Editing Jewel Box (star cluster)

{{Short description|Open cluster in the constellation Crux}}
{{About|article is about the star cluster||Jewel box (disambiguation){{!}}Jewel box}}

{{Infobox open cluster|
| name = Jewel Box
| image = [[Image:A Snapshot of the Jewel Box cluster with the ESO VLT.jpg|300px]]
| caption = NGC 4755 taken by the [[:Very Large Telescope|VLT]]
| credit = [[ESO]]
| epoch = [[J2000]]
| class =
| ra = {{RA|12|53|42}}<ref name=simbad>
{{cite simbad
  | title=NGC 4755
  | access-date=2006-12-14
}}
</ref>
| dec = {{DEC|-60|22.0}}<ref name=simbad/>
| dist_ly = 6.50 [[light year|kly]]<ref name=simbad/>
| dist_pc = 1.99 [[parsec|kpc]]<ref name=simbad/>
| appmag_v =
| size_v =
| mass_kg =
| mass_msol = –
| radius_ly = –
| v_hb = –
| age = 16 Myr<ref name=kaltcheva/>
| constellation = [[Crux]]
| notes = –
| names = Herschel's Jewel Box,<ref name=simbad/> [[Kappa|κ]]&nbsp;Crucis cluster,<ref name=simbad/> [[New General Catalogue|NGC]]&nbsp;4755,<ref name=simbad/> [[Collinder catalogue|Cr]]&nbsp;264, [[Caldwell catalogue|Caldwell]]&nbsp;94<ref name=DOBdb>
{{cite web
 |title=Results for NGC&nbsp;4755
 |website=Deep sky observer companion database (docdb.net)
 |url=http://www.docdb.net/show_object.php?id=ngc_4755
 |access-date=2013-06-08 }}
</ref>
}}

The '''Jewel Box''' (also known as the Kappa Crucis cluster, NGC&nbsp;4755, or Caldwell&nbsp;94) is an [[open cluster]] in the [[constellation]] [[Crux]], originally discovered by [[Nicolas Louis de Lacaille]] in 1751–1752.<ref name=Jones_1969>
{{cite journal
 | last=Jones | first=K.G.
 | date=March 1969
 | title=The search for the nebulae - VI
 | journal=[[Journal of the British Astronomical Association]]
 | volume=79 | pages=213–222
 | bibcode=1969JBAA...79..213J
}}
</ref> This cluster was later named the Jewel Box by [[John Herschel]] when he described its telescopic appearance as "...&nbsp;a superb piece of fancy jewellery". It is easily visible to the naked eye as a hazy star some 1.0°&nbsp;southeast of the first-magnitude star [[Mimosa (star)|Mimosa]] (Beta Crucis). This hazy star was given the [[Bayer designation|Bayer star designation]] "Kappa Crucis", from which the cluster takes one of its common names. The modern designation [[Kappa Crucis (star)|Kappa Crucis]] has been assigned to one of the stars in the base of the A-shaped [[Asterism (astronomy)|asterism]] of the cluster.

This cluster is one of the youngest known, with an estimated age of 14&nbsp;million years. It has a total integrated [[magnitude (astronomy)|magnitude]]&nbsp;4.2, is located 1.99&nbsp;[[parsecs|kpc]], or 6497&nbsp;[[light year]]s from Earth,<ref name=simbad/> and contains just over 100&nbsp;stars.

==Discovery and observation==

The Jewel Box as a star cluster was first found by [[Nicolas Louis de Lacaille]] while doing astrometric observations for his 1751–1752 southern star catalogue ''[[Cœlum Australe Stelliferum]]'' at the [[Cape of Good Hope]] in [[South Africa]]. He saw this as a nebulous cluster in his small 12&nbsp;mm {{nobr|({{small|{{sfrac| 1 | 2 }}}} inch)}} telescope, but was first to recognise it as a group of many stars.<ref name=DOCdb>{{cite web |title=Jewel Box (NGC&nbsp;4755) |website=Deep sky observer companion database (docdb.net) |url=http://www.docdb.net/show_object.php?id=ngc_4755 }}</ref><ref name=southastrodel04>
{{cite web
 |last1=James |first1=Andrew
 |date=22 April 2016
 |title=Part one: 1752–1834
 |department=History of the Jewel Box
 |website=Southern astronomical delights (southastrodel.com)
 |url=http://www.southastrodel.com/Page004.htm
 |access-date=2016-04-22
}}
</ref>
The name "Jewel Box" comes from [[John Herschel]]'s own description of it:
: "...&nbsp;this cluster, though neither a large nor a rich one, is yet an 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."<ref name=DOCdb/>

Herschel recorded the positions of just over 100&nbsp;members of the cluster in 1834–1838.<ref name=Thackeray>
{{cite journal
 | last = Thackeray  | first = A.D.
 | year = 1949
 | title = The Kappa Crucis Cluster
 | journal = Monthly Notes of the Astronomical Society of South Africa
 | volume = 8 | page = 30
 | bibcode = 1949MNSSA...8...30T
}}
</ref>

==Prominent members==

The central part of the cluster is framed by bright stars making up an A-shaped [[asterism (astronomy)|asterism]].<ref name=southastrodel02>
{{cite web
 |last1=James |first1=Andrew
 |date=22 April 2016
 |title=Introduction
 |department=NGC&nbsp;4755 : The Jewel Box "The Jewel of the South" 
 |website=Southern astronomical delights (southastrodel.com)
 |url=http://www.southastrodel.com/Page002.htm
 |access-date=2016-04-22
}}</ref>
The upper tip of this asterism is HD 111904 ([[HR 4887]], HIP 62894), a B9 supergiant and suspected variable star. It is the brightest member of the A asterism at magnitude 5.77.  The brightest star in the region of the cluster is the variable [[DS Cru]] (HD&nbsp;111613, HR&nbsp;4876), which lies well beyond the A asterism. It is a B9.5 [[Alpha Cygni variable|α&nbsp;Cyg variable]] supergiant with an average visual brightness of magnitude&nbsp;5.72, but is thought to be a foreground object.<ref name=kharchenko>
{{cite journal
 |last1= Kharchenko |first1=N.V.  |last2=Piskunov  |first2=A.E.
 |last3=Röser       |first3=S.    |last4=Schilbach |first4=E.
 |last5=Scholz      |first5=R.-D.
 |year=2004
 |title= Astrophysical supplements to the ASCC-2.5&nbsp;. II.&nbsp;Membership probabilities in 520&nbsp;Galactic open cluster sky areas
 |journal=[[Astronomische Nachrichten]]
 |volume=325 |issue=9 |page=740
 |doi= 10.1002/asna.200410256
 |bibcode= 2004AN....325..740K
}}
</ref>

The bar of the "A" consists of a line of four stars. On the right (south) is [[BU Crucis|BU&nbsp;Cru]], a magnitude&nbsp;6.92 B2 supergiant and [[eclipsing binary]].  Next to it is BV&nbsp;Cru, a magnitude&nbsp;8.662 B0.5 [[giant star|giant]] and [[Beta Cephei variable]].  Next in line is [[DU Crucis|DU&nbsp;Cru]], an M2 [[red supergiant]] that varies irregularly between magnitude&nbsp;7.1 and 7.6&nbsp;. The last of the four is CC&nbsp;Cru, a magnitude&nbsp;7.83 B2 giant and [[Rotating ellipsoidal variable|ellipsoidal variable]].<ref name=kharchenko/>

Each leg of the base of the asterism's outline is marked by a blue supergiant star. HD&nbsp;111990 (HIP&nbsp;62953) is magnitude&nbsp;6.77 and B1/2&nbsp;. The star κ&nbsp;Cru itself is magnitude&nbsp;5.98 and B3.<ref name=kharchenko/>

==Physical characteristics==

The Jewel Box cluster is one of the youngest known [[open cluster]]s. The mean [[radial velocity]] of the Jewel Box cluster is {{convert|-21|km/s|mi/s}}.<ref name=kaltcheva>
{{Cite journal
 |first1=N. |last1=Kaltcheva
 |first2=V. |last2=Golev
 |first3=K. |last3=Moran
 |year=2013
 |title=Massive stellar content of the Galactic supershell GSH&nbsp;305+01-24
 |journal=[[Astronomy & Astrophysics]]
 |volume=562  |page=A69
 |doi=10.1051/0004-6361/201321454
 |arxiv=1312.5592  |s2cid=54222753
 |bibcode = 2014A&A...562A..69K
}}
</ref>
The brightest stars in the Jewel Box cluster are [[supergiant]]s, and include some of the brightest stars in the [[Milky Way galaxy]].<ref name=Burnham>
{{cite book
 | last = Burnham | first = Robert | author-link = Robert Burnham Jr.
 | year = 1978
 | title = Burnham's Celestial Handbook: An observers' guide to the universe beyond the Solar system
 | edition = reprint
 | location = New York, NY
 | publisher = [[Dover Publications]]
 | isbn = 978-0-486-23568-4
 | page = 730
 | url = https://books.google.com/books?id=wB9uZ9lH5bgC&pg=PA730
 | via = Google books
}}
</ref>

Calculating its distance is difficult due to the proximity of the [[Coalsack Nebula]], which [[extinction (astronomy)|obscures]] some of its light.<ref name=ConsolmagnoEtAl>
{{cite book
 | first1 = Guy | last1 = Consolmagno
 | first2 = Dan | last2 = Davis
 | year = 2005
 | title = Turn Left at Orion: A hundred night sky objects to see in a small telescope
 | publisher = Cambridge University Press
 | place = Cambridge, UK
 | isbn = 978-0-521-78190-9
 | page = 189
 | url = https://books.google.com/books?id=PexKTfPy3voC&pg=PA189
 | via = Google books
}}
</ref>

==Observation==

The Jewel Box cluster is regarded as one of the finest objects in the southern sky.<ref name=Kaler>
{{cite book
 | last = Kaler | first = James B.
 | year = 1989
 | title = Stars and Their Spectra: An introduction to the spectral sequence
 | publisher = Cambridge University Press
 | place = Cambridge, UK
 | isbn = 978-0-521-58570-5
 | page = 13
 | url = https://books.google.com/books?id=ycLg34SaJWwC&pg=PA13
 | via = Google books
}}
</ref>
It is visible to the naked eye as a hazy object of the fourth magnitude.<ref name=RidpathTirion>
{{cite book
 | last1 = Ridpath |first1 = Ian  | author1-link = Ian Ridpath
 | last2 = Tirion  |first2 = Wil
 | year = 2007
 | title = Stars and Planets
 | publisher = Princeton University Press
 | isbn = 978-0-691-13556-4
 | page = 134
 | url = https://books.google.com/books?id=-pfuAAAAMAAJ
 | via = Google books
}}
</ref>
It can be easily located using the star [[Beta Crucis]] as a guide, and appears as a fourth magnitude object.<ref name=Mobberley>
{{cite book
 | last = Mobberley  | first = Martin
 | year = 2009
 | title = The Caldwell Objects
 | series = Astronomers' Observing Guides
 | publisher = Springer
 | doi = 10.1007/978-1-4419-0326-6
 | isbn = 978-1-4419-0325-9
 | page = 196
 | url = https://books.google.com/books?id=amPrWoOWgHcC
 | via = Google books
}}
</ref>
It is impressive when viewed with binoculars or a small or large telescope. Three members along the crossbar of the A-shaped asterism lie in a straight line known as the 'traffic lights' due to their varying colours.<ref name=Inglis>
{{cite book
 | last = Inglis  | first = Mike
 | year = 2004
 | title = Astronomy of the Milky Way: The observer's guide to the southern Milky Way
 | publisher = Springer
 | isbn = 978-1-85233-709-4
 | pages = 78–79
 | url = https://books.google.com/books?id=1r0qvMjSCGAC&pg=SA3-PA7
 | via = Google books
}}
</ref>

==Gallery==
<gallery class="center">
File:Wide Field Image of the Jewel Box.jpg|Wide Field Image of the Jewel Box
File:Digitized Sky Survey 2 Image of NGC 4755.jpg|Digitized Sky Survey 2 image of the Jewel Box
File:A Hubble gem - the Jewel Box.jpg|[[Hubble Space Telescope|Hubble]] image of the Jewel Box
File:Putting the Jewel Box in perspective (composite image).jpg|Putting the images in perspective
File:NGC 4755 "El Joyero" a través de un pequeño telescopio.jpg|The Jewel Box seen through a small amateur telescope
</gallery>

==References==
{{reflist|25em}}

==External links==
{{commons category}}
* {{cite AV media
 |title=Image of NGC&nbsp;4755
 |medium=astrophoto
 |website=[[SEDS]]
 |quote=Image of NGC&nbsp;4755 copyright [[Anglo-Australian Observatory]]
 |url=http://messier.seds.org/xtra/ngc/n4755.html
}}
*{{WikiSky|name=The Jewel Box|1=NGC4755}}
* {{cite AV media
 |title=Amateur image of NGC&nbsp;4755
 |medium=astrophoto
 |url=http://www.pbase.com/trevrw/image/115713085
 |quote=Image copyright T.&nbsp;Warner 
}}

{{Sky|12|53|42|-|60|22|00|6400}}
{{Catalogs|C=94|Collinder=265|NGC=4755}}
{{Caldwell catalogue}}
{{Ngc50}}
{{Crux}}

{{DEFAULTSORT:Jewel Box (star cluster)}}
[[Category:Open clusters]]
[[Category:Crux]]
[[Category:NGC objects]]
[[Category:Caldwell objects|094b]]