• Journal of Astronomy and Space Sciences
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• v.23 no.4
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• pp.303-310
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• 2006

We model the aspherical dust envelopes around O-rich AGB stars. We perform the radiative transfer model calculations for axisymmetric dust distributions. We simulate what could be observed from the aspherical dust envelopes around O-rich AGB stars by presenting the model spectral energy distributions and images at various wave-lengths for different optical depths and viewing angles. The model results are very different from the ones with spherically symmetric geometry.

• Publications of The Korean Astronomical Society
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• v.15 no.spc1
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• pp.85-91
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• 2000

Infrared spectroscopic observations and their analysis revealed many physical and chemical characteristics of the various stars with dust envelopes. Especially, AGB stars and young stellar objects are believed to be major contributors of infrared radiation from galaxies. The wavelength of the peak spectral energy for typical galaxies is about $100{\mu}m$. Therefore, infrared spectral observations of galaxies provide important information for their overall properties. The qualitative analysis of the infrared spectra which are made of various stars and interstellar matter will be possible through a new population synthesis.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.118.1-118.1
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• 2014

Stars create and expel new chemical elements and dust at the end of the stellar life cycle. Therefore, understanding the evolved stars, their mass loss process, and the conditions of the returning material to be mixed with the surrounding interstellar medium is an important step toward studies on the new generation of stars as well as the evolution of cosmic elements in galactic scale. I will review the first results from the ALMA Early Science on the evolved stars and direct future works.

• Publications of The Korean Astronomical Society
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• v.2 no.1
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• pp.30-38
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• 1985

We derived initial mass functions (IMF) of massive stars in three different regions of spiral arms within 2.5kpc from the sun. The derived IMF slope $\beta$ of Local arm stars is found to be $-2.09{\sim}-2.06$, very close to that of Bisiacchi et al. (1983). For Sagittarius-Carina arm stars $\beta$ ranges from -1.77 to - 1.72 which is close to that of overall stars given by Germany et al. (1982). Possible causes inducing the regional difference in IMFs are discussed.

• Publications of The Korean Astronomical Society
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• v.2 no.1
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• pp.39-46
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• 1985

We analyzed the reddening of 873 bright G and K stars from the DDO photometry in combination with MK spectral classes and (B-V) colors. About a quarter of the sample stars have DDO indices beyond the limits of DDO calibrations. To extend the reddening determination to all stars, we applied a scheme for reddening determination of field G and K stars by using the DDO calibrations (Janes 1977, 1979b) and MK-(B-V) relation of FitzGerald (1970).

• The Research Journal of the Costume Culture
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• v.7 no.6
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• pp.28-40
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• 1999

The purpose of this study was to understand the Korean teenagers\` clothing behavior through pointing out the factors that clothing behavior of teenagers that was initiated from the important reference group, TV stars. The subject of this study were 570 purposively selected students at female middle and high school students in Seoul. The results were as follows : 1. The clothing conformity to TV stars relating to demographic variables was influenced significantly by location and personal expense variable in the high school group. 2. The exhibition showed a more important role to the clothing conformity in middle school group than in high school group. 3. The clothing conformity to TV stars relating to the clothing related variables was significantly affected by self-confidence to clothing than clothing normative recognition, clothing risk recognition and degree of clothing importance regardless of groups. 4. The clothing conformity to TV stars relating to TV media variables was affected by TV media star identification variable in both groups. And in case of middle school group, interests in TV stars also had influence on the clothing conformity to TV stars. And in case of high school group, interests in TV had effect on the imitation to TV stars\` clothing. As middle school students tend to have self-identification about a particular person, TV media stars become the reference group for the adolescence to follow their clothing.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.57.3-57.3
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• 2015

The formation of the Milky Way stellar halo is thought to be the result of merging and accretion of building blocks such as dwarf galaxies and massive globular clusters. Recently, Deason et al. (2015) suggested that the Milky Way outer halo formed mostly from big building blocks, such as dwarf spheroidal galaxies, based on the similar number ratio of blue straggler (BS) stars to blue horizontal-branch (BHB) stars. Here we demonstrate, however, that this result is seriously biased by not taking into detailed consideration on the formation mechanism of BHB stars from helium enhanced second-generation population. In particular, the high BS-to-BHB ratio observed in the outer halo fields is most likely due to a small number of BHB stars provided by GCs rather than to a large number of BS stars. This is supported by our dynamical evolution model of GCs which shows preferential removal of first generation stars in GCs. Moreover, there are sufficient number of outer halo GCs which show very high BS-to-BHB ratio. Therefore, the BS-to-BHB number ratio is not a good indicator to use in arguing that more massive dwarf galaxies are the main building blocks of the Milky Way outer halo. Several lines of evidence still suggest that GCs can contribute a signicant fraction of the outer halo stars.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.55.2-55.2
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• 2012

Silicate-carbon stars are characterized by oxygen-rich (O-rich) dust features despite their carbon-rich (C-rich) photospheres. While the origin of silicate-carbon stars has been a mystery ever since their discovery, the most widely accepted hypothesis is that the silicate-carbon stars have a low-luminosity companion and the O-rich material is stored in a circumbinary disk or a circumstellar disk even after the primary star becomes a carbon star. In order to study the properties of circumstellar dust envelopes of silicate-carbon stars, we perform radiative transfer model calculations using RADMC-3D with an axi-symmetric dust density distribution (a disk) as well as a spherically symmetric dust distribution. For various dust envelope models with different shapes and chemistry, we calculate the model spectral energy distributions (SEDs) and compare the model results with the observed SEDs of selected 5 silicate-carbon stars. The Circumstellar disk models are fairly well fitted with the observational data of 5 silicate-carbon stars. We find some evidences that the circumbinary disk model could be a better explanation for the origin of silicate carbon stars than the simple detached silicate dust shell model of the transition phase of the stellar chemistry.

• Communications for Statistical Applications and Methods
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• v.20 no.4
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• pp.271-281
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• 2013

This paper considers a problem of classification of variable stars based on functional data analysis. For a better understanding of galaxy structure and stellar evolution, various approaches for classification of variable stars have been studied. Several features that explain the characteristics of variable stars (such as color index, amplitude, period, and Fourier coefficients) were usually used to classify variable stars. Excluding other factors but focusing only on the curve shapes of variable stars, Deb and Singh (2009) proposed a classification procedure using multivariate principal component analysis. However, this approach is limited to accommodate some features of the light curve data that are unequally spaced in the phase domain and have some functional properties. In this paper, we propose a light curve estimation method that is suitable for functional data analysis, and provide a classification procedure for variable stars that combined the features of a light curve with existing functional data analysis methods. To evaluate its practical applicability, we apply the proposed classification procedure to the data sets of variable stars from the project STellar Astrophysics and Research on Exoplanets (STARE).

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.147.1-147.1
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• 2011

We investigate the chemical differentiation in F, G, K type stars with and without planets to extend the work by Kang et al. (2011) to various spectral types. Since the primordial chemical composition has been preserved in the stellar atmosphere, stellar metallicity can provide the information on the primordial material, which is the potential building block of planets. Therefore, we can explore the favored conditions for planet formation through the comparison of chemical compositions between planet-host stars (PHSs) and stars without planets. In this work, we analyze 19 F, G, and K type stars. In each spectrum, we measure equivalent widths (EWs) of Fe, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni using TAME (Tools for Automatic Measurement of Equivalent width). The abundances of these species can be derived with the measured EWs and MOOG code (Sneden 1973). Like results by precedent studies, we find that planet-host stars have abundances higher than stars without planets. The typical difference in the abundances of Na, Mn, Co and Ni is $0.4{\pm}0.2dex$. In addition, as found in Kang et al. (2011), Mn is the most different element between PHSs and comparison stars.