Pollux (star)

**Pollux**, also designated **Beta Geminorum** (**β Geminorum**, abbreviated **Beta Gem**, **β Gem**), is an orange-hued evolved giant star approximately 34 light-years from the Sun in the northern constellation of Gemini. It is the brightest star in the constellation of Gemini and the closest giant star to the Sun.

Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. In 2006, an extrasolar planet (designated Pollux b or β Geminorum b, later named Thestias) was confirmed to be orbiting it.

## Nomenclature

*β Geminorum* (Latinised to *Beta Geminorum*) is the star's Bayer designation.

The traditional name *Pollux* refers specifically to the twins Castor and Pollux in Greek and Roman mythology. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included *Pollux* for this star.

Castor and Pollux are the two "heavenly twin" stars giving the constellation Gemini (Latin, 'the twins') its name. The stars, however, are quite different in detail. Castor is a complex sextuple system of hot, bluish-white A-type stars and dim red dwarfs, while Pollux is a single, cooler yellow-orange giant. In Percy Shelley's 1818 poem *Homer's Hymn To Castor And Pollux*, the star is referred to as "..mild Pollux, void of blame."

Following its discovery the planet was designated Pollux b. In July 2014 the International Astronomical Union launched 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 name was Thestias for this planet. The winning name was based on that originally submitted by theSkyNet of Australia; namely Leda, Pollux's mother. At the request of the IAU, 'Thestias' (the patronym of Leda, a daughter of Thestius) was substituted. This was because 'Leda' was already attributed to an asteroid and to one of Jupiter's satellites.

In the catalogue of stars in the *Calendarium of Al Achsasi Al Mouakket*, this star was designated *Muekher al Dzira*, which was translated into Latin as *Posterior Brachii*, meaning *the end in the paw*.

In Chinese, 北河 (*Běi Hé*), meaning *North River*, refers to an asterism consisting of Pollux, ρ Geminorum and Castor. Consequently, Pollux itself is known as 北河三 (*Běi Hé sān*, English: the Third Star of North River.)

## Stellar characteristics

Parallax measurements made with the Hipparcos astrometry satellite place Pollux at a distance of about 33.78 light-years (10.36 parsecs) from the Sun.

 File:Sun from Pollux (star).jpg
At an apparent visual magnitude of 1.14, Pollux is the brightest star in the constellation, brighter even than its neighbor Castor (Alpha Geminorum). The star is larger than the Sun, with about two times its mass and almost nine times its radius. Once an A-type main sequence star, Pollux has exhausted the hydrogen at its core and evolved into a giant star with a stellar classification of K0 III. The effective temperature of this star's outer envelope is about 7003466600000000000♠4666 K, which lies in the range that produces the characteristic orange hue of K-type stars. Pollux has a projected rotational velocity of 2.8 km·s−1. The abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is somewhat uncertain, with estimates ranging from 85% to 155% of the Sun's abundance.

Evidence for a low level of magnetic activity came from the detection of weak X-ray emission using the ROSAT orbiting telescope. The X-ray emission from this star is about 1027 erg s−1, which is roughly the same as the X-ray emission from the Sun. A magnetic field with a strength below 1 Gauss has since been confirmed on the surface of Pollux; one of the weakest fields ever detected on a star. The presence of this field suggests that Pollux was once an Ap star with a much stronger magnetic field. The star displays small amplitude radial velocity variations, but is not photometrically variable.

Pollux is 6.69 degrees north of the ecliptic, so on rare occasions viewers in Earth's southern hemisphere see it occulted by the moon.

## Planetary system

Since 1993, scientists have suspected an extrasolar planet orbiting Pollux, from measured radial velocity oscillations. The existence of the planet, Pollux b, was confirmed and announced on June 16, 2006. Pollux b is calculated to have a mass at least 2.3 times that of Jupiter. The planet is orbiting Pollux with a period of about 590 days.

The Pollux planetary system

## See also

* Aldebaran
* Pollux in fiction

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
2. ↑ 2.0 2.1 2.2 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
3. ↑ 3.0 3.1 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
4. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
5. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
6. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
7. ↑ 7.0 7.1 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
9. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
10. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
11. ↑ 11.0 11.1 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
12. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
13. ↑ "POLLUX -- Variable Star", *SIMBAD*, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-14<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
14. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
15. ↑ "Pollux". *STARS*. University of Illinois, Urbana–Champaign Campus. 2008. Retrieved 2009-05-29.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
16. ↑ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
17. ↑ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
18. ↑ "Homer's Hymn To Castor And Pollux by Percy Bysshe Shelley". *allpoetry.com*. Retrieved 13 April 2018.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
19. ↑ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
20. ↑ "NameExoWorlds". *nameexoworlds.iau.org*. Retrieved 13 April 2018.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
21. ↑ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
22. ↑ "NameExoWorlds". *nameexoworlds.iau.org*. Retrieved 13 April 2018.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
23. ↑ YOU helped name an exoplanet!, TheSkyNet, 2015-12-17
24. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
25. ↑ (in Chinese) *中國星座神話*, written by 陳久金. Published by 台灣書房出版有限公司, 2005, <templatestyles src="Module:Citation/CS1/styles.css" />ISBN 978-986-7332-25-7.
26. ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-30 at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
27. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
28. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
29. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
30. ↑ 30.0 30.1 **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
31. ↑ "The Colour of Stars", *Australia Telescope, Outreach and Education*, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
32. ↑ The abundance is determined by taking the value of [Fe/H] in the table to the power of 10. Hence, 10−0.07 = 0.85 while 10+0.19 = 1.55.
33. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**
34. ↑ **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**

## External links

* "Notes for star HD 62509". *The Extrasolar Planets Encyclopaedia*. Retrieved 2008-06-24.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
* "Pollux". *SolStation*. Retrieved 2005-11-21.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
* **Lua error in Module:Citation/CS1/Identifiers at line 47: attempt to index field 'wikibase' (a nil value).**

Coordinates: Sky map 07h 45m 19.4s, 28° 01′ 35″