No abstract

No abstract

SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to be flown on ESA's Herschel Space Observatory. It contains a three-band submillimetre camera and an imaging Fourier transform spectrometer, and uses arrays of feedhorn-coupled bolometric detectors operating at a temperature of 300 mK. Detailed software simulators are being developed for the SPIRE photometer and spectrometer. The photometer simulator is based on an adaptable modular representation of the relevant instrument and telescope subsystems, and is designed to produce highly realistic science and housekeeping data timelines. It will be used for a variety of purposes, including instrument characterisation during ground testing and in orbit, testing and optimisation of operating modes and strategies, evaluation of data reduction software using simulated data streams (derived by "observing" a simulated sky intensity distribution with the simulator), observing time estimation, and diagnostics of instrument systematics. In this paper we present the current status of the photometer simulator and the future development and implementation strategy.

We present observations that were carried out with the Two HUndred Micron PhotometER (THUMPER) mounted on the James Clerk Maxwell Telescope (JCMT) in Hawaii, at a wavelength of 200 μm (frequency 1.5 THz). The observations utilize a small atmospheric window that opens up at this wavelength under very dry conditions at high‐altitude observing sites. The atmosphere was calibrated using the sky‐dipping method and a relation was established between the optical depth, τ, at 1.5 THz and that at 225 GHz: τ1.5 THz= (95 ± 10) ×τ225 GHz. Mars and Jupiter were mapped from the ground at this wavelength for the first time, and the system characteristics measured. A noise‐equivalent flux density (NEFD) of ∼ 65 ± 10 Jy (1σ 1s) was measured for the THUMPER–JCMT combination, consistent with predictions based upon our laboratory measurements. The main beam resolution of 14 arcsec was confirmed and an extended error beam detected at roughly two‐thirds of the magnitude of the main beam. Measurements of the Sun allow us to estimate that the fraction of the power in the main beam is ∼15 per cent, consistent with predictions based on modelling the dish surface accuracy. It is therefore shown that the sky over Mauna Kea is suitable for astronomy at this wavelength under the best conditions. However, higher or drier sites should have a larger number of useable nights per year.