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The Visible and Infrared Survey Telescope for Astronomy (VISTA): Design, Technical Overview and Performance

Will Sutherland, Jim Emerson, Gavin Dalton, Eli Atad-Ettedgui, Steven Beard, Richard Bennett, Naidu Bezawada, Andrew Born, Martin Caldwell, Paul Clark, Simon Craig, David Henry, Paul Jeffers, Bryan Little, Alistair McPherson, John Murray, Malcolm Stewart, Brian Stobie, David Terrett, Kim Ward, Martin Whalley, Guy Woodhouse

arXiv:1409.4780v2astro-ph.IM

TL;DR

VISTA addresses the need for a high-throughput, wide-field near-infrared survey telescope with demanding optical alignment and thermal-background constraints. The paper reviews the telescope and VIRCAM’s design, construction, control systems, and performance, reporting excellent wide-field imaging, approximately 0.9 arcsec median delivered image quality, and improving reliability. Its scope includes operational artefacts and field-dependent optical effects that require calibration or data-quality handling.

  • Problem

    Wide-field near-infrared surveying requires a large field, efficient detectors, stringent alignment, and control of thermal radiation and stray light.

  • Method

    The paper presents an end-to-end overview of VISTA and VIRCAM, covering optical design, cold baffling, active optics, enclosure systems, construction, commissioning, and operations.

  • Results

    Approximately 0.9 arcsec median delivered image quality and technical time loss now comparable to the VLT characterize routine performance after reliability improvements.

  • Takeaways & Limitations

    VISTA with VIRCAM routinely delivers excellent wide-field images with sensitivity exceeding the original specifications.

  • Takeaways & Limitations

    Field distortion changes pixel scale and pixel solid angle toward the corners, so image processing must account for its effects on jitter offsets and photometry.

Abstract

from arXiv · show

The Visible and Infrared Survey Telescope for Astronomy (VISTA) is the 4-metre wide-field survey telescope at ESO's Paranal Observatory, equipped with the world's largest near-infrared imaging camera (VISTA IR Camera, VIRCAM), with 1.65 degree diameter field of view, and 67 Mpixels giving 0.6 square degrees active pixel area, operating at wavelengths 0.8 - 2.3 microns. We provide a short history of the project, and an overview of the technical details of the full system including the optical design, mirrors, telescope structure, IR camera, active optics, enclosure and software. The system includes several innovative design features such as the f/1 primary mirror, the dichroic cold-baffle camera design and the sophisticated wavefront sensing system delivering closed-loop 5-axis alignment of the secondary mirror. We conclude with a summary of the delivered performance, and a short overview of the six ESO public surveys in progress on VISTA.

1. Introduction

VISTA emerged from a UK consortium proposal for a Southern-hemisphere, 4-metre wide-field survey telescope and entered science operations at Paranal in 2009. The paper surveys its development, full-system design, performance, and operational context.

  • 1. Introduction: Wide-field imaging surveys provided the scientific and technological context for VISTA, following photographic surveys and later large-format CCD and near-infrared detector programs.Examples include SDSS, 2MASS, CFHTLS, and UKIDSS.
  • 1. Introduction: A consortium of 18 UK universities proposed a new 4-metre-class Southern-hemisphere survey telescope through the UK Joint Infrastructure Fund in late 1998.The proposal targeted multicolour imaging surveys.
  • 1. Introduction: Since 2009, VISTA and VIRCAM have operated at ESO’s Paranal Observatory as a 4-metre-aperture, 0.6 deg2 active-pixel-area near-infrared survey system.The paper describes this combination as the world’s fastest near-infrared survey system at the time discussed.
  • 1. Introduction: The paper provides an intermediate-detail overview of VISTA’s development, technical subsystems, on-sky performance, commissioning, operations, data processing, and archiving.It directs readers to more detailed subsystem papers where appropriate.

2. System Overview

VISTA is a compact Paranal-based, two-mirror survey telescope optimized for efficient wide-area near-infrared imaging. Its fast optics, active alignment, large VIRCAM camera, and cooled enclosure support high-throughput survey operations.

  • 2. System Overview: VISTA operates from a Southern Paranal site that shares the observatory’s weather conditions and complements major Northern-hemisphere wide-area surveys.The telescope is on a subsidiary summit approximately 1.5 km from the main Paranal summit.
  • 2. System Overview: The optical system is a fast two-mirror quasi-Ritchey-Chretien design with a 4.1 m f/1.0 primary and 1.24 m secondary producing an f/3.25 Cassegrain focus.The Cassegrain is the sole focal station and accommodates one large instrument at a time.
  • 2. System Overview: Active optics use an 84-point axial support for the primary mirror and a hexapod-mounted secondary mirror providing five-axis position control.A future 2400-fibre multi-object spectrograph was approved for installation after 2019.
  • 2. System Overview: VIRCAM is a 2.9-tonne, 2.8 m-long cryogenic camera with a 95 cm vacuum window, cold baffle, corrector lenses, filter wheel, and sixteen 2048^2 HgCdTe detectors.Its mean pixel scale is 0.339 arcsec.
  • 2. System Overview: A 19 m enclosure uses daytime air cooling, cooled electronic boxes, ventilation doors, and a movable windscreen to manage thermal and airflow conditions.The enclosure also includes a movable moonscreen for stray-light reduction.
  • 2. System Overview: The system targets efficient large-area surveys through a wide field, moderately large aperture, high detector quantum efficiency, and reduced observing overheads.At least 75% of observing time is dedicated to large-scale survey programs.

3. Basic requirements and design selection

VISTA’s design was selected by balancing aperture, field of view, detector economics, infrared wavelength coverage, and system complexity. The final f/1.0 two-mirror architecture replaced several alternatives because it reduced mass and enclosure requirements while enabling a wider near-infrared field.

  • 3. Basic requirements and design selection: The initial requirements specified an approximately 4 m aperture and baseline visible and near-infrared cameras with 0.3 deg2 and 36 Mpixel near-infrared capability.The baseline also included a 2 deg2, 450 Mpixel visible camera.
  • 3. Basic requirements and design selection: A Southern-hemisphere site was required because leading wide-field imaging systems then operating or under construction were concentrated in the Northern hemisphere.The Southern site was intended to provide survey complementarity.
  • 3. Basic requirements and design selection: The visible camera was not built because of funding constraints and anticipated access to the 2.6 m VST, although the telescope preserved capability for a visible camera with field diameter ≥2.1 degrees.The infrared camera took precedence in the original tradeoffs.
  • 3. Basic requirements and design selection: The design emphasized dedicated infrared and visible camera operation, assigning zero weight to additional foci, nighttime instrument changes, and mid-infrared operations to constrain cost.Spectroscopic capability was not an initial requirement.
  • 3. Basic requirements and design selection: Near-infrared and visible pixel scales were targeted near 0.33 arcsec and 0.25 arcsec respectively, reflecting the much higher cost of near-infrared detector pixels.Near-infrared detectors were estimated to cost approximately 20 times more per pixel than visible CCDs.
  • 3. Basic requirements and design selection: The infrared camera was required to cover Y through Ks bands with a long-wavelength cutoff of at least 2.3 µm, creating thermal-background and transmissive-optics challenges.A novel cold-baffle solution addressed the large-field infrared camera design challenge.
  • 3. Basic requirements and design selection: Three-mirror designs were rejected because they were more costly, had a large central obstruction, and made it difficult to accommodate a large infrared camera near the top-end.Alternative two-Nasmyth-focus and f/2.5 concepts were also studied before the final selection.
  • 3. Basic requirements and design selection: The selected f/1.0 design reduced moving mass from 250 tonnes to 90 tonnes, reduced enclosure size, and enabled a wider near-infrared field supporting an upgrade path to 16 detectors.It was selected over the f/2.5 baseline during the Phase-A downselect.

4. Optics Overview

VISTA combines a fast two-mirror telescope with a direct-focus infrared camera and cold-baffle architecture to deliver a wide, high-quality field. The design achieves strong optical performance while requiring distortion correction and careful control of alignment, baffling, and ghosting.

  • Optical design: VISTA uses a quasi-Ritchey-Chretien two-mirror design with an f/1.0 primary, 1.24 m secondary, and single f/3.25 Cassegrain focus.The direct Cassegrain focus supports the VIRCAM and potential future instruments.
  • Camera optics: The direct-focus camera uses three Infrasil corrector lenses to correct off-axis and chromatic aberrations and flatten the focal surface for flat detectors.The corrector avoids re-imaging optics and uses a single robust, large-format lens material.
  • Performance: The system delivers high throughput and excellent image quality across a 350 mm, 1.65 degree flat field without cryogenic mirrors or exotic lens materials.The design was jointly optimized across the telescope mirrors and VIRCAM corrector surfaces.
  • Performance: The modeled image quality is ≤0.36 arcsec at 50% EED and ≤0.68 arcsec at 80% EED across the field, with mean values of approximately 0.27 and 0.45 arcsec.These values assume perfect optical surfaces and alignment while allowing margin for several real-world degradations.
  • Optical limitations: Cubic distortion changes radial pixel scale by 2.4 percent and pixel solid angles by 3.2 percent from field centre to corner, requiring correction in data processing.The distortion does not affect image quality but changes jitter sampling and photometric uniformity.
  • Baffles and stray light: The cold and Narcissus baffles block direct sky and dome rays, with intentional corner vignetting rising to 1 percent to reduce baffle size and improve diffraction and throughput.The design also required careful control of scattered light and filter-reflection ghosts.

5. Mirrors and Mirror Support

VISTA’s mirrors combine fast hyperbolic optics with active pneumatic support and kinematic alignment systems designed to preserve figure and position under operational loads.

  • Primary mirror: The 4.10 m Zerodur primary is a 17 cm thick, 5.5-tonne solid meniscus with a 1.20 m central hole and 0.066 ppm/K thermal expansion.
  • Primary mirror: 35 nm rms wavefront error was achieved after polishing the highly aspheric hyperboloid through repeated wavefront-measurement and polishing cycles.
  • M1 supports: Six definers kinematically locate M1 relative to the Cell, with 30 N µm−1 axial stiffness and rigid-body rocking frequency above 15 Hz.
  • M1 supports: 81 individually software-controlled pneumatic axial actuators provide 5–990 N forces with approximately 1 N rms accuracy.
  • M1 supports: The support system balances changing wind and gravity loads at approximately 20 Hz and can redistribute force around a defective actuator.
  • M1 supports: Passive rest-pads and a spring-loaded restraint clamp protect M1 when supports are inactive, during parking, earthquakes, or major software faults.

6. Telescope Structure

The compact steel alt-azimuth structure prioritizes stiffness, tracking, fast offsets, maintainability, and active compensation of structural deflection, achieving strong measured telescope performance.

  • Design goals: The structure was designed for tracking, windshake rejection, low M1–camera deflection, fast offsetting, fault tolerance, and low-cost maintenance.
  • Structure and axes: Rolling-element bearings on all three rotation axes reduce maintenance and cost relative to hydrostatic bearings, while meeting performance specifications.
  • Structure and axes: Approximately 0.4 mm of altitude-dependent top-end deflection is compensated in closed loop by active optics and the M2 hexapod.
  • Structure and axes: The moving telescope mass is 90 tonnes, and the lowest natural frequency including the pier is 9.2 Hz.
  • Performance: Absolute pointing errors are approximately 1.0 arcsec rms for full-sky runs at altitude ≥25°, with closed-loop corrections normally applied at target acquisition.
  • Performance: Offset-and-settle times are approximately 7 s for 10 arcmin offsets and 10 s for degree-sized moves, without observed image oscillations.
  • Performance: No significant windshake was observed, while occasional electrical glitches and early force-control electronics problems were reported.

7. IR Camera

VIRCAM is a large, mechanically simplified near-infrared camera whose optical, thermal, and vacuum systems support a wide active field while limiting thermal background and operational downtime.

  • Camera overview: VIRCAM provides a 1.65° corrected field with 16 HgCdTe detectors totaling 67 Mpixels and 0.60 deg² active area.
  • Camera overview: The optical path uses a 95 cm vacuum window, three Infrasil corrector lenses, a filter, and sixteen detectors receiving the f/3.25 beam.
  • Camera overview: The camera has only one internal moving part, the filter wheel, reducing the observing loss associated with opening the cryostat after faults.
  • Thermal and vacuum design: A four-layer thermal design uses radiation shields near 240 K, a main cold structure near 100–110 K, and detector control near 72 K.
  • Thermal and vacuum design: Liquid-nitrogen precooling reduces camera cooldown from approximately 7 days to around 2.5 days using about 400 litres of LN2.
  • Vacuum window: The 95 cm, 79 mm thick Infrasil window was designed for atmospheric loads of 60 kN during testing and 45 kN at Paranal.
  • Vacuum window: Window production required three ingots because the first two cracked during cooling, while an edge break after flowout remained outside the final diameter.

7.3. Lens Barrel

VIRCAM’s lens barrel and cold-baffle systems address cryogenic alignment, stray light, detector filtering, and thermal background through compensated mounts and wavelength-selective baffling.

  • Lens barrel: The three-lens Infrasil corrector uses alignment shims to re-optimize spacings after polishing and thermally compensated mounts for cryogenic operation.
  • Lens barrel: Series-connected PTFE rods and springs maintain lens centration while avoiding the approximately 2 kN spring forces predicted for uncompensated mounts.
  • Lens barrel: Copper flexi-straps thermally couple each lens at 12 points, making temperature-dependent refractive-index variation nearly axisymmetric.
  • Filter wheel: The 1.37 m filter wheel has eight main positions, including a dark position, and accommodates seven sets of sixteen science filters.
  • Cold baffles: The cold baffle blocks detector heat radiation and reduces radiative heat loss from the window into the cryostat.
  • Cold baffles: Fully reflective baffles would add almost 15% emissivity at Ks because the baffles subtend around 15% of M2’s solid angle as viewed from the detectors.
  • Cold baffles: A dichroic coating reflects wavelengths above 4 µm while absorbing science wavelengths below 2.5 µm, balancing thermal rejection against infrared throughput.

7.6. Detectors

VIRCAM uses a 4 × 4 array of sixteen HgCdTe detectors totaling 67 Mpixels, with high near-infrared sensitivity and readout characteristics suited to survey imaging. Detector packaging, calibration, and electronics support efficient operation, while stable defects and non-linearity are handled in processing.

  • The sixteen 2048^2 HgCdTe detectors are arranged in a 4 × 4 grid with deliberate spacing for efficient sky tiling.
  • Near 90% quantum efficiency is measured from 1.0 to 2.35 µm, within an operating range of approximately 0.75–2.45 µm.
  • 67 Mpixels make VIRCAM the largest near-IR focal plane in astronomical use.
  • Typical defects include 1% dead or hot pixels and 2–4% non-linearity at 10,000 ADU, both addressed through calibration and pipeline processing.
  • The detectors use 256 parallel readout channels and a default 1-second readout, with standard double-correlated sampling.
  • 24 electrons readout noise with double-correlated sampling is well below sky noise for typical broadband exposures.

7.8. Autoguider and Wavefront sensors

VIRCAM’s auxiliary sensing and camera systems were developed and tested as an integrated telescope-camera assembly. Testing established the absence of severe camera-optics errors, while commissioning identified and corrected a camera-dependent astigmatism; subsequent operation was generally reliable.

  • The simulator reproduced the telescope’s f/3.25 beam and deliberate aberrations at near-axis and off-axis field locations.
  • Testing used a short-nose camera configuration with a smaller BK7 window and J-band observations for simplicity.
  • End-to-end simulator testing provided independent proof that the camera optics contained no severe error before shipment to Chile.
  • A ∼300 nm astigmatic term co-rotating with the camera was corrected quasi-automatically by active optics and an added software force term on M1.
  • The camera was transported fully assembled in a package exceeding 9 tonnes, with recorded shocks below 0.5 g during transport.
  • Since commissioning, VIRCAM has generally been reliable, with the cold baffle matching modeled Ks-band background and the thermal design supporting year-long cold intervals.

8. Active Optics

VISTA combines active control of the secondary and primary mirrors with distributed wavefront sensing to preserve image quality in an extremely alignment-sensitive f/1–f/3.25 optical system. Its closed-loop five-axis secondary collimation works during observing, supported by low-order sensors and an on-demand high-order sensor, though the system required substantial software development.

  • Active optics controls M2 in five axes and the M1 figure in up to 18 eigenmodes to maintain near-optimal image quality.
  • Closed-loop five-axis secondary collimation operates in parallel with observing, exceeding the usual three closed-loop M2 degrees of freedom.
  • The f/1 primary and f/3.25 system require approximately 3 µm M1–M2 spacing, 20 µm centration, and few-arcsecond tilt accuracy.
  • Two edge-of-field low-order sensors support quasi-continuous control and provide a usable star at almost any telescope pointing.
  • An on-demand beam-splitter cuboid produces paired intra- and extra-focal images without additional detectors or moving secondary-mirror parts.
  • A target-plane alignment condition enables near-optimal images across rotator angles when the M1 and camera axes pass through a ∼0.1 mm-radius bullseye.
  • The wavefront-sensing system required substantially more software manpower than initially estimated, despite working reliably after commissioning.

9. Enclosure and infrastructure

VISTA’s enclosure combines thermal control, ventilation, weather and stray-light protection, and infrastructure for maintaining the telescope and instruments. Its unusual below-floor rotation system and operational features supported strong enclosure performance, while later modifications addressed space and coating durability issues.

  • Enclosure functions: The enclosure protects the telescope from weather, windshake, stray light, and temperature changes while supporting daytime calibration.Its functions include weather protection, ventilation, thermal control, stray-light reduction, and a constant-brightness calibration surface.
  • Infrastructure: The enclosure comprises a rotating octagonal dome, a cylindrical concrete base, and an auxiliary building for coating, electrical, glycol, and compressed-air infrastructure.The base includes control, laboratory, electronics, helium-compressor, clean-room, lifting, and cooling facilities.
  • Dome systems: The dome provides a 5.4 m observing slit, six large ventilation doors, slanted louvres, and an adjustable porous windscreen for airflow and wind control.The windscreen adjusts from approximately 3 m to 7.5 m and has open slots covering about 20% of its area.
  • Dome design: The rotation rail and bogies are located below the observing floor, an unusual arrangement that increases dome height but provides several stated benefits.The passage introduces this placement as a distinctive dome feature before detailing its consequences.
  • Performance: The enclosure delivered smooth, quiet rotation, reliable slit-door operation, excellent ventilation, windshake protection, and effective cooling, although the cooling system was noisy.Only minor water leaks were reported and were believed to have been fixed.
  • Infrastructure changes: A 9 × 10 m auxiliary-building extension added a dedicated clean mirror-wash area and storage after the original facilities proved too small and cluttered.The original wash area was busy and difficult to keep optimally clean, while storage space was limited.
  • Mirror infrastructure: The initial silver coating degraded significantly after ∼1 year on M1, prompting aluminium recoating of both mirrors in April 2011.A later upgrade aimed to enable a longer-life silver coating with a Silicon Nitride protective overcoat.

10. Software and electronics

VISTA’s software reuses ESO VLT control software while adding VISTA-specific active-optics and enclosure modules. A layered architecture separates high-level observation control from real-time hardware control through dedicated LCUs and specialised controllers.

  • High-level software: VISTA largely reuses ESO VLT control software, preserving a similar operator interface while adding VISTA-specific active-optics and enclosure modules.The software is mainly written in C++ and runs on standard Linux PCs.
  • Control architecture: High-level software sends commands to Local Control Units rather than controlling hardware directly.The LCUs are diskless VXWorks computers programmed in C, with one independent unit per moving axis or subsystem.
  • Hardware control: Eleven LCUs control telescope axes, mirror supports, the M2 hexapod, VIRCAM, autoguiders, and low-order wavefront sensors.Additional customised electronics handle axis servo loops, M1 pneumatic supports, and M2 hexapod drives.
  • Observation control: Standard ESO BOB and P2PP tools manage observation blocks, while SADT creates overlapping survey pointings with guide and active-optics stars.SADT exports an XML file that populates observing blocks for survey operations.

11. Assembly and Commissioning

Assembly proceeded through staged construction, subsystem reviews, preliminary pointing tests, mirror installation, and commissioning with test and final cameras. The system showed no severe design flaws and achieved good performance, but commissioning lasted longer than planned because of numerous technical glitches.

  • Project development: The project began in April 2000, with the Phase A design completed in September 2001 and major contracts in place by early 2003.Mountain preparation, road construction, enclosure-base work, and subsystem design reviews occurred during 2003–4.
  • Early testing: A March 2007 ‘first glimmer’ using a 20 cm Maksutov telescope established a preliminary pointing model and helped tune control software before mirror installation.The temporary telescope viewed the sky through a pre-designed hole in the top-end structure.
  • Mirror installation: The secondary mirror arrived in May 2007 and the primary mirror in March 2008, followed by intensive on-sky commissioning.A test camera first supplied imaging and Shack-Hartmann wavefront sensing for pointing and active-optics lookup tables.
  • Commissioning outcome: Commissioning found no severe design flaws and demonstrated good system performance, but took significantly longer than planned because of many mundane technical glitches.Wiring and connection problems were among the notable causes of delay.

12. Observing, data processing and archiving

VISTA’s observing and archive workflow combines tiled pawprint acquisition, real-time quality assessment, calibrated reduction, catalogue generation, and long-term archive services. The system handles roughly 300 GB of data per night and supports cross-band and external-catalogue queries.

  • Observing strategy: Six offset pawprints provide gap-free sky coverage for one filled rectangular tile despite sparse detector placement.A tile includes a 1.475 × 1.017 degree central rectangle covered by at least two pawprints, plus two 0.092 deg edge stripes.
  • Data flow: Quick-look processing runs in real time at Paranal to assess data quality and detect problems rather than perform final reduction.The average data volume is ∼300 GB per night, now transferred over the internet via optical fibre.
  • Data processing: The reduction sequence applies dark, linearity, flat-field, sky-background, and destriping corrections after reset correction is handled automatically during sampling.Linearity uses dome-flat sequences, flat fields use twilight sky flats, and sky correction uses object-masked median operations.
  • Catalogue generation: Catalogues are generated and astrometrically and photometrically calibrated using 2MASS stars.This calibration follows the detector and image-correction stages.
  • Archiving: The VISTA Science Archive combines processed pawprints into tiles, associates detections across passbands, and constructs matches with catalogues such as SDSS and 2MASS.Its indexed SQL Server engine supports fast advanced queries.

13. System performance and public surveys

VISTA routinely delivers high-quality, reliable wide-field infrared imaging while supporting six public surveys spanning hemispheric, Galactic, Magellanic Cloud, and extragalactic science. Its performance includes sub-arcsecond image quality, accurate astrometry, calibrated photometry, and improving technical reliability, alongside documented detector and optical artefacts.

  • Performance summary: The system routinely delivers excellent wide-field images with sensitivity exceeding its original specifications.The paper attributes this notably to the high quantum efficiency of the detectors.
  • Performance summary: Median delivered image quality is ≈0.9 arcsec, with 10th-percentile values around 0.7 arcsec and sub-0.6 arcsec FWHM images not uncommon.These values are reported for images averaged across the full field.
  • Performance summary: Technical time loss improved from around 10% in the first year to a level comparable to the VLT.The improvement followed fixes and workarounds for system glitches, despite the vulnerability of a single-instrument telescope to instrument faults.
  • Astrometry and photometry: Astrometric residuals from the fifth-order distortion pattern are below 0.025 arcsec, while overlap comparisons show typical systematic offsets of ∼0.05 arcsec.The latter accuracy is described as sufficient for object matching to other wavebands and follow-up spectroscopy.
  • Astrometry and photometry: Archive photometry is calibrated in the native VISTA filter system relative to Vega using matching 2MASS stars and colour equations.The procedure is good for J, H, and Ks, but more uncertain at Z and Y because 2MASS extrapolation is required.
  • Public surveys: The six public surveys cover the Southern Hemisphere, Galactic bulge and plane, Magellanic Clouds, and nested extragalactic fields, with over 75% of observing time allocated to them during the first five years.Examples include VIKING over 1500 deg2, VIDEO over 12 deg2, and UltraVISTA as an ultra-deep single-tile survey.

14. Conclusions

VISTA’s design, construction, and performance are reviewed through science operations, highlighting its f/1.0 primary, cold-baffled infrared camera, and 5-axis closed-loop collimation. Its surveys are progressing and providing resources for selecting targets for major facilities.

  • VISTA’s design, construction and performance were traced from the April 2000 Phase A study to science operations beginning in October 2009.
  • The system’s novel features include an f/1.0 primary, a cold-baffled infrared camera with dichroic baffle coating, and 5-axis closed-loop collimation using dual off-axis curvature wavefront sensors.
  • VISTA with VIRCAM was expected to remain the world’s fastest wide-area near-infrared imaging system and the only such system in the Southern hemisphere until the predicted Euclid launch.
  • The six ESO public surveys were making steady progress, with emerging science results and importance for target selection for ALMA, SKA pathfinders, MOONS and JWST.
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