Upsilon Andromedae

υ Andromedae (Latinised to Upsilon Andromedae) is the system's Bayer designation. Under the rules for naming objects in binary star systems, the two components are designated A and B. Under the same rules, the first planet discovered orbiting υ Andromedae A should be designated υ Andromedae Ab. Though this more formal form is occasionally used to avoid confusion with a secondary star υ Andromedae B, it is more commonly referred to as υ Andromedae b. The other planets discovered were designated υ Andromedae c, d, and e, in order of their discovery. In July 2014 the International Astronomical Union (IAU) launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars. The process involved public nomination and voting for the new names. In December 2015, the IAU announced the winning names were Titawin for υ Andromedae A and Saffar, Samh and Majriti for three of its planets (b, c and d, respectively). The winning names were those submitted by the Vega Astronomy Club of Morocco. The star is named after the Berber name Tiṭṭawin, ⵜⵉⵟⵟⴰⵡⵉⵏ, of Morocco's Tétouan city and Tunisia's Tataouine city, both cities' old town quarters are considered UNESCO World Heritage Sites. The planets honour the 10th- and 11th-century astronomers Ibn al-Saffar, Ibn al-Samh and Maslama al-Majriti of Muslim Spain. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. In its first bulletin of July 2016, the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names. ==Stellar system==

Upsilon Andromedae is located fairly close to the Solar System: the parallax of Upsilon Andromedae A was measured by the Gaia astrometry satellite as 74.19 milliarcseconds, corresponding to a distance of . A fainter and closer star, discovered in 2002, is confusingly referred to in the discovery paper as υ Andromedae B even though that designation is also used for a different companion. This 13th-magnitude red dwarf is 55" from υ Andromedae A and is believed to be the only one of the companions physically associated, at the same distance and a projected separation of . It has been added to the WDS as component D. The X-ray emission of Upsilon Andromedae A is low for a star of its spectral class. This means that the star may be moving, or move soon, out of the main sequence and expand its radius to become a red giant star. This is consistent with the upper limits on the age of this star. The absolute magnitude for this star is about 0.6 magnitudes brighter that if it were still on the main sequence. The star rotates at an inclination of degrees relative to Earth. The star is less massive and far less luminous than the Sun, and its age seems to be consistent with that of the system. == Planetary system ==

The innermost planet of the Upsilon Andromedae system was discovered in 1996 and announced in January 1997, together with the planet of Tau Boötis and the innermost planet of 55 Cancri. Even when the first planet was taken into account, there still remained significant residuals in the radial velocity measurements, and it was suggested there might be a second planet in orbit. In 1999, astronomers at both San Francisco State University and the Harvard-Smithsonian Center for Astrophysics independently concluded that a three-planet model best fit the data. The two outer planets were designated Upsilon Andromedae c and Upsilon Andromedae d in order of increasing distance from the star. Both of these planets are in more eccentric orbits than any of the planets in the Solar System (including Pluto). Upsilon Andromedae d resides in the system's habitable zone. Such a mechanism could have been triggered by perturbations on the orbit of the companion star, which arise from close encounters with other stars and from the tidal field of the Milky Way. The orbits of the two inner planets seems to be shaped by tidal interactions, while the evolution of c and d orbits is secular. Additional planets Astronomers initially thought that a fourth planet in this system could not exist because it would have made the planetary system unstable and would have been ejected. But in 2007, an island region of stability was reported where a fourth planet could exist. The existence of further planets too small or distant to detect has not been ruled out, though the presence of Jupiter-mass planets as close as 5 AU from Upsilon Andromedae A would make the system unstable. However, a potential fourth planet (Upsilon Andromedae e) was discovered in 2010. This planet seems to be in a 3:1 resonance with Upsilon Andromedae d. This may be the result of perturbations from the companion star removing material from the outer regions of the Upsilon Andromedae A system. == See also ==