The Western Veil in Hydrogen Alpha (NGC 6960)

Western Veil in Hydrogen Alpha
All Images Copyright Steve Cannistra

Please click here or on image for a higher resolution view.
Please click here for the Ha(HaR:G:B) color version.

Magnitude:  ? (but fainter than the Eastern Veil, which is roughly magnitude 5.0)
Size: about 70'
Distance: 2600 light years
RA: 20h 45m 42s
Dec: 30 degrees 43' 00"

The Western Veil is a supernova remnant that is part of a larger complex that includes the Eastern Veil (NGC 6992) and Pickering's Triangle (this complex is also known as the "Cygnus Loop").  In the orientation shown above, the Western Veil is sometimes referred to as the "Witch's Broom" Nebula.  It is estimated that the supernova explosion occured about 10,000 years ago, before the age of recorded history.  The star that gave rise to this supernova remnant is no longer visible, but it must have been massive.  Supernovas represent the final stages of stars that generally contain more than 10 solar masses.  Sequential fusion of hydrogen to helium, and subsequently to other elements like carbon, silicon, and oxygen, eventually leads to the formation of iron in the star's core.  However, fusion of iron is energetically unfavorable and actually requires input of energy to occur.  No further fusion will occur, iron will quickly accumulate, and once the mass of this iron core reaches 1.4 solar masses (the Chandrasekhar limit), a supernova will result.  Since there is no longer any outward pressure being generated by fusion, the gas surrounding the core undergoes gravitational collapse and subsequently rebounds against the core, forming a supernova explosion. 
The elements formed within the star as a result of fusion during its lifetime are expelled into space during supernova explosions, later to become part of other stars, planets, and lifeforms like ourselves.  52 Cygnus is the bright star seen in the top half, just left of the center, and it is not related to the formation of the Veil.  The Western veil is relatively rich in oxygen, which is excited by radiation from nearby stars, resulting in emission in the blue green spectrum (OIII).  There is a component of red light from excited hydrogen gas as well.  The Veil complex is a stunning view in large aperture scopes, especially with the use of an OIII filter.

Photographic Details:

Date:  May 30, 2004
Takahashi Sky 90 at f4.5 with field flattener/focal reducer, on the G11 Losmandy Mount.
Autoguider:  SBIG STV with e-finder.
Camera:  SXV-H9
Astronomik Ha filter (13 nm bandpass).
Exposures:  12 x 5' each, binned 1 x 1, 60 minutes total.
Conditions:  Temperature 55 degrees F; above average transparency; above average seeing; intermittent breeze.
No dark, bias, or flat frames used.  Auto-aligned in MaximDL; Sigma combined using RC Sigma Reject MaximDL, followed by DDP in ImagesPlus (IP).  Subsequent levels and curves adjustments in Photoshop CS (16 bit format).

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