Difference: PacsCalibrationWeb (129 vs. 130)

Revision 1302015-12-11 - KatrinaExter

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PACS instrument and calibration web pages

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    • wavelength calibration, including information on a skew our native line profile develops as a point source moves off the centre of a spaxel
    • table of the point source correction factors for different wavelengths
  • The calibration of the spectrometer is based on repeated measurements of planets, asteroids, and stars. The RMS scatter of these measurements are just over 10% within any spectral band, about the same when comparing different spaxels, and similar (but higher in the red) when looking for broad-band features within any band. See the PACS Spectrometer Calibration Document for the exact numbers. These calibration certainties are independent, and should be combined when quoting calibration errors.
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  • An explanation of the data errors for any particular observation is provided in the PACS Data Reduction Guide for spectroscopy (sec. 7.6 in the HIPE 13 version of the document)
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  • An explanation of the data errors for any particular observation is provided in the PACS Data Reduction Guide for spectroscopy (sec. 7.6)
 
  • 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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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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  • The PACS Launch Pad from HIPE 14 for photometry is provided here. The PACS Launch Pad from HIPE 14 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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  • The PACS Launch Pad from HIPE 14 for photometry is provided here. The PACS Launch Pad from HIPE 14 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
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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).
  • 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.
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  • 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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  • Expected signal-to-noise ratios and line sensitivity: this depends on the AOT, this information is also provided in the AOT Release Notes (see also update in sec. 6.1.3 of the PACS Observer's Manual) and can also be computed by running HSPOT.

Photometry

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    • Colour corrections: these are provided on this page in the section 'Photometer calibration in scan maps'
    • Aperture corrections/EEFs (encircled energy fractions) are provided in sec. 8 of the PACS Photometer Point Spread function document. See the section 'Photometer calibration in scan maps' on this page.
  • Effects of nonlinearity, saturation, stray light, crosstalk and ghosts: can be found in sec. 6 of the PACS Photometer Point Spread function document
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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
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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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