What is the spectral coverage and resolution of CDS?
Information on the spectral coverage and resolution of NIS is given here. After the SOHO recovery the NIS line profiles changed, exhibiting extended wings and an asymmetry in the NIS2 profiles. The software was modified to permit fitting of these new profiles and is described in CDS Software Note 53: Post-recovery broadened line profiles (PostScript 128 Kb) The PSF of the spectrograph (as opposed to the telescope) optics affects the line profiles and can, if asymmetric, affect the interpretation of velocity information. This is discussed in a paper by S. V. H. Haugan Anomalous Line Shifts from Local Intensity Gradients on the SOHO/CDS NIS Detector (Solar Physics 185, 275, 1999) where it is predicted that the NIS spectrograph PSF must be slightly elliptical and rotated. From NIS observations taken with the small 2″x2″ slit, this indeed appears to be the case. See the routine CDS_CORR_GRADIENT for a possible correction technique. Information on the spectral coverage and resolution of GIS
