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

Valtchanov, I. and Hopwood, R. and Bendo, G. and Benson, C. and Conversi, L. and Fulton, T. and Griffin, M. J. and Joubaud, T. and Lim, T. and Lu, N. and Marchili, N. and Makiwa, G. and Meyer, R. A. and Naylor, D. A. and North, C. and Papageorgiou, A. and Pearson, C. and Polehampton, E. T. and Scott, J. and Schulz, B. and Spencer, L. D. and van der Wiel, M. H. D. and Wu, R. (2017) Correcting the extended-source calibration for the Herschel-SPIRE Fourier-transform spectrometer. Monthly Notices of the Royal Astronomical Society, 475 (1). pp. 321-330. ISSN 0035-8711. doi:10.1093/mnras/stx3178.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Valtchanov, I.0000-0001-9930-7886
Lu, N.0000-0002-8948-1044
Papageorgiou, A.0000-0002-3039-9257
Pearson, C.0000-0001-6139-649X
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.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Space Agency (ESA)UNSPECIFIED
Subject Keywords:instrumentation: spectrographs, space vehicles: instruments, techniques: spectroscopic
Issue or Number:1
Record Number:CaltechAUTHORS:20180411-135404961
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85763
Deposited By: George Porter
Deposited On:11 Apr 2018 21:25
Last Modified:15 Nov 2021 20:31

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