New optical fibre spectroscopic imaging devices for astronomy are being developed with very high throughput and excellent optical performance. Hector is a new generation multi-object Integral Field Spectroscopy (IFS) instrument that will utilise these high-performance fibre imaging devices called hexabundles". They are being developed in the Sydney Astrophotonic Instrumentation Laboratories (SAIL) at the University of Sydney. Hector is planned to be using these hexabundles on-sky by 2020 to carry out one of the world largest IFS galaxy surveys at the Anglo-Australian Telescope (AAT). The hexabundles contain up to 169 multi-mode Ceramoptec WF103/123um fibres per device, subtending a 26 arcseconds view with a spectrum at each fibre position for each galaxy. For astronomical instruments, optical fibres give significant flexibility in configuring a focal plane, but focal ratio degradation (FRD) can affect the performance of the optical fibres and directly influence the efficiency of any galaxy survey observed. Breakthroughs in glass fibre processing at SAIL have enabled hexabundles with minimal FRD - and therefore optimal performance. We will present the new developments in the SAIL labs and the resulting performance of new hexabundle devices for Hector and for other future applications.
Hector is a multi-IFU spectrograph in phase-A building for the Anglo-Australian Telescope (AAT) using fibers. Its goal is to observe 30,000 galaxies when fully complete. It is a follow up instrument of SAMI which has 13 IFUs 15" wide. The full project will have a 2 degree field corrector and at least 3 spectrographs. The IFUs are hexabundles 15" to 30" wide made of bare fibers with no buffer tightly packed and fused together to minimize the surface losses between their cores. Many different transparent spectrograph designs were studied covering a large parameter space. An important trade-off study was between the use of microlenses on the slit or just bare fibers. Microlenses have disadvantages but permit considerable simplification of the collimator by making the beam very slow. With microlenses, the collimator can be a unique spherical plano-convex lens significantly smaller than the mirror that would be needed in a reflective design. In the first part of the design, 26 different cameras where designed to cover the parameter space for 2k x 2k, 2k x 4k, or 4k x 4k detectors, and for 50, 75 or 100 micron fiber cores, with or without microlenses, with a triplet in the camera or a doublet plus singlet, and with a maximum wavelength of 1 or 1.05 microns. Not all combinations were designed but for each parameter there are at least two representative cameras with all other parameters identical. A preliminary cost estimate was made for the most promising designs which permitted to reduce them to 3 set of parameters for detailed designing, then to 2 with 4k x 4k detectors and 100 micron fiber cores. One design was made to be simple and low risk with only singlets in the collimator and cameras, the other complex with a mirror in the collimator, doublets and triplets, and innovations that could give better performance at a lower cost but with increased risk. For similar cost, the safe design has lower performances but also lower risks than the complex design. In the final stage of design, a trade-off hybrid design that keep the best of both ended being much cheaper, lower risk and with a shorter schedule than the complex design and with much better performances than the safe design. For this design, a model of the cost using lens diameter, glass cost and asphere complexity as the parameters was directly included in the Zemax Merit Function leading to significant cost improvement at fixed performances. The final design has 2 cameras covering 372 nm to 778 nm at an average resolution of 0.12 nm and able to accommodate about 1000 fibers of 1.6" core diameter. The collimator has 4 lenses and the cameras 4 and 5. There are no microlenses on the slit. The spectrograph can be upgraded with a third camera extending the coverage to 1000 nm.
The original optical fibre imaging bundles called `hexabundles' have proven to be exceptionally effective in the Sydney-AAO Multi-object IFS (SAMI) instrument, enabling one of the worlds largest IFS galaxy surveys<sup>5, 6</sup>. We are now developing an improved next-generation hexabundle design. These IFUs use a novel assembly technique developed in the Sydney Astrophotonic Instrumentation Laboratories (SAIL) at the University of Sydney, that enable very high fill-fraction and an evenly distributed, hexagonally packed, array of 217 fibre cores. These new hexabundles will see first light in 2019 on the new Hector-I instrument for the Anglo-Australian Telescope (AAT). The large number of fibre cores will measure spatially-resolved spectroscopy of galaxies out to 2 effective radii. The hexabundles are currently being prototyped, and characterised. The impact of the hexagonal packing of the fibre cores on Focal Ratio Degradation (FRD), total throughput of the device and overall performance will be presented.
Based on the success of the SAMI integral field spectrograph (IFS) instrument on the Anglo-Australian Telescope (AAT) the capacity for large IFS nearby galaxy surveys on the AAT is being substantially expanded with a new instrument called Hector. The high filling-fraction imaging fibre bundles ‘hexabundles’ of the type used on SAMI, are being enlarged to cover up to 30-arcsec diameter. The aim is to reach two effective radii on most galaxies, where the galaxy rotation curve flattens and >75% of the specific angular momentum of disk galaxies is accounted for. Driven by the key science case, Hector will have a 1.3A spectral resolution, enabling high-order stellar kinematics to be measured on a larger fraction of galaxies than with any other IFS instrument. Hector will be on sky in 2019.
The first module of Hector, Hector-I, will have 21 hexabundles and >42 sky fibres to observe 20 galaxies and a calibration star simultaneously. It consists of new blue and red-arm spectrographs that have been designed at the Australian Astronomical Observatory (AAO; now called AAO-Macquarie), coupled to the new hexabundles and robotic positioner from AAO-USydney (formerly the Sydney Astrophotonics Instrumentation Laboratory, SAIL) at Sydney University. A novel robotic positioning concept will compensate for varying telecentricity over the 2-degree-field of the AAT to recoup the 20% loss in light at the edge of the field. Hector-I will survey 15,000 galaxies. Additional modules in the future would result in 30,000 galaxies.
Hector will take integral field spectroscopy on galaxies with z<0.15 in the 4MOST WAVES-North and WAVES-South∗ regions. The WAVES data, which will come later, will give the environment metrics neces- sary to relate how local and global environments influence galaxy growth through gas accretion, star formation and spins measured with Hector. The WALLABY ASKAP† survey will trace HI gas across the Hector fields, which in combination with Hector will give a complete view of gas accretion and star formation.
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.
ULTIMATE is an instrument concept under development at the AAO, for the Subaru Telescope, which will have the unique combination of ground layer adaptive optics feeding multiple deployable integral field units. This will allow ULTIMATE to probe unexplored parameter space, enabling science cases such as the evolution of galaxies at z ~ 0:5 to 1.5, and the dark matter content of the inner part of our Galaxy. ULTIMATE will use Starbugs to position between 7 and 13 IFUs over a 14 × 8 arcmin field-of-view, pro- vided by a new wide-field corrector. All Starbugs can be positioned simultaneously, to an accuracy of better than 5 milli-arcsec within the typical slew-time of the telescope, allowing for very efficient re-configuration between observations. The IFUs will feed either the near-infrared nuMOIRCS or the visible/ near-infrared PFS spectrographs, or both. Future possible upgrades include the possibility of purpose built spectrographs and incorporating OH suppression using fibre Bragg gratings. We describe the science case and resulting design requirements, the baseline instrument concept, and the expected performance of the instrument.
Hector<sup>[1,2,3]</sup> will be the new massively-multiplexed integral field spectroscopy (IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the next main dark-time instrument for the observatory. Based on the success of the SAMI instrument, which is undertaking a 3400-galaxy survey, the integral field unit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is being improved to a new innovative design for Hector. The distribution of hexabundle angular sizes is matched to the galaxy survey properties in order to image 90% of galaxies out to 2 effective radii. 50-100 of these IFU imaging bundles will be positioned by ‘starbug’ robots across a new 3-degree field corrector top end to be purpose-built for the AAT. Many thousand fibres will then be fed into new replicable spectrographs. Fundamentally new science will be achieved compared to existing instruments due to Hector's wider field of view (3 degrees), high positioning efficiency using starbugs, higher spectroscopic resolution (R=3000-5500 from 3727-7761Å, with a possible redder extension later) and large IFUs (up to 30 arcsec diameter with 61-217 fibre cores). A 100,000 galaxy IFS survey with Hector will decrypt how the accretion and merger history and large-scale environment made every galaxy different in its morphology and star formation history. The high resolution, particularly in the blue, will make Hector the only instrument to be able to measure higher-order kinematics for galaxies down to much lower velocity dispersion than in current large IFS galaxy surveys, opening up a wealth of new nearby galaxy science.
Hector is an instrument concept for a multi integral-field-unit spectrograph aimed at obtaining a tenfold increase in
capability over the current generation of such instruments. The key science questions for this instrument 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. The baseline design for Hector incorporates multiple
hexabundle fibre integral-field-units that are each positioned using Starbug robots across a three-degree field at the
Anglo-Australian Telescope. The Hector fibres feed dedicated fixed-format spectrographs, for which the parameter space
is currently being explored.
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
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.
SAMI (Sydney-AAO Multi-object Integral field spectrograph) has the potential to revolutionise our understanding
of galaxies, with spatially-resolved spectroscopy of large numbers of targets. It is the first on-sky application of
innovative photonic imaging bundles called hexabundles, which will remove the aperture effects that have biased
previous single-fibre multi-object astronomical surveys. The hexabundles have lightly-fused circular multi-mode
cores with a covering fraction of 73%. The thirteen hexabundles in SAMI, each have 61 fibre cores, and feed
into the AAOmega spectrograph at the Anglo-Australian Telescope (AAT). SAMI was installed at the AAT in
July 2011 and the first commissioning results prove the effectiveness of hexabundles on sky. A galaxy survey of
several thousand galaxies to z 0.1 will begin with SAMI in mid-2012.
Optical fibre imaging bundles (hexabundles) are proving to be the next logical step for large galaxy surveys as they offer spatially-resolved spectroscopy of galaxies and can be used with conventional fibre positioners. Hexabundles have been effectively demonstrated in the Sydney-AAO Multi-object IFS (SAMI) instrument at the Anglo-
Australian Telescope<sup></sup>. Based on the success of hexabundles that have circular cores, we have characterised a bundle made instead from square-core fibres. Square cores naturally pack more evenly, which reduces the interstitial holes and can increase the covering, or filling fraction. Furthermore the regular packing simplifies the process of combining and dithering the final images. We discuss the relative issues of filling fraction, focal ratio degradation (FRD), and cross-talk, and find that square-core bundles perform well enough to warrant further development as a format for imaging fibre bundles.
We present an inexpensive (<US$500) and easily replicable integral field unit for use on small aperture telescopes.
Based on a commercial small spectrograph (SBIG Self-Guiding Spectrograph) and a 37 optical fibre bundle integral field
unit with each fibre having 50μm cores and a pitch of 125μm. It has an overall field-of-view of 40 arc seconds
(2.6arcsec/core), a resolution of 9Å from 3995Å to 7170Å and an average system efficiency of 9%, yielding a signal-tonoise
ratio of 10 for a 20min exposure of a 13mag/arcsec<sup>2</sup> source. Still in commissioning, we present first light
observations of Vega and M57.
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.
ERASMUS-F is a pathfinder study for a possible E-ELT 3D-instrumentation, funded by the German Ministry for
Education and Research (BMBF). The study investigates the feasibility to combine a broadband optical spectrograph
with a new generation of multi-object deployable fibre bundles. The baseline approach is to modify the spectrograph of
the Multi-Unit Spectroscopic Explorer (MUSE), which is a VLT integral-field instrument using slicers, with a fibre-fed
input. Taking advantage of recent developments in astrophotonics, it is planed to equip such an instrument with fused
fibre bundles (hexabundles) that offer larger filling factors than dense-packed classical fibres.
The overall project involves an optical and mechanical design study, the specifications of a software package for 3Dspectrophotometry,
based upon the experiences with the P3d Data Reduction Software and an investigation of the
science case for such an instrument. As a proof-of-concept, the study also involves a pathfinder instrument for the VLT,
called the FIREBALL project.
We demonstrate for the first time an imaging fibre bundle ("hexabundle") that is suitable for low-light applications in
astronomy. The most successful survey instruments at optical-infrared wavelengths today have obtained data on up to a
million celestial sources using hundreds of multimode fibres at a time fed to multiple spectrographs. But a large fraction
of these sources are spatially extended on the celestial sphere such that a hexabundle would be able to provide
spectroscopic information at many distinct locations across the source. Our goal is to upgrade single-fibre survey
instruments with multimode hexabundles in place of the multimode fibres. We discuss two varieties of hexabundles: (i)
closely packed circular cores allowing the covering fraction to approach the theoretical maximum of 91%; (ii) fused noncircular
cores where the interstitial holes have been removed and the covering fraction approaches 100%. In both cases,
we find that the cladding can be reduced to ~2μm over the short fuse length, well below the conventional ~10λ thickness
employed more generally. We discuss the relative merits of fused/unfused hexabundles in terms of manufacture and
deployment, and present our first on-sky observations.
New multi-core imaging fibre bundles - hexabundles - being developed at the University of Sydney will provide
simultaneous integral field spectroscopy for hundreds of celestial sources across a wide angular field. These are a
natural progression from the use of single fibres in existing galaxy surveys. Hexabundles will allow us to address
fundamental questions in astronomy without the biases introduced by a fixed entrance aperture. We have begun
to consider instrument concepts that exploit hundreds of hexabundles over the widest possible field of view. To
this end, we have characterised the performance of a 61-core fully fused hexabundle and 5 unfused bundles with
7 cores each. All fibres in bundles have 100 micron cores. In the fused bundle, the cores are distorted from a
circular shape in order to achieve a higher fill fraction. The unfused bundles have circular cores and five different
cladding thicknesses which affect the fill fraction. We compare the optical performance of all 6 bundles and find
that the advantage of smaller interstitial holes (higher fill fraction) is outweighed by the increase in FRD, crosstalk
and the poor optical performance caused by the deformation of the fibre cores. Uniformly high throughput
and low cross-talk are essential for imaging faint astronomical targets with sufficient resolution to disentangle
the dynamical structure. Devices already under development will have 100-200 unfused cores, although larger
formats are feasible. The light-weight packaging of hexabundles is sufficiently flexible to allow existing robotic
positioners to make use of them.