担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aaf72a

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3847/1538-4357/aacd0c

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We propose a new simple computational model to estimate the adsorption energies of atoms and molecules to low-temperature amorphous water ice, and we present the adsorption energies of carbon (3 P), nitrogen (4 S), and oxygen (3 P) atoms based on quantum chemistry calculations. The adsorption energies were estimated to be 14,100 ±420 K for carbon, 400 ±30 K for nitrogen, and 1440 ±160 K for oxygen. The adsorption energy of oxygen is consistent with experimentally reported values. We found that the binding of a nitrogen atom is purely physisorption, while that of a carbon atom is chemisorption, in which a chemical bond to an O atom of a water molecule is formed. That of an oxygen atom has a dual character, with both physisorption and chemisorption. The chemisorption of atomic carbon also implies the possibility of further chemical reactions to produce molecules bearing a C-O bond, though this may hinder the formation of methane on water ice via sequential hydrogenation of carbon atoms. These properties would have a large impact on the chemical evolution of carbon species in interstellar environments. We also investigated the effects of newly calculated adsorption energies on the chemical compositions of cold dense molecular clouds with the aid of gas-ice astrochemical simulations. We found that abundances of major nitrogen-bearing molecules, such as N2 and NH3, are significantly altered by applying the calculated adsorption energy, because nitrogen atoms can thermally diffuse on surfaces, even at 10 K.

DOI： 10.3847/1538-4357/aaaa6a

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

To study a molecular-cloud-scale chemical composition, we conducted a mapping spectral line survey toward the Galactic molecular cloud W3(OH), which is one of the most active star-forming regions in the Perseus arm. We conducted our survey through the use of the Nobeyama Radio Observatory 45 m telescope, and observed the area of 16' x 16', which corresponds to 9.0 pc x 9.0 pc. The observed frequency ranges are 87-91, 96-103, and 108-112 GHz. We prepared the spectrum averaged over the observed area, in which eight molecular species (CCH, HCN, HCO+, HNC, CS, SO, (CO)-O-18, and (CO)-C-13) are identified. On the other hand, the spectrum of the W3(OH) hot core observed at a 0.17 pc resolution shows the lines of various molecules such as OCS, H2CS CH3CCH, and CH3CN in addition to the above species. In the spatially averaged spectrum, emission of the species concentrated just around the star-forming core, such as CH3OH and HC3N, is fainter than in the hot core spectrum, whereas emission of the species widely extended over the cloud such as CCH is relatively brighter. We classified the observed area into five subregions according to the integrated intensity of (CO)-C-13, and evaluated the contribution to the averaged spectrum from each subregion. The CCH, HCN, HCO+, and CS lines can be seen even in the spectrum of the subregion with the lowest (CO)-C-13 integrated intensity range (< 10 K km s(-1)). Thus, the contributions of the spatially extended emission is confirmed to be dominant in the spatially averaged spectrum.

DOI： 10.3847/1538-4357/aa89e5

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have conducted a mapping spectral line survey toward the Galactic giant molecular cloud W51 in the 3mm band with the Mopra 22m telescope in order to study an averaged chemical composition of the gas extended over a molecular-cloud scale in our Galaxy. We have observed the area of 25'x30', which corresponds to 39 pcx47 pc. The frequency ranges of the observation are 85.1-101.1 GHz and 107.0-114.9 GHz. In the spectrum spatially averaged over the observed area, spectral lines of 12 molecular species and 4 additional isotopologues are identified. An intensity pattern of the spatially averaged spectrum is found to be similar to that of the spiral arm in the external galaxy M51, indicating that these two sources have similar chemical compositions. The observed area has been classified into five subregions according to the integrated intensity of (CO)-C-13( J =1-0) ( I-13CO), and contributions of the fluxes of 11 molecular lines from each subregion to the averaged spectrum have been evaluated. For most of the molecular species, 50% or more of the flux comes from the subregions with I13CO from 25 to 100Kkms(-1), which does not involve active star-forming regions. Therefore, the molecular-cloudscale spectrum observed in the 3mm band hardly represents the chemical composition of star-forming cores, but mainly represents the chemical composition of an extended quiescent molecular gas. The present result constitutes a sound base for interpreting the spectra of external galaxies at a resolution of a molecular-cloud scale (similar to 10pc) or larger.

DOI： 10.3847/1538-4357/aa7ece

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.5303/PKAS.2017.32.1.105

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.5303/PKAS.2017.32.1.077

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.5303/PKAS.2017.32.1.083

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.5303/PKAS.2017.32.1.141

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have conducted a spectral line survey observation in the 3 mm band toward the low-metallicity dwarf galaxy IC10 with the 45 m radio telescope of the Nobeyama Radio Observatory to explore its chemical composition at a molecular-cloud scale (similar to 80 pc). The CS, SO, CCH, HCN, HCO+, and HNC lines are detected for the first time in this galaxy in addition to the CO and (CO)-C-13 lines, while the c-C3H2, CH3OH, CN, (CO)-O-18, and N2H+ lines are not detected. The spectral intensity pattern is found to be similar to those observed toward molecular clouds in the Large Magellanic Cloud (LMC), whose metallicity is as low as IC10. Nitrogen-bearing species are deficient in comparison with the Galactic molecular clouds due to a lower elemental abundance of nitrogen. CCH is abundant in comparison with Galactic translucent clouds, whereas CH3OH may be deficient. These characteristic trends for CCH and CH3OH are also seen in the LMC, and seem to originate from photodissociation regions more extended in the peripheries of molecular clouds due to the lower metallicity condition.

DOI： 10.3847/0004-637X/829/2/94

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). Molecular emission lines of CO, (CO)-O-17, HCO+, (HCO+)-C-13, H2CO, NO, SiO, H2CS, (SO)-S-33, (SO2)-S-32, (SO2)-S-34, and (SO2)-S-33 are detected from a compact region (similar to 0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis of SO2 and (SO2)-S-34 lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH3OH, H2CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1-3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO2 and its isotopologue line detections in ST11 imply that SO2 can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.

DOI： 10.3847/0004-637X/827/1/72

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Spectral line survey observations of seven. molecular clouds in the Large Magellanic Cloud (LMC) have been conducted in the 3 mm band with the Mopra 22 m telescope to reveal chemical compositions in low metallicity conditions. Spectral lines of fundamental species such as CS, SO, CCH, HCN, HCO+, and HNC are detected in addition to those of CO and (CO)-C-13, while CH3OH is not detected in any source and N2H+ is marginally detected in two sources. The molecular-cloud scale (10 pc scale) chemical composition is found to be similar among the seven. sources regardless of different star formation activities, and hence, it represents the chemical composition characteristic of. the LMC without influences by. star formation activities. In comparison with chemical compositions of Galactic sources, the characteristic features are (1) deficient N-bearing molecules, (2) abundant CCH, and (3) deficient CH3OH. Feature (1) is due to a lower elemental abundance of nitrogen in the LMC, whereas. features (2) and (3) seem to originate from extended photodissociation regions and warmer temperature in cloud peripheries due to a lower abundance of dust grains in the low metallicity condition. In spite of general resemblance of chemical abundances among the seven sources, the CS/HCO+ and SO/HCO+ ratios are found to be slightly higher in a quiescent molecular cloud. An origin of this trend is discussed in relation to possible depletion of sulfur along the molecular cloud formation.

DOI： 10.3847/0004-637X/818/2/161

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present infrared multi-epoch observations of the dust-forming nova V1280 Sco over similar to 2000 days from the outburst. The temporal evolution of the infrared spectral energy distributions at 1272, 1616, and 1947 days can be explained by the emissions produced by amorphous carbon dust of mass (6.6-8.7) x 10(-8) M-circle dot with a representative grain size of 0.01. mu m and astronomical silicate dust of mass (3.4-4.3) x 10(-7) M-circle dot with a representative grain size of 0.3-0.5 mu m. Both of these dust species travel farther away from the white dwarf without apparent mass evolution throughout those later epochs. The dust formation scenario around V1280 Sco suggested from our analyses is that the amorphous carbon dust is formed in the nova ejecta followed by the formation of silicate dust either in the expanding nova ejecta or as a result of the interaction between the nova wind and the circumstellar medium.

DOI： 10.3847/0004-637X/817/2/145

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1051/0004-6361/201526559

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

This study investigates the temporal evolution of the infrared emission from the dusty nova V1280 Sco over 2000 days from the outburst. We have revealed that the infrared spectral energy distributions at 1272, 1616 and 1947 days are explained by the emissions produced by amorphous carbon dust of mass (6.6-8.7) x10(-8) M circle dot with a representative grain size of 0.01 mu m and astronomical silicate dust of mass (3.4-4.3) x10(-7) M circle dot with a representative grain size of 0.3-0.5 mu m. Both of carbon and silicate dust travel farther away from the white dwarf without an apparent mass evolution throughout those later epochs.

DOI： 10.1088/1742-6596/728/6/062006

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We report CO2/H2O ice abundance ratios in seven nearby star-forming galaxies based on the AKARI near-infrared (2.5-5.0 mu m) spectra. The CO2/H2O ice abundance ratios show clear variations between 0.05 and 0.2 with the averaged value of 0.14 +/- 0.01. The previous study on M82 revealed that the CO2/H2O ice abundance ratios strongly correlate with the intensity ratios of the hydrogen recombination Bra line to the polycyclic aromatic hydrocarbon (PAH) 3.3 mu m feature. In the present study, however, we find no correlation for the seven galaxies as a whole due to systematic differences in the relation between CO2/H2O ice abundance and Bra/PAH 3.3 mu m intensity ratios from galaxy to galaxy. This result suggests that there is another parameter that determines the CO2/H2O ice abundance ratios in a galaxy in addition to the Bra/PAH 3.3 mu m ratios. We find that the CO2/H2O ice abundance ratios positively correlate with the specific star formation rates of the galaxies. From these results, we conclude that CO2/H2O ice abundance ratios tend to be high in young star-forming galaxies.

DOI： 10.1088/0004-637X/807/1/29

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Cambridge University Press  

The Infrared Camera (IRC) onboard AKARI has a near-infrared (2-5μm) spectroscopic capability with high sensitivity that allows us to study the major ice components in various objects. In particular, H2O and CO2 ice absorption features have been detected towards nearby galaxies, including several young stellar objects (YSOs) in the Large Magellanic Cloud (LMC), as well as a number of HII region-PDR complexes for the first time by IRC spectroscopy. While observations in the LMC show a high ratio (~0.34) of the CO2 to H2O ice column densities, the ratios in Galactic HII-region-PDR complexes are in the range of 0.1-0.2, being compatible with those found in Galactic massive YSOs in previous studies. The good correlation supports concurrent formation of the two ice species on the grain surface and the higher ratio in the low-metallicity LMC suggests possible environmental effects in the formation process.

DOI： 10.1017/S1743921316003161

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

Spectral line survey observations in the 3 mm band have been conducted toward 7 molecular clouds in the Large Magellanic Cloud (LMC) with the Mopra 22 m telescope. Spectral lines of the fundamental species CCH, HCN, HCO+, HNC, CS, SO, and c-C3H2 are detected. Although the 7 sources are different in star-formation activities, chemical compositions averaged over the 10 pc beam are similar to one another. We find that N-bearing species are deficient and CCH is relatively abundant in comparison with metal-rich environments. In spite of overall similarity of the chemical compositions, we also find a trend that the CS/HCO+ and SO/HCO+ ratios are higher for starless clouds.

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記述言語：英語   出版者・発行元：{IOP} Publishing  

DOI： 10.1088/0004-637X/792/1/80

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出版者・発行元：Sissa Medialab  

DOI： 10.22323/1.207.0112

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

This paper reports variations of polycyclic aromatic hydrocarbons (PAHs) features that were found in Spitzer Space Telescope spectra of carbon-rich post-asymptotic giant branch (post-AGB) stars in the Large Magellanic Cloud (LMC). The paper consists of two parts. The first part describes our Spitzer spectral observing programme of 24 stars including post-AGB candidates. The latter half of this paper presents the analysis of PAH features in 20 carbon-rich post-AGB stars in the LMC, assembled from the Spitzer archive as well as from our own programme. We found that five post-AGB stars showed a broad feature with a peak at 7.7 mu m, that had not been classified before. Further, the 10-13 mu m PAH spectra were classified into four classes, one of which has three broad peaks at 11.3, 12.3 and 13.3 mu m rather than two distinct sharp peaks at 11.3 and 12.7 mu m, as commonly found in H ii regions. Our studies suggest that PAHs are gradually processed while the central stars evolve from post-AGB phase to planetary nebulae, changing their composition before PAHs are incorporated into the interstellar medium. Although some metallicity dependence of PAH spectra exists, the evolutionary state of an object is more significant than its metallicity in determining the spectral characteristics of PAHs for LMC and Galactic post-AGB stars.

DOI： 10.1093/mnras/stt2495

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Using a large collection of near-infrared spectra (2.5-5.4 mu m) of Galactic H II regions and H II region-like objects, we perform a systematic investigation of astronomical polycyclic aromatic hydrocarbon (PAH) features. Thirty-six objects were observed using the infrared camera on board the AKARI satellite as a part of a director's time program. In addition to the well known 3.3-3.6 mu m features, most spectra show a relatively weak emission feature at 5.22 mu m with sufficient signal-to-noise ratios, which we identify as the PAH 5.25 mu m band (previously reported). By careful analysis, we find good correlations between the 5.25 mu m band and both the aromatic hydrocarbon feature at 3.3 mu m and the aliphatic hydrocarbon features at around 3.4-3.6 mu m. The present results give us convincing evidence that the astronomical 5.25 mu m band is associated with C-H vibrations, as suggested by previous studies, and show its potential to probe the PAH size distribution. The analysis also shows that the aliphatic-to-aromatic ratio of I-3.4-3.6 mu m/ I-3.3 mu m decreases against the ratio of the 3.7 mu m continuum intensity to the 3.3 mu m band, I-cont, 3.7 mu m/ I-3.3 mu m, which is an indicator of the ionization fraction of PAHs. The midinfrared color of I-9 mu m/ I-18 mu m also declines steeply against the ratio of the hydrogen recombination line Bra at 4.05 mu m to the 3.3 mu m band, I-Br alpha / I-3.3 mu m. These facts indicate possible dust processing inside or at the boundary of ionized gas.

DOI： 10.1088/0004-637X/784/1/53

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

With AKARI, we obtain the spatially resolved near-infrared (NIR) (2.5-5.0 μm) spectra for the nearby starburst galaxy M 82. These spectra clearly show absorption features due to interstellar ices. Based on the spectra, we created the column density maps of H2O and CO2 ices. As a result, we find that the spatial distribution of H2O ice is significantly different from that of CO2 ice
H2O ice is widely distributed, while CO2 ice is concentrated near the galactic center. Our result reveals for the first time variations in CO2/H 2O ice abundance ratio on a galactic scale, suggesting that an ice-forming interstellar environment changes within a galaxy. We discuss the cause of the spatial variations in the ice abundance ratio, utilizing spectral information on the hydrogen recombination Brα and Brβ lines and the polycyclic aromatic hydrocarbon 3.3 μm emission appearing in the AKARI NIR spectra. © 2013. The American Astronomical Society. All rights reserved.

DOI： 10.1088/2041-8205/773/2/L37

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We performed a near-infrared spectroscopic survey toward an area of 10 deg2 of the Large Magellanic Cloud (LMC) with the infrared satellite AKARI. Observations were carried out as part of the AKARI Large-area Survey of the Large Magellanic Cloud (LSLMC). The slitless multi-object spectroscopic capability of the AKARI/IRC enabled us to obtain low-resolution (R 20) spectra in 2-5 μm for a large number of point sources in the LMC. As a result of the survey, we extracted about 2000 infrared spectra of point sources. The data are organized as a near-infrared spectroscopic catalog. The catalog includes various infrared objects such as young stellar objects (YSOs), asymptotic giant branch (AGB) stars, supergiants, and so on. It is shown that 97% of the catalog sources have corresponding photometric data in the wavelength range from 1.2 to 11 μm, and 67% of the sources also have photometric data up to 24 μm. The catalog allows us to investigate near-infrared spectral features of sources by comparison with their infrared spectral energy distributions. In addition, it is estimated that about 10% of the catalog sources are observed at more than two different epochs. This enables us to study a spectroscopic variability of sources by using the present catalog. Initial results of source classifications for the LSLMC samples are presented. We classified 659 LSLMC spectra based on their near-infrared spectral features by visual inspection. As a result, it is shown that the present catalog includes 7 YSOs, 160 C-rich AGBs, 8 C-rich AGB candidates, 85 O-rich AGBs, 122 blue and yellow supergiants, 150 red super giants, and 128 unclassified sources. Distributions of the classified sources on the color-color and color-magnitude diagrams are discussed in the text. Continuous wavelength coverage and high spectroscopic sensitivity in 2-5 μm can only be achieved by space observations. This is an unprecedented large-scale spectroscopic survey toward the LMC in the near-infrared. A large number of near-infrared spectral data provided by the survey possess scientific potential that can be applied to various studies. In this paper, we present the details of the spectroscopic survey and the catalog, and discuss its scientific applications. © 2013. The American Astronomical Society. All rights reserved..

DOI： 10.1088/0004-6256/145/2/32

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

For the last few years, it has been pioneer days for infrared spectroscopic studies of extragalactic young stellar objects (YSOs). A number of embedded YSOs are spectroscopically identified in the Magellanic Clouds with AKARI and Spitzer, and their near- to mid-infrared spectral features are investigated in detail. In this proceeding, we are going to present our current research on the infrared spectroscopic observations of ices and dust around embedded YSOs in the Magellanic Clouds with AKARI.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present a near-to mid-infrared point-source catalog of five photometric bands at 3.2, 7, 11, 15, and 24 mu m for a 10 deg(2) area of the Large Magellanic Cloud (LMC) obtained with the Infrared Camera on board the AKARI satellite. To cover the survey area the observations were carried out at three separate seasons from 2006 May to June, 2006 October to December, and 2007 March to July. The 10 sigma limiting magnitudes of the present survey are 17.9, 13.8, 12.4, 9.9, and 8.6 mag at 3.2, 7, 11, 15, and 24 mu m, respectively. The photometric accuracy is estimated to be about 0.1 mag at 3.2 mu m and 0.06-0.07 mag in the other bands. The position accuracy is 0 ''.3 at 3.2, 7, and 11 mu m and 1 ''.0 at 15 and 24 mu m. The sensitivities at 3.2, 7, and 24 mu m are roughly comparable to those of the Spitzer SAGE LMC point-source catalog, while the AKARI catalog provides the data at 11 and 15 mu m, covering the mid-infrared spectral range contiguously. Two types of catalog are provided: a Catalog and an Archive. The Archive contains all the detected sources, while the Catalog only includes the sources that have a counterpart in the Spitzer SAGE point-source catalog. The Archive contains about 650,000, 140,000, 97,000, 43,000, and 52,000 sources at 3.2, 7, 11, 15, and 24 mu m, respectively. Based on the catalog, we discuss the luminosity functions at each band, the color-color diagram, and the color-magnitude diagram using the 3.2, 7, and 11 mu m band data. Stars without circumstellar envelopes, dusty C-rich and O-rich stars, young stellar objects, and background galaxies are located at distinct regions in the diagrams, suggesting that the present catalog is useful for the classification of objects toward the LMC.

DOI： 10.1088/0004-6256/144/6/179

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We conducted a spectroscopic survey of cometary volatiles with the Infrared Camera on board the Japanese infrared satellite AKARI in the wavelength range from 2.5 to 5 mu m. In our survey, 18 comets, including both the Oort cloud comets and the Jupiter-family comets, were observed in the period from 2008 June to 2010 January, most of which were observed at least twice. The prominent emission bands in the observed spectra are the fundamental vibrational bands of water (H2O) at 2.7 mu m and carbon dioxide (CO2) at 4.3 mu m. The fundamental vibrational band of carbon monoxide (CO) around 4.7 mu m and the broad emission feature, probably related to carbon-hydrogen-bearing molecules, can also be recognized around the 3.3-3.5-mu m region in some of the comets. With respect to H2O, gas production rate ratios of CO2 have been derived in 17 comets, except for the comet 29P/Schwassmann-Wachmann 1. Our data set provides the largest homogeneous database of CO2/H2O production rate ratios in comets obtained so far. The CO2/H2O production rate ratios are considered to reflect the composition of cometary ice when a comet is observed at a heliocentric distance within similar to 2.5 AU, since H2O ice fully sublimates there. The CO2/H2O ratio in cometary ice spans from several to similar to 30% among the comets observed at <2.5 AU (13 out of the 17 comets). Alternatively, the ratio of CO/CO2 in the comets seems to be smaller than unity based on our observations, although we only obtain upper limits for CO in most of the comets.

DOI： 10.1088/0004-637X/752/1/15

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPIE-INT SOC OPTICAL ENGINEERING  

AKARI, the Japanese satellite mission dedicated to infrared astronomy was launched in 2006 February and exhausted its liquid helium in 2007 August. During the cold mission phase, the Infrared Camera (IRC) onboard carried out an all-sky survey at 9 and 18 mu m with better spatial resolution and higher sensitivity than IRAS. Both bands also have slightly shorter wavelength coverage than IRAS 12 and 25 mu m bands and thus provide different information on the infrared sky. All-sky image data of the IRC are now in the final processing and will be released to the public within a year. After the exhaustion of the cryogen, the telescope and focal plane instruments of AKARI had still been kept at sufficiently low temperatures owing to the onboard cryocooler. Near-infrared (NIR) imaging and spectroscopic observations with the IRC had continued until 2011 May, when the spacecraft had a serious problem in the power supply system that forced us to terminate the observation. The IRC carried out nearly 20000 pointing observations in total despite of its near-earth orbit. About a half of them were performed after the exhaustion of the cryogen in the spectroscopic modes, which provided high-sensitivity NIR spectra from 2 to 5 mu m without disturbance of the terrestrial atmosphere. During the warm mission phase, the temperature of the instrument gradually increased and changed the array operation conditions. We present a summary of AKARI/IRC observations, including the all-sky mid-infrared diffuse data as well as the data taken in the warm mission phase.

DOI： 10.1117/12.926717

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the spatially resolved near-infrared (2.5-5.0 mu m) spectra of the edge-on starburst galaxy NGC 253 obtained with the Infrared Camera on board AKARI. Near the center of the galaxy, we clearly detect the absorption features of interstellar ices (H2O: 3.05 mu m, CO2: 4.27 mu m, and XCN: 4.62 mu m) and the emission of polycyclic aromatic hydrocarbons (PAHs) at 3.29 mu m and the hydrogen recombination line Br alpha at 4.05 mu m. We find that the distributions of the ices differ from those of the PAH and gas. We calculate the column densities of the ices and derive the abundance ratios of N(CO2)/N(H2O) = 0.17 +/- 0.05. They are similar to those obtained around the massive young stellar objects in our Galaxy (0.17 +/- 0.03), although a much stronger interstellar radiation field and higher dust temperature are expected near the center of NGC 253.

DOI： 10.1088/2041-8205/731/1/L20

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：E D P SCIENCES  

Near-infrared (NIR; 2.5-5 mu m) low-resolution (lambda/Delta lambda similar to 100) spectra were obtained for a number of Galactic and extragalactic objects with the Infrared Camera (IRC) in the AKARI warm mission. These data provide us with the first opportunity to make a systematic study of the 3.3-3.5 mu m PAH features in a galactic scale as well as within an object. Whereas the 3.3 mu m band is well resolved in most spectra, the 3.5 mu m band is not clearly separated from the 3.4 mu m band in the IRC spectrum. The intensity ratio of the summation of the 3.4 and 3.5 mu m bands to the 3.3 mu m band shows a tendency to increase towards the Galactic center, although a large variation in the ratio is also seen in a local scale. A search for deuterated PAH features in the 4 mu m region is carried out in IRC NIR spectra. Emission lines originating from the ionized gas together with the detector anomaly hamper an accurate search at certain wavelengths, but little convincing evidence has so far been obtained for the presence of significant features in 4.2-4.7 mu m. A conservative upper limit of a few percents is obtained for the integrated intensity ratio of the 4.4-4.7 mu m possible features to the 3.3-3.5 mu m PAH features in the spectra so far obtained.

DOI： 10.1051/eas/1146006

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDP SCIENCES S A  

Aims. The aim of this study is to understand the chemical conditions of ices around embedded young stellar objects (YSOs) in the metal-poor Large Magellanic Cloud (LMC).
Methods. We performed near-infrared (2.5-5 mu m) spectroscopic observations toward 12 massive embedded YSOs and their candidates in the LMC using the infrared camera (IRC) onboard AKARI. We estimated the column densities of the H2O, CO2, and CO ices based on their 3.05, 4.27, and 4.67 mu m absorption features, and we investigated the correlation between ice abundances and physical properties of YSOs.
Results. The ice absorption features of H2O, CO2, (CO2)-C-13, CO, CH3OH, and possibly XCN are detected in the spectra. In addition, hydrogen recombination lines and PAH emission bands are detected toward the majority of the targets. The derived typical CO2/H2O ice ratio of our samples (similar to 0.36 +/- 0.09) is greater than that of Galactic massive YSOs (similar to 0.17 +/- 0.03), while the CO/H2O ice ratio is comparable. It is shown that the CO2 ice abundance does not correlate with the observed characteristics of YSOs: the strength of hydrogen recombination line and the total luminosity. Likewise, clear correlation is not seen between the CO ice abundance and YSO characteristics, but it is suggested that the CO ice abundance of luminous samples is significantly lower than in other samples.
Conclusions. The systematic difference in the CO2 ice abundance around the LMC's massive YSOs, which was suggested by previous studies, is confirmed with the new near-IR data. We suggest that the strong ultraviolet radiation field and/or the high dust temperature in the LMC are responsible for the observed high abundance of the CO2 ice. It is suggested that the internal stellar radiation does not play an important role in the evolution of the CO2 ice around a massive YSO, while more volatile molecules like CO are susceptible to the effect of the stellar radiation.

DOI： 10.1051/0004-6361/200913815

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPIE-INT SOC OPTICAL ENGINEERING  

AKARI, the Japanese satellite mission dedicated for infrared astronomy launched in 2006 February, exhausted its 180 litter liquid helium (LHe) in 2007 August. After the LHe exhaustion, the telescope and focal plane of AKARI have still been kept less than 50K by the onboard cryocooler and near-infrared (NIR) observations with the Infrared Camera (IRC) are continuing. The data reduction software optimized for the warm mission enables us to carry out efficient and sensitive observations in the NIR despite the increase of hot pixels. In particular, the NIR spectroscopic capability of the IRC provides a unique opportunity to obtain spectra in 2.5-5 mu m with a high sensitivity, which will not be able to be carried out with any other facilities until JWST. An overview of the AKARI warm mission is given together with the performance and some observational results taken during the warm mission.

DOI： 10.1117/12.856568

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：CAMBRIDGE UNIV PRESS  

We present the first results of the AKARI Infrared Camera near-infrared spectroscopic survey of the Large Magellanic Cloud (LMC). The circumstellar material of young stellar objects (YSOs) are affected by galactic environments such as a metallicity or radiation field. Ices control the chemical balance of circumsellar environments of embedded YSOs. We detected absorption features of the H2O ice 3.05 mu m and the CO2 ice 4.27 mu m stretching mode toward seven massive YSOs in the LMC. This is the first detection of the 4.27 mu m CO2 ice confirmed to be YSOs. We used a curve-of-growth method to evaluate the column densities of the ices and derived the CO2/H2O ratio to be 0.45 +/- 0.17. This is clearly higher than that seen in Galactic massive YSOs (0.17 +/- 0.03). We suggest that the strong ultraviolet radiation field and/or the high dust temperature in the LMC may be responsible for the observed high CO2 ice abundance.

DOI： 10.1017/S1743921308028494

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASTRONOMICAL SOC PACIFIC  

The infrared spectra of young stellar objects (YSOs) often show absorption features of ices. So far, almost all of the observations of ices around YSOs have been limited to Galactic objects. We here report the result of 2.5-5 mu m spectroscopy of YSOs in the Large Magellanic Cloud with infrared satellite AKARI. Absorption features of H2O, CO2 and CO ices are detected toward these extragalactic YSOs, and derived CO2/H2O ice ratio in the LMC shows a higher value than Galactic YSOs. In this paper, we discuss the different chemical conditions around extragalactic YSOs.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AMER INST PHYSICS  

We report the result of the 2-5 mu m spectroscopy of massive young stellar objects (YSOs) in the Large Magellanic Cloud (LMC) using the infrared satellite AKARI. Absorption features of H2O, CO2 and CO ices are detected toward these extragalactic YSOs, and derived CO2/H2O ratio in the LMC showed a higher value than galactic YSOs. In this proceeding, we discuss the difference of a chemical conditions around extragalactic YSOs.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

We observed an area of 10 deg(2) of the Large Magellanic Cloud using the Infrared Camera (IRC) on board AKARI. The observations were carried out using five imaging filters (3, 7, 11, 15, and 24 mu m) and a dispersion prism (2-5 mu m, lambda/Delta lambda similar to 20) equipped in the IRC. This paper describes an outline of our survey project, and presents some initial results using imaging data that detected over 5.9 x 10(5) near-infrared and 6.4 x 10(4) mid-infrared point sources. The 10 sigma detection limits of our survey are about 16.5, 14.0, 12.3, 10.8, and 9.2 in Vega-magnitude at 3, 7, 11, 15, and 24 mu m, respectively. The 11 and 15 Am data, which are unique to AKARI IRC, allow us to construct color-magnitude diagrams that are useful to identify stars with circumstellar dust. We found a new sequence in the color-magnitude diagram, which is attributed to red giants with luminosity fainter than that of the tip of the first red-giant branch. We suggest that this sequence is likely to be related to the broad emission feature of aluminum oxide at 11.5 mu m. The 11 and 15 mu m data also indicate that the ([11]-[15]) color of both oxygen-rich and carbon-rich red giants once becomes blue, and then turns red again in the course of their evolution, probably due to a change in the flux ratio of the silicate or silicon carbide emission feature at 10 or 11.3 mu m to the 15 mu m flux.

DOI： 10.1093/pasj/60.sp2.S435

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We present the first results of AKARI Infrared Camera near-infrared spectroscopic survey of the Large Magellanic Cloud (LMC). We detected absorption features of the H2O ice 3.05 mu m and the CO2 ice 4.27 mu m stretching mode toward seven massive young stellar objects (YSOs). These samples are for the first time spectroscopically confirmed to be YSOs. We used a curve-of-growth method to evaluate the column densities of the ices and derived the CO2/H2O ratio to be 0.45 +/- 0.17. This is clearly higher than that seen in Galactic massive YSOs (0.17 +/- 0.03). We suggest that the strong ultraviolet radiation field and/or the high dust temperature in the LMC may be responsible for the observed high CO2 ice abundance.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

We present the first results of AKARI Infrared Camera near-infrared spectroscopic survey of the Large Magellanic Cloud (LMC). We detected absorption features of the H2O ice 3.05 μm and the CO2 ice 4.27 μm stretching mode toward seven massive young stellar objects (YSOs). These samples are for the first time spectroscopically confirmed to be YSOs. We used a curve-of-growth method to evaluate the column densities of the ices and derived the CO2/H2O ratio to be 0.45 ± 0.17. This is clearly higher than that seen in Galactic massive YSOs (0.17 ± 0.03). We suggest that the strong ultraviolet radiation field and/or the high dust temperature in the LMC may be responsible for the observed high CO2 ice abundance. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.

DOI： 10.1086/592948

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