Data Reduction Frequently Asked Questions

Some of my extracted NIR STARE spectra show a jump at about 2.3μm - why and how can I correct it?


The fit of the sky background used by the X-shooter pipeline relies on the assumption that there is no gradient in flux along the slit. For the reddest part of the NIR spectra this assumption is not fulfilled and therefore the sky subtraction does not work well. The jump you see is caused by a bad sky correction and shows up most prominently for sky-dominated observations, i.e. sources with little flux compared to the flux of the sky background in that wavelength range.

If this wavelength region is important for your analysis you need to process the data without sky subtraction and then use independent software tools to fit and subtract the sky from the rectified, wavelength calibrated 2-dimensional frame (MERGE2D).