IC 447/2169 A large reflection nebula

[RickJ]

IC 447/2169 is a reflection nebula but like SH2-235, posted earlier, it has an identity crisis. The NGC project - now back on line at a new URL, http://www.ngcicproject.org/, under new ownership but same content by Dr. Robert E. Erdmann, Jr. - has this to say about the nebula and a nearby reflection nebula (half degree north and just out of my field) reflection nebula (IC-446/IC-2167) I haven't as yet imaged. They, though, are connected by a dark nebula. I need a wide angle scope to capture this however.

"The same two objects [IC-446/IC-2167, and IC-447/IC-2169] were apparently discovered twice by Barnard... Neither of Barnard's positions is particularly good, though we can get close to the apparent center of his large, diffused nebulosity if we adopt his RA for IC 447 and his Dec for IC 2169. Even though his two positions are more than 10 arcmin apart, they clearly refer to the same object: it is big (I make it about 30 x 30 arcmin on the DSS). Barnard notes "several stars 9-10 involved"; those stars are indeed there."

Barnard never realized they were the same object. Though in a later publication he did retract his discovery of IC 447 saying it was a duplicate of NGC 2245 -- the cone nebula. Which, of course is incorrect. He did though send the data on both to Dreyer who did publish it in his second IC catalog without apparent verification and likely accepted Barnard's description without viewing it himself. So even the most careful of visual astronomer's, and Barnard is considered one of the best, did make mistakes that the later photographic era would have prevented. Or maybe not considering the SH2-235 problems.

IC 447/2169 (it is also known as Dreyer's Nebula) is located in Monoceros, the unicorn. So obviously another that has been waiting on the hard drive for some time. It is thought to be part of the huge cloud of dust and gas that includes the far more famous emission and dark nebula known as the Cone Nebula as well as the Christmas Tree open star cluster and the Fox Fur Nebula. If so it is about 2700 light years distant, considerably further away than the nearby Orion Nebula complex.

Being a reflection nebula it is a blue color. The color comes from scattered star light of the illuminating stars which are either in or behind it. The nebula is blue for the same reason our sky is blue. The tiny molecules of dust and gas scatter blue light better than the other colors due to its short wavelength. It matters little what color the illuminating stars are, as long as they emit some blue light the nebula was take on a blue color same as the somewhat yellow sun still results in our blue sky.

I've reproduced this image at 1.5" of arc per pixel as there is little more to see at its native 1" per pixel. It is an exceedingly faint nebula and quite an imaging challenge due to its low surface brightness. Due to bandwidth restrictions the attached image has been reduced to 2.2" per pixel. See link for the 1.5" version.

Image with less compression:
http://www.spacebanter.com/attachmen...tid=2473&stc=1

14" LX200R @ f/10, L=6x10' binned 2x2 RGB=2x10' binned 3x3, STL=11000XM, Paramount ME

Rick

[mexhunter]

Hello Rick:
A precious image, has a great balance of color, but the stars, are the best thing.
A photo of first level.
Many greetings
César

[RickJ]

I decreased the intensity of the brightest stars before adding the RGB data. They are super hot and thus very blue stars. By decreasing their intensity during processing the color was preserved across the disk. Not sure if that was a good idea however. They look rather odd so blue across the core. I did the processing on my old monitor and it didn't show this effect as strongly as the new one. Now I'm going to want to reprocess everything I've done!

Rick

Rick

[Amber Robot]

Being a reflection nebula it is a blue color. The color comes from scattered star light of the illuminating stars which are either in or behind it. The nebula is blue for the same reason our sky is blue. The tiny molecules of dust and gas scatter blue light better than the other colors due to its short wavelength. It matters little what color the illuminating stars are, as long as they emit some blue light the nebula was take on a blue color same as the somewhat yellow sun still results in our blue sky.

That's not quite true. The sky is blue from Rayleigh scattering and dust scattering is more of a Mie scattering process (most dust particles being much larger than the wavelengths of light). Most reflection nebulae are blue because the stars are blue. They can sometimes have slightly different colors due to the combination of scattering and extinction occurring in the nebular region.

[kvwood]

Beautiful shot Rick. Great job on the processing. I'll have to take a look at this time next time it passes by.

Kent

[RickJ]

While Mie radiation is certainly present in this one and the main cause of most reflection nebula I read a paper some 30 years ago on this object indicating it was dominated by Rayleigh not Mie. I tried to find it on the net but couldn't come up with it, at least in any free site I found. If anyone does find it please let me know. Also if it has shown to be wrong since then I'd like to see that as well. Unfortunately, my notes from that era didn't survive the move to my present location in northern Minnesota making my search more difficult. I miss having a good physics library at my disposal.

Nearby NGC 2245 and IC 446 are much whiter yet illuminated by bluer stars indicating they do show Mie radiation to a greater extent than IC447. Someone with a wider field could catch all three in one exposure to best show this.

Rick

[andyschlei]

Beautiful shot and excellent discussion.

[JAICOA]

A Beautiful reflection nebula, Very nice blue it reminds me of the pleades dust and its stars. Thanks for the info also and Clear Skies.

[Amber Robot]

While Mie radiation is certainly present in this one and the main cause of most reflection nebula I read a paper some 30 years ago on this object indicating it was dominated by Rayleigh not Mie. I tried to find it on the net but couldn't come up with it, at least in any free site I found. If anyone does find it please let me know. Also if it has shown to be wrong since then I'd like to see that as well. Unfortunately, my notes from that era didn't survive the move to my present location in northern Minnesota making my search more difficult. I miss having a good physics library at my disposal.

Nearby NGC 2245 and IC 446 are much whiter yet illuminated by bluer stars indicating they do show Mie radiation to a greater extent than IC447. Someone with a wider field could catch all three in one exposure to best show this.

Rick

Well, I'm not sure what paper that would have been, but here's a more recent review of scattering by interstellar dust:

http://www.iop.org/EJ/article/0004-6...8023.text.html

Everything I've read always talks about Mie scattering. I'll see if I can dig up more references.

[RickJ]

I agree that Mie scattering is the common mode in reflection nebula. But from what I read a long time ago this was one of the few exceptions. Since the other two reflection nebula I mentioned were likely due to the same cloud yet were Mie scattering it added to the problem from what I remembered. It meant this part was of a very low dust concentration and mostly cold molecular gas with dark obscuring dust in the foreground. I'm going on 30 year old memory here. In my search before posting I came up with nothing useful for this particular nebula which surprised me. But I have a house full of grandkids and can't spend the time I'd like right now.

Rick

[mahesh]

How nice!

...But I have a house full of grandkids and can't spend the time I'd like right now.

Lucky grandkids! To have such a gradpa!

[iceman]

That's a beautiful image, Rick! Nice work.