Clamshell Nebula
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The Clamshell Nebula, cataloged as Sh 2-119, is an emission nebula and star-forming region in Cygnus. It gets its name from its two-lobed structure, split into eastern and western sections by the blue giant star 68 Cygni, which sits between them. This star is the nebula’s main source of ionization. The nebula’s shape is that of a Strömgren sphere, and it contains multiple dust lanes and Bok globules.
First spotted in the early 1950s by Grigory Shajn and Vera Gaze during a photographic survey, they labeled it Gaze+Shajn [GS55] 240. In 1959, Stewart Sharpless mapped the area in greater detail, finding the nebula far larger than initially thought, and added it to his catalog as Sh 2-119. Originally, astronomers thought the nebula formed from 68 Cygni’s stellar wind, but it now appears the wind is actually a bow shock caused by the star’s high speed through space. Within the nebula lies the planetary nebula PK 87-3.1, and the open cluster NGC 7044 is nearby.
Background
The Clamshell Nebula was discovered in the early 1950s by Grigory Abramovich Shajn and Vera Fedorovna Gaze while conducting a photographic survey, and they named it Gaze+Shajn [GS55] 240. Stewart Sharpless would survey the region of the sky in more detail in 1959, revealing that the nebula was much more extensive than originally thought. He included it in his Sharpless catalog, giving it the designation Sh 2-119.
The nebula surrounds blue giant 68 Cygni and contains multiple dust lanes and Bok globules. 68 Cygni is the primary source of ionization within the nebula. The structure of the nebula is that of a Strömgren sphere, and is divided into an eastern and western section, with 68 Cygni between the two.
These two sections are the reason for the 'clamshell' name. It was originally proposed that this nebula was formed from 68 Cygni's stellar wind. Instead, the stellar wind is likely due to the star's high velocity through space, forming a bow shock.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Clamshell Nebula (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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