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PACS instrument and calibration web pages

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Introduction

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Important message about drizzled cubes in HIPE 13

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Due to an oversight in the pipeline scripts of HIPE 13, the drizzled cubes you get for chop-nod line scan observations created by "SPG 13" will have incorrect fluxes. Therefore you should not use the drizzled cubes downloaded from the HSA if the Meta datum "creator" is "SPG 13.0", whether they are within the ObservationContext at Level 2, or part of a Standalone Browse Product download. Any drizzled cubes created for unchopped mode observations will be unaffected. For chop-nod range scan observations, drizzled cubes are not created by the SPG 13 pipeline anyway. This oversight will be corrected in HIPE/SPG 14.
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Due to an oversight in the pipeline scripts of HIPE 13, the drizzled cubes you get for chop-nod line scan observations created by "SPG 13" will have incorrect fluxes. Therefore you should not use the drizzled cubes downloaded from the HSA if the Meta datum "creator" is "SPG 13.0", whether they are within the ObservationContext at Level 2, or part of a Standalone Browse Product download. Any drizzled cubes created for unchopped mode observations will be unaffected. For chop-nod range scan observations, drizzled cubes are not created by the SPG 13 pipeline anyway. This oversight will be corrected in HIPE/SPG 14.
  For the affected observations you have the following alternatives:
  • Use the projected cubes instead, which you will also find within the ObservationContext at Level 2, but which are not part of the Standalone Browse Product download for the affected observations.
  • Run one of the interactive pipeline scripts to create the drizzled cubes yourself. Contact the Herschel Helpdesk first to ask for an updated pipeline script to do this, since the interactive pipeline scripts in HIPE 13 (and 12) also contain the mistake.
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For Your Information: Drizzled cubes FITS files, and their name as listed in an ObservationContext, are: HPS3DD [R|B] (red and blue) Standalone browse product drizzled cube FITS files, and their name as listed in an ObservationContext in the browse product section are: HPS3DEQ [R|B] (red and blue, equidistant wavelength grid version of the drizzled cubes). Projected cubes have the name: HPS3DP [R|B].
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For Your Information: Drizzled cubes FITS files, and their name as listed in an ObservationContext, are: HPS3DD [R|B] (red and blue) Standalone browse product drizzled cube FITS files, and their name as listed in an ObservationContext in the browse product section are: HPS3DEQ [R|B] (red and blue, equidistant wavelength grid version of the drizzled cubes). Projected cubes have the name: HPS3DP [R|B].
  For more information about the standard and the standalone browse cubes provided for PACS spectroscopy, see the PACS Products Explained HIPE help document (which is also linked as a PDF file in the Data Reduction section).

Important message about Unimap maps in HIPE 13

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Some Unimap maps 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 not optimised convergence of the GLS algorithm and it will be corrected in HIPE/SPG14.
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Some Unimap maps 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 not optimised convergence of the GLS algorithm and it will be corrected in HIPE/SPG14.
 

Observing with PACS

  • The PACS Observer's Manual HTML PDF (11 Mb), version 2.3, 8-June-2011 : the first thing to read before applying for time with PACS (or even before working on PACS data for the first time), as it tells you how the instrument works. This includes:
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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).
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  • 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 files are the EEF tables for all the scanning strategies (Parallel/Prime mode, Fast/Medium scan speed) and the Vesta PSFs FITS files for Prime (51 MB) and Parallel (29MB) observations.
 
  • 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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  • 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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A new responsivity calibration (version) is deployed on the HCSS 7 track (this is explained in the internal report PICC-ME-TN-033 v1.01, where the associated encircled energy fraction [EEF] is given). This improves the accuracy of photometry to 3% in the blue channel and 5% in the red channel. 
"PACS photometer point-source flux calibration (3.1 Mb) (PICC-ME-TN-037), version 1.0, 12 April 2011.
We refer to: PACS Photometer: chop/nod point-source & mini-scan map AOT release note: (2 Mb) version 2.0, 12 November 2010. We recommend you use the mini scan-map technique in all science cases related to point-sources, compact sources and also in cases of faint extended emission around point-sources. The chop/nod mode is no longer recommended for use  
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A new responsivity calibration (version) is deployed on the HCSS 7 track (this is explained in the internal report PICC-ME-TN-033 v1.01, where the associated encircled energy fraction [EEF] is given). This improves the accuracy of photometry to 3% in the blue channel and 5% in the red channel.
"PACS photometer point-source flux calibration (3.1 Mb) (PICC-ME-TN-037), version 1.0, 12 April 2011.
We refer to: PACS Photometer: chop/nod point-source & mini-scan map AOT release note: (2 Mb) version 2.0, 12 November 2010. We recommend you use the mini scan-map technique in all science cases related to point-sources, compact sources and also in cases of faint extended emission around point-sources. The chop/nod mode is no longer recommended for use
* However, for a technical assessment of the original chop/nod mode sensitivity intended for point-sources, we refer to SAp-PACS-MS-0711-09 (5.5 Mb) and to the paper "The Herschel PACS photometer calibration - A time dependent flux calibration for the PACS chopped point-source photometry AOT mode" for the calibration of that 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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  • 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 reducing data with HIPE 12, 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.
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    • Scanamorphos by H. Roussel can be used to build maps from scan observations made with bolometer arrays, in particular with the PACS and SPIRE photometers
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    • Scanamorphos by H. Roussel can be used to build maps from scan observations made with bolometer arrays, in particular with the PACS and SPIRE photometers
 
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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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<!-- 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.-->
 

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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  • PACS spectrometer beams, version 3, can be downloaded here: PCalSpectrometer_Beam_v3.tar.gz. These beams are based on measurements of a raster with step size 2.5" around Neptune. These beam maps are useful e.g. if you want to compare to the flux distribution of your observation of a point source. Version 3 has the beam efficiencies for all IFU spaxels, and is a drastic improvement wrt version 2 as the spacecraft pointing was reconstructed more accurately. This reconstruction resulted in a non-equidistant sampling of the beam efficiency in the sky, but the beam products offered are equidistantly-sampled on a grid of 0.5 arcseconds. Each beam is normalised to the fitted peak value of the central spaxel. The WCS associated with the beam is in sky coordinates for position angle 0. The central part of the beam is the Gaussian fit to the measured beam efficiencies. This has been verified to be a very good description on the different raster observations we have of the central spaxels for wavelengths longer than 80 micron. Below 80 micron, the actual beam shows the square detector footprint, and the Gaussian approximation in the beam products v3 over-predicts the real beam efficiency by 1.5 to 2 percent. The outer part of the beams contains the interpolated values of the irregularly sampled measurements. Version 3 of the spectrometer beams are sharper than version 2, and shows the ghosts (ghosts are discussed in the Spectrometer Calibration Document ) more clearly, as well as the three-lobe structure of the Herschel telescope PSF.
  • The raw data from which the PACS spectrometer beams (all versions) have been derived is also available as tables (y, z offset - signal):
    • SpecSpatial_BeamEfficiency_central_spaxel_tables_v1.tar.gz:This contains a FITS file for each wavelength measured for the central spaxel only. Raw data of the coarse and fine rasters are combined. The array dimension of the fits file is [3,npoints] where the first column gives the y raster position, the 2nd column the z raster position and the 3rd column the normalised flux measured at this raster position.
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    • SpecSpatial_BeamEfficiency_tables_v1.tar.gz: Raw measurements PACS beams - all spaxels, coarse raster measurements only: each fits files corresponds to one wavelength. Each file contains the data for all spaxels of the coarse raster measurement only. Each fits file holds an array of 3x25x25x25 where: (0,25,25,25)=y raster position, (1,25,25,25)=z raster position, (2,25,25,25)=flux normalized to the central spaxel. The second and third dimensions are the raster position indices (y and z) and the last dimension is the module number (=spaxel number).
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    • SpecSpatial_BeamEfficiency_tables_v1.tar.gz: Raw measurements PACS beams - all spaxels, coarse raster measurements only: each fits files corresponds to one wavelength. Each file contains the data for all spaxels of the coarse raster measurement only. Each fits file holds an array of 3x25x25x25 where: (0,25,25,25)=y raster position, (1,25,25,25)=z raster position, (2,25,25,25)=flux normalized to the central spaxel. The second and third dimensions are the raster position indices (y and z) and the last dimension is the module number (=spaxel number).
 
  • 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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  • 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.
 
  • 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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Reducing PACS data

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 A brief introduction to reducing PACS data in HIPE. You can consult the PACS Data Reduction Guides (photometry and spectroscopy; available via HIPE) for more detail.
  • PACS data are reduced with pipeline scripts which are a set of command-line tasks that process the data from Level 0 (raw) to Level 2/2.5 (science-ready). There is more than one flavour of pipeline script, tailored to different types of science target, AOT, and observing plan. These 'interactive' pipeline scripts are provided in HIPE and explained in the data reduction guides.
  • The data you get from the the HSA will have been processed by the 'SPG' (Standard Product Generator) using one pipeline script flavour per AOT. Which script is used is documented in the PDRG.
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  • The SPG scripts include all the stable pipeline tasks within those scripts, with task settings that correspond to the most common type of science target for each AOT. But some pipeline tasks still can only be run via the interactive pipeline scripts, and to modify the parameter settings for the important pipeline tasks also requires you re-process the data. The Launch Pads (see below) include a guide to understanding the pipeline scripts and how to decide whether to reprocess your data and if so, with which script.
  • 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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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.
  • 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
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    • 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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    • Re-creating the standalone browse products
    • Convolution for spectral images
  • See the various walkthroughs on the NHSC PACS page.
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  • 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

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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  • Second-pass spectral ghosts: see sec. 4.2 of the PACS Spectrometer Calibration Document to learn about ghosts. These are bright spectral lines at one wavelength "echoing" to another wavelength in another spaxel. This is also documented in sec. 4.9 of the PACS Observer's Manual * The footprint of the integral field unit: text and figures showing the footprint of the PACS IFU, and how that compares to the beam, can be found in the PACS Spectrometer Calibration Document (sec. 3) where you will also find information about the beam maps (at high spatial resolution and for various wavelengths), beam efficiencies, and the point source loss corrections. The same information can be found in the PACS Observer's Manual (sec. 4.6).
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  • Second-pass spectral ghosts: see sec. 4.2 of the PACS Spectrometer Calibration Document to learn about ghosts. These are bright spectral lines at one wavelength "echoing" to another wavelength in another spaxel. This is also documented in sec. 4.9 of the PACS Observer's Manual * The footprint of the integral field unit: text and figures showing the footprint of the PACS IFU, and how that compares to the beam, can be found in the PACS Spectrometer Calibration Document (sec. 3) where you will also find information about the beam maps (at high spatial resolution and for various wavelengths), beam efficiencies, and the point source loss corrections. The same information can be found in the PACS Observer's Manual (sec. 4.6).
 
  • The FWHM of a point source (i.e. of the beam): this information can be found in fig. 4.12 of the PACS Observer's Manual and again in the PACS Spectrometer Calibration Document
  • Spectral line profile skews for off-centred sources: point sources that are not centrally located in a spaxel will show a skew to their spectral lines. The effect of this is to move the peak wavelength and slightly change the measured FWHM. Some calibration of this has been done and this can be found in sec. 4.7.2 and 4.7.3 of the PACS Observer's Manual and sec. 5.2 of the PACS Spectrometer Calibration Document.
  • Calibration certainties: these are all documented in the beginning of the PACS Spectrometer Calibration Document. Data errors are discussed in the PACS DRG for spectroscopy (sec. 7.6 in the HIPE 13 version).
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  • PSF and beams: the beams maps are provided as FITS files, and information about then can be found in the section 'Photometer calibration in scan maps'
  • Point source photometry
    • Colour corrections: these are provided on this page in the section 'Photometer calibration in scan maps'
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  • Calibration certainty: is discussed on this page in the section 'Photometer calibration in scan maps'), with links there to two publications. You can also read sec 3.3 of the PACS Observer's Manual
  • Sensitivity: this depends on the AOT, this information is also provided in the AOT Release Notes, and can also be computed by running HSPOT.
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META FILEATTACHMENT attr="" autoattached="1" comment="PACS Products Explained document (pdf)" date="1435065463" name="ppe-hipe13.pdf" path="ppe-hipe13.pdf" size="831421" user="Main.KatrinaExter" version="1"
META FILEATTACHMENT attr="" autoattached="1" comment="Raw measurements PACS beams - central spaxel only" date="1362764493" name="SpecSpatial_BeamEfficiency_central_spaxel_tables_v1.tar.gz" path="SpecSpatial_BeamEfficiency_central_spaxel_tables_v1.tar.gz" size="123836" user="Main.BartVandenbussche" version="1"
META FILEATTACHMENT attr="" autoattached="1" comment="Mueller exp. astr. paper 2013" date="1383609091" name="ExpAstr_PrimeAsteroids_revision1.pdf" path="ExpAstr_PrimeAsteroids_revision1.pdf" size="950563" user="Main.BrunoAltieri" version="1"
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