40 Eridani

40 Eridani is the system's Flamsteed designation and ο2 Eridani (Latinised to Omicron2 Eridani) its Bayer designation. The designations of the sub-components – B and C – derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU). also bears the variable star designation DY Eridani. The system bore the traditional name Keid derived from the Arabic word القيض () meaning "the eggshells", alluding to its neighbour Beid (Arabic "egg"). In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name Keid for the component on 12 September 2016 and it is now so included in the List of IAU-approved Star Names. ==Properties==

40 Eridani A is a main-sequence dwarf of spectral type K0.5, 40 Eridani B is a 9th magnitude white dwarf of spectral type DA4, and 40 Eridani C is an 11th magnitude red dwarf flare star of spectral type M4.5e. When component B was a main-sequence star, it is thought to have been the most massive member of the system at , but ejected much of its mass before it became a white dwarf. wider than the Sun does on Earth. An observer on a planet in the system would see the B–C pair as unusually bright white and reddish-orange stars in the night sky – magnitudes −8 and −6, slightly brighter than the appearance of Venus seen from Earth as the evening star. It is unlikely that habitable planets exist around because they would have been sterilized by its evolution into a white dwarf. As for , it is prone to flares, which cause large momentary increases in the emission of X-rays as well as visible light. This would be lethal to Earth-type life on planets near the flare star. ==Search for planets==

40 Eridani A shows periodic radial velocity variations, which were suggested to be caused by a planetary companion. The 42-day period is close to the stellar rotation period, which made the possible planetary nature of the signal difficult to confirm. A 2018 study found that most evidence supports a planetary origin for the signal, but this was controversial, with a 2021 study characterizing the signal as a false positive, and a 2022 study getting inconclusive results. Further studies in 2023 and 2024 concluded that the radial velocity signal very likely does originate from stellar activity, and not from a planet. The candidate planet would have had a minimum mass of , and lie considerably interior to the habitable zone, receiving nine times more stellar flux than Earth, which is an even greater amount than Mercury, the innermost planet in the Solar System, on average receives from the Sun. ==Appearance of the Solar System==

As seen from the 40 Eridani system, the Sun is a 3.4-magnitude star in Hercules, near the border with Serpens Caput. ==In fiction==

compared to the one of the Solar System, with the fictional planet Vulcan in Star Trek In the Star Trek franchise, the planet Vulcan orbits 40 Eridani A. Vulcan has been referenced in relation to the real-life search for exoplanets in this system. The planet is called "Erid" in both the book and its 2026 film adaptation. In the Dune franchise the fourth planet of 40 Eridani A is an inhabited and technologically advanced planet called Richese. In the Bobiverse series by Dennis E. Taylor, a double planet is found orbiting 40 Eridani A, and named Vulcan and Romulus by an uploaded intelligence in a von Neumann probe. ==Notes==