ON THE INFORMATION-CONTENT OF STELLAR SPECTRA

The basic aim of stellar spectroscopy is to determine the parameters o f the emitting object (e.g. for stellar atmospheres the two ''basic'' parameters effective temperature T(eff), surface gravity g as well as, to some extent, chemical element abundances epsilon(alpha) and microt urbulence xi). However, an inadequate resolution of the spectrum can l ead to a grossly incorrect interpretation of the spectrum (i.e. effone ous parameters). These incorrect interpretations may be considered as a result of a loss of spectral information associated with the inadequ ate spectral resolution and/or with the intrinsic smearing of spectral features. We introduce the apparent spectral information (ASI) of a s pectrum as a numerical measure for the apparent spectral information c ontent. To demonstrate the role of ASI, its numerical value is calcula ted for a B-star spectrum at different spectral resolutions and compar ed to the extent of elements observable at that resolution. Consequenc es for the analysis of spectra from fast moving objects and from very distant stars are addressed.