Wavelength Calibration for 150I

For some offsets both in LSS and MOS the pipeline cannot correctly align the redmost part of the 150I arc spectrum. This can be done manually by changing the parameters of the pipeline slightly.

Cosmic correction/spectrum extraction

The correction for cosmic rays done in the new pipeline since 2006-10-01 can distort line profiles, esp. of narrow lines. Users are therefore urged to check their extracted spectra carefully.

Sky background in MOS observations

The assumption of the new pipeline (since 2006-10-01) that at least 50% of the pixels contain only sky background is violated in many cases, so that the sky will be overestimated. Comparing the mapped science frame and the mapped sky frame allows to check this effect.  

Sky background in LSS observations

The use of a median to estimate the sky background (since 2006-10-01) does not correct for large spatial gradients.

Flat-fielding in MOS mode

Due to the problems induced by the stray light contamination, in some cases the pipeline may introduce small-scale, artificial patterns in the flatfielding. These patterns are mostly located close to the slit edges and are below the 3% level. Artifical patterns can also be introduced close to bad pixels regions, like the one located at (252,1658) and (1705,722)
The effect is shown below for the grisms 150I, 600B and 300V. Note that the intensity levels in the images have been set to enhance the effects.  

GRISM 150I

GRISM 300V

GRISM 600B