• 천문학회보
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• 제40권1호
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• pp.78.3-78.3
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• 2015

About 70 high redshift quasars with $z{\geq}5$ have been discovered through combinations of standard broad-band filters to distinguish them from contaminating sources. However, among the discovered quasars so far, there is a redshift gap at $5{\leq}z{\leq}6$ due to the limitation of traditional filter sets and selection techniques. To understand the early mass growth of supermassive black holes and the final stage of the cosmic reionization, it is important to find a statistically meaningful sample of quasars with various physical properties. Here we suggest a new selection technique of high redshift quasars using medium-band filters: nine filters with bandwidths of 50nm and central wavelengths from 625 to 1025nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with R~15. We installed these filters to SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1m telescope at McDonald Observatory, and conducted test observations of known high redshift quasars at $4.7{\leq}z{\leq}6.1$ and also dwarf stars for comparison. We found differences in SED shapes between high redshift quasars and dwarf stars, determined their locations on color-color diagrams, and demonstrated that the medium-band filters can enhance the efficiency of selecting robust quasar candidates in this redshift range. In this poster, we propose an effective selection method of high redshift quasars using these medium-band filters and discuss its effect on our high redshift quasar survey.

• 천문학논총
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• 제30권2호
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• pp.279-281
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• 2015

We adopt the PASTEL catalog combined with SIMBAD radial velocities as a testing standard to validate the stellar parameters (effective temperature $T_{eff}$, surface gravity log g, metallicity [Fe/H] and radial velocity $V_r$) from the first data release (DR1) of The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey. After applying data reduction and temperature constraints to the sample obtained by cross-identification, we compare the stellar parameters from DR1 and PASTEL. The results show that the DR1 results are reliable under certain conditions. We derive a dispersion of 110 K, 0.19 dex, 0.11 dex and $4.91kms^{-1}$ in specified effective temperature ranges, for $T_{eff}$, log g, [Fe/H] and $V_r$ respectively. Systematic errors are negligible except for those of $V_r$. In addition, for stars with PASTEL [Fe/H] < -1:5, the metallicities in DR1 are systematically higher than those in PASTEL.

• 천문학회보
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• 제40권1호
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• pp.86.4-87
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• 2015

We will soon complete the installation of 1m telescope at Deokheung Optical Astronomy Observatory (DOAO), National Youth Space Center (NYSC). Before the test observation with NYSC 1m telescope, we present the specs of the 1M telescope and observational conditions of the DOAO site, such as the seeing data at DOAO and the atmospheric extinction coefficients obtained from the observations of standard stars and stellar clusters with 120mm and 150mm refractor in 2014. Since atmospheric extinction coefficients depend on the observational instruments as well as the atmospheric conditions of the site, the improved data with NYSC 1m telescope will be obtained right after the completion of 1M telescope installation. We are planning to invite all astronomers to use 1m telescope for their sciences via regular proposal processes in this year.

• 천문학논총
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• 제27권4호
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• pp.141-144
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• 2012

We present the results of Spectral Energy Distribution (SED) fitting of far-infrared galaxies detected in the AKARI Deep Field-South (ADF-S) Survey and discuss their physical properties. Additionally, we perform a comparison between photometric redshifts estimated using only optical and both optical and infrared data. We conclude that our sample consists mostly of nearby galaxies rich in dust and young stars. We observe an improvement in the estimation of photometric redshifts when the IR data are included, comparing to a standard approach based mainly on the optical to UV photometry.

• Journal of Astronomy and Space Sciences
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• 제1권1호
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• pp.41-53
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• 1984

Photoelectric observations of the close eclipsing binary system CW Cep, which is well known of its apsidal motion, were made on 20 nights during August and November in 1983 using two 61cm reflectors at the Sobaeksan Observing Station of Korean National Astronomical Observatory and I1san Observing Station of Yonsei University Observatory. Standardized new light curves in UBV system are presented with a total of 1,422 individual observations. For the corrections of regional and instrumental differences, same standard stars were observed at the two observatories. Four new times of minimum light were determined with the method of Kwee and van Woerden(1956). With all of the collected times of minima, apsidal motion of this system was checked, but the O-C values calculated by the light elements of Nha(1975) and Soderhjelm (1976) did not coincide well with new times of minima. New light elements which satisfy most times of minima better, and are deduced the apsidal period derived by the new light elements turns out to be 43 years, somewhat longer than those of values previously known.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.91-100
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• 1998

자외선 영역에서 색지수와 유효온도의 상관관계를 구하기 위한 pilot project 로 25개의 표준상태에 대하여 유효온도와 색지수를 산출하였다. 유효온도는 자외선 영역의 IUE 저분산 스펙트럼의 에너지 분포 곡선을 Kurucx 모델과 비교하여 산출하였고, 자외선 색지수는 IUE 저분산 스펙트럼의 플럭스를 $300{\AA}$ 단위로 적분하여 등급으로 환산하여 산출하였다. 자외선 영역으 상관관계는 가시관선 영역의 상관관계와 유사한 형태로 나타났다.

• 천문학회보
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• 제39권2호
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• pp.38-38
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• 2014

Despite the great success that stellar evolution theory have enjoyed during the last 50 years, new challenges are emerging with recent observations of supernovae: many aspects of supernovae cannot be easily explained by the standard scenarios on supernova progenitors. A few examples include the red supergiant problem - the dearth of Type IIP supernova progenitors with masses higher than about 16 Msun, the non-detection of Type Ib/c supernova progenitors despite very deep searches in pre-supernova optical images, the unexpected blue colors of some Type IIn supernova progenitors, and the exotic stellar explosions of both ultra-faint and super-luminous types that have been only recently discovered. By confronting these observations with new stellar evolution models, we are making significnt progress in better understanding the role of metallicity, rotation and binary interactions for the pre-supernova evolution of massive stars. In this talk, I will give a brief review on the recent observational constraints on supernova progenitors and a progress report on several research projects that deal with pair-instability supernovae from the local Universe, type Ib/c supernovae from massive binary systems, and some peculiar stellar explosions like SN2012Z.

• 천문학회지
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• 제15권2호
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• pp.59-70
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• 1982

We have observed 85 UBV standard stars(V<6) with SNU photoelectric photometer system and 24" Cassegrain reflector at Sobaeksan Observing Station during the period between January and May, 1980 in order to examine the photometer system and to determine atmospheric extinction coefficients. From five night observations, the following results were obtained: (1) The set of filters(V=2mm GG 495, B=2mm GG 385+1mm BG 12, U=2mm UG 2) is better than the other filter set used in our tests on the basis of linear instrumental calibrations for V and B filters. (2) The SNU detecting system is very stable within ${\sigma}=0.002$ in magnitude in a night but the variation in its stability from night to night is not negligible. (3) The extinction coefficients were derived from two different methods and we have found no systematic seasonal variation in the extinction coefficients although the mean dispersion is considerable.

• 천문학회보
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• 제44권1호
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• pp.58.1-58.1
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• 2019

Gravitational-wave (GW) sources for the next decades would be in majority binaries consisting of neutron stars and/or black holes reside in the extragalactic environment. For example, GW170817 was the first extragalactic neutron star - neutron star binary found by GW observations and it was proved the power of multi-messenger astronomy (MMA) including the KMTNet observations. With the ever increased sensitivity, the $3^{rd}$ observation run (O3) led by the advanced LIGO and advanced Virgo this year aims to search for more 'standard' populations as well as 'exotic' ones expected by stellar evolution. I will present highlights of on-going efforts by researchers in Korea and those in abroad for estimating physical parameters of a source. Mass, spin, distance, and location are prerequisite information to constrain theoretical understanding of the source formation and evolution. Furthermore, these information are to be shared with the international community for follow-up multi-messenger observations. I will present the observational accuracy expected for the future GW observations and discuss their implications. If time allows, I will make a few remarks on prospects of O3 with KAGRA collaborations, which many domestic researchers are closely involved in.

• Nuclear Engineering and Technology
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• 제53권11호
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• pp.3741-3758
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• 2021

Outcomes of the FALCON code analysis-related part of the STARS-ENSI Service Project on Evaluation of the new U.S.NRC RIA Fuel Safety Criteria and Application to the Swiss Reactors are presented. Substantial conservatism of the updated safety limits for high-temperature and PCMI cladding failure, as proposed in the NRC Regulatory Guide RG 1.236, is confirmed. Applicability of the updated failure limits to fuel safety analysis in the Swiss PWRs, as applied to standard fuel designs using UO2 fuel pellets and SRA Zry-4 as cladding materials is discussed. Conducting of new integral RIA tests with irradiated samples using doped- and gadolinia fuel pellets to support appropriate fuel safety criteria for RIA events is recommended.