Astronomical observations with ISO are carried out via predefined observing modes known as AOTs , Astronomical Observation Templates. These are modes in which the basic operating parameters for the instruments are set (e.g. which sub-instrument to use at what wavelength resolution), leaving the user to select wavelengths to scan between, enter flux levels etc.
During an AOT observation, SWS scans the source spectrum by rotating the scanning mirror of the grating or varying the gap of the Fabry-Pérot . Each AOT may perform one or more exposures with an internal calibrator for a photometric check and a number of dark current measurements with the aperture closed. Hence, the data produced by any single AOT is generally of several different types.
Four AOT's , listed below, are defined for SWS. Operating modes have changed since the start of PV, and any such changes are noted in this document.
Table 4.1 summarises their properties. In all of these AOT's the measurements of photometric check, dark current and science data are interleaved in the ERD and SPD , while the AAR only contains science detector data for which an unique wavelength could be assigned to the light falling on that detector.
|AOT #||scan direction||reference scan|
Example output from all AOTs are given in sections 4.2 to 4.5.
In all cases AOTs are actually commanded as sets of ICSs , Instantiated Command Sequences. These are more basic instrument commands to open the shutter, start the grating moving etc. The eight defined for SWS are listed in table 4.2. The use of these ICSs is described in the following sections.
|SS0001||Diffuse cal (not used)|
|SS0002||Grating cal (dark - on low - wait)|
|SS0004||SW grating scan for AOT 7|
|SS0005||SW/LW grating scan for AOTs 1, 2 & 6|
|SS0006||Dark and Wait for AOTs 1 & 2|