Beta Ophiuchi

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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
Distance 81.8 ± 0.3 ly
(25.1 ± 0.1 pc)
Absolute magnitude (MV) +0.77 ± 0.04[7]
Mass 1.13[8] M
Radius 12.42 ± 0.13[9] R
Luminosity 63.4 ± 3.2[9] L
Surface gravity (log g) 2.22[3] cgs
Temperature 4,467[8] K
Metallicity [Fe/H] 0.04[3] dex
Rotational velocity (v sin i) 5.4[10] km/s
Age 3.82 ± 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]

Beta Ophiuchi (β Oph, β Ophiuchi) is a star in the equatorial constellation of Ophiuchus. It has the traditional names Celbalrai,[11] which comes from the Arabic كلب الراعي kalb al-rā‘ī meaning "shepherd dog".[citation needed] It is also called Cheleb,[11] Kelb Alrai, or sometimes just Alrai. 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).[1]

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.[13] 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]

Planetary system?[edit]

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


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


  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 
  2. ^ a b c d Oja, T., "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series 65 (2): 405–4 
  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 
  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: 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 
  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 
  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 
  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 
  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. ^ a b c 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. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16