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ARP 29 with SN 2017eaw

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Old August 10th 17, 06:52 PM
WA0CKY WA0CKY is offline
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First recorded activity by SpaceBanter: Feb 2008
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Default ARP 29 with SN 2017eaw

Back on May 14, 2017, amateur astronomer and super nova hunter Patrick Wiggins discovered a brightening SN in Arp 29/NGC 6946. It eventually became known as SN 2017eaw. While I'd already taken the galaxy I retake Arp galaxies and some others when a supernova blows. With nothing but clouds this spring it wasn't until July 16th I finally had skies equal to those when I first took it. I like to match sky conditions if possible as it makes animating the SN much easier. Turns out the glare of the SN is blocking a faint star. Likely a star in our galaxy, not NGC 6946. I discovered my original processing of this galaxy was harsh so I had to completely reprocess it for this image. Even then matching the two was difficult for some reason. The text below is from my original post.

Arp 29 is far better known as NGC 6946, the Fireworks Galaxy. This is because it is undergoing massive star formation and close enough that we can easily resolve many of the HII regions as well as a massive star cluster. The cluster is well resolved in the upper left corner of the Gemini North image. http://antwrp.gsfc.nasa.gov/apod/ap050125.html My image scale and seeing weren't sufficient to fully resolve it so only a few of the stars show with the rest forming what appears to be a blue reflection nebula. Note the Gemini image has south up while mine is north up. Another reason for its common name is all the super nova that have been seen blowing in it. The last was in 2008. NED list 9 known super nova in this galaxy; SN 1917A, N 1939C, SN 1948B, SN 1968D, SN 1969P, SN 1980K, SN 2002hh, SN 2004et and SN 2008S. 27 supernova remnants are also known in this galaxy according to NED.

But none of this is the reason it is in Arp's catalog. He included it under Spiral galaxies with one heavy arm. Most in this category have a rather obvious heavy arm. I'm not even sure which arm he is speaking of. Maybe it's the one to the northeast (upper left) of the core in my image. Though his comment addressed the supernovas saying "Supernova once observed in tip of thick arm." This may refer to the 1948 supernova though it was well back of what I'd call the "tip" of the eastern arm. Though closer to the end than those appearing in other arms.
Every paper I found shows a different distance to this obviously nearby galaxy. In fact, two different papers analyzed the 1980 super nova and came up with wildly different distance estimates! One decided it was 18.5 million light-years away, the other over 41 million light-years. One is obviously wrong very wrong. The APOD link above says 10 million light-years, closer than any paper I found. So I'll give the wide range of about 10 to 20 million light-years as its distance. This galaxy is in the Milky Way and thus heavily obscured. This likely complicates distance estimates. It certainly is close enough for Cepheid variables to be seen but unless the dust between us and the galaxy is accurately known the distance becomes uncertain. I suspect it is differences in dust estimates that account for much of the uncertainty of the distance to this galaxy.

I should have taken far more data on this one. I see a hint of a long blue arm going north. The field is full of clouds. Some so close to the galaxy I can't tell if they are pieces of the galaxy or pieces of junk in our galaxy. Most likely in ours. Note the area just along the western edge of Arp 29 that has no stars, just a faint fuzz patch. A brighter but smaller one below it doesn't seem to obscure stars. I see no reason to question my flats so suspect these clouds are real. But they are right at the noise level. Something a lot more time would certainly help decide.

Arp's image with the 200" is at:
He was pushing the field corrector to its limits with the wide field needed to cover this one. Note the distorted stars at the corners.

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME, both images

Animation can be seen at: https://www.cloudynights.com/uploads...1502388612.gif
Cloudy nights doesn't block animated GIF files like this site does unless too small to be useful.

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ID:	6654  Click image for larger version

Name:	Arp29SN2017eaw_NGC6946SN_L4X10RGB2X10CROP.JPG
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Last edited by WA0CKY : August 10th 17 at 07:20 PM.
Old August 15th 17, 11:28 PM
slilge slilge is offline
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First recorded activity by SpaceBanter: Aug 2008
Posts: 151

Beautiful image Rick. I got a glimpse (well my camera did) of the SN on May 20, but only enough for a snapshot (waiting to be processed).


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