An AOT is an "Astronomical Observation Template". This will be familiar to users of ISO and Spitzer. An AOT is a standard observing mode with an instrument that can be translated into instructions for the spacecraft to carry out the observations autonomously. Herschel will observe autonomously between DTCPs, so each observation must be carried out in a standard way that the spacecraft can understand. Thus, for each of the instruments only pre-defined types of observations can be carried out. The astronomer produces an AOR (Astronomical Observing Request) by taking an AOT and customising it for the required observations.
Following the experience of ISO, the number of AOTs has been deliberately restricted to allow observers as many options as possible, without requiring an unwieldy number of observing modes to be calibrated.
The first stage in AOR entry is to define the target. If it is a known object its name can be resolved with SIMBAD or with NED or, for a solar system target, as a NAIF ID. For unknown names (e.g. start points for scans), J2000 coordinates must be supplied by the observer. After defining the object, the observer should check that it is observable by Herschel by calculating its visibility windows. Bear in mind that when you define your observation further you may end up limiting its visibility to part of the target's unrestricted observing window.
Once the target is defined the observer must then select the required instrument and AOT to be used. Nine basic observing modes are supported: for HIFI, single point (point source spectrophotometry), mapping and spectral scans; for PACS, photometry, line spectroscopy and range spectroscopy; for SPIRE, SPIRE photometer and spectrometer; and the SPIRE PACS Parallel Mode. Each of these modes is further subdivided, HIFI, for example, offers a choice of fourteen different mixer bands. PACS photometry allows five variants including point-source photometry and chopped raster maps. SPIRE Spectrometer offers point source and raster maps, three choices of image sampling, and four choices of spectral resolution, etc. HSpot will guide you through this process of definition with a series of pull-down menus and pop-up windows.
For each observation there is a basic minimum unit of observing time required; the observer need only specify how many repetitions of this unit time are required -- obviously greater sensitivity is obtained through more repetitions (four integrations will give twice the sensitivity of a single one), but the observation takes longer. At any time the "Observation Est..." (Observation Estimate) button can be pressed and HSpot will give an estimate of the total time that the observation will take, including the overheads involved, with a break-down of information about the observation. If the total length of the observation exceeds the maximum permitted, HSpot will give a warning that the observation duration is out of limits.
The observer can vary the parameters of the observation (more or fewer repetitions, nodding on or off, larger or smaller chopper throw, a wider or narrower range of wavelengths or length of scan, etc.) and see how the time estimate varies. Once an acceptable combination of parameters has been found the observer accepts the parameters that are defined to fix the AOR; this AOR can however be modified later, if necessary.
When a proposal is submitted, HSpot takes the currently defined list of AORs and links them to the proposal. It is thus essential to ensure that the correct AOTs and AORs are defined and that the source visibility and observing time are correct for each target.