We have used a Fourier Transform Spectrometer (FTS) on the James Clerk Maxwell Telescope (JCMT) to study the submillimetre continuum emission from dust in three hot molecular cores (HMCs). The spectral index β of the dust emission for these sources has been determined solely within the 30-GHz wide 350-GHz (850 µm) passband to an accuracy comparable to those determined through multiwavelength observations. We find an average β � 1.6, in agreement with spectral indices determined from previous submillimetre observations of these sources and with those determined for HMC in general. The largest single source of uncertainty in these results is the variability of the atmosphere at 350 GHz, and with better sky subtraction techniques we show that the dust spectral index can clearly be determined within one passband to high accuracy with a submillimetre FTS. Using an imaging FTS on the Submillimetre Common User Bolometer Array (SCUBA)-2, the next generation wide-field submillimetre camera currently under development to replace SCUBA at the JCMT in 2006, we calculate that at 350 GHz it will be possible to determine β to ±0.1 for sources as faint as 400 mJy beam −1 and to ±0.3 for sources as faint as 140 mJy beam −1 . Ke yw ords: instrumentation: spectrographs ‐ dust, extinction ‐ stars: formation.

We present the results of a comparison of measured water vapour content above Mauna Kea obtained using the Submillimetre Common User Bolometer Array (SCUBA) and an infrared radiometer at the James Clerk Maxwell Telescope. We show that for most weather conditions the Infrared Radiometer for Millimetre Astronomy (IRMA) produces results that correlate well with the SCUBA measurements. However, for nights with thick cirrus cover, the IRMA results deviate from those obtained with SCUBA.

We present the recent developments and current design and of an imaging Fourier transform spectrometer (IFTS) for use with SCUBA-2, the second generation, wide-field, submillimetre camera currently under development for the James Clerk Maxwell Telescope (JCMT). The spectrometer will offer variable resolution with resolving powers ranging from R ~10 to 5000. The IFTS uses a folded Mach-Zehnder configuration with novel intensity beam dividers and dual input ports for continuous atmospheric cancellation. This system, which is planned for operation in 2006, will provide simultaneous, broadband, intermediate spectral resolution imaging across both the 850 and 450 μm bands. The optics, observing modes, and projected telescope performance of the IFTS are discussed.

The Infrared Radiometer for Millimetre wavelength Astronomy (IRMA) is a compact, light weight, low cost, low maintainance water vapour monitor, with an accuracy that enables it to be used to correct the phase distortions caused by atmospheric water vapour in millimetre wavelength interferometers. The IRMA III prototype is a major improvement on earlier versions of IRMA, with an emphasis on simplicity and reliability. We present results of tests conducted on the Smithsonian Millimeter Array (SMA) telescope on Mauna Kea in February 2004. The test campaign involved using three IRMA III devices with the SMA to provide phase correction information for improving the quality of the astronomical interferometric data.

Imaging Fourier transform spectrometers (IFTS) are becoming the preferred systems for remote sensing spectral imaging applications because of their ability to provide, simultaneously, both high spatial and spectral resolution images of a scene. IFTS can be operated in either step-and-integrate or rapid-scan modes, where it is common practice to sample interferograms at equal optical path difference intervals. The step-and-integrate mode requires a translation stage with fast and precise point-to-point motion and additional external trigger circuitry for the detector focal plane array (FPA), and produces uniformly position-sampled interferograms which can be analyzed using standard FFT routines. In the rapid-scan mode, the translation stage is continuously moving and interferograms are often acquired at the frame-rate of the FPA. Since all translation stages have associated velocity errors, the resulting interferograms are sampled at non-uniform intervals of optical path difference, which requires more sophisticated analysis. This paper discusses the processing pipeline which is being developed for the analysis of the non-uniform rapid-scan data produced by the Herschel/SPIRE IFTS.

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel mission. The spectroscopic capabilities of SPIRE are provided by an imaging Fourier transform spectrometer (IFTS). A software simulator of the IFTS has been constructed to predict the instrument performance under operational conditions. We describe in detail the design and integration of the simulator. Examples of simulated data of astronomical targets are presented.

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three instruments on the European Space Agency's Herschel mission. A detailed understanding of the SPIRE instrument is essential for a successful mission. In particular, it is important to characterize both the in-band spectral profile, and any out-of-band spectral leaks, which would severely degrade performance. A test Fourier Transform Spectrometer (TFTS), with its braod spectral coverage and intermediate spectral resolution, was selected for the spectral characterization of SPIRE. The integration of the TFTS with the existing Ground Support Equipment of the Hershel/SPIRE test facility at the Rutherford Appleton Laboratory imposed several mechanical, optical, electrical, and software constraints. In this paper we describe the design and implementation of the TFTS, and present preliminary results from its use in the SPIRE verification and performance tests.

Fourier Transform Spectrometers (FTS) are commonly operated in a rapid-scan (RS) mode, in which an interferogram of an astronomical source is obtained as quickly as possible, followed by one of a nearby background position. In an alternate operating mode, known as step-and-integrate (SI), the optical path difference in the interferometer is incremented in discrete steps, and the signal is integrated only when the interferometer mirrors are stationary. This mode requires some other means of modulating the signal, such as chopping the secondary mirror so that the detector alternately views source and background. The noise bandwidth in the SI mode (typically ~1 Hz) is much smaller than in the RS mode (~1 KHz), which in principle can lead to an increase in overall sensitivity. The main problem with the SI mode is that it takes much longer (~30x) to acquire an interferogram. At submillimetre wavelengths, through the use of narrowband optical filters, which are matched to regions of low atmospheric opacity, it is possible to sample the interferogram at less than the interval determined from the DC band limited Nyquist frequency (a condition known as aliasing) and still unambiguously recover the spectral information. We describe in detail the aliased, SI mode of operation of an FTS at the JCMT and present first results of astronomical spectra obtained using this mode. The resulting spectra are compared and contrasted to data obtained in the RS mode.

Embedded microcontroller modules offer many advantages over the standard PC such as low cost, small size, low power consumption, direct access to hardware, and if available, access to an efficient preemptive real-time multitasking kernel. Typical difficulties associated with an embedded solution include long development times, limited memory resources, and restricted memory management capabilities. This paper presents a case study on the successes and challenges in developing a control system for a remotely controlled, Alt-Az steerable, water vapour detector using the Rabbit 2000 family of 8-bit microcontroller modules in conjunction with the MicroC/OS-II multitasking real-time kernel.

We present the conceptual design of an imaging Fourier transform spectrometer (IFTS) for use with SCUBA-2, the second generation, wide-field, submillimetre camera currently under development for the James Clerk Maxwell Telescope (JCMT). This system, which is planned for operation in 2006, will provide simultaneous, broadband, intermediate spectral resolution imaging across both the 850 and 450 mum bands. The spectrometer will offer variable resolution with resolving powers ranging from Rsimilar to10 to 5000. When operated at low resolution, the IFTS will provide continuum measurements, well suited to spectral index mapping of molecular clouds, as well as bright nearby galaxies. The IFTS uses a folded Mach-Zehnder configuration and novel intensity beamdividers. The preliminary design, projected telescope performance and scientific impact of the IFTS are discussed. The preliminary design, novel observing modes, projected telescope performance and scientific impact of the IFTS are discussed.

Astronomical arrays operating at (sub)millimeter wavelengths are seriously compromised by rapid variations in atmospheric water vapor that distort the phase coherence of incoming celestial signals. The signal received by each antenna of the array suffers a phase delay that varies rapidly with time and from antenna to antenna. Unless corrected, these distortions limit the coherence time of the array and seriously compromise its sensitivity and image quality. Building on the success of a prototype infrared radiometer for millimeter astronomy (IRMA), which operates in the 20μm region to measure the column abundance of atmospheric water vapor, this paper describes the latest version of the IRMA concept, which has been developed for operation at Llano de Chajnantor, future site of the Atacama Large Millimeter Array (ALMA). Since there is presently limited infrastructure at the Chilean site the design must pay careful attention to all aspects of remote operation.

Astronomical spectroscopy at submillimeter wavelengths holds much promise for fields as diverse as the study of planetary atmospheres, molecular clouds and extragalactic sources. Fourier transform spectrometers (FTS) represent an important class of spectrometers well suited to observations that require broad spectral coverage at intermediate spectral resolution. In this paper we present the design and performance of a novel FTS, which has been developed for use at the James Clerk Maxwell, Telescope (JCMT).. The design uses two broadband intensity beamsplitters in a Mach-Zehnder configuration, which provide access to all four interferometer ports while maintaining a high and uniform efficiency over a broad spectral range. Since the interferometer processes both polarizations it is twice as efficient as the Martin-Puplett interferometer (MPI). As with the MPI, the spatial separation of the two input ports allows a reference blackbody to be viewed at all times in one port, while continually viewing the astronomical source in the other.. Furthermore, by minimizing the size of the optical beam at the beamsplitter, the design is well suited to imaging Fourier transform spectroscopy (IFTS) as evidenced by its selection for the SPIRE instrument on Herschel.

Over the last decade we have used a Fourier transform spectrometer at the James Clerk Maxwell telescope in a variety of astronomical programs. Results from these programs will be reviewed, and future plans for an imaging submillimetre FTS at the JCMT discussed. (C) 2000 Optical Society of America.

Future missions to measure the mid-infrared spectra of extrasolar planets will obtain spectra spatially integrated over the visible hemisphere of the planet. Interpretation of these spectra will be difficult because they will depend on several imponderable factors; the axial inclination of the planet to the line of sight, the illumination of the planet by its parent star, and the planets' season and climatic state. The spectra will also contain variable components due to changing clouds, planetary rotation and the presence of large satellites. In order to interpret better such spectra, and to constrain the design of missions to measure them, a study is underway of a dedicated mission to take spectra of the spatially-unresolved Earth and to quantify the dependence of the spectrum on these variables.

Submillimetre spectra taken near to the solar limb with a polarizing interferometer on the James Clerk Maxwell Telescope have been compared with disk-centre spectra to reveal a limb-brightened feature whose peak intensity occurs at the predicted frequency of the n=20-19 Rydberg transition in Hi at 29.622 cm 1 . A shoulder on this peak, at 29.65 cm 1 , has been tentatively assigned to the equivalent transition in Mg i. The Hi line exhibits limb brightening of up to 9% of the disk- centre continuum intensity. The intensity of the Mg i line is about half of the Hi line intensity across the observed region near to the limb. Widths of the Hi line are between 0.020 and 0.027 cm 1 , smaller than predicted by current models of this line in the Sun's spectrum. These measurements represent the highest-n Rydberg lines detected to date in the solar spectrum. The measured line intensity, line width, limb brightening and the relative heights of the contributions from H i and Mgi place constraints upon further modelling of the solar atmosphere.

This letter reports the discovery of excess emission at the position of the H I n=22-21 Rydberg transition in submillimetre solar spectra taken at the extreme solar limb. This emission feature at 22.096+/-0.003 cm(-1) shows significant limb brightening, reaching intensities of 11% above the adjacent spectral continuum with line shapes fitted best by Gaussian functions with widths of 0.018 +/- 0.004 cm(-1). This measurement represents the highest-n. Rydberg line of H I detected to date in the solar spectrum.

The submillimetre atmospheric transmission spectrum above Mauna Kea has been measured at a resolution of 0.005 cm(-1) (150 MHz) with a Fourier transform spectrometer at the James Clerk Maxwell Telescope, using the Sun as a source. Column abundances of O-2, H2O and O-3 determined from these spectra are found to be in excellent agreement with independent measurements. The derived column abundances have been used as inputs to the atmospheric spectral modelling program fascod. The synthetic transmission spectrum is found to be in excellent agreement with the measured spectrum, and provides a template for submillimetre observations from the JCMT.

The first two rotational lines of HD were measured in all four giant planets using LWS. For Uranus and Neptune, medium-resolution observations of the R(0) line of HD have been analysed using both Mars and Callisto as calibrators. The results for Callisto are promising, but those for Mars are inconsistent for reasons which have not yet been identified. For Jupiter and Saturn, analysis of the high-resolution observations reveals the presence of the R(0) and R(1) lines in both planets.

The design of a dual polarizing bolometer detector system for use with a polarizing Fourier transform spectrometer to conduct broadband astronomical spectroscopy at submillimeter wavelengths is presented. While inclement weather precluded astronomical observations during the commissioning run, the initial performance of the system, as determined from observing laboratory calibration sources, is presented, and the implications for astronomical spectroscopy discussed.

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 microns to 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 and user interface, performance figures on the telescope, and present a sample of the exciting new results that have revolutionised submillimetre astronomy.