View source for NGC 654

{{short description|Open star cluster in the constellation Cassiopeia}}
{{Infobox cluster
| name = NGC 654
| image = NGC_654,VdB6,LDN_1332,1334,1337_(Cassiopeia).jpg
| caption = NGC 654 in Cassiopeia
| credit = Antonio F. Sánchez
| type = [[Open Cluster]]
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| constellation = [[Cassiopeia (constellation)|Cassiopeia]]
| ra = {{RA|01|44|00}}<ref name="simbad">
{{cite simbad
| title=NGC 654
| access-date=2015-06-19
}}</ref>
| dec = {{DEC|+61|53|06}}<ref name="simbad"/>
| dist_ly = 7,830 [[light year|ly]]
| dist_pc = 2,400 [[parsec|pc]]
| appmag_v = 6.5 <ref name="simbad"/>
| size_v = 5'
| mass_msol =
| age = 14 million years<ref>[https://www.univie.ac.at/webda/cgi-bin/ocl_page.cgi?dirname=ngc0654 WEBDA: NGC 654]</ref>
| notes =
| names = [[Collinder catalogue|Cr]] 18
}}
'''NGC 654''' is an [[open cluster]] in the constellation [[Cassiopeia (constellation)|Cassiopeia]]. It was discovered by [[William Herschel]] in 1787. With [[apparent magnitude]] 6.5, it can be observed by binoculars.<ref>{{cite book|last1=Stephen James O'Meara|title=Deep-Sky Companions: The Secret Deep vol. 4|date=2011|publisher=[[Cambridge University Press]]|isbn=978-1-139-50007-4|pages=31–33|url=https://books.google.com/books?id=v859bKO0A4gC&pg=PA31|ref=O'Meara}}</ref> It is located 2,5° northeast of the star [[Delta Cassiopeiae]]. In the same low power field can also be seen the open clusters [[NGC 663]] and [[NGC 659]]. It surrounds a 7th magnitude yellowish star, an F5Ia [[supergiant]], which is a possible member of the group.<ref>{{cite journal|author1=Huestamendia, G. |author2=del Rio, G. |author3=Mermilliod, J.-C. |title=UBV photometry of open clusters in the Cassiopeia region. II - Photoelectric observations of NGC 654|journal=Astronomy and Astrophysics Supplement Series|date=July 1993|volume=100|issue=1|pages=25–32|url=http://cdsads.u-strasbg.fr/abs/1993A%26AS..100...25H|access-date=29 December 2015|bibcode = 1993A&AS..100...25H }}</ref>

It is 2,400 parsec away. It is a very young cluster, aged approximately 15 million years, but it could be as old as 40 million years, with a time spread of star formation of at least ~20 Myr. The central region of the cluster shows less reddening than the rest of the cluster.<ref>{{cite journal|author1=A. K. Pandey |author2=K. Upadhyay |author3=K. Ogura |author4=Ram Sagar |author5=V. Mohan |author6=H. Mito |author7=H. C. Bhatt |author8=B. C. Bhatt |title=Stellar contents of two young open clusters: NGC 663 and 654|journal=MNRAS|date=April 2005|volume=358|issue=4|pages=1290–1308|doi=10.1111/j.1365-2966.2005.08784.x|url=http://mnras.oxfordjournals.org/content/358/4/1290.full|bibcode = 2005MNRAS.358.1290P |doi-access=free }}</ref> One explanation is that between the Solar System and the cluster lie two dust layers, one at 200pc and one more at 1Kpc.<ref>{{cite journal|author1=Biman J. Medhi |author2=Maheswar G. |author3=J. C. Pandey |author4=T. S. Kumar |author5=Ram Sagar |title=Optical polarimetric study of open clusters: distribution of interstellar matter towards NGC 654|journal=MNRAS|date=2008|volume=388|issue=1|pages=105–116|doi=10.1111/j.1365-2966.2008.13405.x|doi-access=free |url=http://mnras.oxfordjournals.org/content/388/1/105|access-date=29 December 2015|arxiv = 0804.4739 |bibcode = 2008MNRAS.388..105M |s2cid=119297788 }}</ref> Behind the cluster is one more dust layer. The cluster has approx. 80 members, including three [[Be star]]s and a few luminous stars like HD 10494 and F5Ia. The earliest spectral type is around B0.<ref>{{cite journal|last1=H.M. Shi - J.Y. Hu|title=Spectroscopic observations of young open clusters: IC 1805, NGC 654 and NGC 6823|journal=Astron. Astrophys. Suppl. Ser.|date=April 1999|volume=136|issue=2|pages=313–331|doi=10.1051/aas:1999217|url=http://aas.aanda.org/articles/aas/pdf/1999/08/ds8200.pdf|access-date=29 December 2015|bibcode = 1999A&AS..136..313S |doi-access=free}}</ref>

NGC 654 is assumed to form part of the [[stellar association]] Cassiopeia OB8, that is located in the [[Perseus arm]] of the [[Milky Way]], along with the open clusters [[Messier 103|M103]], [[NGC 663]], [[NGC 659]], and some [[supergiant]] stars scattered between them, all of them having similar ages and distances.<ref name="aaa528">{{cite journal
 | author=Negueruela, I.
 | author2=González-Fernández, C.
 | author3=Marco, A.
 | author4=Clark, J. S.
 | title=A massive association around the obscured open cluster RSGC3
 | journal=Astronomy & Astrophysics 
 | volume=528
 | pages=A59
 | date=2011
 | doi=10.1051/0004-6361/201016102
 | bibcode=2011A&A...528A..59N|arxiv = 1102.0028 | s2cid=53517711
 }}</ref><ref name="ApJS1978">{{cite journal
 | author=Humphreys, R. M.
 | title=Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.
 | journal=Astrophysical Journal Supplement Series 
 | volume=38
 | pages=309–350 | date=1978
 | doi=10.1086/190559
 | bibcode=1978ApJS...38..309H}}</ref>

==Gallery==
{{Gallery|width=200
|File:NGC654-Rev.01-THIS IS FINAL.jpg|NGC 654 - by Kanwar Singh
|File:NGC 654 map.png|Map showing location of NGC 654
}}

== References ==
{{Reflist|30em}}

==External links==
{{commonscat}}
* {{WikiSky}}


{{NGC10}}
{{Cassiopeia (constellation)}}
{{Sky|01|44|00|+|61|53|6}}

{{DEFAULTSORT:NGC 0654}}
[[Category:Open clusters]]
[[Category:Cassiopeia (constellation)]]
[[Category:NGC objects|0654]]
[[Category:Astronomical objects discovered in 1787|?]]
[[Category:Discoveries by William Herschel]]