AKARI
Observer’s Manual
for the Post-Helium (Phase 3) Mission
Version 1.2— for Open Time Observation Planning —AKARI User Support Teamin
Institute of Space and Astronautical Science / JAXA
contact: iris help@ir.isas.jaxa.jp
European Space Astronomy Centre / ESA
contact: http://akari.esac.esa.int/esupport/

May 22, 2009

Revision Record
2008 May 122008 June 122009 May 8

Version 1.0 released, adapted from ASTRO-F Observer’s Manual Version 3.2,
Version 1.1 released. Cookbook section added in Appendix.
Version 1.2. Small revisions to update the performance.

Contents
1 Introduction
1.1 Purpose of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Relevant Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1
1
3

2 Mission Overview
2.1 The AKARI Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Satellite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1 The Bus Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2 Attitude Determination and Control System . . . . . . . . . . . . . . . . .
2.2.3 Cryogenics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Telescope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.1 Speciﬁcation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3.2 Capability and Performance in Phase 3 . . . . . . . . . . . . . . . . . . .
2.4 Focal-Plane Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.1 Speciﬁcation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.2 Focal-Plane Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.3 The Focal-Plane Star Sensor (FSTS) . . . . . . . . . . . . . . . . . . . . .
2.5 The AKARI Observation Programms in Phase 3 . . . . . . . . . . . . . . . . . .
2.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5
5
6
6
7
8
9
9
10
11
11
13
14
15
16

3 Satellite Operations
17
3.1 Orbit and Observing Attitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 Attitude Operation Modes for Observations . . . . . . . . . . . . . . . . . . . . . 19
3.2.1 Survey Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.2 Pointing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3 Mission Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.4 Sky Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4 IRC: Infrared Camera
4.1 Hardware Speciﬁcation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.2 Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.3 Filters and Dispersion Elements . . . . . . . . . . . . . . . . . . . . . . .
4.1.4 Field of View (FoV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.5 Slits for Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.6 Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Flight performance in phase 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.1 Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.2 Detector system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 The IRC Instrument Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii

25
26
26
27
28
29
29
30
31
31
35
36

Version 1.2 (May 22, 2009)

4.4

4.5

4.3.1 Pointed Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The IRC AOTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.1 Detection Limits and Saturation Limits: General Remarks . . . . . . . . .
4.4.2 IRCZ0: Deep Imaging Mode . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.3 Expected Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.4 IRCZ2: Imaging and Spectroscopy with Two Filters or Filter and Prism .
4.4.5 Expected Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.6 IRCZ3: Imaging with Three Filters . . . . . . . . . . . . . . . . . . . . . .
4.4.7 Expected Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.8 IRCZ4: Spectroscopic mode . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.9 Expected Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Notes and Restrictions for the IRC Observations . . . . . . . . . . . . . . . . . .

iii
36
38
39
40
41
42
43
44
45
46
48
50

5 Data Reduction and Products
51
5.1 Basic Policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.1.1 IRC Data Reduction: AOT IRCZ0, Z2, Z3 . . . . . . . . . . . . . . . . . 52
5.1.2 IRC Data Reduction: AOT IRCZ4 . . . . . . . . . . . . . . . . . . . . . . 52
5.1.3 Phase 3 data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
A AKARI Cookbook for Post-Helium (Phase 3) mission Open Time observations
53
A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
A.2 Example 1: Spectroscopy of distant galaxies with the NG grism in the point
source aperture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
A.2.1 Scientiﬁc Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
A.2.2 Selection of Targets and Target Visibility . . . . . . . . . . . . . . . . . . 55
A.2.3 The Choice of Observation Mode . . . . . . . . . . . . . . . . . . . . . . . 57
A.2.4 Preparation of Target List . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
A.2.5 Target List Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
A.2.6 Duplication Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
A.2.7 Submission of Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
A.3 Example 2: Spectroscopy of Planetary Nebulae with the IRC . . . . . . . . . . . 63
A.3.1 Scientiﬁc Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
A.3.2 Target Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
A.3.3 The Choice of Observation Mode . . . . . . . . . . . . . . . . . . . . . . . 65
A.3.4 Preparation of Target List . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
A.3.5 Target List Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
A.3.6 Duplication Checker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
A.3.7 Submission of Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
A.4 Example 3: Near-infrared imaging of extragalactic ﬁelds with the IRC . . . . . . 70
A.4.1 Scientiﬁc Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
A.4.2 Selection of Target Field and Target Visibility . . . . . . . . . . . . . . . . 71
A.4.3 The Choice of Observation Mode . . . . . . . . . . . . . . . . . . . . . . . 71
A.4.4 Preparation of Target List . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
A.4.5 Target List Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
A.4.6 Duplication Check Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
A.4.7 Submission of Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Chapter 1

Introduction
1.1

Purpose of this document

This AKARI Observer’s Manual, is issued as the reference for AKARI observers, for observation
planning and the preparation for the data analysis for the post-Helium mission (hereafter calledphase 3).
The document covers the speciﬁcations of the satellite and the instruments, their performance, ﬂight operation plan, including deﬁnitions of the Astronomical Observation Templates(AOTs), and a brief desscription on the scope of data analysis. It contains the most up-to-dateestimates of the detection limits of the instrument based on the phase 3 performance evaluation
observations carried out in early 2008.
Note that some of the instrumental performance information was not yet available by thetime of the publication of this version of the manual. Frequent updates will be given on the
Observer’s support Web page.

1

2

AKARI Observer’s Manual

Figure 1.1.1: AKARI (ASTRO-F) waiting for the launch (January, 2006).

Version 1.2 (May 22, 2009)

1.2

3

Relevant Information

AKARI Observer’s Web
The AKARI Observers Web pages contains some additional information and data usefulfor the observers, including links to the user support tools:
http://www.ir.isas.jaxa.jp/AKARI/Observation/ for Japanese & Korean Open Time users
http://akari.esac.esa.int/ for the ESA Call: for ESA Open Time Users
Helpdesk
Any questions and comments on AKARI observations and user support shall be addressedto the AKARI Helpdesks.
iris help@ir.isas.jaxa.jp: for Japanese & Korean Open Time Users
http://akari.esac.esa.int/esupport/ : for ESA Open Time Users

4

AKARI Observer’s ManualChapter 2

Mission Overview
2.1

The AKARI Mission

AKARI (previously known as ASTRO-F) is the second Japanese space mission for infrared
astronomy. It was launched on February 21, 2006 (UT) by JAXA’s M-V rocket. The orbit is a
Sun-synchronous polar orbit with an altitude of 700 km and a period of 100 minutes. A pair of
Stirling cycle mechanical coolers enabled a long cryogenic mission lifetime with only 170 litresof liquid Helium. The liquid Helium boiled oﬀ on August 26, 2007. After the liquid Helium
exhaustion the telescope system is kept at about 40 K by the mechanical cooler and observations
at near-infrared wavelengths are continued.
AKARI is equipped with a 68.5 cm cooled telescope and two scientiﬁc instruments, namely
the Far-Infrared Surveyor (FIS) and the Infrared Camera (IRC). The FIS has two 2-dimensional
detector arrays and observes in four far-infrared bands between 50 and 180 μm at cryogenic
temperatures. The IRC consists of three cameras covering 1.8–26 μm in 9 bands with ﬁelds ofview of approximately 10 ×10 . Both instruments have low- to moderate-resolution spectroscopic
capability. Only the near-infrared channel (1.8–5.5 μm) is available for phase 3 observations.
A major goal of the mission is to carry out an All-Sky Survey with the FIS and additionallywith the IRC at 9 and 18 μm. The AKARI All-Sky Survey will signiﬁcantly surpass the previous
all-sky survey in the infrared by IRAS in both spatial resolution and wavelength coverage.
The results will be published as AKARI infrared source catalogues. In addition to the survey
observations, AKARI allowed for dedicated pointed observations with both the FIS and IRC.
Five thousand pointed observations were performed in the cryogenic phase of the mission.
Many pointed observations are used for the legacy observations by the AKARI project teammembers. Such programmes are referred to as “Mission Programmes”. In addition, 30 percent
of pointed observation opportunities were open for general users in Phase 2 in Japan/Korea and
ESA related countries via parallel peer-reviewed Call for Proposals.
Many international collaborations are ongoing with the AKARI project. The European Space
Agency (ESA) supplied a ground station operated by ESOC, and ESAC carries out the pointing
reconstruction of the All-Sky Survey observations. ESAC also handles the user support for theEuropean Open Time observing programmes. A consortium of Imperial College University of
London, the Open University, University of Sussex, and SRON-Groningen with University ofGroningen (IKSG consortium) participates on the data reduction of the FIS All-Sky Survey.
Seoul National University representing the Korean community also joins the data reduction
activity. Several collaborations at the personal level are also ongoing especially on the celestial
calibrators.

5

AKARI Observer’s Manual

6

2.2

Satellite

Figure 2.2.1 shows the overall structure of the AKARI spacecraft. The height is about 3.7 m(excluding the aperture lid) and the launch weight mass 952 kg. The satellite consists of twoparts, the bus module and the cryostat. The two parts are connected by a truss structure.

20

00

2170

Telescope

Sun Shield

Stirling-Cycle Cooler
Star Trackers
Focal-Plane Instrument Electronics

Sol

ar P

add

le

S-band Antenna

60
Thrusters

S-band Antenna
Earth Sensor

1550

18

930

Figure 2.2.1: An overall view of the AKARI spacecraft (scales are in mm).

2.2.1

The Bus Module

The bus module takes care of the power supply, house keeping, spacecraft attitude control, dataacquisition and the telecommunication link to the ground station. AKARI uses the S-band(mainly for command and house-keeping telemetry data) and the X-band (mainly for scientiﬁcdata) for telecommunication. Due to its’ near-Earth orbit, communication between the satellite
and the ground stations is limited. Therefore, AKARI has a two-Gigabyte data recorder.

Version 1.2 (May 22, 2009)

2.2.2

7

Attitude Determination and Control System

The attitude of the AKARI satellite is determined and controlled by on-board sensors and acomputer unit. Figure 2.2.2 shows the block diagram of the attitude and orbit control system(AOCS). The framework of the system is as follows: The IRU (Gyro) measures the motion of
the satellite. The TFSS (Two-dimensional Fine Sun Sensor) were meant to monitor the positionof the Sun in two-dimensions perpendicular to the Sun-satellite direction, and to correct any
long-term drift of the IRU signal. A pair of Star Sensors (STT) mounted on the wall of thecryostat are used to observe the attitude along the third axis and the alignment change between
the bus module, where IRU and TFSS are located, and the cryostat in which the telescopeis installed. Other instruments provide additional information for attitude determination. A
dedicated computer (AOCU) determines the satellite attitude. A set of reaction wheels (RW)
control the spacecraft attitude, with the help of Magnetic Torque Rods (MTQ). In the case ofany very large required motion, a set of thrusters may be used.
In the initial phase of the mission, the TFSS were found not to detect the Sun properly. Thiswas overcome with a new version of the on-board software for the attitude and orbit control
subsystem, making use of the Star Trackers.

STT-A

RW-A

STT-B

RW-B

TFSS
IRU-A
IRU-B
NSAS

AOCU
AOCP-A
AOCP-B
AOCP-C

CES-A

RW-C
RW-D
MTQ-X
MTQ-Y
MTQ-Z

CES-B
RCS20Nx4

GAS

RCS 3Nx4

ACM
Sensors

Data Handling Unit

Drivers

Figure 2.2.2: Block diagram of the AKARI attitude determination and control system.

AKARI Observer’s Manual

8

2.2.3

Cryogenics

Scientiﬁc instruments are all stored in the cryostat and were maintained at cryogenic temperatures by 170 litres of super-ﬂuid liquid Helium with the help of two sets of Stirling-cycle coolers.
The near-infrared instrument is operated with the mechanical coolers after the liquid Heliumboil-oﬀ. AKARI is operated with the Sun-shield always directed to the Sun. The cryostat iscovered by silver coated ﬁlm that reﬂects visible light but radiates in the infrared.
The Scientiﬁc Instrument Assembly (SIA), namely the telescope and the Focal-Plane Instruments (FPI) are thermally shielded by two layers of Vapour Cooled Shield (VCS) in which
Helium vapour evaporated from the tank was running through. The inner VSC is also cooled by
the mechanical coolers. The SIA was mainly cooled by the Helium vapour down to about 6 K.
The FIS body and two detectors are directly connected to the Helium tank via thermal straps
and were operated at 2.0–2.2 K. After the liquid Helium boiled-oﬀ, the SIA is kept around 40 K
and near-infrared observations are being carried out.

Figure 2.2.3: The AKARI Cryogenic system in the clean room for maintenance. (Left) The
Cryostat. (Right) Close-up of the Two-Stage Stirling cooler. (Photo: July, 2005)

Version 1.2 (May 22, 2009)

2.3

Telescope

2.3.1

Specification

9

The telescope is a Rithcy-Chrétien system with an eﬀective aperture of 68.5 cm and a focal ratioof 6.1 (Figure 2.3.4). The mirrors are made of SiC porous+CVD coated material. This rigidmaterial allowed to reduce the weight of the mirrors signiﬁcantly. The primary mirror, with aphysical diameter of 71 cm, weighs only 11 kg. The total weight of the telescope system is 42
kg. The focus may be adjusted in orbit during the PV phase by moving the position of thesecondary mirror. The parameters for the telescope are summarized in Table 2.3.1.
The primary mirror was replaced in 2004 as a part of a refurbishment of the telescope system.
The eﬀective aperture has been increased slightly (previously 67 cm). The telescope has beentested in the cryogenic vibration tests, and the mirror support system which previously had aproblem has been conﬁrmed to be secure.

Figure 2.3.4: The AKARI telescope system.

Table 2.3.1: Telescope Speciﬁcation
Eﬀective diameter
Focal length
Focal ratio
Optical design

68.5 cm (primary mirror)
420 cm
6.1
Ritchey-Chrétien type

AKARI Observer’s Manual

10

2.3.2

Capability and Performance in Phase 3

Mirror surface accuracy has been measured at cryogenic temperatures to be as low as 9 K. Due tothermal stress at the supporting points, the wave front error becomes larger at low temperaturesand is at its’ worst at around 50 K.
The in-orbit performance of the AKARI telescope system was measured to be diﬀraction
limited at a wavelength of 7.3 μm at 6 K. The image quality in phase 3 has been estimated to
be by about 10% degraded from that at 6 K after the focus adjustment.
During the Helium period, the stray light scattered oﬀ the top of the baﬄe was noticed
particularly during the periods around solstices. This stray light is expected to persist in phase
3 and observations of diﬀuse emission need to be arranged carefully.
AKARI phase 3 observations provide a unique capability in broad band imaging with a large
FoV (10 ×9.3 ) as well as low-resolution spectroscopy in 2–5 μm. In particular, the spectroscopicmode provides slit-less spectroscopy for the ﬁrst time in space missions. It enables eﬃcient multiobject spectroscopy in one pointing observation. High-sensitivity near-infrared spectroscopy freefrom disturbance of the terrestrial atmosphere can be applied for studies in various astronomical
objects.

Version 1.2 (May 22, 2009)

11

2.4

Focal-Plane Instruments

2.4.1

Specification Overview

Two scientiﬁc instruments are placed in the Focal-Plane of the telescope; the Far-Infrared Surveyor (FIS) and the Infrared Camera (IRC). In addition, two sets of Focal-Plane Star Sensors(FSTS) are installed for observing guide stars in the Near Infrared band (∼ J-band) for pointing
reconstruction during the survey observations. In phase 3, only the near-infrared channelof the IRC is available for observations. The whole payload capability is reported below
for historical reasons.
The FIS is equipped with two sets of two-dimensional detector arrays. The Short-Wavelength
channel (SW; 50–110 μm) uses two monolithic Ge:Ga arrays1 of 20 × 3 and 20 × 2 pixels, while
the Long-Wavelength channel (LW; 110–180 μm) has a stressed Ge:Ga array of 15 × 3 + 15 × 2
pixels. Each of the four arrays corresponds to a diﬀerent wavelength band. The pixel sizes are
27 and 44 arcsec2 , respectively.
The IRC consists of three independent cameras; the NIR (2–5 μm), the MIR-S (5–13 μm),
and the MIR-L (13–26 μm). The NIR camera has a 512 × 412 pixel InSb array, of which
100 × 412 pixels are dedicated for slit spectroscopy. The two MIR cameras use 256 × 256 pixel
Si:As detectors.
The wavelength range and resolving power provided by the scientiﬁc instruments are shownin Figure 2.4.5. The spatial resolution and the Field of View (FoV) of the instruments are
summarized in Figure 2.4.6.

IRC

1000

FTS
Prism & Grism

100
λ/Δλ

FIS

10

Wide-band PhotometryWide-band (Imaging)

1
1

10
Wavelength (μm)

100Ver. 05/08/15 I.Yamamura

Figure 2.4.5: The wavelength coverage and resolving power of the AKARI instruments.

1

The SW detector was manufactured by NICT.

AKARI Observer’s Manual

12

1000

IRC

FIS

Field of View

Field of View
(cross-scan)arcsec100
10Telescope Limit

Pixel Size

Limit
ction
DiffraPixel Size

1
1

10
Wavelength (μm)

100Ver. 04/07/27 I.Yamamura

Figure 2.4.6: Pixel size and ﬁeld of view (FoV) of the AKARI on board instruments.

Version 1.2 (May 22, 2009)

2.4.2

13

Focal-Plane Layout

Figure 2.4.7 shows the Focal-Plane layout projected onto the sky. There are three light entrances
to the instruments; one for the FIS and two for the IRC. The two instruments essentially canobserve simultaneously, but they see diﬀerent areas of the sky as shown in the ﬁgure. Therefore,
observations of a sky position with diﬀerent aperture have to be made on diﬀerent orbits.
The incident infrared radiation coming into the FIS aperture is divided into two spectral
domains by a dichroic beam splitter, as a result of which the FIS-SW and LW detector arrays
observe almost the same sky position. Similarly, the NIR and MIR-S cameras of the IRC sharethe same FoV so as to observe the same sky position. Only the MIR-L channel observes adiﬀerent sky position.
The scan path is approximately parallel to the Ecliptic meridian line. The scan direction
depends on the launch conﬁguration, namely the launch time (morning or evening). The actual
launch has been in the morning. The FoV is thus moving downward, i.e., stars go through thedetector from bottom to top on the ﬁgure.
Note that the real position and the shape of each Focal-Plane Instrument on the sky will beslightly diﬀerent from those shown in Figure 2.4.7, due to optical aberration. See Section 4.1.4(IRC) for details.

FSTS-SSCAN
DIRECTION.3'

1226.5deg
2.5' 6.5'

38.7 deg

FIS

IRC

9.4' 0.6'

7.0' 2.5'

NIR
&
MIR-S

8.2'

44.4deg

7.0'

MIR-L
10.7'

8'

Telescope
Axis
10.0'

10.2'

25.0'

0.8'
for all the FSTS detectors

19.2'

18.

20.5'

8.2'

7.0'

12.4'

44.4deg
'

.3

12

23.3'

20

04

Oc

t. 5

FSTS-L

Figure 2.4.7: Focal-Plane layout projected onto the sky. The distortion due to the telescope andinstrumental optics have to be taken into account for the data reduction. See the Instrument
Data User Manuals for details.

AKARI Observer’s Manual

14

2.4.3

The Focal-Plane Star Sensor (FSTS)

A pair of star sensors are installed in the Focal-Plane. The FSTS-L consists of four Ge detector
elements2 , while the FSTS-S has three. They observe stars with their intrinsic wavelength band
proﬁle close to the J-band (1.25 μm). The readout is a TIA (TransImpedance Ampliﬁer) circuitwith a sampling rate of about 50 Hz. The seven detectors are sampled almost simultaneously.
As the satellite scans the sky, stars cross the detectors in the in-scan direction one after another. The detection interval between a pair of two horizontal detectors placed in parallel deﬁnes
the scan speed, and the interval between the tilted and horizontal detectors can be converted
to the cross-scan position. The two FSTS’s located in opposite corners provide information on
the roll angle of the Focal-Plane with respect to the scan direction, as well as a redundancy
for the star detection. The absolute positional information is given by comparing the detection
information with the position reference catalogue. The pointing reconstruction using the FSTS
assumes (all-sky) survey operation mode.
The FSTS is not used in phase 3.

2
One of the four elements is known to be dead. The eﬀect of this loss to the pointing reconstruction is expected
to be small.

Version 1.2 (May 22, 2009)

2.5

15

The AKARI Observation Programms in Phase 3

Phase 3 Observations with AKARI can be divided into the following three categories.
Director and Calibration time (DT): 10 percent of the pointed observation opportunities
are reserved for calibration and director’s time.
Mission Programmes (MP): 60 percent of the pointed observation opportunities are allocated to the AKARI team members as a kind of guaranteed observation time. Speciﬁcworking groups in every scientiﬁc ﬁeld have worked to establish the observing programmes.
In total 16 Mission Programmes are now assigned. The data will be used by the teammembers for a one year prioritized period and then will be opened to the public. The MP
observations are regarded as the legacy of the AKARI mission.
Open Time Programmes (OT): 30 per cent of the total pointing opportunities are available
to the general research community. Two thirds of the opportunities (= 20 percent of
the total) are reserved for Japanese/Korean astronomers, and 10 percent are for the ESA
member countries. (see document “Call for Observing Proposals: Policies and Procedures”
for more details)

AKARI Observer’s Manual

16

2.6

References

The following papers in the special issue of the Publications of the Astronomical Society ofJapan (PASJ) give detailed information on the AKARI mission as well as AKARI instruments. They describe the in-orbit performance in the cryogenic period and are available at
http://pasj.asj.or.jp/v59/v59sp2.html. The performance of phase 3 is described in the present
manual as well as on the web.
Mission Overview: The Infrared Astronomical Mission AKARI
Murakami, H. et al. 2007, PASJ, 59, S369.
Cryogenics: Flight Performance of the AKARI Cryogenic System
Nakagawa, T. et al. 2007, PASJ, 59, S377.
Telescope: In-Orbit Focal Adjustment of the AKARI Telescope with Infrared Camera (IRC)
ImagesKaneda, H. et al. 2007, PASJ, 59, S411.
FIS: The Far-Infrared Surveyor (FIS) for AKARI
Kawada, M. et al. 2007, PASJ, 59, S389.
IRC: The Infrared Camera (IRC) for AKARI – Design and Imaging Performance
Onaka, T. et al. 2007, PASJ, 59, S401.
IRC spectroscopy: Near-Infrared and Mid-Infrared Spectroscopy with the Infrared Camera(IRC) for AKARI
Ohyama, Y. et al. 2007, PASJ, 49, S411.

Chapter 3

Satellite Operations
3.1

Orbit and Observing Attitude

The orbit of AKARI is a Sun-synchronous polar orbit along the twilight zone with an altitudeof 700 km, corresponding to an orbital period of 100 min. After the liquid Helium boil-oﬀ, theorbit was readjusted to a nearly ideal Sun-synchronous polar orbit.
In principle, the spacecraft always points in the direction perpendicular to the Sun–Earthline, keeping the Sun-shield towards the Sun, and rotates once per orbit to look out in the
opposite direction to the Earth. The spacecraft attitude in the cross-scan direction1 has a
ﬂexibility of ±1 degree about the canonical scan path.
89 - 91 degfrom the Sun
Return to
Survey( 7.5 min )

Sun
Light

Pointing(10 min )Stabilize( 5 min )Attitude Change
Maneuvour( 7.5 min )EARTHContinuous Survey

Figure 3.1.1: The in-orbit attitude of AKARI (left) and the pointed observation maneuver(right).
In the survey mode, the satellite is operated such that the telescope scans the sky witha constant speed (3.6 arcmin / sec) usually along the great-circle at a solar-elongation of 90
degrees. In the pointing mode, the telescope can point at an area of the sky along the scan pathfor up to 10 minutes, with the total cost of 30 minutes including maneuver for the operation.
Observations in phase 3 will be carried out only in pointing mode. The survey mode satellite
operations will however still be conducted as designed. Fine control of the observing position1

the direction perpendicular to the scanning (in-scan) direction.

17

AKARI Observer’s Manual18

in a pointing operation is possible. Observations in the pointing mode are deﬁned by a set of
Astronomical Observation Templates (AOT; see Sections 4.4).
The satellite Attitude and Orbit Control System (AOCS) has the capability of determining/ controlling the absolute attitude to an accuracy of 30 arcsec. The dominant source of thepointing uncertainty is the alignment of the focal-plane axis with respect to the AOCS reference
frame on the bus module and its time variation due to thermal distortion of the spacecraft.
Table 3.1.1 summarizes the nominal operation parameters and expected performance of the
AKARI AOCS for astronomical observations.
Table 3.1.1: AKARI AOCS Speciﬁcations
Absolute Pointing Control Accuracy
Scan Speed Stability (in-scan)
Scan Speed Stability (cross-scan)
Pointing Stability

30 arcsec< 0.1 per cent3 × 10−5 arcsec/min< 1 arcsec/min (peak-to-peak)Version 1.2 (May 22, 2009)

3.2

Attitude Operation Modes for Observations

3.2.1

Survey Mode

19

The survey mode is not used in observations of phase 3. This section is left over for information.
In the survey mode, AKARI performs a continuous scan of the sky. The spacecraft spinsaround the Sun-pointed axis once every orbit, keeping the telescope pointed toward the opposite
direction to the Earth (see left-hand of Figure 3.1.1); as a result, the telescope traces a great
circle with a solar elongation of 90 deg. The orbital period of 100 minutes corresponds to ascan-speed of 3.6 arcmin s−1 . In Table 3.2.2, the speciﬁcation and performance of the survey
mode operation are summarized.
Table 3.2.2: Summary of Survey mode operation (nominal).
Speciﬁcation of Survey mode operation
Survey Scan Speed
3.6 arcmin s−1
1
Survey In-scan Stability≤ 0.1 per cent
Survey Cross-scan Stability1∼ 3 × 10−5 deg/sec (3σ)
Pointing determination error (goal)
On-board< 30 arcsec (in-scan and cross-scan)
G-ADS
15–30 arcsec (in-scan and cross-scan)
Pointing Reconstruction (During Mission) < 5 arcsec (in-scan), < 7 arcsec (cross-scan)
Pointing Reconstruction (Post-Mission)< 3 arcsec (in-scan), < 5 arcsec (cross-scan)
1 Based on the performance evaluation tests.

The accurate position of the survey scan path on the sky is determined during the pointing
reconstruction processing. There are three levels of the processing: on-board determination by
the attitude and orbit control system (AOCS), on-ground processing using the same dataset (GADS), and detailed analysis together with the Focal-Plane Star Sensor (FSTS) and IRC survey
data.
The outline of the attitude determination process is summarized in Figure 3.2.2. The onboard attitude analysis has an absolute error of ∼ 30 arcsec. The main source of this error
is the alignment uncertainty between the satellite AOCS and the telescope’s focal-plane. The
results of the on-board analysis are downloaded to the ground with the sensor signal data. The
data is re-analyzed by the G-ADS for cross-check and to prepare the initial pointing data forreconstruction. At this stage, the pointing data (in the survey mode) still has an error of 15–30
arcsec.
Then, the data from the FSTS and the IRC survey are analyzed together with the initialpointing data for reﬁnement (pointing reconstruction). The ESA European Space Astronomy
Centre (ESAC) is in charge of the ﬁnal pointing reconstruction. The goal of the pointing accuracy
after the reconstruction is 5 arcsec (in-scan) and 7 arcsec (cross-scan) during the survey. Thisaccuracy can be improved to 3 arcsec (in-scan) and 5 arcsec (cross-scan) when the survey iscompleted and all data are analyzed and reprocessed.

3.2.2

Pointing ModeIn the pointing mode, AKARI will observe a speciﬁc sky position. Both imaging and spectroscopic observations with longer exposure times than the survey are possible. A single pointed
observation consists of four continuous operations (Figure 3.1.1, right);

AKARI Observer’s Manual

20

Control

On-Board
ADS

FSTS
Data

AOCS
Sensors

IRC ScanData

Realtime~ one day

ISAS
Ground ADS
Pointing
Obs. data

1~2 weeks

All-Sky Survey
Data Reduction
On-flyCatalogue" (in-scan)7" (cross-scan)
After Phase 2

All-Sky Survey
Data Reduction
AKARI
Catalogues

ESA
Pointing
Reconstruction~

Improvements

Pointing
Reconstruction3" (in-scan)5" (cross-scan)Figure 3.2.2: The outline of the AKARI attitude determination for the All-Sky Survey, includingtime scales and envisioned accuracy improvement. Note that the pointing reconstruction by ESA
is not carried out for the pointed observations.
1. Slewing maneuver to point the telescope at the target position,
2. Stabilization of the telescope,
3. Observation of the target,
4. Returning to the survey mode.
The total operation is completed in 30 minutes. This means that the maximum number ofpointed observations per orbit is three, if and when we can ﬁnd a suitable set of targets separatedby ∼ 120 deg. The actual net observation time per pointing is however limited to 10 minutes.
To increase the ﬂexibility of the observation opportunity for any target, the telescope can pointat any position on the sky in a stripe of 2 degree (±1 deg) perpendicular to the nominal scanpath. However, this allowance is much smaller than previous missions such as IRAS, ISO andSpitzer. Observers have to understand that the visibility of AKARI to observe a speciﬁc target
is extremely limited.
In order to avoid the Earth-light, the satellite starts slewing back to the survey mode automatically if the avoidance angle exceeds the limit. This happens without notifying the instruments to complete the observation. As a result, the very last part of some observation data
may be lost in some unfortunate cases. In Table 3.2.3, we summarize the speciﬁcations of thepointing mode.
The FoV is allowed to shift by a small amount in a pointed observation in the way summarizedin Table 3.2.4.
These ﬁne control operations are all included in the AOTs, and users do not have to concern themselves with them. An IRC observation uses Micro-Scan for dithering. See the AOT
description page for more details.
The Micro-Scan will cause a disturbance of the satellite attitude at the level of a few arcseconds. Therefore, each exposure has to be started after waiting for the stabilization of theVersion 1.2 (May 22, 2009)21

Table 3.2.3: Summary of Pointing mode operation (nominal)
Speciﬁcation of Pointing mode operation
Total operation time
30 minMaximum observation time
10 minAbsolute accuracy of pointing 30 arcsec
Cross-scan Oﬀset±1 deg
Performance
Pointing Stability1≤ 1 arcsec (peak-to-peak) in 1 minutes
1 Based on the performance evaluation tests.

Table 3.2.4: Pointing adjustment during a Pointed observation.
Amount of shift Direction Purpose
Micro-Scan 15–30 arcsec/step arbitrary Dithering of IRC imaging
Use of the Micro-scan is deﬁned in the AOT and observers are not allowed to change it.

telescope attitude. The IRC waits for notiﬁcation from the AOCS and then starts an exposure.
This waiting time will be a dead time for observers. The dead time for Micro-Scan operations
is typically about 30 sec and 40–50 sec. It is noted that the actual stabilization time varies
depending on the given condition. These dead times are taken into account in the AOTs of the
IRC and the corresponding sensitivity estimates.
No pointing reconstruction using the Focal-Plane instruments is planned for the pointed
observations. The users will receive position information from the G-ADS. Since the source ofthe pointing uncertainty is the alignment of the telescope and the AOCS, it is expected that theaccuracy will be improved as the analysis progresses. The users can reﬁne the position using
the data themselves for the IRC imaging observations.
Due to the trouble encountered at the start of the mission, the TFSS is not used in the attitude control. This leads to an attitude control heavily relying on the Star Trackers, thus imposing
additional constraints in the pointed observations. Pointed observations requiring maneuveringin the South Atlantic Anomaly (SAA) are not allowed. In addition, pointed observations in anarea where few stars are detectable by the Star Trackers will not be executed.

AKARI Observer’s Manual

22

3.3

Mission Phases

The mission lifetime of AKARI is divided into three observation phases excluding the performance veriﬁcation (PV) phases.
Phase 0 (PV Phase) The ﬁrst month after the jettison of the aperture lid was assigned to
the PV phase. In this period, a check out of the spacecraft system and the Focal-Plane
Instruments was made, the in-ﬂight performance was evaluated and the initial calibrationof the Focal-Plane Instruments was carried out. Test observations were also performed.
This phase lasted from April 13, 2006 to May 8, 2006.
Phase 1 The ﬁrst half year, during which AKARI scanned the entire ecliptic longitude isreferred to as Phase 1. In this period, the Large Area Survey Programmes, namely the
All-Sky Survey and the NEP / LMC pointing surveys were carried out with highest priority.
Some Mission Programme observations were also performed,
Phase 2 This phase continued until 2007 August 26, when all liquid Helium evaporated. Pointed
observations of Mission Programmes and Open Time proposals were performed as well as
supplemental scan observations to complete the All-Sky Survey.
Phase 3 After the boil-oﬀ of the liquid Helium, the mechanical cooler keeps the temperature
low enough to observe with the IRC/NIR camera. Phase 3, where only the IRC/NIR
camera is operated, continues until any of the on-board instrument (the NIR camera
itself, mechanical coolers etc.) cease to function. Performance veriﬁcation observations forphase 3 had been carried out until phase 3 Mission Programme observations started onJune 1, 2008. Open Time programmes for phase 3 started on October 15, 2008.

Version 1.2 (May 22, 2009)

3.4

23

Sky Visibility

As noted earlier, the direction of the telescope pointing is always perpendicular to the direction
toward the Sun with a ﬂexibility of ±1 deg in the cross-scan direction. Since AKARI is in apolar-orbit, the visibility, deﬁned as the number of scan paths covering a particular sky position,
is a strong function of ecliptic latitude. Targets in the ecliptic pole regions are observable on anumber of orbits, while targets near the ecliptic plane are visible by AKARI for only two days (29orbits) in a half year at most. In addition, visibility is also aﬀected by the SAA (South Atlantic
Anomaly; where a large ﬂux of charged particles disturbs the observation when the satellite
pass through the region) and the Moon (the moonlight can enter the telescope aperture. The
avoidance angle is 33 deg).
Observers should understand that opportunities to observe particular objects or ﬁelds withAKARI are strictly limited and are a strong function of the ecliptic latitude. It is strongly
recommended to the observers to check the visibility at each target position. A Web interface
visibility check tool is provided on the Phase 3 observers pages, with which the observers cancheck the visibility.
[Notes for the Solar System Observation]
Due to the severe visibility constraint, observation planning for Solar System Targets requires
additional procedures. The following steps are suggested.
1. Calculate the target position for the corresponding observation dates. This can be donewith NASA/JPL’s HORIZON system (http://ssd.jpl.nasa.gov/cgi-bin/eph) by giving thecondition of solar elongation angle as 90 ± 1 deg.
2. Use the visibility tool following the link from the Phase 3 AO page, to check if the target
is really visible at that position at that date.
3. Create the Target List with the coordinates. The corresponding observing date has to begiven in the comment ﬁeld of the Target List.
4. Check the visibility again with the visibility tool.

24

AKARI Observer’s ManualChapter 4

IRC: Infrared Camera
The Infrared Camera (IRC) on board AKARI is designed to perform deep imaging observationsin pointed observing mode. It’s unique wide ﬁeld coverage of 10 × 10 arcmin2 is ideal for surveytype observations. The IRC’s low-resolution spectroscopic capabilities in the imaging ﬁeld arealso well suited for multi-object spectroscopic surveys. In this section the description of the midinfrared channels is left over for reference in several places, but only the near-infrared channel isavailable for phase 3 observations. The performance numbers given in this section were derived
from observations in phase 2. Changes from phase 2 observations are indicated. For details of
the data processing, please see the IRC Data User Manual.

25

AKARI Observer’s Manual

26

4.1

Hardware Specification

4.1.1

Overview

The IRC consists of three cameras: NIR, MIR-S and MIR-L, covering the wavelength ranges of
2–5, 5–13, 12–26 μm, respectively. In Table 4.1.1, the speciﬁcations of each camera are listed.
See also ﬁgure 2.4.5 and 2.4.6. Note that only the NIR is available for phase 3 observations.
Table 4.1.1: Speciﬁcations of the Infrared Camera (IRC).
ChannelNIR
MIR-S
Detector
InSb(SBRC-189) Si:As (CRC-744)
Array
512 × 412
256 × 256
2
1
Imaging FoV (arcmin )9.3 × 10.0
9.1 × 10.0
Imaging Area (pixel2 )1
391 × 412
233 × 256
Pixel Size (arcsec)
1.46 × 1.46
2.34 × 2.34
Wavelength (μm)
1.8–5.5
4.6–13.4
Filters
N2, N3, N4
S7, S9W, S11
Dispersion Elements
NP, NG
SG1, SG2
1 Cross-scan × in-scan. Masked areas are excluded.

MIR-L
Si:As (CRC-744)
256 × 25610.3 × 10.2
246 × 2562.51 × 2.39
12.6–26.5
L15, L18W, L24
LG2

Each camera is equipped with three ﬁlters and two dispersion elements. The ﬁlter selection
is preset in the Astronomical Observation Templates (AOTs; Section 4.4) and cannot be freely
chosen by the observers.

Version 1.2 (May 22, 2009)

4.1.2

27

OpticsAll three cameras of the IRC are oﬀ-axis, refractive optical systems. Each camera uses 2–5
lenses. A Ge beam-splitter divides the light between the NIR and MIR-S cameras. Transmitted
light comes into the NIR channel. Chromatic aberration does exist in the cameras and is largest
in the MIR-S camera which uses only two lenses.
A ﬁlter wheel is placed at the iris of each camera. Three ﬁlters, two dispersion elements, anda blind mask are prepared for each camera. The blind position is used for dark measurements
during the ﬂight operation.

AKARI Observer’s Manual

28

4.1.3

Filters and Dispersion Elements

Table 4.1.2 shows the ﬁlters and the dispersion elements of the NIR channel of the IRC.
The NIR camera covers three independent wavelength bands that very roughly correspondto the well known K, L, and M bands. The two dispersion elements of the NIR camera provide
diﬀerent spectral resolutions over a similar wavelength range.
Table 4.1.2: IRC Filters and Dispersion Elements(1)
Channel

(2)
Name

(3)

(4)
λref
(μ m)
2.4
3.2
4.1
—
—

(5)
Wavelength(μ m)
1.9–2.8
2.7–3.8
3.6–5.3
1.8–5.5
2.5–5.0

(6)
λiso
(μ m)
2.34
3.19
4.33
—
—

(7)
Δλ
(μ m)
0.71
0.87
1.53
—
—

(8)
Dispersion(μ m/pix)———
0.06 at 3.5 μm
0.0097

N2
ﬁlter
N3
ﬁlter
NIR
N4
ﬁlter
NP
prism
NG
grism
(4) Reference wavelength(5) Deﬁned as where the responsivity for a given energy is larger than 1/e of the peak.
(6) Isophotal wavelength of the ﬁlter band for Vega.
(7) Eﬀective bandwidth.
(8) Dispersion power of prism depends on wavelength. The actual resolution can be estimatedassuming point spread function (see Table 4.2.4).

Version 1.2 (May 22, 2009)

4.1.4

29

Field of View (FoV)

Figure 4.1.1 shows the location of the FoV of the three IRC cameras on the Focal-Plane projected
onto the sky (See also Figure 2.4.7). As noted earlier, the NIR and MIR-S cameras observe thesame FoV on the sky simultaneously.
Reference positions for the AOT conﬁgurations for pointed observations are indicated inblue in Figure 4.1.1. Phase 3 imaging observations (AOT IRCZ0, IRCZ2, and IRCZ3) havea unique reference position, the center position of the NIR camera,‘N’. Reference positions forspectroscopic observations (AOT IRCZ4) are explained in the following section.

Scan Direction

Slit (MIR-L): 7"x0.4' (Ls)
10.7'

Telescope Axis
5.0'

MIR-L
4.9'

10.2'

0.9'

NIR
& MIR-S(L/Lc)
10.0'

5.0'
Slit (NIR): 3"x1' (Nh)(N/Nc)

0.4'

Slit (NIR): 1'x1' (Np)
Slit (NIR/MIR-S): 5"x0.8' (Ns)

9.1'-9.5'*
25.0'

0.5'*

* 9.3' (0.7') for N2, 9.5'(0.5') for N3 & N4
9.1' for MIR-S (all bands)

Figure 4.1.1: Focal-Plane layout of the IRC cameras. Reference positions for pointed observations are indicated in blue.

4.1.5

Slits for Spectroscopy

The dispersion elements of the IRC are set into the ﬁlter wheel so that all the light in the FoV isdispersed. A spectrum is obtained in the direction parallel to the scan path (in-scan direction),
which runs along the vertical direction in Figures 2.4.7 and 4.1.1. Slits are provided for eachcamera (Figure 4.1.1) in order to avoid contamination by nearby sources / diﬀuse radiation. The
slits are primarily designed for extended sources and it should not be assumed that they can beused to guide a point source into the slit, except for the NIR camera which has an aperture forpoint sources.
The slit for the NIR camera consists of three parts of diﬀerent widths. The left most (closest
to the imaging area) has a 5 arcsec width and was mainly used for simultaneous observationsof diﬀuse light with the MIR-S camera. This slit position is labeled as ‘Ns’ for IRCZ4 AOT
observation parameter. Both the NP (low-resolution prism) and NG (high-resolution grism) will
be used with this slit. The middle 1 × 1 square part, referred to as ‘Np’ is for spectroscopy ofpoint sources. The aperture is large compared to the absolute pointing accuracy of the satellite(designed to be better than 30 arcsec) to ensure that the target can be accurately guided into
the area. Note that for observations of faint sources, confusion due to galaxies may be a serious
problem. The NG (grism) is assumed to be used with this aperture. The rightmost (outer)AKARI Observer’s Manual

30

part (‘Nh’) has a 3 arcsec width and is used for the highest resolution spectroscopy of diﬀuse
radiation with the NG (grism).

4.1.6

Detectors

The detectors of the IRC are provided by Raytheon IRCoE. The NIR camera has an InSb
detector array of 512 × 412 pixels (SBRC-189), in which 391 × 412 pixels are used for imaging
and the other 121 × 412 pixels are for slit spectroscopy.
It is known that the detector performance sensitivity changes with temperature. All detector
arrays are equipped with thermometers to monitor the module temperature during their operation. In phase 3 it is noticed that the number of hot pixels in the NIR detector is increased
drastically from phase 2.

Version 1.2 (May 22, 2009)

31

4.2

Flight performance in phase 3

4.2.1

OpticsField of View (FoV)
The FoV of the NIR is diﬀerent for diﬀerent ﬁlters depending on the alignment of the ﬁlters. A
summary is given in Table 4.2.3.
Table 4.2.3: NIR camera FoV sizes
Band
N2
N3
N4

FoV (arcmin2 )9.3 × 10.0
9.5 × 10.0
9.5 × 10.0

Point Spread Function (PSF)
The performance of the AKARI telescope in phase 2 was derived to be diﬀraction limited at ∼7.3 μm and it was conﬁrmed that the image quality was degraded by 10–20% in phase 3. Thus
the PSF is more extended than the diﬀraction limits in the NIR camera. Table 4.2.4 shows thepreliminary results of the measurements of Full-Width Half Maximum (FWHM) of the PSF forthe imaging bands of the IRC cameras in phase 3.
Table 4.2.4: Preliminary values of Full-Width Half Maximum (FWHM) of the PSF for the IRC
NIR imaging bands for phase 3(1)
Channel

(2)
Band

NIR

N2
N3
N4

(3)
FWHM
(pix)
3.2
3.2
3.2

Chromatic Aberration
The NIR camera has chromatic aberration of 0.3–0.4 mm, which is in fact larger than thedesigned value. The most likely cause is the uncertainty of the optical characteristics of theelements under cryogenic temperature. The mean amount of aberration is comparable to thatof the diﬀraction limited optics at 2 μm and thus eﬀects the image quality.
Optical Transmittance
The throughout transmission functions (RSRF: Relative Spectral Response Function) of the IRC
NIR broad band ﬁlters are shown in Figure 4.2.2. The ﬁlters and optical components as wellas the detector response are taken into account to produce the curves1 . These RSRFs can be
1

These RSRFs have been prepared in collaboration with Dr. Martin Cohen to ensure a common calibrationof the IRC with other missions and ground-based instruments, including Subaru/COMICS, in the framework of
the absolute calibration network provided by him and his colleagues.

32

AKARI Observer’s Manual

directly integrated over spectra given as Fλ to obtain the in-band ﬂuxes (synthetic photometry).
These RSRFs are derived for phase 2 observations. Minor changes are expected in phase 3.
Figure 4.2.3 shows the RSRFs of the dispersion elements (given per photon). These data arealso available in digital format on the Observer’s support web pages.

Version 1.2 (May 22, 2009)33

Relative Response

1

N4

N3

0.8

N2

0.6
0.4
0.2
0
1

2

3

4

5

Wavelength (μm)

6Figure 4.2.2: The Relative Spectral Response Function of the IRC/NIR Camera for Fλ .

Relative Response

1
0.8

NP
NG

0.6
0.4
0.2
0
1

2

3

4

5

Wavelength (μm)

6Figure 4.2.3: The Relative Spectral Response Function of the IRC/NIR dispersion elements per
photon.

34

AKARI Observer’s Manual

Distortion
Image distortion of the IRC NIR camera is negligible. The diﬀerence in the pixel scale in the X
and Y directions is corrected in the data pipeline processing.
GhostsThere are several ghost patterns recognized for the NIR data. They are noticeable only whenbright sources are in the ﬁeld-of-view. For details please refer to the IRC Data Users Manual.

Version 1.2 (May 22, 2009)

4.2.2

35

Detector system

Hot Pixels
The number of hot pixels increased dramatically in phase 3. They are now about 5% of thetotal number of pixels and are more concentrated in the slit spectroscopy area (Figure 4.2.4).
Software that treats these hot pixels is now available. Observers are strongly recommended toperform redundant observations.

Figure 4.2.4: Dark frame images in phase 2 (a) and phase 3 (b) in the same ADU scale.

Linearity
The well-capacity of the NIR array is reduced by a factor of 5–6 in phase 3 compared to thatin phase 2, because of the lower bias voltage used for phase 3 to reduce the number of hot
pixels. Observers should be aware of the dramatic reduction of the saturation level in phase 3.
Observations of bright sources will not provide meaningful data, although they will not make anaftereﬀect and thus will not be prohibited. The linearity correction below the saturation levelset by the well-capacity will be made in the pipeline data processing.
Sensitivity
According to a preliminary study, the sensitivity (ADU to Jy) is reduced by 70% comparedto the phase 2 performance. No appreciable change in the sensitivity during phase 3 has been
noticed.

AKARI Observer’s Manual

36

4.3

The IRC Instrument Operation

4.3.1

Pointed Observations

Exposure cycle
The minimum observation unit of the IRC is called an exposure cycle. An IRC pointed observation consists of an n times repeated exposure cycle with operations such as a ﬁlter change andMicro-Scan inserted between them. The operation sequence of the exposure cycle is designedby the IRC team to optimize the performance of the instrument and observation eﬃciency. The
design of an exposure cycle is illustrated in Figure 4.3.5.
The unit time length for a detector driving is 2.3376 seconds, which corresponds to the time
for the NIR detector to access all pixels in the array. Time durations in the exposure cycle arealways a multiple of this unit time.
One exposure cycle takes 28× unit time (=65.4528 s). The NIR detector carries out one
short (2× unit time = 4.6752 sec) and one long exposure (19× unit time = 44.4144 sec) in acycle. The short exposure is useful for bright stars that may saturate the detector. However, thephotometric accuracy of the short-exposure is worse than the long-exposure. Fowler 4 samplingis taken for the longer integrations to reduce the readout noise by a factor of two.
Two images from the NIR channelare produced in one exposure cycle. They are stored in theframe memory buﬀer, then divided into telemetry packets and down-linked to the ground. The
on ground data reformatting software will reconstruct the frame memory buﬀer and eventuallya set of images, which are then passed to the observers.

Output signal
Reset4.6752s65.4528s

44.4144s
Datatransfer

Fowler 4

Time

Figure 4.3.5: Illustration of the operation of one exposure cycle. A pair of short and longexposures are carried out for the NIR camera.The upward arrows indicate the data read timing.
A pointed observation is carried out by repeating the exposure cycle with Micro-Scans andﬁlter changes inserted between them. These operations cause dead time due to the operations
themselves and stabilization of the satellite attitude. The dead time is 20–80 seconds, dependingon the operation and the performance of the attitude control system. Additional time for sending
the data to the satellite’s data processor (DHU) is also needed. These operations and deadtimes are taken into account in the design of the Astronomical Observation Templates (AOT;
section 4.4).
During a pointed observation, the IRC on-board controller communicates with the Attitudeand Orbit Control Unit (AOCU) via the DHU. When the IRC requests a Micro-Scan for dithering, it asks the AOCU to perform the operation. The AOCU drives the satellite, then waits
for the stabilization. When the AOCU decides that the satellite has stabilized, with a preset
criteria, it sends back a signal to the IRC (via the DHU) to start the next exposure cycle. This

Version 1.2 (May 22, 2009)37

sequence continues until the AOT is completed. If, by some reason, the attitude of the spacecraft
exceeds the allowed range of the angle with respect to the Earth, the AOCU stops the pointing
mode attitude and returns back to the survey attitude, regardless of the observation. The IRC
will continue its programmed exposure sequences but of course those data acquired during the
maneuver are useless and will not be provided to the users. Current AOTs assume that one
pointed observation could last longer than 10 minutes and add extra exposure cycles at the end.

AKARI Observer’s Manual

38

4.4

The IRC AOTs

The Astronomical Observation Templates (AOTs) of the IRC are summarized in Table 4.4.5.
Five AOTs are deﬁned for the instrument.
Note that the actual AOT sequence has been modiﬁed from phase 2 and thus the designationof the AOT is changed from that used in phase 2. AOTs are now called Z# rather than 0#,
where the same number # indicates the corresponding AOT in phase 2. The largest modiﬁcationin the observation sequence consists in 5 dark frames before and after the actual observation
to obtain information on the dark current for each observation. There are also more options(parameter combinations) available for each AOT.
Table 4.4.5: IRC AOTs and user parameters.
AOT

Purpose

Z0
Z2
Z3
Z4

Deep imaging
Imaging with 2 ﬁlters/ch.
Imaging with 3 ﬁlters/ch.
Spectroscopy# of ﬁlters
per ch.
1231DitheringNo
3 pos/ﬁlter
2 pos/ﬁlter
No

Parameters
FilterPointing
3 choicesN
2 choicesN
N/A (ﬁxed)N
2 choices
Ns, Np, Nh, Nc

The procedures for the AOT operations for IRCZ0, Z2, Z3 and Z4 are shown in Figure 4.4.6.
As explained in the previous section (4.3.1) an AOT consists of a combination of exposure
cycles (indicated as “exposure cycle”), Filter Wheel rotations (“W”) and Micro-Scan operations(“M”). They are optimized such that the maximum exposure time is obtained. The AOTs aredesigned to use more than 600 sec in the case that extra observation time is available. The
actual observation time depends on the stability of the target acquisition procedure.
ManeuverIRCZ0

Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle(filter 1)(filter 1)(filter 1)(filter 1)(filter 1)(filter 1)(filter 1)(filter 1)(filter 1)(filter 1)

IRCZ2

Exposure Cycle(filter 1)

IRCZ3

Exposure Cycle(filter 1)

IRCZ4

Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle(disperser 1)(disperser 1)(disperser 1)(disperser 1)

W

W

Exposure Cycle(filter 2)

Exposure Cycle(filter 2)

W

M

Exposure Cycle(filter 2)

Exposure Cycle(filter 3)

M

W

Exposure Cycle(filter 1)

Exposure Cycle(filter 3)

W

Exposure Cycle
(N3)

W

M

Exposure Cycle(filter 1)

Exposure Cycle(filter 2)

W

W

W

Exposure Cycle(filter 1)

Exposure Cycle(filter 2)

M

M

Exposure Cycle(filter 1)

Exposure Cycle(filter 1)

W

Exposure Cycle(filter 2)

Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle Exposure Cycle(disperser 1)(disperser 1)(disperser 1)(disperser 1)(disperser 1)

Figure 4.4.6: Observation sequences of the AOT IRCZ0, Z2, Z3, and Z4. Yellow boxes indicatedas “exposure cycle” with ﬁlter / dispersion element names are exposure cycles. Orange boxes
with “M” are Micro-Scan operations including stabilization, and light-blue boxes with “W” areFilter Wheel rotations. Dead time for a Filter Wheel change depends on the relative positionof the elements. The Green area on the right side is the extra observation time which is notguaranteed. Note that for IRCZ2, ﬁlter 2 corresponds to NP when parameter “b” is speciﬁed.

Version 1.2 (May 22, 2009)

4.4.1

39

Detection Limits and Saturation Limits: General Remarks

In the following sections, the expected detection limits for corresponding AOTs are given. These
are 5σ detection limits per single pointing opportunity, extrapolated from the performance
evaluated in phase 2 for relatively low-background sky (high ecliptic latitude regions) with theassumption that the detection limit is worse by a factor of 2 than in phase 2. The factor of
2 was derived taking into account the degraded PSF, the degradation in the sensitivity, andthe noise level in phase 3, which provides the best estimate at the present. The detection limit
for diﬀuse (extended) source is estimated from the point source detection limit, divided by thearea given by the FWHM of the PSF (Table 4.2.4). Repeating an observation of the same√
region with the same AOT is supposed to improve the sensitivity by a factor of n, where
n is the number of pointing opportunities. Since the number of hot pixels in the NIR
detector is dramatically increased in phase 3, redundant observations are strongly
recommended.
The saturation limits are given as the ﬂux level at which the detector signals deviate fromlinearity by 10 per cent. In fact, it is a rather rapid change from these levels to the absolutesaturation and it is reasonable to use these levels as the saturation limits. The saturation limits
are the same for all the imaging AOTs (IRCZ0, IRCZ2, and IRCZ3). The saturation limits fora short exposure are given in Table 4.4.6.
Table 4.4.6: Saturation limits for IRC imaging modes
CameraFilter

NIR

N2
N3
N4

Fsat
(Jy)
0.13
0.11
0.07

AKARI Observer’s Manual

40

4.4.2

IRCZ0: Deep Imaging Mode

Recommended Usage
IRCZ0 mode is prepared for deep imaging observations of high visibility regions where morethan 6 pointed observations can be easily obtained.
Description
The mode is designed to maximize the exposure time during a pointing opportunity. The
exposure cycle is simply repeated until the end of the pointed observation. No ﬁlter change
nor dithering operation is inserted. It is expected that observations with other ﬁlter(s) anddata redundancy by dithering are taken on additional pointing opportunities. It is strongly
recommended to observe the same sky position with at least three independent pointings withthe same ﬁlter setting. The necessary number of pointings is then multiplied by the number
of ﬁlters. Therefore IRCZ0 is only applicable in very high visibility regions, at high ecliptic
latitudes. It is recommended for observers to use this mode only in areas of the sky that canbe observed more than 6 times (three dithers, two ﬁlters). Due to operational constraints it
is very diﬃcult to ensure such high visibility for Open Time and thus use of this mode has tobe planned with great care. If the multiple observations are requested under the same target
ID, small shifts of the pointing position among independent pointing observations (dithering
operation among pointing observations) are automatically arranged in the scheduling software.
Observers who wish to set the observation positions by themselves should specify the target
position in each pointing opportunity and should not use multiple pointing assignments.
Parameters
Only the ﬁlter to be used can be speciﬁed as deﬁned in Table 4.4.7. The FoV reference positionis ﬁxed at the center of the NIR camera (N).
Table 4.4.7: Filter parameter of IRCZ0Parameter
ﬁlter

a
N2

b
N3

c
N4

Version 1.2 (May 22, 2009)

4.4.3

41

Expected Performance

Detection Limits
The expected 5σ detection limits of the IRCZ0 observing mode are given in Table 4.4.8 assuming
9 exposure cycles for one ﬁlter in a pointing opportunity.
Table 4.4.8: Detection limits (5 σ ) for AOT IRCZ0
FilterN2
N3
N4

Point source
(μJy)
18
18
18

Diﬀuse source(MJy sr−1 )
0.036
0.035
0.035

Saturation Limits
The saturation limits of the IRCZ0 mode are given in Table 4.4.6.

AKARI Observer’s Manual

42

4.4.4

IRCZ2: Imaging and Spectroscopy with Two Filters or Filter and Prism

Recommended UsageIRCZ2 mode is prepared for general purpose imaging or spectroscopic observations. This modecan be used at any sky position even in low visibility regions.
Description
A sky position is observed with two ﬁlters each of which consist of three images with small
position shifts by dither. i.e., this AOT can provide a self-standing data set in just a single
pointing. The net exposure time per ﬁlter is about 1/3 of IRCZ0. The IRCZ2 provides a newimaging (N3) and prism (NP) mode in addition to the original IRC02 mode with two ﬁlters(N3 and N4). The spectroscopic mode provides an imaging and slit-less spectroscopic modewith dithering operation, which is diﬀerent from IRCZ4. With the large number of hot pixels,
dithering operation in one pointing could provide useful redundant information. On the other
hand, it may reduce the accuracy in the determination of the reference wavelength position
because of the dithering.
Parameters
There are two choices for the ﬁlter/disperser combination in this AOT as given in Table 4.4.9.
The parameter a is set for imaging with N3 and N4 and b (new for phase 3) is set for N3 andprism.
Table 4.4.9: Filter combination of IRCZ2Parameter
Filter/Prisma
N3 & N4b
N3 & NPThe FoV reference position is ﬁxed at the center of the NIR camera (N).

Version 1.2 (May 22, 2009)

4.4.5

43

Expected Performance

Detection Limits
The expected 5σ detection limits of the IRCZ2 imaging mode are given in Table 4.4.10, assuming
3 exposure cycles per ﬁlter in a pointing opportunity. The NP mode 5σ detection limit is shownin Figure 4.4.7.
Table 4.4.10: Detection Limits for IRCZ2FilterN3
N4

Point source
(μJy)
31
31

Diﬀuse source(MJy sr−1 )
0.061
0.061

5-σ Detection Limit (mJy)

100

10

1

0.1

2

2.5

3

3.5

4

4.5

Wavelength (μm)

55.5Figure 4.4.7: 5σ detection limit for NP in IRCZ2.

Saturation Limits
The saturation limits of the IRCZ2 imaging mode are given in Table 4.4.6. For the NP mode
it is estimated to be about 3Jy at 3 μm. However the saturation in the N3 mode will make itdiﬃcult to determine the reference wavelength position from the N3 image accurately.

AKARI Observer’s Manual

44

4.4.6

IRCZ3: Imaging with Three Filters

Recommended UsageIRCZ3 is used for general purpose observing. It observes a target with all three ﬁlters ofeach camera. This mode is not recommended for sky areas of low visibility where two pointed
observations cannot be guaranteed.
Description
IRCZ3 is similar to the IRCZ2 mode but diﬀers in the number of ﬁlters and dithering positions
in one pointing opportunity. The target sky position is observed by three ﬁlters. Instead, only
one Micro-Scan (2 dithered images) is applied for each band. To obtain reliable results it isrecommended to have suﬃcient redundancy by observing the same sky position at least twice
on diﬀerent orbits. The net exposure time per ﬁlter is thus 2/9 of the IRCZ0.
Parameters
IRCZ3 uses all ﬁlters of the IRC NIR channel. The advantage of using this mode over IRCZ2
has to be carefully considered from the scientiﬁc viewpoint of each observation. The positionreference is ﬁxed at the center of the NIR camera (N).

Version 1.2 (May 22, 2009)

4.4.7

45

Expected Performance

Detection Limits
Expected 5σ detection limits of the IRCZ3 observing mode are given in Table 4.4.11, assuming
2 exposure cycles per ﬁlter in a pointing opportunity.
Table 4.4.11: Detection limits for IRCZ3
FilterN2
N3
N4

Point source
(μJy)
39
39
38

Diﬀuse source(MJy sr−1 )
0.076
0.075
0.075

Saturation Limits
The saturation limits of the IRCZ3 mode are given in Table 4.4.6.

AKARI Observer’s Manual

46

4.4.8

IRCZ4: Spectroscopic mode

Recommended Usage
IRCZ4 is prepared for spectroscopic observations with the IRC. Observation with this mode canbe made in regions of moderate to high visibility which allow two or more pointed observations
at each target position.
Description
In this mode, the IRC dispersion elements are used to take spectra of the targets. The wavelength
coverage of the NP (moderate resolution) and NG (high resolution) are similar to each other,and the user should choose one of these two for this AOT.
As we explain in section 4.1.5, a slit is provided in each camera in order to observe diﬀuse
radiation. The NIR camera also has an entrance aperture (slit) for a point source, to enableconfusion-less spectroscopy. It is used with the NG in high-resolution mode (see below). In
phase 3 all the combinations of the slit selection are available both for NP and NG.
An image with N3 is taken for pointing alignment. No dithering operation is carried out
during one pointing in this AOT. Observers are highly recommended to observe the same areaof the sky on three or more independent orbits to ensure data redundancy. If the multiple
observations with Np or Nh are requested under the same target ID, small shift along the slit
among independent pointing observations are arranged automatically in the scheduling software.
Observers who wish to set the observation positions by themselves should specify the target
position in each pointing opportunity and should not use multiple pointing assignments.
Parameters
The ﬁrst parameter speciﬁes the dispersion element for the NIR camera.
Table 4.4.12: Dispersion element selection in IRCZ4Parameter
Disperser

a
NP

b
NG

The second parameter gives the position reference for this AOT. It is more complicated thanother AOTs because of the presence of the slits. Np and Nh are intended to be used with theNG, and others with the NP, although all the position reference parameters are allowed both for
NP and NG. It should be noted that for point sources Nh or Ns should not be used.
The absolute pointing accuracy of AKARI does not guarantee that the intended
point source be located on the narrow slit. Also usage of Nc with NG for slit-less
spectroscopy is not recommended unless observers assure that the target will not
be confused by surrounding faint sources.

Version 1.2 (May 22, 2009)

Table 4.4.13: Target position parameter for IRCZ4
Code
Nc
Ns
Np
Nh

Description
The target position is placed at the center of the NIR (FoV).
The target position is placed at the common slit of the NIR and MIR-S.
The target position is placed at the point source aperture of the NIR.
The target position is placed at the high-resolution slit of the NIR.

47

AKARI Observer’s Manual

48

4.4.9

Expected Performance

Detection Limits
Figure 4.4.8 shows the 5σ detection limits for point sources with NP and NG in low sky background regions, assuming 8 exposure cycles in a pointing opportunity Note that for high background regions, such as star-forming regions, the detection will be limited by background ﬂuctuation more severely than plotted in these ﬁgures. Figure 4.4.9 shows the 5σ detection limits fordiﬀuse sources with the Ns slit with NP and NG in low sky background regions, assuming thatthe slit width and the FWHM of the PSF given in Table 4.2.4. For the Nh slit, the detection
limit becomes larger by a factor of 5/3.

5σ Detection Limit (mJy)

100
NP
NG
10

1

0.1

2

2.5

3

3.5

4

4.5

Wavelength (μm)

55.55σ Detection Limit (MJy sr-1)

Figure 4.4.8: 5σ detection limits for point sources with NP or NG in IRCZ4.
100
NP
NG

For Ns

10

1

0.1

2

2.5

3

3.5

4

4.5

Wavelength (μm)

55.5Figure 4.4.9: 5σ detection limits for diﬀuse sources with NP or NG in IRCZ4.

Version 1.2 (May 22, 2009)49

Saturation Limits
The saturation limits for NP and NG are about 3 and 10Jy, respectively. However, the saturationin the N3 imaging data sandwiched by spectroscopic observations could make it diﬃcult todetermine the reference wavelength position accurately for observations with Nc and Np. The
saturation level for N3 is given in Table 4.4.6.
The NP works as a very broad band ﬁlter in the imaging FoV. Thus the background level
becomes very high in high background regions. The low saturation level in phase 3 makes itvery diﬃcult to execute slitless spectroscopy with NP in high background regions, such as thosenear the Galactic plane. It should be noted that high background leaves only a few ADUs forpoint sources.

50

4.5

AKARI Observer’s ManualNotes and Restrictions for the IRC Observations

1. Bright sources Bright sources that saturate the NIR detectors will not leave signiﬁcanteﬀects on the following observations and thus will be planned not to be prohibited. Howeverbright sources in the FoV can produce unwanted array anomalies, such as mux-bleed, andthus should be avoided as much as possible. Some constraint for observing ﬁelds with very
bright sources may be given for IRC observations as observations progress.
2. Eﬀects of South Atlantic Anomaly (SAA) Passage through the SAA does not cause
serious damage to the detectors. However, detector performance may be signiﬁcantly
degraded immediately after the SAA. Current observation scheduling allocates IRC observations relatively close to the SAA region (say, 5 minutes after the passage).

Chapter 5

Data Reduction and ProductsThis section describes the data handling policy, current scope of the data reduction supportand data products, particularly for phase 3 observations. Please note that the data reduction
software is under development and only a preliminary plan is explained here. Details of the data
handling and data reduction guide are prepared as Instrument Data User Manuals.
The data reduction steps for phase 3 IRC observations are performed in a similar mannerto those for phase 2. However the very same software that is used for phase 2 data may not beapplied. The software speciﬁc to phase 3 observations is currently being developed.

51

AKARI Observer’s Manual

52

5.1

Basic Policy

The reduction of pointing observation data is the observer’s responsibility. The AKARI teamwill provide the necessary information to handle the data, e.g., calibration data and software tocorrect instrument related characteristics. Astronomical analysis such as point source extraction
should be carried out by commonly available software.
We welcome any users to participate in the data reduction activity at any level of the work,from giving quantitative reports of their data reduction results to proposing new algorithms to
the programs.

5.1.1

IRC Data Reduction: AOT IRCZ0, Z2, Z3

IRC imaging mode data reduction is straightforward following a similar procedure to groundbase observations. There are instrument speciﬁc corrections such as removing ghost images andspikes by charged particle hits.
Our support is limited to correction and calibration of each observation. We do not plan tosupport photometry of the calibrated images or mosaicing.
Currently the system is developed in the IRAF environment. Exporting it to IDL is TBD.

5.1.2

IRC Data Reduction: AOT IRCZ4

Data reduction of this mode is similar to that of the imaging mode for the basic processing of thedark subtraction, despiking, or bad pixel masking etc. In this AOT, an image is also taken with
the N3 ﬁlter. Source positions are extracted from this image and applied to the spectroscopy
images to clip each target.
Several relevant technical issues for the spectroscopic observations are listed below.
• For reliable spectroscopic observations we need accurate and wavelength dependent ﬂatﬁelding.
• Wavelength calibration is automatically made by the relationship between imaging position and the spectroscopy data. It also includes distortion correction of the image (Section 4.2.1).
• There may be confusion from nearby targets in the case of observations in crowded regions. Currently these are not decomposed but rather masked in the overlap region forthe measurements.
• Measurement of the spectrum is carried out in an aperture on the spectroscopic image.
The software attempts to ﬁt an aperture automatically but the user may want to adjust
this step interactively.
The tools are written in IDL.

5.1.3

Phase 3 data

Phase 3 data in the near-infrared channel suﬀer a number of hot pixels signiﬁcantly. Also thedark current is no longer negligible. The operation sequence of phase 3 is diﬀerent from thatin phase 2 in taking the dark current measurements before and after the celestial observations.
The associated dark measurements will be provided for the dark subtraction rather than the
super-dark data provided in phase 2 data package.

Appendix A

AKARI Cookbook for Post-Helium(Phase 3) mission Open Timeobservations
A.1

Introduction

In order to aid observers with the preparation of proposals for Phase 3 Open Time, we present inthis section three worked examples for observation and submission of Open Time proposals withAKARI. Note that this chapter was originally prepared for the ﬁrst year of Phase 3
as a guideline and descriptions with the ﬁrst year should read as the second year.
We show;
1. IRC Spectroscopy of distant galaxies with the NG grism in the point source aperture.
2. IRC Spectroscopy of a galactic target.
3. IRC Near-infrared imaging of extragalactic ﬁelds.
In general, the preparation of Open Time proposals follows the algorithm below, using dedicated tools available via a web interface. In addition, we expect users to iterate their observations
using the tools before their ﬁnal submission, in order to obtain the best possible observation
strategy. Note that the tools available for Phase 3 Open Time are a scaled down and limited data
set compared to those available in the earlier call. In particular, the Instrument Performance
Tool (IPT) is not available for Phase 3 observation planning.
1. Target selection and visibility check2. Preparation of the “Target list”
3. Validation check of the “Target list”
4. Run Duplication Check Tool
5. Submission via Submission Tool53

AKARI Observer’s Manual

54

A.2

Example 1: Spectroscopy of distant galaxies with the NG
grism in the point source aperture

In this worked example we consider a program to carry out spectroscopy using the AKARIIRC NG high resolution grism in the 1×1 arcmin point source aperture. We will simulate thepreparation of the proposal from scientiﬁc background to proposal submission.

A.2.1

Scientific Background

The advent of the SCUBA instrument on the JCMT, Hawaii, allowed mapping of the submillimetre Universe for the ﬁrst time. The ﬁrst surveys detected a new population of dusty
starburst galaxies, the high redshift analogue of local ULIRGs (Hughes et al. (1998), Smail etal. (1997)). Subsequent surveys have increased both in numbers of detected sources and areal
coverage (e.g. Scott et al. (2002)) with the ﬂagship being the SCUBA Half Degree Extragalatic
Survey (SHADES, Mortier et al. 2005) covering 0.25 square degrees over two ﬁelds. The lack ofany secure evolutionary picture of submm galaxies is partly due to fact that the observational
results on submm galaxies are very limited. Until recently the only photometric data available
for most of submm galaxies, was found mainly at NIR and submm wavelengths. This lackof photometric data has been alleviated somewhat with mid-infrared observations with Spitzer
and AKARI although more detailed diagnostics on the observed diversi! ty and the evolutionary
phase of these sources could be given by spectroscopic observations of a statistical sample ofmassive starburst galaxies. For example, the ratio of Hydrogen recombination lines can be used
to estimate the extinction of starburst galaxies which may cause the observed diversity. Oncethe extinction is estimated from spectra, the extinction-corrected luminosity of the emission
lines can be used to derive the SFR, independently of the observations of dust emission. Notethat the SFR derived from submm ﬂuxes depends on assumed dust temperatures, which aredegenerate (Dunne et al. (2000)). Measurements of the extinction and the SFR from the emission lines, independent of the photometric data, are a key step to investigate the evolutionary
phase of high-z massive galaxies. The measured extinction and SFR put a strong constraint
on the SED model, which is used to investigate the evolutionary phase of starbursts linking
them with the formation of spheroidal! systems. Current measurements of the near-infrared
spectra of dusty s tarbursts have been limited to low redshift studies of local ULIRGS Veilleux(1997), Murphy et al. (1999), Dannerbaur et al. (2005). Our targets for the spectroscopy are
the powerful Hydrogen recombination lines Paschen alpha at 1.875 micons and Paschen beta at
1.282 microns. Observations of the Hydrogen recombination lines in local ULIRGs (Dannerbaur
et al. (2005)) have derived high Paschen alpha luminosities consistent with the predominant
power source within these galaxies being star-formation rather than accretion from an AGN.
Observations of a sample of higher redshift sources can test this measurement as a function ofredshift. Note that at low redshifts (z<<1) both of the Hydrogen recombination lines lie outside
the IRC grism observation window (2.5 < λ < 5 μm). For Paschen alpha the observable redshift
range would be 0.3<z<1.7, while for Paschen Beta it would be 0.95<z<2.9.
The target galaxies are summarized in Table 1.2.1.
Table 1.2.1: Target sources for spectroscopic observations with AKARIName
SMMJ030227 +000653
SMMJ163639 +405635
SMMJ123549 +621536
SMMJ221733 +001352

Equinox
J 2000J 2000J 2000J 2000R.A.
03:02:27.73
16:36:39.01
12:35:49.44
22:17:33.91

Dec.
+00:06:53.5+40:56:35.9+62:15:36.8+00:13:52.1

Version 1.2 (May 22, 2009)

A.2.2

55

Selection of Targets and Target Visibility

A Visibility Tool is provided that gives an approximate estimation of the open time visibility ofthe target ﬁeld during the Phase 3 of the AKARI mission, assuming an observation period of
October 2009 to October 2010. The following constraints are imposed on the target visibility;
1. The instrument is of 10 arcmin width and at the boresight.
2. The maximum number of observations in a day is about 20, since 30% of the total numberof pointings with AKARI are reserved for Open Time which translates roughly into 6
orbits every day or almost a degree interval on the ecliptic longitude
3. The same constraints on the SAA, Moon, and the number of stars in STT as in the ﬁrst
call will be applied.
4. The oﬀset angle to the nominal scan path along the great circle constraint will be relaxedfrom 0.6 degree (but will still be smaller than the maximum 1 degree to ensure a safetymargin for scheduling.)
5. The maximum number of pointed observations at any single pointing has a ceiling set at
50.
In addition to the above, any orbits not scheduled for the Mission Programs are available
for scheduling for open time. However, visibility for speciﬁc targets is quite heavily constrained
and an extremely strong function of ecliptic latitude. Targets in the ecliptic pole regions areobservable ona large number of orbits, while targets near the ecliptic plane are visible by AKARI
for only two days (30 orbits, i.e. 14.4 revolutions per day) in a half year at the most.
The Visibility Tool can be found on the AKARI Phase 3 AO page.
The visibility tool front end is shown in Figure 1.2.1. We have to provide a target list ora single pointing. The input coordinates and equinox shall be in the format HH:MM:SS.S (forJ2000) or in degrees (for J2000, Ecliptic or Galactic).
Although it is not necessary to enter any information on the AOT into the Visibility Tool
itself, at this stage, the visibility tool does take its input in target list format (see table 1.2.2).
The output for our target list is shown in Figure 1.2.2 which lists the query input on theright of the screen and the total number of allocations possible on the left.. position in Ecliptic
coordinates, visibility in Phase 3b1 (2008 Oct. 15 – 2009 Apr. 11 = 179d), Phase 3b2 (2009 Apr.
12 – 2009 Oct. 14 = 186d) and the total visibility in Phase 3 (2008 Oct. 15 – 2009 Oct. 14 =365d). In our case three of our sources are observable for an adequate number of slots. However,
one of our targets (SMMJ030227 +000653) is only observable on four opportunities. In thisparticular case it is a combination of the low Ecliptic latitude and a signiﬁcant number of pointing
opportunities lost to interference from the South Atlantic Anomaly (SAA). This emphasizes
the strong constraint on the visibility imposed by the orbit of AKARI on the scheduling ofobservations. We will therefore drop SMMJ030227 +000653 from our target list.
The output from the visibility tool should be saved as an ASCII ﬁle as it will need to be
uploaded as part of the ﬁnal submission process for our proposal.

56

AKARI Observer’s Manual

Figure 1.2.1: The Visibility Tool user front end for Phase 3 observations.

Figure 1.2.2: Results from the Visibility Tool in batch mode. The result shows the total numberof allocations possible during Phase 3 of the AKARI mission. Each target is listed by positionin Ecliptic coordinates, visibility in Phase 3b1 (2008 Oct. 15 – 2009 Apr. 11 = 179d), Phase
3b2 (2008 Apr. 12 – 2009 Oct. 14 = 186d) and the total visibility in Phase 3 (2008 Oct. 15 –2009 Oct. 14 = 365d). The original user input is shown on the right.

Version 1.2 (May 22, 2009)

A.2.3

57

The Choice of Observation ModeAKARI provides four reasonable methods for spectroscopy of distant galaxies.
• Slitless spectroscopy in the main 10×10 arcmin ﬁeld of view using NP prism.
• Slitless spectroscopy in the main 10×10 arcmin ﬁeld of view using NG grism.
• Slit spectroscopy using the NP prism in the 1×1 arcmin point source aperture.
• Slit spectroscopy using the NG Grism in the 1×1 arcmin point source aperture.
Observations using the slits (Nh,Ns) are not appropriate for point source observations (dueto insuﬃcient pointing accuracy) and should be avoided. The slitless spectroscopy with AKARI
using the NP prism creates low resolution spectra over the entire ﬁeld of view of the imaging
plane. However, to obtain the sensitivity using NP to detect the contiuum of most distant sources
we would have to integrate so far down that we would run into source confusion problems withmultiple overlapping source spectra. The confusion problem with the NG grism in slitless mode
is compounded by an even bigger wavelength dispersion (more overlapping sources). For thedetection of lines, using the 1×1 arcmin point source aperture, the resolution of the NP element
is too low. Therefore we ﬁnd that indeed slit spectroscopy using the high resolution grism on
the IRC is the most eﬃcient method to observe our distant galaxies.
Current estimates of the detection limit for lines in Phase 3 compared to the earlier phasesof the mission assumes a degradation of at least a factor of two and there is still a great deal of
uncertainty surrounding the actual values. For the proposed NIR spectroscopy with AKARI in
the 2.5–5μm range by using the IRC grism, a line sensitivity of ∼5×10−18 Wm−2 for a 10 minuteintegration is achieved. In Figure 1.2.3 we show the predicted line strengths for the Hydrogen
recombination lines Paschen α&β as a function of redshift assuming an ultra-luminous infrared
galaxy similar to our targets with an infrared luminosity of 5×1012 L . In general we may require
between 8 to 10 pointings to detect our sources at z>1.

Figure 1.2.3: Predicted Hydrogen recombination line ﬂuxes for a 5×1012 L Ultraluminous Infrared Galaxy.

AKARI Observer’s Manual

58

A.2.4

Preparation of Target List

The objective of our IRC observations is to detect the Hydrogen recombination lines in dusty,
distant galaxies. as explained in the previous section, the optimum instrument conﬁguration forthis objective is to use the IRC in NG grism mode with our target located in the point source
aperture (Np). Thus we require the following AOT parameters;• AOT : IRCZ4 (note the insertion of the ”Z” in the original AOT name for Phase 3 )• Parameter 1: b (corresponding to the grism NG)• Parameter 2: Np (The target is placed in the point source aperture of the NIR channel)
Our estimates for the required sensitivity for the detection of the target lines are between
8-10 pointings per target. We conservatively select 10 pointings per source since the visibility
constraints are not harsh. Not that the number of hot pixels in the IRC-NIR camera have also
increased dramatically in Phase 3 of the mission and a large number of pointings is important
to ensure adequate dithering of our observations.
Now the appropriate AOT has been selected, we can go ahead and prepare the target list
for our observations. An AKARI target list contains one line per target per AOT per ﬁeld ofview. Since we are only observing our target ﬁelds with the IRC-NIR-NG grism, we will havefour lines in our target list, one per target galaxy. The target list is shown in Table 1.2.2. The
target list consists of a unique I.D. in ascending but not necessarily contiguous order, followedby some identiﬁer for the target name which should if possible be a resolvable by systems such as
SIMBAD, NED. The next 3 ﬁelds are reserved for the coordinate system and target coordinates.
we enter these in ”J2000” equatorial coordinates in the HH : MM : SS.S format although degrees
are also acceptable. Coordinates entered in ”ecliptic” format should b in decimal degrees.
Next we need the AOT, which will be IRCZ4. Following the AOT are the speciﬁc parameters
for each given AOT. For the IRC, we have to specify 2 parameters, the ﬁlter combination (prismor grism) and the aperture (main ﬁeld of view or one of the aperture / slits) with which we wantto observe. We intend to observe with the NG grism in the point source aperture - so we canﬁx the ﬁrst parameter as b and the second parameter as Np, i.e. b;Np.
In the following ﬁeld we input the number of pointings for each AOT, for our case this willbe 10 for each target. We then have to prioritize our targets. AKARI Open Time Observations
are divided into 3 priorities, A , B, C . Our A & B targets, barring any unforeseen events, should
be observed, while the priority C targets should be considered as back-ups. In our target list,
the number of priority A , B, targets should be around the same and the number of C target
should be roughly A + B . For our observations therefore we allocate one priority A target, one
B and the remaining target as priority C .
Note: It is extremely important to include an ample number of C targets (even though wehave not done so in this particular example) as AKARI scheduling is tough and if there are notenough back up targets you may lose your allocation. A good size number of priority C targets is
also necessary to replace any higher priority targets that may incur possible duplication conﬂict(see the discussion on duplication later) with Mission Program targets.
Field 10 (symbiotic) is not used in phase 3 scheduling. Just leave the ﬁeld blank – notforgetting the ”comma” ﬁeld separator. Finally, any notes are appended on the end of eachtarget list line. Our ﬁnal target list is shown in Table 1.2.2.

Version 1.2 (May 22, 2009)

59

Table 1.2.2: Target List for submission
2, ”SMMJ163639 +405635”, ”J2000”, 16:36:39.01, +40:56:35.9, ”IRCZ4”, ”b;Np”, 10, A, , ”redshift 1.488”
3, ”SMMJ123549 +621536”, ”J2000”, 12:35:49.44, +62:15:36.8, ”IRCZ4”,”b;Np”, 10, B, , ”redshift 2.2032”
4, ”SMMJ221733 +001352”, ”J2000”, 22:17:33.91,+00:13:52.1, ”IRCZ4”, ”b;Np”, 10, C, , ”redshift 2.5510”

AKARI Observer’s Manual

60

A.2.5

Target List Validation

Once the target list has been completed, we can proceed towards the submission stage. However
there are still a few steps to complete. We should run our target list through both the Target
List Validation Tool and then we need to submit the target list to the observation Duplication
Check Tool.
The Target List Validation Tool takes a target list and makes a simple check on the target
list format, e.g. correct number of ﬁelds, AOT in expected form etc. It does not perform any
test on the scientiﬁc validation, e.g. on position or sensitivity etc. We can submit the Target
List as a batch ﬁle in a similar manner to the Visibility Tool as in Figure 1.2.4, in fact this(target list) format is accepted by all tools during the submission process. Figure 1.2.5 shows
the output of the Target List Validation Tool. Any errors are highlighted in red and a summary
given at the bottom of the output. In this case an AOT has been input incorrectly and has beenhighlighted. The target list should therefore be edited and re-submitted.
The target list will be automatically validated when we upload it during the ﬁnal proposal
submission stage so there is no need for us to save the output of the Validation Check Tool.

Figure 1.2.4: Input to the Target List Validity Checker

2, "SMMJ163639 +405635", "J2000", 16:36:39.01, +40:56:35.9, "IRCZ4", "b;Np", 10, A, , "redshift 1.488"
3, "SMMJ123549 +621536", "J2000", 12:35:49.44, +62:15:36.8, "IRCZ4","b;Np", 10, B, , "redshift 2.2032"
4, "SMMJ221733 +001352", "J2000", 22:17:33.91,+00:13:52.1, "IRC10", "b;Np", 10, C, , "redshift 2.5510"# AOT name does not exist (options are: IRCZ0, IRCZ2, IRCZ3, IRCZ4)### Pointings ... Total=20 : S=0 A=10 B=10 C=0 D=0### Format error=1

Figure 1.2.5: Output from the Target List Validation Tool. Any Errors are marked in red andthe number of errors are listed at the bottom of the output in the Pointings summary. In thiscase an AOT has been input incorrectly.

Version 1.2 (May 22, 2009)

A.2.6

61

Duplication Check

Duplicate observations are decided on a basis of position, instrument/AOT and the number ofpointings. Figure 1.2.6 shows the input screen for the Duplication Check Tool.
This tool returns all IRC observations within a radius of 5 arcmins from the requested targets,
which are either executed in the cold phase (Phase 1 and 2), or are in the blocked target list
for Phase 3. The observations executed in the cold phase are in the public domain at the timeof Phase 3 Open Time. A strict duplication occurs when AOT and parameters of a requested
target are identical with those of a Phase 3 observation. The other cases returned by the tool
may have to be discussed in the proposal scientiﬁc justiﬁcation.
The output from the duplication tool is shown in Figure 1.2.7 and we can see that all ourtargets pass the Duplication Tool successfully. The output from the Duplication Check tool
should be saved as an ASCII ﬁle as it will need to be uploaded as part of the ﬁnal submission
process for our proposal.

Figure 1.2.6: Input screen for the Duplication Check Tool. The input is the target list as usual.

Figure 1.2.7: Output from the Duplication Check Tool for our target list. All our targets passthe Duplication Tool successfully.

AKARI Observer’s Manual

62

A.2.7

Submission of Proposal

After the duplication check, we can ﬁnally submit our proposal via the web interface. The proposal submission has several stages and we will need to upload various output ﬁles saved from thetools we used earlier. Each proposal has a 5 character abbreviation which will be used to identify
each proposal. The next step is to upload the Target List which will be automatically veriﬁed(syntax only) on uploading. Following this we will be required to upload the results we saved
from the output of the Visibility Tool and Duplication Check Tool respectively. Once all theseﬁles have been uploaded we will have to enter the speciﬁc proposal information (name, address,
telephone number, etc.) and general proposal information (Co-Is, category, title, abstract). The
Scientiﬁc Justiﬁcation must be submitted in PDF format and should not exceed 6 pages in total
including scientiﬁc rationale, objective, references, ﬁgures and tables, and technical feasibilityof the proposal. A conﬁrmation page of the submission is created automatically. Shortly after,
users will receive a formal conﬁrmation by e-mail with the cover page of their proposal.

Version 1.2 (May 22, 2009)

A.3

63

Example 2: Spectroscopy of Planetary Nebulae with the
IRC

In this worked example we consider a program to perform spectroscopy on a few Planetary
Nebulae with the AKARI IRC instrument. We will simulate the preparation of the proposal
from scientiﬁc background to proposal submission.

A.3.1

Scientific BackgroundWe consider 2 planetary nebulae as a study for spectroscopy with AKARI. These objects haveextremely rich and highly ionized spectrum due to their hot central star. Analysis of the spectra
can give insight into the evolution and origin of the ionizing central stars. Our ﬁrst target is
NGC7027, a very well known, bright planetary nebula with a rich spectrum that has previously
been observed by ISO (Bernard-Salas et al., 2001). The second target is the fainter SMP83
planetary nebula in the Large Magellanic Cloud, also observed by Spitzer (Bernard-Salas et al.,2004). We will perform both high and lower resolution slit spectroscopy in the near-infrared
range which is unique to AKARI, since Spitzer has no capability in this wavelength range. The
target positions are given in Table 1.3.3.
Table 1.3.3: Suitable Planetary Nebula for Phase 3 spectroscopic study with AKARI
Name
NGC7027
SMP83

A.3.2

Equinox
J 2000J 2000R.A.
21:07:01.7
05:36:21.0

Dec.
+42:14:11.0−67:18:14.0

Target Visibility

Using the Visibility Tool to check the availability of our targets (entering the coordinates using
the interface in Fig1.2.1) we ﬁnd that both targets have reasonable visibility. The result of the
Visibility Tool for is shown in Figure 1.3.8 and 1.3.9 for NGC7027 and SMP83 respectively
Figure 1.3.8 shows that NGC7027 is visible only twice from October 2008 to April 2009 anda further 13 times in the latter half of Phase 3 (April 2009 - October 2009). This low visibility
is mainly due to conﬂict with the SAA even given the reasonable ecliptic latitude.
Note the much higher visibility of SMP83, shown in Figure 1.3.9 due to its location almoston the South Ecliptic Pole at an ecliptic latitude of -87 degrees, compared to NGC7027 at amore moderate ecliptic l atitude of 55 degrees. This shows the huge advantage in scheduling
gained by targets at extreme latitudes.
The output from the visibility tool should be saved as an ASCII ﬁle as it will need to be
uploaded as part of the ﬁnal submission process for our proposal.

64

AKARI Observer’s Manual

Figure 1.3.8: Results from the Visibility Tool in single target mode for the planetary nebula
NGC7027. The result shows the total number of allocations possible during Phase 3 of the
AKARI mission. Each target is listed by position in Ecliptic coordinates, visibility in Phase 3b1(2008 Oct. 15 – 2009 Apr. 11 = 179d), Phase 3b2 (2009 Apr. 12 – 2009 Oct. 14 = 186d) andthe total visibility in Phase 3 (2008 Oct. 15 – 2009 Oct. 14 = 365d). The original user input isshown on the right.

Figure 1.3.9: Results from the Visibility Tool in single target mode for the planetary nebula
SMP83.

Version 1.2 (May 22, 2009)

A.3.3

65

The Choice of Observation Mode

The estimated sensitivity of the IRC in slit spectroscopy mode during the ”cold” phase of the
IRC mission was around a few × 10−18 Wm−2 . For Phase 3 we can expect at least a factor of
two degradation in this sensitivity, to for example 5× 10−18 Wm−2 . The near-infrared spectra ofplanetary nebula are rich Hydrogen and Helium lines and some ions such as MgIV, etc. For ourﬁrst target (NGC7027) all the lines are brighter than 10−15 W m−2 (Bernard-Salas et al., 2001),
therefore this is well above the IRC detection limits and should be easily observable in a single
pointing. For our second target (SMP83) as a ﬁrst approximation, we can scale the line ﬂuxesof NGC7027 by the distance to the LMC. Under this assumption, we could expect the H2 line
at 2.8 microns to be of the order of ∼ 3.0 × 10−17 W m−2 and the Br alpha line at 4.05 microns
to be ∼ 92.0 × 10−17 W m−2 . A non-exhaustive list of example brighter line strengths estimatedfor SMP83 is given in Table 1.3.4. Fainter lines (e.g. He I 4-6, H I 6-15, 6-17 transitions) are of
the order of 10−18 W m2 , and maybe be more diﬃcult to detect at the IRC line detection limits.
Note that the saturation level for the NIR detectors is also signiﬁcantly degraded for AKARI
Phase 3 observations. For the grism and prism we could expect saturation limits of as low as∼ f ew × 10−15 W m−2 which may pose problems for our brighter lines. In addition there is adegradation in the saturation level of the continuum of around a factor of 5. This is importantsince the N3 imaging data taken in IRCZ4 is necessary to determine the wavelength origin.
A rough estimation of the ﬂux level that can be expected can be calculated by assuming anunresolved line with Flux Fl (W/m62) without continuum, where the dispersion elements works
like a narrow band ﬁlter and we get the image on the detector just like the imaging mode.
The line ﬂux can be roughly converted to the ’continuum equivalent ﬂux density’ per pixel, Fc
as, Fc /pixel = (Fl × 1026 /P SF 2 )/dν Jy. Where dν is estimated from the instrument element
resolution (i.e., dλ = 0.06 & 0.0097 for NP and NG respectively) in μm / pixel at 3.5μm. For
NGC 7027 most lines are brighter than 10−15 W m−2 giving a corresponding continuum ﬂux of
6.7 mJy & 42 mJy for NP and NG respectively. The saturation level of the N3 band is 110 mJy
Note that this image does not have to be a particularly high quality image,and even if some
portion of it is saturated, it may still be possible to estimate the wavelength scale.
Table 1.3.4: SMP83 line strengths
Wavelength (microns)
2.8
2.626
3.74
4.05
4.654

Line
H2
Br β
Pf γ
Br α
Pf β

Flux 10−17 W/m2
3.0
46
11.0
92
11.0

Concentrating on just the brighter lines in both nebulae, we can see the IRC is sensitive
enough to detect these lines in SMP83 in a single pointing. Although we still require at least 3
pointings for dithering (see below).

AKARI Observer’s Manual

66

A.3.4

Preparation of Target List

We intend to carry out high resolution slit spectroscopy with the IRC grism (NG) in the nearinfrared as our ﬁrst priority. Following this, as our second priority, we will observe the same
dust spectrum at a lower resolution using the IRC prism (NP).
The spectroscopic IRC AOT for Phase 3 is IRCZ4. This AOT has 2 parameters, the ﬁrst is
the ﬁlter set and the second is the position of the slit. The NIR camera has 3 slits. A common
slit with the IRC MIR-S camera for spectroscopy of diﬀuse sources using the NP element, an
entrance aperture for point source spectroscopy and another slit for high resolution spectroscopy
with the NG element.
We wish to carry out both high resolution spectroscopy with the NG element at the andlower resolution spectroscopy with the NP element, so we require an entry in the target list for
both sets of observations for each target, making a total number of four lines in our target list.
In addition since no dithering is carried out during this AOT, we must observe each sky area
at least three times for data redundancy. Therefore we are looking at a minimum of 3 pointings
per target per observation mode. For our fainter target (the high visibility SMP83) we will
decide to double the number of pointings to ensure high signal to noise detection of our lines.
The complete target list is shown in Table 1.3.5.
Table 1.3.5: Target List for submission
1,”NGC7027”,”J2000”, 21:07:01.7, +42:14:11.0,”IRCZ4”,”b;Nh”,3,A,””,”NGC7027 high resolution”
2,”NGC7027”,”J2000”, 21:07:01.7, +42:14:11.0,”IRCZ4”,”a;Ns”,3,C,””,”NGC7027 lower resolution”
3,”SMP83”,”J2000”, 05:36:21.0, -67:18:14.0,”IRCZ4”,”b;Nh”,4,B,””,”SMP83 high resolution”
4,”SMP83”,”J2000”, 05:36:21.0, -67:18:14.0,”IRCZ4”,”a;Ns”,4,C,””,”SMP83 lower resolution”
As in the previous example, the target list comprises of a unique I.D. in ascending but notnecessarily contiguous order, followed by some identiﬁer for the target name which in the caseof many of our targets should resolvable the NED/SIMBAD systems. The IRCZ4 AOT has 2
parameters to set, the ﬁlter set and the slit position. The ﬁlter set is determined by whether wewish to use the NP (ﬁlter set a) or NG (ﬁlter set b) element of the NIR camera. A tool (iris sky)
is provided to aid us with the positioning of the instruments over our ﬁelds. With it, we canproject our instrument arrays onto our target ﬁelds (on images from IRAS and 2MASS). Withiris sky it is also possible to create our target list in its’ entirety although we shall constructours manually in this case. The use of iris sky has been decribed in Version 3.2 of the Observers
manual including an example in the cookbook. iris sky has been modiﬁed for Phase 3 of the
AKARI mission.
The FIS and IRC/MIR information has been removed from the Target list editing panel andmessages amended accordingly.
Only the IRC-NIR detector is shown on the display by default (other detectors can be switchedon via the options panel).
Detector positions are updated from the ’nominal’ position in the Observer’s Manual, to berelatively consistent with the images.
We can use the iris sky tool to visualize our observations and Figure 1.3.10 shows the iris sky
tool with the outmost slit of the IRC-NIR camera positioned over the target (NGC7027). In
this ﬁgure, the entrance aperture for point sources and the common inner slit for diﬀuse sources
can also be seen.

Version 1.2 (May 22, 2009)67

Figure 1.3.10: Using the iris sky tool to overlay the IRC NIR high resolution spectroscopy slit(N h) over the Planetary Nebula NGC7027.

AKARI Observer’s Manual68

Next we have to choose the slit parameter. For the high resolution spectroscopy, this parameter is Nh : the target position is placed at the high resolution slit of the NIR camera. For the
lower resolution spectroscopy, the parameter is Ns. We set the number of pointings as 3 for thebrighter source and 4 for our fainter source. For this example, we prioritize our targets by thehigh and low resolution spectroscopy, giving thigh resolution observations with NG a priority A& B and the lower resolution spectroscopy with NP priority C respectively.

A.3.5

Target List Validation

The Target List syntax is validated in an identical manner to the previous example in Section
A.2. The target list will also be automatically validated when we upload it during the ﬁnal
proposal submission stage so there is no need for us to save the output of the Validation Check
Tool at this stage.

A.3.6

Duplication Checker

Duplicate observations are decided on a basis of position, instrument/AOT and the number ofpointings. The Duplication Tool returns all IRC observations within a radius of 5 arcmins fromthe requested targets. Putting our target list into the duplication checker we ﬁnd that indeed
there is a conﬂict of position for both of our targets (see Figure 1.3.11). Although the targets
are indeed duplicated with a previous program during Phase 2 and another program planned
for Phase 3, the AOTs are slightly diﬀerent and it my fall to the responsibility of the Telescope
Allocation Committee’s interpretation of our scientiﬁc justiﬁcation as to whether we can observe
our targets! The output from the Duplication Check tool should be saved as an ASCII ﬁle as it
will need to be uploaded as part of the ﬁnal submission process for our proposal.

A.3.7

Submission of Proposal

After all the tools have been used and the Target List checked, we can ﬁnally submit our proposal
via the web interface in an identical manner as that described for the previous imaging example
in SectionA.4. Remember that we will need to upload the previously saved ASCII ﬁles from theoutputs of the Visibility and Duplication Tools.

Version 1.2 (May 22, 2009)

69

Query : target list: S=0, A=2, B=4, C=6, D=0 (total=12), search radius = 5.000 arcmin.

4 targets in your list are duplicated with the blocked target list.
ID |
R.A.
Dec. | AOT| Target name| Result|-----------------------------------------------------------------------------------------------------------1 316.757 +42.236 IRCZ4,b;NhNGC7027 (A)Duplication (2)############################################################################################################
# ID
R.A.
Dec.
AOT
Target named(') status# ---------------------------------------------------------------------------------------------------------# 4081016 316.757 +42.236 IRC04,b;Ns
NGC7027 (CERN1,B)
0.0 Observed# 1740550 316.757 +42.236 IRCZ4,b;Np
NGC 7027 (AGBGA,B)
0.0 Scheduled############################################################################################################
2 316.757 +42.236 IRCZ4,a;Ns
NGC7027 (C)Duplication (2)############################################################################################################
# ID
R.A.
Dec.
AOT
Target named(') status# ---------------------------------------------------------------------------------------------------------# 4081016 316.757 +42.236 IRC04,b;Ns
NGC7027 (CERN1,B)
0.0 Observed# 1740550 316.757 +42.236 IRCZ4,b;Np
NGC 7027 (AGBGA,B)
0.0 Scheduled############################################################################################################
3
84.088 -67.304 IRCZ4,b;Nh
SMP83 (B)
Duplication (1)############################################################################################################
# ID
R.A.
Dec.
AOT
Target named(') status# ---------------------------------------------------------------------------------------------------------# 1740328
84.087 -67.302 IRCZ4,b;Np
LMC-SMP083 (AGBGA,A)
0.1 Scheduled############################################################################################################
4
84.088 -67.304 IRCZ4,a;Ns
SMP83 (C)Duplication (1)############################################################################################################
# ID
R.A.
Dec.
AOT
Target named(') status# ---------------------------------------------------------------------------------------------------------# 1740328
84.087 -67.302 IRCZ4,b;Np
LMC-SMP083 (AGBGA,A)
0.1 Scheduled############################################################################################################

Command executed on 2008/05/16_19:48:05 (JST).

Figure 1.3.11: Results from the Duplication Checker Tool. We see that our targets are in conﬂictwith guaranteed time on AKARI and a previous OT observation in Phase 2. Duplication canbe made on position, instrument/AOT and the number of pointings.

AKARI Observer’s Manual

70

A.4

Example 3: Near-infrared imaging of extragalactic fields
with the IRC

In this worked example we consider a program to image several deep extragalactic ﬁelds with the
AKARI IRC-NIR instrument. We will simulate the preparation of the proposal from scientiﬁcbackground to proposal submission.

A.4.1

Scientific BackgroundStudies with the Infrared Space Observatory (ISO), of the Hubble Deep Fields have revealed
star formation rates at least comparable to, or higher than those of optical/UV studies (Mannet al. 2002). At submillimetre wavelengths, surveys with SCUBA on the JCMT have revealed alarge (>3000 deg−2 at S850 > 2 mJy) strongly evolving population of sources with bolometricluminosities > 1012 Lo and star formation rates of ∼ 300–1000 M yr−1 with a median redshiftof 2.4 (Chapman et al. 2003). The star formation rate at z∼1 requires signiﬁcant evolution in
the IR galaxy population from the current epoch. Deep observations with the Spitzer Space
Telescope have conﬁrmed this strong evolution in the galaxy population out to ISO redshifts
and furthermore provided insight into the higher redshift Universe in the so called redshiftdesert z∼ 1–3 (Papovich et al. 2004). To connect the local and intermediate redshift IRAS/ISO
Universe to the higher and high z Universe observed by Spitzer and SCUBA, comprehensive
multiwavelength imaging is required throughout the extragalactic populations. Observations
have been during Phase I and Phase II of the AKARI mission with the IRC-MIR-S & MIR-L
cameras which have observed the full mid-infrared wavelength range in 6 bands from 7–24 μm
to much higher sensitivities than obtained in the previous ISO surveys (Elbaz et al 2002) inorder to constrain the dusty mid-infrared spectra of these sources.
Our targets are the same sources but at shorter wavelengths. Just as the mid-infraredobservations can constrain the star-formation history of the Universe, the shorter near-infared
wavelength bands can constrain the mass assembly history through the observation of the older
stellar populations of these sources. It is known the stellar mass correlates well with the central
black hole mass in massive galaxies (Magorrian et al. 1998) and by combining the near-infraredobservations in Phase 3 with the previous results in Phase I & II we may move some way toconstraining the energy budget of the Universe into the contributions from star-formation andblack hole accretion.
For our program we will chose a set of well known ﬁelds where there is already a lot of follow
up data including the Phase I and II observations with AKARI. These are the ISO-MARANO
ﬁeld, UKIDSS-UDS ﬁeld, the COSMOS ﬁeld, the HDF-N ﬁeld, and the ISO southern ELAIS
ﬁeld. These ﬁelds are summarized in Table 1.4.6.
Table 1.4.6: Extragalactic target ﬁelds for observations with AKARIName
ISO MARANO
UKIDSS-UDSCOSMOSHDF-N
ELAIS-S1

Equinox
J 2000J 2000J 2000J 2000J 2000R.A.
03:11:00.0
02:21:20.0
10:00:28.60
12:36:49.9
00:38:30.0

Dec.
−54:45:00.0−04:30:00.0+02:12:21.01+62:12:58.0-44:00:00.0

Version 1.2 (May 22, 2009)

A.4.2

71

Selection of Target Field and Target Visibility

A Visibility Tool is provided that gives an approximate estimation of the open time visibilityof the target ﬁeld during the Phase 3 of the AKARI mission. The available allocation for OpenTime observations corresponds to around 6 pointings every day or almost a degree interval on theecliptic longitude. Visibility is a strong function of ecliptic latitude and observations requiring
very deep imaging and/or wide area mapping should choose their ﬁelds very carefully to avoid
disappointment. Targets are input into the Visibility Tool in the same manner as described in
the earlier sections. The results of the Visibility Tool for our ﬁelds are shown in Figure 1.4.12,
the columns have already been explained in the ﬁrst example in the cookbook section. The
constraint on visibility can again be clearly seen in the input target ﬁelds. The Marano ﬁeld
is at a moderate ecliptic latitude of +35 degrees above the ecliptic while the COSMOS & UDS
ﬁelds is only 9 & 17 degrees below the ecliptic plane respectively and is thus heavily constrained(only a total of 8 & 7 pointings in Phase 3 !). Combined with the poor visibility, we also ﬁnd theMoon in the COSMOS ﬁeld and it is thus probably unlikely that we will be able to carry out all
our desired pointings. Therefore, we shall drop the COSMOS and UDS ﬁelds and concentrateon the remaining three ﬁelds.
The output from the visibility tool should be saved as an ASCII ﬁle as it will need to be
uploaded as part of the ﬁnal submission process for our proposal.

Figure 1.4.12: Results from the Visibility Tool in batch mode. The result shows the total numberof allocations possible during Phase 3 of the AKARI mission. Each target is listed by positionin Ecliptic coordinates, visibility in Phase 3b1 (2008 Oct. 15 – 2009 Apr. 11 = 179d), Phase
3b2 (2009 Apr. 12 – 2009 Oct. 14 = 186d) and the total visibility in Phase 3 (2008 Oct. 15 –2009 Oct. 14 = 365d). The original user input is shown on the right.

A.4.3

The Choice of Observation Mode

The objective of the IRC observations is to detect the near-infrared emission from massive
star-forming galaxies such as dusty ULIRGs. There are 3 observation AOTs available for nearinfrared imaging.

AKARI Observer’s Manual72

1. AOT IRCZ0 : Formerly referred to as IRC00 or IRC05, this AOT carries out the deepest
imaging in a single band only.
2. AOT IRCZ2 : Formerly referred to as IRC02, this AOT carries out intermediate depth
imaging in two bands
3. AOT IRCZ3 : Formerly referred to as IRC03, this AOT carries out imaging in all three
IRC bands (N2,N3,N4)
The typical ﬂux densities for the colder ULIRGs in the near-infrared are around 10 μJy (seeFigure 1.4.13). For our purpose, we require deep images of our ﬁelds, therefore we will selectthe IRCZ0 AOT. The current sensitivity estimates for this AOT are 18μJy in all three IRC
bands which should be adequate to detect our sources (the multiband IRC AOT IRCZ3 has asensitivity of around 40μJy which will probably be too shallow to detect our sources).

Figure 1.4.13: Estimated required sensitivities to detect dusty ULIRGs to redshift unity. We
assume a single pointing with AOT IRCZ0.

A.4.4

Preparation of Target List

Once the AOTs have been selected we can go ahead and prepare the target list for our observations. An AKARI target list contains 1 line per target per AOT per ﬁeld of view. We
are observing our target ﬁelds with the IRC NIR camera using AOT IRCZ0, therefore we have
3 lines in our target list per target ﬁeld (one each for the N2,N3 & N4 bands). We have 3
target ﬁelds, therefore we have a total of 9 lines in our target list. The target list is shown in
Table 1.4.7. The target list consists of a unique I.D. in ascending but not necessarily contiguous

Version 1.2 (May 22, 2009)73

Table 1.4.7: Target List for submission
1, ”IRC-ISO”, ”J2000”, 03:11:00.0, -54:45:00.0, ”IRCZ0”, ”b;N”, 3, A, , ”ISO FIRBACK”
2, ”IRC-ISO”, ”J2000”, 03:11:00.0, -54:45:00.0, ”IRCZ0”, ”c;N”, 3, B, , ”ISO FIRBACK”
3, ”IRC-ISO”, ”J2000”, 03:11:00.0, -54:45:00.0, ”IRCZ0”, ”a;N”, 3, C, , ”ISO FIRBACK”
4, ”IRC-HDF”, ”J2000”, 12:36:49.9, +62:12:58.0,”IRCZ0”, ”b;N”, 3, A, , ”HDF-N”
5, ”IRC-HDF”, ”J2000”, 12:36:49.9, +62:12:58.0,”IRCZ0”, ”c;N”, 3, B, , ”HDF-N”
6, ”IRC-HDF”, ”J2000”, 12:36:49.9, +62:12:58.0,”IRCZ0”, ”a;N”, 3, C, , ”HDF-N”
7, ”IRC-ELAIS”, ”J2000”, 00:38:30.0, -44:00:00.0,”IRCZ0”, ”b;N”, 3, A, , ”ELAIS-S”
8, ”IRC-ELAIS”, ”J2000”, 00:38:30.0, -44:00:00.0, ”IRCZ0”, ”c;N”, 3, B, , ”ELAIS-S”
9, ”IRC-ELAIS”, ”J2000”, 00:38:30.0, -44:00:00.0, ”IRCZ0”, ”a;N”, 3, C, , ”ELAIS-S”

order, followed by some identiﬁer for the target name which should if possible be a resolvable bysystems such as SIMBAD, NED. The next 3 ﬁelds are reserved for the coordinate system andtarget coordinates.
Following the AOT are the speciﬁc parameters for each given AOT. For the IRC imaging,
we have to specify 2 parameters, the ﬁlter combination and the camera with which we want toobserve. For the IRCZ0 AOT the ﬁlter can be chosen from parameters a,b or c (N2,N3 & N4
respectively). We require one target list line for each. The second parameter can only be N
corresponding to the IRC-NIR camera.
In the following ﬁeld we input the number of pointings for each AOT, for our case this has
to be at least 3 for each IRCZ0 AOT. The reason for this is that this particular AOT (likethe spectroscopic IRCZ4 AOT) is not dithered and the dithering has to be carried out be using
diﬀerent pointings. The observers themselves need do nothing since this operation will be carriedout by the mission controllers.
We then have to prioritize our targets. AKARI Open Time Observations are divided into
3 priorities, A , B, C . Our A & B targets, barring any unforeseen events, should be observed,
while the priority C targets should be considered as back-ups. In our target list, the numberof priority A , B, C targets should be around the same. The objective of the IRC observations
is to detect the near-infrared emission from massive star-forming galaxies to z ∼ 1). Althoughmulti-band detections are preferred the priority is a detection in at least one band. Therefore,
for our observations we prioritize by IRC ﬁlter although we could just as easily prioritize by theobservation ﬁeld instead for example. We select the IRC N3 and N4 bands as priority A , B
respectively. The N2 band is prioritized as C since in fact it is possible to make observations
from the ground at this wavelength (∼2μm).
Finally, any notes are appended on the end of each target list line. Our ﬁnal target list is
shown in Table 1.4.7.

A.4.5

Target List Validation

The Target List syntax is validated in an identical manner to the previous imaging example.
The target list will also be automatically validated when we upload it during the ﬁnal proposal
submission stage so there is no need for us to save the output of the Validation Check Tool at
this stage.

AKARI Observer’s Manual

74

A.4.6

Duplication Check Tool

Duplicate observations are decided on a basis of position, instrument/AOT and the number ofpointings. This tool returns all IRC observations within a radius of 5 arcmins from the requested
targets, which are either executed in the cold phase (Phase 1 and 2), or are in the blocked target
list for Phase 3. Putting our target list into the Duplication Check Tool and selecting summary
for the out put, we ﬁnd that indeed there is a conﬂict of position or instrument for all of ourobservations in the HDF ﬁeld (see Figure 1.4.14), and the TAC will have to look into the scientiﬁcjustiﬁcation to decide whether our observation is unique.
The output from the Duplication Check tool should be saved as an ASCII ﬁle as it will need
to be uploaded as part of the ﬁnal submission process for our proposal.

Version 1.2 (May 22, 2009)75

Figure 1.4.14: Results from the Duplication Checker Tool. We see that 3 of our observations
are in conﬂict with the guaranteed time on AKARI.

AKARI Observer’s Manual

76

A.4.7

Submission of Proposal

After the duplication check, we can ﬁnally submit our proposal via the web interface. The
proposal submission has several stages and we will need to upload various output ﬁles saved
from the tools we used earlier. Each proposal has a 5 character abbreviation which will be
used to identify each proposal. The next step is to upload the Target List which will be automatically veriﬁed (syntax only) on uploading. Following this we will be required to upload theresults we saved from the output of the Visibility Tool, Duplication Check Tool and Instrument
Performance Tool respectively. Once all these ﬁles have been uploaded we will have to enter
the speciﬁc proposal information (name, address, telephone number, etc.) and general proposal
information (Co-Is, category, title, abstract). The Scientiﬁc Justiﬁcation must be submitted
in PDF format and should not exceed 6 pages in total including scientiﬁc rationale, objective,references, ﬁgures and tables, and technical feasibility of the proposal. A conﬁrmation page ofthe submission is created automatically. Shortly after, users will receive a formal conﬁrmationby e-mail with the cover page of their proposal.