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]
 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 mas[1] |
| Distance | 750 ± 20 ly (231 ± 7 pc) |
| Absolute magnitude (MV) | −2.71+0.26 −0.23[8] |
| Details | |
| Mass | 4.94[9] M☉ |
| Radius | 89.97[9] R☉ |
| Luminosity | 2,405.7[9] L☉ |
| Surface gravity (log g) | 1.24[9] cgs |
| Temperature | 4,266[9] K |
| Metallicity [Fe/H] | −0.11[9] dex |
| Rotational velocity (v sin i) | 3.4 ± 0.6[8] km/s |
| Age | 130[9] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
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
editθ 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]
References
edit- ^ a b c d e 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. S2CID 18759600.
- ^ a b McWilliam, Andrew (December 1990). "High-resolution spectroscopic survey of 671 GK giants". Astrophysical Journal Supplement Series. 74: 1075–1128. Bibcode:1990ApJS...74.1075M. doi:10.1086/191527. ISSN 0067-0049.
{{cite journal}}: Unknown parameter|agency=ignored (help) - ^ a b 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.
- ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
{{cite journal}}: Unknown parameter|agency=ignored (help) - ^ "Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR. Centre de Données astronomiques de Strasbourg. Retrieved 2010-07-27.
- ^ a b Muller, P. (January 1935). "Sur la variabilité de θ Herculis". Journal des Observateurs (in French). 18: 177. Bibcode:1935JO.....18..177M.
{{cite journal}}: Unknown parameter|agency=ignored (help) - ^ a b 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. S2CID 17804304.
- ^ a b 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, S2CID 2756572
- ^ a b c d e f g h i j k l 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. S2CID 59334290.
- ^ "tet Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-05-31.
- ^ 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, S2CID 14878976.
- ^ Shapiro, L. (April 1972), "Radial-velocity measurements of theta Herculis", Astronomical Journal, 77: 215, Bibcode:1972AJ.....77..215S, doi:10.1086/111270
- ^ 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.
- ^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.
- ^ (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.
- ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 26 日
- ^ "Allen's Star Names - Hercules". Retrieved 2019-06-01.
External links
edit- Spacedude's Constellation map: Stars in Hercules