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NGC 674-697 One Galaxy two NGC numbers.



 
 
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  #1  
Old March 12th 17, 07:35 PM
WA0CKY WA0CKY is offline
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Default NGC 674-697 One Galaxy two NGC numbers.

NGC 697-674 is a spiral galaxy in northwestern Ares about 130 million light-years distant by redshift and 110 by the consensus of 17 non redshift measurements at NED. It is considered a member of the NGC 691 galaxy group which average about the same redshift as that of this galaxy. Still it is hard to argue with a rather nicely grouped non redshift measurements that have a standard deviation of only 9 million light-years. So I'll split the difference and say 120 million light-years. That makes its size nearly 200,000 light-years including faint plumes my horrid night barely showed. Unfortunately they don't show in the color image. Using the size seen in the posted image it is still very large at a bit under 160,0000 light-years across. So this is a major galaxy. While I've not yet taken NGC 691 its angular size in catalogs is smaller than NGC 697-74. NGC 697 is classified as SAB(r)c: by NED and the NGC Project and Seligman. It's unusual when those three agree though Seligman uses a question mark for a colon they two mean essentially the same, a bit of doubt in the classification as a c arm structure galaxy. Not surprising given the oblique angle we see it at. For a hint of the plume, especially on the east side see http://cseligman.com/text/atlas/ngc674wide.jpg.

So why two NGC listings. Seems William Herschel discovered it on September 15, 1784, got its position correct and earned the NGC 697 entry from Dreyer when he assembled what became the NGC catalog. Then on December 2, 1861, yes, over 77 years later Henrich d'Arrest recorded a galaxy 2 minutes of arc west of NGC 697 which he claimed to have viewed the same night. But there's nothing he could have seen at that position. Also his description is a perfect match, including the position of a 9th magnitude star in relation to the galaxy, for NGC 697. Thus the two are now considered one and the same by nearly all catalogs. SEDS however still uses the incorrect position for NGC 674 and doesn't equate the two in its cross reference guide. You can read a bit more on this mix-up at the NGC Project webpage (which is down as I post this) for either NGC 697 or NGC 674. While Herschel discovered it the galaxy isn't in either of the H400 observing programs.

The night I took this image had awful seeing and even worse transparency due to a nasty haze layer. Sometimes these stabilize seeing but not this night. The 6th magnitude star in the lower left corner SAO 74966, a double star whose combined light is that of a G3III star so virtually white with a tinge of red, gave me fits sending a bright gradient completely across the frame. Combined with the loss due to lousy transparency this image is about 2 magnitudes short of my normal efforts with a FWHM of 4" rather than the 2.5" I often obtain for stars. And that's after rather hard (for me) deconvolution as they were 6". Thus much detail in the galaxy was lost. Taken in late January 2017 it was my last January or February image. It is now well into March with a bright moon as I write this with still no imaging. Worst winter I've ever had for imaging. I got nothing since I could process. I've had to throw out several images due to condition being too bad. I'm now out of anything to process until (if?) the weather ever improves.

With only one other galaxy having redshift data, and it being so faint it barely shows I didn't prepare an annotated image.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Rick
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  #2  
Old March 14th 17, 11:14 PM
slilge slilge is offline
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Rick,

it's a shame that you don't seem to get good conditions recently.
Still your image is better than most could accomplish.
  #3  
Old March 16th 17, 04:30 AM
WA0CKY WA0CKY is offline
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Jet stream seems stuck over my head or it clears only after a front goes through so lots of warm and cool air is mixing. In this case it was rather nasty clouds plus jet stream. So I got a double whammy.

Rick

Quote:
Originally Posted by slilge View Post
Rick,

it's a shame that you don't seem to get good conditions recently.
Still your image is better than most could accomplish.
  #4  
Old March 27th 17, 10:24 PM
slilge slilge is offline
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Rick,

in spite of the bad seeing you got a nice sharp image.

This must be the first time that I hear you saying that you have run out of data. Couldn't happen to me but only because I have a lot of crappy data on my harddisks that I will probably never process ;-)

Stefan
 




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