• 천문학회보
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• 제35권2호
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• pp.30.1-30.1
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• 2010

마젤란형태의 왜소불규칙은하인 NGC 1156은 일정한 별탄생율을 보이고 있고 B밴드에서는 마젤란은하보다 25%나 더 밝은 은하로서 불규칙은하로서는 상당히 밝은 편에 위치해 있는 것으로 나타난다. 그동안 이 은하까지의 거리는 Tully-Fisher 관계식을 이용하거나 그 은하 내에 존재하는 가장 밝은 별을 이용하여 구하였으나 이 두 방법에 의해 구한 값이 큰 차이를 보이고 있다. 우리는 NGC 1156의 HST ACS/HRC 측광자료와 TRGB(Tip magnitude of Red Giant Branch) 방법을 이용하여 이 은하의 거리지수 (m-M)o=$28.0\pm0.15$를 얻었고 (U-B, B-V) 색색도를 이용하여 성간소광값 E(B-V)=$0.35\pm0.05$을 얻었다. 이 거리지수를 적용하면 이 은하의 절대등급은 1mag 어두운 값을 보인다.

• 천문학회보
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• 제35권2호
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• pp.27.1-27.1
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• 2010

Globular cluster (GC) systems in most galaxies, particularly in ellipticals, show bimodal color distributions. Because broadband colors trace metallicity at old ages, this phenomenon has been commonly interpreted as bimodal metallicity distributions, implying the presence of two sub-populations in the globular cluster system within a galaxy. However, a new explanation has recently been proposed, in which the non-linear nature of color-metallicity relations induced by horizontal-branch stars can produce bimodal color distributions even from unimodal metallicity distributions. In this study, we put these two explanations to the test on the origin of color bimodality, using multi-band (U,B,V and I) photometry of globular clusters in NGC 1399, the central giant elliptical galaxy in Fornax galaxy cluster. We find significant changes in the morphology of color distributions when using different colors. The observation is also well reproduced by the Monte Carlo realization of GC color when a unimodal metallicity distribution and the theoretical non-linear color-metallicity relations are assumed. We discuss the implications regarding theories on galaxy formation and evolution.

• 천문학회보
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• 제42권1호
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• pp.49.1-49.1
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• 2017

In order to investigate the origin of multiple stellar populations in the halo and bulge of the Milky Way, we have constructed chemical evolution models for the low-mass proto-Galactic subsystems such as globular clusters (GCs). Unlike previous studies, we assume that supernova blast waves undergo blowout without expelling the pre-enriched gas, while relatively slow winds of massive stars, together with the winds and ejecta from low and intermediate mass asymptotic giant branch stars, are all locally retained in these less massive systems. We first applied these models to investigate the origin of super-helium-rich red clump stars in the metal-rich bulge as recently suggested by Lee et al. (2015). We find that chemical enrichments by the winds of massive stars can naturally reproduce the required helium enhancement (dY/dZ = 6) for the second generation stars. Disruption of these "building blocks" in a hierarchical merging paradigm would have provided helium enhanced stars to the bulge field. Interestingly, we also find that the observed Na-O anticorrelation in metal-poor GCs can be reproduced, when multiple episodes of starbursts are allowed to continue in these subsystems. Specific star formation history with decreasing time intervals between the stellar generations, however, is required to obtain this result, as would be expected from the orbital evolution of these subsystems in a proto-Galaxy. The "mass budget problem" is also much alleviated by our models without ad-hoc assumptions on star formation efficiency and initial mass function.

• 천문학회보
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• 제36권2호
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• pp.145.2-145.2
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• 2011

We present the results of simultaneous observations of SiO v = 1, 2, J = 1-0, $^{29}SiO$ v = 0, J = 1-0, and $H_2O$ $6_{16}-5_{23}$ maser lines toward 152 known $H_2O$-only maser sources (the sources which are previously detected only in the 22 GHz $H_2O$ maser emission) using Yonsei and Tamna 21-m radio telescopes of the Korean VLBI Network from 2009 June to 2011 January. Both SiO and $H_2O$ maser emission were detected from 62 sources giving a detection rate of 40.8 %. SiO-only maser emission was detected from 27 sources, while $H_2O$-only maser was detected from 22 sources. We have identified 19 new detections of SiO maser emission for previous non-detection sources and 51 new detections of SiO maser for previously not observed sources. Characteristics of all observed sources in the IRAS two-color diagram is investigated including their evolutionary sequence and mutual relations between SiO and $H_2O$ maser emission. These observational results will be useful for statistical study of asymptotic giant branch (AGB) stars and future VLBI observation.

• 천문학논총
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• 제30권2호
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• pp.283-287
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• 2015

Within the context of the hugely successful SAGE-LMC and SAGE-SMC surveys, Spitzer photometry observations of the Large and Small Magellanic Clouds have revealed millions of infrared point sources in each galaxy. The brightest infrared sources are generally dust producing and mass-losing evolved stars, and several tens of thousands of such stars have been classified. After photometrically classifying these objects, the dust production by several kinds of evolved stars - such as Asymptotic Giant Branch stars and Red Supergiants - can be determined. SAGE-Spec is the spectroscopic follow-up to the SAGE-LMC survey, and it has obtained Spitzer-IRS $5-40{\mu}m$ spectroscopy of about 200 sources in the LMC. Combined with archival data from other programs, observations at a total of ~1000 pointings have been obtained in the LMC, while ~250 IRS pointings were observed in the SMC. Of these, a few hundred pointings represent dust producing and mass-losing evolved stars, covering a range in colors, luminosities, and thus mass-loss rates. Red Supergiants and O-rich and C-rich AGB stars - the main dust producers - are well represented in the spectroscopic sample. This paper will summarize what we know about the mineralogy of dust producing evolved stars, and discuss their relative importance in the total dust budget.

• 천문학회보
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• 제37권2호
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• pp.75.2-75.2
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• 2012

SNe Ia are a well-known powerful distance indicator. Type Ia supernova (SN) 2011fe was discovered in the nearby spiral galaxy M101 in 2011. It was discovered in less than one day after its explosion and is one of the nearest SNe Ia. Therefore SN 2011fe plays a significant role for calibrating the luminosity of the SNe Ia as well as for studying the progenitors of SNe Ia. However, previous estimates of the distance to M101 based on various methods show a large range. We present a new determination of the distance to M101 using the tip of the red giant branch (TRGB) method. We measure the distance from the F555W and F814W images of nine fields taken with the HST/ACS and HST/WFPC2 available in the HST archive. We derive a distance estimate with much smaller errors than previous studies. We discuss the implication of our results in relation with the calibration of optical and near-infrared maximum magnitudes of SNe Ia and the Hubble Constant.

• 천문학회지
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• 제51권5호
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• pp.155-164
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• 2018

We present various infrared two-color diagrams (2CDs) using WISE data for asymptotic giant branch (AGB) stars and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use the sample of 5036 AGB stars, 660 post-AGB stars, and 2748 PNe in our Galaxy. For each object, we cross-identify the IRAS, AKARI, WISE, and 2MASS counterparts. To investigate the spectral evolution from AGB stars to PNe, we compare the theoretical model tracks of AGB stars and post-AGB stars with the observations on the IR 2CDs. We find that the theoretical dust shell model tracks can roughly explain the observations of AGB stars, post-AGB stars, and PNe on the various IR 2CDs. WISE data are useful in studying the evolution of AGB stars and PNe, especially for dim objects. We find that most observed color indices generally increase during the evolution from AGB stars to PNe. We also find that $Fe_{0.9}Mg_{0.1}O$ dust is useful to fit the observed WISE W3-W4 colors for O-rich AGB stars with thin dust shells.

• 융합경영연구
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• 제9권5호
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• pp.27-37
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• 2021

Purpose: By foreshadowing the historical background and cultural influence of Korean food and economic development in China, this paper demonstrates Chinese market entry strategies taken by TheBorn with its company history and CEO's background. Research design, data and methodology: The eclectic paradigm was utilized to analyze ownership, localization, and internalization advantages for TheBorn's first entry into the Chinese market. The research answers how TheBorn could expand its business in the early 2000s while most were skeptical about the globalization of Korean food. Results: First, possessing various restaurant franchises, food patents, and developments, and media use enabled to achieve a strong ownership advantage. Second, the Chinese market is conveniently located in South Korea. Thus, TheBorn could exercise direct management to its overseas restaurant to maintain the food quality and service. Lastly, establishing a sauce manufacturing plant and its branch company accelerated further expansions to other Chinese cities. Conclusions: Based on those success factors, TheBorn extended its business into different cities in China and emerged as a franchisor giant in the Korean restaurant franchise industry.

• 천문학회보
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• 제44권1호
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• pp.85.4-85.4
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• 2019

Supernovae (SNe) are well known as good cosmological distance probes owing to their brightness and well-characterized light curve property. Specifically, type Ia SNe have contributed greatly to our understanding of acceleration of cosmic expansion. However, type IIP supernovae occur most frequently (~ 40% of all) at low and high redshift. As knowledge on the type IIP SNe increases, distance measurement methods using type IIP SNe have evolved. In this study, we apply Photometric Color Method (PCM), which needs only photometric data using properties of plateau on type IIP SNe light curves, to measure distances of several host galaxies of SNe IIP from the Intensive Monitoring Survey of Nearby Galaxies (IMSNG). The daily monitoring of galaxies at < 50 Mpc allows us to construct a dense light curve of SNe that occurred in our target galaxies. We observed two SNe IIP, SN2014cx and SN2017eaw and measured distances to their host galaxies, NGC 337 and NGC6946 respectively. Our results are comparable with other secondary distance measurement methods, 4-5 Mpc, however smaller than the result derived from the Tip of Red Giant Branch (TRGB) method, $6.7{\pm}0.2$ and $7.7{\pm}0.3Mpc$.

• 천문학회보
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• 제44권1호
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• pp.67.2-67.2
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• 2019

We present the results of KVN and ALMA observations toward WX Psc (IRC+10011) which is a long-period variable OH/IR star. The SiO masers of v=1 and v=2, J=5-4, and the SiO thermal emission of v=0, J=5-4 were observed together with H2O v2=1 (232.6 GHz) and continuum emission at ALMA Band 6 in October 2017 (Cycle 5). This observation aims to investigate the physical association between the inner and outer parts of the circumstellar envelope (CSE) swept by the stellar winds, which is very crucial to understand the asymmetric outward motions developed during the evolutionary phases from the asymptotic giant branch (AGB) stars to the planetary nebulae (PNe). The strong SiO maser features and thermal emissions are detected together with the continuum emission in ALMA observation, which imply the elongated morphology of the CSE of WX Psc. While the spatial resolution of about 20 mas in ALMA observation cannot clearly resolve the detailed characteristics of the inner part of the CSE, the Korean VLBI Network (KVN) observations show the spatial distributions of the v=1 J=1-0, J=2-1, J=3-2 SiO masers emitted from the inner regions of CSE, which are the complementary to the ALMA results. Therefore, we expect these results reveal how the bipolar features of the 22 GHz H2O maser are connected to the innermost region of CSE through the dust condensation region, which is closely related to the enormous mass ejection of the evolved stars.