MULTIFREQUENCY MONITORING OF THE SEYFERT-1 GALAXY NGC-4593 .1. ISOLATING THE NUCLEAR-EMISSION

We present data obtained within a campaign to monitor spectral variati ons in the low-luminosity Seyfert 1 galaxy NGC 4593, at X-ray, ultravi olet, optical and near-IR (J, H, K and L) frequencies. The different ' parasitic' contributions that contaminate the pure nuclear continuous emission have been isolated and modelled. The light from the composite stellar population and the dust in the bulge and disc of the underlyi ng galaxy are characterized by a spectral energy distribution similar to that of the Sb spiral M31. Its surface brightness profile is modell ed with two components and provides the luminosity through any given a perture. Stars are responsible for as much as 70-85 per cent of the 56 00-Angstrom flux through a 4 x 4 arcsec(2) square aperture. The 'small bump' which characterizes the spectral energy distribution of active nuclei in the 2000-4000 Angstrom range is well accounted for by many b lended broad Fe II lines plus Balmer continuum emission. On average si milar to 64 per cent of the total 2710-Angstrom flux is due to Fe II p lus Balmer emission. Almost half of the broad-line cooling is due to F e II line emission. The pattern of variability of the pure nuclear con tinuum, as well as the broad lines and their implications, is discusse d in an accompanying paper.