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.
We present an update on the overall construction progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now that all the major fabrication contracts are in place. 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 effected 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 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. The project has experienced some delays in procurement and now has first light expected for the middle of 2019.
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.
The Observation Queue Scheduler (OQS) for WEAVE is described in this paper, with particular emphasis on the scheduling algorithm. WEAVE is the new 2-deg field of view multi-object (1000 multiplex) spectroscopy facility (R5000 and R20000) at the 4.2-m William Herschel Telescope. The OQS helps to maximize the scientific impact of WEAVE observations by optimising the schedule of the observing blocks, taking into account the science priority, required instrument configuration and observing constraints. On a nightly basis the OQS will assist the observer in creating a flexible queue of suitable observing blocks to be executed. It will be also possible to run a version of the OQS for extended periods of time to provide guidance on the longer-term planning of WEAVE surveys.
WEAVE is the next-generation spectroscopic facility for the William Herschel Telescope (WHT), offering multi-object (1000 fibres) and integral-field spectroscopy at two resolutions (R ~ 5000, 20000) over a 2-deg field of view at prime focus. WEAVE will (mainly) provide optical follow up of ground-based (LOFAR) and space-based (GAIA) surveys. First light is expected in mid 2018. Here, we describe the calibration unit, which will be adapted from an existing unit for the AF2+WYFFOS spectrograph (WEAVE's precursor) at the WHT. We summarise the results from a thorough characterisation of current performance (e.g. intensity, stability and focal-plane coverage of illumination as a function of lamp type and wavelength). We then set out our plans for upgrading the unit and its control systems to meet the WEAVE science and operational requirements. We conclude from this assessment that the upgraded AF2+WYFFOS calibration unit will meet the requirements for WEAVE. The design of the WEAVE calibration unit is now complete.
We present the Final Design of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), together with a status update on the details of manufacturing, integration and the overall project schedule now that all the major fabrication contracts are in place. We also present a summary of the current planning behind the 5-year initial phase of survey operations. 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 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. The project is now in the manufacturing and integration phase with first light expected for early of 2018.
We present an integrated end-end simulation of the spectral images that will be obtained by the weave spectrograph, which aims to include full modelling of all effects from the top of the atmosphere to the detector. These data are based in input spectra from a combination of library spectra and synthetic models, and will be used to provide inputs for an endend test of the full weave data pipeline and archive systems, prior to 1st light of the instrument.
In this paper, we detail the manufacturing process for the lenses that will constitute the new two-degree field-of-view Prime Focus Corrector (PFC) for the 4.2m William Herschel Telescope (WHT) optimised for the upcoming WEAVE Multi-Object Spectroscopy (MOS) facility. The corrector, including an Atmospheric Dispersion Corrector (ADC), is made of six large lenses, the largest being 1.1-meter diameter. We describe how the prescriptions of the optical design were translated into manufacturing specifications for the blanks and lenses. We explain how the as-built glass blank parameters were fed back into the optical design and how the specifications for the lenses were subsequently modified. We review the critical issues for the challenging manufacturing process and discuss the trade-offs that were necessary to deliver the lenses while maintaining the optimal optical performance. A short description of the lens optical testing is also presented. Finally, the subsequent manufacturing steps, including assembly, integration, and alignment are outlined.
The scientific productivity of complex instrumentation strongly depends on the availability of data-reduction pipelines. In the case of AF2+WYFFOS, the multi-object one-degree field-of-view fibre-fed spectrograph at the 4.2 m William Herschel Telescope (WHT), the full scientific exploitation of the data has often been slowed down because of the non-availability of a pipeline. A dedicated pipeline has been developed to overcome this. Running in IDL, it performs full reduction of AF2+WYFFOS data: fibre-to-fibre sensitivity corrections, fibre tracing, wavelength calibration, optimal extraction, sky subtraction.
The ING runs the highly-productive 4.2-mWilliam Herschel Telescope (WHT) and 2.5-m Isaac Newton Telescope (INT) on La Palma in the Canary Islands. I give an overview of the current operational model, commenting on how the model has evolved since the mid-1980s, and on the experience gained with e.g. instrument development; adaptive-optics/LGS deployment; hosting visiting instruments; scheduling; fault handling; student vs staff support of observers; and performance monitoring.
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.
WEAVE is an approved massive wide field multi-object optical spectrograph (MOS) currently entering its build phase, destined for use on the 4.2-m William Herschel Telescope (WHT). It will be commissioned and begin survey operations in 2017. This paper describes the core processing system (CPS) system being developed to process the bulk data flow from WEAVE. We describe the processes and techniques to be used in producing the scientifically validated 'Level 1' data products from the WEAVE data. CPS outputs will include calibrated one-d spectra and initial estimates of basic parameters such as radial velocities (for stars) and redshifts (for galaxies).
We present an overview of and status report on the WEAVE next-generation spectroscopy facility for the William
Herschel Telescope (WHT). WEAVE principally targets optical ground-based follow up of upcoming 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 integral field units, or a single large IFU for each observation. The fibres are fed to a single
spectrograph, with a pair of 8k(spectral) x 6k (spatial) pixel cameras, 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. The project is now in the final
design and early procurement phase, with commissioning at the telescope expected in 2017.
We present the preliminary design of the WEAVE next generation spectroscopy facility for the William Herschel
Telescope (WHT), principally targeting optical ground-based follow up of upcoming ground-based (LOFAR) and spacebased
(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 or up to 30
integral field units for each observation. The fibres are fed to a single spectrograph, with a pair of 8k(spectral) x 6k
(spatial) pixel cameras, 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.
The user support model at the ING telescopes has evolved considerably over the last 20 years, mainly in response
to improvements in the reliability and efficiency of the observing systems. Observers at the 4.2-m William Her-
schel Telescope (WHT) currently get first-night (afternoon + evening) support from staff support astronomers,
and all-night support from telescope operators. As of 2010, the telescope operators also provide engineering sup-
port at night. Observers at the 2.5-m Isaac Newton Telescope (INT) get first-night support from student support
astronomers, but no night-time operator/engineering support. Feedback from observers indicates a continuing
high level of satisfaction with the support they receive.
Wide-field multi-object spectroscopy is a high priority for European astronomy over the next decade. Most 8-10m
telescopes have a small field of view, making 4-m class telescopes a particularly attractive option for wide-field
instruments. We present a science case and design drivers for a wide-field multi-object spectrograph (MOS) with
integral field units for the 4.2-m William Herschel Telescope (WHT) on La Palma. The instrument intends to take
advantage of a future prime-focus corrector and atmospheric-dispersion corrector (Agocs et al, this conf.) that will
deliver a field of view 2 deg in diameter, with good throughput from 370 to 1,000 nm. The science programs cluster into
three groups needing three different resolving powers R: (1) high-precision radial-velocities for Gaia-related Milky Way
dynamics, cosmological redshift surveys, and galaxy evolution studies (R = 5,000), (2) galaxy disk velocity dispersions
(R = 10,000) and (3) high-precision stellar element abundances for Milky Way archaeology (R = 20,000). The multiplex
requirements of the different science cases range from a few hundred to a few thousand, and a range of fibre-positioner
technologies are considered. Several options for the spectrograph are discussed, building in part on published design
studies for E-ELT spectrographs. Indeed, a WHT MOS will not only efficiently deliver data for exploitation of
important imaging surveys planned for the coming decade, but will also serve as a test-bed to optimize the design of
MOS instruments for the future E-ELT.
We present two conceptual optical designs for a new refractive corrector for the prime focus of the 4.2m William
Herschel Telescope, optimised to allow wide-field multi-object spectroscopy. The proposed designs satisfy the
demanding requirement that the PSF be smaller than 0.5 arcsec (80% encircled energy) over a two degree FOV and a
wavelength range of 370 - 1000 nm. We discuss the specifications and describe the design process for the correctors,
which also act as atmospheric dispersion correctors (ADC). The designs we present form the basis of a realistic
manufacturable system.
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.
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.
ACAM will be mounted permanently at a folded-Cassegrain focus of the WHT. It can be used for broad-band
or narrow-band optical imaging of an 8.3-arcmin field, or for low-resolution (R ~ 500) spectroscopy. As the
only wide-field optical imager at the Cassegrain focus, ACAM is designed to cater for a broad range of science
programmes, including those requiring rapid response (e.g. gamma-ray bursts, supernovae) or scheduling at
awkward intervals (e.g. successive exoplanet transits), and those requiring the use of many filters (e.g. Hα
mapping of low-redshift galaxies). The imaging requirements alone are demanding, requiring a trade-off between
field of view (> 8 arcmin), PSF (<< seeing), wavelength coverage (UV to near-IR), throughput (> 0.8) and
radius-dependent wavelength shift (< 0.5 nm, for narrow-band filters). We discuss how the trade-off was effected
and present the final optical and mechanical design, and the expected performance.
The Nasmyth Adaptive Optics for Multi-purpose Instrumentation (NAOMI) on the William Herschel Telescope (WHT) has been developed recently into a common user AO (Adaptive Optics) instrument to accompany OASIS (Optically Adaptive System for Imaging Spectroscopy), a multi-slit spectrograph and INGRID (Isaac Newton Group Red Imaging Device) an Infrared detector. The most recent changes are the addition of an Atmospheric Dispersion Corrector (ADC) to be used for the optical wavelengths and a Dichroic Changer mechanism to select either a pass band or IR light for the Universal Science Ports (UPS).
Future developments on NOAMI are planned as it is due to house the GLAS WFS (Ground Layer Adaptive optics System Wave Front Sensor), a wave front sensor for the future Laser Guide Star (LGS) system to be installed on the WHT in 2006.
This paper describes the changes made with respect to the science ports and the changes to be made for the GLAS WFS; focusing on the GLAS WFS and the optical path and interface to the NAOMI adaptive optics system.
KEYWORDS: Telescopes, Adaptive optics, Control systems, Electronics, Sensors, Servomechanisms, Space telescopes, Imaging systems, Temperature metrology, Domes
The William Herschel Telescope (WHT) has an adaptive optics (AO) suite consisting of the AO system NAOMI, near IR imager INGRID, optical field spectrograph OASIS and coronagraph OSCA. GRACE (GRound based Adaptive optics Controlled Environment) is a dedicated structure at a Nasmyth focus designed to facilitate routine AO use by providing a controlled environment for the instrument system. However, GRACE is not just a building; it is all of the systems associated with providing the controlled environment, especially the control of air quality, temperature and flow. A key concern was that adding the GRACE building to the Nasmyth platform would not adversely change the telescope performance. This paper gives the background to GRACE, its specification and design, the building construction and installation, the environmental controls installed and their performance, the services provided, the effect of the new structure on telescope performance, the results of the project, including the effect having a controlled environment on AO performance and its planned use for a Rayleigh laser guide star system.
NAOMI is the AO system of the 4.2-m William Herschel Telescope on La Palma. It delivers near-diffraction-limited images in the IR, and a significantly improved PSF at optical wavelengths. The science cameras currently comprise an IR imager (INGRID), an optical integral-field spectrograph (OASIS) and a coronagraph which may be placed in the light path to either instrument. 19 science programmes were observed during 2002-3. Observing overheads are small, with as much as 60% of the night spent integrating on science targets. In late 2004 this year, the WFS will be equipped with a low-noise L3 CCD, giving a gain of a factor of 2 in S:N for faint guide stars. A Rayleigh laser guide star is under development, with first light expected summer 2006, providing a unique facility: AO-corrected optical integral-field spectroscopy anywhere on the northern sky.
Using a unique combination of empirical data collected simultaneously by the science camera (INGRID) and the wave front sensor in NAOMI plus the same night profiles of the turbulent layers measured by SLODAR, we discuss the accuracy of the analytic approach to modelling of AO performance. The WFS frames recorded for different atmospheric conditions allow us to make a detailed investigation of the influence of a restricted field of view and sampling of the WFS on the accuracy of the centre of gravity and its propagation to the residual variance. The predictions of Strehl, FWHM and FWHE derived for NAOMI+INGRID using our analytic approach are compared with on-sky performance demonstrated during the commissioning and science observations with NAOMI.
The Nasmyth Adaptive Optics Multipurpose Instrument (NAOMI) is the adaptive optics (AO) platform on the 4.2m William Herschel Telescope (WHT) at the Isaac Newton Group of Telescopes (ING). Until recently NAOMI has been concentrating on near infrared observations using the Isaac Newton Group Red Imaging Device (INGRID). Recent developments have added an extra optical port to NAOMI. The observer can now rapidly switch between infrared and optical instrumentation during AO observing, making the system more appealing for visiting instruments.
To allow for the operation of the common user optical spectrograph OASIS, a new optical path was created around the existing NAOMI optics. Various mechanisms were also added to the whole optical system. The OASIS beam was reshaped to f/20. The original optical/IR beam remains unchanged at f/16, and forms a new universal science port (USP). The existing Nasmyth Calibration Unit (NCU) has been replaced with a new design. This new NCU has multiple fibre-fed light sources that include continuum and arc lamps. The intensity of light can be individually adjusted via computer control. A new acquisition camera is mounted such that it can be used simultaneously with the spectral lamps. Software upgrades now allow faster deformable mirror calibration. A moveable mirror is used to select which science port will receive the light. Enhancements to the NAOMI AO system are discussed in this paper and suggestions for possible future upgrades.
By incorporating spatial coverage with the spectral dimension,
integral-field spectroscopy is uniquely suited for exploiting the
capabilities of adaptive optics (AO) systems. OASIS is a lenslet-based integral-field spectrograph designed to perform high-resolution
observations on AO-corrected sources, operating at visible
wavelengths. This instrument was commissioned at the William Herschel
Telescope, La Palma, in July 2003 to work with the ING's AO system,
NAOMI. Here we present an overview of the capabilities of the
OASIS+NAOMI system, and show results obtained using this technique. The science presented here is a small preview of what will be possible for a large number of objects when the GLAS laser guide system is operational.
NAOMI (Nasmyth Adaptive Optics for Multi-purpose Instrumentation) is a recently completed and commissioned astronomical facility on the 4.2m William Herschel Telescope. The system is designed to work initially with Natural Guide Stars and also to be upgradeable for use with a single laser guide star. It has been designed to work with both near infrared and optical instrumentation (both imagers and spectrographs). The system uses a linearised segmented adaptive mirror and dual-CCD Shack-Hartmann wavefront sensor together with a multiple-DSP real-time processing system. Control system parameters can be updated on-the-fly by monitoring processes and the system can self-optimize its base optical figure to compensate for the optical characteristics of attached scientific instrumentation. The scientific motivation, consequent specification and implementation of NAOMI are described, together with example performance data and information on future upgrades and instrumentation.
Telescope performance can be characterised by two kinds of metric: those which reflect scientific productivity (e.g. citation impact) and those which monitor technical aspects of performance e.g. shutter open time and instrument throughput, assumed to impinge on eventual scientific productivity. These metrics can be used to guide an observatory’s investment of limited operational resources in such a way as to maximise long-term scientific productivity.
We review metrics used at the 4.2-m William Herschel Telescope (WHT) on La Palma, and identify key performance indicators.
Telescope performance can be characterized by a number of metrics e.g. mirror reflectivity, seeing, readout noise, observing overheads. In deciding where to invest limited operational resources to improve performance, one needs to predict the impact of given enhancements on scientific productivity. E.g. for the same cost, is it more important to reduce CCD readout noise by a factor of 2, or to improve instrument throughput by 30%? Knowing the mix of programs at a given telescope, and the dependence of signal-to-noise on the various parameters, the % gain in scientific productivity can be predicted for a given % improvement in any parameter, allowing optimal investment of the operational budget. We describe operational metrics used to monitor the performance of the 4.2-m William Herschel Telescope on La Palma, and give examples of current and planned enhancements which have been prioritized by comparing predicted gains and costs. These enhancements should deliver a total gain approximately 30% in productivity, equivalent to approximately 100 extra observing nights per year.
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