XMM-Newton Science Analysis System: User Guide

5.14 Sun Angle correction to the wavelength scale

Studies of RGS spectra of emission line sources have shown that line positions are systematically shifted with respect to laboratory wavelengths, and that the wavelength scales of both RGS are displaced by a few mÅ. A strong correlation has been found between the line shifts and the angular distance between the spacecraft pointing direction and the Sun (see http://xmmweb.esac.esa.int/docs/documents/CAL-SRN-0297-1-0.pdf). A correction for this effect has been implemented for the first time in SAS v13.0, through the rgsproc parameter withsunaglecorr. Starting in SAS v14.0, this correction is applied by default.

European Space Agency - XMM-Newton Science Operations Centre