Upsilon² Eridani (υ² Eridani, abbreviated Upsilon² Eri, υ² Eri), officially named Theemin , is a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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 ...

of Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.8. Based upon

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements obtained during the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

mission, it is approximately 66 parsecs (214

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s) from the Sun. This is an evolved red clump giant star with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of G8+ III. The measured angular diameter is 2.21

mas Mas, Más or MAS may refer to: Film and TV * Más y Menos, fictional superhero characters, from the Teen Titans animated television series * Más (Breaking Bad), "Más" (''Breaking Bad''), a season three episode of ''Breaking Bad'' Songs * Más ( ...

. At the star's distance, this yields a physical size of around 16 times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.9 ...

. It radiates 138 times the solar luminosity from its outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 5074 K.

Nomenclature

υ² Eridani ( Latinised to ''Upsilon² Eridani'') is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. It bore the traditional name ''Theemin'' (also written as ''Theemim'' and ''Beemin''). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name ''Theemin'' for this star on February 1, 2017 and it is now so now so included in the List of IAU-approved Star Names. In the

Almagest The ''Almagest'' is a 2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy ( ). One of the most influential scientific texts in history, it canoni ...

, Ptolemy called it ''hē kampē'', "the bend in the river;" Arab writers corrupted this to ''bhmn'', later becoming ''beemin'', ''beemun'' in the West. Then, its etymology was incorrectly derived from Hebrew תאומים (''te'omim''), meaning "twins," producing ''Theemin''. In Chinese, (), meaning '' Celestial Orchard'', refers to an asterism consisting of Upsilon² Eridani, Chi Eridani, Phi Eridani,

Kappa Eridani Kappa Eridani, Latinized from κ Eridani, is a solitary star in the constellation Eridanus. With an apparent visual magnitude of 4.25, it is bright enough to be visible to the naked eye on a dark night. Based upon an annual parallax sh ...

HD 16754 HD 16754 is a binary or triple-star system in the constellation Eridanus. It has the Bayer designation s Eridani; ''HD 16754'' is the designation from the '' Henry Draper catalogue''. The system is visible to the naked eye as a faint p ...

HD 23319 HD 23319 (h Eridani) is an orange-hued star in the constellation Eridanus. It has an apparent visual magnitude of 4.59, which is sufficiently bright to make it visible to the naked eye. The distance to HD 23319 can be estimated from its ...

, Theta Eridani, HD 24072,

HD 24160 HD 24160 is a single star in the equatorial constellation of Eridanus. It is visible to the naked eye with an apparent visual magnitude of 4.17. The distance to HD 24160 can be estimated from its annual parallax shift of , yielding a ...

, Upsilon⁴ Eridani, Upsilon³ Eridani and Upsilon¹ Eridani. Consequently, the Chinese name for Upsilon² Eridani itself is (, en, the Twelfth Star of Celestial Orchard).香港太空館 - 研究資源 - 亮星中英對照表
, Hong Kong Space Museum. Accessed on line November 23, 2010.

References

{{DEFAULTSORT:Upsilon2 Eridani G-type giants Horizontal-branch stars Eridanus (constellation)

Theemin Upsilon² Eridani (υ² Eridani, abbreviated Upsilon² Eri, υ² Eri), officially named Theemin , is a star in the constellation of Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.8. Base ...

Eridani, Upsilon2 CD-30 01901 Eridani, 52 029291 021393 01464