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ESPaDOnS: ccd readout modes and characteristics http://webast.ast.obs-mip.fr/magnetisme/espadons_new/ccd.html
slow 1.27 2.9 65 >65,535
xslow 0.84 2.5 90 >65,535
Several attempts were made at reading the chip through the second output line that the eev chip and the sandiego controllers
normally offer. However, our measurements indicate that the analog board of the sandiego controller (untested by cfht before
sending it to us) was bugged, with this second output line not behaving properly. We are therefore sticked to reading the chip
with the first output line only.
Fringing patterns
As all thinned ccds, eev chips are known to exhibit severe fringing patterns when
illuminated with infrared light. This is quite obvious from the image on the right
showing some of the reddest flat field orders obtained with ESPaDOnS. On this
image, the orders run vertically, and each of them show the expected cross order
structure for the polarimetric mode (two spectra per order and three slices per
spectrum). The fringing signature is that the flux along the orders is found to
exhibit very strong variations (with an amplitude of as much as 50%) on very
small scales (a few tens of pixels). These patterns are however observed to flat field
out properly, leaving no apparent residuals in the intensity or polarisation spectra
even when images are corrected using flat field frames with different count levels.
The only signature of this effect is that the error bar in the reduced spectrum is
found to vary, as expected, by relative amounts of as much as 25% on the same
spatial scales.
© Jean-François Donati, last update May 6 2004
2 of 2 08/07/04 11:31 PM