Figure 3.2: SWS AOT Selection Tree
The most common observations will probably use the full SWS grating resolution, using only the grating. Here the principal decision is between observation of a number of individual lines and observation of one or more longer wavelength ranges of interest. The individual line AOT (SWS02) is designed to obtain the best possible line profiles. Since they include finely sampled forward and backward scans over the line to tackle detector memory effects, they will need a minimum execution time of about 2 minutes per pointing and line. With the wavelength range AOT SWS06, the observer may specify wavelength intervals ranging from scans of small segments that cover essentially only one line to a full scan of the SWS wavelength range which can be specified by asking for 12 ranges identical with the 12 grating AOT bands (Chapter 2). Very short AOT SWS06 scans covering only one line are however of less quality than AOT SWS02 line observations, since they are less finely sampled. Furthermore, larger overheads that are tailored to long scans more than offset the saving in integration time caused by the coarser AOT SWS06 sampling.
Since scans of the full SWS wavelength range at the full grating resolution are time-consuming even for bright sources, an AOT SWS01 has been designed to obtain full scans quicker, but at the expense of spectral resolution. Several modes of this AOT provide different tradeoffs between execution time and spectral resolution.
For high spectral resolution observations using the Fabry-Pérot AOT SWS07 is the appropriate choice. It offers the additional advantage of getting simultaneous SW grating data at the expense of a modest increase in overheads.