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RickJ
2012-Dec-23, 09:47 PM
Arp 181 is a pair of NGC objects in northern Draco about 429 to 440 million light-years away. Arp put it in his category for galaxies with narrow filaments. In this case he is apparently referring to the long drawn out tidal arm going to the west of NGC 3212. His comment reads: "Long faint filament extends westward from south arm." But then the confusion sets in. Arp says he is referring to NGC 3210 and NGC 3212. NGC 3212 is indeed the galaxy with the long straight filament but NGC 3210 is just a double star! The other obvious galactic companion lies to the east so has the higher designation of NGC 3215. The NGC Project says this about NGC 3210: "NGC 3210 is a close double star about an arcminute west-northwest of NGC 3212. WH's description is appropriate, and his position (for all three objects; the third is NGC 3215) is good. There is another star of similar magnitude about 23 arcsec preceding the double; is it possible that WH glimpsed this, too? If so, it would probably have added to the illusion of nebulosity. - Dr. Harold G. Corwin, Jr." It is just the two rather bright blue stars north of the filament. Arp's image of Arp 181 cuts off the eastern side of NGC 3215 but does include the double star. So was he meaning 3212 and 3215 when he said 3210 and 3212? All papers seem to think so. But if that is right it is the only image of all 338 entries to fail to include all of the galaxy(s) involved. Since he was so meticulous in his images I find it odd he failed to include all of the object. In any case I'll go with the majority, besides, if I left out 3215 I'd not have much to talk about.

NGC 3212 is classed by NED as S? and as SB by the NGC Project. I really don't see a bar, just a bright spot on one side of a round, typical core of a SA spiral. Redshift puts it at 440 million light-years. NGC 3215 is classed as SB? by NED and S by the NGC Project. So does it have a bar. I see a slight hint of one but I'm not convinced. It would seem to also fit Arp's category for three armed spirals as there appears to be a faint southern arm besides the closer in brighter southern arm. NED gives it a redshift putting it a bit closer, 429 million light-years. That would make it some 140,000 light-years across, a very large spiral. Still could it pull out the tidal arm of NGC 3212 without it showing much distortion? Or is the tidal arm of NGC 3212 due to something it digested or interacted with in the past? I tend to favor the latter.

The only other galaxy in the field that NED has redshift data for is MCG +13-08-013 near the right edge of the image just above centerline. It is listed at 1 billion light-years. NED makes no effort to categorize it. It is huge at about 200,000 light-years in diameter. I'm surprised it isn't the core of a galaxy cluster but apparently it is a huge lone galaxy. Maybe it ate all its companions.

With nothing else in the field with any data to speak of and many of the galaxies not even listed in NED I didn't prepare an annotated image. If you'd prefer I do so anyway with such fields let me know. I lost 4 L images to clouds and horrid seeing as well as 4 color frames. Weather has been a constant menace in 2012 with many images being affected by it I'm finding. I wanted to go much deeper but the weather had other ideas.

Arp's image:
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp181.jpeg

14" LX200R @ f/10, L=4x10' RB=3x10' G=2x10', STL-11000XM, Paramount ME

Rick

danscope
2012-Dec-23, 10:04 PM
Great pictures, Rick. Magnificent spiral threads. How long an exposure?
Best regards,
Dan

RickJ
2012-Dec-23, 10:33 PM
See the last line of my post for exposure detail
Rick

danscope
2012-Dec-24, 12:59 AM
Hi Rick,
Thanks for the reply. Nice stuff.

Dan