Eugene B. Seneta

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.

Software and control for the Magdalena Ridge Observatory interferometer delay lines

The delay lines for the Magdalena Ridge Observatory Interferometer (MROI) will provide remote control of optical delays of up to 380m with sub-wavelength precision in vacuum. The delay-line prototype is now fully functional, all features having been demonstrated in a 20m long evacuated test rig. We describe the architecture, design and performance of the delay line software: this features distributed real-time control and flexible remote logging of diagnostic data from the delay line hardware components at up to 5 kHz.

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.

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.

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.

The MROI fringe tracker: closing the loop on ICoNN

The characterization of ICoNN, the Magdalena Ridge Observatory Interferometers fringe tracker, through labor tory simulations is presented. The performance limits of an interferometer are set by its ability to keep the optical path difference between combination partners minimized. This is the job of the fringe tracker. Understanding the behavior and limits of the fringe tracker in a controlled environment is key to maximize the science output. This is being done with laboratory simulations of on-sky fringe tracking, termed the closed-loop fringe experi ment. The closed-loop fringe experiment includes synthesizing a white light source and atmospheric piston with estimation of the tracking error being fed back to mock delay lines in real-time. We report here on the progress of the closed-loop fringe experiment detailing its design, layout, controls and software.

DIMMWIT measurements of the spatial and temporal scale of atmospheric turbulence at COAST and MROI

The DIMMWIT (Differential Image Motion Monitor, Which Is Transportable) is a portable DIMM that can measure the Fried parameter r0 and the average wind speed of the turbulent layers. Analysing DIMM images to calculate r0 is a standard procedure, but wind speeds have rarely been calculated from differential image motion before. Here, we describe how wind speeds can be derived from either differential image motion power spectra or differential image velocities. The DIMMWIT wind speeds are then compared with a wind speed derived from the coherence times, t0, of interferometric fringes recorded simultaneously at COAST (Cambridge Optical Aperture Synthesis Telescope). Although t0, and hence the wind speed, is routinely measured by the interferometer at the COAST site, the Fried parameter had not been studied. The results of seeing campaigns at COAST and MROI (Magdalena Ridge Observatory Interferometer) are presented, along with a comparison of DIMMWIT r0 measurements with the FWHM of long exposure images recorded at the same time.

Atmospheric spatial and temporal seeing monitor using portable amateur astronomy equipment

Accurate knowledge of the spatial and temporal seeing has become increasingly important as AO systems move from being specialised instruments to standard equipment at large ground-based telescopes. While monitors that measure the spatial seeing scale are now commonplace, devices capable of measuring temporal seeing parameters are much rarer since the sampling requirements are severe. Nevertheless, such information is vital if the bandwidth and control requirements for active and adaptive systems at state-of-the-art telescopes and optical/IR interferometers are to be correctly specified. In this paper we describe a cheap, yet robust, Differential Image Motion Monitor Which Is Transportable (DIMMWIT) that can make both spatial and temporal seeing measurements. It samples starlight at rates up to 500Hz but contains no mechanical parts and uses only technology available to amateur astronomers. We review the design and performance of the device and present examples of results from routine use at the Cambridge Optical Aperture Synthesis Telescope (COAST) site in the UK. An identical system is also being tested at the Magdalena Ridge Optical Interferometer (MROI) site in New Mexico.

Implementing the Magdalena Ridge Observatory interferometer supervisory system

The Magdalena Ridge Observatory Interferometer (MROI) software system contains distributed systems managed by a centralized Supervisory System. Interface software is generated from spreadsheets that describe commands, monitor points, and fault conditions for each subsystem. The Supervisory System consists of an Executive, Operator, Database Manager; one or more Supervisors plus Fault Manager, and Data Collectors. System-wide simulations are discussed: (1) a test framework is generated from the spreadsheets characterizing a subsystem; (2) a detailed simulation of the actual hardware in a subsystem; (3) a system-wide simulation of collecting astronomical data based on executing observing projects. The first two levels have been implemented.

A new path to first light for the Magdalena Ridge Observatory interferometer

The Magdalena Ridge Observatory Interferometer (MROI) was the most ambitious infrared interferometric facility conceived of in 2003 when funding began. Today, despite having suffered some financial short-falls, it is still one of the most ambitious interferometric imaging facilities ever designed. With an innovative approach to attaining the original goal of fringe tracking to H = 14th magnitude via completely redesigned mobile telescopes, and a unique approach to the beam train and delay lines, the MROI will be able to image faint and complex objects with milliarcsecond resolutions for a fraction of the cost of giant telescopes or space-based facilities. The design goals of MROI have been optimized for studying stellar astrophysical processes such as mass loss and mass transfer, the formation and evolution of YSOs and their disks, and the environs of nearby AGN. The global needs for Space Situational Awareness (SSA) have moved to the forefront in many communities as Space becomes a more integral part of a national security portfolio. These needs drive imaging capabilities ultimately to a few tens of centimeter resolution at geosynchronous orbits. Any array capable of producing images on faint and complex geosynchronous objects in just a few hours will be outstanding not only as an astrophysical tool, but also for these types of SSA missions. With the recent infusion of new funding from the Air Force Research Lab (AFRL) in Albuquerque, NM, MROI will be able to attain first light, first fringes, and demonstrate bootstrapping with three telescopes by 2020. MROI’s current status along with a sketch of our activities over the coming 5 years will be presented, as well as clear opportunities to collaborate on various aspects of the facility as it comes online. Further funding is actively being sought to accelerate the capability of the array for interferometric imaging on a short time-scale so as to achieve the original goals of this ambitious facility