Chi Ophiuchi

Chi Ophiuchi
Location of χ Ophiuchi (circled in red)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Ophiuchus
Right ascension 16h 27m 01.43557s
Declination −18° 27′ 22.4500″
Apparent magnitude (V) 4.22 (4.18 to 5.0)
Characteristics
Evolutionary stage main sequence
Spectral type B2Vne
U−B color index −0.75
B−V color index +0.28
R−I color index +0.22
Variable type GCAS + LERI
Astrometry
Radial velocity (Rv)−19.0±2.1 km/s
Proper motion (μ) RA: −5.378 mas/yr
Dec.: −22.308 mas/yr
Parallax (π)6.5402±0.1961 mas
Distance500 ± 10 ly
(153 ± 5 pc)
Absolute magnitude (MV)−2.27
Details
Mass10.1±0.7 M☉
Radius4.44±0.09 R☉
Luminosity55,847 L☉
Surface gravity (log g)3.53±0.04 cgs
Temperature30,000±300 K
Rotational velocity (v sin i)150±3 km/s
Age22.5±2.6 Myr
Other designations
χ Oph, 7 Ophiuchi, BD−18°4282, FK5 3298, GC 22117, HD 148184, HIP 80569, HR 6118, SAO 159918, PPM 231703
Database references
SIMBADdata

Chi Ophiuchi, Latinized from χ Ophiuchi, is a variable star in the equatorial constellation of Ophiuchus. It has a blue-white hue and is faintly visible to the naked eye with an apparent visual magnitude that fluctuates around 4.22. The distance to this object, as determined from parallax measurements, is approximately 500 light years, but it is moving closer to the Sun with a radial velocity of −19 km/s. 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.

A blue-light light curve for Chi Ophiuchi, adapted from Cuypers et al. (1989)

This is a massive Be star with a stellar classification of B2Vne, 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°. It is a Gamma Cassiopeiae variable with an amplitude of 0.15 magnitude. The brightness has been measured varying from magnitude 4.18 down to 5.0.

Chi Ophiuchi is 22.5 million years old with 10.1 times the mass of the Sun. It has four times the Sun's radius and is radiating 56,000 times the luminosity of the Sun from its photosphere at an effective temperature of about 30,000 K. A weak magnetic field has been detected in the chromosphere of this star. It is being orbited by a symmetrical disk of ejected gas extending out to 0.52 AU (112 R☉), and excess radio and infrared emission has been detected from this structure.

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. Eggleton and Tokovinin (2008) list it as a single star.

References

  1. 1 2 3 4 5 6 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. 1 2 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. 1 2 3 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: catalogued as 'ksi Oph'.
  4. 1 2 Houk, Nancy; Smith-Moore, M. (1978). Michigan catalogue of two-dimensional spectral types for the HD stars. Vol. 4. Ann Arbor: Dept. of Astronomy, University of Michigan. Bibcode:1988mcts.book.....H.
  5. 1 2 3 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. 1 2 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. ↑ Melnik, A. M.; Dambis, A. K. (2020). "Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions". Astrophysics and Space Science. 365 (7): 112. arXiv:2006.14649. Bibcode:2020Ap&SS.365..112M. doi:10.1007/s10509-020-03827-0. S2CID 220128144.
  9. 1 2 3 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. 1 2 3 4 Arcos, C.; et al. (March 2018), "Stellar parameters and H α line profile variability of Be stars in the BeSOS survey", Monthly Notices of the Royal Astronomical Society, 474 (4): 5287–5299, arXiv:1711.08675, Bibcode:2018MNRAS.474.5287A, doi:10.1093/mnras/stx3075, S2CID 74872624.
  11. ↑ Zorec, J.; et al. (November 2016). "Critical study of the distribution of rotational velocities of Be stars. I. Deconvolution methods, effects due to gravity darkening, macroturbulence, and binarity". Astronomy & Astrophysics. 595: 26. Bibcode:2016A&A...595A.132Z. doi:10.1051/0004-6361/201628760. hdl:11336/37946.
  12. 1 2 "chi Oph". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved January 12, 2011.
  13. ↑ 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.
  14. ↑ Cuypers, J.; Balona, L. A.; Marang, F. (December 1989). "Intensive photometry of southern Be variables. I. Winter objects". Astronomy and Astrophysics Suppl. Ser. 81: 151–186. Bibcode:1989A&AS...81..151C.
  15. 1 2 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.
  16. ↑ 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.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 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.
  20. ↑ 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.