View source for Sh 2-155

{{Short description|H II region in the constellation Cepheus}}

{{Infobox nebula
| name = Sh 2-155
| image = CaveHunterWilson.jpg
| caption = Sh 2–155
| type = Emission
| type2 =
| epoch = J2000.0
| ra = 22<sup>h</sup> 57<sup>m</sup> 17.14<sup>s</sup>
| dec = +62° 28′ 33.4"
| dist_ly =  2400
| appmag_v = 7.7
| size_v = 50.0'x30.0'
| constellation  = [[Cepheus (constellation)|Cepheus]]
| radius_ly = 35
| absmag_v = 16
| notes =
| names = Sh 2-155, [[Caldwell catalogue|Caldwell 9]], [[Lynds' Catalogue of Bright Nebulae|LBN&nbsp;110.11+02.44]]
}}
'''Sh 2-155''' (also designated [[Caldwell catalogue|Caldwell]] 9, '''Sharpless 155''' or '''S155''', or '''LBN529''') is a [[diffuse nebula]] in the constellation [[Cepheus (constellation)|Cepheus]], within a larger nebula complex containing emission, reflection, and dark nebulosity. It is widely known as the '''Cave Nebula''', though that name was applied earlier to Ced 201, a different nebula in Cepheus.  Sh 2-155 is an ionized [[H II region]] with ongoing [[star formation]] activity,<ref name="GetmanFeigelson2006">{{cite journal|last1=Getman|first1=Konstantin V.|last2=Feigelson|first2=Eric D.|last3=Townsley|first3=Leisa|last4=Broos|first4=Patrick|last5=Garmire|first5=Gordon|last6=Tsujimoto|first6=Masahiro|title=ChandraStudy of the Cepheus B Star-forming Region: Stellar Populations and the Initial Mass Function|journal=The Astrophysical Journal Supplement Series|volume=163|issue=2|year=2006|pages=306–334|issn=0067-0049|doi=10.1086/501453|arxiv = astro-ph/0601405 |bibcode = 2006ApJS..163..306G |s2cid=16305023 }}</ref> at an estimated distance of 725 parsecs (2400 light-years) from Earth.<ref name="BlaauwHiltner1959">{{cite journal|last1=Blaauw|first1=A.|last2=Hiltner|first2=W. A.|last3=Johnson|first3=H. L.|title=Photoelectric Photometry of the Association III Cephei.|journal=The Astrophysical Journal|volume=130|year=1959|pages=69|issn=0004-637X|doi=10.1086/146697|bibcode = 1959ApJ...130...69B }}</ref><ref name="CrawfordBarnes1970">{{cite journal|last1=Crawford|first1=D. L.|last2=Barnes|first2=J. V.|title=Four-color and H-beta photometry of open clusters - VI - the association III Cep.|journal=The Astronomical Journal|volume=75|year=1970|pages=952|issn=0004-6256|doi=10.1086/111045|bibcode = 1970AJ.....75..952C }}</ref>

Sh 2-155<ref name="simbad">{{cite simbad
|title=Sh2-155
|access-date=11 March 2017}}</ref> was first noted as a galactic emission nebula in 1959 in the extended second edition of the [[Sharpless catalog]]ue,<ref name="Sharpless1959">{{cite journal
|last=Sharpless |first=S.
|year=1959
|title=A Catalogue of H II Regions
|journal=[[Astrophysical Journal Supplement]]
|volume=4
|pages=257
|bibcode=1959ApJS....4..257S
|doi=10.1086/190049
}}</ref> being a part of the much larger Cep OB3 [[Stellar associations|Association]].<ref name="Sharpless1959" /> Although Sh 2-155 is relatively faint for amateur observation, some of its structure may be seen visually through a moderately sized telescope under dark skies.<ref name=Moore>Patrick Moore (1990). ''The Amateur Astronomer'' (11th ed), W.W. Norton & Company, {{ISBN|0-393-02864-X}}</ref><ref name=CaldObjDSC >{{Cite web
|last=Trusock |first=T.
|date=11 March 2017
|title=The Caldwell Objects – Deep Sky Companions
|url=http://www.cloudynights.com/documents/caldwell.pdf}}</ref>

Sh 2-155 lies at the edge of the Cepheus B cloud (part of the Cepheus [[molecular cloud]]), and is [[ionized]] by young stars from the Cep OB3 association.<ref name="Panagia81">{{Cite journal
|last1 = Panagia |first1=N.
|last2 = Thum |first2=C.
|year=1981
|title = A study of the S 155A – CEP B cloud and its relation to Cepheus OB3 association
|journal= Astronomy and Astrophysics
|volume=92
|issue=2
|pages= 295–299
|bibcode=1981A&A....98..295P}}</ref> It has been suggested that radiation from the hot [[O-type star]] HD 217086 is compressing the region, triggering the formation of a new generation of stars.<ref name="Minchin92">{{Cite journal
|last1 = Minchin |first1=Nigel R.
|last2 = Ward-Thompson |first2=Derek
|last3 = White |first3=Glenn J.
|year=1992
|title = Carbon monoxide and far-infrared observations of the S 155-Cepheus B region
|journal= Astronomy and Astrophysics
|volume= 265
|issue=2
|pages= 733–742
|bibcode=1992A&A...265..733M}}</ref> A study of the region's [[young stellar objects]] by the [[Chandra X-ray Observatory]] and [[Spitzer Space Telescope]] shows a progression of stellar ages in front of the cloud, supporting the hypothesis of [[triggered star-formation]].<ref name="TriggerHappyStarFormation">{{cite web| url=http://chandra.harvard.edu/photo/2009/cepb/|title= Cepheus B: Trigger-Happy Star Formation|access-date=March 12, 2017|website=chandra.harvard.edu|date=August 12, 2009}}</ref><ref name="GetmanFeigelson2009">{{cite journal|last1=Getman|first1=Konstantin V.|last2=Feigelson|first2=Eric D.|last3=Luhman|first3=Kevin L.|last4=Sicilia-Aguilar|first4=Aurora|last5=Wang|first5=Junfeng|last6=Garmire|first6=Gordon P.|title=Protoplanetary Disk Evolution Around the Triggered Star-Forming Region Cepheus B |journal=The Astrophysical Journal|volume=699|issue=2|year=2009|pages=1454–1472|issn=0004-637X|doi=10.1088/0004-637X/699/2/1454|arxiv = 0904.4907 |bibcode = 2009ApJ...699.1454G |s2cid=18149231 }}</ref>

==Other name designations==
[[File:Cave Finished v2.jpg|thumb|left|Amateur photograph of the Cave Nebula in the [[Hubble palette]]]]
The name "Cave Nebula" was coined for this object by [[Patrick Moore]], presumably derived from photographic images showing a curved arc of emission nebulosity corresponding to a cave mouth.<ref name=Mobberley>{{Cite book
|last=Mobberley|first=M.
|date=9 March 2017
|title=The Caldwell Objects and How to Observe Them
|publisher=Springer
|isbn=9781441903266
|url=https://books.google.com/books?id=amPrWoOWgHcC&pg=PA30
}}</ref> The name was also used earlier to refer to another brighter but unrelated reflection nebula in Cepheus known as Ced 201<ref name="ced 201">{{cite simbad
|title=Ced 201
|access-date=11 March 2017}}</ref> or VdB 152,<ref name="VDB152">{{cite simbad
|title=VdB 152
|access-date=12 March 2017}}</ref><ref name="APODVDB152">{{cite web
|title=APOD: 2012 October 31 – VdB 152: A Ghost in Cepheus
|url=https://apod.nasa.gov/apod/ap121031.html
|website=apod.nasa.gov
|access-date=11 March 2017}}</ref> positioned at [[Right ascension|R.A.]]: 22h 13m 27s [[Declination|Dec.]]: +70° 15′ 18″ ([[Epoch (astronomy)|2000]]). The name's application to Sh 2-155 has come into vogue through the nebula's inclusion in Moore's [[Caldwell catalogue]]<ref name="CaldCat">{{cite book
| last = O'Meara
| first = Stephen James
| title = The Caldwell Objects
| publisher = [[Cambridge University Press]]
| year = 2002
| isbn = 978-0-521-82796-6}}</ref> as object Caldwell 9. ([[SIMBAD]] lists the name for Ced 201, but not for Sh 2-155.)<ref name="simbad"/><ref name="ced 201"/>
{{clear left}}

==References==
{{Reflist}}

==External links==
{{commons category}}
{{WikiSky}}
* [http://apod.nasa.gov/apod/ap120312.html The Scale of the Universe] ([[Astronomy Picture of the Day]] 2012 March 12)

{{Sh2 objects}}
{{Caldwell catalogue}}
{{Cepheus (constellation)}}

{{DEFAULTSORT:Sh 2-155}}
[[Category:Cepheus (constellation)]]
[[Category:Emission nebulae]]
[[Category:Sharpless objects|155]]
[[Category:Caldwell objects|009b]]
[[Category:Star-forming regions]]