Tau Herculis

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Tau Herculis
Hercules Historical View.png
Historical view of the Hercules constellation showing τ as the "northern knee"
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension  16h 19m 44.4368s[1]
Declination 46° 18′ 48.119″[1]
Apparent magnitude (V) 3.89[1]
Characteristics
Spectral type B5 IV[1]
U−B color index -0.57[2]
B−V color index -0.155[2]
Astrometry
Radial velocity (Rv)-13.8[1] km/s
Proper motion (μ) RA: -13.15[1] mas/yr
Dec.: 39.31[1] mas/yr
Parallax (π)10.37 ± 0.53[3] mas
Distance310 ± 20 ly
(96 ± 5 pc)
Absolute magnitude (MV)−0.96[4]
Details
Mass4.9[5] M
Radius3.55±0.19[6] R
Luminosity574[4] L
Surface gravity (log g)4.02±0.05[6] cgs
Temperature15,615±301[6] K
Metallicity [Fe/H]0.15[7] dex
Rotational velocity (v sin i)46[8] km/s
Age1[5] Gyr
Other designations
Rukbalgethi Shemali, τ Her, 22 Her, HR 6092, BD 46° 2169, HD 147394, FK5 608, HIP 79992, SAO 46028, GC 21987, CCDM J16197+4619A
Database references
SIMBADdata

Coordinates: Sky map 16h 19m 44.437s, +46° 18′ 48.12″

Tau Herculis, Latinized from τ Herculis, is a fourth-magnitude star in the constellation Hercules. It is a blue subgiant star, seven hundred times more luminous than the Sun.

Properties[edit]

Tau Herculis has a stellar classification B5IV. Its mass is 4.9 times solar.[5] Though its apparent magnitude is only 3.89, like all B-class stars, it is very luminous, boasting a total bolometric luminosity that is 700 times solar.[5] Hipparcos estimated its distance at roughly 96 parsecs from Earth, or 310 ± 20 light years away.

Pole Star[edit]

Small white disks representing the northern stars on a black background, overlaid by a circle showing the position of the north pole over time
The path of the north celestial pole among the stars due to the precession.

Tau Herculis is a visible star located within 1° of the precessional path traced across the celestial sphere by the Earth's North pole. It was the northern pole star around the year 7400 BC, a phenomenon which is expected to reoccur in the year 18,400 due to precession.[5]

The current pole star is, of course, Polaris. Among the 14 stars that could be reasonably[weasel words] considered eventual northern pole stars, Tau Herculis is the dimmest, but only Polaris itself and Thuban are closer to the precessional path.[citation needed]

Preceded by Pole Star Succeeded by
Iota Herculis 18,400 AD Edasich

Etymology[edit]

Its traditional name, Rukbalgethi Shemali, is of Arabic origin and shares certain etymological characteristics with the stars Ruchbah and Zubeneschamali, signifying Hercules' "northern knee".[9]

In Chinese, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of τ Herculis, 42 Herculis, φ Herculis, χ Herculis, ν1 Boötis, μ1 Boötis and δ Boötis.[10] Consequently, the Chinese name for τ Herculis itself is 七公二 (Qī Gōng èr, English: the Second Star of Seven Excellencies.)[11]

References[edit]

  1. ^ a b c d e f g "* tau Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-06-10.
  2. ^ a b Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M
  3. ^ Perryman, M. A. C.; et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P
  4. ^ a b 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.
  5. ^ a b c d e Kaler, James B., "TAU HER (Tau Herculis)", Stars, University of Illinois, retrieved 2018-04-27
  6. ^ a b c Fitzpatrick, E. L.; Massa, D. (March 2005), "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry", The Astronomical Journal, 129 (3): 1642–1662, arXiv:astro-ph/0412542, Bibcode:2005AJ....129.1642F, doi:10.1086/427855
  7. ^ Smith, K. C.; Dworetsky, M. M. (1993), "Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part One - Iron Peak Elements", Astronomy and Astrophysics, 274 (2): 335, Bibcode:1993A&A...274..335S
  8. ^ Royer, F.; et al. (2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i in the northern hemisphere", Astronomy and Astrophysics, 393 (3): 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943
  9. ^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.
  10. ^ (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.
  11. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日