• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.83.1-83.1
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• 2014

Open clusters consisting of a co-spatial and coeval population with a similar chemical composition are a superb astrophysical test bed in both stellar and galactic astronomy. We introduce not only several scientific issues relating to these objects but also comprehensive studies of the two young open clusters Westerlund 1 and IC 1848 formed in extremely different star-forming conditions. Westerlund 1 is known as the most massive starburst cluster in the Galaxy. Located in the Scutum-Centaurus spiral arm, the cluster is relatively close to the Galactic Center. The apparent surface density is very high. On the other hand, IC 1848 is a core cluster within the large-scale star-forming region W5 lying in the Perseus arm. Unlike Westerlund 1, IC 1848 with a putatively low metallicity exhibits a low surface density. We present the fundamental parameters of those young clusters, such as reddening, distance, and age, obtained from the broadband photometric analysis. The stellar initial mass function (IMF) of the clusters is used to investigate the effects of the different star-forming conditions on the star formation activity. With the results of previous studies for several young open clusters, our preliminary results support a possibility that star formation activity may be affected by the environmental factors or the initial condition of natal clouds. In addition, we shortly discuss the age scale and spread of pre-main sequence stars to understand the formation processes of star clusters.

• Journal of the Korean Society of Costume
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• v.60 no.4
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• pp.30-44
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• 2010

The definition of pregnancy has changed as society and its values have developed through different periods of history. In the ancient period, the definition of a woman's fertility was that female deities provided fecundity to barren women and barren land, and protected both the pregnant women during the period of gestation and also the land during the time of growth. These goddesses also administered the appropriate ceremonial rituals for conception and childbirth, and for planting and harvesting. After that, for the last 2,000 years, the most conspicuous icon has been "The Virgin Mary with the Infant Christ". Mary was the mother of Jesus Christ and model for Christian women. However, the centuries the image of woman and pregnancy has been changed, modern society through education, careers and job opportunities allows many women to be more than just a wife or a mother. Moreover, in the 21st century, many pregnant women want stylish maternity wear because they are proud and their minds are opened by these new icons of birth culture as like the pregnancy of many famous stars. From this the purposes of this study are as follows, Firstly, to study on the meaning of woman's fertility from ancient period to present time by social changes. Secondly, to investigate the historical concept of the maternity wear for current modern maternity fashion market. Finally, to expect to use this study would be helpful basic data for develop of the new researches of the maternity fashion in the future.

• Journal of The Korean Astronomical Society
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• v.32 no.1
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• pp.7-16
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• 1999

Open clusters are useful tools to investigate the structure and evolution of the Galactic disk. We have started a long-term project to obtain UBVI CCD photometry of open clusters which were little studied before, using the Doyak 1.8 m telescope of Bohyunsan Optical Astronomy Observatory in Korea. The primary goals of this project are (1) to make a catalog of UBVI photometry of open clusters, (2) to make an atlas of open clusters, and (3) to survey and monitor variable stars in open clusters. Here we describe this project and report the first results based on preliminary analysis of the data on four open clusters in the survey sample: Be 14, Cr 74, Biu 9, and NGC 2355. Isochrone fitting of the color-magnitude diagrams of the clusters shows that all of them are intermediate age to old (0.3-1.6 Gyrs) open clusters with moderate metallicity.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.177-187
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• 2003

Active galactic nuclei (AGNs) are distant, powerful sources of radiation over the entire electromagnetic spectrum, from radio waves to gamma-rays. There is much evidence that they are driven by gravitational accretion of stars, dust, and gas, onto central massive black holes (MBHs) imprisoning anywhere from $\~$1 to $\~$10,000 million solar masses; such objects may naturally form in the centers of galaxies during their normal dynamical evolution. A small fraction of AGNs, of the radio-loud type (RLAGNs), are somehow able to generate powerful synchrotron-emitting structures (cores, jets, lobes) with sizes ranging from pc to Mpc. A brief summary of AGN observations and theories is given, with an emphasis on RLAGNs. Preliminary results from the imaging of 10000 extragalactic radio sources observed in the MITVLA snapshot survey, and from a new analytic theory of the time-variable power output from Kerr black hole magnetospheres, are presented. To better understand the complex physical processes within the central engines of AGNs, it is important to confront the observations with theories, from the viewpoint of analyzing the time-variable behaviours of AGNs - which have been recorded over both 'short' human ($10^0-10^9\;s$) and 'long' cosmic ($10^{13} - 10^{17}\;s$) timescales. Some key ingredients of a basic mathematical formalism are outlined, which may help in building detailed Monte-Carlo models of evolving AGN populations; such numerical calculations should be potentially important tools for useful interpretation of the large amounts of statistical data now publicly available for both AGNs and RLAGNs.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.189-212
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• 2003

I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at z > 2 (> 10 Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of $\approx$ 20 metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of the RGCs and that of the BGCs varies depending on galaxies. It is concluded that the BGCs might have formed 12-13 Gyr ago, while the RGCs and giant elliptical galaxies might have formed similarly 10-11 Gyr ago. It remains now to explain the existence of a gap between the RGC formation epoch and the BGC formation epoch, and the rapid metallicity increase during the gap (${\Delta}t{\approx}$ 2 Gyr). If hierarchical merging can form a significant number of giant elliptical galaxies > 10 Gyr ago, several observational constraints from stars and globular clusters in elliptical galaxies can be explained.

• Journal of The Korean Astronomical Society
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• v.14 no.2
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• pp.55-71
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• 1981

On the basis of observational constraints, particularly the relationship between metal abundance and cumulative stellar mass, a simple two-zone disk-halo model for the chemical evolution of our Galaxy was investigated, assuming different chemical processes in the disk and halo and the infall rates of the halo gas defined by the halo evolution. The main results of the present model calculations are: (i) The halo formation requires more than 80% of the initial galactic mass and it takes a period of $2{\sim}3{\times}10^9$ yrs. (ii) The halo evolution is divided into two phases, a fast collapse phase ($t=2{\sim}3{\times}10^8$ yrs) during which period most of the halo stars $({\sim}95%)$ are formed and a later slow collapse phase which is characterized by the chemical enrichment due to the inflow of external matter to the halo. (iii) The disk evolution is also divided into two phases, an active disk formation phase with a time-dependent initial mass function (IMF) up to $t{\approx}6{\times}10^9$ yrs and a later steady slow formation phase with a constant IMF. It is found that at the very early time $t{\approx}5{\times}10^8$ yrs, the metal abundance in the disk is rapidly increased to ${\sim}1/3$ of the present value but the total stellar mass only to ${\sim}10%$ of the present value, finally reaching about 80% of the present values toward the end of the active formation phase.

• Publications of The Korean Astronomical Society
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• v.21 no.2
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• pp.101-112
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• 2006

We developed a new program for automatic continuum normalization of Echelle spectrographic data. Using this algorithm, we have determined spectral continuum of almost BOES data. The first advantage of this algorithm is that we can save much time for continuum determination and normalization. The second advantage is that the result of this algorithm is very reliable for almost spectral type of spectrum. But this algorithm cannot be applied directly to the spectrum which has very strong and broad emission lines, for example Wolf-Rayet type spectrum. We implanted this algorithm to the program which was developed in the previous study. And we introduced more upgraded BOES data reduction program. This program has more convenient graphical user interface environment, so users can easily reduce BOES data. Lastly, we presented the result of study on line profile variation of magnetic Ap/Bp stars analyzed using this program.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.121-123
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• 2015

We report our measurements of the trigonometric distance and proper motion of IRAS 20056+3350, obtained from the annual parallax of $H_2O$ masers. Our distance of $D=4.69^{+0.65}_{-0.51}kpc$, which is 2.8 times larger than the near kinematic distance adopted in the literature, places IRAS 20056+3350 at the leading tip of the Local arm and proximal to the Solar circle. We estimated the proper motion of IRAS 20056+3350 to be (${\mu}_{\alpha}cos{\delta}$, ${\mu}_{\delta}$) = ($-2.62{\pm}0.33$, $-5.65{\pm}0.52$) $mas\;yr^{-1}$ from the group motion of $H_2O$ masers, and use our results to estimate the angular velocity of Galactic rotation at the Galactocentric distance of the Sun, ${\Omega}_0=29.75{\pm}2.29km\;s^{-1}kpc^{-1}$, which is consistent with the values obtained for other tangent points and Solar circle objects.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.741-743
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• 2015

We have designed and built three cost effective observatories, in distinct models, which can house Schmidt-Cassegrain type small telescopes having aperture sizes up to 16 inches. Using the available small telescopes, we provided the people of Manipura State in the far north-east corner of India the opportunity to observe directly with their own eyes the rare, spectacular events of the solar eclipse of January 15, 2010, lunar eclipse of December 10, 2011 and the transit of Venus of June 6, 2012. Apart from sharing a platform with the public for astronomy education and popularization through public outreach programs such as workshops, seminars and night watch programs, we have also developed a laboratory infrastructure and gained expertise in observational techniques based on photoelectric photometry, CCD imaging, CCD photometry and spectroscopy. Our team has become a partner in the ongoing international 'Orion project' headquartered in Phoenix, Arizona, USA which will be producing high quality photometric and spectroscopic data for five stars in the Orion constellation, namely Betelgeuse (alpha Orionis), Rigel (beta Orionis), Mintaka (delta Orionis), Alnilam (epsilon Orionis) and Alnitak (zeta Orionis). In the present paper, the authors would like to give a detailed report of their activities for the growth of astronomy in the state of Manipur, India.

• Journal of The Korean Astronomical Society
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• v.41 no.4
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• pp.99-107
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• 2008

When a new counting experiment is proposed, it is crucial to predict whether the desired source signal will be detected, or how much observation time is required in order to detect the signal at a certain significance level. The concept of the a priori prediction of the detection limit in a newly proposed experiment should be distinguished from the a posteriori claim or decision whether a source signal was detected in an experiment already performed, and the calculation of statistical significance of a measured source signal. We formulate precise definitions of these concepts based on the statistical theory of hypothesis testing, and derive an approximate formula to estimate quickly the a priori detection limit of expected Poissonian source signals. A more accurate algorithm for calculating the detection limits in a counting experiment is also proposed. The formula and the proposed algorithm may be used for the estimation of required integration or observation time in proposals of new experiments. Applications include the calculation of integration time required for the detection of faint emission lines in a newly proposed spectroscopic observation, and the detection of faint sources in a new imaging observation. We apply the results to the calculation of observation time required to claim the detection of the surface thermal emission from neutron stars with two virtual instruments.