IC 5146

IC 5146 (also Caldwell 19, Sh 2-125, Barnard 168, and the Cocoon Nebula) is a reflection[2]/emission[3] nebula and Caldwell object in the constellation Cygnus. The NGC description refers to IC 5146 as a cluster of 9.5 mag stars involved in a bright and dark nebula. The cluster is also known as Collinder 470.[4] It shines at magnitude +10.0[5]/+9.3[3]/+7.2.[6] Its celestial coordinates are RA 21h 53.5m , dec +47° 16′. It is located near the naked-eye star Pi Cygni, the open cluster NGC 7209 in Lacerta, and the bright open cluster M39.[2][5] The cluster is about 4,000 ly away, and the central star that lights it formed about 100,000 years ago;[7] the nebula is about 12 arcmins across, which is equivalent to a span of 15 light years.[6]

IC 5146
Reflection nebula
emission nebula
Optical image of IC 5146
Observation data: J2000 epoch
Right ascension21h 53m 28.7s
Declination+47° 16′ 01″
Distance2500±100[1] ly   (780±30 pc)
Apparent magnitude (V)+7.2
Apparent dimensions (V)12′
ConstellationCygnus
Physical characteristics
Radius7.5 ly
DesignationsCocoon Nebula, Caldwell 19, Sh 2-125, Cr 470

When viewing IC 5146, dark nebula Barnard 168 (B168) is an inseparable part of the experience, forming a dark lane that surrounds the cluster and projects westward forming the appearance of a trail behind the Cocoon.


Young Stellar Objects
View of the IC 5146 star-forming region from ESA's Herschel Space Telescope

IC 5146 is a stellar nursery where star-formation is ongoing. Observations by both the Spitzer Space Telescope and the Chandra X-ray Observatory have collectively identified hundreds of young stellar objects.[8][9] Young stars are seen in both the emission nebula, where gas has been ionized by massive young stars, and in the infrared-dark molecular cloud that forms the "tail". One of the most massive stars in the region is BD +46 3474, a star of class B1 that is an estimated 14±4 times the mass of the sun.[10]

Another interesting star in the nebula is BD +46 3471, which is an example of a HAeBe star, an intermediate mass star with strong emission lines in its spectrum.[11]

References
  1. Kuhn, Michael A.; Hillenbrand, Lynne A.; Sills, Alison; Feigelson, Eric D.; Getman, Konstantin V. (2018). "Kinematics in Young Star Clusters and Associations with Gaia DR2". The Astrophysical Journal. 870 (1): 32. arXiv:1807.02115. Bibcode:2019ApJ...870...32K. doi:10.3847/1538-4357/aaef8c. S2CID 119328315.
  2. Eicher, David J. (1988). The Universe from Your Backyard: A Guide to Deep-Sky Objects from Astronomy Magazine. AstroMedia (Kalmbach Publishing Company). ISBN 0-521-36299-7.
  3. Sanqunetti, Doug (2007). "IC 5146 - Cocoon Nebula". dougsastro.net. Retrieved 2008-08-06.
  4. O'Meara, Stephen James: The Caldwell Objects, Sky Publishing Corporation ISBN 0-933346-97-2 page 80
  5. Pasachoff, Jay M. (2000). "Atlas of the Sky". Stars and Planets. New York, NY: Peterson Field Guides. p. 578. ISBN 0-395-93432-X.
  6. Cannistra, Steve (2004). "Cocoon Nebula". starrywonders.com. Retrieved 2008-08-06.
  7. Nemiroff, R.; Bonnell, J., eds. (2002-10-14). "IC 5146: The Cocoon Nebula". Astronomy Picture of the Day. NASA. Retrieved 2008-08-06.
  8. Harvey, Paul M.; Huard, Tracy L.; Jørgensen, Jes K.; Gutermuth, Robert A.; Mamajek, Eric E.; Bourke, Tyler L.; Merín, Bruno; Cieza, Lucas; Brooke, Tim; Chapman, Nicholas; Alcalá, Juan M.; Allen, Lori E.; Evans II, Neal J.; Di Francesco, James; Kirk, Jason M. (2008). "TheSpitzerSurvey of Interstellar Clouds in the Gould Belt. I. IC 5146 Observed With IRAC and MIPS". The Astrophysical Journal. 680 (1): 495–516. Bibcode:2008ApJ...680..495H. doi:10.1086/587687. ISSN 0004-637X.
  9. Getman, Konstantin V.; Broos, Patrick S.; Kuhn, Michael A.; Feigelson, Eric D.; Richert, Alexander J. W.; Ota, Yosuke; Bate, Matthew R.; Garmire, Gordon P. (2017). "Star Formation In Nearby Clouds (SFiNCs): X-Ray and Infrared Source Catalogs and Membership". The Astrophysical Journal Supplement Series. 229 (2): 28. arXiv:1612.05282. Bibcode:2017ApJS..229...28G. doi:10.3847/1538-4365/229/2/28. ISSN 1538-4365. S2CID 59124520.
  10. Weidner, Carsten; Kroupa, Pavel (2006). "The maximum stellar mass, star-cluster formation and composite stellar populations". Monthly Notices of the Royal Astronomical Society. 365 (4): 1333–1347. arXiv:astro-ph/0511331. Bibcode:2006MNRAS.365.1333W. doi:10.1111/j.1365-2966.2005.09824.x. ISSN 0035-8711. S2CID 11688023.
  11. Reipurth, Bo (2008). Handbook of star forming regions. San Francisco: Astronomical Society of the Pacific. ISBN 978-1-58381-670-7.
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