47 research outputs found
Multiple rooks of chess - a generic integral field unit deployment technique
A new field re-configuration technique, Multiple Rooks of Chess (MRC), for
multiple deployable Integral Field Spectrographs has been developed. The method
involves mechanical geometry as well as an optimized deployment algorithm. The
geometry is found to be simple for mechanical implementation. The algorithm
initially assigns the IFUs to the target objects and then devises the movement
sequence based on the current and the desired IFU positions. The
reconfiguration time using the suitable actuators which runs at 20 cm/s is
found to be a maximum of 25 seconds for the circular DOTIFS focal plane (180 mm
diameter). The Geometry Algorithm Combination (GAC) has been tested on several
million mock target configurations with object-to-IFU ({\tau} ) ratio varying
from 0.25 to 16. The MRC method is found to-be efficient in target acquisition
in terms of field revisit and deployment time without any collision or
entanglement of the fiber bundles. The efficiency of the technique does not get
affected by the increase in number density of target objects. The technique is
compared with other available methods based on sky coverage, flexibility and
overhead time. The proposed geometry and algorithm combination is found to have
an advantage in all of the aspects.Comment: 18 Pages, 13 Figures, 1 Tabl
'MOHAWK' : a 4000-fiber positioner for DESpec
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.Comment: 10 pages, to appear in Proc. SPIE 844
'MOHAWK': A 4000-fiber positioner for DESpec
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 compara
Smart Focal Plane Technologies for VLT Instruments
As we move towards the era of ELTs, it is timely to think about the future
role of the 8-m class telescopes. Under the OPTICON programme, novel
technologies have been developed that are intended for use in multi-object and
integral-field spectrographs. To date, these have been targeted at instrument
concepts for the European ELT, but there are also significant possibilities for
their inclusion in new VLT instruments, ensuring the continued success and
productivity of these unique telescopes.Comment: 5 pages, to appear in the proceedings of the ESO Workshop "Science
with the VLT in the ELT era
GNOSIS: the first instrument to use fibre Bragg gratings for OH suppression
GNOSIS is a prototype astrophotonic instrument that utilizes OH suppression
fibres consisting of fibre Bragg gratings and photonic lanterns to suppress the
103 brightest atmospheric emission doublets between 1.47-1.7 microns. GNOSIS
was commissioned at the 3.9-meter Anglo-Australian Telescope with the IRIS2
spectrograph to demonstrate the potential of OH suppression fibres, but may be
potentially used with any telescope and spectrograph combination. Unlike
previous atmospheric suppression techniques GNOSIS suppresses the lines before
dispersion and in a manner that depends purely on wavelength. We present the
instrument design and report the results of laboratory and on-sky tests from
commissioning. While these tests demonstrated high throughput and excellent
suppression of the skylines by the OH suppression fibres, surprisingly GNOSIS
produced no significant reduction in the interline background and the
sensitivity of GNOSIS and IRIS2 is about the same as IRIS2. It is unclear
whether the lack of reduction in the interline background is due to physical
sources or systematic errors as the observations are detector noise-dominated.
OH suppression fibres could potentially impact ground-based astronomy at the
level of adaptive optics or greater. However, until a clear reduction in the
interline background and the corresponding increasing in sensitivity is
demonstrated optimized OH suppression fibres paired with a fibre-fed
spectrograph will at least provide a real benefits at low resolving powers.Comment: 15 pages, 13 figures, accepted to A
The Sydney-AAO Multi-object Integral field spectrograph (SAMI)
We demonstrate a novel technology that combines the power of the multi-object
spectrograph with the spatial multiplex advantage of an integral field
spectrograph (IFS). The Sydney-AAO Multi-object IFS (SAMI) is a prototype
wide-field system at the Anglo-Australian Telescope (AAT) that allows 13
imaging fibre bundles ("hexabundles") to be deployed over a 1-degree diameter
field of view. Each hexabundle comprises 61 lightly-fused multimode fibres with
reduced cladding and yields a 75 percent filling factor. Each fibre core
diameter subtends 1.6 arcseconds on the sky and each hexabundle has a field of
view of 15 arcseconds diameter. The fibres are fed to the flexible AAOmega
double-beam spectrograph, which can be used at a range of spectral resolutions
(R=lambda/delta(lambda) ~ 1700-13000) over the optical spectrum (3700-9500A).
We present the first spectroscopic results obtained with SAMI for a sample of
galaxies at z~0.05. We discuss the prospects of implementing hexabundles at a
much higher multiplex over wider fields of view in order to carry out
spatially--resolved spectroscopic surveys of 10^4 to 10^5 galaxies.Comment: 24 pages, 16 figures. Accepted by MNRA
SAMI - A new multi-object IFS for the Anglo-Australian telescope
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
Suppression of the near-infrared OH night sky lines with fibre Bragg gratings - first results
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.Comment: Accepted for publication in MNRAS. 15 pages, 18 figure