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: http://www.atnf.csiro.au/computing/software/miriad/doc/line.html
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Key: line The ``line'' parameter determines the channels that are to be processed from a uv data-set. The parameter value consists of a string followed by up to four numbers. Defaults are used for any missing trailing portion of the parameter value. A uv data-set can have correlations from either (or both) a spectral or a wideband (continuum) correlator. Both the spectral and wideband correlators produce multiple correlations (channels). The string part of the line parameter is used to select the spectral or wideband channels. It may be one of: "channel" Spectral channels. "wide" Wideband (continuum) channels. "velocity" Spectral channels, resampled at equal increments in velocity (using the radio definition). The resampling involves a weighted average of the spectral channels. This is useful if the source was not Doppler tracked correctly. "felocity" Similar to "velocity", except that the parameters are given using the optical velocity definition. Generally the default is "channel" if the data-set has spectral channel data, and "wide" otherwise. The four numbers that accompany the string give: nchan, start, width, step These four numbers specify which channels to select from the input dataset and how to combine them to produce the output channels that the Miriad task will work on. nchan is the number of output channels produced. Generally it defaults to the number of input channels. start is the first channel from input dataset that is to be used. It defaults to 1 (i.e. first channel). width gives the number of input channels to average together to produce a single output channel. It defaults to 1. step gives the increment between selected input channels. It defaults to the value of "width". For "velocity" linetype, the start, width and step parameters are given in km/s. The output channels are centered on velocities: start, start+step, start+2*step, etc. The `line' parameter interacts with the "select=window" selection for "channel" and "velocity"/"felocity" linetypes. See the help on select for more information. For example: line=channel,10 selects 10 output channels, being input spectral channels 1 to 10. Similarly line=channel,10,8,1,2 selects 10 output channels, starting at input channel 8, and skipping every second input channel, whereas line=channel,10,8,2,2 selects 10 output channels, again starting at input channel 8, but each of the output channels consists of the average of two of the input channels. Finally line=velocity,10,-10,1,1 resamples the spectral data in velocity, to give 10 channels of width 1 km/s. The channels are centered at -10.0,-9.0,-8.0, etc, km/s.