Minimum-component baselines: Fourier analysis for continuum assessment

This describes a technique for fitting baselines or continua to scans or spectra with a large proportion occupied by signal in the form of sources or emission/absorption lines. It is essentially a high-pass filtering technique; the very lowest Fourier frequencies are “filtered out" by using them to construct a model of the continuum. The technique is interactive, and subjective in that some decision is required by the analyst; but it is very stable despite this. Errors are analyzed and some examples are given to demonstrate the versatility of the technique. The route to generating an objective (hands-off) technique is discussed