spire spectrometer data reduction : mapping observations
DESCRIPTION
SPIRE Spectrometer Data Reduction : Mapping Observations. Nanyao Lu NHSC / IPAC (On behalf of the SPIRE ICC). Goals. Overview of the SPIRE spectral mapping mode: AOR and the pipeline. Brief demo on using the Spectral Cube Analysis tool in HIPE: How to visualize a SPIRE spectral cube? - PowerPoint PPT PresentationTRANSCRIPT
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PACSPage 1
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
SPIRE Spectrometer Data Reduction: Mapping Observations
Nanyao Lu NHSC/IPAC
(On behalf of the SPIRE ICC)
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PACSPage 2
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
Goals• Overview of the SPIRE spectral mapping mode: AOR
and the pipeline.
• Brief demo on using the Spectral Cube Analysis tool in HIPE:– How to visualize a SPIRE spectral cube?– How to extract a 1-d spectrum within an aperture?– How to generate a line intensity map?
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PACSPage 3
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
Helpful Resources at Your Fingertips• HIPE -> Help contents:
– SPIRE Data Reduction Guide (SDRG):• Sect. 6. SPIRE spectroscopy mode cookbook.
– Sect. 6.7. Receipes for mapping observations.– Sect. 6.10. Cube analysis.
– Herschel Data Analysis Guide (DAG):• Sect. 6. Spectral analysis for cubes.
– SPIRE instrument and calibration page:• SPIRE Observer’s Manual.
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PACSPage 4
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
SPIRE FTS Observing Modes
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Spectral resolution:
High Res: 1.2 GHz (0.04 cm-1); R= 1290 – 370; ΔV = 230 – 800 km/s;
Medium: 7.2 GHz (0.24 cm-1);
R = 210 – 60.
Low: 25 GHz (0.83 cm-1 ); R = 62 – 18,
Spatial sampling usingan internal jiggle mirror (BSM):
Sparse(1 BSM pointing; 2 beam spacing)
Intermediate (4 BSM pointings; 1 beam spacing)
Full (16 BSM pointings; 1/2 beam spacing)
Telescope pointing:
Single Pointing
Raster (NxM)
Any observation involvingeither BSM jiggling or telescope raster is definedas a mapping observation.
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PACSPage 5
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
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BSM Jiggle Patterns
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PACSPage 6
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
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Telescope Raster Maps
SLW SSW
A 3x3 telescope raster with BSM in intermediate spatial sampling
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PACSPage 7
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
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Pipeline for Mapping DataLevel-1 Spectra
S(σ)
Preprocess Cube
Spatial Projection
Level-2 Product:Spectral Cube
A list of (ra, dec, spectrum)
An algorithm to assign individual spectra to the adopted map pixels.The pipeline uses the Naïve algorithm.
Regularly gridded spectral cube in units of W/(m2 Hz sr).
Collection of spectra per jiggle/raster position, in units of W/(m2 Hz sr).
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PACSPage 8
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
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The Naïve Projection in the Pipeline SSW: 2x2 raster with intermediate spatial sampling
The average of spectral scansfrom the 3 independent pointings is taken to be the spectrum for this map pixel of 19”x19” (SSW).
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PACSPage 9
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
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Coverage MapSSW coverage map in terms of spectral scans
There could be holes, as a result of dead detectors.
These map pixels have spectral values of NaN.
Holes can be eliminated by making map pixel size largerby reprocessing the data yourself.
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PACSPage 10
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
Remarks• By default, the outmost, vignetted detectors are not used in cube construction.
• Unlike photometer, there is only up to a few detectors within any map pixel. Thus, detector-to-detector calibration difference (i.e., flat fielding) is more important here.
• Residual telescope emission (of 0.4 Jy as of HIPE 11) could be still present in the continuum of a spectral cube.
• Aperture flux correction on 1-d spectrum extraction:
– If you can use a large aperture (>> the FTS beam size), it is rather trivial to extract a 1-d spectrum.
– If you have a point source in the map, its photometry is best done by going back to the appropriate Level-1 spectrum that centers on the target, and performing a point-source flux calibration.
– For a source that is slightly extended, aperture flux corrcetion for the extracted 1-d spectrum is tricky at this point.
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PACSPage 11
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
Demo on Spectral Cube Analysis Tool• Described in some detail in Herschel Data Analysis Guide, Chapter 6,
that comes with your HIPE.
• It works on 3-d data cubes of data type “SpectralSimpleCube” or “SimpleCube.”
• What can you do with this tool? We demonstrate some of its capabilities:
– Cube visualization and cropping.
– Extract a 1-d spectrum of data type “Spectrum1d” from a spectral cube. The result can be, as you learnt in one of our previous webinars, analyzed using HIPE Spectrum Toolbox (e.g., to fit a spectral line).
– Extract a 2-d spatial image of data type “SimpleImage” from a spectral cube. The result can be analyzed easily in HIPE or any existing tools outside HIPE. As an example, we will extract a CO line intensity map here.
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PACSPage 12
NHSC Data Processing Workshop – PasadenaAug 26-30, 2013
Demo on Spectral Cube Analysis Tool• We use the following sample data:
– OBSID = 1342198923
– NGC7023; HR, 2 repeats, full spatial sampling.
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