Chapter 4. PACS spectrometer scientific capabilities
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Chapter 4. PACS spectrometer scientific capabilities

Table of Contents

4.1. Diffraction Losses
4.2. Grating efficiency
4.3. Spectrometer filters
4.4. Spectrometer relative spectral response function
4.5. Spectrometer field-of-view and spatial resolution
4.6. Spectrometer Point Spread Function (PSF)
4.6.1. Measured vs. model PSF
4.6.2. Detector sampling of the PSF
4.6.3. Measured beam efficiencies
4.7. Spectrometer spectral resolution and instrumental profile
4.7.1. Spectrometer spectral resolution
4.7.2. Wavelength calibration
4.7.3. Instrumental profile
4.8. Spectral leakage regions
4.9. Second-pass spectral ghost
4.10. Spectrometer flux calibration
4.10.1. Recovering full beam line fluxes and flux densities for point sources
4.10.2. Flux calibration accuracies
4.10.2.1. Absolute flux calibration accuracy
4.10.2.2. Relative flux calibration accuracy within a band and detection limit for broad features
4.10.2.3. Relative flux calibration accuracy between spaxels
4.10.2.4. Flux calibration accuracy of unchopped spectroscopy modes
4.11. Spectrometer sensitivity
4.12. Spectrometer saturation limits
4.13. Astrometric accuracy

4.1. Diffraction Losses

The image slicer is the most critical element of the PACS optics, in the figures below the effect of diffraction/vignetting by the entrance field stop and Lyot stop have been included. For the Lyot stop a worst-case loss of 10% is used. For the losses in the spectrometer the fraction of power arriving at the detector is shown in Figure 4.1.

Diffraction throughput of the spectrometer optics; the diffraction losses mainly occur in the image slicer.

Figure 4.1.  Diffraction throughput of the spectrometer optics; the diffraction losses mainly occur in the image slicer.

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3.6. Astrometric accuracy Home 4.2. Grating efficiency