4.1 Introduction

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.

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AOT 1 : a single up-down scan  for each aperture. It has four possible scan speeds and is primarily intended to quickly scan the entire SWS wavelength range at degraded resolution .

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AOT 2 : slow short up-down scans , designed to measure line profiles.

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AOT 6 : medium length grating scans  with various options. Programmed as long up-down scan, possibly with reference scan . Used to observe long wavelength regions

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AOT 7 : LW section devoted to FP observations. The SW section does almost the same as in AOT 6. In this AOT priority is given to the FP.

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 

1 up-down no

2 up-down no

6 up-down possible

7  LW/FP up no

7  SW/grating up-down possible

 

Example output from all AOTs are given in sections 4.2 to 4.5.

4.1.1 ICS

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.

 

ICS Use

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

SS0007 Reset ICS

SS0008 Reset ICS

SS0009 FP LW