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System Design Note 1.02 Created: 30 April 2003 Last modified: 18 November 2003 |
OPERATIONAL CONCEPT DEFINITION DOCUMENT
Peter J. McGregor[1]
Institute of Advanced
Studies
Revision History
|
Revision
No. |
Author & Date |
Approval & Date |
Description |
|
Revision 1 |
Peter J. McGregor |
Gary Da Costa |
Draft initial document. |
|
Revision 2 |
Peter J. McGregor |
Jan van Harmelen |
Revised initial document. |
|
Revision 3 |
Peter J. McGregor |
Jan van Harmelen |
Revised for CoDR. |
|
Revision 4 |
Peter
J. McGregor |
Jan van Harmelen 9 May 2003 |
Revised
following CoDR |
|
Revision 5 |
Peter
J. McGregor |
Mark Jarnyk |
Version
presented at CDR |
Contents
5.1
Basic Instrument Parameters
5.2.4
Imager Quick Look Displays
5.2.5
Non-Common Path Phase Errors
5.2.7
Imager On-Detector Guide Window Sensitivities
5.2.8
Comments on Astrometric Precision
5.3
Cryostat and Auxiliary Systems
6.2
The Orion Nebula - A Detailed Study of a Nearby Massive Star-Forming Region
6.3
Young Stellar Super-Clusters
6.4
White Dwarf Cooling Ages in Galactic Open Clusters
6.5
Globular Cluster Mass Functions Over a Range of Metallicities
6.6
Missing Mass in Magellanic Cloud Planetary Nebulae
6.7 Proper Motions of Local Group
Galaxies
6.8
Stellar Populations in Dwarf Galaxies.
6.9
Calibration of the Supernovae Ia Zeropoint
6.10 Intracluster Stars in Nearby
Galaxy Clusters
6.11
Measuring H0 Out to 60 Mpc Using Red Supergiants
6.11.3
Guide Star Availability
6.12
Measuring the Bulk Motions of Galaxies to cz < 6000 km/s with Surface
Brightness Fluctuations
6.12.3
Guide Star Availability
6.13 The Formation of the Disks of
Disk Galaxies
6.13.3 Guide Star Availability
6.14
Color Gradients in High Redshift Field Galaxies
6.14.3
Guide Star Availability
6.15
Exploring Dark Energy Via High Redshift Supernovae
6.15.3
Guide Star Availability
7
Setup and Calibration Requirements
7.1
Daytime GSAOI Setup and Calibration
7.1.1
GSAOI Bias and Dark Frames
7.2
Nighttime GSAOI Setup and Calibration.
7.2.1
Twilight GSAOI Flat Field Frames
7.2.2
Nighttime MCAO Calibration
7.2.3
Nighttime GSAOI Flux Calibration
7.2.4
Nighttime GSAOI Geometrical Distortion Calibration
7.3
MCAO Science Field Acquisition
8.1
Evolution of Dwarf Irregular Versus Elliptical Galaxies
8.1.3
Planning the Observation
8.1.6
Setup Prior to Observation
8.1.7
Science Observation Sequence
9
Summary of Scientific Requirements
9.3
Imager Wavelength Coverage
9.8
Imager Non-Common Path Phase Errors
9.11
Imager Pupil Viewer Resolution
9.15
Imager Instrumental Background
9.18
Imager Pupil Viewer Sensitivity
9.20
Mechanism Configuration Time
9.22
Imager On-Detector Guide Window
9.23
Imager Detector Read Noise
9.24
Imager Detector Dark Current
9.25
Imager On-Detector Guide Window Performance
1 Purpose
This document describes the operational concept model for
the Gemini South Adaptive Optics Imager (GSAOI). The document summarizes the
science cases for which the instrument has been designed, relates these to the
design requirements, and discusses the key functional and performance
requirements that the instrument must meet. Key operational scenarios of the
GSAOI instrument are identified and discussed, especially in terms of the
requirements the instrument places on other parts of the Gemini system. These
scenarios are described in sufficient detail for technically and scientifically
skilled, but non-expert, readers to understand.
2 Applicable Documents
|
Document ID |
Source |
Title |
|
|
IGPO |
Conceptual Design
Review Documents, MCAO for Gemini-South |
|
REV-AO-G0172 |
IGPO |
MCAO for Gemini South
Preliminary Design Report |
|
RPT-AO-G0107 |
IGPO |
The Science Case for
the Multi-Conjugate Adaptive Optics System on the Gemini South Telescope
Version 2.0 |
3 List of Acronyms
|
2MASS |
Two Micron All Sky Survey |
|
ACS |
Advanced Camera for Surveys |
|
ADC |
Atmospheric Dispersion Corrector |
|
AGB |
Asymptotic Giant Branch |
|
ALTAIR |
Altitude-Conjugated Adaptive Optics for Infrared |
|
AO |
Adaptive Optics |
|
AOM |
Adaptive Optics Module |
|
BS |
Beam Splitter |
|
BTO |
Beam Transfer Optics |
|
CCD |
Charge Coupled Device |
|
CDM |
Cold Dark Matter |
|
CM |
Centering Mirror |
|
CMD |
Color-Magnitude Diagram |
|
dE |
Dwarf Elliptical |
|
DM |
Deformable Mirror |
|
DSS |
Digitized Sky Survey |
|
DWFS |
Diagnostic Wave Front Sensor |
|
FWHM |
Full Width at Half Maximum |
|
GCAL |
Gemini Calibration Unit |
|
GNIRS |
Gemini Near-InfraRed Spectrograph |
|
GSAOI |
Gemini South Adaptive Optics Imager |
|
|
HgCdTe Astronomical Wide Area Infrared Imager |
|
HST |
Hubble Space Telescope |
|
ICM |
Intracluster Medium |
|
IGPO |
International Gemini Project Office |
|
IMF |
Initial Mass Function |
|
IOC |
Input-Output Controller |
|
ISAAC |
Infrared Spectrometer and Array Camera |
|
ISS |
Instrument Support Structure |
|
KM |
K-Mirror |
|
LGS |
Laser Guide Star |
|
LLT |
Laser Launch Telescope |
|
LMC |
Large Magellanic Cloud |
|
LS |
Laser System |
|
MBE |
Molecular Beam Epitaxy |
|
MCAO |
Multi-Conjugate Adaptive Optics |
|
MCAO-CS |
MCAO Control System |
|
NGS |
Natural Guide Star |
|
NICMOS |
Near-Infrared Camera and Multi-Object Spectrograph |
|
NIFS |
Near-infrared Integral Field Spectrograph |
|
NIRI |
Near Infra-Red Imager |
|
OAP |
Off Axis Parabola |
|
ODGW |
On-Detector Guide Window |
|
OIWFS |
On-Instrument Wave Front Sensor |
|
PDR |
Preliminary Design Review |
|
PM |
Pointing Mirror |
|
PNe |
Planetary Nebulae |
|
PSF |
Point Spread Function |
|
PWFS |
Peripheral Wave Front Sensor |
|
SALSA |
Safe Aircraft Localization and Satellite Acquisition |
|
SBF |
Surface Brightness Fluctuation |
|
SDSU |
|
|
SMC |
Small Magellanic Cloud |
|
SNe |
Supernovae |
|
TTM |
Tip-Tilt Mirror |
|
USNO |
|
|
VLT |
Very Large Telescope |
|
WFPC2 |
Wide Field and Planetary Camera
2 |
|
WFS |
Wave Front Sensor |
4 Introduction
The Gemini 8-m telescopes are designed to achieve
unprecedented ground-based image quality using adaptive optics (AO) techniques.
This has been demonstrated with Hokupa'a on Gemini North, and with ALTAIR.
These are classical AO systems that are restricted in their corrected fields
and sky coverage. The Gemini South Multi-Conjugate Adaptive Optics (MCAO)
system is being designed to overcome these limitations. MCAO will provide
uniform, diffraction-limited image quality at near-infrared wavelengths across
an extended field-of-view. Useful levels of atmospheric seeing correction will
be achieved over a full two arc minute diameter field-of-view, the maximum
possible with the Gemini telescope design. Sky coverage will also be comparable
to the ALTAIR laser guide star (LGS) system, or somewhat superior to it. MCAO
will use three deformable mirrors conjugated to distinct altitude ranges in the
atmosphere. These will be driven with commands computed from wave front sensor
measurements of five LGSs and three natural guide stars (NGSs). Mean zenith
Strehl ratios of 0.2 at J, 0.4 at H, and 0.6 at K will be
achieved in median seeing on Cerro Pachon over a one arc minute diameter field
using bright NGSs. These will decline to 0.05 at J, 0.18 at H,
and 0.39 at K at a zenith distance of 45Ί. The MCAO system will be able
to operate with fewer than three NGSs but with reduced performance.
The Gemini South Adaptive Optics Imager (GSAOI) will be the
workhorse instrument used with MCAO. GSAOI is a near-infrared,
diffraction-limited, imaging system. The imager detector includes an
On-Detector Guide Window that monitors slow tip-tilt variations due to flexure
between MCAO and GSAOI. GSAOI has a single fixed-format camera with 0.02"
pixels that Nyquist sample the 0.042" FWHM diffraction-limited
images produced at 1.65 μm, but slightly under-samples the 0.032"
FWHM images at J, and slightly over-samples the 0.057" FWHM
images at K. GSAOI uses a mosaic of Rockwell HAWAII-2RG HgCdTe/CdZnTe
Molecular Beam Epitaxy (MBE) detectors with 4080Χ4080 18 μm pixels
arranged in four 2040Χ2040 quadrants each separated by 2.5 mm. Thus GSAOI
records a square field-of-view 84.7" on a side. The GSAOI optics
have stable and low distortion that permits high precision astrometric
observations, which are limited in performance only by the stability of MCAO. A
comprehensive suite of broad-band and narrow-band filters is available. GSAOI
combines high throughput with excellent, uniform image quality to provide a
high sensitivity MCAO imaging system.
Section 5
of this document contains a description of the GSAOI instrument. The science
cases for which GSAOI has been designed are described in Section 6.
Setup and calibration requirements for GSAOI are described in Section 7.
Section 8
contains descriptions of observing scenarios. The scientific requirements that
follow from these science programs are listed in Section 9.
5 Instrument Description
5.1 Basic Instrument Parameters
·
Wavelength range: 0.9-2.4 μm.
·
Pixel size: 0.02″Χ0.02″ on sky.
·
Broad-band filters: Z, J, H, Ks, K', K.
·
Narrow-band
filters: zero-redshift emission lines.
·
Detector: 4080Χ4080 pixel Rockwell HAWAII-2RG
HgCdTe/CdZnTe MBE mosaic, 18 μm
pixels.
·
On-Detector Guide Windows: User-selectable, one
per detector mosaic quadrant.
·
Pupil viewer: Inserted without disturbing imager
optics.
·
Curvature wave front sensor: Inserted without
disturbing imager optics.
5.2 Imager Description
The imager is the GSAOI science path. The 2' diameter
f/34 MCAO output field is directed to GSAOI by the science fold mirror in the
Instrument Support Structure (ISS). The beam passes through the GSAOI cryostat
window and the central 85"Χ85" square science field
comes to focus 300 mm inside the cryostat at a field mask. The beam then passes
through a doublet field lens and a four-element optical relay. The field lens
forms a pupil image within the relay optics where the internal cold stop is
located. Two filter wheels are located immediately in front of this cold stop.
The relay reimages the focal plane onto the imager detector at a scale of 0.02"/pixel.
A utility wheel allows a lens group to be positioned temporarily between the
relay and the detector to record an image of the cold stop. This cold stop
image is used to accurately align the cryostat with the MCAO exit pupil. Convex
and concave lenses, also in the utility wheel, produce defocused star images at
the detector. These images are used to measure static wave front phase errors
that are nulled using the MCAO deformable mirror DM0.
5.2.1 Filter Wheels
The contents of the GSAOI filter wheels are listed in Table 1
and Table 2.
These contain standard near-infrared broad-band filters and zero-redshift
near-infrared emission- and absorption-line filters.
Table 1:
Upper Filter Wheel Contents
|
Position |
Filter |
λc (μm) |
Δλ (μm) |
50% cut on |
50% cut off |
|
1 |
Clear |
... |
... |
... |
... |
|
2 |
Z |
1.015 |
0.170 |
0.930 |
1.100 |
|
3 |
J |
1.250 |
0.160 |
1.170 |
1.330 |
|
4 |
H |
1.635 |
0.290 |
1.490 |
1.780 |
|
5 |
K' |
2.120 |
0.340 |
1.950 |
2.290 |
|
6 |
Ks |
2.150 |
0.320 |
1.990 |
2.310 |
|
7 |
K |
2.200 |
0.340 |
2.030 |
2.370 |
|
8 |
J continuum |
1.207 |
0.018 |
1.198 |
1.216 |
|
9 |
H continuum |
1.570 |
0.024 |
1.558 |
1.582 |
|
10 |
CH4 (short) |
1.580 |
0.100 |
1.530 |
1.630 |
|
11 |
CH4 (long) |
1.690 |
0.100 |
1.640 |
1.740 |
|
12 |
Ks continuum |
2.093 |
0.031 |
2.078 |
2.108 |
|
13 |
Kl continuum |
2.270 |
0.034 |
2.253 |
2.287 |
|
14 |
Spare |
... |
... |
... |
... |
|
15 |
Spare |
... |
... |
... |
... |
Table 2: Lower Filter Wheel Contents
|
Position |
Filter |
λc (μm) |
Δλ (μm) |
50% cut on |
50% cut off |
|
|
1 |
Clear |
... |
... |
... |
... |
|
|
2 |
He I 1.0830 μm |
1.083 |
0.016 |
1.075 |
1.091 |
|
|
3 |
H I Pγ |
1.094 |
0.011 |
1.089 |
1.100 |
|
|
4 |
H I Pβ |
1.282 |
0.019 |
1.272 |
1.292 |
|
|
5 |
[Fe II] 1.644 μm |
1.644 |
0.025 |
1.631 |
1.656 |
|
|
6 |
H2O |
2.000 |
0.080 |
1.960 |
2.040 |
|
|
7 |
He I (2p2s) |
2.058 |
0.031 |
2.042 |
2.073 |
|
|
8 |
H2 1-0 S(1) |
2.122 |
0.032 |
2.106 |
2.138 |
|
|
9 |
H I Brγ |
2.166 |
0.032 |
2.150 |
2.182 |
|
|
10 |
H2 2-1 S(1) |
2.248 |
0.034 |
2.231 |
2.265 |
|
|
11 |
CO Δv=2 |
2.360 |
0.080 |
2.320 |
2.400 |
|
|
12 |
Spare |
|
|
|
|
|
|
13 |
Spare |
|
|
|
|
|
|
14 |
Spare |
|
|
|
|
|
|
15 |
Blocked |
|
|
|
|
|
5.2.2 Utility Wheel
The contents of the utility wheel are listed in Table 3.
The Clear position is used for routine imaging. The pupil viewer is used to
accurately align the cold stop with the MCAO exit pupil and so minimize the background
reaching the imager detector. The convex and concave defocus lenses produce
defocused images that are used to derive static wave front phase errors at the
imager detector. These phase errors are nulled using the MCAO deformable mirror
DM0 (§5.2.5).
Table 3:
Utility Wheel Contents
|
Position |
Content |
|
1 |
Clear |
|
2 |
Pupil viewer |