We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.
WEAVE is a new wide-field multi-object spectroscopy (MOS) facility proposed for the prime focus of the 4.2m William Herschel Telescope. The facility comprises a new 2-degree field-of-view Prime Focus Corrector (PFC) with a 1000-multiplex fibre positioner, a small number of individually deployable integral field units, and a large single integral field unit (IFU). The IFUs and the MOS fibres can be used to feed a dual-beam spectrograph that will provide full coverage of the majority of the visible spectrum in a single exposure at a spectral resolution of ~5000 or modest wavelength coverage in both arms at a resolution ~20000. In order to compensate the field rotation, the Prime Focus Rotator (PFR) is assembled in between the WEAVE Fiber Positioner (system that positions the fibers in the focal plane) and with the Central Can (contains the Prime Focus corrector optics) on the William Herschel Telescope (WHT). The Prime Focus Rotator must provide a rotation degree of freedom for the Fibre Positioner with a high bending stiffness (causing a deflection smaller than 0.008° between interface flanges) adding the minimum mass possible to the system (less than 700kg). This is easily identified as the main design driver to be considered. The Prime Focus Rotator positions the Fibre Positioner to an accuracy of 5 arcsec when tracking and guides all the fibres and other power and control lines through a cable wrap, for which the available space is limited. IDOM proposal to comply with these coupled requirements consists of an optimized structural system with a slightly preloaded cross roller bearing providing the highest possible stiffness to weight ratio. The rotation is driven by means of a direct drive motor powered by a servo drive. For the Cable Wrap, a compact design based on a concept previously developed by IDOM for the Folded Cassegrain Sets the GTC was proposed.
KEYWORDS: Control systems, Spectrographs, Databases, Telescopes, Human-machine interfaces, Data acquisition, Picture Archiving and Communication System, Calibration, Observatories, Sensors
WEAVE is the next-generation spectroscopic facility for the William Herschel Telescope (WHT) 1,2. WEAVE offers multi-object (1000 fibres) and integral-field spectroscopy at two resolutions (R ~ 5000, 20000) over a 2-deg field of view at prime focus and will mainly provide follow up of ground-based (LOFAR) and space-based (GAIA) surveys.
The Observatory Control System (OCS) is responsible for providing the software control and feedback framework through which WEAVE will be operated. This paper summarizes the design of the different OCS subsystems and the interfaces between them and other WEAVE components.
In the remainder of this paper, Section 2 outlines the other WEAVE systems with which the OCS interacts, Section 3 describes the system architecture, Section 4 comments on system-architecture decisions, Section 5 describes the main components of the OCS, Section 6 outlines the life-cycle of an OCS Observing Block and, finally, Section 7 gives an overview of the OCS testing plan.
KEYWORDS: Control systems, Device simulation, Telecommunications, LabVIEW, Telescopes, Interfaces, Systems modeling, Mathematical modeling, Picture Archiving and Communication System, Switches
When an alt-azimuth telescope is tracking at a specific field, it is necessary to use a de-rotator system to compensate the Earth’s rotation of the field of view. In order, to keep the telescope tracking the field of view selected, the instrument will need to a rotation system for compensating it [1]. The new WEAVE [2] two degrees field of view requires a new field de-rotator on the top-end of the telescope. The rotator system has been designed with a direct drive motor which eliminates the need for mechanical transmission elements such as gearboxes, speed reducers, and worm gear drives. This design is a huge advantage for the system performance and lifetime because it eliminates undesirable characteristics such as long-time drift, elasticity, and backlash. The hardware control system has been developed with a Rockwell servo-drive and controller. The rotator has to be controlled by the high-level software which is also responsible for the telescope control. This paper summarizes the model developed for simulating and the software which will be used to accept the rotator system. A performance study is also carried out to test the CIP (Common Industrial Protocol) for communications between the high-level software and the rotator hardware.
A method for fast identification of segments and alignment of the segmented mirrors has been developed and applied for the deformable mirror of the WHT AO system (NAOMI) and for the GTC 36-segment primary mirror. By moving each segment by a known but different amount and in a different direction it is possible to identify many segments simultaneously using a pattern-matching algorithm which finds spots that have moved by a segment-specific vector from one image to another. The method does not need any special optical setup. The applicability of the method for the segmented primary mirrors of future telescopes is discussed.
AF2+WYFFOS is the multi-object one degree field-of-view fibre-fed spectrograph at the prime focus of the 4.2 m
William Herschel Telescope (WHT) at the Observatorio del Roque de Los Muchachos (ORM). Demand for this has been
decreasing over the years due to its low overall throughput. Given the strategic importance of multi-fibre spectroscopy
for the WHT’s future, with the coming of WEAVE (the powerful next-generation multi-object spectrograph for the
WHT to be commissioned in 2017), during 2013 and 2014 ING staff carried out an end-to-end analysis of the reasons for
low throughput. The investigations addressed target-acquisition/positioning/guiding, focal-plane geometry, optical
transmission and overall system throughput measurements.
AF2+WYFFOS performance has improved significantly as a result of these enhancements, and it is ready now to
perform as a useful precursor and science test-bed for surveys with WEAVE, the new wide-field multi-object
spectroscopy facility at the WHT.
The Laser Traffic Control System (LTCS) is a software solution to the problem of laser beam avoidance, using priority
based collision resolution and an optional built-in laser shutter command interface. LTCS uses static site survey
information, dynamic telescope pointing and control data, and a configurable "rules" scheme, to monitor laser beam
geometry (Rayleigh and LGS) and warn or prevent undesired emission at participating institutions. LTCS was developed
for use on Mauna Kea in 2001, but through collaborative efforts with multiple institutions, has since been enhanced and
installed at several sites around the world. Functional implementations, either operational or in prototype form, exist for
Mauna Kea, La Palma, Cerro Pachon, Cerro Paranal, and Haleakala. Since the last LTCS SPIE update in 2006, many
important features have been added. There has also been some new site testing activity that has resulted in lessons
learned and the development of new analysis/test tools. Finally, an important lasing operations paradigm shift has
emerged on Mauna Kea and is anticipated for Paranal. The trend is clearly away from static collision priority rule
determination, toward dynamic "negotiated" priority determination. The implications of this paradigm shift, discussion
of forced collision test results and lessons learned, and a status update on development activities since the last update
will be presented in the paper.
The CANARY on-sky MOAO demonstrator is being integrated in the laboratory and a status update about its
various components is presented here. We also discuss the alignment and calibration procedures used to improve
system performance and overall stability. CANARY will be commissioned at the William Herschel Telescope at
the end of September 2010.
The Laser Guide Star commissioned in 2007 at the WHT on La Palma is based on Rayleigh backscattering of a 515 nm
beam provided by a diode pumped Q-switched doubled frequency Yb:YAG laser launched from behind the WHT
secondary mirror. At the time the laser beam is focused at a distance of 15km above the telescope ground and its power
just under 20W. With such a pulsed laser, careful fine tuning of the range gate system is essential to isolate the most
focused part of the LGS and eliminate parts of the laser plume which would degrade the Shack-Hartmann spots and
consequently AO correction. This is achieved by an electro-optic shutter using Pockels cells, triggered by a delay
generator synchronised on the laser pulses, and by spatial filters. Images of 0.15" resolution in J and H bands, very close
to expected performance, have been routinely taken as soon as the third and fourth commissioning runs. Here we show
the performance of the range gate system as measured and improved over the successive commissioning runs, as well as
the off sky and on sky calibration procedures of the LGS AO system.
KEYWORDS: Stars, Telescopes, Cameras, Adaptive optics, Electron multiplying charge coupled devices, Signal to noise ratio, Photons, Imaging systems, Laser guide stars, Control systems
Adaptive optics systems based on laser guide stars still need a natural guide star (NGS) to correct for the image motion
caused by the atmosphere and by imperfect telescope tracking. The ability to properly compensate for this motion using
a faint NGS is critical to achieve large sky coverage. For the laser guide system (GLAS) on the 4.2 m William Herschel
Telescope we designed and tested in the laboratory and on-sky a tip-tilt correction system based on a PC running Linux
and an EMCCD technology camera. The control software allows selection of different centroiding algorithms and loop
control methods as well as the control parameters. Parameter analysis has been performed using tip-tilt only correction
before the laser commissioning and the selected sets of parameters were then used during commissioning of the laser
guide star system. We have established the SNR of the guide star as a function of magnitude, depending on the image
sampling frequency and on the dichroic used in the optical system; achieving a measurable improvement using full AO
correction with NGSes down to magnitude range R=16.5 to R=18. A minimum SNR of about 10 was established to be
necessary for a useful correction. The system was used to produce 0.16 arcsecond images in H band using bright NGS
and laser correction during GLAS commissioning runs.
GLAS is an upgrade of the William Herschel Telescope's existing natural-guide-star (NGS) AO system NAOMI
to incorporate a 20-W Rayleigh laser guide star (LGS) projected to an altitude of 15 km. It is currently being
commissioned on-sky, and we review here the current status of the project. GLAS/NAOMI delivers dramatic
improvements in PSF in both the near-IR (AO-corrected FWHM close to the diffraction limit, >~ 0.15 arcsec)
and in the optical (factor of ~ 2 reduction in FWHM). The performance is similar to that with NGS, and is
consistent with predictions from modelling. The main advantage over NGS AO is the large gain in sky coverage
(from ~ 1% to ~ 100% at galactic latitude 40°). GLAS provides the first on-sky demonstration of closed-loop
ground-layer AO (GLAO), and is the first Rayleigh LGS AO system to be offered for general use, at any telescope.
The GLAS (Ground-layer Laser Adaptive-optics System) project is to construct a common-user Rayleigh laser beacon that will work in conjunction with the existing NAOMI adaptive optics system, instruments (near IR imager INGRID, optical integral field spectrograph OASIS, coronagraph OSCA) and infrastructure at the 4.2-m William Herschel Telescope (WHT) on La Palma. The laser guide star system will increase sky coverage available to high-order adaptive optics from ~1% to approaching 100% and will be optimized for scientific exploitation of the OASIS integral-field spectrograph at optical wavelengths. Additionally GLAS will be used in on-sky experiments for the application of laser beacons to ELTs. This paper describes the full range of engineering of the project ranging through the laser launch system, wavefront sensors, computer control, mechanisms, diagnostics, CCD detectors and the safety system. GLAS is a fully funded project, with final design completed and all equipment ordered, including the laser. Integration has started on the WHT and first light is expected summer 2006.
KEYWORDS: Stars, Cameras, Mirrors, Digital signal processing, Control systems, Adaptive optics, Computing systems, Signal to noise ratio, Signal processing, Image processing
The new ground layer adaptive optics system (GLAS) on the William Herschel Telescope (WHT) on La Palma will be based on the existing natural guide star adaptive optics system called NAOMI. A part of the new developments is a new control system for the tip-tilt mirror. Instead of the existing system, built around a custom built multiprocessor computer made of C40 DSPs, this system uses an ordinary PC machine and a Linux operating system. It is equipped with a high sensitivity L3 CCD camera with effective readout noise of nearly zero. The software design for the tip-tilt system is being completely redeveloped, in order to make a use of object oriented design which should facilitate easier integration with the rest of the observing system at the WHT. The modular design of the system allows incorporation of different centroiding and loop control methods. To test the system off-sky, we have built a laboratory bench using an artificial light source and a tip-tilt mirror. We present results of tip-tilt correction quality using different centroiding algorithms and different control loop methods at different light levels. This system will serve as a testing ground for a transition to a completely PC-based real-time control system.
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