• Journal of the Korean earth science society
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• v.31 no.4
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• pp.370-377
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• 2010

In this study, we investigated the kinematical properties of the L1521F-IRS in Taurus region using HCN (J=1-0) molecular line. The high resolution mapping has carried out by $5{\times}5$ point observations covering $3.7'{\times}3.7'$ area using a 12-m telescope of Arizona Radio Observatory in Tucsan, USA. L1521F which harbors the faint infrared L1521F-IRS, displayed a strong central concentration of integrated intensity in HCN without serious molecular depletion. It showed a symmetric kinematical structure with the opposite infall motion in either side of the central cores. It is a direct evidence of bipolar outflows in the core of L1521F.

• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.276-285
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• 2003

In the undercooled melt of $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy, the solidification behavior including nucleation and growth of crystals at the micrometer level has been observed in-situ by use of a confocal scanning laser microscope combined with an infrared image furnace. The $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy specimens were cooled from the liquid state to glass transition temperature. 575 K, at various cooling late under a helium gas flow. According to the cooling rate, the morphologies of the solidification front are changed among various types, irregular jog like front, columnar dendritic front, cellular grain, star like shape jog and fine grain, etc. The velocities of the solid-liquid interface are measured to be $10^{-5}{\sim}10^{-8}$ m/s which are at least two orders higher than the theoretical crystal growth rates. Combining the morphologies observed in terms of cooling rates and their solidification behaviors, we conclude that phase separation takes place in the undercooled molten $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy. The continuous cooling transformation (CCT) diagram was constructed from solidification onset time at various linear cooling conditions with different rate. The CCT diagram suggests that the critical cooling rate for glassy solidification is about 1.5 K/s, which is in agreement with the previous calorimetric findings.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.147.2-147.2
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• 2011

We have initiated a long-term identification campaign of supernova remnant candidates in X-ray regime. In the short-listed unidentified sources from the ROSAT All Sky Survey, we have chosen the brightest candidate, G308.3-1.4, as our pilot target for a dedicated investigation with Chandra X-ray Observatory. Our observation has revealed an incomplete shell-like X-ray structure which well-correlated with the radio feature. Together with the spectral properties of a shocked heated plasma, we confirm that G308.3-1.4 is indeed a supernova remnant. A bright X-ray point source which locates close to the remnant center is also uncovered in this observation. Its spectral behavior conform with those observed in a rare class of neutron stars. The properties of its optical/infrared counterpart suggests the evidence for a late-type companion star. Interestingly, possible excesses in B-band and H-alpha have been found which indicate this can be an accretion-powered system. With the further support from the putative periodicity of ~1.4 hrs, this source can possibly provide the direct evidence of a binary system survived in a supernova explosion for the first time.

• Publications of The Korean Astronomical Society
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• v.26 no.2
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• pp.71-87
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• 2011

Gravitational waves are predicted by the Einstein's theory of General Relativity. The direct detection of gravitational waves is one of the most challenging tasks in modern science and engineering due to the 'weak' nature of gravity. Recent development of the laser interferometer technology, however, makes it possible to build a detector on Earth that is sensitive up to 100-1000 Mpc for strong sources. It implies an expected detection rate of neutron star mergers, which are one of the most important targets for ground-based detectors, ranges between a few to a few hundred per year. Therefore, we expect that the gravitational-wave observation will be routine within several years. Strongest gravitational-wave sources include tight binaries composed of compact objects, supernova explosions, gamma-ray bursts, mergers of supermassive black holes, etc. Together with the electromagnetic waves, the gravitational wave observation will allow us to explore the most exotic nature of astrophysical objects as well as the very early evolution of the universe. This review provides a comprehensive overview of the theory of gravitational waves, principles of detections, gravitational-wave detectors, astrophysical sources of gravitational waves, and future prospects.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.76-76
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• 2011

The SPICA (SPace Infrared Telescope for Cosmology & Astrophysics) project is a next-generation astronomical mission optimized for mid- and far-infrared observation with a cryogenically cooled 3m-class telescope. Due to its high angular resolution and unprecedented sensitivity, SPICA will enable us to resolve many key issues from the star-formation history of the universe to the planetary formation. As an international collaboration, KASI proposed the near-infrared instrument which is composed of two parts; (1) science observation with the capability of imaging and spectroscopy covering $0.7{\mu}m$ to $5{\mu}m$ (FPC-S) (2) fine guiding to stabilize and improve the attitude (FPC-G). Here, we present the current status of SPICA/FPC.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.81.1-81.1
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• 2015

FIMS/SPEAR is a dual-channel far-ultraviolet imaging spectrograph on board the Korean microsatellite STSAT-1, which was launched on 2003 September 27. While the instrument is optimized for the observation of diffuse emissions, it was able to observe a number of bright stars without much contamination from the diffuse background or other faint stars. In this paper, we present a catalog of the far-ultraviolet spectra for 543 stars observed by FIMS/SPEAR during its mission lifetime of a year and a half, covering over the 80% of the sky. Of these, 296 stars were also observed by the International Ultraviolet Explorer (IUE), which covered a wide spectral band including the FIMS wavelength band (1370--1710 A). The stellar spectral types involved in the catalog span from B0 to A3. We compare the new spectra with those of IUE when they are available, and discuss some examples. We also revised the effective area of FIMS that the FIMS stellar spectra are consistent with the IUE spectra.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.177-179
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• 2012

We present Spitzer IRS spectroscopy of $CO_2$ ice toward 19 young stellar objects (YSOs) with luminosity lower than $1L_{\odot}$. Pure $CO_2$ ice forms only at elevated temperatures, T > 20 K, and thus at higher luminosities. Current internal luminosities of YSOs with L < $1L_{\odot}$ do not provide such conditions out to radii of typical envelopes. Significant amounts of pure $CO_2$ ice would signify a higher past luminosity. We analyze $15.2{\mu}m$ $CO_2$ ice bending mode absorption lines in comparison to the laboratory data. We decompose pure $CO_2$ ice from 12 out of 19 young low luminosity sources. The presence of the pure $CO_2$ ice component indicates high dust temperature and hence high luminosity in the past. The sum of all the ice components (total $CO_2$ ice amount) can be explained by a long period of low luminosity stage between episodic accretion bursts as predicted in an episodic accretion scenario. Chemical modeling shows that the episodic accretion scenario explains the observed total $CO_2$ ice amount best.

• Journal of Astronomy and Space Sciences
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• v.34 no.3
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• pp.199-205
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• 2017

A high resolution spectroscopic observation of the red supergiant star RM_1-390 in the Large Magellanic Cloud was made from a 3.6 m telescope at the European Southern Observatory. Spectral resolving power was R=20,000, with a signal-to-noise ratio S/N > 100. We found the atmospheric parameters of RM_1-390 to be as follows: the effective temperature $T_{eff}=4,250{\pm}50K$, the surface gravity ${\log}\;g=0.16{\pm}0.1$, the microturbulent velocity $v_{micro}=2.5km/s$, the macroturbulence velocity $v_{macro}=9km/s$ and the iron abundance $[Fe/H]=-0.73{\pm}0.11$. The abundances of 18 chemical elements from silicon to thorium in the atmosphere of RM_1-390 were found using the spectrum synthesis method. The relative deficiencies of all elements are close to that of iron. The fit of abundance pattern by the solar system distribution of r- and s-element isotopes shows the importance of the s-process. The plot of relative abundances as a function of second ionization potentials of corresponding chemical elements allows us to find a possibility of convective energy transport in the photosphere of RM_1-390.

• Journal of The Korean Astronomical Society
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• v.43 no.4
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• pp.123-133
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• 2010

In order to study properties of the pulsation in the infrared emission for long period variables, we collect and analyze the infrared observational data at L band for 12 OH/IR. The observation data cover about three decades including recent data from the ISO and Spitzer. We use the Marquardt-Levenberg algorithm to determine the pulsation period and amplitude for each star and compare them with results of previous investigations at infrared and radio bands. We obtain the relationship between the pulsation periods and the amplitudes at L band. Contrary to the results at K band, there is no difference of the trends in the short and long period regions of the period-luminosity relation at L band. This may be due to the molecular absorption effect at K band. The correlations among the L band parameters, IRAS [12-25] colors, and K band parameters may be explained as results of the dust shell parameters affected by the stellar pulsation. The large scatter of the correlation could be due to the existence of a distribution of central stars with various masses and pulsation modes.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.78.1-78.1
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• 2013

The hierarchical model of galaxy formation predicts that galaxy halos contain merger relics in the form of long stellar stream. Thus, tidal substructure of stars around globular clusters, such as tidal tails, could be an essential evidence of the merging scenario in the formation of the Galaxy. From April 2010 to December 2012, we obtained $45^{\prime}{\times}45^{\prime}$ wide-field JHKs near-infrared photometric imaging data for about 20 globular clusters in the Milky Way, and examined the stellar density distribution around globular clusters. Here, we introduce the preliminary results of stellar spatial distributions and radial surface density profiles of four globular clusters. In order to minimize the field star contamination and identify the cluster's member candidates stars, we used a statistical filtering algorithm and gave weights on the CMDs of globular clusters. In two-dimensional stellar density maps, we could found tidal stripping structures for some globular clusters. The orientation of tidal substructure seems to associate with the effects of dynamical interactions with the Galaxy and cluster's orbit. Indeed, the radial surface density profile accurately describes this stripping structures as a break in the slope of profile. The observational results could give us further observational evidence of merging scenario of the formation of the Galaxy.