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Zeta Ophiuchi

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Zeta Ophiuchi (ζ Oph, ζ Ophiuchi) is a single[9] star located in the constellation of Ophiuchus. It has an apparent visual magnitude of 2.6, making it the third-brightest star in the constellation. Parallax measurements give an estimated distance of roughly 440 light-years (130 parsecs) from the Earth.[1] It is surrounded by the Sh2-27 "Cobold" nebula, the star's bow shock as it ploughs through dense dust clouds near the Rho Ophiuchi cloud complex.

ζ Ophiuchi
Location of ζ Oph (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension 16h 37m 09.54001s[1]
Declination −10° 34′ 01.5097″[1]
Apparent magnitude (V) 2.56 – 2.58[2]
Characteristics
Spectral type O9.5 V[3]
U−B color index −0.857[4]
B−V color index +0.032[4]
Variable type γ Cas[2] + β Cep[3]
Astrometry
Radial velocity (Rv)−15.0[5] km/s
Proper motion (μ) RA: +10.465 mas/yr[1]
Dec.: +24.742 mas/yr[1]
Parallax (π)7.4088 ± 0.6596 mas[1]
Distance440 ± 40 ly
(130 ± 10 pc)[1]
Absolute magnitude (MV)−4.2[6]
Details
Mass20.2[7] M☉
Radius9.1 (equator)
7.5 (polar)[6] R☉
Luminosity74,100[7] L☉
Surface gravity (log g)3.58[6] cgs
Temperature30,700 (equatorial)
39,000 (polar)[6] K
Rotational velocity (v sin i)400[3] km/s
Age3.0±0.3[8] Myr
Other designations
13 Oph, BD−10°4350, FK5 622, HD 149757, HIP 81377, HR 6175, SAO 160006, 2MASS J16370954-1034014, Gaia DR2 4337352305315545088
Database references
SIMBADdata

In April 2010, ζ Ophiuchi was occulted by asteroid 824 Anastasia.[10][11][12]

Properties

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ζ Ophiuchi is an enormous star with more than 20[8] times the Sun's mass and eight[13] times its radius. The stellar classification of this star is O9.5 V,[3] with the luminosity class of V indicating that it is generating energy in its core by the nuclear fusion of hydrogen. From Earth, the apparent effective temperature of the star appears to be 34,300K, [13] giving the star the blue hue of an O-type star.[14] However, since the star is rapidly rotating, the exact surface temperature varies across the surface of the star from as high as 39,000K at the poles to as low as 30,700K at the equator.[13] The projected rotational velocity may be as high as 400[3] km s−1 and it may be rotating at a rate of once per day, close to the velocity at which it would begin to break up.

 
A light curve for Zeta Ophiuchi, adapted from Howarth et al. (2014)[15]

This is a young star with an age of only three million years.[8] Its luminosity is varying in a periodic manner similar to that of a Beta Cephei variable. This periodicity has a dozen or more frequencies ranging between 1–10 cycles per day.[3] In 1979, examination of the spectrum of this star found "moving bumps" in its helium line profiles. This feature has since been found in other stars, which have come to be called ζ Oph stars. These spectral properties are likely the result of non-radial pulsations.[16]

This star is roughly halfway through the initial phase of its stellar evolution and will, within the next few million years, expand into a red supergiant star wider than the orbit of Jupiter before ending its life in a supernova explosion, leaving behind a neutron star or pulsar. From the Earth, a significant fraction of the light from this star is absorbed by interstellar dust, particularly at the blue end of the spectrum. In fact, were it not for this dust, ζ Ophiuchi would shine several times brighter and be among the very brightest stars visible.[17] If the star's luminosity were not obscured, it would shine at magnitude 1.54, becoming the twenty-third brightest star in the night sky.[note 1]

X-ray emissions have been detected from Zeta Ophiuchi that vary periodically. The net X-ray flux is estimated at 1.2×1024 W. In the energy range of 0.5–10 keV, this flux varies by about 20% over a period of 0.77 days. This behavior may be the result of a magnetic field in the star. The measured average strength of the longitudinal field is about 14.1±4.5 mT.[3]

Bow shock

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Infrared image of the shockwave (yellow arc) created by the runaway star Zeta Ophiuchi in an interstellar dust cloud

ζ Ophiuchi is moving through space with a peculiar velocity of 30 km s−1. Based upon the age and direction of motion of this star, it is a member of the Upper Scorpius sub-group of the Scorpius–Centaurus association of stars that share a common origin and space velocity.[18] Such runaway stars may be ejected by dynamic interactions between three or four stars. However, in this case the star may be a former component of a binary star system in which the more massive primary was destroyed in a type II supernova explosion.[3] It is possible that ζ Ophiuchi accreted mass from its companion before it was ejected.[19] The pulsar PSR B1929+10 may be the leftover remnant of this supernova, as it too was ejected from the association with a velocity vector that fits the scenario.[3]

Due to the high space velocity of Zeta Ophiuchi, in combination with high intrinsic brightness and its current location in a dust-rich area of the galaxy, the star is creating a bow-shock in the direction of motion. This shock has been made visible via NASA's Wide-field Infrared Survey Explorer.[20] The formation of this bow shock can be explained by a mass loss rate of about 1.1×10−7 times the mass of the Sun per year, which equals the mass of the Sun every nine million years.[3]

Traditional names

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ζ Ophiuchi was a member of indigenous Arabic asterism al-Nasaq al-Yamānī, "the Southern Line" of al-Nasaqān "the Two Lines",[21] along with α Serpentis (Unukalhai), δ Ser (Qin, Tsin), ε Ser (Ba, Pa), δ Ophiuchi (Yed Prior), ε Oph (Yed Posterior) and γ Oph (Tsung Ching).[22]

According to the catalogue of stars in the Technical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars, al-Nasaq al-Yamānī or Nasak Yamani was the title for two stars: δ Serpentis as Nasak Yamani I and ε Ser as Nasak Yamani II (exclude this star, α Ser, δ Ophiuchi, ε Oph and γ Oph)[23]

In Chinese, 天市右垣 (Tiān Shì Yòu Yuán), meaning Right Wall of Heavenly Market Enclosure, refers to an asterism which is represent eleven old states in China which is marking the right borderline of the enclosure, consisting of ζ Ophiuchi, β Herculis, γ Herculis, κ Herculis, γ Serpentis, β Serpentis, α Serpentis, δ Serpentis, ε Serpentis, δ Ophiuchi and ε Ophiuchi.[24] Consequently, the Chinese name for ζ Ophiuchi itself is 天市右垣十一 (Tiān Shì Yòu Yuán shíyī, English: the Eleventh Star of Right Wall of Heavenly Market Enclosure), represent the state Han (韓),[25][26][27] together with 35 Capricorni[28] in Twelve States (asterism).

Notes

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  1. ^ The absolute magnitude of Zeta Ophiuchi, at a distance of 140.45 parsecs, is −4.2.[6] Putting it into the equation Mabs−5+5×log(Distance (ly)/3.26), it results in magnitude 1.54.

References

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  1. ^ a b c d e f Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ a b Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. ^ a b c d e f g h i j Hubrig, S.; Oskinova, L. M.; Schöller, M. (February 2011). "First detection of a magnetic field in the fast rotating runaway Oe star ζ Ophiuchi". Astronomische Nachrichten. 332 (2): 147. arXiv:1101.5500. Bibcode:2011AN....332..147H. doi:10.1002/asna.201111516. S2CID 119270857.
  4. ^ a b Cousins, A. W. J. (1984). "Standardization of Broadband Photometry of Equatorial Standards". South African Astronomical Observatory Circulars. 8: 59. Bibcode:1984SAAOC...8...59C.
  5. ^ Wielen, R.; et al. (1999). "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions". Veröff. Astron. Rechen-Inst. Heidelb. 35 (35). Astronomisches Rechen-Institut Heidelberg: 1. Bibcode:1999VeARI..35....1W.
  6. ^ a b c d e Howarth, I. D.; Smith, K. C. (2001). "Rotational mixing in early-type main-sequence stars". Monthly Notices of the Royal Astronomical Society. 327 (2): 353. Bibcode:2001MNRAS.327..353H. doi:10.1046/j.1365-8711.2001.04658.x.
  7. ^ a b Repolust, T.; Puls, J.; Herrero, A. (2004). "Stellar and wind parameters of Galactic O-stars. The influence of line-blocking/blanketing". Astronomy and Astrophysics. 415 (1): 349–376. Bibcode:2004A&A...415..349R. doi:10.1051/0004-6361:20034594.
  8. ^ a b c Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
  9. ^ Hutter, D. J.; Tycner, C.; Zavala, R. T.; Benson, J. A.; Hummel, C. A.; Zirm, H. (2021). "Surveying the Bright Stars by Optical Interferometry. III. A Magnitude-limited Multiplicity Survey of Classical Be Stars". The Astrophysical Journal Supplement Series. 257 (2): 69. arXiv:2109.06839. Bibcode:2021ApJS..257...69H. doi:10.3847/1538-4365/ac23cb. S2CID 237503492.
  10. ^ "Asteroid To Hide Naked-Eye Star". Sky & Telescope. 31 March 2010. Archived from the original on 20 July 2012. Retrieved 20 November 2022.
  11. ^ "Asteroid To Hide Bright Star". Archived from the original on 5 May 2010. Retrieved 17 July 2019.
  12. ^ "(824) Anastasia / HIP 81377 event on 2010 Apr 06, 10:21 UT". Archived from the original on 17 July 2019. Retrieved 17 July 2019.
  13. ^ a b c Villamariz, M. R.; Herrero, A. (October 2005). "Chemical composition of Galactic OB stars. II. The fast rotator ζ Ophiuchi". Astronomy and Astrophysics. 442 (1): 263–270. arXiv:astro-ph/0507400. Bibcode:2005A&A...442..263V. doi:10.1051/0004-6361:20052848. S2CID 14474019.
  14. ^ "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. 21 December 2004. Archived from the original on 2019-09-04. Retrieved 21 November 2022.
  15. ^ Howarth, Ian D.; Goss, K. J. F.; Stevens, I. R.; Chaplin, W. J.; Elsworth, Y. (May 2014). "Amplitude variability in satellite photometry of the non-radially pulsating O9.5 V star ζ Oph". Monthly Notices of the Royal Astronomical Society. 440 (2): 1674–1679. arXiv:1402.6551. Bibcode:2014MNRAS.440.1674H. doi:10.1093/mnras/stu398.
  16. ^ Balona, L. A.; Dziembowski, W. A. (October 1999). "Excitation and visibility of high-degree modes in stars". Monthly Notices of the Royal Astronomical Society. 309 (1): 221–232. Bibcode:1999MNRAS.309..221B. doi:10.1046/j.1365-8711.1999.02821.x.
  17. ^ Kaler, James B. "ZETA OPH (Zeta Ophiuchi)". Stars. University of Illinois.
  18. ^ de Geus, E. J.; de Zeeuw, P. T.; Lub, J. (June 1989). "Physical parameters of stars in the Scorpio-Centaurus OB association". Astronomy and Astrophysics. 216 (1–2): 44–61. Bibcode:1989A&A...216...44D.
  19. ^ Renzo, M.; Götberg, Y. (2021). "Evolution of Accretor Stars in Massive Binaries: Broader Implications from Modeling ζ Ophiuchi". The Astrophysical Journal. 923 (2): 277. arXiv:2107.10933. Bibcode:2021ApJ...923..277R. doi:10.3847/1538-4357/ac29c5. S2CID 236318269.
  20. ^ "Runaway Star Plows Through Space". Jet Propulsion Laboratory. Archived from the original on 11 May 2011. Retrieved 20 November 2022.
  21. ^ Kunitzsch, P., Smart, T. (2006). A Dictionary of Modern Star names: A Short Guide to 254 Star names and Their Derivations (Second revised ed.). Cambridge, MA: Sky publishing. p. 31. ISBN 1-931559-44-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
  22. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 243. ISBN 0-486-21079-0. Retrieved 12 December 2010.
  23. ^ Jack W. Rhoads (15 November 1971). "Technical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars" (PDF). Jet Propulsion Laboratory, California Institute of Technology.
  24. ^ 陳久金 (2005). 中國星座神話 (in Chinese). 台灣書房出版有限公司. ISBN 978-986-7332-25-7.
  25. ^ R.H.Allen. "Star Names". p. 302.
  26. ^ "香港太空館 – 研究資源 – 亮星中英對照表" (in Chinese). Hong Kong Space Museum. Archived from the original on 29 January 2011. Retrieved 23 November 2010.
  27. ^ "English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name" (in Chinese). Hong Kong Space Museum. Archived from the original on 10 August 2010. Retrieved 23 November 2010.
  28. ^ Ian Ridpath. "Star Tales – Capricornus the Sea Goat". Archived from the original on 8 September 2022. Retrieved 21 November 2022.
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