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 4,000ly away, and the central star that lights it formed about 100,000 years ago;[7] the nebula is about 12arcmins across, which is equivalent to a span of 15 light years.[6]
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". 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
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. S2CID119328315.
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. ISSN1538-4365. S2CID59124520.
"IC 5146". SIMBAD. Centre de données astronomiques de Strasbourg.
"NED results for object IC 5146". NASA/IPAC Extragalactic Database. National Aeronautics and Space Administration / Infrared Processing and Analysis Center.
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