Sh2-155

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,[1] at an estimated distance of 725 parsecs (2400 light-years) from Earth.[2][3]

Sh2-155
Emission nebula
Sh2–155
Observation data: J2000.0 epoch
Right ascension22h 57m 17.14s
Declination+62° 28′ 33.4"
Distance2400 ly
Apparent magnitude (V)7.7
Apparent dimensions (V)50.0'x30.0'
ConstellationCepheus
Physical characteristics
Radius35 ly
Absolute magnitude (V)16
DesignationsSh2-155, Caldwell 9, LBN 110.11+02.44

Sh2-155[4] was first noted as a galactic emission nebula in 1959 in the extended second edition of the Sharpless catalogue,[5] being a part of the much larger Cep OB3 Association.[5] 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.[6][7]

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.[8] 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.[9] 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.[10][11]

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.[12] The name was also used earlier to refer to another brighter but unrelated reflection nebula in Cepheus known as Ced 201[13] or VdB 152,[14][15] 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[16] as object Caldwell 9. (SIMBAD lists the name for Ced 201, but not for Sh2-155.)[4][13]

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References
  1. 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:astro-ph/0601405. Bibcode:2006ApJS..163..306G. doi:10.1086/501453. ISSN 0067-0049.
  2. 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.
  3. 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.
  4. "Sh2-155". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 11 March 2017.
  5. 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.
  6. Patrick Moore (1990). The Amateur Astronomer (11th ed), W.W. Norton & Company, ISBN 0-393-02864-X
  7. Trusock, T. (11 March 2017). "The Caldwell Objects – Deep Sky Companions" (PDF).
  8. 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.
  9. 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.
  10. "Cepheus B: Trigger-Happy Star Formation". chandra.harvard.edu. August 12, 2009. Retrieved March 12, 2017.
  11. 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:0904.4907. Bibcode:2009ApJ...699.1454G. doi:10.1088/0004-637X/699/2/1454. ISSN 0004-637X.
  12. Mobberley, M. (9 March 2017). "The Caldwell Objects and How to Observe Them".
  13. "Ced 201". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 11 March 2017.
  14. "VdB 152". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 12 March 2017.
  15. "APOD: 2012 October 31 – VdB 152: A Ghost in Cepheus". apod.nasa.gov. Retrieved 11 March 2017.
  16. O'Meara, Stephen James (2002). The Caldwell Objects. Cambridge University Press. ISBN 978-0-521-82796-6.


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