List of Figures

• Lay-out of SWS
• Block diagram of the SWS. The diagram shows the optical functions of the spectrometer, excluding its internal calibration sources, but including the shutter, the collimation and the imaging optics
• Optical schematic of the SWS. The diagram indicates the location of the six separate entrance slits behind the dichroics after the three apertures. It shows all the spectral order-separation filters and the internal wavelength calibrators. The shutters and the collimation and imaging optics have been left out
• Overview of possibilities for simultaneous use of LW grating and SW grating (top) and F-P and SW grating (bottom). Only combinations within the hatched area are allowed. The corresponding AOT band designations and aperture numbers are indicated.  
• SWS AOT Selection Tree  
• SWS grating instrumental profiles. The solid lines represent Gaussian fits. SW: laser plus continuum. LW: laser and dark current  
• Calculated SWS grating spectral resolution (confirmed by spot checks) as a function of wavelength for extended sources. The spectral orders are indicated in circles. For point sources the resolution of SW spectra will be about a factor two larger; for LW spectra this effect is not significant
• Measured SWS grating spectral response function for SWS AOT Bands 1A and 1B. The data of Band 1A are affected by noise. Vertical lines indicate the wavelength limits of the bands
• Measured SWS grating spectral response function for SWS AOT Bands 1D and 1E. The data of Band 1D are affected by noise
• Measured SWS grating spectral response function for SWS AOT Bands 2A and 2B. The fringes are real
• Measured SWS grating spectral response function for SWS AOT Bands 2C and 3A. The fringes in the data for Band 2C are real
• Measured SWS grating spectral response function for SWS AOT Bands 3C and 3D. The fringes are real
• Measured SWS grating spectral response function for SWS AOT Bands 3E and 4. The fringes are real
• SWS Fabry-Pérot spectral resolution as a function of wavelength, computed from measured mesh properties and confirmed by checks at selected wavelengths
• SWS Fabry-Pérot spectral response. The flux scale corresponds to a point source, diffraction losses at the aperture have been taken into account
• Computed ISO diffraction losses for the SWS F-P channels. The fraction of the ISO diffraction disk accepted by the effective SWS F-P aperture is shown as a function of wavelength
• Basics of leakage in F-P spectra. The instrumental profile of the combination of F-P and grating is given by the solid line. Residual transmission from neighbouring F-P orders occurs if the instrumental profile of the grating alone (dashed line) is too wide
• SWS Fabry-Pérot leakage. Leakage is defined here as the fraction of the total detected signal that originates in unwanted Fabry-Pérot orders. Preliminary data shown here are based on extrapolation from measurements at a few wavelengths. A better characterization is expected from in-orbit calibration
• Effects of leakage on a crowded spectrum. A wavelength range of high leakage has been selected for demonstration. The upper line shows the assumed true source spectrum at the SWS F-P spectral resolution, the lower line how it will appear in the presence of leakage.
• SWS Fabry-Pérot effective gap as a function of wavelength. To obtain the effective gap width for a given wavelength, the gap correction has to be added to the gap width for the reference wavelength of 25m. Both F-P units have gap widths of about 12.500 m.
• Sensitivity of AOT SWS01. Spectral flux density vs. wavelength, detectable at SNR = 20 per resolution element for a = 1 sec. For = 2 sec, allowed at the lower scan speeds, the achieved SNR will be a factor of 2 larger.
• Sensitivity of AOT SWS02. Flux density vs. wavelength, detectable at SNR = 20 per resolution element in a 2500 second observation.  
• Sensitivity of AOT SWS02. Line flux vs. wavelength (line confined within one resolution element), detectable at SNR = 20, in a 2500 second observation.  
• Sensitivity of AOT SWS06. Spectral flux density vs. wavelength, detectable at SNR = 20 per resolution element. It is assumed that a pure integration time of 120 sec is used for the wavelength range of 30 scanner steps covered by AOT SWS06
• Sensitivity of AOT SWS07 F-P. Flux levels that can be reached in an observation of approximately 1200 seconds, covering a wavelength range of 50 km/s at a S/N ratio of 10.  
• Off-line processing - flow diagram of the standard product generation pipeline.