EOS P96 User manual

ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
VERY LARGE TELESCOPE
X-shooter
User Manual
Doc. No.: VLT-MAN-ESO-14650-4942
Issue: P96
Date: 24.06.2015
Prepared: Christophe Martayan, originally written by Joël Vernet & Elena Mason
Name Date Signature
Approved: Andreas Kaufer, originally approved by Sandro D’Odorico
Name Date Signature
Released: Christophe Dumas
Name Date Signature
European Organisation
for Astronomical
Research in the
Southern Hemisphere
Organisation Européenne
pour des Recherches
Astronomiques
dans l’Hémisphère Austral
Europäische Organisation
für astronomische
Forschung in der
südlichen Hemisphäre

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CHANGE RECORD
ISSUE
DATE
SECTION/PARA.
AFFECTED
REASON/INITIATION
DOCUMENTS/REMARKS
0.1
13.01.06
All
FDR version: Table of
Content prepared by Céline
Péroux
0.2
14.08.08
All
PAE version prepared by
Joël Vernet
1
01.03.09
All
First release prepared by
Joël Vernet, with
contributions by Elena
Mason
2
01.07.09
All
Prepared by Joël Vernet and
Elena Mason.
- Added description of IFU
centring and tracking
wavelength
- Updated all TSF in Sec 5.
- Added spectrograph
orientation figure.
- Added description of
Threshold Limited
Integration in the NIR
- Added information about
ghost spectra
- Added information about
slit/ifu position information in
acq image header.
- Updated limiting mags with
measured NIR sensitivity
and background between
OH lines in VIS
- Updated UVB/VIS/NIR
detector parameters
- Added warning about 2x2
binning mode and inter-order
bck subtraction
2.1
15.01.2010
Section 5
- Templates name changed
from SHOOT to
XSHOOTER; default
parameters and hidden
parameters.
Sections 2.4.3 and 3.3.1
-... plus sparse minor
corrections.
86.1
09.02.2010
None
cmmModule creation

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87
25.08.2010
26.08.2010
All
CMa, sections 2.4.7 and
2.4.8, 2.4.9, 4.4, 4.7, 4.8
added. Sections 2.2.1, 3.2,
4.5.2, 4.6, 5.1.1, 5.1.2
modified. Figure added in
5.1.1, Table 11 updated, old
Table 3 removed. + modified
structure of the sections
88
27.02.2011
01.03.2011
03.03.2011
07.03.2011
28.03.2011
20.06.2011
Modified sects. 1.3, 2.2.1.3,
2.2.4.2, 2.3.2, 2.4, 2.4.3,
2.4.4, 2.4.6.1, 2.4.7, 3, 3.2,
3.3.1, 3.3.2, 3.3.3, 3.3.4,
4.1.1, 5, 5.1, 5.6.1, 5.6.2,
5.7, 5.9, 6.1.3, 6.2.3
New Sects 2.4.10, 2.4.11,
2.4.12, 2.4.13, 2.4.13,
2.4.14, 3.4, 3.4.1, 3.4.2,
3.4.3, 3.4.4, 3.4.5, 3.4.6
Modified tables: 2, 7, 11, 12,
66
New tables: 10, 13
Modified figures: 10, 15
New figures: 5, 11
New subsections 2.4.6, 6.1.3
CMa,
update wrt
the performances,
new identified problems
and status + description of
the current ones.
New items in the FAQ,
new calibration plan,
new section about the
observation strategy.
Figures updated to be more
clear and useful.
NIR 1.5” slit removed.
Intervention of July 2011
briefly described
+additional corrections of
figures and sections
according to IOT comments.
Very minor changes.
New templates added +
minor corrections
89
04.08.2011
30.11.2011
Modified Sections: 2.1,
2.2.1.4, 2.2.4.2, 2.2.4.5,
2.3.2, 2.4.6, 2.4.9, 2.4.13,
2.4.15, 3.4.1, 5.1, 5.5, 5.7,
6.1.5, 6.2.3.
New sections: 2.2.4.3, 2.4.7
Modified tables: 1, 9, 12, 13,
16, 72
New tables: 3, 4, 10
CMa, major modifications wrt
the new slits in the NIR +
new slits with K-band
blocking filter added and
background performances +
the new TCCD
performances + the new
calibration plan + correction
of typos and clarification of
different points (attached
calibrations, known
problems, etc), weblinks
modified.
Modifications regarding
phase2 + changes for the
acquisition+setup+readout+
wiping overheads.
+ additional information
regarding integration times
for the TCCD.

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90
20.02.2012
03.04.2012
Modified sections: 2.2.1.4,
2.2.4.5, 2.4.3, 3.4.3, 4.1.2,
5.1, 5.4, Table 16 revised
Clarification of 2.2.4.3 (new
NIR slits)
New 6.1.2 for better
explanation of slit orientation
and offsets.
DIT of 1800s with JH slits,
TCCD limiting magnitudes +
direct acquisition. Telluric std
star observations,
How to minimize the
overheads and optimize the
integration times. Calibration
plan revised.
Phase 2: minor
modifications, re-writing
sentences + new draws+
contacts added at the
beginning (already present
in other pages) Other minor
adjustments of the tables
and links.
90/91
08.08.2012
No ADCs mode: sect. 2.2.2,
updates of sects. 2.4.2,
24.13-1.4.15, 3.1, 3.4.3, 5.7,
5.9
Adding a new section about
the observations without
ADCs (2.2.2). Updates of
sections for the observations
in slit with disabled ADCs +
more infos for the IFU.
Updates wrt the telluric std
star policy starting in P91.
91
09.10.2012
Transmission curve of the K-
band blocking filter added.
Telluric std star policy
updated for P91.

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91/92
10.02.2013
Section 3.2 split in 2: 3.2.1
3.2.2
New section 3.3
New section 1.6
Sects 3.2.1/3.2.2: main acq
loop and 3.2.2 blind offset
precision
---
New section 3.3 about
examples of OBs
preparation with p2pp3
especially regarding the
acqs (direct or blind offsets)
---
new section 1.6 regarding
the acknowledgements
---
warning about the snapshots
during the acquisitions
offsets that will not be saved
anymore, only last
snapshots end of acquisition
kept.
---
warning about the exposure
times of all calibration
frames that will be revised.
---
warning about the
wavelength calibration at
night that should be
performed with 2dmap
template instead of ARC.
P92
Change of format .doc to
.odt, allowed 2dmap wave
calibrations at night, Move of
XSHOOTER from UT2 to
UT3
minor changes in various
sections
P93
Back to format .doc
Introduction of the
XSHOOTER imaging mode
(new sect 4), comments in
various sections
Minor changes every where

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P94
26.02.2014
Minor changes, references
to the imaging mode user
manual added. New table
about the limiting magnitude
for a S/N=10 in sec 2.2.1.4.
Some details provided for
the dichroic dip oscillation,
corrected cross-references.
30.06.2014
All
CMA: Merging imaging
mode manual with main
manual as per ESO
standard.
Correction of some language
issues, obsolete sections
removed or reorganized.
Radial velocity accuracy
added, telluric lines
correction tool reference
added, updates of
references and features
P95
20.11.2014
Updates Sects. 1.8, 2.2.2,
new sections 2.4.7, 2.4.14
P96
26.02.2015
Homogenizing the
overheads and references.
Adding the mapping
templates information
23.06.2015
24.06.2015
Adding: offset convention at
Paranal (obvious), info about
mapping tpl, and how to use
the imaging mode (Pelletier
cooling effect)

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TABLE OF CONTENTS
1. Introduction...................................................................................................................11
1.1 Scope ...................................................................................................................12
1.2 X-shooter in a nutshell ..........................................................................................12
1.3Shortcuts to most relevant facts for proposal preparation......................................12
1.4 List of Abbreviations & Acronyms..........................................................................13
1.5 Reference Documents ..........................................................................................14
1.6 Acknowledgements...............................................................................................15
1.7 Contact .................................................................................................................15
1.8 News.....................................................................................................................16
2. Technical description of the instrument.........................................................................17
2.1 Overview of the opto-mechanical design...............................................................18
2.2 Description of the instrument sub-systems............................................................18
2.2.1 The Backbone ...............................................................................................19
2.2.1.1 The Instrument Shutter and The calibration unit ........................................19
2.2.1.2 The Acquisition and Guiding slide..............................................................20
2.2.1.3 The IFU .....................................................................................................21
2.2.1.4 The Acquisition and Guiding Camera ........................................................23
2.2.1.5 The dichroic box ........................................................................................24
2.2.1.6 The flexure compensation tip-tilt mirrors....................................................24
2.2.1.7 The Focal Reducer and Atmospheric Dispersion Correctors .....................25
2.2.2 ADCs problems and disabled ADCs observing mode in SLIT and IFU ..........26
2.2.3 Detector QE curves .......................................................................................35
2.2.4 The UVB spectrograph..................................................................................35
2.2.4.1 Slit carriage ...................................................................................................35
2.2.4.2 Optical layout ................................................................................................36
2.2.4.3 Detector ........................................................................................................37
2.2.5 The VIS spectrograph ...................................................................................39
2.2.5.1 Slit carriage ...................................................................................................39
2.2.5.2 Optical layout ................................................................................................39
2.2.5.3 Detector ........................................................................................................39
2.2.6 The NIR spectrograph ...................................................................................40
2.2.6.1 Pre-slit optics and entrance window ..............................................................40
2.2.6.2 Slit wheels.....................................................................................................40
2.2.6.3 NIR Backgrounds ..........................................................................................44
2.2.6.4 Optical layout ................................................................................................47
2.2.6.5 Detector ........................................................................................................48
2.3 Spectral format, resolution and overall performances ...........................................51
2.3.1 Spectral format..............................................................................................51
2.3.2 Spectral resolution and sampling...................................................................52
2.3.3 Overall sensitivity ..........................................................................................53
2.4 Instrument features and known problems to be aware of ......................................55
2.4.1 UVB and VIS detectors sequential readout ...................................................55
2.4.2 Effects of atmospheric dispersion..................................................................55
2.4.3 Remanence...................................................................................................55
2.4.4 Ghosts...........................................................................................................57
2.4.5 Inter-order background..................................................................................58
2.4.6 NIR frames with the K-band blocking filter features .......................................58
2.4.7 NIR detector: interquadrant cross-talk and electrical ghosts ..........................60
2.4.8 Instrument stability ........................................................................................60

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2.4.8.1 Backbone flexures.........................................................................................60
2.4.8.2 Spectrograph flexures ...................................................................................60
2.4.9 Radial velocity accuracy................................................................................60
2.4.10 NIR 11th order vignetting (K band) .................................................................61
2.4.11 VIS CCD pick-up noise..................................................................................62
2.4.12 NIR –IFU parasitic reflections........................................................................62
2.4.13 UVB/VIS ADCs problem................................................................................63
2.4.14 Drift of acquisition reference positions...........................................................63
2.4.15 TCCD features ..............................................................................................63
3. Observing with X-shooter .............................................................................................64
3.1 Observing modes and basic choices.....................................................................64
3.2 Target acquisition..................................................................................................65
3.2.1 Acquisition loop .............................................................................................65
3.2.2 Blind offset precisions ...................................................................................66
3.3 Examples of OBs preparations/acquisitions with p2pp3 ........................................67
3.3.1 Direct acquisition...........................................................................................67
3.3.2 Blind offset acquisition...................................................................................73
3.4 Spectroscopic observations ..................................................................................75
3.4.1 Overview and important remarks...................................................................75
3.4.1.1 Observing modes ..........................................................................................75
3.4.1.2 Effect of atmospheric dispersion....................................................................75
3.4.1.3 Exposure time in the NIR arm .......................................................................75
3.4.2 Staring (SLIT and IFU) ..................................................................................76
3.4.3 Staring synchronized (SLIT and IFU) ............................................................76
3.4.4 Nodding along the slit (SLIT only)..................................................................77
3.4.5 Fixed offset to sky (SLIT and IFU) .................................................................78
3.4.6 Generic offset (SLIT and IFU) .......................................................................78
3.4.7 and IFU) templates........................................................................................78
3.5 Observation strategy, summary, and tricks ...........................................................79
3.5.1 Instrument setup ...........................................................................................79
3.5.2 Observation strategy .....................................................................................80
3.5.3 Telluric standard stars and telluric lines correction (see also Sect.6.6.1) .......82
3.5.4 Observing bright objects, limiting magnitudes, and the diaphragm mode ......82
3.5.5 Readout times in the UVB and VIS arms: minimization of overheads............83
4. The XSHOOTER imaging mode ...................................................................................84
5. Instrument and telescope overheads ..........................................................................100
5.1.1 Summary of telescope and instrument overheads.......................................100
5.1.2 Execution time computation and how to minimize the overheads ................102
6. Calibrating and reducing X-shooter data.....................................................................104
6.1 X-shooter calibration plan ...................................................................................104
6.2 Wavelength and spatial scale calibration.............................................................107
6.3 Flat-field and Wavelength calibrations.................................................................108
6.4 Spectroscopic skyflats.........................................................................................109
6.5 Attached calibrations...........................................................................................110
6.6 Spectrophotometric calibration............................................................................110
6.6.1 Telluric absorption correction ......................................................................110
6.6.2 Absolute flux calibration ..............................................................................112
6.7 The X-shooter pipeline ........................................................................................113
6.8 Examples of observations with X-shooter............................................................114
6.9 Frequently Asked Questions ...............................................................................114
7. Reference material .....................................................................................................116

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7.1 Templates reference ...........................................................................................116
7.1.1 Orientation and conventions........................................................................116
7.1.2 Examples of position angles and offsets......................................................118
7.1.3 Acquisition templates ..................................................................................120
Slit acquisition templates ........................................................................................120
IFU acquisition templates........................................................................................122
7.1.4 Flexure compensation templates that can be used in OBs ..........................124
7.1.5 Science templates.......................................................................................124
Slit observations .....................................................................................................124
IFU observations.....................................................................................................129
7.1.6 Night-time Calibration Templates ................................................................132
Spectro-photometric Standard Stars .......................................................................132
Telluric standards ...................................................................................................137
Attached night calibrations: must be taken after a science template .......................140
Arcs multi-pinhole: 2d wave maps (wavelength calibration) ....................................143
7.1.7 Daytime Calibration templates.....................................................................145
Slit and IFU arc lamp calibrations (resolution, tilt) ...................................................145
Flatfield (pixel response, orders localization) ..........................................................146
Format check (1st guess of wavelength solution).....................................................149
Order definition (1st guess of order localization) ......................................................149
Arcs multi-pinhole: 2d wave maps (wavelength calibration) ....................................150
Detector calibrations ...............................................................................................151
7.1.8 Imaging mode templates manual.................................................................154
7.2 Slit masks ...........................................................................................................160
7.2.1 UVB ............................................................................................................160
7.2.2 VIS ..............................................................................................................160
7.2.3 NIR..............................................................................................................161

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1.Introduction
Figure 1: 3D CAD view of the X-shooter spectrograph at the Cassegrain focus of one of the VLT
Unit Telescopes.
Table 1: X-shooter characteristics and observing capabilities
Wavelength range
300-2500 nm split in 3 arms
UV-blue arm
Range: 300-550 nm in 12 orders
Resolution: 5100 (1" slit)
Slit width: 0.5”, 0.8”, 1.0”, 1.3”, 1.6”, 5.0”
Detector: 4k x 2k E2V CCD
Visual-red arm
Range: 550-1000 nm in 14 orders
Resolution: 8800 (0.9" slit)
Slit width: 0.4”, 0.7”, 0.9”, 1.2”, 1.5”, 5.0”
Detector: 4k x 2k MIT/LL CCD
Near-IR arm
Range: 1000-2500 nm in 16 orders
Resolution: 5100 (0.9" slit)
Slit width: 0.4”, 0.6”, 0.9”, 1.2”, 1”, 5.0”,
0.6”JH, 0.9”JH
Detector: 2k x 1k Hawaii 2RG
Slit length
11” (SLIT) or 12.6” (IFU)
Beam separation
Two high efficiency dichroics
Atmospheric dispersion compensation
In the UV-Blue and Visual-red arms
Disabled on Aug. 1st ,2012
Integral field unit
Acquisition and guiding camera
1.8" x 4" reformatted into 0.6" x 12"
1.5’x1.5’ +Johnson and SDSS filters

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1.1 Scope
The X-shooter User Manual provides extensive information on the technical characteristics of
the instrument, its performances, observing and calibration procedures and data reduction.
1.2 X-shooter in a nutshell
X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs
covering in a single exposure the spectral range from the UV to the K band. The spectral
format is fixed. The instrument is designed to maximize the sensitivity in the spectral range
through the splitting in three arms with optimized optics, coatings, dispersive elements and
detectors. It operates at intermediate resolutions (R=4000-18000, depending on wavelength
and slit width) sufficient to address quantitatively a vast number of astrophysical applications
while working in a background-limited S/N regime in the regions of the spectrum free from
strong atmospheric emission and absorption lines. A 3D CAD view of the instrument
attached to the telescope is shown on Figure 1. Main instrument characteristics are
summarized in Table 1.
A Consortium involving institutes from Denmark, Italy, The Netherlands, France and ESO
built x-shooter. Name of the institutes and their respective contributions are given in Table 2.
1.3 Shortcuts to most relevant facts for proposal preparation
The fixed spectral format of X-shooter: see Table 11 on page 50
Spectral resolution as a function of slit width: see Table 12 on page 52
Information on the IFU: see Section 2.2.1.3
Information on limiting magnitudes in the continuum: see Section 2.3.3 on page 53
Information on observing modes: see section 3.1 on page 64
Observing strategy and sky subtraction: see Section 3.3 on page 67
Overhead computation: see Section 4 on page 84
Table 2: collaborating institutes and their contributions
Collaborating institutes
Contribution
Copenhagen University
Observatory
Backbone unit, UVB spectrograph, Mechanical
design and FEA, Control electronics
ESO
Project Management and Systems Engineering,
Detectors, final system integration,
commissioning, logistics, Data Reduction
Software
Paris-Meudon Observatory,
Paris VII University
Integral Field Unit, Data Reduction Software
INAF - Observatories of Brera,
Catania, Trieste and Palermo
UVB and VIS spectrograph, Instrument Control
Software, optomechanical design.
Astron, Universities of
Amsterdam and Nijmegen
NIR spectrograph, contribution to Data
Reduction Software

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1.4 List of Abbreviations & Acronyms
This document employs several abbreviations and acronyms to refer concisely to an item,
after it has been introduced. The following list is aimed to help the reader in recalling the
extended meaning of each short expression:
A&G/AG
Acquisition and Guiding
ADC
Atmospheric Dispersion Compensator
AFC
Active Flexure Compensation
DCS
Detector Control Software
DEC
DFS
Declination
Data Flow System
DIT
Detector Integration Time
ESO
European Southern Observatory
ETC
FDR
Exposure Time Calculator
Final Design Review
FF
Flat Field
GUI
Graphical User Interface
ICS
Instrument Control Software
IFU
Integral Field Unit
ISF
Instrument Summary File
IWS
Instrument Workstation
LCU
Local Control Unit
N/A
Not Applicable
OB
PAE
Observing Block
Preliminary Acceptance Europe
P2PP
Phase 2 Proposal Preparation
RA
RMS
RON
SM
TBC
Right Ascension
Root Mean Square
Readout Noise
Service Mode
To Be Clarified
TCCD
QE
Technical CCD
Quantum Efficiency
SNR
Signal to Noise Ratio
TBD
To Be Defined
TCS
Telescope Control Software
TLI
Threshold Limited Integration
TSF
Template Signature File
VLT
VM
Very Large Telescope
Visitor Mode
WCS
ZP
World Coordinate System
Zeropoint

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1.5 Reference Documents
1. X-shooter Calibration plan, v1.0, XSH-PLA-ESO-12000-0088
2. X-shooter Templates Reference Manual, v0.2, XSH-MAN-ITA-8000-0031
3. X-shooter technical note about the 11th order vignetting in K band
4. X-shooter A&A article: Vernet et al. 2011A&A...536A.105V
5. Report about the non destructive NIR readout mode
http://www.eso.org/sci/facilities/paranal/instruments/xshooter/doc/reportNDreadoutpublic.pdf

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1.6 Acknowledgements
Please if you use XSHOOTER data, cite the following articles:
1. main article:
Vernet et al., 2011A&A...536A.105V
X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very
Large Telescope
2. For the flux calibrations:
Vernet et al., 2010HiA....15..535V
Building-up a database of spectro-photometric standards from the UV to the NIR
Hamuy et al., 1994PASP..106..566H
Southern spectrophotometric standards, 2
3. For the pipeline and data reduction:
Modigliani et al., 2010SPIE.7737E..56M
The X-shooter pipeline
4. For the Reflex interface:
Freudling et al., 2013A&A...559A..96F
Automated data reduction workflows for astronomy. The ESO Reflex environment
5. For the imaging mode:
Martayan et al., The Messenger, 156, June 2014
The X-shooter Imaging Mode
1.7 Contact
In case of instrument related questions, use [email protected]g
In case of phase1/2 related questions, use [e-mail] or usd-hel[email protected]

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1.8 News
-in P96 a new ETC is available using the image quality on the instrument
(instrument+telescope+sky contributions) instead of the seeing. However, the seeing is still
used as input in V band at the zenith. There is not yet a new sky model available for
XSHOOTER and the NIR background is underestimated in K band.
-Since P94, XSHOOTER is available again at UT2.
- In P93 as in P92, XSHOOTER will be available at UT3 instead of UT2. This would allow
decreasing a bit the pressure factor on this instrument.
- In P93 is introduced the light imaging mode of XSHOOTER performed with the acquisition
and guiding camera. At the same time only a single snapshot is taken of the last image
during the acquisition loop (2 in case of blind offset before and after the blind offset). More
details will come in a dedicated document.
- Note: in P92 some tests were started of a new mode that allows observing very bright
objects (even negative magnitudes). Once the tests completed this mode could eventually be
offered to the community (manpower and time dependent).
Some results are available in the news page of XSHOOTER.

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2.Technical description of the instrument
Figure 2: Schematic overview of X-shooter

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2.1 Overview of the opto-mechanical design
Figure 2 shows a schematic view of the layout of the instrument. It consists of four main
components:
The backbone which is directly mounted on the Cassegrain derotator of the
telescope. It contains all pre-slit optics: the calibration unit, a slide with the 3-
positions mirror and the IFU, the acquisition and guiding camera, the dichroic box
which splits the light between the three arms, one piezo tip-tilt mirror for each arm to
allow active compensation of backbone flexures, atmospheric dispersion
compensators (ADCs) in the UVB and VIS arms and a warm optical box in the NIR
arm.
The three arms are fixed format cross-dispersed échelle spectrographs that operate
in parallel. Each one has its own slit selection device.
oThe UV-Blue spectrograph covers the 300 –550 nm wavelength range with a
resolving power of 5100 (for a 1” slit)
oThe Visible spectrograph covers the range 550 - 1000 nm with a resolving
power of 7500 (0.9” slit).
oThe near-IR spectrograph: this arm covers the range 1000 - 2500 nm with a
resolving power of 5300 (0.9” slit). It is fully cryogenic.
2.2 Description of the instrument sub-systems
This section describes the different sub-systems of X-shooter in the order they are
encountered along the optical path going from the telescope to the detectors (see
Figure 2). The functionalities of the different sub-units are explained and reference is made
to their measured performance.

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2.2.1 The Backbone
2.2.1.1 The Instrument Shutter and The calibration unit
In the converging beam coming from the telescope, the first element is the telescope
entrance shutter.
Then follows the Calibration Unit that allows to select a choice of flat-fielding and wavelength
calibration lamps. This unit consists of a mechanical structure with calibration lamps, an
integrating sphere, relay optics that simulate the f/13.6 telescope beam, and a mirror slide
with 3 positions that can be inserted in the telescope beam:
one free position for a direct feed from the telescope,
one mirror which reflects the light from the integrating sphere equipped with:
oWavelength calibration Ar, Hg, Ne and Xe Penray lamps operating
simultaneously
othree flat-field halogen lamps equipped with different balancing filters to
optimize the spectral energy distribution for each arm
one mirror which reflects light from:
oa wavelength calibration hollow cathode Th-Ar lamp
oa D2lamp for flat-fielding the bluest part of the UV-Blue spectral range
A more detailed description of the functionalities of the calibration system is given in Sect. 6.
Figure 3: 3D view of a cut through the backbone.

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2.2.1.2 The Acquisition and Guiding slide
Light coming either directly from the telescope or from the Calibration Unit described above
reaches first the A&G slide. This structure allows putting into the beam either:
a flat 45˚ mirror with 3 positions mirror:
oacquisition and imaging: send the full 1.5’1.5’ field of view to the A&G
camera. This is the position used during all acquisition sequences;
ospectroscopic observations and monitoring: a slot lets the central 10”15” of
the field go through to the spectrographs while reflecting the peripheral field to
the A&G camera. This is the position used for all science observations.
oartificial star: a 0.5” pinhole used for optical alignment and engineering
purposes;
the IFU (described in Sect. 2.2.1.3);
a 50/50 pellicle beam splitter at 45˚ which is to used look down into the instrument
with the A&G camera and is exclusively used for engineering purposes.