Optionally a constraint can be added that the line shape is constant, and its strength is proportional to the continuum level. This is a good approximation in many recombination line experiments. In this case, an iterative algorithm is used to estimate the line shape and to optimally disentangle the line and the continuum.
See the related tasks CONTSEN and CONTERR, which give estimates of the noise amplification and the residual continuum.
line,nchan,start,width,stepThe default is all channels. Note that if there are multiple spectral windows, the fitting process is performed on each window separately.
line The output data-set is the line data. This is the default. fit The output data-set is the fitted line shape data. This is valid only when using the 'lpropc' option. chan0 The output data-set is an average of all the continuum data in a visibility record. continuum The output data-set is the continuum data. This has the same number of channels as the input data-set.
sun With this options, the OFFSET keyword is ignored, and a shift appropriate for the Sun is determined This can be useful to eliminate solar interference. twofit If either the OFFSET parameter is set, or the SUN option invoked, this options instructs UVLIN to perform a simultaneous polynomial fit for a emission both at the phase centre and at the appropriate offset. nowindow Normally uvlin processes the different windows separately. This will usually give the best result when the different windows are at quite different frequencies. However when the windows are at similar frequencies, or perhaps even abutting, then it is better to perform a single fit over all windows simultaneously. The "nowindow" option causes uvlin to do a single fit over all windows. lpropc The line shape is constant throughout the data-set, and the intensity is proportional to the continuum strength. This cannot be used together with the 'twofit' option. relax Normally UVLIN attempts to avoid overfitting the data by reducing the order of the fit. It does this if a significant number of channels are flagged (more than 40% bad) or if it believes there is inadequate data to perform the fit (less than 5*(order+1) channels). You can overwrite this conservatism, if you know what you are doing, with the `relax' option.The following options can be used to turn off calibration corrections. The default is to apply any calibration present.
nocal Do not apply the gains table. nopass Do not apply bandpass corrections. It is unwise to turn off bandpass correction, as the continuum estimation process will be confused by a bandpass which is not flat. nopol Do not apply polarization corrections.