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NGC 3938 a multi-arm blue spiral



 
 
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  #1  
Old October 12th 14, 09:49 AM
WA0CKY WA0CKY is offline
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First recorded activity by SpaceBanter: Feb 2008
Posts: 689
Default NGC 3938 a multi-arm blue spiral

NGC 3938 is a very photogenic, face on, many armed, blue spiral galaxy that is often imaged. It was discovered by William Herschel on April 27, 1785. It made my list because it is on the original Herschel 400 list. I take these when nothing on the main list is well positioned, or in this case seeing wasn't up to the object I wanted to capture. In fact it was very poor this night. So poor none of the H alpha regions I wanted to capture survived the seeing, especially since I took red when it was lowest and in the worst seeing. I hoped its longer wave length would help but it didn't. Another for the proverbial reshoot list.

It is located near the back leg of Ursa Major. Redshift puts it some 48 million light-years away though a single Tully Fisher estimate says 55 million light-years and an estimate using a 2005 type II (not 1A) supernova comes up with 58 million light-years. Flip a three sided coin. I also saw a paper saying 43 million light-years so make that a 4 sided coin. Using the 48 million light-year distance I get a diameter of about 77 million light-years making this a good sized spiral galaxy.

My visual note from April 16, 1985 reads: "Large, round, apparently face on galaxy with an even halo. It has a starlike object (core?) but not at its center. Is this an off center nucleus of just a 14th magnitude field star?" This photo shows it to be be the nucleus and the galaxy to be rather unsymmetrically distributed around it leading to my off center comment.

A couple background galaxies are seen through it, two had redshift data so are marked on the annotated image. There are several galaxy clusters and groups in the image as well. Many have a good spectroscopic redshift for the Bright Cluster Galaxy but only a photographic estimate for the cluster itself. Both are shown with a "p" denoting the photographically determined value. In some cases there was no redshift for the BCG which is noted with /na. In other cases it used the same photographic redshift. When that happened I only note the photographic redshift value once (no second value or na). UvES denotes quasar candidates with only photographic redshift estimates. Objects with only coordinates for a designation are noted by type GG for galaxy group, GC for galaxy cluster, G for Galaxy, Q for quasar etc.

The glow about the middle of the far right edge is from a bright star just off the chip. I should have cloned it out.

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

Rick
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  #2  
Old October 28th 14, 12:08 AM posted to alt.binaries.pictures.astro
Stefan Lilge
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Posts: 2,269
Default NGC 3938 a multi-arm blue spiral

Rick,

NGC 3938 is probably my favourite galaxy. I don't think I have ever gotten
such fine detail in spite of trying several times. The bad seeing you
mentioned probably cost you the tiny HII regions, but I would think that few
have captured them...

Stefan


"WA0CKY" schrieb im Newsbeitrag ...


NGC 3938 is a very photogenic, face on, many armed, blue spiral galaxy
that is often imaged. It was discovered by William Herschel on April
27, 1785. It made my list because it is on the original Herschel 400
list. I take these when nothing on the main list is well positioned, or
in this case seeing wasn't up to the object I wanted to capture. In
fact it was very poor this night. So poor none of the H alpha regions I
wanted to capture survived the seeing, especially since I took red when
it was lowest and in the worst seeing. I hoped its longer wave length
would help but it didn't. Another for the proverbial reshoot list.

It is located near the back leg of Ursa Major. Redshift puts it some 48
million light-years away though a single Tully Fisher estimate says 55
million light-years and an estimate using a 2005 type II (not 1A)
supernova comes up with 58 million light-years. Flip a three sided
coin. I also saw a paper saying 43 million light-years so make that a 4
sided coin. Using the 48 million light-year distance I get a diameter
of about 77 million light-years making this a good sized spiral galaxy.

My visual note from April 16, 1985 reads: "Large, round, apparently face
on galaxy with an even halo. It has a starlike object (core?) but not
at its center. Is this an off center nucleus of just a 14th magnitude
field star?" This photo shows it to be be the nucleus and the galaxy to
be rather unsymmetrically distributed around it leading to my off center
comment.

A couple background galaxies are seen through it, two had redshift data
so are marked on the annotated image. There are several galaxy clusters
and groups in the image as well. Many have a good spectroscopic
redshift for the Bright Cluster Galaxy but only a photographic estimate
for the cluster itself. Both are shown with a "p" denoting the
photographically determined value. In some cases there was no redshift
for the BCG which is noted with /na. In other cases it used the same
photographic redshift. When that happened I only note the photographic
redshift value once (no second value or na). UvES denotes quasar
candidates with only photographic redshift estimates. Objects with only
coordinates for a designation are noted by type GG for galaxy group, GC
for galaxy cluster, G for Galaxy, Q for quasar etc.

The glow about the middle of the far right edge is from a bright star
just off the chip. I should have cloned it out.

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

Rick


--
WA0CKY

  #3  
Old October 28th 14, 08:29 AM
WA0CKY WA0CKY is offline
Senior Member
 
First recorded activity by SpaceBanter: Feb 2008
Posts: 689
Default

I bet some H alpha will pick them up if it isn't too shifted out of my passband. Doesn't take much redshift to move it out of the filter unfortunately. Mine is 6nm but even 12nm can't go out all that far. I wonder how HST manages it. Is the filter tunable or just rather broad?

Rick

Quote:
Originally Posted by Stefan Lilge View Post
Rick,

NGC 3938 is probably my favourite galaxy. I don't think I have ever gotten
such fine detail in spite of trying several times. The bad seeing you
mentioned probably cost you the tiny HII regions, but I would think that few
have captured them...

Stefan


"WA0CKY" schrieb im Newsbeitrag ...


NGC 3938 is a very photogenic, face on, many armed, blue spiral galaxy
that is often imaged. It was discovered by William Herschel on April
27, 1785. It made my list because it is on the original Herschel 400
list. I take these when nothing on the main list is well positioned, or
in this case seeing wasn't up to the object I wanted to capture. In
fact it was very poor this night. So poor none of the H alpha regions I
wanted to capture survived the seeing, especially since I took red when
it was lowest and in the worst seeing. I hoped its longer wave length
would help but it didn't. Another for the proverbial reshoot list.

It is located near the back leg of Ursa Major. Redshift puts it some 48
million light-years away though a single Tully Fisher estimate says 55
million light-years and an estimate using a 2005 type II (not 1A)
supernova comes up with 58 million light-years. Flip a three sided
coin. I also saw a paper saying 43 million light-years so make that a 4
sided coin. Using the 48 million light-year distance I get a diameter
of about 77 million light-years making this a good sized spiral galaxy.

My visual note from April 16, 1985 reads: "Large, round, apparently face
on galaxy with an even halo. It has a starlike object (core?) but not
at its center. Is this an off center nucleus of just a 14th magnitude
field star?" This photo shows it to be be the nucleus and the galaxy to
be rather unsymmetrically distributed around it leading to my off center
comment.

A couple background galaxies are seen through it, two had redshift data
so are marked on the annotated image. There are several galaxy clusters
and groups in the image as well. Many have a good spectroscopic
redshift for the Bright Cluster Galaxy but only a photographic estimate
for the cluster itself. Both are shown with a "p" denoting the
photographically determined value. In some cases there was no redshift
for the BCG which is noted with /na. In other cases it used the same
photographic redshift. When that happened I only note the photographic
redshift value once (no second value or na). UvES denotes quasar
candidates with only photographic redshift estimates. Objects with only
coordinates for a designation are noted by type GG for galaxy group, GC
for galaxy cluster, G for Galaxy, Q for quasar etc.

The glow about the middle of the far right edge is from a bright star
just off the chip. I should have cloned it out.

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

Rick


--
WA0CKY
 




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