ULTRAVIOLET PROPERTIES OF EARLY-TYPE GALAXIES

We analyse the UV properties of early-type galaxies from their UV spec tra in the IUE library, including both normal and active nuclei. We co -added the spectra, and hence the objects into groups of similar spect ral properties in the UV, also taking into account their properties in the visible/near-infrared ranges. Although, owing to the presence of a residual fixed pattern noise, IUE data cannot be improved by co-addi tion as expected for spectra containing only random noise, this proced ure still provided spectra of higher signal/noise ratio than in previo us studies, often based on individual spectra and therefrom derived co lour indices. Thanks to the co-adding procedure, information on spectr al features can now be assessed. The red stellar population groups exh ibit a far-UV flux at different levels. The higher ones denote the pre sence of the UV turnup, which possibly exhibits absorption features, a t least as detected through the IUE aperture. As to the blue stellar p opulation groups and/or AGNs, we have carried out simple syntheses wit h UV star cluster templates and galaxy spectra in order to infer the p roperties such as burst ages and contamination by an active nucleus. I t has been possible to derive information on the extinction law affect ing some internally reddened galaxies; there are cases where the prese nce of the lambda 2200 Angstrom absorption feature suggests a reddenin g law similar to the Galactic one, and others without the lambda 2200 Angstrom feature, suggesting that it is rather an SMC type law which a pplies, then.