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We present HST/STIS observations and analysis of two prominent nebularstructures around the central source of Eta Carinae, the knots C and D. Theformer is brighter than the latter for emission lines from intermediate or highionization potential ions. The brightness of lines from intermediate and highionization potential ions significantly decreases at phases around periastron.We do not see conspicuous changes in the brightness of lines from lowionization potential (<13.6 eV) that the total extinction towards the Weigeltstructures is that the total extinction towards the Weigelt structures is AsubV=2/0. that the total extinction towards the Weigelt structures is AV = 2.0.Weigelt C and D are characterized by an electron density of that the totalextinction towards the Weigelt structures is AV = 2.0. Weigelt C and D arecharacterized by an electron density of 10exp6.9 cm-3 that does notsignificantly change throughout the orbital cycle. The electron temperaturevaries from 5500 K (around periastron) to 7200 K (around apastron). Therelative changes in the brightness of He I lines are well reproduced by thevariations in the electron temperature alone. We found that, at phases aroundperiastron, the electron temperature seems to be higher for Weigelt C than thatof D. The Weigelt structures are located close to the Homunculus equatorialplane, at a distance of about 1240 AU from the central source. From theanalysis of proper motion and age, the Weigelt complex can be associated withthe equatorial structure called the Butterfly Nebula surrounding the centralbinary system.

On the changes in the physical properties of the ionized region around the Weigelt structures in Eta Carinae over the 5.54-yr spectroscopic cycle