View Full Version : Arp 208

2010-Feb-14, 09:16 PM
Returning to the easy stuff after capturing the asteroid crash debris.

Arp 208, also known as CGCG 252-007, is a pair of interacting galaxies a bit over 400 million light-years away seen against northern Hercules. Red shift data is available only for the eastern galaxy. Arp classed this pair under: Galaxies (not classifiable as S or E), material ejected from nuclei. We now know what he was seeing were pieces tidally pulled from these galaxies rather than ejected. Individually they are cataloged as MCG+08-31-010 and MCG+08-31-011, left to right. The Knipe-Webb book though have them reversed. While that does fit RA ordering it doesn't match any of the catalogs I consulted. There's no consensus on how to classify these too. Most either don't try or say S?. VV catalog calls both irregular. The edge on nearby is MCG+08-31-09, an Sd spiral with the same red shift as Arp 208 so a nearby member. Arp had no comment on this entry and I find little useful on it in the literature. CGCG catalog considers this a 3 galaxy system with the note: "Triple system [with] bridges." I don't see any sign of a bridge to the edge on spiral.

The lack of information continues to the entire field. NED has no redshift or other distance data on any other galaxy in the image. I debated about an annotated image and decided to post one with names of galaxies. There's one Quasar in the image, PC 1650+4713. It is noted by distance in the lower left corner. I've noted a few obvious galaxies that aren't listed in NED or the SDSS. I find this is rather common. I don't know why. This image was taken through a rather thick haze which created a nasty haze around many stars making them look like galaxies. Usually the PSF of the object will give away a galaxy. Only those with no entry and a PSF that was obviously that of a galaxy are marked "No Entry". Most others are stars with nasty halos. The haze also limited my image to about magnitude 21.75 rather than my normal 22.5 to 23. Still it stabilized my seeing quite a bit allowing me to reproduce this image at 0.75 seconds per pixel rather than my usual 1". The annotated image is at 1" per pixel however to save bandwidth.

Arp's image:

14" LX 200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Attached images at 1" per pixel along with the annotated and SDSS images

Image at 0.75 seconds per pixel and less compression (http://www.usenet-replayer.com/cgi/content/framebanner_3?http://www.usenet-replayer.com/1/9/4/6/1266146491.34.jpeg)


2010-Feb-14, 10:50 PM
I've noted a few obvious galaxies that aren't listed in NED or the SDSS. I find this is rather common.

The NED folks have noted that they are snowed under trying to ingest the entire SDSS catalog, so they seem to list only things above some brightness or data-availability criterion. If you look at for example, the SDSS explorer page for Arp 208E (http://cas.sdss.org/dr6/en/tools/explore/obj.asp?ra=252.762574&dec=47.221006) and follow the "navigate" link, you can get to a display of all photometric objects (that is, image detections) that looks like this, with each object clickable to its own Explorer link and listed in a direct SDSS database search:


Some care is needed in counting these, since big galaxies often get multiple detections.

You must be making a real dent in the Arp atlas - do you have a count of how many you're done? For some of them, this is probably the first time anyone has paid that much attention since 1966.

2010-Feb-15, 12:57 AM
I've not found any consistency on which are omitted. Certainly not magnitude as I've seen some of 19.5 missed when 24 is picked up.

Thanks though for pointing out I forgot to attached the SDSS image. I've added it to the post.

There are those who have imaged all 338 Arp entries but most are black and white images. I may have the largest color collection. I won't be imaging them all. Due to my 47 north location I can't get decent resolution on those below -15 degrees. Even that takes an exceptional night so I'm missing many with southerly declinations due to not having enough good nights that low as yet. Then I can't image above 70 degrees due to my Polaris Tree, a 100 foot tall Northern Pine. In the past it has kept a lot of snow off the observatory so I've considered it a good trade but this year snows have come from the south so it hasn't been any help at all. When your roof is two stories up getting the snow off is no easy task. Takes a 12 foot ladder and a 24 foot snow rake to reach it. The ladder is 9 feet up making the fall all the worse if I screw up and being in my 7th decade that wouldn't be much fun even if it was into a 3 foot snow base.

Counting images processed I have a bit over 154. I have 154 processed images but some of those contain 2 and one 4 Arp entries. I didn't count the total. More confusing in that some galaxies like M65 are in twice! Once individually and once as part of a group. So I count by entries not galaxies. Then there's about 63 still waiting processing. Some I will find not usable and have to retake. I've not sorted through but exepct about 5% to need at least one frame reshot. I take this automatically. I live on a lake with boaters by summer and snowmobilers and other vehicles in winter. Their headlights can ruin a frame when they hit just right. That's the main reason for reshooting one. I work with minimal data making the loss of even one frame often unacceptable. Weather has caused me to miss some fall Arps so I will likely need yet another year to get all within my limited range. Just finding time to process them is difficult.