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Browsing Faculty Research & Publications by Author "Benielli, D."

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    Calibration of the Herschel SPIRE Fourier Transform Spectrometer
    (Oxford University Press, 2014) Swinyard, B. M.; Polehampton, E. T.; Hopwood, R.; Valtchanov, I.; Lu, N.; Fulton, T.; Benielli, D.; Imhof, P.; Marchili, N.; Baluteau, J.-P.; Bendo, G. J.; Ferlet, M.; Griffin, M. J.; Lim, T. L.; Makiwa, G.; Naylor, David A.; Orton, G. S.; Papageorgiou, A.; Pearson, C. P.; Schulz, B.; Sidher, S. D.; Spencer, Locke Dean; van der Wiel, M. H. D.; Wu, R.
    The Herschel Spectral and Photometric REceiver (SPIRE) instrument consists of an imaging photometric camera and an imaging Fourier Transform Spectrometer (FTS), both operating over a frequency range of∼450–1550GHz. In this paper, we briefly review the FTS design, operation, and data reduction, and describe in detail the approach taken to relative calibration (removal of instrument signatures) and absolute calibration against standard astronomical sources. The calibration scheme assumes a spatially extended source and uses the Herschel telescopeasprimarycalibrator.Conversionfromextendedtopoint-sourcecalibrationiscarried out using observations of the planet Uranus. The model of the telescope emission is shown to beaccuratetowithin6percent andrepeatable tobetterthan0.06percent and,bycomparison with models of Mars and Neptune, the Uranus model is shown to be accurate to within 3 per cent. Multiple observations of a number of point-like sources show that the repeatability of the calibration is better than 1 per cent, if the effects of the satellite absolute pointing error (APE) are corrected. The satellite APE leads to a decrement in the derived flux, which can be up to∼10 per cent (1 σ) at the high-frequency end of the SPIRE range in the first part of the mission, and∼4 per cent after Herschel operational day 1011. The lower frequency range of the SPIRE band is unaffected by this pointing error due to the larger beam size. Overall, for well-pointed, point-like sources, the absolute flux calibration is better than 6 per cent, and for extended sources where mapping is required it is better than 7 per cent.
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    Systematic characterization of the Herschel SPIRE Fourier Transform Spectrometer
    (Oxford University Press, 2015) 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.; Baluteau, J.-P.; Pearson, C.; Clements, D. L.; Griffin, M. J.; Lim, T. L.; Makiwa, G.; Naylor, David A.; Noble, G.; Puga, E.; Spencer, Locke Dean
    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.