MAVIS passed the Preliminary Design Review in March 2023 and kick started its phase C early June. We are aiming at a Final Design Review in December 2024. I will report on the state of MAVIS design, as well as general project updates, schedule, procurement, risks. We are working on early procurement (Long Lead Item review held on October 2023) as well as on a number of prototype activities I will report on.
Despite Python being the preferred programming language of choice for most astronomers, building or extending data reduction pipelines in the language can be problematic. A common approach is to write Python functions or classes as wrappers, calling individual pipeline recipes underneath, but this does not scale well with increasing pipeline complexity. Data management is also fraught since housekeeping code must be written to carefully handle input and output products between recipes. We have addressed these issues by creating an extensible pipeline development framework that leverages the Python bindings for the ESO Common Pipeline Library (PyCPL) toolkit. Pipeline recipes can be defined in a regulated manner using existing ESO pipeline recipes or new Python recipes compliant with ESO standards. Users can easily build their own pipeline workflows for execution by the PyCPL companion package PyEsorex. The ability to define Python recipes offers a powerful means to extend existing ESO pipelines or develop entirely new pipelines. An overview of the framework is presented along with an illustrative MUSE pipeline workflow.
The ESO Common Pipeline Library (CPL) and High-Level Data Reduction Library (HDRL) together form a comprehensive, efficient and robust software toolkit for data reduction pipelines. They were developed in C for reasons of efficiency and speed, however, with the community’s preference towards Python for algorithm prototyping and data reduction, there is a need for access from Python. PyCPL and PyHDRL provide this, making it possible to run existing CPL data reduction recipes from Python as well as developing new recipes in Python. These new recipes are built using the PyCPL and PyHDRL libraries, which provide idiomatic Python interfaces to CPL and HDRL while allowing users to take advantage of the scientific Python ecosystem. PyCPL and PyHDRL are already being used to prototype recipes for the MAVIS instrument pipeline and have been used to develop an extensible pipeline development framework. Here we describe their design, implementation and usage.
We outline the two workflows used for the reduction of science data from the MCAO Assisted Visible Imager and Spectrograph (MAVIS), and describe the inputs, outputs, and static calibration files required for each process of the workflows. Ronchi masks and pinhole masks are used in combination to determine the geometry of the spectrograph slices, and wavelength calibrations will be enhanced with Etalons. The precision required for the Imager astrometry is obtained by the mid-spatial frequency distortion calibrations. To prototype these complex methods and to test the efficacy of pixel tables and error handling we are using the new ESO PyCPL and PyHDRL libraries, which provide an interface to ESO’s classic Common Pipeline Library (CPL) in the Python ecosystem.
MAVIS, the Multi-Conjugate Adaptive Optics Assisted Visible Imager and Spectrograph, is the world’s first facility-grade visible MCAO instrument, currently in the final design phase for ESO’s VLT. The AO system will feed an imager and an integral field spectrograph, with 50% sky coverage at the Galactic pole. MAVIS has unique angular resolution and sensitivity at visible wavelengths, and is highly complementary to both JWST and ELTs. We describe both instruments in detail and the broad range of science cases enabled by them. The imager will be diffraction-limited in V, with 7.36 mas per pixel covering a 30” FOV. A set of at least 5 broad-band, 3 medium-band and 16 narrow-band filters will provide imaging from u to z. The spectrograph uses an advanced image slicer with a selectable spatial sampling of 25 or 50 mas to provide integral field spectroscopy over a FOV of 2.5′′ × 3.6′′, or 5′′ × 7.2′′. The spectrograph has two identical arms each covering half the FOV. Four interchangeable grisms allow spectroscopy with R=4,000 to R=15,000, from 370 – 935 nm.
MAVIS is the next instrument to go on the VLT. It is an imager and IFU spectrograph fed by Multi-Conjugate Adaptive Optics. It is presently in Phase-B (Preliminary Design Phase). The spectrograph will be preceded by an Integral Field Unit (IFU) with a choice of fields of 3.6"x2.5" with square spaxels 25 mas wide or 7.2"x5.0" with 50 mas spaxels. Two sets of interchangeable fore-optics permit the change of field size. The IFU will be based on the concept of Advanced Image Slicer present in many instruments as MUSE and KMOS on the VLT. In the present design, the field is first split in 2 and each subfield is imaged on a slicer mirror array made of long thin mirrors that slice the field into 50 images and send them in different directions to be reimaged side by side on the slit by another mirror array. A final and third mirror array on the slit places the pupil of each slice image at the right place in the spectrograph. Toroidal surfaces in each fore optics arm give the 2X magnification needed in the spectral direction. Each of the 2 subfields has its own lens spectrograph with a 9k x 9k detector and 4 interchangeable grisms giving a resolution from 5000 to 15000. High transmission glasses are used to ensure excellent throughput across the full wavelength range into the blue, covering 370- 950 nm. The slice width being near the diffraction limit, special consideration was given to the diffraction focal ratio degradation.
MAVIS is the world’s first facility-grade visible MCAO instrument, currently under development for the VLT. The AO system will feed an imager and an integral field spectrograph, with 50% sky coverage at the Galactic pole. MAVIS has unique angular resolution and sensitivity at visible wavelengths, and is highly complementary to both JWST and ELTs. We describe both instruments in detail and the broad range of science cases enabled by them. The imager will be diffraction-limited in V, with 7.36 mas per pixel covering a 30” FOV. A set of at least 7 broad-band and 15 narrow-band filters will provide imaging from u to z. The spectrograph uses an advanced image slicer with a selectable spatial sampling of 25 or 50 mas to provide integral field spectroscopy over a FOV of 2.5”x3.6”, or 5”x7.2”. The spectrograph has two identical arms each covering half the FOV. Four interchangeable grisms allow spectroscopy with R=5,000 to R=15,000, from 380-950 nm.
The TAIPAN instrument is installed on the UK Schmidt Telescope and has undergone 5 years of commissioning and verification. It utilizes the Starbug fibre positioning technology and is a proof-of-concept design for future Starbug-based instrumentation. The installation and commissioning of this new technology has provided opportunities to understand the Starbugs in detail. Science verification began in 2021 and has demonstrated the sub-10 minute configuration time, efficiency of small field ‘tweaks’ to correct for atmospheric refraction, and positioning accuracy of the Starbugs. Lessons learned from the commissioning of TAIPAN will directly impact future projects in which the Starbug technology is proposed, such as MANIFEST and FOBOS.
SkyHopper is a proposed CubeSat mission to simultaneously observe 4 bands in the wavelength range from 0.8 to 1.7 micron. The light is captured by a telescope with a 100 mm × 200 mm primary and a field of view of 0.6° × 2.6°. A preliminary definition (phase B) of the optical telescope assembly for the mission is now completed. It is designed to make high precision intensity measurements of every object in the field of view. This brought a series of constraints to avoid stray light. Different optical designs were studied. A Kösters prism is used to split the light into 4 bands on a 2k x 2k detector. The telescope design is based on a 3 mirror anastigmat with additional lenses to provide good image quality in the final focal plane for all bands and also in the intermediate focal plane and the pupil plane where cold stops are needed. Aberrations and vignetting of the prism had to be removed. Science applications include exoplanet transits in front of low-mass stars, rapid Infrared follow-up of Gamma Ray Bursts and exploring the Cosmic Infrared Background.
KEYWORDS: Visible radiation, James Webb Space Telescope, Observatories, Adaptive optics, Large telescopes, Spectrographs, Spatial resolution, Hubble Space Telescope, Telescopes
A consortium of several Australian and European institutes – together with the European Southern Observatory (ESO) – has initiated the design of MAVIS, a Multi-Conjugate Adaptive Optics (MCAO) system for the ground- based 8-m Very Large Telescope (VLT). MAVIS (MCAO-assisted Visible Imager and Spectrograph) will deliver visible images and integral field spectrograph data with 2-3x better angular resolution than the Hubble Space Telescope, making it a powerful complement at visible wavelengths to future facilities like the space-based James Webb Space Telescope and the 30 to 40m-class ground-based telescopes currently under construction, which are all targeting science at near-infrared wavelengths. MAVIS successfully passed its Phase A in May 2020. We present the motivations, requirements, principal design choices, conceptual design, expected performance and an overview of the exciting science enabled by MAVIS.
The MCAO Assisted Visible Imager and Spectrograph (MAVIS) is a facility-grade visible MCAO instrument, currently under development for the Adaptive Optics Facility at the VLT. The adaptive optics system will feed both an imager and an integral field spectrograph, with unprecedented sky coverage of 50% at the Galactic Pole. The imager will deliver diffraction-limited image quality in the V band, cover a 30" x 30" field of view, with imaging from U to z bands. The conceptual design for the spectrograph has a selectable field-of-view of 2.5" x 3.6", or 5" x 7.2", with a spatial sampling of 25 or 50 mas respectively. It will deliver a spectral resolving power of R=5,000 to R=15,000, covering a wavelength range from 380 - 950 nm. The combined angular resolution and sensitivity of MAVIS fill a unique parameter space at optical wavelengths, that is highly complementary to that of future next-generation facilities like JWST and ELTs, optimised for infrared wavelengths. MAVIS will facilitate a broad range of science, including monitoring solar system bodies in support of space missions; resolving protoplanetary- and accretion-disk mechanisms around stars; combining radial velocities and proper motions to detect intermediate-mass black holes; characterising resolved stellar populations in galaxies beyond the local group; resolving galaxies spectrally and spatially on parsec scales out to 50 Mpc; tracing the role of star clusters across cosmic time; and characterising the first globular clusters in formation via gravitational lensing. We describe the science cases and the concept designs for the imager and spectrograph.
The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. We are now close to solving this problem for the first time with the PRAXIS instrument. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background, and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. The OH lines are suppressed by a factor of ~1000, leading to a reduction of the integrated background of a factor ≈9. A future upgrade to multicore fibre Bragg gratings will further increase this reduction. PRAXIS has had two commissioning runs, with a third commissioning run planned for July 2019, which will be presented at the conference. PRAXIS has a measured throughput of ≈20 %, demonstrating high efficiency in an OH suppression instrument for the first time. Science verification observations of Seyfert galaxies demonstrate the potential of OH suppression.
The Starbug technology1 developed by AAO-MQ allows fibre positioners to be built with large multiplexing capabilities. The Starbug robots are positionable individually and in parallel, which results in significant configuration time improvements over what can be achieved by single-arm pick and place robots. Their design allows the Starbugs to carry a complex payload, and their movement mechanism and vacuum adhesion to the instrument's glass field plate at the telescope's focal plane means that they can be used to position fibres on a non-planar surface.
The Huntsman Telescope* is a wide field imager based on the successful Dragonfly Telescope concept.1 It consists of an array of co-aligned telephoto DSLR lenses with cooled CCD cameras. The ten 140 mm apertures have a combined collecting area equivalent to a 0.5 m class telescope but have lower stray light levels than a typical telescope of this size.1, 2 Its primary purpose is low surface brightness imaging of nearby galaxies, and it also observes exoplanet transits and other optical transients.
Given enough exposure time the sensitivity of an astronomical instrument is ultimately limited by systematic errors, and the dominant source of systematic errors for most optical/infrared instruments is imperfect sky subtraction. In turn the limiting factor for sky subtraction accuracy is frequently the accuracy of flat field calibration, making these calibrations critical to the overall performance of the instrument.
The Anglo-Australian Telescope’s fibre-fed spectrographs, and in particular the multi-object integral field spectrograph SAMI, are reaching sky subtraction systematic error limits and this has motivated an upgrade to the calibration systems. SAMI and its successor HECTOR are calling for sky subtraction accuracies of at least 0.25%, with a goal of 0.06%, an improvement of 4-17 times.
Flat field calibrations can use dark sky, twilight sky or an illuminated screen (‘dome flats’). For multi-object spectrographs such as SAMI recalibration is required for each set of targets. This makes twilight flats impractical as it is impossible to guarantee the availability of clear twilight sky for every configuration. The dark night sky is the ideal calibrator, but the long integration times required result in onerous overheads. What is needed is a dome flat field system accurate enough to replace dark sky flats. To achieve this we have replaced both the existing screen and its illumination system.
The effective throughput of optical fibres feeding an instrument vary slightly as their paths change, so high accuracy demands that calibration be done with the telescope in the same position as the science observations. We have applied two new screens to the dome windscreen, either side of the aperture, so that it is possible to move a screen in front of the telescope while in any position.
There are two distinct purposes for flat fielding: photometric calibration and sky subtraction. For an ideal telescope these are equivalent but the existence of stray light creates subtle differences, and this has implications for design of the screen. When the primary purpose is sky subtraction the highest possible accuracy will be achieved with a screen that illuminates the telescope from all the directions that the night sky does. Consequently our screens match the size, shape and relative position of the windscreen aperture. The screens are implemented as Avian D diffuse reflectance coating applied to the dome windscreen itself. Avian D is highly Lambertian, has high reflectance and is durable enough for the observatory environment.
The screens must be illuminated uniformly, in terms of spatial variations of both total intensity and spectral energy distribution (SED). We use an array of lamps around the end of the telescope tube. By using LEDs we are able to customise the SED and obtain a signal to noise ratio that is more consistent across wavelengths than is possible with traditional quartz tungsten halogen flat field lamps.
We present the design of the new flat field calibration system, explain the main design decisions and discuss results from commissioning. These include comparisons between dome and dark sky flats, and measurements of the sky subtraction accuracy.
The TOLIMAN space telescope is a low-cost, agile mission concept dedicated to astrometric detection of exoplanets in the near-solar environment, and particularly targeting the Alpha Cen system. Although successful discovery technologies are now populating exoplanetary catalogs into the thousands, contemporary astronomy is still poorly equipped to answer the basic question of whether there are any rocky planets orbiting any particular star system. Toliman will make a first study of stars within 10 PC of the sun by deploying an innovative optical and signal encoding architecture that leverages the most promising technology to deliver data on this critical stellar sample: high precision astrometric monitoring. Here we present results from the Foundational Mission Study, jointly funded by the Breakthrough Prize Foundation and the University of Sydney which has translated innovative underlying design principles into error budgets and potential spacecraft systems designs.
VELOCE is an IFU fibre feed and spectrograph for the AAT that is replacing CYCLOPS2. It is being constructed by the AAO and ANU. In this paper we discuss the design and engineering of the IFU/fibre feed components of the cable. We discuss the mode scrambling gain obtained with octagonal core fibres and how these octagonal core fibres should be spliced to regular circular core fibres to ensure maximum throughput for the cable using specialised splicing techniques. In addition we also describe a new approach to manufacturing a precision 1D/2D array of optical fibres for some applications in IFU manufacture and slit manufacture using 3D printed fused silica substrates, allowing for a cheap substitute to expensive lithographic etching in silicon at the expense of positional accuracy. We also discuss the Menlo Systems laser comb which employs endlessly-singlemode fibre to eliminate modal noise associated with multimode fibre transmission to provide the VELOCE spectrograph with a stable and repeatable source of wavelength calibration lines.
The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS uses the same fibre Bragg gratings as GNOSIS in its first implementation, and will exploit new, cheaper and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of ∼ 1000, and the expected increase in the
signal-to-noise in the interline regions compared to GNOSIS is a factor of ∼ 9 with the GNOSIS gratings and a
factor of ∼ 17 with the new gratings.
PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS (a retrofit to an existing instrument that was not OH-Suppression optimised) due to high thermal emission, low spectrograph transmission and detector noise. PRAXIS has extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and the fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS has low detector noise through the use of a Hawaii-2RG detector, and a high throughput through a efficient VPH based spectrograph. PRAXIS will determine the absolute level of the interline continuum and enable observations of individual objects via an IFU. In this paper we give a status update and report on acceptance tests.
Atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph, currently in the build-phase, which is fed by a fibre array that removes the OH background. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS will use the same fibre Bragg gratings as GNOSIS in the first implementation, and new, less expensive and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of ~1000, and the expected increase in the signal-to-noise in the interline regions compared to GNOSIS is a factor of ~ 9 with the GNOSIS gratings and a factor of ~ 17 with the new gratings. PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS due to high thermal emission, low spectrograph transmission, and detector noise. PRAXIS will have extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and a fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS will achieve low detector noise through the use of a Hawaii-2RG detector, and a high throughput through an efficient VPH based spectrograph. The scientific aims of the instrument are to determine the absolute level of the interline continuum and to enable observations of individual objects via an IFU. PRAXIS will first be installed on the AAT, then later on an 8m class telescope.
KEYWORDS: Space telescopes, Eye, Galactic astronomy, Telescopes, Image sensors, Control systems, Space operations, Signal to noise ratio, Light scattering, Stars
The Australian Space Eye is a proposed astronomical telescope based on a 6U CubeSat platform. The Space Eye will exploit the low level of systematic errors achievable with a small space based telescope to enable high accuracy measurements of the optical extragalactic background light and low surface brightness emission around nearby galaxies. This project is also a demonstrator for several technologies with general applicability to astronomical observations from nanosatellites. Space Eye is based around a 90 mm aperture clear aperture all refractive telescope for broadband wide field imaging in the i' and z' bands.
PRAXIS is a second generation instrument that follows on from GNOSIS, which was the first instrument using fibre
Bragg gratings for OH suppression to be deployed on a telescope. The Bragg gratings reflect the NIR OH lines while
being transparent to the light between the lines. This gives in principle a much higher signal-noise ratio at low resolution
spectroscopy but also at higher resolutions by removing the scattered wings of the OH lines. The specifications call for
high throughput and very low thermal and detector noise so that PRAXIS will remain sky noise limited even with the
low sky background levels remaining after OH suppression. The optical and mechanical designs are presented. The
optical train starts with fore-optics that image the telescope focal plane on an IFU which has 19 hexagonal microlenses
each feeding a multi-mode fibre. Seven of these fibres are attached to a fibre Bragg grating OH suppression system while
the others are reference/acquisition fibres. The light from each of the seven OH suppression fibres is then split by a
photonic lantern into many single mode fibres where the Bragg gratings are imprinted. Another lantern recombines the
light from the single mode fibres into a multi-mode fibre. A trade-off was made in the design of the IFU between field of
view and transmission to maximize the signal-noise ratio for observations of faint, compact objects under typical seeing.
GNOSIS used the pre-existing IRIS2 spectrograph while PRAXIS will use a new spectrograph specifically designed for
the fibre Bragg grating OH suppression and optimised for 1.47 μm to 1.7 μm (it can also be used in the 1.09 μm to 1.26
μm band by changing the grating and refocussing). This results in a significantly higher transmission due to high
efficiency coatings, a VPH grating at low incident angle and optimized for our small bandwidth, and low absorption
glasses. The detector noise will also be lower thanks to the use of a current generation HAWAII-2RG detector.
Throughout the PRAXIS design, from the fore-optics to the detector enclosure, special care was taken at every step along
the optical path to reduce thermal emission or stop it leaking into the system. The spectrograph design itself was
particularly challenging in this aspect because practical constraints required that the detector and the spectrograph
enclosures be physically separate with air at ambient temperature between them. At present, the instrument uses the
GNOSIS fibre Bragg grating OH suppression unit. We intend to soon use a new OH suppression unit based on multicore
fibre Bragg gratings which will allow an increased field of view per fibre. Theoretical calculations show that the gain in
interline sky background signal-noise ratio over GNOSIS may very well be as high as 9 with the GNOSIS OH
suppression unit and 17 with the multicore fibre OH suppression unit.
KEYWORDS: Collimation, Microlens, Signal to noise ratio, Spectral resolution, Fiber Bragg gratings, Performance modeling, Near field, Telescopes, Spectrographs, Systems modeling
Photonic lanterns are an important enabling technology for astrophotonics with a wide range of potential applications including fibre Bragg grating OH suppression, integrated photonic spectrographs and fibre scramblers for high resolution spectroscopy. The behaviour of photonic lanterns differs in several important respects from the conventional fibre systems more frequently used in astronomical instruments and a detailed understanding of this behaviour is required in order to make the most effective use of this promising technology. To this end we have undertaken a laboratory study of photonic lanterns with the aim of developing an empirical model for the mapping from input to output illumination distributions. We have measured overall transmission and near field output light distributions as a function of input angle of incidence for photonic lanterns with between 19 and 61 cores. We present the results of this work, highlight the key differences between photonic lanterns and conventional fibres, and illustrate the implications for instrument design via a case study, the design of the PRAXIS spectrograph. The empirical photonic lantern model was incorporated into an end-to-end PRAXIS performance model which was used to optimise the design parameters of the instrument. We describe the methods used and the resulting conclusions. The details of photonic lantern behaviour proved particularly important in selecting the optimum on sky field of view per fibre and in modelling of the instrument thermal background.
The KOALA optical fibre feed for the AAOmega spectrograph has been commissioned at the Anglo-Australian
Telescope. The instrument samples the reimaged telescope focal plane at two scales: 1.23 arcsec and 0.70 arcsec per
image slicing hexagonal lenslet over a 49x27 and 28x15 arcsec field of view respectively. The integral field unit consists
of 2D hexagonal and circular lenslet arrays coupling light into 1000 fibres with 100 micron core diameter. The fibre run
is over 35m long connecting the telescope Cassegrain focus with the bench mounted spectrograph room where all fibres
are reformatted into a one-dimensional slit. Design and assembly of the KOALA components, engineering challenges
encountered, and commissioning results are discussed.
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.
CYCLOPS2 is an upgrade for the UCLES high resolution spectrograph on the Anglo-Australian Telescope, scheduled for commissioning in semester 2012A. By replacing the 5 mirror Coud´e train with a Cassegrain mounted fibre-based image slicer CYCLOPS2 simultaneously provides improved throughput, reduced aperture losses and increased spectral resolution. Sixteen optical fibres collect light from a 5.0 arcsecond2 area of sky and reformat it into the equivalent of a 0.6 arcsecond wide slit, delivering a spectral resolution of R= 70000 and up to twice as much flux as the standard 1 arcsecond slit of the Coud´e train. CYCLOPS2 also adds support for simultaneous ThAr wavelength calibration via a dedicated fibre. CYCLOPS2 consists of three main components, the fore-optics unit, fibre bundle and slit unit. The fore optics unit incorporates magnification optics and a lenslet array and is designed to mount to the CURE Cassegrain instrument interface, which provides acquisition, guiding and calibration facilities. The fibre bundle transports the light from the Cassegrain focus to the UCLES spectrograph at Coud´e and also includes a fibre mode scrambler. The slit unit consists of the fibre slit and relay optics to project an image of the slit onto the entrance aperture of the UCLES spectrograph. CYCLOPS2 builds on experience with the first generation CYCLOPS fibre system, which we also describe in this paper. We present the science case for an image slicing fibre feed for echelle spectroscopy and describe the design of CYCLOPS and CYCLOPS2.
GNOSIS has provided the first on-telescope demonstration of a concept to utilize complex aperioidc fiber Bragg
gratings to suppress the 103 brightest atmospheric hydroxyl emission doublets between 1.47-1.7 μm. The unit is
designed to be used at the 3.9-meter Anglo-Australian Telescope (AAT) feeding the IRIS2 spectrograph. Unlike
previous atmospheric suppression techniques GNOSIS suppresses the lines before dispersion. We present the
results of laboratory and on-sky tests from instrument commissioning. These tests reveal excellent suppression
performance by the gratings and high inter-notch throughput, which combine to produce high fidelity OH-free
spectra.
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.
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.
Fibre Bragg grating (FBG) OH suppression is capable of greatly reducing the bright sky background seen by near infrared
spectrographs. By filtering out the airglow emission lines at high resolution before the light enters the spectrograph this
technique prevents scattering from the emission lines into interline regions, thereby reducing the background at all wavelengths.
In order to take full advantage of this sky background reduction the spectrograph must have very low instrumental
backgrounds so that it remains sky noise limited. Both simulations and real world experience with the prototype GNOSIS
system show that existing spectrographs, designed for higher sky background levels, will be unable to fully exploit the sky
background reduction. We therefore propose PRAXIS, a spectrograph optimised specifically for this purpose.
The PRAXIS concept is a fibre fed, fully cryogenic, fixed format spectrograph for the J and H-bands. Dark current
will be minimised by using the best of the latest generation of NIR detectors while thermal backgrounds will be reduced
by the use of a cryogenic fibre slit. Optimised spectral formats and the use of high throughput volume phase holographic
gratings will further enhance sensitivity. Our proposal is for a modular system, incorporating exchangeable fore-optics
units, integral field units and OH suppression units, to allow PRAXIS to operate as a visitor instrument on any large
telescope and enable new developments in FBG OH suppression to be incorporated as they become available. As a high
performance fibre fed spectrograph PRAXIS could also serve as a testbed for other astrophotonic technologies.
GNOSIS is an OH suppression unit to be used in conjunction with existing spectrographs. The OH suppression
is achieved using fibre Bragg gratings (FBGs), and will deliver the darkest near-infrared background of any
ground-based instrument. Laboratory and on-sky tests demonstrate that FBGs can suppress OH lines by 30dB
whilst maintaing > 90% throughput between the lines, resulting in a 4 mag decrease in the background.
In the first implementation GNOSIS will feed IRIS2 on the AAT. It will consist of a seven element lenslet
array, covering 1.4" on the sky, and will suppress the 103 brightest OH lines between 1.47 and 1.70 μm. Future
upgrades will include J-band suppression and implementation on an 8m telescope.
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 present FLEX, an instrument to demonstrate the power of fibre Bragg grating OH suppression. This ground
breaking technology promises great gains in sensitivity for near infrared instrumentation and the time is now
right for a pioneer instrument to prove the effectiveness of the technique. Our proposal is for an adaptive optics
fed integral field unit for an 8 metre class telescope. We envisage a 61 element IFU with 0.22" sampling and a
2.2" field of view. J and H-band OH suppression units would cleanly suppress the atmospheric emission lines,
effectively lowering the sky background by 3 or 4 magnitudes respectively. The capabilities of FLEX will make
it ideal for deep Epoch of Reionisation studies, as well as studies of star formation at z~1-4. To enable rapid
and economical deployment FLEX would use an existing near infrared spectrograph with R ≈ 1000 and employ
facility adaptive optics.
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.
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.
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.
FLEX is a concept for a fully OH suppressed near infrared integral field spectrograph, being developed at the AAO.
FLEX will be the first instrument to employ fibre Bragg gratings for OH suppression, a radical new technology which
cleanly suppresses the atmospheric OH emission lines at 30dB whilst maintaining a high overall throughout of ~90%. In
this paper we simulate the expected performance of FLEX, and discuss its impact on the science case. FLEX will
effectively make the near-infrared sky 4 mags fainter in the H band and 3 mags fainter in the J band, offering
unprecedentedly deep views of the near-infrared Universe. The FLEX concept is optimised for the identification of the
sources of first light in the Universe - high redshift galaxies or quasars identified through Lyman-alpha emission or a
Lyman break in the continuum spectrum. As such it will consist of a 2x2" integral field unit, composed of a 61 lenslet
hexagonal array, feeding an existing moderate spectral resolution spectrograph, via an OH-suppression unit. We have
simulated the performance of FLEX and show that it can provide robust identification of galaxies at the epoch of
reionisation. A FLEX-like instrument on an ELT could measure the ionisation and enrichment of the inter-galactic
medium beyond a redshift of 7 via metal absorption lines.
The burgeoning field of astrophotonics explores the interface between astronomy and photonics. Important applications include photonic OH suppression at near-infrared wavelengths, and integrated photonic spectroscopy. These new photonic mechanisms are not well matched to conventional multi-mode fibre bundles, and are best fed with single or few-mode fibres. We envisage the largest gains in astrophotonics will come from instruments that operate with single or few mode fibres in the diffraction limited or near diffraction limited regime. While astronomical instruments have largely solved the problem of coupling light into multi-mode fibres, this is largely unexplored territory for few-mode and single-mode fibres. Here we describe a project to explore this topic in detail, and present initial results on coupling light into single and few-mode fibres at the diffraction limit. We find that fibres with as few as ~ 5 guided modes have qualitatively different behaviour to single-mode fibres and share a number of the beneficial characteristics of multi-mode fibres.
In recent years, a great deal of emphasis has been placed on achieving the diffraction limit with large aperture telescopes. For a well matched focal-plane instrument, the diffraction limit provides the highest possible angular resolution and sensitivity per pixel. But it offers another key advantage as we now show. Conventionally, as the telescope aperture D grows, the instrument size grows in proportion to D, and the cost increases as D2 or faster. However, an instrument that operates at the diffraction limit can break the trend of spiralling costs. In traditional instruments, the light must pass through a succession of large lenses, mirrors and gratings, making it difficult to conserve the integrity of such a small psf. An alternative approach, as we now show, is to couple the diffraction-limited beam directly into an integrated photonic spectrograph operating in low-order modes.
DAzLE is a near infrared narrowband differential imager being built by the Institute of Astronomy, Cambridge, in collaboration with the Anglo-Australian observatory. It is a special purpose instrument designed with a sole aim; the detection of redshifted Lyman-α emission from star forming galaxies at z>7. DAzLE will use pairs of high resolution (R=1000) narrowband filters to exploit low background 'windows' in the near infrared sky emission spectrum. This will enable it to reach sensitivities of ~2 x 10-21Wm-2, thereby allowing the detection of z>7 galaxies with star formation rates as low as a few solar masses per year. The design of the instrument, and in particular the crucial narrowband filters, are presented. The predicted performance of DAzLE, including the sensitivity, volume coverage and expected number counts, is discussed. The current status of the DAzLE project, and its projected timeline, are also presented.
The Cambridge Infra-red Panoramic Survey Spectrograph (CIRPASS) is described. This near-infrared (NIR) spectrograph has been used on the 8m Gemini-South Telescope, the 3.9m Anglo-Australian Telescope (AAT) and the 4.2m William Herschel Telescope (WHT). Its performance in both integral field mode and multi-object mode is discussed and some scientific highlights are presented. A multi-IFU system, which is currently under construction, is also described.
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