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Designations:
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IC59 & IC63, SH2-185, Emperor Nebula
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Object Type:
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Sharpless HII Region
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Constellation:
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Cassiopeia
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01 hr 00 min 0.0 sec (Epoch 2000)
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+60° 59 min 23 sec (Epoch 2000)
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IC63, "The Emperor" or "Ghost" (the bright, pointed object near the
middle of the image) and IC59 (the weaker object near the upper left portion of the image) are collectively
known as Sharpless 2-185 (Sh 2-185). They are both illuminated by the B0 IV star , Gamma Cassiopeia, which
is off the top right portion of the image. Both nebulae are close to this ionizing star at about 190 pc, but
have very different visual appearances. IC63 can be referred to as a "cometary cloud", is pointing toward
Gamma Cassiopeia, and is narrower and more sharply defined than IC59. Spectral measurements suggest that IC59
is slightly cooler at 590K and less dense than IC63 at 630K. They are not separate nebulae, but are part of a
much larger nebulous region surrounding Gamma Cassiopeia based upon the WHAM (Wisconsin
H-Alpha
Mapper) survey
that is approximately 2 degrees in size. IC63 has bright filaments that are suggested by Karr et. al to be
ionized
fronts of gas created by Gamma (γ) Cassiopeia, and seen by us as nearly edge-on. Both nebulae exhibit
spectroscopic evidence from the mid-infrared of molecular hydrogen and polycyclic aromatic hydrocarbons (PAH).
In summary, the contrast in appearance between IC63 and IC59 is consistent with a difference in actual distances
from Gamma (γ) Cassiopeia and small differences in temperature and column density.
There is some discussion in professional circles as to whether the Hydrogen-Alpha (H-a) signal that we pick up in our images is actual emission from the nebula, as posited by Karr et. al, or reflection of the H-a emitted from Gamma Cassiopeia that is scattered by the dust in IC59 and IC63. This light scattering and reflection is called ERE, extended red emission. Gamma Cassiopeia is the prototype B0 IV star, emitting significant H-a. It is above the main sequence with a more extended atmosphere. Being somewhat cooler than a BO V star, it is only marginally capable of ionizing molecular hydrogen in its vicinity. Thus, it is possible that the H-a we pick up in our images is a mixture of both processes; direct H-a emission from ionization, and ERE. Multiwavelength spectroscopic analysis is the means to resolve this issue, and much of this lies in the realm of professional equipment and analysis. Nevertheless, it is fascinating to be able image these objects with modest backyard equipment and be aware that an understanding of these objects is still being researched. From Karr et. al "A Multiwavelength Study of IC63 and IC59, The Astronomical Journal, v129, February 2005, pp 954-968.
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Telescope:
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Focal Length:
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816 mm
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Mount:
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Camera
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Guider:
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Exposures:
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15 10-Minute Exposures through a Hydrogen-Alpha filter
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Location:
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Cicero, IN
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Software:
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CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
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