Jewel Box (star cluster)

This article is about article is about the star cluster. For other uses, see Jewel box.

Jewel Box
NGC 4755 taken by the VLT Credit: ESO
Observation data (J2000 epoch)
Constellation	Crux
Right ascension	12h 53m 42s[1]
Declination	-60° 22.0′[1]
Distance	6.4 kly[2] (1.98 kpc)
Physical characteristics
Mass	- M☉
Radius	-
Estimated age	14±2Myr[3]
Notable features	-
Other designations	NGC 4755,[1] Herschel's Jewel Box,[1] Kappa Crucis Cluster[1]
See also: Open cluster, List of open clusters

The Jewel Box (also known as NGC 4755, the Kappa Crucis Cluster and Caldwell 94) is an open cluster in the constellation of Crux. As Kappa Crucis, it has a Bayer designation despite the fact that it is a cluster rather than an individual star.

It is one of the finest open clusters discovered by Nicolas Louis de Lacaille when he was in South Africa during 1751–1752. This cluster is one of the youngest known, with an estimated age of only 14 million years. It has an apparent magnitude of 4.2, and is located 6,440 light years from Earth and contains around 100 stars.

This famous group of young bright stars was named the Jewel Box from its description by Sir John Herschel as "a casket of variously coloured precious stones," which refers to its appearance in the telescope. The bright orange star Kappa Crucis contrasts strongly against its predominantly blue, hot companions. Kappa Crucis is a very large (hence very luminous) young star in its red supergiant stage, which paradoxically indicates that its life is drawing to a close. The cluster looks like a star to the unaided eye and appears close to the easternmost star of the Southern Cross, (Beta Crucis), so is only visible from southern latitudes.

Another cluster, NGC 457, has also a jewel-box-like appearance and lies virtually diametrally opposite this one in the sky in the constellation Cassiopeia.

Discovery and observation

The Jewel Box cluster was discovered by Nicolas Louis de Lacaille when he was in the Southern Hemisphere from 1751 to 1753. He saw the object as a nebulous cluster due to the small aperture of his telescope, but was the first to recognize it as consisting of multiple stars.^[4] The name "Jewel Box" comes from John Herschel's description of it:

"this cluster, though neither a large nor a rich one, is yet and extremely brilliant and beautiful object when viewed through an instrument of sufficient aperture to show distinctly the very different colour of its constituent stars, which give it the effect of a superb piece of fancy jewellery"

—John Herschel, ^[4]

Herschel recorded the positions of 100 members of the cluster in 1834–1838.^[5]

Physical characteristics

The Jewel Box cluster is one of the youngest known open clusters.^[6] It contains the M-type supergiant Kappa Crucis.

The mean radial velocity of the Jewel Box cluster is −17.9 kilometres per second (−11.1 mi/s).^[7]

The brightest stars in the Jewel Box cluster are supergiants, and include some of the brightest stars in the Milky Way galaxy.^[8]

Calculating its distance is difficult due to the proximity of the Coalsack Nebula, which obscures some of its light.^[9]

Observation

The Jewel Box cluster is regarded as one of the finest objects in the southern sky.^[10] It exhibits subtle colours, aside from the vivid red supergiant Kappa Crucis from which the cluster takes its name.^[11] It is visible to the naked eye as a hazy object of the fourth magnitude.^[12] The Jewel Box cluster can be easily located using the star Beta Crucis as a guide, and appears as a fourth magnitude object.^[13] The three brightest members of the cluster lie in a straight line known as the 'traffic lights' due to their varying colours.^[11]

The Jewel Box cluster is impressive when viewed with binoculars^[11] or a small telescope, but even more so in a large telescope because the background nebulosity becomes more prominent.^[9]

Gallery

• 

  Wide Field Image of the Jewel Box.

• 

  Digitized Sky Survey 2 image of the Jewel Box.

• 

  Hubble image of the Jewel Box.

• 

  Putting the images in perspective.

References

1. ^ ^{a b c d e} "SIMBAD Astronomical Database". Results for NGC 4755. http://simbad.u-strasbg.fr/Simbad. Retrieved 2006-12-14. 
2. ^ "WEBDA Open cluster". Results for NGC 4755. http://www.univie.ac.at/webda/cgi-bin/ocl_page.cgi?dirname=ngc4755. Retrieved 2007-01-12. 
3. ^ Bonatto, C; E Bica, S Ortolani, B Barbuy (July 2006). "Detection of K_s-excess stars in the 14 Myr open cluster NGC 4755.". Astronomy & Astrophysics 453: 121–132. arXiv:astro-ph/0603394. Bibcode 2006A&A...453..121B. doi:10.1051/0004-6361:20054620. http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/abs/2006/25/aa4620-05/aa4620-05.html. 
4. ^ ^{a b} O'Meara, Stephen James (2002). The Caldwell objects. Cambridge, USA: Sky Publishing Corporation. pp. 378. ISBN 0-933346-97-2. http://books.google.com/?id=3Hg6YHgx9nAC&pg=PA378&dq=%22kappa+crucis%22+cluster&cd=1#v=onepage&q=%22kappa%20crucis%22%20cluster&f=false. 
5. ^ Thackeray, A. D. (1949). "The Kappa Crucis Cluster". Monthly Notes of the Astronomical Society of South Africa 8: 30. Bibcode 1949MNSSA...8...30T. 
6. ^ Judge, Harry George; Toyne, Anthony (1993). Oxford Illustrated Encyclopedia, Volume 8. pp. 76. http://books.google.com.au/books?id=4UgUAQAAIAAJ&q=%22jewel+box+cluster%22&dq=%22jewel+box+cluster%22&cd=7. 
7. ^ Feast, M. W. (1963). "The galactic cluster NGC 4755 (κ Crucis)". Monthly Notices of the Royal Astronomical Society 126: 11. Bibcode 1963MNRAS.126...11F. 
8. ^ Burnham, Robert (1978). Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System. New York: Dover Publications. pp. 730. ISBN 9780486235684. http://books.google.com/?id=wB9uZ9lH5bgC&pg=PA730&dq=%22kappa+crucis%22+cluster&cd=12#v=onepage&q=%22kappa%20crucis%22%20cluster&f=false. 
9. ^ ^{a b} Consolmagno, Guy; Davis, Dan (2005). Turn left at Orion: a hundred night sky objects to see in a small telescope. Cambridge, United Kingdom: University of Cambridge. pp. 189. ISBN 0 521 78190 6. http://books.google.com/?id=PexKTfPy3voC&pg=PA189&dq=%22jewel+box%22+cluster&cd=19#v=onepage&q=%22jewel%20box%22%20cluster&f=false. 
10. ^ Kaler, James B. (1989). Stars and their spectra: an introduction to the spectral sequence. University of Cambridge. pp. 13. ISBN 0 521 30494. http://books.google.com/?id=ycLg34SaJWwC&pg=PA13&dq=%22jewel+box%22+cluster&cd=6#v=onepage&q=%22jewel%20box%22%20cluster&f=false. 
11. ^ ^{a b c} Inglis, Mike (2004). Astronomy of the Milky Way: The observer's guide to the southern Milky Way. Springer. pp. 78–79. ISBN 1-85233-709-5. http://books.google.com/?id=1r0qvMjSCGAC&pg=SA3-PA7&dq=%22jewel+box+cluster%22&cd=15#v=onepage&q=%22jewel%20box%20cluster%22&f=false. 
12. ^ Ridpath, Ian; Tirion, Wil (2007). Stars and Planets. pp. 134. ISBN 9780691135564. http://books.google.com/?id=-pfuAAAAMAAJ&q=%22kappa+crucis%22+cluster&dq=%22kappa+crucis%22+cluster&cd=13. 
13. ^ Mobberley, Martin (2009). The Caldwell Objects. Springer. pp. 196. doi:10.1007/978-1-4419-0326-6. ISBN 978-1-4419-0325-9. http://books.google.com/?id=amPrWoOWgHcC&printsec=frontcover#v=onepage&q=&f=false. 

External links

• A Copyright Anglo-Australian Observatory Image of NGC 4755
• The Jewel Box on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
• A Copyright T. Warner Amateur Image of NGC4755

Coordinates: 12^h 53^m 42^s, −60° 22′ 00″