How do hot and warm pixels affect line fitting?#
As of February 2009 warm pixels account for around 11 % of the EIS CCD pixels, while hot pixels account for an additional 0.6 %. Hot and warm pixels, along with cosmic rays, saturated pixels and pixels affected by dust absorption are flagged by EIS_PREP as missing pixels and the recommendation from the EIS team up to now has been to not include them in your data analysis.
The number of warm pixels is now so large, however, that inspection of images formed from Gaussian line fit parameters (intensity, width, velocity) reveals many 'streaks' that result from distortions of the Gaussian fits due to the neglect of pixels in the line profile. The following questions thus arise:
- is simply ignoring warm pixels the best way of dealing with them?
- to what extent are derived line fit parameters affected by warm pixels?
- is there a critical number of warm pixels for which accurate line fit parameters will no longer be accurate?
A report has been prepared to investigate these issues and is available through the link below as a pdf file.
