The Infrared Astronomical Mission AKARI
ABSTRACT AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared. The instruments also have the capability for imaging and spectroscopy in the wavelength range 2 - 180 micron in the pointed observation mode, occasionally inserted into the continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90 percent of the whole sky with higher spatial resolution and wider wavelength coverage than that of the previous IRAS all-sky survey. Point source catalogues of the All-Sky Survey will be released to the astronomical community. The pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission. Comment: 13 pages, 4 figures, and 3 tables. Accepted for publication in the AKARI special issue of the Publications of the Astronomical Society of Japan
- SourceAvailable from: François R. Bouchet[Show abstract] [Hide abstract]
ABSTRACT: (abridged) We perform a detailed investigation of sources from the Cold Cores Catalogue of Planck Objects (C3PO). Our goal is to probe the reliability of the detections, validate the separation between warm and cold dust emission components, provide the first glimpse at the nature, internal morphology and physical characterictics of the Planck-detected sources. We focus on a sub-sample of ten sources from the C3PO list, selected to sample different environments, from high latitude cirrus to nearby (150pc) and remote (2kpc) molecular complexes. We present Planck surface brightness maps and derive the dust temperature, emissivity spectral index, and column densities of the fields. With the help of higher resolution Herschel and AKARI continuum observations and molecular line data, we investigate the morphology of the sources and the properties of the substructures at scales below the Planck beam size.Astronomy & Astrophysics - ASTRON ASTROPHYS. 01/2011; 536.
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ABSTRACT: We present pre- and post-outburst observations of the new FU Orionis-like young stellar object PTF 10qpf (also known as LkHa 188-G4 and HBC 722). Prior to this outburst, LkHa 188-G4 was classified as a classical T Tauri star on the basis of its optical emission-line spectrum superposed on a K8-type photosphere, and its photometric variability. The mid-infrared spectral index of LkHa 188-G4 indicates a Class II-type object. LkHa 188-G4 exhibited a steady rise by ~1 mag over ~11 months starting in Aug. 2009, before a subsequent more abrupt rise of > 3 mag on a time scale of ~2 months. Observations taken during the eruption exhibit the defining characteristics of FU Orionis variables: (i) an increase in brightness by > 4 mag, (ii) a bright optical/near-infrared reflection nebula appeared, (iii) optical spectra are consistent with a G supergiant and dominated by absorption lines, the only exception being Halpha which is characterized by a P Cygni profile, (iv) near-infrared spectra resemble those of late K--M giants/supergiants with enhanced absorption seen in the molecular bands of CO and H_2O, and (v) outflow signatures in H and He are seen in the form of blueshifted absorption profiles. LkHa 188-G4 is the first member of the FU Orionis-like class with a well-sampled optical to mid-infrared spectral energy distribution in the pre-outburst phase. The association of the PTF 10qpf outburst with the previously identified classical T Tauri star LkHa 188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions represent periods of enhanced disk accretion and outflow, likely triggered by instabilities in the disk. The early identification of PTF 10qpf as an FU Orionis-like variable will enable detailed photometric and spectroscopic observations during its post-outburst evolution for comparison with other known outbursting objects.The Astrophysical Journal 11/2010; 730(2). · 6.73 Impact Factor
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ABSTRACT: Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5 % with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 μm, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths.Experimental Astronomy 10/2013; · 2.97 Impact Factor
arXiv:0708.1796v1 [astro-ph] 14 Aug 2007
The Infrared Astronomical Mission AKARI∗
Hiroshi Murakami1, Hajime Baba1, Peter Barthel2, David L. Clements3,
Martin Cohen4, Yasuo Doi5, Keigo Enya1, Elysandra Figueredo6, Naofumi Fujishiro1,7†,
Hideaki Fujiwara8, Mikio Fujiwara9, Pedro Garcia-Lario10, Tomotsugu Goto1,
Sunao Hasegawa1, Yasunori Hibi11‡, Takanori Hirao11§, Norihisa Hiromoto12,
Seung Soo Hong13, Koji Imai1, Miho Ishigaki1¶, Masateru Ishiguro13, Daisuke Ishihara8,
Yoshifusa Ita1?, Woong-Seob Jeong1, Kyung Sook Jeong13, Hidehiro Kaneda1,
Hirokazu Kataza1, Mitsunobu Kawada11, Toshihide Kawai14, Akiko Kawamura11,
Martin F. Kessler10,15, Do Kester16, Tsuneo Kii1, Dong Chan Kim17, Woojung Kim1∗∗,
Hisato Kobayashi1,7, Bon Chul Koo13, Suk Minn Kwon18, Hyung Mok Lee13,
Rosario Lorente10, Sin’itirou Makiuti1, Hideo Matsuhara1, Toshio Matsumoto1,
Hiroshi Matsuo19, Shuji Matsuura1, Thomas G. M¨ uller20, Noriko Murakami11,
Hirohisa Nagata1, Takao Nakagawa1, Takahiro Naoi1 ††, Masanao Narita1,
Manabu Noda21, Sang Hoon Oh13, Akira Ohnishi1, Youichi Ohyama1, Yoko Okada1,
Haruyuki Okuda1, Sebastian Oliver22, Takashi Onaka8, Takafumi Ootsubo11,
Shinki Oyabu1, Soojong Pak23, Yong-Sun Park13, Chris P. Pearson1,10,
Michael Rowan-Robinson3, Toshinobu Saito1,7, Itsuki Sakon8, Alberto Salama10,
Shinji Sato11, Richard S. Savage22Stephen Serjeant6, Hiroshi Shibai11,
Mai Shirahata1, Jungjoo Sohn13, Toyoaki Suzuki1,7, Toshinobu Takagi1,
Hidenori Takahashi24, Toshihiko Tanab´ e25, Tsutomu T. Takeuchi26, Satoshi Takita1,27,
Matthew Thomson22, Kazunori Uemizu1, Munetaka Ueno5, Fumihiko Usui1,
Eva Verdugo10, Takehiko Wada1, Lingyu Wang3Toyoki Watabe14, Hidenori Watarai1‡‡,
Glenn J. White6,28, Issei Yamamura1, Chisato Yamauchi1, and Akiko Yasuda1,29
1Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara,
Kanagawa 229-8510, Japan
2Kapteyn Astronomical Institute, University of Groningen, Groningen, 9700 AV, The Netherlands
3Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, U.K.
4Radio Astronomy Laboratory, 601 Campbell Hall, University of California, Berkeley, CA94720,
5Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The
University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan
6Department of Physics and Astronomy, The Open University, Milton Keynes MK7 6AA, U.K.
7Department of Physics, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo
8Department of Astronomy, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo
9Research Department 1, National Institute of Information and Communications Technology,
Koganei, Tokyo 184-8795, Japan
10European Space Agency, ESAC, P.O. Box 78, 28691 Villanueva de la Ca˜ nada, Madrid, Spain
11Division of Particle and Astrophysical Sciences, Graduate School of Science, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
12Optelectronics and Electromagnetic Wave Engineering, Shizuoka University, 3-1-5 Johoku,
13Department of Physics and Astronomy, Seoul National University, Shillimdong Kwanak-gu, Seoul
14Technical Center of Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
15European Space Agency, ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
16Netherlands Institute for Space Research SRON, AV Groningen, Groningen, The Netherlands
17Department of Astronomy, University of Maryland, College Park, MD 20742-2421, U.S.A.
18Department of Science Education, Kangwon National University, Hyoja-dong, Kangwon-do,
Chunchon 200-701, Korea
19National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Mitaka,
Tokyo 181-8588, Japan
20Max-Planck-Institut f¨ ur extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
21Nagoya City Science Museum, Sakae, Naka-ku, Nagoya 460-0008, Japan
22Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton BN1
23Department of Astronomy and Space Science, Kyung Hee University, Seocheon-dong, Giheung-gu,
Yongin-si, Gyeonggi-do 446-701, Korea
24Gunma Astronomical Observatory, Takayama, Agatsuma, Gunma 377-0702, Japan
25Institute of Astronomy, Graduate School of Science, The University of Tokyo, Mitaka, Tokyo
26Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601,
27Department of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo
Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan
28Space Science & Technology Department, CCLRC Rutherford Appleton Laboratory, Chilton,
Didcot, Oxfordshire OX11 0QX, U.K.
29The Graduate University for Advanced Studies, Shonan Village, Hayama, Kanagawa 240-0193,
(Received 2007 May 31; accepted 2007 August 9)
AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched
on 2006 February 21, and started observations in May of the same year. AKARI has
a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey
the sky in six wavelength bands from the mid- to far-infrared. The instruments also
have the capability for imaging and spectroscopy in the wavelength range 2 – 180
µm in the pointed observation mode, occasionally inserted into the continuous survey
operation. The in-orbit cryogen lifetime is expected to be one and a half years.
The All-Sky Survey will cover more than 90 percent of the whole sky with higher
spatial resolution and wider wavelength coverage than that of the previous IRAS
all-sky survey. Point source catalogues of the All-Sky Survey will be released to the
astronomical community. The pointed observations will be used for deep surveys
of selected sky areas and systematic observations of important astronomical targets.
These will become an additional future heritage of this mission.
Key words: space vehicles: instruments — infrared: general
ASTRO-F was planned as a Japanese space mission dedicated to infrared astronomy
(Murakami 2004, Shibai 2007). It was successfully launched on 2006 February 21 (UT) on the
M-V-8 rocket, which was developed by the Japan Aerospace Exploration Agency (JAXA), from
Uchinoura Space Center (USC). It was renamed AKARI after the confirmation of successful
insertion of the satellite into the orbit.
AKARI is the second Japanese space mission to carry out infrared astronomy following
the Infrared Telescope in Space (IRTS; Murakami et al. 1996) onboard the Space Flyer Unit
AKARI is a JAXA project with the participation of ESA.
Present Address is Cybernet systems Co. Ltd., Bunkyo-ku, Tokyo 112-0012, Japan
Present Address is National Astronomical Observatory of Japan, National Institutes of Natural Sciences,
Mitaka, Tokyo 181-8588, Japan
Present Address is Research Institute of Science and Technology for Society, Japan Science and Technology
Agency, Kawaguchi, Saitama 332-0012, Japan
Present Address is Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-77, Japan
Present Address is National Astronomical Observatory of Japan, National Institutes of Natural Sciences,
Mitaka, Tokyo 181-8588, Japan
∗∗Present Address is Semiconductor Business Group, Sony Corporation, 4-14-1 Asahi-cho, Atsugi, Kanagawa
††Present Address is National Astronomical Observatory of Japan, National Institutes of Natural Sciences,
Mitaka, Tokyo 181-8588, Japan
‡‡Present Address is Office of Space Applications, Japan Aerospace Exploration Agency, Tsukuba, Ibaraki
(SFU). AKARI is designed as an All-Sky Survey mission in the infrared. The primary purpose of
the mission is to provide second-generation infrared catalogues to better spatial resolution and
wider spectral coverage than the first catalogues by the Infra-Red Astronomy Satellite (IRAS)
mission (Neugebauer et al. 1984). AKARI is equipped with a cryogenically cooled telescope
of 68.5 cm aperture diameter and two scientific instruments, the Far-Infrared Surveyor (FIS;
Kawada et al. 2007) and the Infrared Camera (IRC; Onaka et al. 2007). The wide fields
of view (∼ 10 arcmin) covered by the large-format arrays in these instruments makes them
highly suitable for efficient surveys. AKARI has the capability to make pointed observations in
addition to the All-Sky Survey, although AKARI is not a fully observatory-type mission in the
same guise as the Infrared Space Observatory (ISO; Kessler et al. 1996) and the Spitzer Space
Telescope (Werner et al. 2004), due to the nature of its low-Earth Sun-synchronous orbit.
AKARI has operated normally since the launch, and is now generating large amounts
of high-quality data on infrared sources ranging from nearby solar system objects to galaxies
at the cosmological distances.
This paper describes the overview of the design, operation and observation of AKARI.
Details of the scientific instruments and initial astronomical results based on the data mainly
taken in the performance-verification phase (the first month after the opening of the aperture
lid) are given in companion papers in this special issue.
2. AKARI Satellite
The AKARI satellite consists of two main sections, the satellite bus module and the
science module as shown in figure 1. The science module is a cryostat which contains the
telescope and focal-plane instruments. The cryostat with a sun shield is mounted on the
bus module through carbon-fiber reinforced plastic (CFRP) trusses, and is thereby thermally
isolated from the bus. The satellite bus module includes the subsystems which provide functions
such as the power supply, communications, command and data handling, attitude and orbit
control, and temperature control and monitoring. The key structure of the bus module is the
cylindrical thrust tube (1 m high and 1.2 m diameter) also made of CFRP. The propellant
tanks of the reaction control system are stored inside this thrust tube. Subsystems of the bus
module are installed on eight instrument panels, and the panels are integrated together around
the thrust tube. The lower end of the thrust tube is connected to top of the third stage of the
M-V rocket. Two solar paddles are secured around the bus module in the launch configuration,
and are deployed in orbit. Major features of AKARI are summarized in table 1.
Fig. 1. Illustration of AKARI in orbit (left panel), and the sectional view (right panel).
Table 1. Design features of the AKARI satellite.
Sizediameter 2.0 m max., hight 3.7 m (launching configuration)
width 5.5 m, hight 3.3 m (observation configuration in orbit)
Mass 952 kg in the launch configuration
OrbitSun-synchronous polar orbit, altitude 700 km
Downlink rate 4 Mbps for scientific data
Data generation rateapproximately 2 GBytes/day
Data recorder capacity2 GBytes
Prism & Grism
Fig. 2. Wavelength coverage and the resolution of IRC and FIS.
A liquid-Helium cryostat of very high efficiency, providing a long cryogenic lifetime with
a small amount of liquid Helium, was specifically designed for AKARI (Nakagawa et al. 2007).
This small Helium tank can provide enough room for a large aperture telescope in the cryostat
within the weight and volume limits imposed by the launch vehicle. The amount of cryogen
is only 179 liters at launch and the expected hold-time of the liquid Helium in orbit is about
one and a half years. This high efficiency has been realized by utilizing mechanical cryocoolers
and efficient radiative cooling. The cryocoolers on board AKARI are two-stage Stirling-cycle
coolers (Narasaki et al. 2004). The outer shell of the cryostat is shaded from the sunlight by
the sun-shield, and is cooled down to about 200 K by radiative cooling.
The AKARI telescope system is a Ritchey-Chretien type with an effective aperture size
of 68.5 cm and an f/6 system (Kaneda et al. 2005, Kaneda et al. 2007). Its focal plane is shared
between two infrared instruments and focal-plane star sensors, it has a clear field of view of 38
arcmin in radius. The mirror material is sandwich-type Silicon Carbide (SiC), which consists
of a porous SiC core coated with CVD (Chemical Vapor Deposition) SiC. The high stiffness of
SiC enables us to make very light-weight mirrors. The primary mirror, which has a physical
diameter of 71 cm, weighs only 11 kg.
3.3. Focal-plane instruments
One of the focal-plane instruments, FIS (Kawada et al. 2007), is designed to perform an
All-Sky Survey in four far-infrared wavelength bands using Ge:Ga and stressed Ge:Ga detector
arrays. This instrument also has a spectroscopic capability via a Fourier transform spectrom-
eter. The other instrument, IRC (Onaka et al. 2007), consists of three channels, NIR, MIR-S,
Fig. 3. AKARI Focal-plane layout. This figure shows a projection onto the sky. FSTS-S and FSTS-L are
focal-plane star sensors. The scan direction in the All-Sky Survey is in a sense that, in this figure, FoV
moves downward on the sky and stars go upward.
and MIR-L, which cover the 1.8–5.5µm, 4.6–13.4µm, and 12.6–26.5µm wavelength range, re-
spectively. Each channel has three broad-band filters and additional dispersive elements. the
FIS and IRC instruments can be operated simultaneously.
The IRC was originally designed to perform imaging and spectroscopic observations with
large-format array detectors, pointing the telescope to a given object. However, the additional
acceptable performance of continuous survey-type observations with two rows of the array was
confirmed in the ground tests (Ishihara et al. 2006), and the All-Sky Survey in S9W and L18W
bands were subsequently added to the operation modes.
The wavelength coverage and the spectral resolution of FIS and IRC are shown in figure 2,
while Figure 3 shows the focal-plane layout. A brief summary of AKARI’s scientific instruments
is given in table 2. In addition to the two scientific instruments, AKARI is also equipped with
focal-plane star sensors (referred to as FSTS-S and FSTS-L), which are used to determine the
telescope boresight during the All-Sky Survey.
Table 2. AKARI scientific instruments.
Cryogenics Liquid-Helium cryostat with Stirling-cycle coolers
179-liter super-fluid liquid Helium
Telescope Ritchey-Chretien type optics
Effective aperture 68.5 cm, total f/6 system
SiC light-weight telescope
Far-Infrared Surveyor All-Sky Survey, Imaging and Spectroscopy with FTS
(FIS) Bands: N60 (65 µm), Wide-S (90 µm), Wide-L (140 µm), N160 (160 µm)
Detectors: 20 × 2 & 20 × 3 Ge:Ga arrays for N60 and Wilde-S bands
15 × 3 & 15 × 2 stressed Ge:Ga arrays for Wide-L, N160 bands
Pixel pitch: 29.5 arcsec for N60 and Wide-S bands,
49.1 arcsec for Wide-L and N160 bands
Resolution for Spectroscopy: ∆ν=0.19 cm−1
Infrared CameraAll-Sky Survey, Imaging and Spectroscopy with grisms and a prism
(IRC) Photometric Bands: NIR: N2 (2.4 µm), N3 (3.2 µm), N4 (4.1 µm)
MIR-S: S7 (7.0 µm), S9W (9.0 µm), S11 (11.0 µm)
MIR-L: L15 (15.0 µm), L18W (18.0 µm), L24 (24.0 µm)
Detectors: InSb 512 × 412 array for NIR,
two 256 × 256 Si:As arrays for MIR-S and MIR-L
Pixel scale: 1.46×1.46 arcsec for NIR, 2.34×2.34 arcsec for MIR-S,
and 2.51×2.39 arcsec for MIR-S
Effective pixel scale in the All-Sky Survey: 10 arcsec (4 pixels are binned.)
Resolution for Spectroscopy: ∆λ=0.0097 – 0.17 µm
AKARI was initially launched into an elliptical orbit by the M-V rocket. The reaction
control system then drove up the perigee altitude to bring the satellite to the observing orbit, a
circular Sun-synchronous polar orbit at an altitude of approximately 700 km and inclination of
98.2 deg. AKARI flies along the day-night border with an orbital period of approximately 100
min. This orbit is similar to that of the previous IRAS satellite, and is the most suitable orbit
for scanning the sky while keeping the telescope direction away from the Sun and the Earth
whose strong emission would be ruinous for the cooled telescope.
Just after the launch, it was found that the Sun aspect sensors could not detect the Sun
properly. The cause of this problem is still unknown to date. This problem forced us to rewrite
the on-board software for the attitude and orbit control subsystem, and delayed the opening of
the aperture lid by a month. The aperture lid was finally opened on 2006 April 13, after which
AKARI began to observe the sky. In the performance-verification phase, one month after the
Table 3. Major events in the AKARI operation timeline.
Launch2006 February 21 21:28:00
Injection into initial orbit2006 February 21 21:36:39
Completion of orbit change maneuver2006 March 4 08:39
to the observation orbit
Aperture lid ejection 2006 April 13 07:55
(Start of performance-verification phase)
Start of Phase 1 observation 2006 May 8
Start of Phase 2 observation2006 November 10
Fig. 4. Attitude control for observations.
aperture lid opening, tuning of the scientific instruments and the attitude and orbit control
subsystem, and telescope focus adjustment were performed. AKARI started the all-Sky Survey
on 2006 May 8. Major events in the AKARI operation timeline are summarized in table 3.
The attitude of AKARI observations are controlled as follows: during the All-Sky Survey,
the spacecraft rotates around the axis directed toward the Sun once every orbital revolution,
avoiding the Earth. This results in a continuous scan of the sky at a scan speed of 3.6 arcmin/s
(figure 4). The whole sky can in principle be covered in half a year. The FIS and the IRC
are also operated in a pointing mode, where the instruments observe a certain sky position for
a longer exposure (approximately 10 minutes for one pointing with a maneuvering time of 20
The attitude control system provides additional capabilities to shift the pointing direc-
tion by small amounts during the pointed observations, i.e. micro and slow scans. In the micro
scan, the pointing direction is shifted by less than 30 arcsec for the purpose of dithering the
IRC images. The slow scan is a continuous scan at a much slower scan speed (4-30 arcsec/s)
compared to the All-Sky Survey. This is used to obtain sky images to significantly higher
sensitivities than the All-Sky Survey.
The communications subsystem provides the command uplink in the S band, and teleme-
try downlink in the S and X bands. The commands are uplinked from the JAXA Uchinoura
Space Center. The telemetry data are stored in the onboard data recorder which has a 2 GB
memory, and then transmitted to the ground. The S-band telemetry normally includes low-rate
engineering housekeeping data, while the high-rate (4 Mbps) X-band telemetry is used for sci-
entific data transmission. The telemetry data are received at Uchinoura station, ESA’s Kiruna
station and also the KSAT Svalbard station. The AKARI data amounts to approximately 2
GB per day.
The scientific instruments are all operating normally in orbit. The temperature of the
telescope and the IRC structure is 5.8 K, and the temperature of the FIS detectors and the
structure is 2 K or lower. Measurements of the Helium content performed in orbit has shown
that the expected hold-time of the liquid Helium in orbit is longer than 500 days (Nakagawa
et al. 2007), which means that the All-Sky Survey can be executed more than twice within the
cryogen lifetime. The telescope has a diffraction-limited performance for wavelengths longer
than 7.3 µm (Kaneda et al. 2007). The telescope pointing error is less than 3 arcsec. The
attitude stability in the pointing mode is approximately 1 arcsec, and the rate stability in the
All-Sky Survey is less than 10−4deg/s. These numbers meet the scientific specifications for the
requirements of the mission.
The point-source flux detection limits at S/N > 5 for one scan in the All-Sky Survey
are 0.05, 0.13, 2.4, 0.55, 1.4, and 6.3 Jy for S9W, L18W, N60, Wide-S, Wide-L, and N160
bands, respectively. These were estimated on the basis of the noise measured in orbit using
the preliminary version of the pipeline software and could be improved with upgraded data
reduction techniques. The chief advantage of the AKARI survey over the IRAS survey will
be the wide spectral coverage and the higher spatial resolution. The detection limits in the
two mid-infrared bands are much better than those of IRAS. In the far-infrared bands, the
higher spatial resolution of AKARI is expected to improve source detection and flux estimations
significantly particularly in confused regions (Jeong et al. 2007).
More details on the in-orbit performance of the focal-plane instruments are described by
Kawada et al. (2007), Onaka et al. (2007), and Ohyama et al. (2007).
6. Observation strategy
The AKARI observations are classified into three categories, Large-Area Surveys
(Matsuhara et al. 2005, Matsuhara et al. 2006), Mission Programs (MP), and Open-Time
programs (OT). The Large-Area Survey of central importance is of course the All-Sky Survey.
The field of view is 8 arcmin for the FIS and 10 arcmin for the IRC. Successive sky scans cover
the same sky area at least twice, and enable efficient confirmation of the detection of celestial
sources excluding false signals due to cosmic ray hits and sources of noise. The achieved sky
coverage is greater than 90 % of the whole sky during the first year, although some areas are
left unobserved or observed only once due to the Moon interference and disturbance by charged
particles in the South Atlantic anomaly.
In addition to the All-Sky Survey, we are also conducting two further Large-Area Survey
programs, consisting of a survey of the North Ecliptic Pole region (NEP) and the Large
Magellanic Cloud. These two regions are covered with the pointed observations. Both are
located at high ecliptic latitudes, where the density of scan paths for the All-Sky Survey is high
and thus some observing time can be spared for pointed observations. Approximately 25 %
of the total available pointed observations for AKARI are for use in the Large-Area Survey
The Mission Programs are organized to interweave a series of pointed observations.
Fifteen programs on solar-system objects, star-forming regions, stars, interstellar matter, in-
frared galaxies and cosmology are being executed. About 45 % of the total pointed observations
for AKARI are assigned to the Mission Programs.
In addition to the above observation programs, 30 % of the pointed observations in
Phase 2 (see below) of the mission are opened to the Japanese, Korean, and European astro-
Lastly, some pointed-observation opportunities are reserved for the calibration of instru-
ments and Directors discretionary observations.
The observation periods are separated into three phases. The Phase 1 observations
were made in the first six months after the performance-verification phase. AKARI performed
the first All-Sky Survey during this phase and also some pointed observations at high ecliptic
latitudes. The actual period of Phase 1 began on 2006 May 8 and ended six months later on
2006 November 9. Approximately 70 % of the sky has been covered with two or more scans in
this period. In addition, a part of the Large-Area Surveys in the North Ecliptic Pole region and
the Large Magellanic Cloud, were also executed. The Phase 2 period began on 2006 November
10, and will last until all the Helium is exhausted. The second All-Sky Survey to increase the
sky coverage, and the pointed observations for the Mission Programs are being executed during
this phase. The Phase 3 observations are defined as those after the Helium is exhausted. In
Phase 3, only pointed observations using the IRC/NIR channel are possible.
The point source catalogues of the All-Sky Survey are planned for release to the astro-
nomical community in a timely fashion after the end of the survey.
The AKARI mission is operating normally and has been generating 2 GB of data every
day since May 2006. Its All-Sky Survey will provide new infrared source catalogs which are
expected to surpass the IRAS catalogs with higher spatial resolutions and wider spectral cov-
erage. The AKARI mission will provide an important and valuable database for the present
and future research in galaxy evolution, star formation, and planet formation.
The AKARI project, formerly known as ASTRO-F, is managed and operated by the
Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency
(JAXA), with the participation of universities and research institutes in Japan, the European
Space Agency (ESA), the IOSG (Imperial College, UK, Open University, UK, University
of Sussex, UK, and University of Groningen, Netherlands) Consortium, and Seoul National
University, Korea. The FIS instrument is developed by Nagoya University, ISAS/JAXA, the
University of Tokyo, and the National Astronomical Observatory of Japan and other insti-
tutes, with contributions of NICT to the development of the detectors. The IRC instrument
is developed by ISAS/JAXA and the University of Tokyo and other supporting institutes.
ESA/ESAC provides support for the All-Sky Survey data processing, through the pointing re-
construction. ESAC also provides user support for the observing opportunities distributed to
European astronomers. ESA/ESOC is providing the mission with ground support through its
ground station in Kiruna.
We owe the success of AKARI to the dedication of many people.
searchers of the engineering section of ISAS/JAXA have very much contributed to the de-
velopment of the AKARI satellite system. Here we list their names to express our grati-
tude: M. Hashimoto, T. Hashimoto, H. Hatta, E. Hirokawa, K. Hirose, K. Hori, T. Ichikawa,
T. Ikenaga, Y. Inatani, K. Inoue, N. Ishii, T. Kato, Y. Kawakatsu, J. Kawaguchi, Y. Matogawa,
K. Minesugi, H. Nakabe, T. Nakajima, I. Nakatani, M.C. Natori, H. Ogawa N. Okuizumi,
J. Onoda, E. Sato, H. Saito, H. Saito, S. Sawai, M. Shida, Y. Sone, M. Tajima, T. Toda,
K.T. Uesugi, T. Yamada, H. Yamakawa. Z. Yamamoto, and M. Yoshikawa.
We also would like to thank the M-V rocket team led by Y. Morita for successfully
launching the spacecraft into orbit.
Finally, we would like to thank the Science Advisory Committee of AKARI (N. Arimoto,
T. Hasegawa, T. Mukai, Y. Nakada, S. Okamura, M. Tamura, and Y. Taniguchi) for their
valuable guide to maximize the scientific outputs from AKARI.
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