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Saturday, November 26, 2011

NGC 7023 - Iris Nebula in LRGB

The Iris Nebula is an interesting and beautiful reflection nebula in the constellation Cepheus. Discovered by Herschel in 1794, this object is often mistakenly labeled for its associated open star cluster NGC 7023, which is present in the triangular "top hat" just above center in the image.

The Iris Nebula (LBN 487 / VDB 139) is illuminated by a central hot star named SAO 19158 (aka HD 200775), which is 10 times the mass of our sun. Although not officially designated as an emission nebula, closer examination of the above image will reveal a linear ridge on either side of SAO 19158 that represents HII emission. In addition to this small emission region, there is a much more extensive reflection component comprised of microscopic dust particles that preferentially scatter blue light from the central star. The peripheral regions are comprised of reddish dust that obscures light from background stars.

In the center of the nebula, there are several ruddy-colored wisps and filaments of dust that emit broad band red light, instead of reflecting the more typical blue light of a reflection nebula. These red regions represent extended red emission (ERE), which is a type of phospholuminescence associated with dust particles that are bombared by high energy UV radiation from SAO 19158. Recent investigation of this region has revealed radiation in the near infrared range of the spectrum, thought to be related to the presence of polycyclic aromatic hydrocarbons in this region of space.

Telescope: APM Astrograph 107, f/6.5 with Baader Steeltrack Focuser and 2.5'' TS FF
Mount: NEQ6 Pro with EQ Mod and XBOX Wireless Controller
Camera: ATIK 314L+
Image Scale: 1.91 arcsec/pixel
Filter: Baader L,R,G,B, IDAS LPS
Filter Wheel: Starlight Xpress Motor USB, 7x1.25''
Guide Camera: QHY5 with PHD Guiding and TS UV/IR Block
Guide Scope: Skywatcher Finderscope 8x50
Total Exp. Time: 3 hours & 36 min, Lum: 128 min(bin 1x1),R,G,B: 28,28,32 min(bin 2x2)
Temperature: Ambient (15C), CCD (-10C)
Capture: Nebulosity 2.3.0
Register, Stack: Maxim DL, CCD Stack
Processing: Photoshop CS3
Date: 29 July 2011
Location: Parnon Mount, Arcadia, GR

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