Epsilon Nel system

The Epsilon Nel system, also known as the Nel system, was an inhabited planetary system which was located somewhere in the Alpha or Beta Quadrant. The system had two inhabited planets, including Nel III.

This system was one of eight visited by a group of Ullian telepathic historians in the 2360s, who collected a library of memories from the inhabitants. Soon after the visit, one of the planets in the system, Nel III, reported two unexplained comas. The comas were later determined to be a result of telepathic memory invasion perpetuated by Jev. A person of interest in the case, Tarmin, was exonerated as he was on his species' homeworld at the time of the visit. (TNG: "Violations")

The designation "Epsilon Nel" was seen on a computer monitor in the episode.
The Star Trek Encyclopedia, 4th ed., vol. 2, p. 72 dated the Ullians' visit to this system to the year 2368.