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Thread: Snow Galaxy Clusters

  1. #1
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    Snow Galaxy Clusters

    A couple months ago I was looking at the Interstellarum Deep Sky Atlas' index and noticed they had plotted three "Snow" galaxy clusters, numbers 6, 9, and 20. I had not heard of these before, and could not find anything written about them on the internet except for the April 1970 Astronomical Journal by T.P. Snow where he lists 34 objects (file attached below). These are southern galaxy clusters found on the plates from the Yale-Columbia southern proper-motion program—the same which Klemola used for his relatively better-known list of objects. Somehow they meet the criteria the Interstellarum editors used to select objects for the atlas. I was interested to try for them; the night of December 28-29 was my first opportunity. I used IRSA to generate field charts based on the J2000 coordinates I found on the SIMBAD database.

    The site was private property in San Benito County in central California, elevation 2160 feet. I used my 20-inch f/5.25 reflector and 8mm Ethos for 333x 0.3° TFOV, and a 5mm Nagler for 553x 0.2° TFOV. Seeing while observing Snow 6 and Snow 9 was Pickering 6 and SQML pointed to the target was 21.2. Seeing improved to Pickering 7-8 while observing Snow 20, and SQML was 21.4. Transparency 4/5 and temperatures in the upper 30s F.

    My star hop starting point was NGC 247, an impressive, large, but low surface brightness galaxy in Cetus. I nudged my scope a few minutes NNE to see Burbidge’s Chain (VV 518), a line of four small MCG galaxies. I could see three components – a, b, and c. MCG-4-3-10 = a was easy, small, yet the largest and brightest of the group, with an evenly bright core slightly elongated NE-SW, 14.4 mag. MCG-4-3-13 = b was on the other end of the chain; it is smaller than a, round, 14.6 mag., and also picked up easily. MCG-4-3-11 = c was nearby to b, seen averted vision only held about 70% of the time once noticed; 15.7 mag. MCG-4-3-12 = d was not seen; it is closer to a in the chain, and very small and too faint for me, 17.0 mag. Being able to see Burbidge’s Chain gave me some hope I might see something of the Snow galaxies, but more importantly gave me something to gauge galaxy size and brightness by, since the brightest members of the Snow galaxies are 15-16th magnitude – so I should expect marginal observations at best. I star-hopped to Snow 6 first, because is was further west and I needed to catch it before it got much lower.

    Snow 6 (centered at J2000 00 17 37.0 -24 17 36): I with averted vision picked up one small, very faint round glow, which I later found to be MGC-04-01-29 (15.81B, 0.933’x0.747) – which is 7.8” north of where the cluster is centered (the darkest splotch to the upper center of the image below). Since Snow’s paper gives the magnitude range of 16-19B, it is not likely this is a cluster member. There were some very faint small stars in the field, but not galaxies. I tried 333x and 553x, but still only had the one galaxy. Aladin shows a string of three very small and faint galaxies to the east of the cluster center and to the east of the MGC I saw, but these are well beyond my scope.
    Snow 6.png

    Snow 9 (centered at J2000 00 30 22.0 -22 58 12): I searched the area earnestly with averted vision but can only say I suspected two excessively faint very small glows – which unfortunately I can’t correspond my sketch to my finder chart image. This was a “no show”
    snow 9.png

    Snow 20 (centered at J2000 05 19 48.0 -25 17 00, near M79): I waited until Lepus culminated before attempting this one. It turned out to be the most engaging, as it is framed to the north by IC 408 and to the southeast by IC 411, both of which were very plain at 333x 0.3° TFOV. In the below image IC 408 is cut in half at the upper center, and IC 411 is to the center left. I centered my view near the bright star (HD 34895 – which appears as an optical double) at the center of the image, and strained my eyes with averted vision. I had the strong impression of a glow between this star and IC 411, and another glow to the west of the star. 553x strengthened the impression but did not resolve any galaxies. A friend who was with me, a far more experienced observer than me, had the same “feeling” and called it a “maybe.” Aladin shows galaxies in these areas but they are 16-17th magnitude.
    snow 20.png

    Clearly to see these clusters requires more aperture, better / southern skies, and more experienced eyes than my own. I hope others on the forum might take these up and find out if there's anything to be seen with these.
    Attached Files Attached Files

  2. #2
    Member Steve Gottlieb's Avatar
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    Mark, I took a look at Snow's paper and it appears that some of his positions including #1-6 are poor. He mentions, though, that #1-5 may include (or be part of) Abell Galaxy Cluster 14. Also, I think his position for Snow 6 is too far south (there's nothing at the original position) and that MCG -04-01-029, which you observed, is the brightest galaxy.

    AGC 14 is centered about 38' NW (it doesn't sound like you tried for any of these?), though it's pretty spread out and may consist of 2 or more line of sight clusters. The following 3 galaxies appear to be part of Snow 2, assuming he made a 1 minute time error in RA (too large). I observed these 10 years back.

    ESO 473-002 = MCG -04-01-022 = PGC 991
    00 14 55.5 -24 05 23
    V = 14.3; Size 0.8'x0.6'; Surf Br = 13.4; PA = 121d
    18": extremely faint, very small, round, 15" diameter. A mag 15 star lies 1.5' SSW. First in a tight trio of galaxies in AGC 14 and located 4' SW of brighter E473-004.


    ESO 473-004 = MCG -04-01-025 = PGC 1013
    00 15 08.1 -24 02 41
    V = 14.1; Size 1.1'x0.5'; Surf Br = 13.3; PA = 151d
    18": the brightest member of AGC 14 (~1 degree SSE of NGC 45) appeared very faint, small, slightly elongated, 0.4'x0.3' diameter. A few very faint cluster members nearby were resolved with E473-002 4' SW, ESO 473-006 3.4' ESE.



    ESO 473-006 = MCG -04-01-027 = PGC 1029
    00 15 22.5 -24 03 37
    V = 14.3; Size 0.6'x0.3'; Surf Br = 12.5; PA = 17d
    18": extremely faint, very small, round, 15" diameter. Located 3.4' ESE of E473-004 in AGC 14. A mag 15 star lies 1.6' WNW (midway between the two galaxies.

    ... and the next galaxy is probably part of Snow 1

    ESO 473-005 = PGC 1016
    00 15 11.0 -23 52 55
    V = 13.6; Size 1.4'x0.6'; PA = 49d
    18": this marginal member of AGC 14 was just glimpsed momentarily off the NE side of a mag 10 star (just 28" separation) which greatly detracts from viewing, making the observation difficult. A trio of cluster members lies 12' S.

    Also, looking over his list of groups and clusters, Snow 11 includes NGC 142/143/144 and Snow 14 includes NGC 554/555/556. Also Snow 19 is NGC 1592, a multiple interacting system.
    Steve
    24" f/3.7 Starstructure
    18" f/4.3 Starmaster
    Adventures in Deep Space
    Contributing Editor, Sky & Tel

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    Hi Steve

    I relied on Interstellarum to locate 6, 9, and 20. I didn't plan ahead to try to find other related objects. The J2000 positions I gave above are from SIMBAD, which I presume are correctly precessed from the 1875 coordinates given in Snow's paper. I used those J2000s to print out my IRSA field photos.

    AGC 14 is not plotted in Interstellarum, so I didn't try for it. NGC 142/143/144 are not plotted. 554A/B is plotted but 555 & 556 are not, nor is there a symbol around the group to indicate it's a Snow cluster--meaning the other members would be too faint to meet the atlas' selection criteria. NGC 1592 is not plotted. I don't have DSC or a drive on my scope, but could always print out finder charts for these to star hop to.

    Interstellarum is designed for a 12-inch scope in reasonably dark skies, with a few challenge objects thrown in. It has its limits for very deep sky work with large scopes. All the same, I ought to be able to see everything plotted in this atlas, but some of them elude me. You recall the "Cloverleaf Nebula" IRAS 19477+2401 which we discussed a few months ago, being infrared only; and K 3-35 the "Seahorse Nebula" which has a B mag of 19.7 -- what are these doing here? In any case, it was fun to give the observations a try & learn about the objects; I don't consider it wasted time (not yet anyway!).

  4. #4
    Member Clear Skies's Avatar
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    Quote Originally Posted by Mark McCarthy View Post
    Interstellarum is designed for a 12-inch scope in reasonably dark skies, with a few challenge objects thrown in. It has its limits for very deep sky work with large scopes. All the same, I ought to be able to see everything plotted in this atlas, but some of them elude me. You recall the "Cloverleaf Nebula" IRAS 19477+2401 which we discussed a few months ago, being infrared only; and K 3-35 the "Seahorse Nebula" which has a B mag of 19.7 -- what are these doing here?
    That is exactly why I write my own observing guides. Snow Groups and Clusters of Galaxies, Klemola Groups and Clusters of Southern Galaxies and Holmberg Galaxy Groups will be part of the next update.
    Victor van Wulfen

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    SQM is nothing, transparency is everything.

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    I set out to compile observing guides for Snow's Groups and Clusters of Galaxies. As described in preceding posts, I too found a lot of empty sky. At first I suspected an error in my coordinate conversion; Snow listed RA in decimal minutes of arc which, if confused with seconds of arc can create quite an offset. That and the fact that the coordinates are epoch J1875. My conversion was correct though. After scrutinising quite a few images (DSS with help of Aladin) I think I can safely conclude that the size of the groups as described by Snow is in degrees, with the sole exception being the first object on the list. If correct, many of Snow's groups are truly huge, the largest being Snow 20 at 10x50 degrees. That's quite a large patch of sky. Too large in my opinion to allow for a decent observing run.
    Victor van Wulfen

    clearskies.eu - Clear Skies Observing Guides - CSOG - Blog - Observing Log - Observing Sessions

    SQM is nothing, transparency is everything.

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