A&A Supplement series, Vol. 122, April II 1997, 371-380
Received November 22, 1994; accepted July 22, 1996
J.V. WallRoyal Greenwich Observatory, Madingley Road, Cambridge CB30EZ, UK
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.
keywords: methods: data analysis; numerical -- techniques: image processing