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Spectral scans

The new 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. The maximum number of tunings that can be observed within one Science Goal is 5, 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 2 Science Goals). Spectral averaging is possible in the same way as for Spectral Line observations, and the Representative Frequency can be edited to lie anywhere within the frequency range covered by the scan. Since the atmospheric transmission at the Representative Frequency is used to calculate the Time Estimate (see Step 3.8), careful attention should be paid to its location, particularly for Bands 7, 8 and 9. Like in the Single Continuum case the correlator setup is defined in the sky reference frame, implying that the same frequency range will be observed on sky regardless of the source velocity. The requested frequency range is reported in the rest frame for the source highlighted in the Targets table for reference purposes only.

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 2, 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: Finalise the spatial setup Up: Configure the spectral setup Previous: Spectral Line   Contents
The ALMA OT Team, 2014 May 21