Beta Tauri

Beta Tauri (Latinised from β Tauri, abbreviated Beta Tau, β Tau), officially named Elnath[10] (pronounced /ɛlˈnæθ/[11] or /ˈɛlnæθ/,[12] sometimes spelled Alnath), is the second-brightest star located in the constellation borders of Taurus and Auriga with an apparent magnitude of 1.65. It is a chemically peculiar B7 giant star, 134 light years away from Earth. It had a co-existing name Gamma Aurigae.

β Tauri
Location of β Tauri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
Right ascension  05h 26m 17.51312s[1]
Declination 28° 36′ 26.8262″[1]
Apparent magnitude (V) 1.65[2]
Characteristics
Spectral type B7III[3]
U−B color index −0.49[2]
B−V color index −0.13[2]
Astrometry
Radial velocity (Rv)9.2[4] km/s
Proper motion (μ) RA: +22.76[1] mas/yr
Dec.: −173.58[1] mas/yr
Parallax (π)24.36 ± 0.34[1] mas
Distance134 ± 2 ly
(41.1 ± 0.6 pc)
Absolute magnitude (MV)−1.42[5]
Details
Mass5.0 ± 0.1[6] M☉
Radius4.2[7] R☉
Luminosity700[8] L☉
Surface gravity (log g)3.65[9] cgs
Temperature13,824 ± 475[7] K
Metallicity [Fe/H]+0.08[9] dex
Rotational velocity (v sin i)59[9] km/s
Age100 ± 10[6] Myr
Other designations
Elnath, El Nath, Alnath, β Tau, 112 Tauri, BD+28°795, FK5 202, GC 6681, HD 35497, HIP 25428, HR 1791, SAO 77168, CCDM 05263+2836
Database references
SIMBADdata

Nomenclature

This star has two Bayer designations: β Tauri (Latinised to Beta Tauri) and γ Aurigae (Latinised to Gamma Aurigae). Ptolemy considered the star to be shared by Auriga, and Johann Bayer assigned it a designation in both constellations. When the modern constellation boundaries were fixed in 1930, the designation γ Aurigae largely dropped from use.[13]

The traditional name Elnath, variously El Nath or Alnath, comes from the Arabic word النطح an-naţħ, meaning "the butting" (i.e. the bull's horns). As in many other (but not all) Arabic star names, the article ال is transliterated literally as el, despite the fact that in Arabic pronunciation it is assimilated to the following n; it can also be omitted: Nath. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two batches of names approved by the WGSN; which included Elnath for this star.

In Chinese, 五車 (Wǔ Chē), meaning Five Chariots, refers to an asterism consisting of β Tauri, ι Aurigae, Capella, β Aurigae and θ Aurigae.[16] Consequently, the Chinese name for β Tauri itself is 五車五 (Wǔ Chē Wǔ; English: Fifth of the Five Chariots.)[17]

Physical properties

Elnath's absolute magnitude is -1.34, similar to another star in Taurus, Maia in the Pleiades star cluster. Like Maia, β Tauri is a B-class giant with a luminosity 700 times solar.[8] It has evolved away from the main sequence to become a giant star, larger and cooler than when it was on the main sequence.[18] However, being approximately 130 light-years distant compared to Maia's estimated 360 light-years, β Tauri ranks as the second-brightest star in the constellation.

It is a mercury-manganese star, a type of non-magnetic chemically peculiar star with unusually large signatures of some heavy elements in its spectrum.[9] Relative to the Sun, β Tauri is notable for a high abundance of manganese, but little calcium and magnesium.[8][19] However, the lack of strong mercury signatures, together with notably high levels of silicon and chromium, have led some authors to give other classifications, including as a "SrCrEu star" or even an Ap star.[20][21]

At the southern edge of the quite narrow plane of the Milky Way Galaxy a few degrees west of the galactic anticenter, β Tauri figures (appears) as a foreground object south of many nebulae and star clusters such as M36, M37, and M38.[22] It is 5.39 degrees north of the ecliptic, so it can be occulted by the Moon. Such occultations occur when the Moon's ascending node is near the vernal equinox, as was the case in 2007. Most occultations are visible only in the Southern Hemisphere, because the star is at the northern edge of the lunar occultation zone. Rarely, it may be occulted as far north as southern California.[23]

Companions

There is a faint star that appears close enough to β Tauri for astronomers to consider it a double star. Its visual companion, known as BD+28 795B, has a position angle of 239 degrees and is separated from the main star by 33.4 arcseconds.[24][25]

Six closer and even fainter stars have been detected during a search for brown dwarf and planetary companions, but all are considered to be background objects.[26]

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See also

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  3. Garrison, R. F; Gray, R. O (1994). "The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation". The Astronomical Journal. 107: 1556. Bibcode:1994AJ....107.1556G. doi:10.1086/116967.
  4. Evans, D. S (1967). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and their Applications. 30: 57. Bibcode:1967IAUS...30...57E.
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. Janson, Markus; et al. (August 2011), "High-contrast Imaging Search for Planets and Brown Dwarfs around the Most Massive Stars in the Solar Neighborhood", The Astrophysical Journal, 736 (2): 89, arXiv:1105.2577, Bibcode:2011ApJ...736...89J, doi:10.1088/0004-637X/736/2/89
  7. Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601
  8. Kaler, James B., ELNATH (Beta Tauri), University of Illinois, retrieved 2010-03-07
  9. Ghazaryan, S; Alecian, G (2016). "Statistical analysis from recent abundance determinations in HgMn stars". Monthly Notices of the Royal Astronomical Society. 460 (2): 1912. Bibcode:2016MNRAS.460.1912G. doi:10.1093/mnras/stw911.
  10. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  11. "Alnath". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
  12. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  13. Ian Ridpath. "Bayer's Uranometria and Bayer letters". Retrieved 2017-11-27.
  14. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  16. (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, ISBN 978-986-7332-25-7.
  17. (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.
  18. Knyazeva, L. N; Kharitonov, A. V (2000). "The Normal Energy Distributions in Stellar Spectra: Giants and Supergiants". Astronomy Reports. 44 (8): 548. Bibcode:2000ARep...44..548K. doi:10.1134/1.1306355.
  19. Heacox, W. D. (1979). "Chemical abundances in Hg-Mn stars". Astrophysical Journal Supplement Series. 41: 675. Bibcode:1979ApJS...41..675H. doi:10.1086/190637.
  20. Chen, P. S; Liu, J. Y; Shan, H. G (2017). "A New Photometric Study of Ap and Am Stars in the Infrared". The Astronomical Journal. 153 (5): 218. Bibcode:2017AJ....153..218C. doi:10.3847/1538-3881/aa679a.
  21. Bychkov, V. D; Bychkova, L. V; Madej, J (2009). "Catalogue of averaged stellar effective magnetic fields - II. Re-discussion of chemically peculiar a and B stars". Monthly Notices of the Royal Astronomical Society. 394 (3): 1338. Bibcode:2009MNRAS.394.1338B. doi:10.1111/j.1365-2966.2008.14227.x.
  22. Nemiroff, R.; Bonnell, J., eds. (5 March 2010). "Deep Auriga". Astronomy Picture of the Day. NASA. Retrieved 2010-03-07.
  23. "Skywatcher's Diary". Abrams Planetarium. Archived from the original on August 30, 2007.
  24. "CCDM (Catalog of Components of Double & Multiple stars (Dommanget+ 2002)". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-03-07.
  25. "Al Nath". Alcyone Bright Star Catalogue. Retrieved 2010-03-07.
  26. Janson, Markus; Bonavita, Mariangela; Klahr, Hubert; Lafrenière, David; Jayawardhana, Ray; Zinnecker, Hans (2011). "High-contrast Imaging Search for Planets and Brown Dwarfs around the Most Massive Stars in the Solar Neighborhood". The Astrophysical Journal. 736 (2): 89. arXiv:1105.2577. Bibcode:2011ApJ...736...89J. doi:10.1088/0004-637X/736/2/89.

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