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The EEV10 CCD for use on IDS

  1. General information on the device
  2. Spectral resolutions and wavelength coverage
  3. Spatial scale on IDS, and degradation of spatial profile at the CCD edges
  4. Fringing and Cosmetic defects
  5. Charge spreading variations and effects on spectral resolutions
  6. Flux standard data and empirical through-puts
  7. Quality control history of EEV10a

Spectral resolutions
and wavelength coverage

The table linked here gives the dispersion provided by each grating when mounted on the 235mm camera. The EEV10 is mounted with its 4096 pixel axis along the wavelength direction, giving maximum use of the beam width leaving the cameras. However the camera optics severely vignette the outer regions of the dispersed light beam such that approximately only 2275 of the CCD pixels are clear and unvignetted. The attenuation runs rises steeply at each end of the spectra. The unvignetted portion is roughly from pixel number 870 to 3145 in the spectral direction. Here is an example plot of a Lamp Flat on the 235mm camera. The points were vignetting starts, and the full free range are marked. The Y-axis is a real measure of the attenuation ratios. 

Spatial scale on IDS, and degradation
of spatial profile at the CCD edges

The 235mm camera with the EEV10 CCD provides a spatial scale of 0.40 arcsec/pixel. The maximum unvignetted slit-length usable with IDS is 3.3 arcmin, corresponding to some 500 detector pixels for EEV10.

Note that the spatial (=along the slit) profile degrades toward the upper and bottom parts of the CCD, giving the impression that in these regions the star image is out-of-focus (most evident in the vignetted regions where a stellar profiles becomes double-peaked). This is a feature due to the IDS optics, in particular the CCD corrector lens, that was not designed for large format detectors like the EEV10 CCD.

Fringing and Cosmetic defects

The thinned chip suffers from severely from fringing in the red part if the spectrum, which limits its usefulness in this region despite their continued good QE down to 8000Å. Here you have an illustrative flat field spectra for a similar EEV chip, but in the meantime the following numbers should serve as a reference guide to the severity of the problem :
 
Wavelength     Peak-to-Peak Amplitude
6500Å                 5%
7000Å                 15%
7500Å                 30%
8000Å                 50%   
8500Å                 60%
9000Å                 60-70%
There are a few cosmetic defects on the surface of the chip, but nothing particularly severe.

Charge spreading variations and effects on spectral resolutions

The diffusion of charges between pixels during integrations causes a degrading of the spatial and spectral resolution. For a long-slit spectrograph like IDS, with the INT mean seeing around 1".0-1".5, spatial degradation is not a significant worry with the pixel size of the EEV10, but it  is a consideration in the spectral direction. For a back illuminated CCD this charge diffusion (often referred to as the Modulation Transfer Function; MTF) becomes progressively worse for shorter wavelength incident light. For example, using a slit-width projecting to 2 pixels on the detector results in a FWHM measured of 2.4 pixels (measured at ~4000Å) when the spectrograph is at best focus. Similarly a slit-width projecting to 4 detector pixels will produce a FWHM of ~4.4 pixels (again at ~4000Å). This effect becomes less severe towards redder wavelengths and is negligible at around 6000Å. 

Flux standard data and
empirical throughput

Quality control history of EEV10a

More information on the performance of IDS with time can be found in the Quality Control page.

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Contact:  (IDS Instrument Specialist)
Last modified: 05 May 2011