Consisting of a primary and four planets, the Romulan system was an inhabited star system in Sector Z-6 of the Alpha Quadrant. Its second and third planets were Romulus and Remus, the homeworlds of the Romulans and Remans, respectively. (TOS: "Balance of Terror", display graphic; Star Trek VI: The Undiscovered Country, production art; DS9: "The Search, Part II"; Star Trek Nemesis)
According to Startrek.com, the primary star in the system was called Romulus. According to Star Trek Maps (page 29) and The Worlds of the Federation (page 148), the Romulan star system was a binary star system of two white dwarfs known by the Federation as Romulus (primary) and Romulus B (secondary). In Diane Duane's Rihannsu novels, the indigenous name for the Romulan sun was Eisn.
According to the Star Trek: Star Charts (pg. 66), this system was located in or near the Romulan War Theater of Operations (2156-2160).
The location of the system in the Alpha Quadrant of the Milky Way Galaxy was depicted on a Federation star chart, in 2293. This "The Explored Galaxy" star map was first seen chronologically in Star Trek VI: The Undiscovered Country. It was also seen in several Star Trek: The Next Generation and Star Trek: Deep Space Nine episodes set in the 24th century, from the year 2364 to 2370. These were TNG: "Conspiracy", "The Measure Of A Man", "The Emissary", "The Mind's Eye", "The Game", and DS9: "In the Hands of the Prophets" and "Cardassians".