The SPIRE Fourier Transform Spectrometer (FTS) Spectral Feature Finder (FF), developed within the Herschel Spectral and Photometric Imaging Receiver (SPIRE) FTS instrument team, is an automated spectral feature fitting routine that attempts to find significant features in SPIRE FTS spectra. The 3P1–3P0 and 3P2–3P1 neutral carbon fine structure lines are common features in carbon-rich far-infrared astrophysical sources. These features can be difficult to detect using an automated feature detection routine due to their typically low amplitude and line blending. In this paper, we describe and validate the FF subroutine designed to detect the neutral carbon emission observed in SPIRE spectral data.

The European Space Agency Herschel Spectral and Photometric Imaging Receiver (SPIRE) Fourier Transform Spectrometer (FTS) Spectral Feature Finder (FF) project is an automated spectral feature fitting routine developed within the SPIRE instrument team to extract all prominent spectral features from all publicly available SPIRE FTS observations. We present the extension of the FF to include the off-axis detectors of the FTS in sparsely sampled single-pointing observations, the results of which have been ingested into the catalogue. We also present the results from an automated routine for identifications of the atomic/molecular transitions that correspond to the spectral features extracted by the FF. We use a template of 307 atomic fine structure and molecular lines that are commonly found in SPIRE FTS spectra for the cross-match. The routine makes use of information provided by the line identification to search for low signal-to-noise ratio features that have been excluded or missed by the iterative FF. In total, the atomic/molecular transitions of 178 942 lines are identified (corresponding to 83 per cent of the entire FF catalogue), and an additional 33 840 spectral lines associated with missing features from SPIRE FTS observations are added to the FF catalogue.

The Herschel SPIRE FTS Spectral Feature Finder (FF) detects significant spectral features within SPIRE spectra and employs two routines, and external references, to estimate source radial velocity. The first routine is based on the identification of rotational 12CO emission, the second cross-correlates detected features with a line template containing most of the characteristic lines in typical far infrared observations. In this paper, we outline and validate these routines, summarize the results as they pertain to the FF, and comment on how external references were incorporated.

We provide a detailed description of the Herschel/SPIRE Fourier Transform Spectrometer (FTS) Spectral Feature Finder (FF). The FF is an automated process designed to extract significant spectral features from SPIRE FTS data products. Optimizing the number of features found in SPIRE-FTS spectra is challenging. The wide SPIRE-FTS frequency range (447–1568 GHz) leads to many molecular species and atomic fine structure lines falling within the observed bands. As the best spectral resolution of the SPIRE-FTS is ∼1.2 GHz, there can be significant line blending, depending on the source type. In order to find, both efficiently and reliably, features in spectra associated with a wide range of sources, the FF iteratively searches for peaks over a number of signal-to-noise ratio (SNR) thresholds. For each threshold, newly identified features are rigorously checked before being added to the fitting model. At the end of each iteration, the FF simultaneously fits the continuum and features found, with the resulting residual spectrum used in the next iteration. The final FF products report the frequency of the features found and the associated SNRs. Line flux determination is not included as part of the FF products, as extracting reliable line flux from SPIRE-FTS data is a complex process that requires careful evaluation and analysis of the spectra on a case-by-case basis. The FF results are 100 per cent complete for features with SNR greater than 10 and 50–70 per cent complete at SNR of 5. The FF code and all FF products are publicly available via the Herschel Science Archive.

We present an analysis of the updated publicly available Herschel SPIRE spectral Feature Finder data products, focusing primarily on mapping observations, radial velocity estimates, and neutral carbon detection.

Characterization results are presented for a double-Fourier spatial/spectral laboratory interferometer. This instrument is a testbed platform for developing imaging techniques, data processing algorithms, and component characterization for space-based astronomical applications in the far-infrared.

This feature issue highlights contributions from authors who presented their research at the OSA Light, Energy and the Environment Congress, held in Leipzig, Germany from November 14 to 17, 2016.

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The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on board the European Space Agency's Herschel Space Observatory which ended its operational phase on 29 April 2013. The low to medium resolution spectroscopic capability of SPIRE is provided by an imaging Fourier transform spectrometer (iFTS) of the Mach-Zehnder configuration. With their high throughput, broad spectral coverage, and variable resolution, coupled with their well-defined instrumental line shape and intrinsic wavelength and intensity calibration, iFTS are becoming increasingly common in far-infrared space astronomy missions. The performance of the SPIRE imaging spectrometer will be reviewed and example results presented. The lessons learned from the measured performance of the spectrometer as they apply to future missions will be discussed.

We describe recent progress in the development of a lab-based spatial/spectral double Fourier interferometer within the Astronomical Instrumentation Group (AIG) laboratories at the University of Lethbridge, Canada (UL). This testbed interferometer is used in the development of spatial/spectral interferometry observation, data processing, characterization, and analysis techniques in the Far-Infrared (FIR) region of the electromagnetic spectrum. Several interferometry technological development milestones on the FIR astrophysics roadmap are addressed by this ongoing research program of the UL AIG, all of which are needed as precursors to an eventual space-based FIR interferometry mission. This research program is supported by recent CRC, CFI, and NSERC grants.

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In general, a dual-input Fourier transform spectrometer (FTS) produces interferograms that have components of both even and odd symmetry. In addition to the desired interferogram contribution due to the source under study, which has even symmetry, each FTS output is often found to exhibit a component of odd symmetry that arises from the fact that the beam splitter is not ideal. Additionally, the beam splitter itself can be a source of emission that produces a modulated signal component at the output of the interferometer. An exploration of the effects, and correction, of nonideal beam-splitter characteristics in FTS interferograms is presented, including examples from the Herschel/SPIRE submillimeter wavelength imaging FTS.

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