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PACS instrument and calibration web pages

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PACS calibration and performance

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Data processing known issues of standard products for photometry and spectroscopy: Bulk-processed Level 2/2.5 products are provided in the Herschel Science Archive. This Data Processing Known Issues page describes typical problems and caveats the observer needs to be familiar when looking at the results of this "SPG" (standard product generation) processing. Aspects of product quality which can be further optimised by interactive processing are also summarised here. The document refers to the version of data processing pipeline currently being used for processing of incoming Herschel data.
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Data processing known issues of standard products for photometry and spectroscopy: Bulk-processed Level 2/2.5 products are provided in the Herschel Science Archive. This Data Processing Known Issues page describes typical problems and caveats the observer needs to be familiar when looking at the results of this "SPG" (standard product generation) processing. Aspects of product quality which can be further optimised by interactive processing are also summarised here. The document refers to the version of data processing pipeline currently being used for processing of incoming Herschel data.
 

Photometer calibration in scan maps

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  • Point Spread Function: PACS Photometer Point Spread function (10 Mb), version 2.2, 16 November 2015. A detailed document of the in-flight observed PSF. The accompanying tarball can be found here (76 Mb).
 
  • Herschel/PACS modelled point spread functions (3.1 Mb) is a related document presenting Zemax modelled point spread functions for both an `ideal' and an 'as built' Herschel telescope model. Tarballs with corresponding broad-band and monochromatic PSFs for these two cases are at http://pacs.ster.kuleuven.ac.be/pubtool/PSF. These are useful in addition to the observed PSFs but cannot replace them, since the models do not capture all effects found in the observed PSFs.
  • Point-source photometry: PACS uses 5 stars as primary calibrators with fluxes ranging from 0.6 to 15 Jy, plus fainter stars and asteroids as secondary calibrators. The absolute flux scale accuracy is dominated by the model uncertainties and amounts to 5% in the 3 filter bands. At the same time, the reproducibility for a given non-variable point source is better than 2% for all PACS bands. The flux calibration is described in detail in Balog et al, 2013, Experimental Astronomy and confirmed with asteroids in Müller et al., 2013, Experimental Astronomy.
  • Point-source photometry in deep PACS maps/surveys: The e ffect of the high-pass fi lter data reduction technique on the PACS Photometer PSF, point-source photometry, and noise has been investigated in depth in this technical note.
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    • We refer to the paper , G. Aniano et al. (2011) for kernels and associated routines (IDL) to match spatial resolution between several infrared instruments PSFs (PACS, SPIRE, Spitzer/MIPS, Spitzer/IRAC, WISE) as well as GALEX (UV) and other PSF families (gaussian, bi-gaussian, Moffat)
 
  • Chop/nod observations:
    • Chop/nod observations were not used for scientific observations during the mission, however they were heavily used for the photometry monitoring and well as numerous observations for the pointing accuracy check/monitoring. See Nielbock et al., 2013, Experimental Astronomy for the time dependent flux calibration for the PACS chopped point-source photometry AOT mode.
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Photometer map-makers

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  • Four fundamentally different map-makers are offered in HIPE 13 with interactive pipeline scripts, starting from Level 1. These map-makers are used in different ways to generate standard products ("SPG" product) provided by the Herschel Science Archive: high-pass filtering is applied to generate Level2 products, while Unimap and JScanam are used to create Level2.5 products. Level3 products are mosaics of Level2.5 products that belong to the same sky field and to the same observing program.
    • Highpass filtering branch, where the bolometer timelines are high-pass filtered to remove the 1/f noise, but at the expense of extended emission. It provides optimum sensitivity to point-sources
    • MADmap, a GLS (generalised least square) map-maker, that allows one to preserve extended emission at all scales. MADMap is not used anymore in the SPG processing, but it is still available as an interactive script.
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<-- This is corrected for MADmap in HIPE 12 by the task convertToFixedPixelSize() at the end of level1. The flux difference come from the fact that the mean values of the optical flat are significantly different from 1, in other words it cannot be assumed by external map-makers that the pixel sizes is constant of the field of view at 3.2"/6.4 in the blue/red channel respectively. Scanamorphos and Unimap are also affected, but not JScanam that makes use of photProject.-->
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PACS spectrometer calibration

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  • PACS Spectrometer performance and calibration: The PACS Spectrometer Calibration Document v2.4 (16-June-2011) provides details on the calibration accuracy and the necessary information to optimally interpret PACS spectroscopy observations. (Please note, this document refers to the calibration status and performance of pipeline version v8.0. An update compatible with HIPE v13 release will be provided soon.) This includes:
    • flux calibration accuracies for chop nod and unchopped observations
    • the beam efficiencies and the PACS integral field footprint
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  • Point source observations. To extract and calibrate the spectrum of a point source, it is necessary to use one of the tasks provided: it is not enough to add up the field-of-view of use the central spaxel only. How to do this is documented in the PACS DRG for spectroscopy.
  • Telescope background model: a script to compute the telescope background model calibration tables and a technical note explaining the method used can be found here. Warning: the calibration tables computed with this script are not the same as the ones in the calibration tree. See the technical note for details.
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PACS calibration file versions

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  • When starting HIPE, you will be informed if new calibration files are available. Clicking on 'show details' will show you the release note of the new calibration set, with details about the changes. This is further explained in the PDRGs. Clicking on 'Install' will install the latest calibration files.
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  • The history of the calibration files that have been released to the community is provided here: PACS Calibration File History.
  • You can inspect the release notes for the calibration sets installed on your machine from within HIPE. Open the Calibration Sets View from the menu Window -> Show Views -> Workbench.
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  • The history of the calibration files that have been released to the community is provided here: PACS Calibration File History.
  • You can inspect the release notes for the calibration sets installed on your machine from within HIPE. Open the Calibration Sets View from the menu Window -> Show Views -> Workbench.

 
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  • For a explanation of PACS products, i.e. what you get when you download a complete or part of an observation from the HSA, see the PACS Products Explained, which can also be found on the HIPE help pages.
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HIPE, data reduction documentation, and useful links for data issues

  • HIPE (Herschel Interactive Processing Environment) is the tool used to inspect, reduce, and analyse Herschel data. The latest User Release HCSS (Herschel common science system) version that you should use for reducing PACS data is HIPE v13.0 It can be downloaded from: http://herschel.esac.esa.int/HIPE_download.shtml. In the CIB (continuous integration build) this version corresponds to Track 13, build 5130. The CIB is the continuously bug-fixed/upgraded/improved version of HIPE, which every few months (in the beginning of the mission) or yearly (in the post-operations phase) becomes a stable User Release.
  • Within HIPE you can access all the PACS data reduction documentation and the general HCSS and HIPE user documentation for Track 13 here. The documentation provided via HIPE opens in a web browser, but for those of you who prefer PDF, we include the PACS Data Reduction Guides as PDF files here (note that within the standalone pdf versions, external links will not work):
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  • The what's new in HIPE 13 page lists the changes in HIPE version 13.x with respect to the 12.x series, and provides a detailed list of updated functionalities, product changes, and calibration aspects.
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  • The what's new in HIPE 13 page lists the changes in HIPE version 13.x with respect to the 12.x series, and provides a detailed list of updated functionalities, product changes, and calibration aspects.
 
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Cookbooks and interactive pipeline scripts

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  • The various interactive pipeline scripts PACS photometry and spectroscopy provide in HIPE can be seen as cookbooks, since they take you through each pipeline, task by task, explaining briefly what each task does, commenting on the more crucial pipeline tasks, and showing you how to plot, image, visualise and inspect your data as you work through the pipeline. An example public observation is included with each so you can test it out before using it on your data. These data reduction scripts are available in HIPE under the menu: Pipeline --> PACS --> Photometer/Spectrometer.
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  • The various interactive pipeline scripts PACS photometry and spectroscopy provide in HIPE can be seen as cookbooks, since they take you through each pipeline, task by task, explaining briefly what each task does, commenting on the more crucial pipeline tasks, and showing you how to plot, image, visualise and inspect your data as you work through the pipeline. An example public observation is included with each so you can test it out before using it on your data. These data reduction scripts are available in HIPE under the menu: Pipeline --> PACS --> Photometer/Spectrometer.
 
  • The PACS Launch Pad from HIPE 13 for photometry is provided here. The PACS Launch Pad from HIPE 13 for spectroscopy is provided here. These are taken from the first chapters of the respective PDRGs and are a useful quick-start guide to loading your data into HIPE, looking at them, and then what to know and do before you begin reprocessing your data with one of the pipelines. Also included is
    • why we recommend you do re-pipeline your data
    • what you need to pay attention to for different types of astronomical source
    • what the crucial pipeline tasks are
    • what the post-pipeline processing tasks that we provide are
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Tutorials and scripts

  • The Scripts menu in HIPE takes you to a set of PACS photometry and spectroscopy useful scripts. In HIPE 13 these are:
    • Point source aperture photometry
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  PACS Data Processing Tutorials.
  • HIPE Academy on YouTube: here you can find recordings of various seminars and webinars that the HSC have given on working in HIPE, reducing Herschel data, using various tools to visualise and manipulate data in HIPE, and etc.

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Quick links: wavelengths, sensitivity, PSFs

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 A summary of instrumental and calibration details that a data-reducing astronomer often wants know.

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 Spectroscopy
  • Wavelength ranges, resolution, band names
    • The blue bands are B2A (blue, second order) and B2B (green, second order), and B3A (blue, third order), and in the red we have R1 (first order)
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