21h53m32s, +47° 16′06″| Reflection nebula | |
|---|---|
| emission nebula | |
Optical image of IC 5146
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| Observation data: J2000 epoch | |
| Right ascension | 21h53m 28.7s |
| Declination | +47° 16′ 01″ |
| Distance | 2500±100[1] ly (780±30 pc) |
| Apparent magnitude (V) | +7.2 |
| Apparent dimensions (V) | 12′ |
| Constellation | Cygnus |
| Physical characteristics | |
| Radius | 7.5 ly |
| Designations | Cocoon Nebula, Caldwell 19, Sh 2-125, Cr 470 |
| See also: Lists of nebulae | |
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 7209inLacerta, 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]
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.
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]
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