Data Reduction Frequently Asked Questions

My MERGE1D spectrum shows a gap although the MERGE2D spectrum does not.


During the 1-dimensional extraction the local spatial profile (along the cross-order direction) of the spectrum is determined by collapsing the 2-dimensional spectrum along the dispersion axis. The stdextract-interp-hsize parameter defines the half size of the region across which the spectrum is collapsed.

This parameter affects the interpolation of flagged pixels - if all columns are affected by bad pixels the result is set to 0, which causes the gap. In this case one needs to increase the default value to an optimal value of

stdextract-interp-hsize = size_of_gap[nm]/(2*size_of_pixel[nm])+1,

where size_of_pixel is given by the value of rectify-bin-lambda (by default 0, corresponding to 0.02nm for UVB and VIS data and to 0.06nm for NIR data, recorded in the CDELT1 FITS keyword of the products).