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AKARI NEAR-INFRARED SPECTROSCOPIC SURVEY FOR COMETARY VOLATILES
Ootsubo, T.,Kawakita, H.,Kobayashi, H.,Usui, F.,AKARI SOSOS team, AKARI SOSOS team The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
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.
SMALL-SCALE STRUCTURE OF THE ZODIACAL DUST CLOUD OBSERVED IN FAR-INFRARED WITH AKARI
TAKAFUMI OOTSUBO,YASUO DOI,SATOSHI TAKITA,SHUJI MATSUURA,MITSUNOBU KAWADA,TAKAO NAKAGAWA,KO AROMATSU,MASAHIRO TANAKA,TORU KONDO,DAISUKE ISHIHARA,Fumihiko Usui,MAKOTO HATTORI 한국천문학회 2017 天文學論叢 Vol.32 No.1
The zodiacal light emission is the thermal emission from the interplanetary dust and the dominant diffuse radiation in the mid- to far-infrared wavelength region. Even in the far-infrared, the contribution of the zodiacal emission is not negligible at the region near the ecliptic plane. The AKARI far-infrared all-sky survey covered 97\% of the whole sky in four photometric bands with band central wavelengths of 65, 90, 140, and 160~$\mu$m. AKARI detected the small-scale structure of the zodiacal dust cloud, such as the asteroidal dust bands and the circumsolar ring, in far-infrared wavelength region. Although the most part of the zodiacal light structure in the AKARI far-infrared all-sky image can be well reproduced with the DIRBE zodiacal light model, there are discrepancies in the small-scale structures. In particular, the intensity and the ecliptic latitude of the peak position of the asteroidal dust bands cannot be reproduced precisely with the DIRBE models. The AKARI observational data during more than one year has advantages over the 10-month DIRBE data in modeling the full-sky zodiacal dust cloud. The resulting small-scale zodiacal light structure template has been used to subtract the zodiacal light from the AKARI all-sky maps.
ADVANTAGES OF THE AKARI FIR ALL-SKY MAPS
YASUO DOI,SATOSHI TAKITA,TAKAFUMI OOTSUBO,KO ARIMATSU,MASAHIRO TANAKA,TAKAHIRO MORISHIMA,MITSUNOBU KAWADA,SHUJI MATSUURA,YOSHIMI KITAMURA,MAKOTO HATTORI,TAKAO NAKAGAWA,GLENN WHITE,NORIO IKEDA 한국천문학회 2017 天文學論叢 Vol.32 No.1
We present the {\it AKARI} far-infrared (FIR) all-sky maps and describe its characteristics, calibration accuracy and scientific capabilities. The {\it AKARI} FIR survey has covered 97\% of the whole sky in four photometric bands, which cover continuously 50--180 micron with band central wavelengths of 65, 90, 140, and 160 microns. The data have been publicly released in 2014 \citep{2015PASJ...67...50D} with improved data quality that have been achieved since the last internal data release \citep{2012PKAS...27..111D}. The accuracy of the absolute intensity is $\leq10$\% for the brighter regions. Quantitative analysis of the relative intensity accuracy and its dependence upon spatial scan numbers has been carried out. The data for the first time reveal the whole sky distribution ofinterstellar matter with arcminute-scale spatial resolutions at the peakof dust continuum emission, enabling us to investigate large-scaledistribution of interstellar medium in great detail. The filamentarystructure covering the whole sky is well traced by the all-sky maps. We describe advantages of the AKARI FIR all-sky maps for the study of interstellar matter comparing to other observational data.
FIR VIEW OF DISKS OF WEAK-LINE T TAURI STARS
SATOSHI TAKITA,YASUO DOI,KO ARIMATSU,TAKAFUMI OOTSUBO 한국천문학회 2017 天文學論叢 Vol.32 No.1
We have observed $\sim$60 Weak-line T Tauri stars (WTTSs) toward the Chamaeleon star forming region using the AKARI Far-Infrared Surveyor (FIS) All-Sky maps. We could not detect any significant emission from each source even at the most sensitive WIDE-S band. Then, we have performed stacking analysis of these WTTSs using the WIDE-S band images to improve the sensitivity. However, we could not detect any significant emission in the resultant image with a noise level of 0.05~MJy~sr$^{-1}$, or 3 mJy for a point source. The three-sigma upper limit of 9~mJy leads to the disk dust mass of 0.01~M$_{\oplus}$. This result suggests that the disks around Chamaeleon WTTSs are already evolved to debris disks.
AKARI/AcuA PHYSICAL STUDIES OF THE CYBELE ASTEROID FAMILY
Kasuga, Toshihiro,Usui, Fumihiko,Hasegawa, Sunao,Kuroda, Daisuke,Ootsubo, Takafumi,Mü,ller, Thomas G.,Ishiguro, Masateru American Institute of Physics 2012 The Astronomical journal Vol.143 No.6
<P>We present a study of 107 Cybele asteroids based on the archival database 'Asteroid Catalog Using AKARI (AcuA)' taken by the Infrared Astronomical Satellite. The database provides diameters D > 10 km, geometric albedos, and taxonomic information (75%) of the Cybeles. We find taxonomic diversity (mainly C-, D-, and P-type) in the population of 78 small Cybeles with diameters 10 km <D < 80 km. Their cumulative power-law size distribution index shows a shallow value of 0.86 ± 0.03. By contrast, 29 large Cybeles with D > 80 km are mostly classified as C- or P-types (90%), with a power-law index of 2.39 ± 0.18. The total mass of Cybele asteroids is estimated to be ~10<SUP>–5</SUP> M<SUB>Earth</SUB>. We also discuss the origin and formation process of the Cybele asteroid family.</P>
INFRARED OBSERVATIONS OF DUST AROUND HELIUM NOVA V445 PUPPIS
SAYAKA SHIMAMOTO,ITSUKI SAKON,TAKASHI ONAKA,Fumihiko Usui,TAKAFUMI OOTSUBO,YASUO DOI,RYOU OHSAWA,DAISUKE ISHIHARA 한국천문학회 2017 天文學論叢 Vol.32 No.1
We detected bright mid- to far-infrared emission from the helium nova V445 Puppis in the AKARI all-sky survey data taken in 2006. Assuming an optically thin condition, we decomposed the spectral energy distribution (SED) of V445 Puppis in October 2006 by model fitting and found that the SED can be explained by a combination of cold amorphous carbon (125~K and the mass of $4.5^{+6.6}_{-2.7}\times 10^{-4} ~{\rm M}_{\odot}$) and warm amorphous carbon (250~K and the mass of $1.8^{+1.0}_{-0.5}\times 10^{-5} ~{\rm M}_{\odot}$). Assuming that the former is pre-existing dust formed in the past nova outbursts and the latter is newly formed dust in December 2000's nova wind, this result suggests that the amount of dust formed around V445 Puppis in a single outburst is larger than $10^{-5} ~{\rm M}_{\odot}$, which is larger than those in any other classical novae ever reported.
HIGH-RESOLUTION IMAGING OF THE GEGENSCHEIN AND THE GEOMETRIC ALBEDO OF INTERPLANETARY DUST
Ishiguro, Masateru,Yang, Hongu,Usui, Fumihiko,Pyo, Jeonghyun,Ueno, Munetaka,Ootsubo, Takafumi,Kwon, Suk Minn,Mukai, Tadashi IOP Publishing 2013 The Astrophysical journal Vol.767 No.1
<P>We performed optical observations of the Gegenschein using a liquid-nitrogen-cooled wide-field camera, the Wide-field Imager of Zodiacal light with ARray Detector (WIZARD), between 2003 March and 2006 November. We found a narrow brightness enhancement superimposed on the smooth gradient of the Gegenschein at the exact position of the antisolar point. Whereas the Gegenschein morphology changed according to the orbital motion of the Earth, the maximum brightness coincided with the antisolar direction throughout the year. We compared the observed morphology of the Gegenschein with those of models in which the spatial density of the interplanetary dust cloud was considered and found that the volume scattering phase function had a narrow backscattering enhancement. The morphology was reproducible with a spatial distribution model for infrared zodiacal emission. It is likely that the zero-phase peak (the so-called opposition effect) was caused by coherent backscattering and/or shadow-hiding effects on the rough surfaces of individual dust particles. These results suggest that big particles are responsible for both zodiacal light and zodiacal emission. Finally, we derived the geometric albedo of the smooth component of interplanetary dust, assuming big particles, and obtained a geometric albedo of 0.06 +/- 0.01. The derived albedo is in accordance with collected dark micrometeorites and observed cometary dust particles. We concluded that chondritic particles are dominant near Earth space, supporting the recent theoretical study by dynamical simulation.</P>
A PANORAMIC VIEW OF THE ASTEROIDS IN THE INNER SOLAR SYSTEM WITH AKARI
Usui, F.,Kuroda, D.,Muller, T.G.,Hasegawa, S.,Ishiguro, M.,Ootsubo, T.,Ueno, M.,AKARI SOSOS team, AKARI SOSOS team The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We constructed an unbiased asteroid catalog from the mid-infrared part of the All-Sky Survey with the Infrared Camera (IRC) on board AKARI. About 20% of the point source events recorded in the IRC All-Sky Survey observations were not used for the IRC Point Source Catalog in its production process because of a lack of multiple detection by position. Asteroids, which are moving objects on the celestial sphere, are included in these "residual events" We identified asteroids out of the residual events by matching them with the positions of known asteroids. For the identified asteroids, we calculated the size and albedo based on the Standard Thermal Model. Finally we had a new brand of asteroid catalog, which contains 5,120 objects, about twice as many as the IRAS asteroid catalog.
MODELING OF THE ZODIACAL EMISSION FOR THE<i>AKARI</i>/IRC MID-INFRARED ALL-SKY DIFFUSE MAPS
Kondo, Toru,Ishihara, Daisuke,Kaneda, Hidehiro,Nakamichi, Keichiro,Takaba, Sachi,Kobayashi, Hiroshi,Ootsubo, Takafumi,Pyo, Jeonghyun,Onaka, Takashi American Astronomical Society 2016 The Astronomical journal Vol.151 No.3
<P>The zodiacal emission, which is the thermal infrared (IR) emission from the interplanetary dust (IPD) in our solar system, has been studied for a long time. Nevertheless, accurate modeling of the zodiacal emission has not been successful to reproduce the all-sky spatial distribution of the zodiacal emission, especially in the mid-IR where the zodiacal emission peaks. Therefore, we aim to improve the IPD cloud model based on Kelsall et al., using the AKARI 9 and 18 mu m all-sky diffuse maps. By adopting a new fitting method based on the total brightness, we have succeeded in reducing the residual levels after subtraction of the zodiacal emission from the AKARI data and thus in improving the modeling of the zodiacal emission. Comparing the AKARI and the COBE data, we confirm that the changes from the previous model to our new model are mostly due to model improvements, but not temporal variations between the AKARI and the COBE epoch, except for the position of the Earth-trailing blob. Our results suggest that the size of the smooth cloud, a dominant component in the model, is about 10% more compact than previously thought, and that the dust sizes are not large enough to emit blackbody radiation in the mid-IR. Furthermore, we detect a significant isotropically distributed IPD component, owing to an accurate baseline measurement with AKARI.</P>