• 천문학회보
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• 제35권1호
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• pp.70.2-70.2
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• 2010

We present near- and mid-infrared images of the Crab Nebula, taken with the Infrared Camera (IRC) onboard the AKARI infrared space telescope. These images have a field-of-view of 10'*10' and show the full extent of the nebula at 3, 4, 7, 11, 15, and 24 um. The Crab nebula in near infrared is dominated by synchrotron emission while, in mid infrared, the ionic forbidden lines of Ar, Ne, S, and Fe makes significant contribution. We separate the line emission from synchrotron emission in 3-15 um AKARI bands using the ISOCAM CVF data, and present separate images for the line and synchrotron emissions in each band. We derive the total synchrotron fluxes of the Crab nebula in these bands, which are used to complete the synchrotron spectral energy distribution of the Crab nebula from radio to X-rays. We discuss the spectral variations of the Crab nebula.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.3102-3102
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• 2001

Constituents of several .representative seaweeds, such as wakame Undaria pinnatifida; hijikia Hizikia fusifome; and kombu Laminaria japonica, were found to have fairly large reaction rates determined by quenching experiments of emission spectra in the near-infrared region (1max: 1270 nm) from singlet oxygen (102). Emission spectra of singlet oxygen generated from an aqueous solution of Rose Bengal under irradiation with a green laser (330 nm) were measured by a near-infrared (NIR) emission spectrometer constructed in our laboratory. The quenching experiments were as follows: Intensities of emission spectra were measured in the absence (I0) and in the presence of the seaweed constituents (I): Ratios of I0/I were plotted against every concentration of the quenchers (Stern-Volmer plots) which gives a straight line. The slope of each line gives a kqt value which gives a quenching constant kq value (an antioxidative constant against singlet oxygen) when the t value (half-life time of singlet oxygen in the solvent used) was given. The determined reaction rates are between 103-105 (g/l)-ls-1; the larger ones are as large as that of ascorbic acid, 8.4 ${\times}$ 104 (g/1)-ls-1. Most of these seaweed constituents also showed antioxidative activity against auto-oxidation and superoxide as well as their immunological enhancing activity. These results suggest a possibility that dietary fibers which are supposed to prevent the large-intestine cancer by their physical properties may prevent the cancer, at least in parts, by their chemical, antioxidative activity.

• Rapid Communication in Photoscience
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• 제4권2호
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• pp.34-36
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• 2015

New spectroscopic characteristics of amorphous ferric hydroxide ($Fe(OH)_3$), interestingly in the near infrared (NIR) region, are presented in this study. The absorption spectrum of ferric hydroxide covers wide spectral regions from ultraviolet to NIR (200~900 nm). Unique emission bands were newly observed in the NIR regions (800~1400 nm). Several bands of this NIR emission are quiet well overlapped with the combinational vibrational absorption bands of water. From photothermal conversion study, very interestingly, temperature of aqueous mixture solution including the amorphous ferric hydroxide was significantly increased from ambient temperature to $38^{\circ}C$ for 30 minutes under irradiation of a standard helium lamp.

• 천문학논총
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• 제27권4호
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• pp.161-164
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• 2012

We performed a spectroscopic survey for cometary volatiles with the Infrared Camera onboard the Japanese infrared satellite AKARI. The observations were carried out in the near-infrared wavelength range in the period from 2008 June to 2010 January. In this paper, we summarize the observations and results of the AKARI survey for the mixing ratios of major volatiles in comets. We derived the $2.5-5{\mu}m$ spectra of 18 comets including both Oort cloud comets and Jupiter-family comets. Prominent emission bands in the observed spectra are the fundamental vibrational bands of water ($H_2O$) at $2.7{\mu}m$ and carbon dioxide ($CO_2$) at $4.3{\mu}m$. The fundamental vibrational band of carbon monoxide (CO) at $4.7{\mu}m$ and the broad emission feature probably related to C-H bearing molecules can also be recognized around the $3.4-3.5{\mu}m$ region in some comets. We detect $CO_2$ in 17 out of 18 comets, and derived gas production rate ratios of $CO_2$ with respect to $H_2O$ in 17 comets. We detect a reliable CO emission band only in three of the comets. Our data set provides the largest homogeneous database of $CO_2/H_2O$ ratios in comets obtained so far.

• 천문학회보
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• 제37권1호
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• pp.50.2-50.2
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• 2012

We present the results of near infrared (2.5-5 micron) spectroscopy of nearby luminous infrared galaxies (LIRGs) using AKARI. The LIRG catalog is constructed from the cross-correlation between the Infrared Astronomical Satellite and the Sloan Digital Sky Survey data, and optically non-Seyfert type LIRGs are selected for main targets. We search for optically elusive active galactic nuclei (AGNs), based on the strengths of 3.3 micron polycyclic aromatic hydrocarbon emission and dust absorption features at 3-4 micron. We investigate the hidden AGN fraction as a function of the infrared luminosity and correlation between optical and near infrared star formation indicators.

• 천문학논총
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• 제32권1호
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• pp.157-161
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• 2017

The dusty torus of Active Galactic Nuclei (AGNs) is one of the important components for the unification theory of AGNs. The geometry and properties of the dusty torus are key factors in understanding the nature of AGNs as well as the formation and evolution of AGNs. However, they are still under discussion. Infrared observation is useful for understanding the dusty torus as thermal emission from hot dust with the dust sublimation temperature (~ 1500 K) has been observed in the infrared. We have analyzed infrared spectroscopic data of low-redshift and high-redshift quasars, which are luminous AGNs. For the low-redshift quasars, we constructed the spectral energy distributions (SEDs) with AKARI near-infrared and Spitzer mid-infrared spectra and decomposed the SEDs into a power-law component from the nuclei, silicate features, and blackbody components with different temperatures from the dusty torus. From the decomposition, the temperature of the innermost dusty torus shows the range between 900-2000 K. For the high-redshift quasars, AKARI traced rest-frame optical and near-infrared spectra of AGNs. Combining with WISE data, we have found that the temperature of the innermost dusty torus in high redshift quasars is lower than that in typical quasars. The hydrogen $H{\alpha}$ emission line from the braod emission line region in the quasars also shows narrow full width at half maximum of $3000-4000km\;s^{-1}$. These results indicate that the dusty torus and the broad emission line region are more extended than those of typical quasars.

• 천문학논총
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• 제27권4호
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• pp.187-193
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• 2012

AKARI has 4 imaging bands in the far-infrared (FIR) and 9 imaging bands that cover the near-infrared (NIR) to mid-infrared (MIR) contiguously. The FIR bands probe the thermal emission from sub-micron dust grains, while the MIR bands observe emission from stochastically-heated very small grains and the unidentified infrared (UIR) band emissions from carbonaceous materials that contain aromatic and aliphatic bonds. The multi-band characteristics of the AKARI instruments are quite efficient to study the spectral energy distribution of the interstellar medium, which always shows multi-component nature, as well as its variations in the various environments. AKARI also has spectroscopic capabilities. In particular, one of the onboard instruments, Infrared Camera (IRC), can obtain a continuous spectrum from 2.5 to $13{\mu}m$ with the same slit. This allows us to make a comparative study of the UIR bands in the diffuse emission from the 3.3 to $11.3{\mu}m$ for the first time. The IRC explores high-sensitivity spectroscopy in the NIR, which enables the study of interstellar ices and the UIR band emission at $3.3-3.5{\mu}m$ in various objects. Particularly, the UIR bands in this spectral range contain unique information on the aromatic and aliphatic bonds in the band carriers. This presentation reviews the results of AKARI observations of the interstellar medium with an emphasis on the observations of the NIR spectroscopy.

• 천문학논총
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• 제27권4호
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• pp.195-200
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• 2012

We show how the rotation emission from isolated interstellar Polycyclic Aromatic Hydrocarbons (PAHs) can explain the so-called anomalous microwave emission (AME). AME has been discovered in the last decade as microwave interstellar emission (10 to 70 GHz) that is in excess compared to the classical emission processes: thermal dust, free-free and synchrotron. The PAHs are the interstellar planar nano-carbons responsible for the near infrared emission bands in the 3 to 15 micron range. Theoretical studies show that under the physical conditions of the interstellar medium (radiation and density) the PAHs adopt supra-thermal rotation velocities, and consequently they are responsible for emission in the microwave range. The first results from the PLANCK mission unexpectedly showed that the AME is not only emitted by specific galactic interstellar clouds, but it is present throughout the galactic plane, and is particularly strong in the cold molecular gas. The comparison of theory and observations shows that the measured emission is fully consistent with rotation emission from interstellar PAHs. We draw the main lines of our PLANCK-AKARI collaborative program which intends to progress on this question by direct comparison of the near infrared (AKARI) and microwave (PLANCK) emissions of the galactic plane.

• 천문학논총
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• 제32권1호
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• pp.73-75
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• 2017

Debris disks are important observational clues to understanding on-going planetary system formation. They are usually identified by significant mid-infrared excess on top of the photospheric emission of a central star on the basis of prediction from J-, H-, and Ks-band fluxes and the stellar model spectra. For bright stars, 2MASS near-infrared fluxes suffer large uncertainties due to the near-infrared camera saturation. Therefore we have performed follow-up observations with the IRSF 1.4 m near-infrared telescope located in South Africa to obtain accurate J-, H-, and Ks-band fluxes of the central stars. Among 754 main-sequence stars which are detected in the AKARI $18{\mu}m$ band, we have performed photometry for 325 stars with IRSF. As a result, we have successfully improved the flux accuracy of the central stars from 9.2 % to 0.5 % on average. Using this dataset, we have detected $18{\mu}m$ excess emission from 57 stars in our samples with a $3{\sigma}$ level. We find that some of them have high ratios of the excess to the photospheric emission even around very old stars, which cannot be explained by the current planet-formation theories.

• 천문학회보
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• 제46권1호
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• pp.27.2-27.2
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• 2021

The unknown excess emission in the near-infrared is thought to be related to the evolution of galaxies in the early epoch of Universe. Due to its extremely faint brightness, it can be observed only in space. Many infrared space missions have been tried to trace the origin of the Cosmic Infrared Background through the measurement of its absolute brightness and its spatial fluctuation. In addition, the infrared observations can address questions ranging from the origin of first galaxies in the Universe to the formation of stars. I will overview the Korean infrared space missions and introduce the status of the recent international collaboration mission, SPHEREx.