Upsilon Andromedae (υ Andromedae, abbreviated Upsilon And, υ And) is a binary star located 44 light-years from Earth in the constellation of Andromeda. The system consists of an F-type main-sequence star (designated υ Andromedae A, officially named Titawin in the Amazigh language <!--the Berber allophone of /i/ before the pharyngealized C2 just happens to match the trisyllabic laxing expected for Latinized words-->) and a smaller red dwarf.

, three extrasolar planets (designated Upsilon Andromedae b, c, d; named Saffar, Samh and Majriti, respectively) are believed to orbit υ Andromedae A. All three are likely to be jovian planets that are comparable in size to Jupiter. This was both the first multiple-planet system to be discovered around a main-sequence star, and the first multiple-planet system known in a multiple-star system.

Nomenclature

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.

  • HR 0458
  • CCDM 01367+4125