John F. Lightfoot

SCUBA: A common-user submillimetre camera operating on the James Clerk Maxwell Telescope

SCUBA, the Submillimetre Common-User Bolometer Array, built by the Royal Observatory Edinburgh for the James Clerk Maxwell Telescope, is the most versatile and powerful of a new generation of submillimetre cameras. It combines a sensitive dual-waveband imaging array with a three-band photometer, and is sky-background-limited by the emission from the Mauna Kea atmosphere at all observing wavelengths from 350 μμto 2 mm. The increased sensitivity and array size mean that SCUBA maps close to 10 000 times faster than its single-pixel predecessor (UKT14). SCUBA is a facility instrument, open to the world community of users, and is provided with a high level of user support. We give an overview of the instrument, describe the observing modes, user interface and performance figures on the telescope, and present a sample of the exciting new results that have revolutionized submillimetre astronomy.

On the atmospheric limitations of ground-based submillimetre astronomy using array receivers

The calibration of ground-based submillimetre observations has always been a difficult process. We discuss how to overcome the limitations imposed by the submillimetre atmosphere. Novel ways to improve line-of-sight opacity estimates are presented, resulting in tight relations between opacities at different wavelengths. The submillimetre camera SCUBA, mounted on the James Clerk Maxwell Telescope (JCMT), is the first large-scale submillimetre array, and as such is ideal for combating the effects of the atmosphere. For example, we find that the off-source pixels are crucial for removing sky noise. Benefiting from several years of SCUBA operation, a data base of deep SCUBA observations has been constructed to help us understand better the nature of sky noise and the effects of the atmosphere on instrument sensitivity. This has revealed several results. First, there is evidence for positive correlations between sky noise and seeing and sky noise and sky opacity. Furthermore, 850-μm and 450-μm sky noise are clearly correlated, suggesting that 450-μm data may be used to correct 850-μm observations for sky noise. Perhaps most important of all: if off-source bolometers are used for sky noise removal, there is no correlation between instrument sensitivity and chop throw, for chop throws out to 180 arcsec. Understanding the effects of submillimetre seeing is also important, and we find that the JCMT beam is not significantly broadened by seeing, nor is there an obvious correlation between seeing and pointing excursions.

SCUBA: a submillimeter camera operating on the James Clerk Maxwell Telescope

The Submillimeter Common-User Bolometer Array (SCUBA) is one of a new generation of cameras designed to operate in the submillimeter waveband. The instrument has a wide wavelength range covering all the atmospheric transmission windows between 300 and 2000 micrometer. In the heart of the instrument are two arrays of bolometers optimized for the short (350/450 micrometer) and long (750/850 micrometer) wavelength ends of the submillimeter spectrum. The two arrays can be used simultaneously, giving a unique dual-wavelength capability, and have a 2.3 arc-minute field of view on the sky. Background-limited performance is achieved by cooling the arrays to below 100 mK. SCUBA has now been in active service for over a year, and has already made substantial breakthroughs in many areas of astronomy. In this paper we present an overview of the performance of SCUBA during the commissioning phase on the James Clerk Maxwell Telescope (JCMT).

Progress in the critical assessment for a far-infrared space interferometer with double fourier modulation (FP7-FISICA)

The progress and results of the ongoing FP7-FISICA programme to re-asses the scientific goals of a Far-Infrared Space Interfereometer and push the development of some of its key technology elements are reported.

JCMT observatory control system

The JCMT, the worlds largest sub-mm telescope, has had essentially the same VAX/VMS based control system since it was commissioned. For the next generation of instrumentation we are implementing a new Unix/VxWorks based system, based on the successful ORAC system that was recently released on UKIRT. The system is now entering the integration and testing phase. This paper gives a broad overview of the system architecture and includes some discussion on the choices made. (Other papers in this conference cover some areas in more detail). The basic philosophy is to control the sub-systems with a small and simple set of commands, but passing detailed XML configuration descriptions along with the commands to give the flexibility required. The XML files can be passed between various layers in the system without interpretation, and so simplify the design enormously. This has all been made possible by the adoption of an Observation Preparation Tool, which essentially serves as an intelligent XML editor.

Optical and quasi-optical analysis of system components for a far-infrared space interferometer

Many important astrophysical processes occur at wavelengths that fall within the far-infrared band of the EM spectrum, and over distance scales that require sub-arc second spatial resolution. It is clear that in order to achieve sub-arc second resolution at these relatively long wavelengths (compared to optical/near-IR), which are strongly absorbed by the atmosphere, a space-based far-IR interferometer will be required. We present analysis of the optical system for a proposed spatial-spectral interferometer, discussing the challenges that arise when designing such a system and the simulation techniques employed that aim to resolve these issues. Many of these specific challenges relate to combining the beams from multiple telescopes where the wavelengths involved are relatively short (compared to radio interferometry), meaning that care must be taken with mirror surface quality, where surface form errors not only present potential degradation of the single system beams, but also serve to reduce fringe visibility when multiple telescope beams are combined. Also, the long baselines required for sub-arc second resolution present challenges when considering propagation of the relatively long wavelengths of the signal beam, where beam divergence becomes significant if the beam demagnification of the telescopes is not carefully considered. Furthermore, detection of the extremely weak far-IR signals demands ultra-sensitive detectors and instruments capable of operating at maximum efficiency. Thus, as will be shown, care must be taken when designing each component of such a complex quasioptical system.

New spectral line multibeam correlator system for the James Clerk Maxwell Telescope

A new Auto-Correlation Spectral Imaging System (ACSIS) for the James Clerk Maxwell Telescope (JCMT) is being developed at the National Research Council of Canada, in collaboration with the Joint Astronomy Centre and the United Kingdom Astronomy Technology Centre. The system is capable of computing the integrated power-spectra over 1-GHz bandwidths for up to 32 receiver beams every 50 ms. An innovative, multiprocessor computer will produce calibrated, gridded, 3-D data cubes so that they can be viewed in real-time and are in hand when an observation is over. When connected to arrays of receivers at the Nasmyth focus of the telescope, the system will be able to rapidly make large-scale images with high spectral resolution and map multiple transitions. The ACSIS system will be mated initially with the multibeam 350-GHz receiver system. Heterodyne ARray Program (HARP), under development at the Mullard Radio Astronomy Observatory in Cambridge, England. In this paper we describe ACSIS, how it is designed and the results of key performance tests made.

NIX, the imager for ERIS: the AO instrument for the VLT

ERIS will be the next-generation AO facility on the VLT, combining the heritage of NACO imaging, with the spectroscopic capabilities of an upgraded SINFONI. Here we report on the all-new NIX imager that will deliver diffraction-limited imaging from the J to M band. The instrument will be equipped with both Apodizing Phase Plates and Sparse Aperture Masks to provide high-angular resolution imagery, especially suited for exoplanet imaging and characterization. This paper provides detail on the instrument’s design and how it is suited to address a broad range of science cases, from detailed studies of the galactic centre at the highest resolutions, to studying detailed resolved stellar populations.

Longwavelength issues for far infrared space interferometers

We discuss issues associated with diffraction effects in far-infared space interferometers, particularly wide field spacio-spectral space interferometers now being proposed. We present examples of the application of various useful quasi-optical approaches in such instruments.