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Published March 21, 2017 | Published + Submitted
Journal Article Open

Correcting the extended-source calibration for the Herschel-SPIRE Fourier-transform spectrometer

Abstract

We describe an update to the Herschel-Spectral and Photometric Imaging Receiver (SPIRE) Fourier-transform spectrometer (FTS) calibration for extended sources, which incorporates a correction for the frequency-dependent far-field feedhorn efficiency, ηff. This significant correction affects all FTS extended-source calibrated spectra in sparse or mapping mode, regardless of the spectral resolution. Line fluxes and continuum levels are underestimated by factors of 1.3–2 in thespectrometer long wavelength band (447–1018 GHz; 671–294 μm) and 1.4–1.5 in the spectrometer short wavelength band (944–1568 GHz; 318–191 μm). The correction was implemented in the FTS pipeline version 14.1 and has also been described in the SPIRE Handbook since 2017 February. Studies based on extended-source calibrated spectra produced prior to this pipeline version should be critically reconsidered using the current products available in the Herschel Science Archive. Once the extended-source calibrated spectra are corrected for ηff, the synthetic photometry and the broad-band intensities from SPIRE photometer maps agree within 2–4 per cent – similar levels to the comparison of point-source calibrated spectra and photometry from point-source calibrated maps. The two calibration schemes for the FTS are now self-consistent: the conversion between the corrected extended-source and point-source calibrated spectra can be achieved with the beam solid angle and a gain correction that accounts for the diffraction loss.

Additional Information

© 2017 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 December 5. Received 2017 December 4; in original form 2017 August 30. The authors wish to thank the referee for their useful comments that helped improve the paper, as well as J. Kamenetzky, C. Wilson, D. Teyssier, K. Rygl, E. Puga, and K. Exter for valuable discussions. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). This research is supported in part by the Canadian Space Agency (CSA) and the Natural Sciences and Engineering Research Council of Canada (NSERC). Most of the data processing and analysis in this paper was performed in the Herschel Interactive Processing Environment (HIPE, Ott 2010). Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

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Published - stx3178.pdf

Submitted - 1708.09203

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Additional details

Created:
August 19, 2023
Modified:
October 18, 2023