Naylor, David

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https://opus.uleth.ca/handle/10133/3634

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Calibration of Herschel SPIRE FTS observations at different spectral resolutions
(Oxford University Press, 2017) Marchili, N.; Hopwood, R.; Fulton, T.; Polehampton, E. T.; Valtchanov, I.; Zaretski, J.; Naylor, David A.; Griffin, M. J.; Imhof, P.; Lim, T.; Lu, N.; Makiwa, G.; Pearson, C.; Spencer, Locke Dean
The SPIRE Fourier Transform Spectrometer on-board the Herschel Space Observatory had two standard spectral resolution modes for science observations: high resolution (HR) and low resolution (LR), which could also be performed in sequence (H+LR). A comparison of the HR and LR resolution spectra taken in this sequential mode revealed a systematic discrepancy in the continuum level. Analysing the data at different stages during standard pipeline processing demonstrates that the telescope and instrument emission affect HR and H+LR observations in a systematically different way. The origin of this difference is found to lie in the variation of both the telescope and instrument response functions, while it is triggered by fast variation of the instrument temperatures. As it is not possible to trace the evolution of the response functions using housekeeping data from the instrument subsystems, the calibration cannot be corrected analytically. Therefore, an empirical correction for LR spectra has been developed, which removes the systematic noise introduced by the variation of the response functions.
The data processing pipeline for the Herschel SPIRE Fourier Transform Spectrometer
(Oxford University Press, 2016) Fulton, T.; Naylor, David A.; Polehampton, E. T.; Valtchanov, I.; Hopwood, R.; Lu, N.; Baluteau, J.-P.; Mainetti, G.; Pearson, C.; Papageorgiou, A.; Guest, S.; Zhang, L.; Imhof, P.; Swinyard, B. M.; Griffin, M. J.; Lim, T. L.
We present the data processing pipeline to generate calibrated data products from the Spectral and Photometric Imaging Receiver (SPIRE) imaging Fourier Transform Spectrometer on the Herschel Space Observatory. The pipeline processes telemetry from SPIRE observations and produces calibrated spectra for all resolution modes. The spectrometer pipeline shares some elements with the SPIRE photometer pipeline, including the conversion of telemetry packets into data timelines and calculation of bolometer voltages. We present the following fundamental processing steps unique to the spectrometer: temporal and spatial interpolation of the scan mechanism and detector data to create interferograms; Fourier transformation; apodization; and creation of a data cube. We also describe the corrections for various instrumental effects including ﬁrst- and second-level glitch identiﬁcation and removal, correction of the effects due to emission from the Herschel telescope and from within the spectrometer instrument, interferogram baseline correction, temporal and spatial phase correction, non-linear response of the bolometers, and variation of instrument performance across the focal plane arrays. Astronomical calibration is based on combinations of observations of standard astronomical sources and regions of space known to contain minimal emission.
Spatial variation of the cooling lines in the Orion Bar from Hersehel/PACS
(EDP Sciences, 2012) Bernard-Salas, J.; Habart, E.; Arab, H.; Abergel, A.; Dartois, E.; Martin, P.; Bontemps, S.; Joblin, C.; White, G. J.; Bernard, J.-P.; Naylor, David A.
Context. The energetics in photo-dissociation regions (PDRs) are mainly regulated by the balance between the heating from the photo-electric eﬀect acting on dust grains, and the cooling via the copious emission of photons in far-infrared lines. The Orion Bar is a luminous and nearby PDR, which presents to the observer an ideal edge-on orientation in which to study this energy balance. Spatially resolved studies of such a nearby system are essential as they enable us to characterise the physical processes that control the energetics of the regions and can serve as templates for distant systems where these processes cannot be disentangled. Aims. We characterise the emission of the far-infrared ﬁne-structure lines of [Cii](158 μm),[Oi](63and145 μm),and[Nii](122 μm) that trace the gas local conditions, via spatially resolved observations of the Orion Bar. The observed distribution and variation of the lines are discussed in relation to the underlying geometry and linked to the energetics associated with the Trapezium stars. Methods. Herschel/PACS observations are used to map the spatial distribution of these ﬁne-structure lines across the Bar, with a spatial resolution between 4 and 11 and covering a total square area of about 120 ×105 . The spatial proﬁle of the emission lines are modelled using the radiative transfer code Cloudy. Results. TheHerschel observations reveal in unprecedented detail the morphology of the Bar.The spatial distribution of the [Cii] line coincides with that of the [Oi] lines. The [Nii] line peaks closer to the ionising star than the other three lines, but with a small region of overlap. We can distinguish several knots of enhanced emission within the Bar indicating the presence of an in homogenous and structured medium. The emission proﬁles cannot be reproduced by a single PDR, clearly indicating that, besides the Bar, there is a signiﬁcant contribution from additional PDR(s)over the area studied. The combination of both the [Nii] and [Oi] 145 μm lines can be used to estimate the [Cii] emission and distinguish between it sionised or neutral origin. We have calculated how much[Cii] emission comes from the neutral and ionised region, and ﬁnd that at least ∼82% originates from the photo-dissocciation region. Together, the [Cii] 158 μm and [Oi] 63 and 145 μm lines account for∼90% of the power emitted by the main cooling lines in the Bar (including CO, H2, etc.), with [Oi] 63μm alone accounting for 72% of the total.
Systematic characterization of the Herschel SPIRE Fourier Transform Spectrometer
(Oxford University Press, 2015) Hopwood, R.; Polehampton, E. T.; Valtchanov, I.; Swinyard, B. M.; Fulton, T.; Lu, N.; Marchili, N.; van der Wiel, M. H. D.; Benielli, D.; Imhof, P.; Baluteau, J.-P.; Pearson, C.; Clements, D. L.; Griffin, M. J.; Lim, T. L.; Makiwa, G.; Naylor, David A.; Noble, G.; Puga, E.; Spencer, Locke Dean
A systematic programme of calibration observations was carried out to monitor the performance of the Spectral and Photometric Imaging REceiver (SPIRE) Fourier Transform Spectrometer (FTS) instrument on board the Herschel Space Observatory. Observations of planets (including the prime point-source calibrator, Uranus), asteroids, line sources, dark sky and cross-calibration sources were made in order to monitor repeatability and sensitivity, and to improve FTS calibration. We present a complete analysis of the full set of calibration observations and use them to assess the performance of the FTS. Particular care is taken to understand and separate out the effect of pointing uncertainties, including the position of the internal beam steering mirror for sparse observations in the early part of the mission. The repeatability of spectral-line centre positions is <5kms−1, for lines with signal-to-noise ratios>40, corresponding to <0.5–2.0 percent of a resolution element. For spectral-lineﬂux,the repeatability is better than 6percent, which improves to 1–2percent for spectra corrected for pointing offsets. The continuum repeatability is 4.4percent for the SPIRE Long Wavelength spectrometer (SLW) band and 13.6percent for the SPIRE Short Wavelength spectrometer (SSW) band, which reduces to ∼1percent once the data have been corrected for pointing offsets. Observations of dark sky were used to assess the sensitivity and the systematic offset in the continuum, both of which were found to be consistent across the FTS-detector arrays. Theaveragepoint-sourcecalibratedsensitivityforthecentredetectorsis0.20and0.21Jy[1σ; 1h],forSLWandSSW.Theaveragecontinuumoffsetis0.40JyfortheSLWbandand0.28Jy for the SSW band.