Sigma Ophiuchi

Sigma Ophiuchi, Latinized from σ Ophiuchi, is a single,[11] orange-hued star in the equatorial constellation Ophiuchus. Its apparent visual magnitude is 4.31,[2] which is bright enough to be faintly visible to the naked eye. The annual parallax shift of 3.62 mas as seen from Earth provides a distance estimate of roughly 900 light years. It is moving closer to the Sun with a radial velocity of −28 km/s.[5]

σ Ophiuchi
Location of σ Ophiuchi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension  17h 26m 30.8806s[1]
Declination 4° 08′ 25.2876″[1]
Apparent magnitude (V) 4.31[2] (4.25 - 4.51[3])
Characteristics
Spectral type K2 III[4]
U−B color index +1.57[2]
B−V color index +1.51[2]
Variable type suspected[3]
Astrometry
Radial velocity (Rv)-27.81[5] km/s
Proper motion (μ) RA: +1.583[1] mas/yr
Dec.: +7.133[1] mas/yr
Parallax (π)3.8431 ± 0.2836[1] mas
Distance850 ± 60 ly
(260 ± 20 pc)
Absolute magnitude (MV)-2.85[6]
Details
Mass4.87[7] M☉
Radius94[8] R☉
Luminosity1,995 - 2,032[8] L☉
Surface gravity (log g)1.52[9] cgs
Temperature3,986±170[8] K
Metallicity [Fe/H]-0.07[7] dex
Rotational velocity (v sin i)4.2[10] km/s
Other designations
σ Oph, 49 Ophiuchi, NSV 8664, BD+04° 3422, FK5 1459, GC 23621, HD 157999, HIP 85355, HR 6498, SAO 122387
Database references
SIMBADdata

This is an evolved giant star of type K with a stellar classification of K2 III.[4] Wittkowski et al. (2017) consider it to have a luminosity class of II-III, suggesting it is in a transitional zone between giants and supergiant stars.[12] It has around 5 times the mass of the Sun and 73 times the Sun's radius. The star is radiating 2,047 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,540 K.[7]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  4. Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". Michigan Spectral Survey. 05: 0. Bibcode:1999MSS...C05....0H.
  5. 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". Astronomy & Astrophysics. 430: 165. arXiv:astro-ph/0409579. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  6. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. Vizier catalog entry
  7. Reffert, Sabine; Bergmann, Christoph; Quirrenbach, Andreas; Trifonov, Trifon; Künstler, Andreas (2015). "Precise radial velocities of giant stars". Astronomy & Astrophysics. 574: A116. arXiv:1412.4634. Bibcode:2015A&A...574A.116R. doi:10.1051/0004-6361/201322360. hdl:10722/215277. Vizier catalog entry
  8. Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158: 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd.
  9. Hekker, S.; Meléndez, J. (2007). "Precise radial velocities of giant stars". Astronomy and Astrophysics. 475 (3): 1003. arXiv:0709.1145. Bibcode:2007A&A...475.1003H. doi:10.1051/0004-6361:20078233.
  10. De Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series. 139 (3): 433. arXiv:astro-ph/0608248. Bibcode:1999A&AS..139..433D. doi:10.1051/aas:1999401. Vizier catalog entry
  11. 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.
  12. Wittkowski, M.; et al. (January 2017), "VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), σ Oph, BM Sco, and HD 206859", Astronomy & Astrophysics, 597: 16, arXiv:1610.01927, Bibcode:2017A&A...597A...9W, doi:10.1051/0004-6361/201629349, A9.
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