16.4.2 Continuum Subtraction

Continuum subtraction is a related problem. It is in principle needed to compute properly moment maps. However, it may be completely impossible, for example in the case of an optically thick line partially covering a continuum source. Continuum subtraction can be done in the image plane or in the uv plane. uv plane subtraction avoid the non linearity in the deconvolution, and thereby any amplification of errors induced in this process. Task UV_SUBTRACT performs this operation. Although signal to noise on the continuum is often much better than on the spectral line, it may be advantageous to subtract a source model rather than the measured visibilities; this is only true when thermal noise is more important than phase noise. Task UV_MODEL compute visibilities from an input image.