3.10  Spectral resolution and line profiles. Pre/post-recovery

From launch to the loss in June 1998, the CDS/NIS line profiles were very approximately Gaussians.

The CDS preflight calibration came up with the following numbers for the line half-widths in pixels:

        Slit    NIS1            NIS2
        4       3.4 +/- 0.3     3.2 +/- 0.2
        5       3.7 +/- 0.4     3.7 +/- 0.2

the line width in both bands is about 4.3 pixels FWHM with slit 4 and only slightly wider with slit 5, about 4.6 pixels.

After recovery the NIS line profiles have changed. The bakeout that CDS suffered during the SOHO loss changed the line profiles produced by the NIS spectrometer. The NIS1 profiles exhibit broader wings and the NIS2 profiles show a broadened and asymmetrical long wavelength wing.

See Software note #53 for details on the effect and on the broadened gaussian asymmetric profiles.

Figure 17: [Figures from the CDS user guide]