The Visible and Infrared Survey Telescope for Astronomy \(VISTA\)
Total Page:16
File Type:pdf, Size:1020Kb
A&A 575, A25 (2015) Astronomy DOI: 10.1051/0004-6361/201424973 & c ESO 2015 Astrophysics The Visible and Infrared Survey Telescope for Astronomy (VISTA): Design, technical overview, and performance Will Sutherland1, Jim Emerson1, Gavin Dalton2;3, Eli Atad-Ettedgui4;5, Steven Beard4, Richard Bennett4, Naidu Bezawada4, Andrew Born4, Martin Caldwell2, Paul Clark6, Simon Craig7, David Henry4, Paul Jeffers7, Bryan Little4, Alistair McPherson8, John Murray4, Malcolm Stewart9, Brian Stobie4, David Terrett2, Kim Ward2, Martin Whalley2, and Guy Woodhouse2 1 School of Physics and Astronomy, Queen Mary University of London, Mile End Rd, London E1 4NS, UK e-mail: [email protected] 2 RAL Space, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK 3 Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK 4 UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK 5 Senior Optical Consultant, 9 Abercorn Road, Edinburgh EH8 7DD, UK 6 Centre for Astronomical Instrumentation, University of Durham, South Road, Durham DH1 3LE, UK 7 National Solar Observatory, NSO/DKIST, 950 N. Cherry Avenue, Tucson, AZ 85719, USA 8 SKA Organisation, Jodrell Bank Observatory, Lower Withington, Macclesfield, Cheshire SK11 9DL, UK 9 Solaire Systems, 55/10 Bath Street, Edinburgh EH15 1HE, UK Received 12 September 2014 / Accepted 15 December 2014 ABSTRACT The Visible and Infrared Survey Telescope for Astronomy (VISTA) is the 4-m 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 diam- eter field of view, and 67 Mpixels giving 0.6 deg2 active pixel area, operating at wavelengths 0:8−2:3 µm. 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 mir- ror, 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. Key words. telescopes – instrumentation: photometers – instrumentation: miscellaneous – instrumentation: detectors 1. Introduction telescope, sited in the southern hemisphere and mainly dedicated to multicolour imaging surveys; this was named the Visible and Wide-field imaging surveys have long formed a cornerstone of Infrared Survey Telescope for Astronomy (VISTA). Since 2009, observational astronomy, from the photographic Schmidt tele- the VISTA telescope and its near-infrared camera (VIRCAM) scope surveys from Palomar, the UK Schmidt Telescope and have been in science operations at ESO’s Paranal Observatory: ESO in the 1950–1980 era. After the advent of large-format the product of 4 m aperture and 0:6 deg2 on-pixel field of view CCDs and near-IR detectors during the 1990s, these were fol- makes VISTA the world’s fastest near-infrared survey system, lowed by a number of major multi-colour digital sky surveys, and it seems likely to retain this advantage until the launch of a notably the Sloan Digital Sky Survey (SDSS; Gunn et al. 2006; dedicated space mission such as Euclid or WFIRST in around Abazajian et al. 2009), the 2 Micron All-Sky Survey (2MASS; 2020. Skrutskie et al. 2006), the CFHT Legacy Survey (CFHTLS; This paper provides an overview of the development, techni- Cuillandre et al. 2012), and the UK Infrared Deep Sky Survey cal details and on-sky performance of the VISTA telescope and (UKIDSS; Lawrence et al. 2007). As well as forming a funda- VIRCAM. The intention is to provide an intermediate level of mental legacy resource (notably as an atlas for identifications detail across the whole system, plus references to more detailed of sources discovered at many other wavelengths, from radio papers for each subsystem. The remainder of the paper is divided and sub-mm to X-rays and gamma rays), these surveys have led into sections as follows: in Sect.2 we provide a short outline of to a very wide range of new discoveries covering most areas the full system, to place in context the more detailed later sec- and scales of observational astronomy, ranging from asteroids, tions. In Sect.3 we outline the early history of the project and brown dwarfs, Galactic structure, new Milky Way satellite galax- rationale of the basic design choices; in Sect.4 we provide an ies, through external galaxies and clusters, out to large-scale overview of the system optical design and overall layout; Sect.5 structure, weak lensing and the highest redshift quasars. describes the two mirrors and their support systems; Sect.6 de- In late 1998, a new science funding opportunity was pro- scribes the telescope structure and axes rotation systems; Sect.7 vided by the UK Joint Infrastructure Fund; a consortium of describes the infrared camera; Sect.8 describes the active op- 18 UK universities (see Acknowledgements) put together a suc- tics control; Sect.9 describes the enclosure and ancillary equip- cessful proposal to build a new 4-m class wide-field survey ment; Sect. 10 describes computer control and software; Sect. 11 Article published by EDP Sciences A25, page 1 of 27 A&A 575, A25 (2015) Fig. 1. VISTA telescope at sunset, with the main Paranal summit and VLTs in the background. The VIRCAM vacuum window is visible in the centre of the tube. On the telescope top-end, the M2 hexapod is behind the top ring; the M2 Cell (black) below it, and the M2 Baffle is the metallic annulus. (Photo credit: G.Hudepohl/ESO.) summarises the commissioning; Sect. 12 summarises observa- from 2MASS) the major wide-area optical and near-IR surveys tion control, data processing and archiving; and Sect. 13 gives since 2000 (notably SDSS, CFHT Legacy Survey, UKIDSS) are a short summary of the operational performance. These sections all concentrated in the northern hemisphere. are largely self-contained, so the reader interested in particular During routine observing, VISTA is operated entirely in aspects is advised to read Sect.2 then skip to the specific sec- queue-scheduled mode, controlled remotely by a single tele- tion(s) of interest. scope operator in the main VLT control room; evening startup and morning shutdown procedures are done by an operator adja- 2. System overview cent to the telescope for safety reasons. The VISTA telescope (Fig.1) is located at ESO’s Cerro Paranal The telescope optics (Sect.4) use a very fast two-mirror Observatory in northern Chile, at latitude 24◦3605700 south, lon- quasi-Ritchey-Chretien design. The 4.1 m diameter primary mir- gitude 70◦2305100 west; this is approximately 120 km south of ror is a hyperboloid of f =1:0 focal ratio; together with a 1.24 m Antofagasta city, and 12 km from the Pacific coast. Locally, convex hyperboloid secondary mirror, this produces an f =3:25 VISTA is sited on a subsidiary summit of elevation 2518 m, ap- Cassegrain focus located behind the M1 cell, ≈1.17 m below proximately 1.5 km NNE from the main Paranal summit which the M1 pole (Fig.2). The Cassegrain is the only focal sta- hosts the four VLTs, the VLT Interferometer and the VLT Survey tion, so VISTA carries one large instrument at any time; cur- Telescope; thus VISTA shares the same outstanding weather rently the IR Camera is the only instrument available for VISTA. conditions. Though VISTA is at approximately 100 m lower el- The telescope is designed for occasional instrument interchange, evation than the main summit, it is rarely downwind of the main and a wide-field 2400-fibre multi-object spectrograph (4MOST; summit. Clearly, the southern hemisphere site is very impor- de Jong et al. 2012) is approved by ESO for installation after tant for complementarity with next-generation major projects 2019. The telescope uses active (not adaptive) optics; the pri- including ALMA, SKA Pathfinders and E-ELT, since (apart mary mirror has an 84-point active axial support system, while A25, page 2 of 27 W. Sutherland et al.: VISTA: Technical overview and performance The system is designed mainly for efficient surveying of large areas of sky: clearly the main design drivers for this are the very wide field of view, moderately large aperture, and the high QE of the detectors; other important contributing factors are the high fraction ≥75% of observing time dedicated to large-scale survey programs, and the minimisation of times for necessary observing overheads, e.g. detector readout and telescope jitter movements. An overview of the on-sky performance is given in Sect. 13. 3. Basic requirements and design selection 3.1. Top-level specifications At the start of the project “Phase A” design in April 2000, the basic requirements were as follows. The telescope aperture was set to approximately 4 m for budget and schedule reasons, avail- Fig. 2. Schematic view of the general layout of VISTA optical compo- ability of an existing mirror blank, and also because achieving a nents; this shows the two mirrors, the VIRCAM entrance window and wide field of view becomes progressively more challenging on lenses, and the main components of VIRCAM. larger telescopes. The initial baseline was to accommodate two cameras: a 0:3 deg2 36 Mpixel (9 detector) near-infrared cam- era, and a 2 deg2 450 Mpixel visible camera, both with image the secondary mirror is mounted on a hexapod for 5-axis posi- quality commensurate with seeing-limited images at a top-class tion control. Physical details of the two mirrors and their support ground-based site.