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Thread: Object of the Week Oct 12, 2014 - NGC40 The Bow Tie Nebula

  1. #1
    Member ChristianR's Avatar
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    Object of the Week Oct 12, 2014 - NGC40 The Bow Tie Nebula

    NGC40 - Caldwell 2 / Cepheus
    Planetary Nebula
    RA: 00h 13' 01", Dec: +72 31' 19"
    12,3 mag / Size: 38 x 35 arcseconds

    The planetary nebula NGC40 is located one-third of the way from Gamma Cephei to Kappa Cassiopeiae in an area devoid of bright stars. To find it I use a red dot finder and the triangle set up by Gamma Cephei, Pi Cephei and NGC40. Using a moderate power eyepiece, the object can usually quickly be found.

    The approximately 3500 light-years distant planetary nebula was discovered by William Herschel on November 25, 1788. The dying star has ejected its outer layer which has left behind a smaller, hot white dwarf with a surface temperature of 50000 degree C. The central star has, typical for white dwarfs, a very high density. It's mass is about 70% of the mass of our sun, the diameter is comparable to our earths one.

    The central star is a late-type Wolf-Rayet star. Radiation from the star causes the outer layer to heat to about 10,000 degree C. It is about one light-year across.

    The PN is estimated to be 4000 years old, the hot gas is still expanding. About 30,000 years from now, scientists theorize that NGC 40 will fade away, leaving only the white dwarf star.

    The following picture is from Johannes Schedler (Panther Observatory):
    NGC40_STX_c80.jpg

    The beautiful object is an interesting aim for a wide area of apertures! Due to its relative high brightness, the PN can already be seen using small refractors.

    Using my 12" dobson, I was able to identify a number of details, e.g.
    - the central star,
    - outer shells with details (one of it split!) and
    - two darker areas within the nebula itself.
    NGC40_comp1000.jpg
    NGC40 (Caldwell 2)NGC40 (Caldwell 2)
    Observing Place: Sudelfeld, Germany
    Date, Time: Nov. 16 2012, 00am
    SQML = 21,45 mag/arcsec*2, rel. Hum. = 45%, 4 GradC, seeing= II
    Dobson "Hofheim Instruments" 12" / f5
    Power: 300x (Nagler 5mm)
    used Filter: none

    But this is not the end of the story.

    Using larger apertures, there is far more to be discovered!
    NGC40_STX_c80_beschr.jpg

    With increasing difficulty there are
    - more details in the bright part of the object (such as different peaks in the outer shells or structures in the inner part)
    - the complex outer areas labeled with "2"
    - the filament labeled with "3" (you probably need a really big scope!!!)

    The two filaments labeled with "4" and "5" are maybe outside from what is visually possible today (and maybe also tomorrow and the day after tomorrow ...).

    However, as outlined above the object is a grateful aim for all apertures and I would be interested in your experiences with it.

    “Give it a go and let us know”
    Clear Skies, Christian

    http://www.licht-stimmungen.de/
    Germany

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    Thanks for the very nice written OOTW Christian. You picked up a really genuine pearl of the heaven.

    Next to the presented details this PN is one of only a few which shows strong Hß filter reaction. While most PNe became much darker this one reserves its brightness especially within the brighter shell structure. Monochromatic images shows the very different character.

    I also tried the PN several times with different aperture. With 16" the bright CS was also visible like two black holes within the nebula and the split in the W shell. Detail 2-5 were not visible.

    16", 600x, no filter, NELM 6m5+


    Last new moon I revisited the PN with the 27". As I wrote very different filter reaction but I decided to sketch the PN without any filter. Detail 2 were visible. The northern "2" very a little bit easier because of an superimposed star? The southern 2 was also visible with averted vision. I tried detail 3 with different filters but could not see anything. I did not try detail 4 and 5, maybe a visual target for the new build 1535-inch?
    What I missed was the second CS a few arcsec SE of the main CS. Maybe an detail for the 30" telescope class?

    27", 586x, no filter, NELM 7m+, seeing III
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

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    Revisited the PN yesterday with my small 8" under moderate conditions. Puhh, not that easy even to find. Best view unfiltered with 320x. Around bright CS 2:3 elongated ring which was open to the S and N side. Could not see the split in the W shell. Very good observation with 12" Christian. What I thought to see was the very faint star at the SW End of the W shell. It pops in and out of view. Difficult to confirm. Anyone see the split or star with this aperture?
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

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    Member Howard B's Avatar
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    Here's an observation from several years ago with my 20 inch f5:

    N40_crop.jpg N40_cropinvert.jpg

    "A beauty of an annular planetary...my first impression is that it's perfectly round with two opposing sides of the ring being obviously the brightest parts. The central star is bright and easy, with a fainter star right off the ends of one of the bright arcs. 721x to 100x."

    Great post Christian, as it reminds me that I need to have a look at NGC 40 with my 28 inch and to use the h-beta filter too!
    Howard
    28 inch f/4 alt-az Newtonian

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    Member ChristianR's Avatar
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    Hi Uwe, Hi Howard,

    thanks for the feedback!

    I can confirm that the fainter star at the SW End of the shell is more difficult to see compared to the central star. I remember observations with my 12" aperture where I noted down "... maybe a faint star near the shell, not sure ..." .

    With 25"+ also the area marked with "2" (see picture of J. Schedler above) seems to be reachable visually at least in parts as both, Uwes and Howards sketches show!. No chance in this case with 12" or 16" (see other two sketches) so far.
    Clear Skies, Christian

    http://www.licht-stimmungen.de/
    Germany

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    Member hajuem's Avatar
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    Hi Christian
    Excellent observation with 12 inches of you. I have with 16 inches at good seeing for the first time observed the split at the SW End. With 12 inches I can never see.
    A reference observation with 12 inches! Super Christian !!
    Here is my observation result of September 2014 . The seeing was very good.
    The dark regions within the shell you have observed excellent. These dark regions I could watch almost identical. I was able to observe very faint detail loose structures north and south...
    NGC 40 2014.jpg
    520-700x fst.6m5 1080m Adelegg

    CS Hajü
    www.astromerk.de:

  7. #7
    Member ChristianR's Avatar
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    Servus HaJü,

    great sketch, pretty close to the visual impression.
    And you even noted something on the south and especially on the north end of the object!
    Clear Skies, Christian

    http://www.licht-stimmungen.de/
    Germany

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    Tonight I had a look at this planetary nebula with my 20" dob from the ESA site near Madrid, where I work. The lightpollution is considerable there and my SQM only measured 19.1 which is quite poor. Still, the seeing was great. At 640x I saw something very similar to Uwe Glahn's drawing made with the 16" telescope, except I didn't see the dark patches in the disk and in the one arc. An OIII didn't really help and I preferred the view without filter. I'll need to see this nebula from a dark site


    Clear skies,

    Wouter

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