This page (revision-5) was last changed on 07-Dec-2016 14:14 by PeterYoung

This page was created on 18-Apr-2008 10:23 by PeterYoung

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!!! The effects of the spectral tilt on line ratios
[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
!!! The effects of the spectrum rotation on line ratios
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The EIS spectral images are not exactly aligned relative to the CCD and, for the SW band, images at shorter wavelengths are slightly higher on the CCD compared to longer wavelengths. The effect is small and, for example, for the Fe XII 186.88 and 195.12 lines it's less than 1 pixel. The effect is caused by the dispersion axis of the grating not being exactly aligned with the CCD axis.
The EIS spectral images are not exactly aligned relative to the CCD and, for the SW band, images at shorter wavelengths are slightly higher on the CCD compared to longer wavelengths. The effect is small and, for example, for the Fe XII 186.88 and 195.12 lines it's less than 1 pixel. The effect is caused by the dispersion axis of the grating not being exactly aligned with the CCD axis (i.e., the grating is tilted) and we refer to it here as the "spectrum rotation". This is different to the "slit tilt" which arises from a misalignment of the EIS slits relative to the CCD.
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Both the spectrum rotation and slit tilt were features of SOHO/CDS and the attached image (CCD.gif) produced for CDS illustrates what both effects do to the spectral images. Note that the spectrum rotation makes no contribution to the slit tilt.