An Objective Multi-color Method for the Characterization of Low Resolution X-ray Spectra

We describe a new technique for the characterization of low{resolution X-ray spectra, based on generalized colors deened by means of a principal component analysis. Application of the method to a sample of optically and radio-selected Einstein Observatory X-ray sources yields groups that are dominated either by stars or by extragalactic sources. The method thereby provides an immediate interpretation in terms of diierences in the physics of the emission processes dominating the objects studied. The principal advantages of the method are that it provides an objective means of classifying source spectra and that it provides an objective means of obtaining the minimal set of spectral classiication parameters. Though the method does not signiicantly improve results obtained with previously employed techniques when applied to Einstein data, its objective operation should prove powerful in aiding source classiication in the more recent medium spectral resolution X-ray surveys based on the ROSAT and ASCA missions.