The Anglo-Australian Observatory 2dF facility

Monthly Notices of the Royal Astronomical Society, Jun 2002

The 2dF (Two-degree Field) facility at the prime focus of the Anglo-Australian Telescope provides multiple-object spectroscopy over a 2° field of view. Up to 400 target fibres can be independently positioned by a complex robot. Two spectrographs provide spectra with resolutions of between 500 and 2000, over wavelength ranges of 440 and 110 nm respectively. The 2dF facility began routine observations in 1997. 2dF was designed primarily for galaxy redshift surveys and has a number of innovative features. The large corrector lens incorporates an atmospheric dispersion compensator, essential for wide wavelength coverage with small-diameter fibres. The instrument has two full sets of fibres on separate field plates, so that re-configuring can be done in parallel with observing. The robot positioner places one fibre every 6 s, to a precision of 0.3 arcsec (20 μm) over the full field. All components of 2dF, including the spectrographs, are mounted on a 5-m diameter telescope top end ring for ease of handling and to keep the optical fibres short in order to maximize UV throughput. There is a pipeline data reduction system which allows each data set to be fully analysed while the next field is being observed. 2dF has achieved its initial astronomical goals. The redshift surveys obtain spectra at the rate of 2500 galaxies per night, yielding a total of about 200 000 objects in the first four years. Typically a B=19 galaxy gives a spectrum with a signal-to-noise ratio of better than 10 per pixel in less than an hour; redshifts are derived for about 95 per cent of all galaxies, with 99 per cent reliability or better. Total system throughput is about 5 per cent. The failure rate of the positioner and fibre system is about 1:10 000 moves or once every few nights, and recovery time is usually short. In this paper we provide the historical background to the 2dF facility, the design philosophy, a full technical description and a summary of the performance of the instrument. We also briefly review its scientific applications and possible future developments.

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The Anglo-Australian Observatory 2dF facility

I. J. Lewis et al. 0 Department of Astronomy, California Institute of Technology , Pasadena, CA 91125-2400 , USA 1 Department of Physics , Keble Road, Oxford OX1 3RH 2 Anglo-Australian Observatory , PO Box 296, Epping, NSW 1710 , Australia 3 Department of Physics, University of Durham , South Road, Durham DH1 3LE 4 Institute of Astronomy , Madingley Road, Cambridge CB3 0HA 5 ESO Paranal Observatory , PO Box 540, Antofagasta , Chile 6 Department of Physics and Astronomy, Johns Hopkins University , 3400 North Charles Street, Baltimore, MD 21218-2686 , USA 7 Australian Centre for Field Robotics , Rose Street, Building J04 , University of Sydney , NSW 2006 , Australia A B S T R A C T The 2dF (Two-degree Field) facility at the prime focus of the Anglo-Australian Telescope provides multiple-object spectroscopy over a 28 field of view. Up to 400 target fibres can be independently positioned by a complex robot. Two spectrographs provide spectra with resolutions of between 500 and 2000, over wavelength ranges of 440 and 110 nm respectively. The 2dF facility began routine observations in 1997. 2dF was designed primarily for galaxy redshift surveys and has a number of innovative features. The large corrector lens incorporates an atmospheric dispersion compensator, essential for wide wavelength coverage with small-diameter fibres. The instrument has two full sets of fibres on separate field plates, so that re-configuring can be done in parallel with observing. The robot positioner places one fibre every 6 s, to a precision of 0.3 arcsec (20 mm) over the full field. All components of 2dF, including the spectrographs, are mounted on a 5-m diameter telescope top end ring for ease of handling and to keep the optical fibres short in order to maximize UV throughput. There is a pipeline data reduction system which allows each data set to be fully analysed while the next field is being observed. 2dF has achieved its initial astronomical goals. The redshift surveys obtain spectra at the rate of 2500 galaxies per night, yielding a total of about 200 000 objects in the first four years. Typically a B 19 galaxy gives a spectrum with a signal-to-noise ratio of better than 10 per pixel in less than an hour; redshifts are derived for about 95 per cent of all galaxies, with 99 per cent reliability or better. Total system throughput is about 5 per cent. The failure rate of the positioner and fibre system is about 1:10 000 moves or once every few nights, and recovery time is usually short. In this paper we provide the historical background to the 2dF facility, the design philosophy, a full technical description and a summary of the performance of the instrument. We also briefly review its scientific applications and possible future developments. I N T R O D U C T I O N The value of equipping telescopes with a large field of view has been recognized for some time. In 1986 the Royal Astronomical Society report Review of Scientific Priorities for UK Astronomical Research 1990 2000 (Royal Astronomical Society 1986) put a wide-field multi-object spectroscopic facility at the top of its priority list for new projects. Subsequently the UK Large Telescope Panel recommended that a wide-field survey facility be pursued in tandem with an 8-m-telescope project. The general scientific case for a wide-field spectroscopic facility on a 4-m telescope was twofold: to provide spectra for large samples of objects found in the multi-colour imaging surveys from the UK, European Southern Observatory (ESO) and Oschin (Palomar) Schmidt telescopes; and to generate targets for the coming generation of 8 10 m optical telescopes. The biggest specific science driver was to obtain redshifts of tens or even hundreds of thousands of galaxies and quasars, to elucidate the three-dimensional structure and evolution of the Universe. Other major projects required spectra for large samples of stars, to determine their kinematics and composition and hence the dynamical and chemical history of our Galaxy; for similar studies of the Magellanic Clouds; and for detailed studies of star clusters and clusters of galaxies. One possibility was to provide a multi-fibre upgrade to the 3.9-m Anglo-Australian Telescope (AAT). This was particularly advantageous for two reasons. First, the optical design of the telescope (a hyperboloidal primary mirror and relatively slow f-ratio of f /3:3 at prime focus) enabled a wide field of 28 to be achieved using a large but straightforward optical corrector. Secondly, the AngloAustralian Observatory (AAO) already had extensive experience with multi-object fibre spectroscopy. This dates from the pioneering days of optical fibres and its brass plug-plate system FOCAP (Gray 1983) and more recently the fully automated AUTOFIB fibre positioner system (Parry & Gray 1986). At the end of 1988 the AAT Board (AATB) commissioned a full design study of a wide-field fibre optic spectroscopic facility for the AAT (Taylor & Gray 1990). Following further (...truncated)


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I. J. Lewis, R. D. Cannon, K. Taylor, K. Glazebrook, J. A. Bailey, I. K. Baldry, J. R. Barton, T. J. Bridges, G. B. Dalton, T. J. Farrell, P. M. Gray, A. Lankshear, C. McCowage, I. R. Parry, R. M. Sharples, K. Shortridge, G. A. Smith, J. Stevenson, J. O. Straede, L. G. Waller, J. D. Whittard, J. K. Wilcox, K. C. Willis. The Anglo-Australian Observatory 2dF facility, Monthly Notices of the Royal Astronomical Society, 2002, pp. 279-298, 333/2, DOI: 10.1046/j.1365-8711.2002.05333.x