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The EEV10 CCD for use on IDS
- General information on the device
- Spectral resolutions and wavelength coverage
- Spatial scale on IDS
- Fringing and Cosmetic defects
- Charge spreading variations and effects on spectral resolutions
- Flux standard data and empirical through-puts
- Quality control history of EEV10a
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Spectral resolutions and wavelength
coverage
The table linked here gives the dispersion
provided by each grating when mounted on the 235mm and the 500mm cameras.
Observers can calculate the dispersion provided, given that the pixel size
is 13.5 microns. The EEV10 is mounted on both cameras with it's 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. 
Observers should note that the 13.5 micron pixels
allow a higher spectral (and spatial) resolution to be achieved than when
using the TEKS. However this is of course at the expense of slit width.
Since the two cameras have different magnifications, and hence different
slit-width specfications for a particaular required resolution, Observers
should think carefully about what is the best option for their programs.
For example, it is now possible to reach a dispersion of higher than 0.8
Angstroms per pixels with the 235mm camera and this chip. The best focus
we have achieved so far on the 235mm camera is a FWHM of 2.2 pixels per
arc line, with a 1 arcsec slit-width. This is unlikely to decrease to exactly
2.0 pixels during normal setups, due to the accuracy that one can adjust
the capstans, and the slight charge spreading visible with these thinned
chips.
Spatial scale on IDS
A spatial scale of 0.4 arcsec/pixel and 0.19 arcsec/pixel is achieved on
the 235mm and the 500mm cameras respectively. The maximum unvignetted slit-length
usable with IDS is 3.3 arcmin and 1.6 arcmin for the 235/500mm respectively
(corresponding to a 500 detector pixels, spanning ~[800:1300, 1:4096]).
Fringing and Cosmetic defects
These thinned chips suffer severely from fringing in the red part if the
spectrum, which limits their 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. A flat
field image plus bias image will be visible from here shortly.
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's mean seeing (of around 1.0-1.5") spatial degradation
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 through-puts
Quality control history of EEV10
Coming soon .....!
This page is undergoing continual change and enhancements, if there
is anything you wish to see changed or added then please mail me.
