The Starfleet Technical Manual, a licensed work, established the location of Vulcan at 40 Eridani, a real star system that modern astronomers have observed. While the 1973 Technical Manual reference was the earliest description of this system's inhabitation, the system location was not established in canon until episodes of Enterprise described the world as being 16 light years from Earth, the real-life measurement of 40 Eridani's distance. The STreference: Spaceflight Chronology is one source that differed with canon, listing the Vulcan system as orbiting Epsilon Eridani, a system that is not 16 ly away. Likewise, the Star Trek Online website's defunct Points of Interest section stated that Vulcan is located in the Sirius system, a star 8.6 LY from Sol (though the game itself gives the 40 Eri location in the Vulcan system's tooltip).
The Worlds of the Federation omits mention of the second and third star amd additional planets outside of the asteroid belt. The film Star Trek also established another planet called Delta Vega, which orbited close enough to Vulcan that it could be seen clearly from Delta Vega's surface. According to the novelization of that film, a planet named T'Khul is "the Vulcan system's third world."