Theta Ophiuchi

Theta Ophiuchi (θ Oph, θ Ophiuchi) is a multiple star system in the equatorial constellation of Ophiuchus. It lies on the "right foot" of the serpent-bearer, just southwest of Kepler's Star, the nova of 1604. According to Richard H. Allen's, Star Names: Their Lore and Meaning (1899), θ Oph together with ξ Oph formed the Sogdian Wajrik "the Magician", the Khorasmian Markhashik "the Serpent-bitten" and with η Oph the Coptic Tshiō, "the Snake", and Aggia, "the Magician".[11] This star has an apparent visual magnitude of +3.26,[2] making it readily visible to the naked eye. Based upon parallax measurements from the Hipparcos mission, it is roughly 436 light-years (134 parsecs) from Earth.[1] It is 1.8 degrees south of the ecliptic.

Theta Ophiuchi
Location of θ Ophiuchi(circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension  17h 22m 00.57935s[1]
Declination –24° 59′ 58.3670″[1]
Apparent magnitude (V) +3.26[2]
Characteristics
Spectral type B2 IV[3]
U−B color index –0.86[4]
B−V color index –0.23[4]
Variable type β Cep
Astrometry
Radial velocity (Rv)–2[5] km/s
Proper motion (μ) RA: –7.37[1] mas/yr
Dec.: –23.94[1] mas/yr
Parallax (π)7.48 ± 0.17[1] mas
Distance436 ± 10 ly
(134 ± 3 pc)
Absolute magnitude (MV)–2.4[2]
Details
Mass8.8 ± 0.2[3] M☉
Radius6.3[6] R☉
Luminosity5,000[2] L☉
Surface gravity (log g)3.950 ± 0.006[7] cgs
Temperature22,260 ± 280[7] K
Metallicity [Fe/H]–0.15 ± 0.12[8] dex
Rotational velocity (v sin i)30[9] km/s
Age21.3 ± 5.8[3] Myr
Other designations
42 Ophiuchi, CD–24 13292, HD 157056, HIP 84970, HR 6453, SAO 185320, FK5 644, GC 23451.[10]
Database references
SIMBADdata

Theta Ophiuchi appears to be a triple star system. The brightest component is a spectroscopic binary with an orbital period of 56.71 days and an eccentricity of 0.17. The third component is 5.5 magnitude star with a stellar classification of B5. Its angular separation from the binary pair is 0.15 arcseconds.[12] This system is a proper motion member of the Upper Scorpius sub-group in the Scorpius-Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.[2]

The primary component of this system is a variable star of the Beta Cephei type with a period of just 3h 22m.[13] It has nearly nine[3] times the mass of the Sun and more than six[6] times the Sun's radius. Although only 21 million years old,[3] it has begun to evolve away from the main sequence and has become a subgiant star with a stellar classification of B2 IV.[3] This massive star is radiating around 5,000 times the luminosity of the Sun from its outer atmosphere at an effective temperature of about 22,260 K,[7] giving it the blue-white hue of a B-type star.[14]

References
  1. van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752v1, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 Note: see VizieR catalogue I/311.
  2. 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
  3. 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
  4. Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J.
  5. Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E
  6. 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: 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601
  7. Briquet, M.; Morel, T.; Thoul, A.; Scuflaire, R.; Miglio, A.; Montalbán, J.; Dupret, M.-A.; Aerts, C. (November 2007), "An asteroseismic study of the β Cephei star θ Ophiuchi: constraints on global stellar parameters and core overshooting" (PDF), Monthly Notices of the Royal Astronomical Society, 381 (4): 1482–1488, arXiv:0706.3274, Bibcode:2007MNRAS.381.1482B, doi:10.1111/j.1365-2966.2007.12142.x
  8. Daszyńska-Daszkiewicz, J.; Niemczura, E. (April 2005), "Metallicity of mono- and multiperiodic β Cephei stars", Astronomy and Astrophysics, 433 (3): 1031–1035, arXiv:astro-ph/0410442, Bibcode:2005A&A...433.1031D, doi:10.1051/0004-6361:20040397
  9. Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590
  10. "tet Oph". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-01-21.
  11. Allen, R.H. (1899), Star Names: Their Lore and Meaning, p. 297
  12. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  13. Burnham, Robert (1978), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, 3, Courier Dover Publications, p. 1372, ISBN 978-0-486-23673-5
  14. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
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