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NGC 2304 Another rarely imaged open cluster

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#1 Rick J

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Posted 17 February 2018 - 03:05 PM

A search for "NGC 2304" didn't turn up an image of it at CN.  Odd as it is in the original H400 program so not hiding.  Many consider it one of the most difficult in that list, however.  Though there are a few reports of it seen in 10x50 or 12x50 binoculars and larger as fuzz patch. 

 

NGC 2304 is a type II1p open cluster in between the legs of the Pollux twin of Gemini.  WEBDA puts it 13,000 light-years distant.  Since it is seen about opposite the core of the galaxy it must be about 38,000 light-years from the galaxy's core.  This allows it to see less disruption from our galaxies forces and thus have a good chance for long-term survival.  WEBDA puts its age at 800 million years.  Long enough for most of its really bright massive stars to have long since died.  They show it little reddened by dust and gas in our galaxy with a reddening of only 0.1 magnitude.  Even at its age, A and F stars survive to give it a rather strong blue color. 

The cluster was discovered by William Herschel on December 30, 1783.  It is in the original Herschel 400 observing program.  My comments from March 16,
1985 with my trusty 10" f/5 at 60 to 120x on an average night reads: "An open cluster that reminds me of M-35's companion, NGC 2158.  Unresolved at 60x it was resolved into a mass of 13.5 magnitude and fainter stars at 120x.  The cluster may be difficult in a 6" scope."  Looking at my image I see the orange star on its southern edge is magnitude 12.8 but all others are 13.5 or fainter.  I'm surprised my estimate was so accurate.  I'm finding such comments from my mostly visual days to often be wrong. 

Quite a few asteroids were in the FITS images but as I processed the image to tone down the fainter background stars all but two were so faint I didn't try to annotate them.  You will notice the trail of the brightest has a gap as does the fainter one but the asteroid reappears mostly behind a star so it isn't easily seen.  Why the gap?  Wish I knew.  For some reason after 3 luminance frames, two more were taken but apparently not saved by my system.  Since they are numbered all I see is a gap in the numbering.  But the gap in the time isn't 20 minutes but 40 minutes indicating 4 frames worth of time was lost.  But no imaging was attempted during two of the four.  Usually, my system leaves some note about what happened but not this time.  Something caused the system to decide two frames were too bad to save and never took two more.  Cloud sensor didn't trigger this as it would have left an indication in its log.  It's a mystery without a chance for a solution.

Since I needed to point out the fainter asteroid I checked for other objects in the image.  All I found was a few galaxies from the 2-micron survey.  No magnitude or distance data, just position information.  There weren't many so I took a few minutes to annotate them.  Only the spiral toward the bottom showed any detail. It shines, according to my measurement at a "brilliant" 17.5 magnitude.  All the others are quite a bit fainter but being small possibly easier to see visually in a very large telescope. 


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

 

Full image at 1" per pixel

 

Annotated for some background galaxies

 

Rick

Attached Thumbnails

  • NGC2304L4X10RGB2X10CROP.JPG

  • Gregory, Joe F Gafford, rigel123 and 4 others like this

#2 Strongmanmike

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Posted 18 February 2018 - 05:51 AM

Beautiful star colours Rick waytogo.gif

 

Mike



#3 rigel123

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Posted 18 February 2018 - 07:32 AM

Agree on the star colors and had a fascinating time exploring the annotated version peeking at all the tiny galaxies in the background!



#4 Dan G

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Posted 18 February 2018 - 10:06 AM

Wonderful image and write up as always Rick!  Thanks for sharing.

 

Dan in NY



#5 ccmdfd

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Posted 18 February 2018 - 09:18 PM

Good job!

 

I love open clusters.

 

cc



#6 lambermo

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Posted 19 February 2018 - 03:38 PM

Agree on the star colors and had a fascinating time exploring the annotated version peeking at all the tiny galaxies in the background!

I always do that too. Most of the time I even only look at the annotated versions




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