Chi Ophiuchi

(Redirected from Chi_Oph)

Chi Ophiuchi, Latinized from χ Ophiuchi, is a variable star in the equatorial constellation of Ophiuchus.[11] It has a blue-white hue and is faintly visible to the naked eye with an apparent visual magnitude that fluctuates around 4.22.[2] The distance to this object, as determined from parallax measurements, is approximately 530 light years,[1] but it is moving closer to the Sun with a radial velocity of −19 km/s.[7] This star 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.[8]

Chi Ophiuchi
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Ophiuchus
Right ascension 16h 27m 01.43499s[1]
Declination −18° 27′ 22.4938″[1]
Apparent magnitude (V) 4.22[2] (4.18 to 5.0)[3]
Evolutionary stage main sequence
Spectral type B2Vne[4]
U−B color index −0.75[5]
B−V color index +0.28[5]
R−I color index +0.22[5]
Variable type GCAS[3] + LERI[6]
Radial velocity (Rv)−19.0±2.1[7] km/s
Proper motion (μ) RA: −5.41[1] mas/yr
Dec.: −21.12[1] mas/yr
Parallax (π)6.21 ± 0.23[1] mas
Distance530 ± 20 ly
(161 ± 6 pc)
Absolute magnitude (MV)−4.6[8]
Mass10.1±0.7[9] M
[10] R
Luminosity245±10[10] L
Surface gravity (log g)4.13[8] cgs
[10] K
Rotational velocity (v sin i)134[5] km/s
Age22.5±2.6[9] Myr
Other designations
χ Oph, 7 Ophiuchi, BD−18°4282, FK5 3298, GC 22117, HD 148184, HIP 80569, HR 6118, SAO 159918, PPM 231703[11]
Database references

This is a massive Be star with a stellar classification of B2Vne,[4] where the 'n' indicates "nebulous" lines due to rapid rotation. It is spinning with a projected rotational velocity of 144 km/s. As the critical velocity for the star is 477 km/s, the inclination angle of its poles must be small; estimated as ~20°.[12] It is a Gamma Cassiopeiae variable with an amplitude of 0.15 magnitude.[13] The brightness has been measured varying from magnitude 4.18 down to 5.0.[3]

Chi Ophiuchi is 22.5[9] million years old with 10.1[9] times the mass of the Sun. It has 12.6[10] times the Sun's radius and is radiating 245[10] times the luminosity of the Sun from its photosphere at an effective temperature of 6,432 K.[10] A weak magnetic field has been detected in the chromosphere of this star.[14] It is being orbited by a symmetrical disk of ejected gas extending out to 0.52 AU (112 R),[12] and excess radio and infrared emission has been detected from this structure.[15]

Abt and Levy (1978) cataloged Chi Ophiuchi as a single-lined spectroscopic binary with a period of 138.8 days and an eccentricity of 0.44, although the orbital elements are considered marginal.[16] Eggleton and Tokovinin (2008) list it as a single star.[17]


  1. ^ a b c d e f van Leeuwen, F. (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 .
  2. ^ a b 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 . S2CID 119257644 .
  3. ^ a b c Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S . doi:10.1134/S1063772917010085 . S2CID 125853869 . Note: cataloged as 'ksi Oph'.
  4. ^ a b Houk, Nancy; Smith-Moore, M. (1978). Michigan catalogue of two-dimensional spectral types for the HD stars. 4. Ann Arbor: Dept. of Astronomy, University of Michigan. .
  5. ^ a b c d Hoffleit, D.; Warren, Jr., W. H. "The Bright Star Catalogue" (5th Revised ed.). CDS. Retrieved 2019-10-24. HR 6118 , database entry.
  6. ^ Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W .
  7. ^ a b Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053 . Bibcode:2006AstL...32..759G . doi:10.1134/S1063773706110065 . S2CID 119231169 .
  8. ^ a b c de Geus, E. J.; et al. (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 .
  9. ^ a b c d Tetzlaff, N.; et al. (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 .
  10. ^ a b c d e f 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.
  11. ^ a b "chi Oph" . SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved January 12, 2011.
  12. ^ a b Tycner, C.; et al. (December 2008). "Constraining the Physical Parameters of the Circumstellar Disk of χ Ophiuchi". The Astrophysical Journal. 689 (1): 461–470. arXiv:0807.3971 . Bibcode:2008ApJ...689..461T . doi:10.1086/592097 . S2CID 16779318 .
  13. ^ Adelman, S. J.; et al. (December 2000). "On the Variability of O4-B5 Luminosity Class III-V Stars". Information Bulletin on Variable Stars. 5008: 1. Bibcode:2000IBVS.5008....1A .
  14. ^ Hubrig, S.; et al. (December 2007). "Evidence for weak magnetic fields in early-type emission stars". Astronomische Nachrichten. 328 (10): 1133. arXiv:0711.2085 . Bibcode:2007AN....328.1133H . doi:10.1002/asna.200710877 . S2CID 15213781 .
  15. ^ Taylor, A. R.; et al. (October 1987). "Radio detection of the Be star psi Persei" . Monthly Notices of the Royal Astronomical Society. 228 (4): 811–817. Bibcode:1987MNRAS.228..811T . doi:10.1093/mnras/228.4.811 .
  16. ^ Abt, H. A.; Levy, S. G. (February 1978). "Binaries among B2 - B5 IV, V absorption and emission stars". Astrophysical Journal Supplement Series. 36: 241–258. Bibcode:1978ApJS...36..241A . doi:10.1086/190498 .
  17. ^ 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 .


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