NGC 6256
{{Short description|Globular cluster in the constellation Scorpius}}
{{Infobox globular cluster
| name = NGC 6256
| image = NGC 6256 hst 11628 R814B555.png
| caption = NGC 6256 as seen through the Hubble Space Telescope
| credit =
| epoch = J2000
| class =
| constellation = Scorpius
| dist_ly = {{convert|6.8|kpc|kly|order=flip|abbr=on|lk=on}}
| dist_pc =
| size_v = {{val|7|u=arcminute}}
| absmag_v = −7.15{{CN|date=May 2024}}
| mass_msol =
| mass_kg =
| radius_arcminsec =
| radius_ly =
| radius_pc =
| radius_tidal_arcminsec =
| radius_tidal_ly =
| radius_tidal_pc =
| v_hb =
| metal_fe =
| metal_z =
| age = {{val|13.0|0.5|u=Gyr}}
| notes =
| names = NGC 6256, GCL 49.1, ESO 391-SC6 and vdB-Hagen 208
}}
NGC 6256 is a globular cluster of stars in the southern constellation of Scorpius. It was discovered by the Scottish astronomer James Dunlop on Aug 2, 1826. In J. L. E. Dreyer's New General Catalogue annotation it is described as, "very faint, very large, very gradually bright in the middle, well resolved clearly consisting of stars." The cluster is located at a distance of {{convert|6.8|kpc|e3ly|order=flip|abbr=out|lk=on}} from the Sun.
This is an ancient cluster with an estimated age of about 13 billion years; it was formed during the very early stages of assembly of the Milky Way galaxy. The cluster is orbiting within the galactic bulge with a low orbital eccentricity. It is heavily reddened by extinction due to interstellar gas and dust. The structure is very concentrated at the center, showing a post core collapse morphology.
The HR diagram for this cluster displays two sequences of blue straggler stars, which are the products of stellar mergers. The bluer sequence is well-defined and narrow, most likely being generated over a short time span. The redder sequence is more sparse, being the result of a continuous process of formation. It is hypothesized that the bluer sequence was formed around the time of the cluster's core collapse about one billion years ago; an event that made stellar collisions more likely.
The cluster contains a millisecond X-ray pulsar, designated IGR J16597-3704.
References
{{reflist|refs=
| title=NGC 6256 | access-date=2024-05-23 }}
| title=RR Lyrae-based calibration of the Globular Cluster Luminosity Function
| last1=Di Criscienzo | first1=M. | last2=Caputo | first2=F.
| last3=Marconi | first3=M. | last4=Musella | first4=I.
| display-authors=1 | journal=Monthly Notices of the Royal Astronomical Society
| volume=365 | issue=4 | pages=1357–1366 | date=February 2006
| doi=10.1111/j.1365-2966.2005.09819.x | doi-access=free | s2cid=17838243
| bibcode=2006MNRAS.365.1357D | arxiv=astro-ph/0511128 }}
| title=Digging for Relics of the Past: The Ancient and Obscured Bulge Globular Cluster NGC 6256
| last1=Cadelano | first1=M. | last2=Saracino | first2=S.
| last3=Dalessandro | first3=E. | last4=Ferraro | first4=F. R.
| last5=Lanzoni | first5=B. | last6=Massari | first6=D.
| last7=Pallanca | first7=C. | last8=Salaris | first8=M.
| display-authors=1 | journal=The Astrophysical Journal
| volume=895 | issue=1 | at=id.54 | date=May 2020
| doi=10.3847/1538-4357/ab88b3 | doi-access=free | arxiv=2004.06131
| bibcode=2020ApJ...895...54C }}
| title=The Cluster NGC 6256
| last1=Terzan | first1=A. | last2=Lelievre | first2=G.
| journal=Astronomy and Astrophysics
| volume=29 | page=431 | date=December 1973
| bibcode=1973A&A....29..431T }}
| title=Colour-magnitude diagrams of the post-core collapse globular clusters NGC 6256 and NGC 6717 (Palomar 9)
| display-authors=1 | last1=Ortolani | first1=S.
| last2=Barbuy | first2=B. | last3=Bica | first3=E.
| journal=Astronomy and Astrophysics Supplement
| volume=136 | pages=237–243 | date=April 1999
| issue=2 | doi=10.1051/aas:1999210 | bibcode=1999A&AS..136..237O }}
| title=Discovery of a Double Sequence of Blue Straggler Stars in the Core-collapsed Globular Cluster NGC 6256
| last1=Cadelano | first1=Mario | last2=Ferraro | first2=Francesco R.
| last3=Dalessandro | first3=Emanuele | last4=Lanzoni | first4=Barbara
| last5=Pallanca | first5=Cristina | last6=Saracino | first6=Sara
| display-authors=1 | journal=The Astrophysical Journal
| volume=941 | issue=1 | at=id. 69 | date=December 2022
| doi=10.3847/1538-4357/aca016 | doi-access=free | arxiv=2211.02671
| bibcode=2022ApJ...941...69C }}
| title=A Radio Frequency Study of the Accreting Millisecond X-ray Pulsar, IGR J16597-3704, in the Globular Cluster NGC 6256
| display-authors=1 | last1=Tetarenko | first1=A. J.
| last2=Bahramian | first2=A. | last3=Wijnands | first3=R.
| last4=Heinke | first4=C. O. | last5=Maccarone | first5=T. J.
| last6=Miller-Jones | first6=J. C. A. | last7=Strader | first7=J.
| last8=Chomiuk | first8=L. | last9=Degenaar | first9=N.
| last10=Sivakoff | first10=G. R. | last11=Altamirano | first11=D.
| last12=Deller | first12=A. T. | last13=Kennea | first13=J. A.
| last14=Li | first14=K. L. | last15=Plotkin | first15=R. M.
| last16=Russell | first16=T. D. | last17=Shaw | first17=A. W.
| journal=The Astrophysical Journal
| volume=854 | issue=2 | at=id. 125 | date=February 2018
| doi=10.3847/1538-4357/aaa95a | doi-access=free | arxiv=1801.05778
| bibcode=2018ApJ...854..125T }}
| title=Deep-Sky Companions: Southern Gems
| first=Stephen James | last=O'Meara | year=2013
| page=331 | publisher=Cambridge University Press
| isbn=9781107015012
| url=https://books.google.com/books?id=S5QIEKns33sC&pg=PA331 }}
| title=NGC 6256
| first=Hartmut | last=Frommert
| work=Students for the Exploration and Development of Space
| url=https://spider.seds.org/spider/MWGC/n6256.html
| access-date=2024-05-23 }}
| title=NGC Objects: NGC 6250 - 6299
| first=Courtney | last=Seligman
| work=Celestial Atlas
| url=https://cseligman.com/text/atlas/ngc62a.htm#6256
| access-date=2024-05-23 }}
}}
External links
- {{commons category-inline}}
{{NGC objects:6000-6499}}
{{scorpius}}