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The representative frequency

Every spectral setup is characterised by a representative frequency, which is used to compute the spatial parameters of the Science Goal (primary beam, synthesised beamsize, maximum recoverable scale) and controls the atmospheric transmission used in the time estimate (see Step 3.8). It defaults to the centre of the last spectral window defined, but can be changed by the user to lie anywhere within the spectral windows of the setup using the representative window radio button and/or typing in the relevant field below the baseband tables. Note that the representative frequency is a rest frequency that will be transformed to a sky frequency using the velocity information for each source. Please check it carefully for each source, and modify it if necessary. For spectral line observations, the representative frequency should normally correspond to your transition of greatest interest, or if you are interested in several lines the one that has the poorest atmospheric transmission.

to to by -2 bp
Image Warning-icon-hi The exact choice of representative frequency can severely impact the time estimate, especially in the higher frequency bands 7, 8, 9 and 10. If it falls in a region of poor atmospheric transmission the time estimate will skyrocket compared to a setup with a representative frequency in an area of good atmospheric transmission. It is important that the representative frequency is set to the line of interest that falls into the region of the poorest atmospheric transmission, otherwise the requested sensitivity will not be reached for this line.
0.85 0.85 0.85 rg


width height depth 0 0 0 rg =0bpto


next up previous contents
Next: Finalise the spatial setup Up: Configure the spectral setup Previous: Spectral scans   Contents
The ALMA OT Team, 2016 Aug 23