40 Eridani system
Located a mere 16.5 light years from the Sol system, the 40 Eridani system— also known as the Vulcan system or the Vulcanis system—is a trinary star system consisting of a Type K1V orange dwarf primary and two companion stars: a Type F VII white dwarf and a Type M4V red dwarf. The system's location in the Vulcan Sector (aka Sector 005) in the Beta Quadrant, is strategically important—its position at the heart of Federation space made it a tempting target for Dominion forces during the Dominion War.
The system's primary star, 40 Eridani A, is known to the Vulcans as Ko'vel. A Type K1V orange dwarf, Ko'vel is orbited by three planets. The first planet is Class B. The second and third planets—Vulcan (Class M) and T'Khut (Class G)—share an orbit,  which regularly gave magnificent views of T'Khut and its moon, Delta Vega,[Notes 1] from the Vulcan surface.
The system's companion stars are 40 Eridani B—known as Surak, for the founder of Vulcan philosophy—a Type D VII white dwarf, and 40 Eridani C—known as Sudoc, who was often considered to be Surak's opposite number—a Type M4V red dwarf. The stars were thus renamed following the Time of Awakening, as the two stars in the Vulcan sky would represent the dual nature of the Vulcan spirit: logic and emotion, respectively. The stars orbit each other at a distance of 400 AUs from Ko'vel, the system primary.
- Although not explicitly stated to be located within the Vulcan system, the most likely location for the Delta Vega seen in the film Star Trek would be the previously-unnamed moon of Vulcan's sister world, T'Khut. Established to be close enough to loom large in the Vulcan sky in Star Trek: The Motion Picture, this moon is near enough to Vulcan to not only provide the view of that planet's destruction during the Battle of Vulcan (as witnessed by Spock (Prime)), but also for Spock (Kelvin) to leave Kirk without a significant detour. Additionally, the Enterprise's warp drive was damaged in the battle (the Enterprise warp nacelles collided with the wreckage of the U.S.S. Mayflower's saucer section, and the bridge viewscreen didn't show the warp distortion until well after Kirk was left at Delta Vega), making it impossible for the ship to have traveled out of the system in the first place.
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- "In the Pale Moonlight." Star Trek: Deep Space Nine, episode 543. Television. 13 April 1998.