Theta Ophiuchi

Theta Ophiuchi, Latinized from 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".^[12] This star has an apparent visual magnitude of +3.3,^[6] 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 and therefore subject to lunar occultations and less frequently occulted by a planet.

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)	3.25 - 3.31[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[2]
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 mas[1]
Distance	436 ± 10 ly (134 ± 3 pc)
Absolute magnitude (MV)	−2.4[6]
Details
Mass	8.8±0.2[3] M☉
Radius	6.3[7] R☉
Luminosity	5,000[6] L☉
Surface gravity (log g)	3.950±0.006[8] cgs
Temperature	22,260±280[8] K
Metallicity [Fe/H]	−0.15±0.12[9] dex
Rotational velocity (v sin i)	30[10] km/s
Age	21.3±5.8[3] Myr
Other designations
42 Ophiuchi, CD–24 13292, FK5 644, GC 23451, HD 157056, HIP 84970, HR 6453, SAO 185320[11]
Database references
SIMBAD	data

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.^[13] 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.^[6]

A light curve for Theta Ophiuchi, plotted from Hipparcos data^[14]

The primary component of this system is a variable star of the Beta Cephei type with a period of just 3h 22m.^[15] It has nearly nine^[3] times the mass of the Sun and more than six^[7] 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,^[8] giving it the blue-white hue of a B-type star.^[16]

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, S2CID 18759600 Note: see VizieR catalogue I/311.
2. 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. 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
4. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 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", Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E
6. 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
7. 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 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601
8. 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, S2CID 18255593
9. 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, S2CID 119340011
10. 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
11. "tet Oph", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2007-01-21
12. Allen, R.H. (1899), Star Names: Their Lore and Meaning, p. 297
13. 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, S2CID 14878976
14. "Light Curve", Hipparcos ESA, ESA, retrieved 20 August 2022
15. Burnham, Robert (1978), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, vol. 3, Courier Dover Publications, p. 1372, ISBN 978-0-486-23673-5
16. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2013-12-03, retrieved 2012-01-16