The Seyfert 1 galaxy NGC 4593 - I. Variability of the UV spectrum andphysical conditions in the broad line emitting region.

Abstract

Results obtained for UV observations of NGC 4593 are reported. The observations were carried out at two epochs using the low resolution spectrograph and the large apertures of the IUE satellite. The data reduction is presented. The properties of the UV continuum as well as its variability are investigated, discussing the selection of continuum windows and the correction for reddening. The UV emission and absorption lines are discussed in conjunction with the optical data. The broad line emitting region is found to be a composite region where high-excitation lines might be formed in a spherical system of optically thin clouds and the low excitation lines in a dense region heated by a nonradiative mechanism and shielded by the Lyman continuum. This dense region might be identifed with an accretion disk whose inner region provides the bulk of the Balmer lines and whose outer and thicker region emits Fe II lines.