Sigma Nelvana was the primary of the Nelvana system. The star was located within the Romulan Neutral Zone.
In 2366, the location of Sigma Nelvana was labeled on both a tactical intelligence analysis star chart and system map. (TNG: "The Defector", display graphic)
Sigma Nelvana was a Class M star. Magnitude was +9. This star was located in the Beta Quadrant. (Star Trek: Star Charts, page 66)