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Thread: Object Of The Week December 10, 2017: NGC 1084

  1. #1
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    Object Of The Week December 10, 2017: NGC 1084

    NGC 1084, MCG -1-8-7, PGC 10464

    SAc, Galaxy in group of galaxies

    Constellation: Eridanus
    RA: 02 45 59.9
    DE: -07 34 43

    Mag: 10.73

    Size: 3'.1 x 2'.0

    The winter sky of course is dominated by the Milky Way, but we are still in astronomical autumn. This means that constellations like Cetus and Eridanus, which contain loads of bright and structured galaxies, are visible right after astronomical dusk ends until almost midnight.

    One of these bright and structured galaxies is NGC 1084, right at the border of Cetus and Eridanus but within the borders of Eridanus. It was discovered by William Herschel on 10 January 1785. The Vaucouleurs galaxy type SAc tells us that this galaxy has a small core with not too tightly wound spiral arms and no bar. In fact, this galaxy has multiple arms which are not too well defined.

    An image taken from SDSS:

    NGC 1084.jpg

    and from Hubble:

    NGC 1084_Hubble_small.jpg

    Over the past 50 years, 5 supernovae have been seen in NGC 1084! The galaxy is known for its chaotic star formation which is not confined to the spiral arms. However, it is not classified as a starburst galaxy since star formation has taken place in only small bursts over the part 40 million years. The cause of this star formation is thought to be a merger with a gas rich dwarf.

    Several faint galaxies lie to the south south east of NGC 1084, being LEDA 1016283 (m=18.0), LEDA 1015643 (m=16.6) and LEDA 1015393 (m=18.0). These three galaxies, and a few more, are visible in the SDSS image. Make sure to check those out when you observe this galaxy and your telescope is big enough.

    However, that is not why Simbad classifies this galaxy as a "galaxy in a group of galaxies". According to Wikipedia the galaxy belongs to a group with NGC 988, NGC 991, NGC 1022, NGC 1035, NGC 1042, NGC 1047, NGC 1052 and NGC 1110. And this group again is associated with the M77 group.

    My observation of this galaxy was done on September 20, 2015, and reads

    At 320x I see a very impressive galaxy. I see a large oval smudge with a faint stellar nucleus. The galaxy is speckled and motted as if spiral arms are about to pop into view. On one side the edge of the galaxy is dented. I'll revisit this galaxy under even darker skies.


    As always,

    "Give it a go and let us know!
    Good luck and great viewing!"

  2. #2
    Member Ivan Maly's Avatar
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    I saw it first in 4" and then with the supernova of 2012 in 16. Here is the rough sketch from the last observation, with traces of the possibly structural asymmetry of brightness that was seen. 225-360x with Ethos, Abbe II, and XO. All the detail was independently seen by my observing companion Steve (not our S. Gottlieb and could be discerned already in his 10". Good seeing (sub-arcsec detail on Jupiter later that night).

    Ivan
    20" Sky-Watcher
    deepskyblog.net

  3. #3
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    Nice and often overlooked object Wouter. Good choice for the OOTW.

    I got a catch a few years ago with my 27-inch. Really nice and structured galaxy body with interesting surrounding field.

    sketch: 27", 419x, NELM 6m5+, Seeing III
    NGC1084.jpg
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

  4. #4
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    By sheer coincidence, I observed this one on the 10th.

    12/10/17
    EAGLE'S RIDGE (spur road)

    MOON: 22 days (44% illuminated; rose at 12:56 AM)

    SEEING: 6

    TRANSPARENCY: 7
    SQM: 21.5 (at 11 PM)

    NELM: not checked
    
WEATHER CONDITIONS: temps in low 30s, breezy early

    All observations: 12.5" f/5 Discovery truss-tube Dobsonian, 14mm ES 82˚ eyepiece (112x, 0.7˚ TFOV); 10mm Delos (158x, 0.5˚ TFOV) used for observation of Arp 141


    9:25
    NGC 1084 (Eri): very very bright impressive galaxy--also Messier-worthy--elongated SP-NF--2.25' x 1.5'--large bright core but no detectable nucleus--well-defined halo--due N by 13' is the middle star of a bent line of three 10th-mag stars bending slightly toward galaxy; middle star is 10.5-mag; 10th-mag star P slightly N of it by 6'; 10.5-mag star F and very slightly N of middle star by 6.25'--galaxy forms tip of arrowhead-shaped pattern with these three stars--two 12th-mag stars between galaxy and brighter stars in bent line; one N very slightly P by 9' and one N very slightly F by 9.5'--S very slightly P galaxy by 11' is a 12.5-mag star--13th-mag star SP galaxy by 6'--SP galaxy by 35' is a 7th-mag star--SP galaxy is a pair of 8th- and 9th-mag stars 30' from galaxy separated by 2.25'; brighter is P slightly N of the fainter--poor seeing this low

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