WASP-21 is a G-type star ( spectral type G3V) that is reaching the end of its

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

lifetime approximately 850 light years from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

. The star is relatively metal-poor, having 40% of heavy elements compared to the Sun. Kinematically, WASP-21 belongs to the thick disk of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. It has an exoplanet named WASP-21b. The survey in 2012 have failed to find any stellar companions to WASP-21.

Naming

In 2019 the WASP-21 system was chosen as part of the NameExoWorlds campaign organised by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

, which assigned each country a star and planet to be named. WASP-21 was assigned to

Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...

. The winning proposal named the star Tangra after a deity worshipped by the early

Bulgars The Bulgars (also Bulghars, Bulgari, Bolgars, Bolghars, Bolgari, Proto-Bulgarians) were Turkic semi-nomadic warrior tribes that flourished in the Pontic–Caspian steppe and the Volga region during the 7th century. They became known as nomad ...

, and the planet Bendida after a deity worshipped by the

Thracians The Thracians (; grc, Θρᾷκες ''Thrāikes''; la, Thraci) were an Indo-European languages, Indo-European speaking people who inhabited large parts of Eastern Europe, Eastern and Southeast Europe, Southeastern Europe in ancient history.. ...

Planetary System

In 2010 WASP-21 was discovered to host a

hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

type planet by the Wide Angle Search for Planets (WASP). and confirmed by

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

by the WASP team in 2010. Transit-timing variation analysis in 2015 did not find an additional planets in the system. In 2020, spectroscopic analysis has found the WASP-21 b atmosphere is mostly cloudless and contains sodium.

References

{{DEFAULTSORT:WASP-21 Pegasus (constellation) Planetary systems with one confirmed planet G-type main-sequence stars Tangra J23095825+1823459 21