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Thread: Object of the Week September 14, 2014: Arp 86 (NGC 7752 and NGC 7753) and Friends

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    Member RolandosCY's Avatar
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    Object of the Week September 14, 2014: Arp 86 (NGC 7752 and NGC 7753) and Friends

    Object data:

    Arp 86
    NGC 7753: RA 23h 47’ 05”, Dec +29 29’ 02”, size 3.3’ x 2’, mag 12.8
    NGC 7752: RA 23h 46’ 59”, Dec +29 27’ 32”, size 1.0’ x 0.5’, mag 14.3

    Arp 86 “Friends”
    PGC 72238: RA 23h 43’ 58”, Dec +29 06’ 55”, size 0.9’ x 0.2, mag 16.5
    PGC 72239: RA 23h 43’ 57”, Dec +29 07’ 58”, size 0.7’ x 0.3, mag 15.6
    PGC 72249: RA 23h 44’ 05”, Dec +29 07’ 15”, size 0.3’ x 0.2, mag 16.7

    Ever since I started observational astronomy, I have been fascinated by galaxy pairs, and especially those actively interacting, such as the glorious M51 and NGC 5195. So, when I encountered Arp 86 in Kanipe and Webb’s “The Arp Atlas of Peculiar Galaxies” it immediately grabbed my attention.

    big_arp86a.jpg

    http://ned.ipac.caltech.edu/level5/A...big_arp86.jpeg


    Arp 86 is an interacting galaxy pair in eastern Pegasus, one third of the way from Alpheratz (Alpha And) to Scheat (Beta Peg), approximately 270 million light years away. NGC 7753 is a huge, 12th magnitude spiral (classified as SAB (rs) bc), with a smaller, 14th magnitude elliptical galaxy (NGC 7752) at the edge of a long spiral arm. Most photographs do show that the spiral arm leading to the elliptical is definitely distorted due to gravitational attraction, while very deep photographs such as the ones below from Skinakas Observatory at Crete, Greece (http://www.capella-observatory.com/I...xies/Arp86.htm) and Adam Block (http://annesastronomynews.com/annes-...ngc-7753-7752/) show extremely faint streamers of gas, dust, and stars at the edges of the main spiral arms.

    NGC7753.jpgNGC-7753-by-Adam-Block.jpg


    The distorted arms of NGC 7753, along with abnormal rates of star formation in both the galaxies and the connecting “bridge”, indicate that NGC 7752 has already made at least one close pass (and most likely several close passes) very near its larger neighbor, and it is certain that it will be consumed by the larger spiral in the not too distant future (see http://ebooks.cambridge.org/chapter....0511564789A113, http://arxiv.org/abs/1404.7037, and http://www.researchgate.net/publicat...body_modeling).

    All photos indicate a very fascinating target for photography, but how does it stand to visual scrutiny? Well, under nice dark skies, both galaxies were readily visible in the 18”, especially at medium to high magnifications. I found that they appeared most detailed at 275X. NGC 7753 appeared as a rather large, elliptical (3’ X 2’) nebulous patch oriented east – west, with a significantly brighter center area, though no distinct nucleus was visible. The extended halo did appear somewhat mottled, hinting that spiral structure could be possibly detected with larger telescopes. NGC 7752 was a small elliptical glow to the south of the 7753, approximately similar in size and orientation to the brighter core of 7753. Surprisingly, although listed as magnitude 14.3, the smaller galaxy was more eye-catching than the larger spiral, presumably because of a higher surface brightness. A single 14th magnitude star appeared between the two galaxies, but alas, no bridge was seen. Despite my trying very hard, I was unable to detect any hints of the beautiful spiral arm connecting the two galaxies, so apparent in photographs of Arp 86.

    A86INV1a.jpgA86a.jpg

    After observing this galaxy pair, I checked my books and the web for further visual observations of these galaxies. To my surprise, I discovered that very few visual observations of Arp 86 are available. Alvin Huey (observing with his 22”), David Tosteson (observing with a 25” dob) and Barbara Wilson (observing with a 20” dob) have all observed the mottling of the larger galaxy, but all have failed to detect the arm “connecting” the two galaxies. Maybe someone with a larger scope could possibly detect it. Barbara Wilson mentions “outer arms faintly visible”, I am not though sure if she means the outer, very faint edges of the halo or if she has seen actual arms. Mind you, those of you with smaller scopes should also give it a shot. With my 6” achro under SQM 21.0 skies I could detect an amorphous, faint glow though I couldn’t split the two galaxies at 129X. I had a similar view through an 8” SCT, while Steve Gottlieb has managed to observe both galaxies with a 13.1 dob in the past. I believe that both galaxies should be visible in a 10 to 12 inch class telescope. By the way, three (albeit faint) supernovae have appeared in NGC 7753 over the last few years, so this is another reason for keeping an eye on this galaxy.

    As usual, I always like to check if there are further, “hidden” objects near an object of interest, and the vicinity of Arp 86 could not be an exception. Indeed, about 45 arc-minutes west – southwest of Arp 86, I located a trio of 16th magnitude galaxies (PGC 72238, 72239, and 72249) surrounding a (distracting) 13th magnitude field star.

    TrioDss_search.jpg

    They were all detected with my 18” dob at 275X and they could all be held steady, so they should be a possible quarry for even smaller scopes. They were all different from each other: PGC 72238 appeared quite longish, PGC 72239 had a more roundish elliptical shape, and PGC 72249 was round with a brighter center. Has anybody observed these little ghosts?

    A86TRIOinv1a.jpgA86TRIO1a.jpg

    So, next time you are in Pegasus, remember to stop by Arp 86 and visit along with its friends. And as always,
    “GIVE IT A GO AND LET US KNOW!”. Good luck and Great viewing!
    Attached Images Attached Images
    The Darker the Better!
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    18" f4.5 Obsession Classic #1934
    10" f5 Skyatcher Dob
    152mm f5.9 Teleskop Service
    Takahashi FS128
    SkyWatcher 120 f5
    Takahashi FS102
    Takahashi FSQ106N
    SkyWatcher ED80 Pro
    SkyWatcher ED72 Evostar
    Televue Naglers and Ethos

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    Member Ivan Maly's Avatar
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    The connecting arm was vaguely seen at 225x in my 16" from the club site last year. It really calls for darker skies than ~21 mpsas we had that night.
    Ivan
    20" Sky-Watcher
    deepskyblog.net

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    Member Ciel Extreme's Avatar
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    NGC7753 is a Herschel object (H-II-213) originally discovered by William Herschel on September 12, 1784. He described it as: “Faint, pretty large, very little extended, a little brighter to the middle.” Herschel did not see NGC7752; it was not discovered until 1854 by Mitchell working with Lord Rosse’s 72-inch reflector in Ireland. From my book on the Herschel objects: ”Together with NGC7752, situated 1.9' SW, this galaxy (NGC7753) has also been catalogued as Arp 86. Photographs show a nearly face-on spiral with a very faint, short bar emerging from the brighter core. The faint spiral arms have some condensations and the northern spiral arm extends towards NGC7752, which appears slightly disturbed. Visually, NGC7753 is the larger and brighter of the pair; it is a roundish patch of light with a brighter core which is somewhat offset towards the N. The envelope is uneven in brightness and there appears to be a darkish patch to the SW, where a faint field star borders the envelope. NGC7752 is a small, faint oval with an opaque core. Radial velocity: 5352 km/s. Distance: 239 mly. Diameter: 229,000 ly.” The visual observation was made with a 15-inch reflector.
    Mark Bratton
    18" f/4.5 Litebox reflector (travel scope)
    22" f/3.3 SpicaEyes Slipstream reflector (LittleTime Observatory)
    25x100mm binoculars
    “The Complete Guide to the Herschel Objects” (CUP 2011)

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    Also no success with seeing the connecting arm with my old 16" under exceptional good but not perfect skies. But I wrote "indicated spiral structure" on NGC 7753. I have to revisit this group with the 27".

    And nice trio of friends around the Arp, thanks Rolandos.
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

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    Member Clear Skies's Avatar
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    It does not happen very often that I can pitch in with an "Arp feature" observed in my 12" SCT!
    Observation from 27 September 2013 in France, 179x / 27' & 254 / 19'. Using the higher magnification the northern arm of NGC7753 popped into view.

    17mm TeleVue Nagler Type 4: NGC7752 and NGC7753 are both visible.
    NGC7753 is the large, round, NE galaxy: A round, faint glow, slightly brighter in a small, round central part, otherwise even in brightness, no detail visible. To the SSW is a mag. 13 star.
    NGC7752 is the small SW galaxy: Clearly brighter than NGC7753, slightly elongated east to west, spindle shaped, even in brightness (no change when using AV).

    12mm TeleVue Nagler Type 4: Using this magnification the northern spiral arm of NGC7753 sometimes faintly jumps into view, along with a mag. 14-15 superimposed star on the NW edge. The northern arm of the galaxy appears separated from the galaxy by a darker part in between the central part and the arm.
    Victor van Wulfen

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  6. #6
    Member RolandosCY's Avatar
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    Quote Originally Posted by Ivan Maly View Post
    The connecting arm was vaguely seen at 225x in my 16" from the club site last year. It really calls for darker skies than ~21 mpsas we had that night.
    Ivan, this sounds impressive, considering that the "bridge" was not seen in much latger scopes. I will hopefully be able to try again for Arp86 from SQM 21.6+ skies next weekend with the 18".
    The Darker the Better!
    -------------------------
    18" f4.5 Obsession Classic #1934
    10" f5 Skyatcher Dob
    152mm f5.9 Teleskop Service
    Takahashi FS128
    SkyWatcher 120 f5
    Takahashi FS102
    Takahashi FSQ106N
    SkyWatcher ED80 Pro
    SkyWatcher ED72 Evostar
    Televue Naglers and Ethos

  7. #7
    Member RolandosCY's Avatar
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    Quote Originally Posted by Clear Skies View Post
    It does not happen very often that I can pitch in with an "Arp feature" observed in my 12" SCT!...
    ...12mm TeleVue Nagler Type 4: Using this magnification the northern spiral arm of NGC7753 sometimes faintly jumps into view, along with a mag. 14-15 superimposed star on the NW edge. The northern arm of the galaxy appears separated from the galaxy by a darker part in between the central part and the arm.
    Victor, I have not really noted the arm as you describe it. Again, this feature was noted and I hope I will be able to observe it next week from a very dark location.
    The Darker the Better!
    -------------------------
    18" f4.5 Obsession Classic #1934
    10" f5 Skyatcher Dob
    152mm f5.9 Teleskop Service
    Takahashi FS128
    SkyWatcher 120 f5
    Takahashi FS102
    Takahashi FSQ106N
    SkyWatcher ED80 Pro
    SkyWatcher ED72 Evostar
    Televue Naglers and Ethos

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