Pollux (star)
 The position of Pollux within the constellation of Gemini. |
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| Observation data Epoch J2000.0 Equinox J2000.0 |
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|---|---|
| Constellation | Gemini |
| Right ascension | 07h 45m 18.94987s[1] |
| Declination | +28° 01′ 34.3160″[1] |
| Apparent magnitude (V) | 1.14[2] |
| Characteristics | |
| Spectral type | K0 III[3] |
| U−B color index | +0.86[2] |
| B−V color index | +1.00[2] |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | +3.23[4] km/s |
| Proper motion (μ) | RA: –626.55[1] mas/yr Dec.: –45.80[1] mas/yr |
| Parallax (π) | 96.54 ± 0.27[1] mas |
| Distance | 33.78 ± 0.09 ly (10.36 ± 0.03 pc) |
| Details | |
| Mass | 2.04 ± 0.3[5] M☉ |
| Radius | 8.8 ± 0.1[6] R☉ |
| Luminosity | 43[7] L☉ |
| Surface gravity (log g) | 2.685 ± 0.09[6] |
| Temperature | 4,666 ± 95[6] K |
| Metallicity [Fe/H] | –0.07 to +0.19[6] dex |
| Rotation | 558 days[8] |
| Rotational velocity (v sin i) | 2.8[9] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
Pollux (β Gem, β Geminorum, Beta Geminorum) is a star in the northern constellation of Gemini, the Twins. With an apparent visual magnitude of 1.1,[2] Pollux is the brightest star in the constellation; brighter even than its neighbor Castor (Alpha Geminorum). Parallax measurements place it at a distance of about 33.78 light-years (10.36 parsecs) from Earth. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[11] In 2006, Pollux was confirmed to have an extrasolar planet orbiting it.[6]
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[edit] Properties
This star is larger than the Sun, with about two times its mass and almost nine times its radius.[6] Once an A-type main sequence star,[5] Pollux has exhausted the hydrogen at its core and evolved into a giant star with a stellar classification of K0 III.[3] The effective temperature of this star's outer envelope is about 4,666 K,[6] which lies in the range that produces the characteristic orange hue of K-type stars.[12] Pollux appears to be rotating at a leisurely rate, with a protected rotational velocity of 2.8 km s–1[9] The abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is somewhat uncertain, with estimates ranging from 85% to 155% of the Sun's abundance.[6][13]
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.[5]
[edit] Etymology
The name Pollux refers specifically to Castor and Pollux, the sons of Leda.[14] The star also bears Arabic name Al-Ras al-Tau'am al-Mu'akhar,(الرأس التؤام المؤخر), literally, 'The Head of the Second Twin.' Castor and Pollux together correspond to the Nakshatra Punarvasu in Hindu astronomy. The star is named Punartham in Malayalam.
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 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.[15]
In Chinese, 北河 (Běi Hé), meaning North River, refers to an asterism consisting of Pollux, ρ Geminorum and Castor.[16] Consequently, Pollux itself is known as 北河三 (Běi Hé sān, English: the Third Star of North River.)[17]
[edit] Planetary system
The detection of a suspected extrasolar planet Pollux b was announced on June 16, 2006. Pollux b is calculated to have a minimum mass of 2.3 times that of Jupiter. It is orbiting Pollux with a period of about 590 days.[6]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity |
|---|---|---|---|---|
| b | >2.30 ± 0.45 MJ | 1.64 ± 0.27 | 589.64 ± 0.81 | 0.02 ± 0.03 |
[edit] See also
[edit] References
- ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c d Lee, T. A. (October 1970), "Photometry of high-luminosity M-type stars", Astrophysical Journal 162: 217, Bibcode 1970ApJ...162..217L, doi:10.1086/150648
- ^ a b Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics 11: 29, Bibcode 1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333
- ^ Famaey, B. et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode 2005A&A...430..165F, doi:10.1051/0004-6361:20041272
- ^ a b c Aurière, M. et al. (September 2009), "Discovery of a weak magnetic field in the photosphere of the single giant Pollux", Astronomy and Astrophysics 504 (1): 231–237, Bibcode 2009A&A...504..231A, doi:10.1051/0004-6361/200912050
- ^ a b c d e f g h i j Hatzes, A. P. et al. (2006), "Confirmation of the planet hypothesis for the long-period radial velocity variations of β Geminorum", Astronomy and Astrophysics 457: 335–341, arXiv:astro-ph/0606517, Bibcode 2006A&A...457..335H, doi:10.1051/0004-6361:20065445
- ^ Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics 352: 495–507, Bibcode 1999A&A...352..495M
- ^ Koncewicz, R.; Jordan (January 2007), "OI line emission in cool stars: calculations using partial redistribution", Monthly Notices of the Royal Astronomical Society 374 (1): 220–231, Bibcode 2007MNRAS.374..220K, doi:10.1111/j.1365-2966.2006.11130.x
- ^ a b Massarotti, Alessandro et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal 135 (1): 209–231, Bibcode 2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
- ^ "POLLUX -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Beta+Geminorum, retrieved 2012-01-14
- ^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society 25: 1319, Bibcode 1993AAS...183.1710G, http://www.astro.utoronto.ca/~garrison/mkstds.html, retrieved 2012-02-04
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16
- ^ 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.
- ^ "Pollux". STARS. University of Illinois, Urbana–Champaign Campus. 2008. http://stars.astro.illinois.edu/sow/pollux.html. Retrieved 2009-05-29.
- ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 429. Bibcode 1895MNRAS..55..429K.
- ^ (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, ISBN 978-986-7332-25-7.
- ^ (Chinese) 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.
[edit] External links
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Wikimedia Commons has media related to: Pollux (star) |
- "Notes for star HD 62509". The Extrasolar Planets Encyclopaedia. http://exoplanet.eu/star.php?st=HD+62509. Retrieved 2008-06-24.
- "Pollux". SolStation. http://www.solstation.com/stars2/pollux.htm. Retrieved 2005-11-21.
- Sabine Reffert; Andreas Quirrenbach; Mitchell; Simon Albrecht; Saskia Hekker; Fischer; Marcy; Paul Butler (2006-07-07). "Precise Radial Velocities of Giant Stars II. Pollux and its Planetary Companion". Astrophys.J.652:661-665,2006 652: 661–665. arXiv:astro-ph/0607136. Bibcode 2006ApJ...652..661R. doi:10.1086/507516.
Coordinates: 
07h 45m 19.4s, +28° 01′ 35″
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