• Publications of The Korean Astronomical Society
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• v.27 no.4
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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.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.155-158
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• 2015

The traditional view of dust in the interstellar medium is that it is made of graphite and silicates. In this paper, we discuss the evidence for complex organics being a major component of interstellar dust. Comparison between astronomical infrared spectra and laboratory spectra of amorphous carbonaceous materials suggests that organics of mixed aromatic-aliphatic structures are widely present in circumstellar, interstellar, and galactic environments. Scenarios for the synthesis of these compounds in the late stages of stellar evolution are presented.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.209-212
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• 2012

We present the results of the near-infrared (NIR) to mid-infrared (MIR) slit spectroscopic observations of the diffuse emission toward nine positions in the nearby irregular galaxy Large Magellanic Cloud (LMC) with the Infrared Camera (IRC) on board AKARI. The unique characteristic of AKARI/IRC provides a great opportunity to analyze variations in the unidentified infrared (UIR) bands based on continuous spectra from 2.5 to $13.4{\mu}m$ of the same slit area. The observed variation of $I_{3.3}/I_{11.3}$ suggests destruction of small-sized UIR band carriers, polycyclic aromatic hydrocarbons (PAHs) in harsh environments. This result demonstrates that the UIR $3.3{\mu}m$ band provides us powerful information on the excitation conditions and/or the size distribution of PAHs, which is of importance for understanding the evolutionary process of hydrocarbon grains in the Universe. It also suggests a new diagnostic diagram of two band ratios, such as $I_{3.3}/I_{11.3}$ versus $I_{7.7}/I_{11.3}$, for the interstellar radiation conditions. We discuss on the applicability of the diagnostic diagram to other astronomical objects, comparing the LMC results with those observed in other galaxies such as NGC 6946, NGC 1313, and M51.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.62.1-62.1
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• 2013

The Cassini/Visual Infrared Mapping Spectrometer (VIMS) observed the sun through the atmosphere of Titan, and provided vertically-resolved 63 spectra from 49 km to 987 km for the 1 - 5 micron range (Bellucci, 2008). Bellucci et al. (2009) analyzed selected spectral ranges where the band absorptions of $CH_4$ and CO are strong by constructing synthetic spectra including $CH_4$ and CO lines, but without including haze absorptions in their synthetic spectra. Kim et al. (2011) and Sim et al. (2013) were able to extract detailed spectral features of fundamental (Dv = 1) and overtone (Dv = 2) bands of the haze from the VIMS spectra by excluding the adjacent influences of strong $CH_4$ absorptions using a radiative transfer program, which includes effects of absorption and emission of lines of these molecules, and absorption and scattering of haze particles. In this presentation, we extend our detailed analyses to other remaining wavelengths in order to provide the spectral characteristics of the Titanian haze for the entire 1 - 5 micron range and to identify any additional haze spectral features and an unidentified feature near 4.3 microns reported by Bellucci et al. (2009).