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Revision 1322015-12-14 - LucaCalzoletti

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META TOPICPARENT name="WebHome"

PACS instrument and calibration web pages

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Introduction

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 This oversight has been corrected in HIPE/SPG 14. The drizzled cubes you get in an observation downloaded from the HSA with "creator" of "SPG 14.0" have correct fluxes. In HIPE 14 there is a dedicated script to produce these drizzled cubes. Therefore we recommend you use the SPG 14.0 products, or use the dedicated pipeline in HIPE 14 if you need your drizzled cubes before the SPG 14 products are available.

Photometry

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Some Unimap maps produced by SPG 13 and using HIPE 13 scripts show overshooting effects around very bright sources that are surrounded by a diffuse and relatively faint background. See, as an example, the blue image of NGC253 (obsID: 1342221743). This effect is due to a non-optimised convergence of the GLS algorithm and it will be corrected in HIPE/SPG14.
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Some Unimap maps produced by SPG 13 and using HIPE 13 scripts show overshooting effects around very bright sources that are surrounded by a diffuse and relatively faint background. See, as an example, the blue image of NGC253 (obsID: 1342221743). This effect is due to a non-optimised convergence of the GLS algorithm and it will be corrected in HIPE/SPG14.
  This has been corrected in HIPE 14, and products with "creator" of "SPG 14" have no overshooting effects.

Observing with PACS

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Photometer calibration in scan maps

  • Point Spread Function/Encircled Energy Fraction : PACS Photometer Point Spread function (10 Mb), version 2.2, 16 November 2015. A detailed document of the in-flight observed PSF and of the derivation of the EEF curves. The accompanying TAR file can be downloaded here (79 MB). It contains the Vesta PSFs FITS files and the EEF tables for all the scanning modes.
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  • 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.
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  • 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.
  • Colour corrections:
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Photometer map-makers

  • Four fundamentally different map-makers are offered in HIPE 14 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 Level2.5 products are generated by combining pairs of observations acquired in the scan plus cross-scan mode, using the Unimap, JScanam, and High-pass filtering mappers. Level3 products are mosaics of Unimap and Jscanam Level2.5 products that belong to the same sky field and to the same observing program.
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    • 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
  • JScanam, Unimap and MadMap mappers all clean the dataset of systematic effects and remove the correlated 1/f noise while preserving the sky signal over large spatial scales. They are suited for analysing both point sources and extended emission.
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    • Highpass filtering branch, where the bolometer timelines are high-pass filtered to remove the 1/f noise, but at the expense of extended emission.
 
    • JScanam, a Java-version of the IDL Scanamorphos map-maker, an IDL map-maker from Hélène Roussel (IAP), with an advanced and powerful destriper for PACS maps
    • Unimap, a GLS (generalised least square) map-maker from Lorenzo Piazzo ('La Sapienza' University of Rome) running under a free Matlab runtime environment, with advanced pre-processing (drift correction, jump detection) and post-processing stages (bright sources). The runUnimap task is used to invoke the Unimap Matlab routine on the users's computer
    • MADmap, a GLS (generalised least square) map-maker, a GLS map-maker that is not used anymore in the SPG processing, but it is still available as an interactive script
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Highpass filtering provides optimum sensitivity to point-sources while JScanam, Unimap and MadMap mappers all clean the dataset of systematic effects and remove the correlated 1/f noise, preserving at the same time the sky signal over large spatial scales. They are suited for analysing both point sources and extended emission.
 
  • A report of the map-making working group compiled by Roberta Paladini is available: PACS map-making tools: analysis and benchmarking, 1 Nov. 2013.
  • An updated version of that report, concentrating on JScanam, MADmap and Unimap in their latest versions is available: PACS map-making tools: analysis and benchmarking, 30 March 2014.
  • If you are using data with SPG v 12 or lower, or reducing data with HIPE 12 or lower, remember that the optical field distortion in not applied at level 1. As a result, external map-makers starting from level 1 have a systematic flux overestimate of 6-7% in the red channel and a lower underestimate (~2%) in the blue channel of the flux scale. From HIPE 13/SPG 13 onwards, this has been corrected.
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  • Link to the General HCSS Public Twiki page (with general framework information and updates): http://herschel.esac.esa.int/twiki/bin/view/Public/WebHome
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Cookbooks and interactive pipeline scripts

  • 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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