Systematic characterization of the Herschel SPIRE Fourier Transform Spectrometer

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Hopwood, R.
Polehampton, E. T.
Valtchanov, I.
Swinyard, B. M.
Fulton, T.
Lu, N.
Marchili, N.
van der Wiel, M. H. D.
Benielli, D.
Imhof, P.
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Oxford University Press
A systematic programme of calibration observations was carried out to monitor the performance of the Spectral and Photometric Imaging REceiver (SPIRE) Fourier Transform Spectrometer (FTS) instrument on board the Herschel Space Observatory. Observations of planets (including the prime point-source calibrator, Uranus), asteroids, line sources, dark sky and cross-calibration sources were made in order to monitor repeatability and sensitivity, and to improve FTS calibration. We present a complete analysis of the full set of calibration observations and use them to assess the performance of the FTS. Particular care is taken to understand and separate out the effect of pointing uncertainties, including the position of the internal beam steering mirror for sparse observations in the early part of the mission. The repeatability of spectral-line centre positions is <5kms−1, for lines with signal-to-noise ratios>40, corresponding to <0.5–2.0 percent of a resolution element. For spectral-lineflux,the repeatability is better than 6percent, which improves to 1–2percent for spectra corrected for pointing offsets. The continuum repeatability is 4.4percent for the SPIRE Long Wavelength spectrometer (SLW) band and 13.6percent for the SPIRE Short Wavelength spectrometer (SSW) band, which reduces to ∼1percent once the data have been corrected for pointing offsets. Observations of dark sky were used to assess the sensitivity and the systematic offset in the continuum, both of which were found to be consistent across the FTS-detector arrays. Theaveragepoint-sourcecalibratedsensitivityforthecentredetectorsis0.20and0.21Jy[1σ; 1h],forSLWandSSW.Theaveragecontinuumoffsetis0.40JyfortheSLWbandand0.28Jy for the SSW band.
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Instrumentation , Spectrographs - Methods , Data analysis - Space vehicles , Instruments , SPIRE
Hopwood, R., Polehampton, E. T., Valtchanov, I., Swinyard, B. M., Fulton, T., Lu, N., ... Spencer, L. D. (2015). Systematic characterization of the Herschel SPIRE Fourier Transform Spectrometer. Monthly Notices of the Royal Astronomical Society, 449(3), 2274-2303. doi:10.1093/mnras/stv35