Valtchanov, I.I.ValtchanovHopwood, R.R.HopwoodBendo, G.G.BendoBenson, C.C.BensonConversi, L.L.ConversiFulton, T.T.FultonGriffin, M. J.M. J.GriffinJoubaud, T.T.JoubaudLim, T.T.LimLu, N.N.LuMARCHILI, NicolaNicolaMARCHILIMakiwa, G.G.MakiwaMeyer, R. A.R. A.MeyerNaylor, D. A.D. A.NaylorNorth, C.C.NorthPapageorgiou, A.A.PapageorgiouPearson, C.C.PearsonPolehampton, E. T.E. T.PolehamptonScott, J.J.ScottSchulz, B.B.SchulzSpencer, L. D.L. D.Spencervan der Wiel, M. H. D.M. H. D.van der WielWu, R.R.Wu2020-12-092020-12-0920180035-8711http://hdl.handle.net/20.500.12386/28757We 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, η<SUB>ff</SUB>. 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 η<SUB>ff</SUB>, 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.STAMPAenArticle10.1093/mnras/stx31782-s2.0-85041284677000427144200025https://academic.oup.com/mnras/article/475/1/321/47184702018MNRAS.475..321VFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems