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ASTRO: NGC 6749 another golden globular(?) cluster



 
 
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  #1  
Old January 28th 14, 07:43 AM posted to alt.binaries.pictures.astro
Rick Johnson[_2_]
external usenet poster
 
Posts: 3,085
Default ASTRO: NGC 6749 another golden globular(?) cluster

NGC 6749 is a globular cluster (maybe) in Aquila that is seen through a
lot of galactic dust that is dimming it by up to 4.5 magnitudes. Most
consider it the most difficult NGC listed globular star cluster north of
the celestial equator and second only to NGC 6830 at -39 degrees. It
was discovered by John Herschel in 1827 with his 18.7" reflector. He
described it as consisting of large and small stars. This is odd
because I find no reports of any stars being seen it in with a modern
17" scope. But he also says it fills the field with stars. Considering
it is only 3 minutes of arc across at most in a modern 17" scope it
sounds like he was seeing field stars rather than actual members of the
cluster.

It is also cataloged as Berkeley 42, an open star cluster. WEBDA just
notes "May be a globular cluster." All other modern sources are
confident it is a globular. I do find WEBDA's data conflicting with
most other sources. For instance they put it at 6000 light years from
us while most other sources say 25,800 light-years, over 4 times more
distant. WEBDA also gives it an age of 2.1 billion years. Old for an
open cluster but too young for any other known globular cluster. They
do have it cataloged as Berkeley 42 open cluster not its NGC
designation. SEDS gives it a size of 5.2 arc minutes. That would make
it only 9 light-years across. Again, that doesn't fit a globular
cluster. But at 25,800 it would be 39 light-years. Still small for a
globular but considering the 4.5 magnitudes of extinction it is likely
much larger than the 5.2 minutes cited. The long dimension, mostly
north to south, in my image is about 3.5 minutes across.

The Sky and others seem to list the position of Berkeley 42 a few
minutes west and a bit south of the position for 6749. Sufficiently far
that even the outer edges of NGC 6749 doesn't overlap the center
position given for Berkeley 42. The Sky lists the two separately.
Giving the position of NGC 6749 correctly and showing Berkeley 42 as
being 2.6 minutes away at position angle 245 degrees. That would put it
near the blue star at about 3:30 and one cluster diameter away. I see
no cluster in the area other than the obvious one. Also in researching
this I found a paper, http://arxiv.org/pdf/astro-ph/0410325.pdf , from a
Chinese Observatory that does consider it an open cluster with an age of
6 billion years. They make no mention it might be a globular cluster.
I'd think that important. Maybe not. In all, I'm left "Lost in Space"
without a robot to help me.

14" LX200R @ f/10, L=4x10' RGB=2x10' (hurt by clouds), STL-11000XM,
Paramount ME.

Rick
--
Prefix is correct. Domain is arvig dot net

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Name:	NGC6749L4X10RGB2X10-67.JPG
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  #2  
Old January 28th 14, 09:48 PM posted to alt.binaries.pictures.astro
Stefan Lilge
external usenet poster
 
Posts: 2,269
Default ASTRO: NGC 6749 another golden globular(?) cluster

Rick,

this seems to be the "golden age of globular clusters" :-)
Another fine one.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
...

NGC 6749 is a globular cluster (maybe) in Aquila that is seen through a
lot of galactic dust that is dimming it by up to 4.5 magnitudes. Most
consider it the most difficult NGC listed globular star cluster north of
the celestial equator and second only to NGC 6830 at -39 degrees. It
was discovered by John Herschel in 1827 with his 18.7" reflector. He
described it as consisting of large and small stars. This is odd
because I find no reports of any stars being seen it in with a modern
17" scope. But he also says it fills the field with stars. Considering
it is only 3 minutes of arc across at most in a modern 17" scope it
sounds like he was seeing field stars rather than actual members of the
cluster.

It is also cataloged as Berkeley 42, an open star cluster. WEBDA just
notes "May be a globular cluster." All other modern sources are
confident it is a globular. I do find WEBDA's data conflicting with
most other sources. For instance they put it at 6000 light years from
us while most other sources say 25,800 light-years, over 4 times more
distant. WEBDA also gives it an age of 2.1 billion years. Old for an
open cluster but too young for any other known globular cluster. They
do have it cataloged as Berkeley 42 open cluster not its NGC
designation. SEDS gives it a size of 5.2 arc minutes. That would make
it only 9 light-years across. Again, that doesn't fit a globular
cluster. But at 25,800 it would be 39 light-years. Still small for a
globular but considering the 4.5 magnitudes of extinction it is likely
much larger than the 5.2 minutes cited. The long dimension, mostly
north to south, in my image is about 3.5 minutes across.

The Sky and others seem to list the position of Berkeley 42 a few
minutes west and a bit south of the position for 6749. Sufficiently far
that even the outer edges of NGC 6749 doesn't overlap the center
position given for Berkeley 42. The Sky lists the two separately.
Giving the position of NGC 6749 correctly and showing Berkeley 42 as
being 2.6 minutes away at position angle 245 degrees. That would put it
near the blue star at about 3:30 and one cluster diameter away. I see
no cluster in the area other than the obvious one. Also in researching
this I found a paper, http://arxiv.org/pdf/astro-ph/0410325.pdf , from a
Chinese Observatory that does consider it an open cluster with an age of
6 billion years. They make no mention it might be a globular cluster.
I'd think that important. Maybe not. In all, I'm left "Lost in Space"
without a robot to help me.

14" LX200R @ f/10, L=4x10' RGB=2x10' (hurt by clouds), STL-11000XM,
Paramount ME.

Rick
--
Prefix is correct. Domain is arvig dot net

  #3  
Old January 30th 14, 08:20 AM posted to alt.binaries.pictures.astro
Rick Johnson[_2_]
external usenet poster
 
Posts: 3,085
Default ASTRO: NGC 6749 another golden globular(?) cluster

Think that was the last one in my too process hopper of some 70 or so
objects. Maybe I should have saved it for the Olympics.

Rick

On 1/28/2014 2:48 PM, Stefan Lilge wrote:
Rick,

this seems to be the "golden age of globular clusters" :-)
Another fine one.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
...

NGC 6749 is a globular cluster (maybe) in Aquila that is seen through a
lot of galactic dust that is dimming it by up to 4.5 magnitudes. Most
consider it the most difficult NGC listed globular star cluster north of
the celestial equator and second only to NGC 6830 at -39 degrees. It
was discovered by John Herschel in 1827 with his 18.7" reflector. He
described it as consisting of large and small stars. This is odd
because I find no reports of any stars being seen it in with a modern
17" scope. But he also says it fills the field with stars. Considering
it is only 3 minutes of arc across at most in a modern 17" scope it
sounds like he was seeing field stars rather than actual members of the
cluster.

It is also cataloged as Berkeley 42, an open star cluster. WEBDA just
notes "May be a globular cluster." All other modern sources are
confident it is a globular. I do find WEBDA's data conflicting with
most other sources. For instance they put it at 6000 light years from
us while most other sources say 25,800 light-years, over 4 times more
distant. WEBDA also gives it an age of 2.1 billion years. Old for an
open cluster but too young for any other known globular cluster. They
do have it cataloged as Berkeley 42 open cluster not its NGC
designation. SEDS gives it a size of 5.2 arc minutes. That would make
it only 9 light-years across. Again, that doesn't fit a globular
cluster. But at 25,800 it would be 39 light-years. Still small for a
globular but considering the 4.5 magnitudes of extinction it is likely
much larger than the 5.2 minutes cited. The long dimension, mostly
north to south, in my image is about 3.5 minutes across.

The Sky and others seem to list the position of Berkeley 42 a few
minutes west and a bit south of the position for 6749. Sufficiently far
that even the outer edges of NGC 6749 doesn't overlap the center
position given for Berkeley 42. The Sky lists the two separately.
Giving the position of NGC 6749 correctly and showing Berkeley 42 as
being 2.6 minutes away at position angle 245 degrees. That would put it
near the blue star at about 3:30 and one cluster diameter away. I see
no cluster in the area other than the obvious one. Also in researching
this I found a paper, http://arxiv.org/pdf/astro-ph/0410325.pdf , from a
Chinese Observatory that does consider it an open cluster with an age of
6 billion years. They make no mention it might be a globular cluster.
I'd think that important. Maybe not. In all, I'm left "Lost in Space"
without a robot to help me.

14" LX200R @ f/10, L=4x10' RGB=2x10' (hurt by clouds), STL-11000XM,
Paramount ME.

Rick



--
Prefix is correct. Domain is arvig dot net
 




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