Calibration of the Herschel SPIRE Fourier Transform Spectrometer

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Swinyard, B. M.
Polehampton, E. T.
Hopwood, R.
Valtchanov, I.
Lu, N.
Fulton, T.
Benielli, D.
Imhof, P.
Marchili, N.
Baluteau, J.-P.
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Oxford University Press
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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Instrumentation , Spectrographs , Space vehicles , Instruments - Techniques , Spectroscopic , Herschel Spectral and Photometric REceiver , SPIRE , Fourier Transform Spectrometer
Swinyard, B. M., Polehampton, E. T., Hopwood, R., Valtchanov, I., Lu, N., Fulton, T., ... Wu, R. (2014). Calibration of the Herschel SPIRE Fourier Transform Spectrometer. Monthly Notices of the Royal Astronomical Society, 440(4), 3658-3674. doi:10.1093/mnras/stu409