Because the spectra of close binaries such as UX For and AG Dor appear as composites, we need to separate the two stellar spectra at all phases in order to extract activity features from each spectrum. This is done by generating an artificial composite spectrum from two non-active MK standard stars closely matching our object stars. A modified version of the computer program originally developed by Huenemoerder & Barden ([1984]) (see also Huenemoerder et al. [1989]) was used. The procedure includes rotational broadening, radial-velocity shifting, and intensity weighting of both standard-star spectra in the Fourier domain. The resulting difference spectrum is minimized by a least-squares approach. The input set of reference spectra then gives the overall best-fit combination (following Strassmeier & Fekel [1990]). Finally, we subtract the ``synthetic'' binary spectrum from each observed spectrum to eliminate the contribution from the underlying inactive part of the stellar photospheres and chromospheres.
Observed spectra of UX For and AG Dor, together with the
respective synthesized spectra, were already shown in Washuettl &
Strassmeier ([1995]) and are not repeated here. In
Fig. 4, we show the sequence of the 14 reference standard
stars that are used for the synthesis, sorted by spectral type. Their
classifications from the literature were uncertain and inhomogeneous and
were partially revised in the course of this work. The criteria applied
were the same as described in Strassmeier & Fekel ([1990]), and
are based on a number of temperature-sensitive line ratios and the
morphology of the H
profile. The adopted spectral types are
indicated in Fig. 4.
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