Donald M. A. Wilson

Design and performance of COAST

The Cambridge Optical Aperture Synthesis Telescope, COAST, is a four-telescope array for high resolution imaging using measurements of complex visibilities and closure phases. This paper describes what its component parts are and why.

Design of the MROI delay line optical path compensator

The delay lines for the Magdalena Ridge Observatory Interferometer in New Mexico are required to provide up to 380m optical path delay with an OPD jitter of better than 15nm, in vacuum, using a single adjustable stroke. In order to meet these demanding requirements in a cost-effective manner a unique combination of techniques has been used in the design and construction of the delay line trolley which operates continuously within 190m of evacuated pipe. These features include contactless delivery of power and control signals, active control of the cats eye optics and the use of composite materials to achieve good thermal stability. A full-size prototype trolley has been built and fully tested and the first production trolley is under construction. We describe the systems key design features and review the construction and alignment of the delay line trolley. Results obtained with the trolley operating in an evacuated 20m-long test rig under the full range of conditions required for successful astronomical observations are presented. An OPD jitter of typically 10nm is achieved over the total tracking velocity range from 0 to 15mm/s.

Current status of COAST

This paper reviews the current performance of the Cambridge Optical Aperture Synthesis Telescope as an imaging array. Tests of the hardware and methods of measuring fringe visibility and closure phase are described in the context of prospects for a Large Optical Array.

COAST: its current status, operation, and results

The Cambridge Optical Aperture Synthesis Telescope, COAST, now has the capacity to measure visibility amplitudes and closure phase for stellar sources. This paper summarizes the current status of the instrument and how the data is analyzed.

Mechanical design of the Magdalena Ridge Observatory Interferometer

We report on the mechanical design currently performed at the Magdalena Ridge Observatory Interferometer (MROI) and how the construction, assembly, integration and verification are planned towards commissioning. Novel features were added to the mechanical design, and high level of automation and reliability are being devised, which allows the number of reflections to be kept down to a minimum possible. This includes unit telescope and associated enclosure and transporter, fast tip-tilt system, beam relay system, delay line system, beam compressor, automated alignment system, beam turning mirror, switchyard, fringe tracker and vacuum system.

The long-stroke MROI vacuum delay lines: from concept to production

We report on test results on the delay line system for the MRO Interferometer, currently under construction in Cambridge, UK. The delay lines are designed to provide 380 metres of vacuum path delay in a single stage, offering rapid star-to-star slews, high throughput and high transmitted wavefront quality. Details of the final design adopted for these delay lines are presented, together with lessons learnt from successful performance tests of the full-scale prototype trolley in a 20-metre long vacuum test rig. Delivery of the first production trolley is expected in New Mexico in early 2009.

COAST: the current status

We present a summary of the status of the Cambridge Optical Aperture Synthesis Telescope (COAST). Since our last report we have concentrated on improving both the efficiency of use of the array and its astrophysical capabilities. In particular we have achieved useful improvements in throughput, detector sensitivity and the efficiency of securing measurements of visibility amplitudes and closure phases. With five telescopes fully operational, COAST is now being used routinely for parallel programs of astrophysics and as a technical test-bed for its proposed successor, the Large Optical Array--LOA.

The MROI fast tip-tilt correction and target acquisition system

The fast tip-tilt correction system for the Magdalena Ridge Observatory Interferometer (MROI) is being designed and fabricated by the University of Cambridge. The design of the system is currently at an advanced stage and the performance of its critical subsystems has been verified in the laboratory. The system has been designed to meet a demanding set of specifications including satisfying all performance requirements in ambient temperatures down to -5 °C, maintaining the stability of the tip-tilt fiducial over a 5 °C temperature change without recourse to an optical reference, and a target acquisition mode with a 60” field-of-view. We describe the important technical features of the system, which uses an Andor electron-multiplying CCD camera protected by a thermal enclosure, a transmissive optical system with mounts incorporating passive thermal compensation, and custom control software running under Xenomai real-time Linux. We also report results from laboratory tests that demonstrate (a) the high stability of the custom optic mounts and (b) the low readout and compute latencies that will allow us to achieve a 40 Hz closed-loop bandwidth on bright targets.

Final mechanical and opto-mechanical design of the Magdalena Ridge Observatory interferometer

Most subsystems of the Magdalena Ridge Observatory Interferometer (MROI) have progressed towards final mechanical design, construction and testing since the last SPIE meeting in San Diego - CA. The first 1.4-meter telescope has successfully passed factory acceptance test, and construction of telescopes #2 and #3 has started. The beam relay system has been prototyped on site, and full construction is awaiting funding. A complete 100-meter length delay line system, which includes its laser metrology unit, has been installed and tested on site, and the first delay line trolley has successfully passed factory acceptance testing. A fully operational fringe tracker is integrated with a prototyped version of the automated alignment system for a closed looping fringe tracking experiment. In this paper, we present details of the final mechanical and opto-mechanical design for these MROI subsystems and report their status on fabrication, assembly, integration and testing.

COAST: recent technology and developments

We present a summary of the activity of the Cambridge Optical Aperture Synthesis Telescope (COAST) team and review progress on the astronomical and technical projects we have been working on in the period 2002--2004. Our current focus has now moved from operating COAST as an astronomical instrument towards its use as a test-bed for strategic technical development for future facility arrays. We have continued to develop a collaboration with the Magdalena Ridge Observatory Interferometer, and we summarise the programmes we expect to be working on over the next few years for that ambitious project. In parallel, we are investigating a number of areas for the European Very Large Telescope Interferometer and these are outlined briefly.