|Observation data: J2000.0 epoch|
|Right ascension||22h 57m 17.14s|
|Declination||+62° 28′ 33.4"|
|Apparent magnitude (V)||7.7|
|Apparent dimensions (V)||50.0'x30.0'|
|Absolute magnitude (V)||16|
|Designations||Sh2-155, Caldwell 9, LBN 110.11+02.44|
Sh2-155 (also designated Sharpless 155 or S155) is a diffuse nebula in the 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. Sh2-155 is an ionized H II region with ongoing star formation activity, at an estimated distance of 725 parsecs (2400 light-years) from Earth.
Sh2-155 was first noted as a galactic emission nebula in 1959 in the extended second edition of the Sharpless catalogue, being a part of the much larger Cep OB3 Association. Although Sh2-155 is relatively faint for amateur observation, some of its structure may be seen visually through a moderately sized telescope under dark skies.
Sh2-155 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. 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. 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.
Other name designations
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. The name was also used earlier to refer to another brighter but unrelated reflection nebula in Cepheus known as Ced 201 or VdB 152, positioned at R.A.: 22h 13m 27s Dec.: +70° 15′ 18″ (2000). The name's application to Sh2-155 has come into vogue through the nebula's inclusion in Moore's Caldwell catalogue as object Caldwell 9. (SIMBAD lists the name for Ced 201, but not for Sh2-155.)
- Getman, Konstantin V.; Feigelson, Eric D.; Townsley, Leisa; Broos, Patrick; Garmire, Gordon; Tsujimoto, Masahiro (2006). "ChandraStudy of the Cepheus B Star‐forming Region: Stellar Populations and the Initial Mass Function". The Astrophysical Journal Supplement Series. 163 (2): 306–334. arXiv: . Bibcode:2006ApJS..163..306G. doi:10.1086/501453. ISSN 0067-0049.
- Blaauw, A.; Hiltner, W. A.; Johnson, H. L. (1959). "Photoelectric Photometry of the Association III Cephei". The Astrophysical Journal. 130: 69. Bibcode:1959ApJ...130...69B. doi:10.1086/146697. ISSN 0004-637X.
- Crawford, D. L.; Barnes, J. V. (1970). "Four-color and H-beta photometry of open clusters - VI - the association III Cep". The Astronomical Journal. 75: 952. Bibcode:1970AJ.....75..952C. doi:10.1086/111045. ISSN 0004-6256.
- "Sh2-155". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 11 March 2017.
- Sharpless, S. (1959). "A Catalogue of H II Regions". Astrophysical Journal Supplement. 4: 257. Bibcode:1959ApJS....4..257S. doi:10.1086/190049. Retrieved 9 March 2017.
- Patrick Moore (1990). The Amateur Astronomer (11th ed), W.W. Norton & Company, ISBN 0-393-02864-X
- Trusock, T. (11 March 2017). "The Caldwell Objects – Deep Sky Companions" (PDF).
- Panagia, N.; Thum, C. (1981). "A study of the S 155A - CEP B cloud and its relation to Cepheus OB3 association". Astronomy and Astrophysics. 92 (2): 295–299. Bibcode:1981A&A....98..295P.
- Minchin, Nigel R.; Ward-Thompson, Derek; White, Glenn J. (1992). "Carbon monoxide and far-infrared observations of the S 155-Cepheus B region". Astronomy and Astrophysics. 265 (2): 733–742. Bibcode:1992A&A...265..733M.
- "Cepheus B: Trigger-Happy Star Formation". chandra.harvard.edu. August 12, 2009. Retrieved March 12, 2017.
- Getman, Konstantin V.; Feigelson, Eric D.; Luhman, Kevin L.; Sicilia-Aguilar, Aurora; Wang, Junfeng; Garmire, Gordon P. (2009). "PROTOPLANETARY DISK EVOLUTION AROUND THE TRIGGERED STAR-FORMING REGION CEPHEUS B". The Astrophysical Journal. 699 (2): 1454–1472. arXiv: . Bibcode:2009ApJ...699.1454G. doi:10.1088/0004-637X/699/2/1454. ISSN 0004-637X.
- Mobberley, M. (9 March 2017). "The Caldwell Objects and How to Observe Them".
- "Ced 201". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 11 March 2017.
- "VdB 152". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 12 March 2017.
- "APOD: 2012 October 31 - VdB 152: A Ghost in Cepheus". apod.nasa.gov. Retrieved 11 March 2017.
- O'Meara, Stephen James (2002). The Caldwell Objects. Cambridge University Press. ISBN 978-0-521-82796-6.
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