40 Eridani A was a star in the Vulcan system. This system was located in Sector 001, a region of space in the Alpha Quadrant. The Federation established the 40 Eridani A Starfleet Construction Yards in this system. In the 24th century, these yards commissioned the starships USS Brattain, USS Phoenix, and USS Prometheus. (ENT: "Home", set decoration, TNG: "The Wounded", "Night Terrors"; DS9: "Second Sight" dedication plaques)
- USS Brattain's dedication plaque made for TNG: "Night Terrors"
- USS Phoenix' dedication plaque made for TNG: "The Wounded"
- USS Prometheus' dedication plaque made for DS9: "Second Sight"
Background information Edit
It was not canonically established that 40 Eridani A is the location of Vulcan, until a draft of Geoffrey Mandel's book Star Trek: Star Charts was used in various ENT episodes which shows the location of "Vulcan (40 Eridani A)."
Previously it has been a popular piece of information throughout licensed works and fandom. The reference has worked its way into a number of background graphics and artwork, for example, the dedication plaques listing the fleet construction shipyards there. References to this star system as Vulcan's date back to James Blish's adaptation of "Tomorrow is Yesterday" in the book Star Trek 2, as well as a mention in the Star Fleet Technical Manual which Franz Joseph researched and compiled. On-screen statements of Vulcan being 16 light years away from Earth in "Home" and "Daedalus" also support 40 Eridani A as the location of Vulcan.
The Star Trek Encyclopedia (4th ed., vol. 1, p. 282) stated that Vulcan orbited the dwarf star 40 Eridani A, which is described as the brightest star of a triple star system.
In 1991, Star Trek creator Gene Roddenberry, along with three scientists from the Harvard-Smithsonian Center for Astrophysics, endorsed 40 Eridani A as Vulcan's primary (rather than Epsilon Eridani, which is occasionally misidentified as Vulcan's primary) stating, in part: "We prefer the identification of 40 Eridani as Vulcan's sun because of what we have learned about both stars at Mount Wilson ... based on the history of life on Earth, life on any planet around Epsilon Eridani would not have had time to evolve beyond the level of bacteria. On the other hand, an intelligent civilization could have evolved over the aeons on a planet circling 40 Eridani. So the latter is the more likely Vulcan sun." 
The Star Fleet Medical Reference Manual also references the Vulcan species as "Homo eridani."
According to Star Trek: Star Charts, (pp. 18, 19, 36, 45, 58, and, 60), the 40 Eridani (Omicron 2 Ceti) system was a trinary star system, with an orbital period of 248 years, located in the Vulcan sector (Sector 005), in the Beta Quadrant.
- 40 Eridani A: The star was classified as a K1V star with an absolute magnitude of 6.0. The system had three planets and an asteroid belt. The second of the three planets was the inhabitable planet Vulcan. It had no moons. (Spock explained this fact in "The Man Trap" when Uhura asked him for what amounted to romantic imagery. The harsh coldness with which he pointed it out made it unsurprising to her.) But the other two, visible only in daytime, both vaguely resemble moons from the surface of the second planet and have sometimes been mistaken for moons. Two thousand years ago, 40 Eridani A was a destination on the Debrune trade routes. On his final voyage, in 2120, Zefram Cochrane visited this system. In the mid-22nd century, 40 Eridani A was a destination on the Earth trade routes.
- 40 Eridani B: The secondary star was classified as a AVII star with an absolute magnitude of 11.2. The distance between Eridani A and B is 400 astronomical units.
- 40 Eridani C: The tertiary star was classified as a M4V star with an absolute magnitude of 12.3. Neither Eridani B nor C had any planets. The distance between Eridani B and C was 44 astronomical units.
According to Stellar Cartography: The Starfleet Reference Library ("Stellar Cartography" pp. 14-15, 17, 22-24, 34, 36, and 46; "The Dominion War: Strategy and Battles, 2373-75"), the 40 Eridani system was known to the Vulcans as Nevasi. This system was located in the Beta Quadrant. The primary star, 40 Eridani A (Nevasi A), was class K. The innermost planet was a rocky class B planet named Ket-Cheleb. Vulcan (T'Khasi) was in a co-orbital relationship with the class G planet T'Khut ("the Watcher"), which had one moon named T'Rukhemai ("the Eye of the Watcher"). The icy planetoid Delta Vega was located in the outer asteroid belt. The two companions of 40 Eridani A, 40 Eridani B (Nevasi B), and 40 Eridani C (Nevasi C), were a white class A4 dwarf and a red flare class M4 dwarf, respectively. In the 2150s, this system was in the Earth Trading/Exploration Region. This system was threatened by the Dominion after they occupied Benzar in 2375.