Kappa Crucis (star)

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κ Crucis
A Hubble gem - the Jewel Box.jpg
The centre of NGC 4755, with κ Cru on the left
Credit: NASA/ESA and Jesús Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)
Observation data
Epoch J2000      Equinox J2000
Constellation Crux
Right ascension  12h 53m 48.91920s[1]
Declination −60° 22′ 34.4808″[1]
Apparent magnitude (V) 5.98[2]
Spectral type B3Ia[3]
U−B color index −0.58[2]
B−V color index +0.22[2]
Radial velocity (Rv)-3.5[4] km/s
Proper motion (μ) RA: −5.046[5] mas/yr
Dec.: −1.093[5] mas/yr
Parallax (π)0.4334 ± 0.0481[5] mas
Distanceapprox. 7,500 ly
(approx. 2,300 pc)
Absolute magnitude (MV)−7.1[6]
Mass23.0 M
Luminosity151,000 L
Surface gravity (log g)2.25 cgs
Temperature16,300 K
Rotational velocity (v sin i)70 km/s
Other designations
κ Cru, CD−59°4460, HD 111973, HIP 62931, HR 4890, SAO 252077, 2MASS J12534890-6022344
Database references

Kappa Crucis (κ Cru, HD 111973) is a spectroscopic binary star in the open cluster NGC 4755, which is also known as the Kappa Crucis Cluster or Jewel Box Cluster.


A Snapshot of the Jewel Box cluster (Credit: ESO VLT)

κ Crucis is one of the brightest members of the open cluster that bears its name, better known as the Jewel Box Cluster.[8] It forms one leg, at bottom right or south, of the prominent letter "A" asterism at the centre of the cluster. The cluster is part of the larger Centaurus OB1 association and lies about 8,500 light years away.

The cluster, and κ Cru itself, is just to the south-east of β Crucis, the lefthand star of the famous Southern Cross.


κ Crucis is a B3 bright supergiant (luminosity class Ia). Radial velocity variations in the spectral lines indicate that it has an unresolved companion star.[9] It is over 100,000 times the luminosity of the sun, partly due to its higher temperature over 26,000 K, and partly to its larger size. The κ Crucis cluster has a calculated age of 11.2 million years.[10]


  1. ^ a b 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 Dachs, J.; Kaiser, D. (November 1984), "UBV photometry of the southern galactic cluster NGC 4755 = Kappa Crucis", Astronomy and Astrophysics Supplement Series, 58: 411–429, Bibcode:1984A&AS...58..411D.
  3. ^ Prinja, R. K.; Massa, D. L. (October 2010), "Signature of wide-spread clumping in B supergiant winds", Astronomy and Astrophysics, 521: 4, arXiv:1007.2744, Bibcode:2010A&A...521L..55P, doi:10.1051/0004-6361/201015252, L55.
  4. ^ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  5. ^ a b c 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.
  6. ^ Humphreys, R. M. (1978). "Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way". Astrophysical Journal. 38: 309. Bibcode:1978ApJS...38..309H. doi:10.1086/190559.
  7. ^ Dufton, P. L.; et al. (2006), "The VLT-FLAMES survey of massive stars: Stellar parameters and rotational velocities in NGC 3293, NGC 4755 and NGC 6611", Astronomy and Astrophysics, 457: 265–280, arXiv:astro-ph/0606409, Bibcode:2006A&A...457..265D, doi:10.1051/0004-6361:20065392.
  8. ^ Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.; Scholz, R.-D. (2004). "Astrophysical supplements to the ASCC-2.5. II. Membership probabilities in 520 Galactic open cluster sky areas". Astronomische Nachrichten. 325 (9): 740–748. Bibcode:2004AN....325..740K. doi:10.1002/asna.200410256.
  9. ^ Chini, R.; Hoffmeister, V. H.; Nasseri, A.; Stahl, O.; Zinnecker, H. (2012). "A spectroscopic survey on the multiplicity of high-mass stars". Monthly Notices of the Royal Astronomical Society. 424 (3): 1925–1929. arXiv:1205.5238. Bibcode:2012MNRAS.424.1925C. doi:10.1111/j.1365-2966.2012.21317.x.
  10. ^ Aidelman, Y.; Cidale, L. S.; Zorec, J.; Arias, M. L. (2012). "Open clusters. I. Fundamental parameters of B stars in NGC 3766 and NGC 4755". Astronomy & Astrophysics. 544: A64. Bibcode:2012A&A...544A..64A. doi:10.1051/0004-6361/201219069.

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