Statistical confirmation of the UV spectral classification system based on IUE Low-Dispersion stellar spectra

In theIUE Low-Dispersion Spectra Reference Atlas (Hecket al., 1984a), a new spectral classification system specific to the UV had to be introduced because of the lack of one-to-one correspondence between the UV and visible ranges. It was elaborated from a classical morphological approach (Jaschek and Jaschek, 1984).This paper presents an independent confirmation of the correctness of this system. A statistical methodology working in a multidimensional parametric space has been applied to variables expressing, as objectively as possible, the information contained in the continuum and the spectral features of a set of stellar low-dispersion IUE spectra. This was done through, on the one hand, an asymmetry coefficient describing the continuum shape and empirically corrected for the interstellar reddening, and, on the other hand, the intensities of sixty objectively selected lines.These line intensities have been weighted in a way we called the variable Procrustean bed method because, contrary to a standard weighting where a variable is weighted in the same way for all the individuals of a sample, the spectral variables were weighted here according to the asymmetry coefficient which varies with the star at hand. The statistical algorithm consisted of a Principal-Component Analysis followed by a Cluster Analysis.The choice of the lines used for the morphological approach in the Atlas is shown to be correct. With respect to the UV classification system introduced in the atlas, the groups constructed by the cluster analysis display good homogeneity and discrimination for spectral types and luminosity classes, especially in the early spectral types which are well represented in the sample used for this study. The UV standard stars can be found in the neighbourhood of the barycenters of the groups. Moreover, the methodology developed here could be used in a later stage to predict UV spectral classifications.Based on observations collected by the International Ultraviolet Explorer (IUE) at the European Space Agency Villafranca Satellite Tracking Station (VILSPA) and on IUE data retrieved from the VILSPA data bank.