Theta Herculis

Theta Herculis is a single,[11] variable star in the northern constellation of Hercules. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 3.851.[2] Based upon parallax measurements, it is located around 750 light years away from the Sun. The star is advancing toward the Earth with a heliocentric radial velocity of –28 km/s.[7]

Theta Herculis

Historical view of the Hercules constellation showing Rukbalgethi Genubi (θ Her) as the "southern knee", right of center
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension  17h 56m 15.18054s[1]
Declination 37° 15′ 01.9343″[1]
Apparent magnitude (V) 3.851[2]
Characteristics
Spectral type K1IIaCN2[3]
U−B color index +1.40 [4]
B−V color index +1.35[4]
R−I color index +0.63[5]
Variable type Irregular (suspected)[6]
Astrometry
Radial velocity (Rv)–28.32[7] km/s
Proper motion (μ) RA: 2.67[1] mas/yr
Dec.: 6.47[1] mas/yr
Parallax (π)4.33 ± 0.13[1] mas
Distance750 ± 20 ly
(231 ± 7 pc)
Absolute magnitude (MV)−2.71+0.26
−0.23[8]
Details
Mass4.94[9] M☉
Radius89.97[9] R☉
Luminosity2,405.7[9] L☉
Surface gravity (log g)1.24[9] cgs
Temperature4,266[9] K
Metallicity [Fe/H]−0.11[9] dex
Rotational velocity (v sin i)3.4 ± 0.6[8] km/s
Age130[9] Myr
Other designations
Rukbalgethi Genubi, θ Her, 91 Her, BD+37°2982, FK5 672, GC 24415, HD 163770, HIP 87808, HR 6695, SAO 66485[10]
Database references
SIMBADdata

This is an aging K-type bright giant with a stellar classification of K1IIaCN2,[3] where the suffix notation indicates a strong overabundance of CN in the spectrum. The brightness variations of this star was first noticed in 1935 by M. Fedtke and confirmed by Erich Przybyllok and Kurt Walter the same year.[12] French astronomer Paul Muller then classified Theta Herculis as an irregular variable with a range of magnitudes between 3.7 and 4.1 and a periodicity of roughly 8–9 days.[6]

The star is about 130[9] million years old with 4.94[9] times the mass of the Sun. With the hydrogen at its core exhausted, the star has expanded to 90[9] times the Sun's radius. It is radiating 2,406[9] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,266 K.[9]

Nomenclature and etymology

θ Herculis is the Bayer designation, Latinised to Theta Herculis, abbreviated to θ Her or Theta Her.

In the Calendarium of Al Achsasi Al Mouakket, this star was designated Rekbet al Jathih al Aisr, which was translated into Latin as Genu Sinistrum Ingeniculi, meaning the left knee of the kneeling man.[13] The traditional name Rukbalgethi Genubi that is encountered in various texts is etymologically similar to the stars Ruchbah and Zubenelgenubi, the term "ruchbah" meaning "knee" while "genubi" signifies "southern"—hence the "southern knee", a meaning which can be gleaned more easily by looking at the accompanying constellation map.[14]

In Chinese, 天紀 (Tiān Jì), meaning Celestial Discipline, refers to an asterism consisting of θ Herculis, ξ Coronae Borealis, ζ Herculis, ε Herculis, 59 Herculis, 61 Herculis, 68 Herculis and HD 160054.[15] Consequently, the Chinese name for θ Herculis itself is 天紀九 (Tiān Jì jiǔ, English: the Ninth Star of Celestial Discipline.)[16] It was also Tien Ke, Heaven's Record.[17]

gollark: The UK adopted this recently for GCSEs but it runs 9 (best) to 1 (worst).
gollark: [REDACTED]
gollark: It looks like the design change is still in their A/B test system, so I can override it for now.
gollark: Or you just haven't updated.
gollark: I think they may be A/B testing.

References
  1. van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. McWilliam, Andrew (December 1990). "High-resolution spectroscopic survey of 671 GK giants". Astrophysical Journal Supplement Series. STI. 74: 1075–1128. Bibcode:1990ApJS...74.1075M. doi:10.1086/191527. ISSN 0067-0049.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. SIMBAD. Bibcode:1986EgUBV........0M.
  5. "Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-07-27.
  6. Muller, P. (January 1935). "Sur la variabilité de θ Herculis". Journal des Observateurs (in French). ADS. 18: 177. Bibcode:1935JO.....18..177M.
  7. Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics. 430: 165. arXiv:astro-ph/0409579. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  8. Carney, Bruce W.; et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal, 135 (3): 892–906, arXiv:0711.4984, Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892
  9. Reffert, Sabine; Bergmann, Christoph; Quirrenbach, Andreas; Trifonov, Trifon; Künstler, Andreas (2015). "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity". Astronomy & Astrophysics. 574: A116. arXiv:1412.4634. Bibcode:2015A&A...574A.116R. doi:10.1051/0004-6361/201322360. hdl:10722/215277.
  10. "tet Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-05-31.
  11. Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  12. Shapiro, L. (April 1972), "Radial-velocity measurements of theta Herculis", Astronomical Journal, 77: 215, Bibcode:1972AJ.....77..215S, doi:10.1086/111270
  13. 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 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  14. Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.
  15. (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.
  16. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日
  17. "Allen's Star Names - Hercules". Retrieved 2019-06-01.

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