• 한국지구과학회지
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• 제28권1호
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• pp.87-104
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• 2007

소형망원경을 이용하여 산개성단 내 단주기 미세 변광성을 체계적으로 탐사하기 위한 보현산 천문대 측광 모니터링 프로그램 Short Period Variability Survey(SPVS)의 일환으로, 젊은 산개성단 NGC 129의 $90'{\times}60'$ 영역에 대한 V필터 시계열 측광 관측을 수행하였다. 성단의 관측은 보현산 천문대 155mm 소형 굴절 망원경과 $3K{\times}2K$ CCD 카메라를 이용하여 2004년 10월 12일부터 2005년 11월 3일까지 총 11일간 수행되었으며, 그 결과 전체 2400장의 V 필터시계열 CCD 영상자료 및 성단의 색-등급도를 얻었다. 시계열 자료의 기기등급을 표준등급으로 변환하기 위하여 앙상블정규화 기법(ensemble normalization technique)을 사용하였다. 측광 후 총 9537개별의 시간에 따른 광도변화를 조사한결과 총 66개의 새로운 변광성을 발견 하였다. 새롭게 찾아낸 변광성들은 DFT(Discrete Fourier Transform) 분석과 위상 맞추기 방법(phase-matching technique)을 이용하여 변광 주기를 결정하였다. 결정된 변광성의 주기 및 진폭 변화, 색-등급도 상에서의 변광성의 위치 등을 고려하여 변광 유형을 조사한 결과 9개의 SPB형 변광성과 9개의 ${\delta}$ Scuti형 변광성, 29개의 식변광성, 17개의 장주기 변광성과 기타 2개의 변광성으로 분류할 수 있었다. 본 연구를 통해, 산개성단에서의 변광성 탐사 연구에 소형망원경이 유용하게 활용될 수 있음을 확인하였다.

• 천문학회보
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• 제35권1호
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• pp.82-82
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• 2010

We measure the topology of the galaxy distribution using the Seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7), examining the dependence of galaxy clustering topology on galaxy properties. The observational results are used to test galaxy formation models. A volume-limited sample defined by Mr<-20.19 enables us to measure the genus curve with amplitude of G=378 at 6h-1Mpc smoothing scale, with 4.8% uncertainty including all systematics and cosmic variance. The clustering topology over the smoothing length interval from 6 to 10h-1Mpc reveals a mild scale-dependence for the shift and void abundance (A_V) parameters of the genus curve. We find strong bias in the topology of galaxy clustering with respect to the predicted topology of the matter distribution, which is also scale-dependent. The luminosity dependence of galaxy clustering topology discovered by Park et al. (2005) is confirmed: the distribution of relatively brighter galaxies shows a greater prevalence of isolated clusters and more percolated voids. We find that galaxy clustering topology depends also on morphology and color. Even though early (late)-type galaxies show topology similar to that of red (blue) galaxies, the morphology dependence of topology is not identical to the color dependence. In particular, the void abundance parameter A_V depends on morphology more strongly than on color. We test five galaxy assignment schemes applied to cosmological N-body simulations to generate mock galaxies: the Halo-Galaxy one-to-one Correspondence (HGC) model, the Halo Occupation Distribution (HOD) model, and three implementations of Semi-Analytic Models (SAMs). None of the models reproduces all aspects of the observed clustering topology; the deviations vary from one model to another but include statistically significant discrepancies in the abundance of isolated voids or isolated clusters and the amplitude and overall shift of the genus curve. SAM predictions of the topology color-dependence are usually correct in sign but incorrect in magnitude.

• 천문학회보
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• 제38권2호
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• pp.55.1-55.1
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• 2013

The properties of bright galaxies are closely related to those neighbors and satellite galaxies. However, the effects of nearby companion are known to be very weak in a galaxy cluster, when the companions are bright galaxies. On the other hand, until now, it has not been clear whether the properties of bright galaxies are affected by their faint satellites in a galaxy cluster. Recently, J. H. Lee et al. (in preparation) have found that the colors of bright galaxies in WHL J085910.0+294957, a galaxy cluster at z = 0.3, show a measurable correlation with the mean colors of faint galaxies around them. To confirm that result and to investigate the host-satellite relationship depending on cluster properties, we carry out follow-up studies of a few galaxy clusters, beginning with Abell 3659 (z ~ 0.0907) imaged in the g' and r' bands using IMACS on the Magellan (Baade) 6.5m telescope. Cluster members are selected based on the distributions of color, size and concentration along magnitude and spatial distribution. In this poster, we present some preliminary results: marginal correlations in color between bright galaxies and their faint companions are found at the central region of Abell 3659. The implication of these results is discussed.

• 한국지리정보학회지
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• 제16권1호
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• pp.59-66
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• 2013

태풍이 해양을 이동할 때 해양환경은 물리 생물학적으로 한반도 주변해역에 영향을 미친다. 태풍이동의 결과로써 해양의 수직적 혼합과 용승작용은 해양 표층수 냉각을 유도하고 태풍의 경로에 따라 식물플랑크톤의 증가를 초래하며, 태풍 전과 후의 해양환경은 해양표층의 생물학적 변화에 중요한 역할을 했다. 비록 태풍 이동의 원인으로 해양 표층수의 냉각이 확대되지만, 엽록소, K490, SST와 같은 다른 물리-생물리적 반응은 서로 다른 경향을 나타낸다. 본 연구의 목적은 한반도 주변해역에 영향을 미치는 태풍 이동경로와 해색센서에 의해 관측된 해양환경변수를 비교하는데 있다. 부유물질, 흡광계수(K490), 엽록소와 같은 해양환경변수는 2002년부터 2005년 MODIS 자료가 적용되었다. 태풍이동 후 동해에서는 평균 엽록소 농도가 1-4배 증가하였고, 태풍 이동경로를 따라 태풍 이후 MODIS 엽록소의 평균 농도가 증가하였다. 그러나 제주도 해역은 동해역과 반대의 경향을 나타내었다.

• 한국의류학회지
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• 제24권4호
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• pp.605-615
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• 2000

This study was carried out to investigate sound characteristics including sound parameters and subjective sensation, and primary hand values related with sound of fabrics for blouse, and furthermore to predict subjective sound sensation with mechanical properties and sound parameters. Sound of specimens was analyzed by FFT. Level pressure of total sound(LPT), loudness(Z), coefficients of autoregressive(AR) functions for fitting the spectra, and sound color factors(ΔL and Δf) were obtained as sound parameters. Primary hand values for women's thin dress were calculated by using KES-FB. Subjective sensation for sound including softness, loudness, sharpness, clearness, roughness, highness, and pleasantness was evaluated by free modulus magnitude estimation. The results were as follows; 1. Fabrics for blouse showed similar spectral shapes to one another in that amplitude values were lower in most ranges of frequencies than fabrics for other uses. 2. It was found that fabrics for blouse were less louder because LPT, loudness(Z), and ARC values were lower than other fabrics. 3. Primary hand values indicated that specimens were soft-touched, flexible, and less crisp. Among primary hands related with sound, Shari values were higher for silk fabrics than for synthetic ones, while the values for Kishimi were similar, 4. Fabrics for blouse were rated more highly for softness, clearness, and pleasantness than for loudness, sharpness. roughness, and highness. Silk fabrics were evaluated more pleasant than synthetic fabrics. 5. Subjective sensation for sound of blouse fabrics were predicted with mechanical properties and physical sound parameters.

• 천문학회보
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• 제40권1호
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• pp.73.1-73.1
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• 2015

Isolated galaxies in low-density regions are significant in the sense that they are least affected by the hierarchical pattern of galaxy growth and interactions with perturbers at least for the last few Gyr. To form a comprehensive picture of the star formation history of isolated galaxies, we construct a catalog of isolated galaxies and their comparison sample in relatively denser environments. The galaxies are drawn from SDSS DR7 in the redshift range of 0.025 < z < 0.044. We performed visual inspection and classified their morphology following the Hubble classification scheme. We have investigated the color-magnitude diagram and found elliptical and unbarred spiral galaxies in isolated systems are relatively fainter and bluer than those in denser regions. For the spectroscopic study, we make use of the OSSY catalog (Oh et al. 2011). Our analysis on the absorption-line properties based on the comparison with stellar population models suggests that isolated elliptical galaxies are likely to be younger and metal poorer, while isolated Sc-type galaxies seem to have older luminosity-weighted ages, than their high-density counterpart. In addition, according to the BPT diagnostics, early-type galaxies among isolated galaxies are rather evenly classified into star forming, composite, Seyfert and LINER, whereas their comparisons are mainly populated in the LINER region. On the other hand, late-type galaxies do not show any prominent difference. We discuss the evolutionary histories of isolated galaxies in the context of the standard ${\Lambda}CDM$ cosmology.

• 천문학회보
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• 제40권1호
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• pp.71.3-71.3
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• 2015

Deep UBVI and $H{\alpha}$ photometry of the ${\eta}$ Carina nebula, one of the brightest nebulae on the sky, was obtained with the CTIO 4m telescope and MOSAIC II CCD Camera to determine the initial mass function down to low-mass (~1 M¤) stars. We modified the spatial variation coefficients in transformation relations of the MOSAIC II CCD. From the cross-identification of optical sources with previous surveys in X-ray, near-infrared, and mid-infrared, a clear PMS sequence is revealed in the optical color-magnitude diagrams down to V=23 mag. Our previous SSO 1m UBVI data for Trumpler 14 (Tr 14) and Trumpler 16 (Tr 16) region, and additional SSO 1m UBVI data for Trumpler 15 (Tr 15) region were combined with the CTIO 4m data to re-examine the reddening law and distance of the young open clusters in the ${\eta}$ Carina nebula. From the new photometric data for Tr 15 region, we report that RV[=AV/E(B-V)], the total-to-selective extinction ratio, decreases from southern part of the nebula (Tr 14 and Tr 16) to northern part (Tr 15) in our field of view.

• 천문학회지
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• 제44권5호
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• pp.177-193
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• 2011

We present a photometric study of five open clusters (Czernik 5, Alessi 53, Berkeley 49, Berkeley 84, and Pfleiderer 3) in the Sloan Digital Sky Survey. The position and size of these clusters are determined using the radial number density profiles of the stars, and the member stars of the clusters are selected using the proper motion data in the literature. We estimate the reddening, distance and age of the clusters based on the isochrone fitting in the color-magnitude diagram. The foreground reddenings for these clusters are estimated to be E(B - V ) = 0.71 - 1.55 mag. The distances to these clusters are derived to be 2.0 - 4.4 kpc, and their distances from the Galactic center range from 7.57 kpc to 12.35 kpc. Their ages are in the range from 250 Myr to 1 Gyr. Berkeley 49 and Berkeley 84 are located in the Orion spur, Czernik 5 is in the Perseus arm, and Pfleiderer 3 and Alessi 53 are located beyond the Perseus arm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.765-770
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• 2001

The objective of the present study is to investigate the effects of the various inlet boundary layer thickness on convective heat transfer distribution in a turbine cascade endwall and blade suction surface. In addition, the proper height of the boundary layer fences for various inlet boundary layer thickness were applied to turbine cascade endwall in order to reduce the secondary flow, and to verify its influence on the heat transfer process within the turbine cascade. Convective heat transfer distributions on the experimental regions were measured by the image processing system. The results show that heat transfer coefficients on the blade suction surface were increased with an augmentation of inlet boundary layer thickness. However, in a turbine cascade endwall, magnitude of heat transfer coefficients did not change with variation of inlet boundary layer thickness. The results also present that the boundary layer fence is effective in reducing heat transfer on the suction surface. On the other hand, in the endwall region, boundary layer fence brought about the subsidiary heat transfer increment.

• 천문학회지
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• 제30권1호
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• pp.83-94
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• 1997

We have identified the candidates for the primordial galaxies in the process of formation in the Hubble Deep Field (hereafter HDF). In order to select these objects we have removed objects brighter than 29-th magnitude in the HDF images and smoothed the maps with the Gaussian filters with the FWHM of 0.8' and 4' to obtain the difference maps. This has enabled us to find. very faint diffuse structures close to the sky level. Peaks are identified in the difference map for each of three HDF chips with three filters (F450W, F606W, and F814W). They have the apparent AB magnitudes typically between 29 and 31. The objects identified in different wavelengths filters have a strong cross-correlations. The correlation lengths are about 0.8'. This means that an object found in one filter can be also found as a peak within 0.8' separation in another filter, thus telling the reality of the identified objects. This angular scale is also the size of the primordial galaxies which have strong color fluctuations on their surfaces. Their large-scale distribution quite resembles that of nearby galaxies, supporting the idea that these objects are ancestors of the present bright galaxies forming at statistically high density regions. Inspections on individual objects show that these primordial galaxy candidates have tiny multiple glares embedded in diffuse backgrounds. Their radial light distributions are quite different from that of nearby bright galaxies. We may be now looking at the epoch of galaxy formation.