The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a fibre-fed multi-object spectrograph for the VISTA telescope at the ESO Paranal Observatory in Chile. The goal of the 4MOST project is to create a general-purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square degree field of view and consists of an optical Wide-Field Corrector (WFC), a fibre positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of 6 lenses grouped into 4 elements, 2 of which are cemented doublets that act as an atmospheric dispersion corrector (ADC). The first lens element is 0.9m in diameter whilst the diameter of the other elements is 0.65m. For the instrument to meet its science goals, each lens needs to be aligned to ∼50µm – a major challenge. This is achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, a novel off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This paper details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC
The High Efficiency and Resolution Multi Element Spectrograph, HERMES, is a facility-class optical spectrograph for the Anglo-Australian Telescope (AAT). It is designed primarily for Galactic Archaeology, the first major attempt to create a detailed understanding of galaxy formation and evolution by studying the history of our own galaxy, the Milky Way. The goal of the GALAH survey is to reconstruct the mass assembly history of the Milky Way through a detailed chemical abundance study of one million stars. The spectrograph is based at the AAT and is fed by the existing 2dF robotic fiber positioning system. The spectrograph uses volume phase holographic gratings to achieve a spectral resolving power of 28,000 in standard mode and also provides a high-resolution mode ranging between 40,000 and 50,000 using a slit mask. The GALAH survey requires an SNR greater than 100 for a star brightness of V=14 in an exposure time of one hour. The total spectral coverage of the four channels is about 100 nm between 370 and 1000 nm for up to 392 simultaneous targets within the 2-degree field of view. HERMES has been commissioned over three runs, during bright time in October, November, and December 2013, in parallel with the beginning of the GALAH pilot survey, which started in November 2013. We present the first-light results from the commissioning run and the beginning of the GALAH survey, including performance results such as throughput and resolution, as well as instrument reliability.
We present advances in the patented Echidna 'tilting spine' fiber positioner technology that has been in operation since 2007 on the SUBARU telescope in the FMOS system. The new Echidna technology is proposed to be implemented on two large fiber surveys: the Dark Energy Spectroscopic Instrument (DESI) (5000 fibers) as well the Australian ESO Positioner (AESOP) for 4MOST, a spectroscopic survey instrument for the VISTA telescope (~2500 fibers). The new 'superspine' actuators are stiffer, longer and more accurate than their predecessors. They have been prototyped at AAO, demonstrating reconfiguration times of ~15s for errors of <5 microns RMS. Laboratory testing of the prortotype shows accurate operation at temperatures of -10 to +30C, with an average heat output of 200 microwatts per actuator during reconfiguration. Throughput comparisons to other positioner types are presented, and we find that losses due to tilt will in general be outweighed by increased allocation yield and reduced fiber stress FRD. The losses from spine tilt are compensated by the gain in allocation yield coming from the greater patrol area, and quantified elsewhere in these proceedings. For typical tilts, f-ratios and collimator overspeeds, Echidna offers a clear efficiency gain versus current r-that or theta-phi positioners.
Wide-Field Corrector designs are presented for the Blanco and Mayall telescopes, the CFHT and the AAT. The designs
are Terezibh-style, with 5 or 6 lenses, and modest negative optical power. They have 2.2°-3° ields of view, with curved
and telecentric focal surfaces suitable for fiber spectroscopy. Some variants also allow wide-field imaging, by changing
the last WFC element. Apart from the adaptation of the Terebizh design for spectroscopy, the key feature is a new
concept for a ‘Compensating Lateral Atmospheric Dispersion Corrector’, with two of the lenses being movable laterally
by small amounts. This provides excellent atmospheric dispersion correction, without any additional surfaces or
absorption. A novel and simple mechanism for providing the required lens motions is proposed, which requires just 3
linear actuators for each of the two moving lenses.
The High Efficiency and Resolution Multi Element Spectrograph, HERMES is an facility-class optical spectrograph for
the AAT. It is designed primarily for Galactic Archeology [21], the first major attempt to create a detailed
understanding of galaxy formation and evolution by studying the history of our own galaxy, the Milky Way. The goal of
the GALAH survey is to reconstruct the mass assembly history of the of the Milky Way, through a detailed spatially
tagged abundance study of one million stars. The spectrograph is based at the Anglo Australian Telescope (AAT) and is
fed by the existing 2dF robotic fiber positioning system. The spectrograph uses VPH-gratings to achieve a spectral
resolving power of 28,000 in standard mode and also provides a high-resolution mode ranging between 40,000 to 50,000
using a slit mask. The GALAH survey requires a SNR greater than 100 for a star brightness of V=14. The total spectral
coverage of the four channels is about 100nm between 370 and 1000nm for up to 392 simultaneous targets within the 2
degree field of view. Hermes has been commissioned over 3 runs, during bright time in October, November and
December 2013, in parallel with the beginning of the GALAH Pilot survey starting in November 2013. In this paper we
present the first-light results from the commissioning run and the beginning of the GALAH Survey, including
performance results such as throughput and resolution, as well as instrument reliability. We compare the abundance
calculations from the pilot survey to those in the literature.
The High Efficiency and Resolution Multi Element Spectrograph, HERMES is an optical spectrograph designed
primarily for the GALAH, Galactic Archeology Survey, the first major attempt to create a detailed understanding of
galaxy formation and evolution by studying the history of our own galaxy, the Milky Way1. The goal of the GALAH
survey is to reconstruct the mass assembly history of the of the Milky way, through a detailed spatially tagged
abundance study of one million stars in the Milky Way. The spectrograph will be based at the Anglo Australian
Telescope (AAT) and be fed with the existing 2dF robotic fibre positioning system. The spectrograph uses VPH-gratings
to achieve a spectral resolving power of 28,000 in standard mode and also provides a high resolution mode ranging
between 40,000 to 50,000 using a slit mask. The GALAH survey requires a SNR greater than 100 aiming for a star
brightness of V=14. The total spectral coverage of the four channels is about 100nm between 370 and 1000nm for up to
392 simultaneous targets within the 2 degree field of view.
Current efforts are focused on manufacturing and integration. The delivery date of spectrograph at the telescope is
scheduled for 2013. A performance prediction is presented and a complete overview of the status of the HERMES
spectrograph is given. This paper details the following specific topics:
The approach to AIT, the manufacturing and integration of the large mechanical frame, the opto-mechanical slit
assembly, collimator optics and cameras, VPH gratings, cryostats, fibre cable assembly, instrument control hardware and
software, data reduction.
We present a concept for a 4000-fibre positioner for DESpec, based on the Echidna ‘tilting spine’ technology. The DESpec focal plane is 450mm across and curved, and the required pitch is ~6.75mm. The size, number of fibers and curvature are all comparable with various concept studies for similar instruments already undertaken at the AAO, but present new challenges in combination. A simple, low-cost, and highly modular design is presented, consisting of identical modules populated by identical spines. No show-stopping issues in accommodating either the curvature or the smaller pitch have been identified, and the actuators consist largely of off-the-shelf components. The actuators have been prototyped at AAO, and allow reconfiguration times of ~15s to reach position errors 7 microns or less. Straightforward designs for metrology, acquisition, and guiding are also proposed. The throughput losses of the entire positioner system are estimated to be ~15%, of which 6.3% is attributable to the tilting-spine technology.
The Australian Astronomical Observatory (AAO) has recently completed a feasibility study for a fiber-positioner facility proposed for the Giant Magellan Telescope (GMT), called MANIFEST (the Many Instrument Fiber System). The MANIFEST instrument takes full advantage of the wide-field focal plane to efficiently feed other instruments. About 2000 individually deployable fiber units are envisaged, with a wide variety of aperture types (single-aperture, image- or pupil-slicing, IFU). MANIFEST allows (a) full use of the GMT's 20' field-of-view, (b) a multiplexed IFU capability, (c) greatly increased spectral resolution via image-slicing, (d) the possibility of OH-suppression in the near-infrared.
We describe the preliminary design of the Dark Energy Spectrometer (DESpec), a fiber-fed spectroscopic instrument
concept for the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO). DESpec would take
advantage of the infrastructure recently deployed for the Dark Energy Camera (DECam). DESpec would be mounted in
the new DECam prime focus cage, would be interchangeable with DECam, would share the DECam optical corrector,
and would feature a focal plane with ~4000 robotically positioned optical fibers feeding multiple high-throughput
spectrometers. The instrument would have a field of view of 3.8 square degrees, a wavelength range of approximately
500<<1000 nm, and a spectral resolution of R~3000. DESpec would provide a powerful spectroscopic follow-up
system for sources in the Southern hemisphere discovered by the Dark Energy Survey and LSST.λ
The Australian Astronomical Observatory is building a 4-channel VPH-grating High Efficiency and Resolution Multi
Element Spectrograph (HERMES) for the 3.9 meter Anglo-Australian Telescope (AAT). HERMES will provide a
nominal spectral resolving power of 28,000 for Galactic Archaeology with an optional high-resolution mode of 45,000
with the use of a slit mask.
HERMES is fed by a fibre positioning robot called 2dF at the telescope prime focus. There are a total of 784 science
fibres, which interface with the spectrograph via two separate slit body assemblies, each comprising of 392 science
fibers. The slit defines the spectral lines of 392 fibres on the detector. The width of the detector determines the spectral
bandwidth and the detector height determines the fibre to fibre spacing or cross talk. Tolerances that follow from this are
all in the 10 micrometer range.
The slit relay optics must contribute negligibly to the overall image quality budget and uniformly illuminate the
spectrograph exit pupil. The latter requirement effectively requires that the relay optics provide a telecentric input at the
collimator entrance slit. As a result it is critical to align the optical components to extreme precision required by the
optical design.
This paper discusses the engineering challenges of designing, optimising, tolerancing and manufacturing of very precise
mechanical components for housing optics and the design of low cost of jigs and fixtures for alignment and assembly of
the optics.
The Gemini High-Resolution Optical SpecTrograph (GHOST) will fill an important gap in the current suite of Gemini
instruments. We will describe the Australian Astronomical Observatory (AAO)-led concept for GHOST, which consists
of a multi-object, compact, high-efficiency, fixed-format, fiber-fed design. The spectrograph itself is a four-arm variant
of the asymmetric white-pupil echelle Kiwispec spectrograph, Kiwisped, produced by Industrial Research Ltd. This
spectrograph has an R4 grating and a 100mm pupil, and separate cross-disperser and camera optics for each of the four
arms, carefully optimized for their respective wavelength ranges. We feed this spectrograph with a miniature lensletbased
IFU that sub-samples the seeing disk of a single object into 7 hexagonal sub-images, reformatting this into a slit
with a second set of double microlenses at the spectrograph entrance with relatively little loss due to focal-ratio
degradation. This reformatting enables high spectral resolution from a compact design that fits well within the relatively
tight GHOST budget. We will describe our baseline 2-object R~50,000 design with full wavelength coverage from the
ultraviolet to the silicon cutoff, as well as the high-resolution single-object R~75,000 mode.
First light from the SAMI (Sydney-AAO Multi-object IFS) instrument at the Anglo-Australian Telescope (AAT) has
recently proven the viability of fibre hexabundles for multi-IFU spectroscopy. SAMI, which comprises 13 hexabundle
IFUs deployable over a 1 degree field-of-view, has recently begun science observations, and will target a survey of
several thousand galaxies. The scientific outputs from such galaxy surveys are strongly linked to survey size, leading the
push towards instruments with higher multiplex capability. We have begun work on a new instrument concept, called
Hector, which will target a spatially-resolved spectroscopic survey of up to one hundred thousand galaxies. The key
science questions for this instrument concept include how do galaxies get their gas, how is star formation and nuclear
activity affected by environment, what is the role of feedback, and what processes can be linked to galaxy groups and
clusters. One design option for Hector uses the existing 2 degree field-of view top end at the AAT, with 50 individual
robotically deployable 61-core hexabundle IFUs, and 3 fixed format spectrographs covering the visible wavelength range
with a spectral resolution of approximately 4000. A more ambitious option incorporates a modified top end at the AAT
with a new 3 degree field-of-view wide-field-corrector and 100 hexabundle IFUs feeding 6 spectrographs.
Following the successful commissioning of SAMI (Sydney-AAO Multi-object IFU) the AAO has undertaken concept
studies leading to a design of a new instrument for the AAT (Hector). It will use an automated robotic system for the
deployment of fibre hexabundles to the focal plane. We have analysed several concepts, which could be applied in the
design of new instruments or as a retrofit to existing positioning systems. We look at derivatives of Starbugs that could
handle a large fibre bundle as well as modifications to pick and place robots like 2dF or OzPoz. One concept uses large
magnetic buttons that adhere to a steel field plate with substantial force. To move them we replace the gripper with a
pneumatic device, which engages with the button and injects it with compressed air, thus forming a magnet preloaded air
bearing allowing virtually friction-less repositioning of the button by a gantry or an R-Theta robot. New fibre protection,
guiding and retraction systems are also described. These developments could open a practical avenue for the upgrade to a
number of instruments.
The AAO is building an optical high resolution multi-object spectrograph for the AAT for Galactic Archaeology. The
instrument has undergone significant design revision over that presented at the 2008 Marseilles SPIE meeting. The
current design is a 4-channel VPH-grating based spectrograph providing a nominal spectral resolving power of 28,000
and a high-resolution mode of 45,000 with the use of a slit mask. The total spectral coverage is about 1000 Angstroms
for up to 392 simultaneous targets within the 2 degree field of view. Major challenges in the design include the
mechanical stability, grating and dichroic efficiencies, and fibre slit relay implementation. An overview of the current
design and discussion of these challenges is presented.
We describe the design of a new CCD system delivered to the Automated Patrol Telescope at Siding Springs NSW
Australia operated by UNSW. A very fast beam (f/1) with a mosaic of two MITLL CCID-34 detectors placed only 1
mm behind the field flattener which also serves as the dewar window, have called for innovative engineering solutions.
This paper describes the design and procedure of the field-flattener mounting, differential screw adjustable detector
mount and dewar suspension on the external ring providing tip/tilt and focus adjustment.
FMOS: the Fiber Multiple-Object Spectrograph is the next common-use instrument of the Subaru Telescope,
having a capability of 400 targets multiplicity in the near-infrared 0.9-1.8μm wavelength range with a field
coverage of 30' diameter. FMOS consists of three units: 1) the prime focus unit including the corrector lenses,
the Echidna fiber positioner, and the instrument-bay to adjust the instrument focus and shift the axis of the
corrector lens system, 2) the fiber bundle unit equipping two fiber slits on one end and a fiber connector box with
the back-illumination mechanism on the other end on the bundle, 3) the two infrared spectrographs (IRS1 and
IRS2) to obtain 2×200 spectra simultaneously. After all the components were installed in the telescope at the
end of 2007, the total performance was checked through various tests and engineering observations. We report
the results of these tests and demonstrate the performance of FMOS.
Mapping out stellar families to trace the evolutionary star formation history of the Milky Way requires a spectroscopic facility able to deliver high spectral resolution (R≥30k) with both good wavelength coverage (~400 Ang) and target multiplex advantage (~400 per 2 degree field). Such a facility can survey 1,200,000 bright stars over 10,000 square degrees in about 400 nights with a 4-meter aperture telescope. Presented are the results of a conceptual design study for such a spectrograph, which is under development as the next major instrument for the Anglo-Australian Observatory. The current design (that builds upon the AAOmega system) makes use of a White Pupil collimator and an R3 echelle that is matched to the existing AAOmega cameras. The fibre slit can be reconfigured to illuminate the Pupil relay side of the collimator mirror bypassing the echelle, thus preserving the lower dispersion modes of the AAOmega spectrograph. Other spectrograph options initially considered include use of an anamorphic collimator that reduces the required dispersion to that achievable with VPH grating technology or possible use of a double-pass VPH grating.
We present the concept design of a new fibre positioner and spectrograph system for the Anglo-Australian Telescope,
as a proposed enhancement to the Anglo-Australian Observatory's well-known 2dF facility. A four-fold multiplex
enhancement is accomplished by replacing the 400-fibre 2dF fibre positioning robot with a 1600-fibre Echidna unit,
feeding three clones of the AAOmega optical spectrograph. Such a facility has the capability of a redshift 1 survey of a
large fraction of the southern sky, collecting five to ten thousand spectra per night for a million-galaxy survey.
AAOmicron is a wide-field, fiber-fed, multi-object, near-infrared spectrograph concept for the Anglo Australian
Telescope (AAT). It is one of a number of instruments concepts (primarily for bright time use) recently considered to
complement the existing instrumentation and in particular the highly popular AAOmega system (primarily dark and grey
time usage). AAOmicron has a two-degree field of view, 240 robotically configured fibers and operates between 0.98
and 1.75μm at a resolution of R~3500. AAOmicron offers a broad suite of applications from the study of low-mass stars,
to determining the structure of the high-redshift Universe. We present an overview of the instrument concept, which is
based heavily on the highly successful AAOmega system, and describe how the AAOmega spectrograph design could be
adapted for near-infrared observations to provide a highly cost effective and scientifically compelling instrument.
The Fiber Multiple-Object Spectrograph for Subaru Telescope (FMOS) is quite large instrument composed of
the prime focus unit, the fiber bundle unit, and the two infrared spectrographs. Among these units, a part of the
prime focus unit and one of the spectrograph were transported from Kyoto University to the Subaru Observatory
in the middle of 2005. We present the optical and the mechanical components of the spectrograph, which was
reassembled on the new floor of the Subaru dome. We also show the preliminary results of the optical alignment
and the cooling test of the instrument at the summit of Mauna Kea.
AAOmega is the new spectrograph for the 2dF fibre-positioning system on the Anglo-Australian Telescope. It is a bench-mounted, double-beamed design, using volume phase holographic (VPH) gratings and articulating cameras. It is fed by 392 fibres from either of the two 2dF field plates, or by the 512 fibre SPIRAL integral field unit (IFU) at Cassegrain focus. Wavelength coverage is 370 to 950nm and spectral resolution 1,000-8,000 in multi-Object mode, or 1,500-10,000 in IFU mode. Multi-object mode was commissioned in January 2006 and the IFU system will be commissioned in June 2006.
The spectrograph is located off the telescope in a thermally isolated room and the 2dF fibres have been replaced by new 38m broadband fibres. Despite the increased fibre length, we have achieved a large increase in throughput by use of VPH gratings, more efficient coatings and new detectors - amounting to a factor of at least 2 in the red. The number of spectral resolution elements and the maximum resolution are both more than doubled, and the stability is an order of magnitude better.
The spectrograph comprises: an f/3.15 Schmidt collimator, incorporating a dichroic beam-splitter; interchangeable VPH gratings; and articulating red and blue f/1.3 Schmidt cameras. Pupil size is 190mm, determined by the competing demands of cost, obstruction losses, and maximum resolution. A full suite of VPH gratings has been provided to cover resolutions 1,000 to 7,500, and up to 10,000 at particular wavelengths.
IRIS2, the infrared imager and spectrograph for the Cassegrain focus of the Anglo Australian Telescope, has been in service since October 2001.
IRIS2 incorporated many novel features, including multiple cryogenic multislit masks, a dual chambered vacuum vessel (the smaller chamber used to reduce thermal cycle time required to change sets of multislit masks), encoded cryogenic wheel drives with controlled backlash, a deflection compensating structure, and use of teflon impregnated hard anodizing for gear lubrication at low temperatures. Other noteworthy features were: swaged foil thermal link terminations, the pupil imager, the detector focus mechanism, phased getter cycling to prevent detector contamination, and a flow-through LN2 precooling system. The instrument control electronics was designed to allow accurate positioning of the internal mechanisms with minimal generation of heat. The detector controller was based on the AAO2 CCD controller, adapted for use on the HAWAII1 detector (1024 x 1024 pixels) and is achieving low noise and high performance.
We describe features of the instrument design, the problems encountered and the development work required to bring them into operation, and their performance in service.
The AAOmega project replaces the two 2dF spectrographs, which are mounted on the top end of the Anglo Australian Telescope, with a bench mounted double beam spectrograph covering 370 to 950nm. The 2dF positioner, field plate tumbler mechanism, and fiber retractors will be retained. The new spectrograph will be fed by 392 fibers from either of the two 2dF field plates, or by the 512 fiber Spiral integral field unit, located at the Cassegrain focus. New instrument control electronics has also been designed to drive the spectrograph.
Stability will be improved by locating the spectrograph off the telescope, but the 2df fibers must be extended to thirty-eight metres length. Despite this, using fibers with improved characteristics, increased pupil diameter, volume phase holographic (VPH) gratings with articulated cameras, and more efficient coatings on optics we achieve a minimum twofold increase in throughput. We will also fit larger (4k x 2k pixel) detectors.
The spectrograph comprises: a F/3.15 Schmidt collimator, incorporating a dichroic beamsplitter; interchangeable VPH gratings; and articulating red and blue F/1.3 Schmidt cameras. The beamsplitter may be exchanged with others which cut off at different wavelengths. A full suite of VPH gratings are provided to cover resolution to 8000.
IRIS2 is a near-infrared imager and spectrograph based on a HAWAII1 HgCdTe detector. It provides wide-field (7.7’×7.7’) imaging capabilities at 0.4486”/pixel sampling, long-slit spectroscopy at λ/Δλ≈2400 in each of the J, H and K passbands, and the ability to do multi-object spectroscopy in up to three masks. These multi-slit masks are laser cut, and have been manufactured for both traditional multiple slit work (≈20-40 objects in a 3’×7.4’ field-of-view), multiple slit work in narrow-band filters (≈100 objects in a 5’×7.4’ field-of-view), and micro-hole spectroscopy in narrow-band filters allowing the observation of ≈200 objects in a 5’×7.4’ field.
AAOmega is a new spectrograph for the existing 2dF and SPIRAL multifibre systems on the Ango-Australian Telescope. It is a bench-mounted, dual-beamed, articulating, all-Schmidt design, using
volume phase holographic gratings. The wavelength range is 370-950nm, with spectral resolutions from 1400-10000. Throughput, spectral coverage, and maximum resolution are all more than doubled compared with the existing 2dF spectrographs, and stability is increased by orders of magnitude. These features allow entirely new classes of observation to be undertaken, as well as dramatically improving
existing ones. AAOmega is scheduled for delivery and commissioning in Semester 2005B.
The Anglo-Australian Observatory's (AAO's) FMOS-Echidna project is for the Fiber Multi-Object Spectroscopy system for the Subaru Telescope. It includes three parts: the 400-fiber positioning system, the focal plane imager (FPI) and the prime focus corrector. The Echidna positioner concept and the role of the AAO in the FMOS project have been described in previous SPIE proceedings. The many components for the system are now being manufactured, after prototype tests have demonstrated that the required performance will be achieved. In this paper, the techniques developed to overcome key mechanical and electronic engineering challenges for the positioner and the FPI are described. The major performance requirement is that all 400 science fiber cores and up to 14 guide fiber bundles are to be re-positioned to an accuracy of 10μm within 10 minutes. With the fast prime focus focal ratio, a close tolerance on the axial position of the fiber tips must also be held so efficiency does not suffer from de-focus. Positioning accuracy is controlled with the help of the FPI, which measures the positions of the fiber tips to an accuracy of a few μm and allows iterative positioning. Maintaining fiber tips sufficiently co-planar requires accurate control in the assembly of the several components that contribute to such errors. Assembly jigs have been developed and proven adequate for this purpose. Attaining high reliability in an assembly with many small components of disparate materials bonded together, including piezo ceramics, carbon fiber reinforced plastic, hardened steel, and electrical circuit boards, has entailed careful selection and application of cements and tightly controlled soldering for electrical connections.
A wide range of positioning technologies has been exploited to flexibly configure fiber ends on the focal surfaces of telescopes. The earliest instruments used manual plugging, or glued buttons on the focal plane. Later instruments have used robotic fisherman-round-the-pond probes and articulated armsto position fibres, each probe or arm operated by its own motors, or buttons on fiber ends moved by pick-and-place robotic positioners. A positioner using fiber spines incorporating individual actuators operating over limited patrol areas is currently being manufactured and a derivative proposed for future large telescopes. Other techniques, using independent agents carrying the fiber ends about the focal plane have been prototyped. We describe these various fiber positioning techniques and compare them, listing the issues associated with their implementation, and consider the factors which make each of them suitable for a given situation. Factors considered include: robot geometries; costs; inherent limits to the number of fibers; clustering of targets; serial and parallel positioning and reconfiguration times; adaptability to curved focal surfaces; the virtues of on-telescope versus off-telescope configuration of the field, and suitability for the various telescope foci. The design issues include selection of actuators and encoding systems, counterbalancing, configuration of fiber buttons and their associated grippers, interchanging field plates, and the need for fiber retractors. Finally we consider the competing technologies: fiber and reflective image slicer IFUs, multislit masks and reconfigurable slits.
The Fiber Multi-Object Spectrograph (FMOS) project is an Australia-Japan-UK collaboration to design and build a novel 400 fiber positioner feeding two near infrared spectrographs from the prime focus of the Subaru telescope. The project comprises several parts. Those under design and construction at the Anglo-Australian Observatory (AAO) are the piezoelectric actuator driven fiber positioner (Echidna), a wide field (30 arcmin) corrector and a focal plane imager (FPI) used for controlling the positioner and for field acquisition. This paper presents an overview of the AAO share of the FMOS project. It describes the technical infrastructure required to extend the single Echidna "spine" design to a fully functioning multi-fiber instrument, capable of complete field reconfiguration in less than ten minutes. The modular Echidna system is introduced, wherein the field of view is populated by 12 identical rectangular modules, each positioning 40 science fibers and 2 guide fiber bundles. This arrangement allows maintenance by exchanging modules and minimizes the difficulties of construction. The associated electronics hardware, in itself a significant challenge, includes a 23 layer PCB board, able to supply current to each piezoelectric element in the module. The FPI is a dual purpose imaging system translating in two coordinates and is located beneath the assembled modules. The FPI measures the spine positions as well as acquiring sky images for instrument calibration and for field acquisition. An overview of the software is included.
The Fibre Multi-Object Spectrograph (FMOS) is a second-generation common-use instrument of the Subaru telescope. Under an international collaboration scheme of Japan, UK, and Australia, a realistic design of FMOS has been already in completion, and the fabrications of hardware components have been in progress. We present the overall design details together with the special features of FMOS subsystems, such as the prime focus corrector, the prime focus mechanical unit including fiber positioners, and the near-infrared spectrograph, etc.
We describe the mechanical, optomechanical and thermal design and development of the IRIS2, an infrared imager and spectrograph for operation at the Cassegrain focus of the Anglo Australian Telescope. IRIS2 is reconfigured by four encoded worm driven wheels which carry slits and slit masks, filters, cold stops, and grisms, and a pupil imager. A detector translator provides fine focus.
The instrument is housed in a split, or dual, vacuum vessel. Helium cryo-coolers provide operational cooling, but to reduce turn around time during commissioning and maintenance a liquid nitrogen pre-cooling system has been implemented in the main vessel. The slit wheel is housed in a separate, smaller vessel, which may be thermally cycled when new slit masks are installed, while the rest of the instrument remains at operational temperature. The common plate between the vessels serves as the structural base on which the instrument is assembled. Matched trusses on opposite sides of the plate minimize the relative deflection between the slit wheel assembly and the spectrograph optics.
The repeatability of positioning of wheels carrying optical components can be critical for the performance of optical instruments. We present the cryogenic worm driven wheel positioning mechanism designed for Anglo-Australian Observatory's Infrared Imager and Spectrograph IRIS2. The mechanism, which was designed for a high vacuum environment and working temperature of 70-90K, utilized an aluminum worm and gearwheel, stepper motor and an encoding system based on infrared sensors. The mechanism has demonstrated repeatability of 1 arcmin.
2dF is a multi-object instrument mounted at prime focus at the AAT capable of spectroscopic analysis of 400 objects in a single 2 degree field. It also prepares a second 2 degree 400 object field while the first field is being observed. At its heart is a high precision robotic positioner that places individual fiber end magnetic buttons on one of two field plates. The button gripper is carried on orthogonal gantries powered by linear synchronous motors and contains a TV camera which precisely locates backlit buttons to allow placement in user defined locations to 10 (mu) accuracy. Fiducial points on both plates can also be observed by the camera to allow repeated checks on positioning accuracy. Field plates rotate to follow apparent sky rotation. The spectrographs both analyze light from the 200 observing fibers each and back- illuminate the 400 fibers being re-positioned during the observing run. The 2dF fiber position and spectrograph system is a large and complex instrument located at the prime focus of the Anglo Australian Telescope. The mechanical design has departed somewhat from the earlier concepts of Gray et al, but still reflects the audacity of those first ideas. The positioner is capable of positioning 400 fibers on a field plate while another 400 fibers on another plate are observing at the focus of the telescope and feeding the twin spectrographs. When first proposed it must have seemed like ingenuity unfettered by caution. Yet now it works, and works wonderfully well. 2dF is a system which functions as the result of the combined and coordinated efforts of the astronomers, the mechanical designers and tradespeople, the electronic designers, the programmers, the support staff at the telescope, and the manufacturing subcontractors. The mechanical design of the 2dF positioner and spectrographs was carried out by the mechanical engineering staff of the AAO and the majority of the manufacture was carried out in the AAO workshops.
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