ASTRO: NGC 2141

NGC 2141 is a rather old open cluster in Orion's Club. It is listed as
being 13,100 light-years away by WEBDA. That puts it far beyond the
Orion Arm. I'd expect it to be greatly dimmed and reddened by the dust
and gas in the Orion Arm but it is listed in WEBDA as being reddened by
only a quarter of a magnitude. However my image shows severely reddened
stars and galaxies which surprised me. Many are redder than in any
image I've done in the 8 years since going digital. It is listed as
being 10 minutes across. At a distance of 13,100 light-years that would
make it 38 light-years across. that's large for an open cluster but it
is thought to be about 1.7 billion years old giving time for tidal
forces to pull away stars which might help to make it larger before the
stars are totally ripped away. Due to its age its stars aren't all that
blue with the brightest being dying red giant stars that were blue not
long ago.

I like the older clusters for imaging because they do have a good mix of
red stars beside the blue ones. Young clusters haven't had time for
many, if any, stars to turn into red giants so aren't as colorful.

According to the NGC Project this cluster was discovered by Edward
Barnard of dark nebula fame. Without explanation they list the "Year of
Discovery" as "1882-7." Anyone have any idea what they mean by this?
They list no telescope for the discovery either. Another source,
Cseligman, says it was found January 1883. Probably the NGC Project is
indicating it was found somewhere betwen 1882 and 1887 while Cseligman
is saying a date within that range. Still I'd like to know more about
this uncertainty.

Conditions were poor when I took the luminance data. I gave up trying
for color data. The following night was much better. Assuming the
luminance from the previous night was good I just took the color data.
In processing this one I found the luminance so poor I just used the
color files to make a pseudo luminance image. So the same 6 color files
were used twice, once for the color image and once to make a pseudo
luminance image. This may help explain why the red stars and distant
galaxies are so unusually red.

While I can see quite a few distant galaxies in the image most look like
red stars until you examine their PSF (Point Spread Function) in the
FITS files. That gives them away as being galaxies. Rather than try
and check every red star to see if it was a distant reddened galaxy I
just annotated those in NED. All are from the 2MASS galaxy listing.
Oddly the faintest one was rather white in color with all the others
being very red. No distance or even magnitude data was available for
any of them. With the field on the western edge of the winter Milky Way
it is surprising any galaxies were seen.

14" LX200R @ f/10, Pseudo L=6x10' RGB=2x10', STL-11000XM, Paramount ME

Rick

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Prefix is correct. Domain is arvig dot net

neat

On 7/6/2014 11:17 AM, wrote:
neat

Thanks That was a super easy one compared to most of what I do.

Rick

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Rick, that must be one of the best open clusters with it's nice spiral
patterns. Went straight on my list.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
om...

NGC 2141 is a rather old open cluster in Orion's Club. It is listed as
being 13,100 light-years away by WEBDA. That puts it far beyond the
Orion Arm. I'd expect it to be greatly dimmed and reddened by the dust
and gas in the Orion Arm but it is listed in WEBDA as being reddened by
only a quarter of a magnitude. However my image shows severely reddened
stars and galaxies which surprised me. Many are redder than in any
image I've done in the 8 years since going digital. It is listed as
being 10 minutes across. At a distance of 13,100 light-years that would
make it 38 light-years across. that's large for an open cluster but it
is thought to be about 1.7 billion years old giving time for tidal
forces to pull away stars which might help to make it larger before the
stars are totally ripped away. Due to its age its stars aren't all that
blue with the brightest being dying red giant stars that were blue not
long ago.

I like the older clusters for imaging because they do have a good mix of
red stars beside the blue ones. Young clusters haven't had time for
many, if any, stars to turn into red giants so aren't as colorful.

According to the NGC Project this cluster was discovered by Edward
Barnard of dark nebula fame. Without explanation they list the "Year of
Discovery" as "1882-7." Anyone have any idea what they mean by this?
They list no telescope for the discovery either. Another source,
Cseligman, says it was found January 1883. Probably the NGC Project is
indicating it was found somewhere betwen 1882 and 1887 while Cseligman
is saying a date within that range. Still I'd like to know more about
this uncertainty.

Conditions were poor when I took the luminance data. I gave up trying
for color data. The following night was much better. Assuming the
luminance from the previous night was good I just took the color data.
In processing this one I found the luminance so poor I just used the
color files to make a pseudo luminance image. So the same 6 color files
were used twice, once for the color image and once to make a pseudo
luminance image. This may help explain why the red stars and distant
galaxies are so unusually red.

While I can see quite a few distant galaxies in the image most look like
red stars until you examine their PSF (Point Spread Function) in the
FITS files. That gives them away as being galaxies. Rather than try
and check every red star to see if it was a distant reddened galaxy I
just annotated those in NED. All are from the 2MASS galaxy listing.
Oddly the faintest one was rather white in color with all the others
being very red. No distance or even magnitude data was available for
any of them. With the field on the western edge of the winter Milky Way
it is surprising any galaxies were seen.

14" LX200R @ f/10, Pseudo L=6x10' RGB=2x10', STL-11000XM, Paramount ME

Rick

--
Prefix is correct. Domain is arvig dot net