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Thread: Arp 331 Another Golden Chain

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    Arp 331 Another Golden Chain

    Arp 331 is another galaxy chain. Again they are ellipticals. The galaxies are all part of a larger group which is part of a still larger group. Arp 331 apparently refers only to the chain. The entire cluster of galaxies, larger than my image is often called the Pisces Cloud or more formally Zwicky 0107.5+3212. It is made of several parts of which C2 contains this chain and many of the other galaxies in my image. Though to add to the confusion some sources consider the Pisces Cloud to only be the chain, others expand it to up to 12 galaxies. See the annotated image to identify the galaxies in the chain region. Many are NGC galaxies. Only one galaxy major galaxy didn't fit on the cropped and reduced ID image. It is PGC 4021 which is about 2/3rds of the way from NGC 383 and the upper left corner. It too is likely a member of the group. Note some catalogs call it NGC 390. That is not correct, at least per the original NGC data. NGC 390 is a star in the field of the ID image so I noted it. It was found by Bigourdan who had a reputation for seeing stars as galaxies. His description says very faint -- stellar. Same as he usually said about his galaxies that turned out to be stars. He missed nearby PGC 4021. Visual observations are no where near as reliable as today's photographic ones but they aren't perfect either as we'll see in an Arp galaxy I'm currently researching.

    The Pisces Cloud is thought to be a bit over 200 million light years away. All of the galaxies show a redshift distance of between 180 and 240 million light years. The range is reasonable for orbital motions expected in such a cluster. Arp's comment on the chain was "Symmetry around large central galaxy." Arp's image of the chain is oddly underexposed. It is at: http://nedwww.ipac.caltech.edu/level...ig_arp331.jpeg Because of the exposure the distance between galaxies seems larger than in my image. Judging by the length of an asteroid trail in his image I'm going to guess his exposure was about 15 minutes long with an uncertainty of +/- 5 minutes. Their speed can vary greatly depending where they are in the asteroid best and where they are in the sky when imaged.

    The image is full of orange "stars" that are really galaxies. For instance half way between the spiral UGC 679 and PGC 1995971 are two of these star-like galaxies. One is slightly above and right of the other, it is very orange. A bit closer and below is a yellow white "star" that is also a spherical galaxy. I have no red shift or other distance indicator but suspect they are part of the same group, just smaller members. They appear like a double star each of which is slightly elongated.

    I had to move the field further north than I wanted due to the 6th magnitude star. When I centered everything it was out of the field but sending in some nasty ghosts. The only way to get rid of the worst of them was to move it into the FOV. For some reason my filters scatter more green and blue than red light so even though it is a K0 star it has a rather cyan halo from the excess green and blue. I didn't try to fix this.

    Many galaxies in the image I didn't mention had red shift data. All of which indicate they are members of this group. Far more either had no red shift data or weren't in any catalog. This area hasn't been covered by SDSS. The only galaxy without red shift data I've pointed out on the annotated image is PGC 1992085. I see no reason it couldn't be a member but that's unknown for sure.

    Imaged November 18, 2008 UT

    14" LX200R @ f/10, L=5x10' RGB=2x10', STL-11000XM, Paramount ME

    Full image with less compression
    http://www.spacebanter.com/attachmen...8&d=1251317112

    Rick
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  2. #2
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    What's that bright object in the bottom right corner?

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    Hi Rick, Very impressive image of this chain of galaxies. Is ngc 382,383 are close to each other or one is closer to us and the other more distant? you did great managing the bright star. And super great info also. Welldone my friend.

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    Quote Originally Posted by Glom View Post
    What's that bright object in the bottom right corner?
    The K0 star I devoted a paragraph to.

    Rick

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    Quote Originally Posted by JAICOA View Post
    Hi Rick, Very impressive image of this chain of galaxies. Is ngc 382,383 are close to each other or one is closer to us and the other more distant? you did great managing the bright star. And super great info also. Welldone my friend.
    The best evidence of which is in front would be a spectrum as absorption lines from the front one would show in the spectrum of the back one. I couldn't find anything on that, though didn't look all that deep. NED quotes two different distances for these galaxies, one pure red shift and the other "red shift independent" meaning they used other indicators such as Cephieds (these are too far for that), and other standard candle measurements etc. Both of these show 383 being in front. Still I'd want to know the spectral data on 382 before voting. One reason I didn't give NED's distance figures. Error bars are likely such that saying they are about 200 million light-years distant is about the best we can do.

    Rick

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