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Thread: Object of the Week – Aug 13, 2017 – KTG 71, A Trio of Dolphins

  1. #1
    Member Steve Gottlieb's Avatar
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    Object of the Week – Aug 13, 2017 – KTG 71, A Trio of Dolphins

    KTG 71 (Karachentsev Triple Galaxies) = LGG 440 (Lyon Group of Galaxies)
    NGC 6956, UGC 11620 and UGC 11623

    Mean RA: 20 44 10, Dec: +12 27 54
    Size: 1.9'x1.9', 0.6'x0.4', and 1.0'x0.7'
    Mag: 12.3V, 13.8V and 13.9V
    Types: NGC 6956 (SBb), UGC 11620 (S), UGC 11623 (SBa)

    This trio swims in the constellation of Delphinus at a distance of ~200 million l.y. You'll find these spirals swimming about 3° northeast of Epsilon, the 4th magnitude star forming the tail of the Dolphin.

    NGC 6956 was discovered by William Herschel during his 299th sweep on 19 Oct 1784 and logged as "extremely faint; very small; stellar; just preceding a small star, 240x verified it with difficulty." His son John observed the galaxy on 29 July 1829 and reported "vF; S; 15"; precedes and is attached to the double star No. 1566 of my 4th catalogue." NGC 6956 is somewhat of a supernova factory, producing supernovae in 2006, 2013 and 2015. The Herschel's missed the two UGCs, which form a near equilateral triangle with sides 6', 7' and 8'.

    Here's the PanSTARRS image of the field
    Attachment 2628

    My first observation of the barred spiral NGC 6956 was 35 years ago (July 1982) using a C-8 and I simply called it "faint, small. A mag 10 star at the east edge interferes." Since then I've made several observations of the trio using 13.1-inch and larger scopes. Here's a more recent one using my 24-inch , which revealed spiral structure in NGC 6956--


    NGC 6956 = KTG 7A, at the NW vertex, appeared moderately bright, elongated ~3:2 NW-SE, 60"x40". The view is somewhat hampered by a mag 11 star that is superimposed on the east edge and a mag 14.5 star is ~20" E of the bright star. The galaxy appears to be a barred spiral with a brighter bar oriented ~N-S extending down the middle of the glow. A brighter nucleus in the center of the bar is quasi-stellar (~5") and similar to the mag 14.5 star in brightness. A faint extension (spiral arm) curves east from the south end of the bar, extending south of the mag 11 star.

    UGC 11620 = KTG 71B is the second brightest member and appeared fairly faint, small, elongated 3:2 SSW-NNE, 21"x14". Two mag 13/14 stars are off the SE end and a mag 15.5 star is near the NNE end [22" from center]. Finally, UGC 11623 = KTG 71C, at the eastern vertex of the triangle, appeared fairly faint, fairly small, elongated 5:3 SW-NE, 36"x20", a small brighter core is embedded in a fairly smooth halo. A small trio of mag 13/14.5.15 stars is close preceding and a mag 10 star 5' S forms the vertex of an isosceles right triangle with UGC 11623 and 11620.

    While you're in the area, check out STF 2723, a double star challenge just 12' SE of UGC 11620 or 19' SE of NGC 6956. It consists of a pair of mag 7.0 and 8.3 stars at 1.2" separation. I've resolved it a few times with my 18" and would recommend at least 250x.

    Speaking of double stars, I'm a bit confused about John Herschel's HJ 1566. He stated NGC 6956 "precedes and is attached to the double star No. 1566 of my 4th catalogue". And my notes mention two stars close east of NGC 6956 -- an 11th mag star and a 14th mag star about 20" to its east. So, I assumed these were HJ 1566. But the Washington Double Star Catalogue (WDS) identifies HJ 1566 as a pair close southeast of UGC 11620! Seems to me that the WDS is incorrect, but I haven't check Herschel's double star catalogue. If WDS is correct, that suggests John Herschel also discovered UGC 11620. Any double star mavens here who can sort this out?

    Finally, here's another image of the trio by Rick Johnson, who specializes in obscure but interesting galaxies.

    http://www.spacebanter.com/attachmen...tid=5469&stc=1

    "Give it a go and let us know!"

    Note: I'm posting this OOTW a couple of days early as I'm heading to Oregon this weekend in preparation for the total solar eclipse. Good luck to all who plan to view it on the 21st!
    Steve
    24" f/3.7 Starstructure
    18" f/4.3 Starmaster
    Adventures in Deep Space
    Contributing Editor, Sky & Tel

  2. #2
    Member Ivan Maly's Avatar
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    Big favorite. Great observation of the spirality, Steve - that's what one needs 24" for. Here is my rough sketch from six years ago. The pen strokes aligned with the spirality in the NGC by chance - I did not see any. 16", 225x.


  3. #3
    Member deepskytraveler's Avatar
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    What a great OOTW Steve, thanks for pointing it out. Can't wait to give it a try with my 15". BTW your PanSTARRS image attachment link is broken.
    Clear Skies,

    Mark Friedman
    Wheaton, IL USA
    15" f/4.5 Obsession Classic #973
    Stellarvue SV90TBV

  4. #4
    Administrator/Co-Founder Dragan's Avatar
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    KTG 71.jpg

    Here is that PanSTARRS image
    Clear Dark Skies,
    Dragan Nikin
    25" f/5 Obsession #610 "Toto"
    www.darkskiesapparel.com

  5. #5
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    Nice trio Steve.

    I have a sketch from NGC 6956, but especially UGC 11620 looks interesting too.

    27", 419x, NELM 7m0+, seeing III
    NGC6956.jpg
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

  6. #6
    Member Daniel_Sp's Avatar
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    Hi all,
    similar to Uwe, I observed a third of the triplett. Here is my sketch with 24", at 421x
    6956.jpg
    24"-Dobson, f/4.16

  7. #7
    Member SusanY's Avatar
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    Hello! I am observing under tremendous winter desert skies - dark, clear, steady (and cold), and this OOTW trio of galaxies in the same high magnification field (225x) were a real treat. I observed them three nights in succession, always a nice thing to be able to do. The three galaxies certainly do lie in a lovely field of stars, although the 11th mag whitish star that touches the east side of NGC 6956 interferes with viewing. Nevertheless, the galaxy appears as a beautiful, faint, ethereal glow, slightly oval elongated NW-SW, and with a faint stellar nucleus. With averted vision I was surprised to see a very faint central bar-like brightening elongated north-south. No sign of spiral structure, although with averted vision and three nights of squinting, the south eastern edge of the galaxy appears to be almost imperceptibly more hazy.

    UGC 11620, the second brightest member of the trio, appears as a very faint, very small ghostly glow; a slightly off-round smooth and even silkiness, but averted vision shows a very slight brightening towards the centre. No sign of a nucleus. A roughly 13th mag grey-white star with a close, and much fainter greyish companion, lies off the south-eastern end of the little galaxy; very pretty.

    UGC 11623, the dimmest member of the trio, certainly is! It appears as a tiny round ghost-like puff of vaporous grey light. Averted vision brightened it up marginally, but it remained a tantalisingly faint wraith of a galaxy.
    Last edited by SusanY; August 19th, 2017 at 01:57 PM.
    Susan
    16" f4.5 Dobs
    sandandstars.co.za

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