an inefficient process, casting doubts on the existence of abundant SNe-dust in the early universe. Recently, Perley et al. reported that the afterglow of GRB 071025—an unusually red gamma-ray burst (GRB) at z ~ 5—shows evidence for SNe-produced dust. Since this is perhaps the only high-redshift GRB exhibiting compelling evidence for SNe-dust but the result could easily be affected by small systematics in photometry, we re-examined the extinction properties of GRB 071025 using our own optical/near-infrared data at a different epoch. In addition, we tested SNe-dust models with different progenitor masses and dust destruction efficiencies to constrain the dust formation mechanisms. By searching for the best-fit model of the afterglow spectral energy distribution, we confirm the previous claim that the dust in GRB 071025 is most likely to originate from SNe. We also find that the SNe-dust model of 13 or 25 M ☉ without dust destruction fits the extinction property of GRB 071025 best, while pair-instability SNe models with a 170 M ☉ progenitor poorly fit the data. Our results indicate that, at least in some systems at high redshift, SNe with intermediate initial masses within 10-30 M ☉ were the main contributors for the dust enrichment, and the dust destruction effect due to reverse shock was negligible.

DUST PROPERTIES IN THE AFTERGLOW OF GRB 071025 ATz∼ 5

At high redshift, the universe is so young that core-collapse supernovae (SNe) are suspected to be the dominant source of dust production. However, some observations indicate that the dust production by SNe is an inefficient process, casting doubts on the existence of abundant SNe-dust in the early universe. Recently, Perley et al. reported that the afterglow of GRB 071025—an unusually red gamma-ray burst (GRB) at z ~ 5—shows evidence for SNe-produced dust. Since this is perhaps the only high-redshift GRB exhibiting compelling evidence for SNe-dust but the result could easily be affected by small systematics in photometry, we re-examined the extinction properties of GRB 071025 using our own optical/near-infrared data at a different epoch. In addition, we tested SNe-dust models with different progenitor masses and dust destruction efficiencies to constrain the dust formation mechanisms. By searching for the best-fit model of the afterglow spectral energy distribution, we confirm the previous claim that the dust in GRB 071025 is most likely to originate from SNe. We also find that the SNe-dust model of 13 or 25 M ☉ without dust destruction fits the extinction property of GRB 071025 best, while pair-instability SNe models with a 170 M ☉ progenitor poorly fit the data. Our results indicate that, at least in some systems at high redshift, SNe with intermediate initial masses within 10-30 M ☉ were the main contributors for the dust enrichment, and the dust destruction effect due to reverse shock was negligible.

Efficient astronomical data classification on large-scale distributed systems

Classification of different kinds of space objects plays an important role in many astronomy areas Nowadays the classification process can possibly involve a huge amount of data It could take a long time for processing and demand many resources for computation and storage In addition, it may also take much effort to train a qualified expert who needs to have both the astronomy domain knowledge and the capability to manipulate the data This research intends to provide an efficient, scalable classification system for astronomy research We implement a dynamic classification framework and system using support vector machines (SVMs) The proposed system is based on a large-scale, distributed storage environment, on which scientists can design their analysis processes in a more abstract manner, instead of an awkward and time-consuming approach which searches and collects related subset of data from the huge data set The experimental results confirm that our system is scalable and efficient.

SWIFTGRB GRB071010B: OUTLIER OF THEEsrcpeak–EγANDEiso–Esrcpeak–tsrcjetCORRELATIONS

We present multi-band results for GRB071010B based on Swift, Suzaku, and ground-based optical observations. This burst is an ideal target to evaluate the robustness of the E{sup src}{sub peak} - E{sub iso} and E{sup src}{sub peak} - E {sub gamma} relations, whose studies have been in stagnation due to the lack of the combined estimation of E{sup src} {sub peak} and long-term optical monitoring. The joint prompt spectral fitting using Swift/Burst Alert Telescope and Suzaku/Wide-band All-sky Monitor data yielded the spectral peak energy as E {sup src} {sub peak} of 86.5{sup +6.4} {sub -6.3} keV and E {sub iso} of 2.25{sup +0.19} {sub -0.16} x 10{sup 52} erg with z = 0.947. The optical afterglow light curve is well fitted by a simple power law with temporal index alpha = -0.60 +- 0.02. The lower limit of temporal break in the optical light curve is 9.8 days. Our multi-wavelength analysis reveals that GRB071010B follows E{sup src}{sub peak} - E{sub iso} but violates the E{sup src}{sub peak} - E{sub gamma} and E{sub iso} - E {sup src}{sub peak} - t {sup src}{sub jet} at more than the 3sigma level.