ccd_offset
- eispac.instr.ccd_offset(wavelength)[source]
Calculate the spatial offset of a line relative to He II 256 Å
Spatial offset of the specified wavelength relative to He II 256 Å. If you see a feature in the He II 256 image at coordinate \(Y\), then the corrected coordinate \(Y^{\prime}\) for any other wavelength \(\lambda\) is,
\[Y^{\prime} = Y - o(\lambda),\]where \(o(\lambda)\) is the CCD offset. Note that the spatial coordinate system for EIS is evalulated for He II 256 Å by cross-correlating with SOT.
The value of
ccd_offsetrepresents the number of pixels that a feature seen in a wavelength sits above the He II 256 Å image on the CCD.The following goes into the calculation of EIS CCD offset:
the tilt of the grating is assumed to be linear with wavelength
the tilt for SW was derived by [young09]
the tilt for LW was assumed to be the same as for SW
the offset between SW and LW was measured by co-aligning images from Fe VIII 185.21 Å and Si VII 275.35 Å
Note
This routine is a (nearly) verbatim translation of the IDL version of eis_ccd_offset written by Peter Young. The above documentation has been adapted from that routine.
- Parameters:
wavelength (array_like) – Wavelength of the spectral line(s) of interest in units of [Å]
- Returns:
offset – The spatial offset between the specified wavelength and He II 256.32. The value represents how many pixels above He II 256.32 the specified wavelength sits on the EIS detectors.
- Return type:
References