Beta Ophiuchi

Beta Ophiuchi (β Ophiuchi, abbreviated Beta Oph, β Oph), also named Cebalrai /ˌsɛbəlˈr./,[13][14] is a star in the equatorial constellation of Ophiuchus. The apparent visual magnitude of this star is 2.7,[2] which is readily visible to the naked eye even from urban skies. The distance to this star can be estimated using parallax measurements, yielding a value of 81.8 light-years (25.1 parsecs) from the Sun.[1]

Beta Ophiuchi
Diagram showing star positions and boundaries of the Ophiuchus constellation and its surroundings
Cercle rouge 100%.svg
Location of β Ophiuchi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Ophiuchus
Right ascension 17h 43m 28.35265s[1]
Declination +04° 34′ 02.2955″[1]
Apparent magnitude (V) 2.749[2] (2.75 to 2.77)
Spectral type K2 III[3]
U−B color index +1.253[2]
B−V color index +1.170[2]
Variable type K-type giant[4],[5]
Radial velocity (Rv)–12.53[6] km/s
Proper motion (μ) RA: 41.45[1] mas/yr
Dec.: +159.34[1] mas/yr
Parallax (π)39.85 ± 0.17[1] mas
Distance81.8 ± 0.3 ly
(25.1 ± 0.1 pc)
Absolute magnitude (MV)+0.77 ± 0.04[7]
Mass1.13[8] M
Radius12.42 ± 0.13[9] R
Luminosity63.4 ± 3.2[9] L
Surface gravity (log g)2.22[3] cgs
Temperature4,467[8] K
Metallicity [Fe/H]0.04[3] dex
Rotational velocity (v sin i)5.4[10] km/s
Age3.82 ± 1.86[3] Gyr
Other designations
Cebalrai, Celbalrai, Cheleb,[11] Kelb Alrai, Bet Oph, β Oph, β Ophiuchi, 60 Oph, 60 Ophiuchi, BD +04°3489, FK5 665, HD 161096, HIP 86742, HR 6603, SAO 122671.[12]
Database references


β Ophiuchi (Latinised to Beta Ophiuchi) is the star's Bayer designation.

It bore the traditional names Cebalrai, Celbalrai, Cheleb and Kelb Alrai (or sometimes just Alrai), all derived from the Arabic كلب الراعي kalb al-rā‘ī "the shepherd's dog".[15] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalogue and standardize proper names for stars. The WGSN approved the name Cebalrai for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[14]


USS Cheleb (AK-138) was a United States Navy Crater class cargo ship named after the star.


This is a giant star with a stellar classification of K2 III.[3] Although it is only 13% greater in mass than the Sun,[8] it has reached a stage in its evolution where the atmosphere has expanded to about 12 times the Sun's radius and is radiating 63 times the luminosity of the Sun.[9] Its outer envelope is relatively cool with an effective temperature of 4,467 K,[8] giving it the orange hue typical of K-type stars.[17] Like some other K-type giants, β Ophiuchi has been found to vary very slightly (0.02 magnitudes) in brightness.[4],[5]

Cebalrai is a member of the thin disk population. It is following a low eccentricity orbit through the Milky Way galaxy that carries it between a distance of 27.3–30.9 kly (8.4–9.5 kpc) from the Galactic Center and up to 0.62 kly (0.19 kpc) above or below the galactic plane.[3]

Possible planetary systemEdit

Radial velocity variations with a period of 142 days hint about the possible presence of a planetary companion orbiting Beta Ophiuchi. Thus far, no planetary object has been confirmed; while periodic radial pulsations caused by intrinsic stellar variability could explain the observed variations.[5]

The proposed Beta Ophiuchi planetary system[citation needed]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b (unconfirmed) ≥ 1 MJ ≥ 0.6 142.3


  1. ^ a b c d e f van Leeuwen, F. (November 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 c d Oja, T. (1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4, Bibcode:1986A&AS...65..405O
  3. ^ a b c d e f Soubiran, C.; et al. (2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788, S2CID 16602121
  4. ^ a b Edmonds, Peter D.; Gilliland, Roland L. (June 1996), "K Giants in 47 Tucanae: Detection of a New Class of Variable Stars", Astrophysical Journal Letters, 464 (2): L157–L160, Bibcode:1996ApJ...464L.157E, doi:10.1086/310108
  5. ^ a b c Hatzes, Artie P.; Cochran, William D. (September 1996), "The Radial Velocity Variability of the K Giant beta Ophiuchi. II. Long-Period Variations", Astrophysical Journal, 468: 391–397, Bibcode:1996ApJ...468..391H, doi:10.1086/177699
  6. ^ Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272, S2CID 17804304
  7. ^ Carney, Bruce W.; et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal, 135 (3): 892–906, arXiv:0711.4984, Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892, S2CID 2756572
  8. ^ a b c d Allende Prieto, C.; Lambert, D. L. (1999), "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: masses, radii and effective temperatures", Astronomy and Astrophysics, 352: 555–562, arXiv:0809.0359, Bibcode:1999A&A...352..555A, doi:10.1051/0004-6361/200811242, S2CID 14531031
  9. ^ a b c Berio, P.; et al. (November 2011), "Chromosphere of K giant stars. Geometrical extent and spatial structure detection", Astronomy & Astrophysics, 535: A59, arXiv:1109.5476, Bibcode:2011A&A...535A..59B, doi:10.1051/0004-6361/201117479, S2CID 17171848
  10. ^ Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
  11. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 301
  12. ^ "rho Per -- Semi-regular pulsating Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-29
  13. ^ Davis, George A. (1944). "The pronunciations, derivations, and meanings of a selected list of star names". Popular Astronomy. 52: 8–30. Bibcode:1944PA.....52....8D.
  14. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016.
  15. ^ Book Of Fixed Stars, Al-Sufi, Bodleian Ms.
  16. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  17. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16