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Spectral scans

The Spectral Scan interface is a convenient way of setting up several correlator tunings to cover a wide, uninterrupted frequency range within a single ALMA band. You need to specify the start and end frequency as well as the desired Bandwidth, Resolution of each spectral window making up the scan. A maximum of 5 tunings can be observed within one Science Goal, which means there is a trade-off between achieving a high spectral resolution and covering a wide frequency range (if you want to cover a wider frequency range than possible with 5 tunings you will have to split the spectral scan across multiple Science Goals). Spectral averaging is possible in the same way as it is for Spectral Line observations.

Figure 3.6: Visualisation of spectral scan observations in the spectral editor pane.
Image fig7

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Image Warning-icon-hi The spectral scan interface may in certain cases yield a very inefficient observing strategy, causing the time estimate to skyrocket. This will happen mostly for observations with relatively long on-source times and many frequency tunings. It may be more efficient to set up such spectral scans using separate Science Goals for each frequency tuning.
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If the requested spectral scan can be set up successfully, the frequency tunings calculated by the OT are displayed in the spectral visualiser (see Fig. 3.6) and also listed in the spectral scan table. If not, a red error message will appear, indicating the origin of the problem. In Cycle 3, spectral scan observations are offered only for Individual Pointing(s) field setups with one pointing per source and a maximum limit of 150 pointings over all tunings (i.e. for 5 tunings the maximum number of pointings is 30).


next up previous contents
Next: The representative frequency Up: Configure the spectral setup Previous: Single Continuum   Contents
The ALMA OT Team, 2016 Aug 23