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Thread: Object of the Week January 5, 2014 – NGC2261 Hubbles Variable Nebula

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    Administrator/Co-Founder Dragan's Avatar
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    Object of the Week January 5, 2014 – NGC2261 Hubbles Variable Nebula

    NGC2261

    Monoceros

    RA 06 39 09.5
    DEC 08 44 52

    Type: Reflection Nebula

    Size: 2.0' x 1.7'

    Mag: 10 to Variable


    Yet another discovery by William Herschel, this time in 1783, NGC2261 is a reflection nebula in the constellation Monoceros. Appearing to fan out northward away from the star R Monocerotis, NGC2261 is a unique object in that its brightness appears to vary over time. For many years the source of its variability was speculated. In 1915, a volunteer astronomer at Yerkes named John Mellish put the first year graduate student Edwin Hubble in charge of determining the source of its variability. A year later in 1916, Hubble published his very first journal paper where several ideas were proposed:

    1. The nebula may be rotating and providing us with different views of itself,
    2. Matter itself in the nebula was brightening and fading and its “nucleus” (what we know today to be R Mon) had no effect on its variability,
    3. Another explanation was the possibility that portions of the nebulosity was being discharged from its “nucleus”.

    I quote “nucleus” because it was William Lassell, discoverer of Neptunes moon Triton, who suggested and later corroborated by EE Barnard, that R Mon was not a star but in fact a “true nucleus, such as that of the great spiral in Andromeda.” Using data obtained from the Yerkes Observatory 40” refractor, Hubble knew R Mon to be a variable star and 2261 belonged to a family of nebulae & stars (T Tauri stars) that had pecularities in common with other variable nebula such as, NGC2245, NGC1555 (Hinds Variable), NGC6729 and even NGC7662, the Blue Snowball! (though I haven't done any research on NGC7662, this paper suggests that Hubble believed it to be variable. Does anyone have any information on this?) Unfortunately, none of his theories at the time proved fruitful.

    It appears that from a paper published in 1997, the most accepted theory today is that Hubbles Variable Nebula does not vary due to its host star being variable. It varies due to matter from the dust envelope surrounding R Mon being strewn out into the stellar wind and the light from R Mon being blocked by these clouds. Essentially, opaque clouds of matter that pass between R Mon and NGC2261 are casting shadows onto the nebulas surface and we see it! Pretty interesting!

    NGC2261 is an object that is visible in scopes as small as 4 inches, though it'll take more aperture to see its finer detail it isn't an inherently difficult object. It's appearance can change in a period as short as 3 days, making this an object to observe on a regular basis! What did you see the last time you were out?

    One little bit of trivia, NGC2261 was the first photograph taken with the 200” Hale Telescope at Palomar in 1948.


    And as always,

    "Give it a go and let us know!"



    Hale_2261.jpg
    The original image taken with the 200" Hale in 1949.

    HST_NGC2261.jpg
    A more recent HST image.
    Clear Dark Skies,
    Dragan Nikin
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    Member Ivan Maly's Avatar
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    I first saw it during my Herschel 400 survey with my 4" f/5.5 Televue, then two years ago, observing with my 12" SCT, I made a sketch of the "fan on ribs":



    Reobservation has long been on my agenda, but looking at the forecast now a 3- to 4-month break in observing this winter seems a possibility.

    This nebula is a cosmic experiment of the kind that I as a boy proposed to my father: if we had a good strong flashlight and waved it from side to side, the ray at a sufficient distance would sweep the space at a speed higher than the light speed. My father argued that it wouldn't, trying to reference the special relativity theory in a way that I might understand.
    Ivan
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    Big Jim Jim Chandler's Avatar
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    2261 was on my list the first time I rented the 82" at McDonald. My notes from October 2005:

    TeleVue Panoptic 41mm, 696x
    TeleVue Nagler Type 5 26mm, 1097x

    Fabulous detail on HVN. Intricate ropes and streamers of nebulosity throughout its comet-like fan shape. The apex of the neb., at the star R Mon, is twisted, calling to mind the crushed tip of a crashed paper airplane.

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    Administrator/Co-Founder Dragan's Avatar
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    Quote Originally Posted by Dragan View Post
    Using data obtained from the Yerkes Observatory 40” refractor, Hubble knew R Mon to be a variable star and 2261 belonged to a family of nebulae & stars (T Tauri stars) that had pecularities in common with other variable nebula such as, NGC2245, NGC1555 (Hinds Variable), NGC6729 and even NGC7662, the Blue Snowball! (though I haven't done any research on NGC7662, this paper suggests that Hubble believed it to be variable. Does anyone have any information on this?)
    Ok, so it was a little late into the night when I wrote the above but it did get me thinking.

    As I was reading through some papers researching for this weeks OOTW, I came across Hubbles paper from 1916. In it, he mentions that NGC7662 is variable, not unlike Hubbles Variable Nebula, NGC2261. Well, being late into the night, I read that as if the nebula itself varies, NOT the central star. Looking further into it this morning, I realized that I misunderstood and its the star that is variable and it varies by as much as 3 magnitudes over a period of 28 days. (As proposed in EE Barnards paper published in 1908)

    But, what I would like to ask the group is this: Could this lend to some variability into the nebula itself? I understand that the mechanics behind 2261's variability is different than my suggestion. 2261 is a reflection nebula and its changes are basically a play on light. But a planetary is glowing excited gas. Couldn't a variation in its central star's energy output also lend itself to a variation in those excited gases? Could a PN with a variable star be itself variable?

    Just some curiosity indoors as a snow storm rages outdoors!
    Clear Dark Skies,
    Dragan Nikin
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    Big Jim Jim Chandler's Avatar
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    "Could a PN with a variable star be itself variable? "

    Sure. Herbig-Haro objects, e.g. McNeil's Nebula, work that way. The star goes into outburst and lights up the nebula.

    Jim

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    Administrator/Co-Founder Dragan's Avatar
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    Quote Originally Posted by Jim Chandler View Post
    "Could a PN with a variable star be itself variable? "

    Sure. Herbig-Haro objects, e.g. McNeil's Nebula, work that way. The star goes into outburst and lights up the nebula.

    Jim
    I don't think I worded my question properly. McNeil's a reflection nebula is it not? I'm referring to planetaries. Planetaries do not shine by reflected light. They "glow" as ionized gases energized by its central star.

    So, here is the original question I intended to ask: If a planetary's central star is variable, as it is in NGC 7662, can the central star influence the surrounding shell enough so that the shell itself can vary in brightness?

    I've never thought of this before so now I'm curious. What I'm really curious is if this effect were to be possible, are there any PN's that appear to vary in brightness in a telescope?
    Clear Dark Skies,
    Dragan Nikin
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    Big Jim Jim Chandler's Avatar
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    Yep, you did say "PN" and it went right by me. Therefore, let me revise my response to "I dunno, but I'm also curious".

    Jim

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    Member Paul Alsing's Avatar
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    This guy was also on my 82" list in November 2006. My notes;

    NGC 2261, Hubble’s Variable Nebula, Monoceros

    NGC 2261 was another winner, a distinctly fan-shaped nebula radiating away from R Mon. The edges of the fan were sharp but the edge farthest from R Mon just sort of dissolved to nothingness. Immediately north of R Mon there is a finger-like dark nebula that seems to wrap around the star, partially detaching it from the nebula, and making the pointy end of the nebula fairly hook-shaped. A recent Amastro post by Tom Polakis indicates that this dark finger of dust might be a new "variable"...
    Paul Alsing
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    Interesting object Dragan,

    at the end of 2006 I planed to observe and sketch this object say every two month I could get it. Unfortunately I only done it two times with two month between the sketches. This could be a very funny project even with small aperture...when the weather would be more steady. By the way, all the best to the northern US especially warmer temperatures.

    12-13-2006
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  10. #10
    Member Howard B's Avatar
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    I agree Uwe, and I've wanted to do this project as well but the weather this time of year keeps me from getting observations that are close enough to show any quick changes. I do have a series of observations from separate years that show changes that I've posted below, and actually observed Hubble's Variable Nebula this past Sunday evening. The conditions were rather poor though , and I haven't scanned my sketch yet, but the overall shape of 2261 certainly looked different than the last time I observed it!

    HubblesVariableNebule_composite_1999to2009.jpg

    HubblesVariableNebule_composite_1999to2009_invert.jpg

    I'll post my recent sketch as soon as I get it scanned, probably this weekend...

    ...and here it is:

    N2261_crop.jpg N2261_crop_invert.jpg

    As I mentioned, conditions were rather poor for this observation - so poor that they convinced me to shut down for the night and hit the sack after making this sketch! I used 408x and the SQM was 20.93.
    Last edited by Howard B; January 10th, 2014 at 07:15 PM.
    Howard
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    I have seen NGC 2261 last week with my C8 under urban skies, SQM 18.3.

    "Easy to see using the Meade SWA 24 mm (85x) as a comet-shaped cloud.

    Best image with the 8 mm TMB Planetary II (245x). Tried a number of filters (CLS, UHC-E) but best without any filters. The star is visible during moments of good seeing. Brightest around the star, the west side of the tail is a bit brigher."

    North on top, west to the left, using a zenithprism.

    NGC2261.jpg

  12. #12
    Member reiner's Avatar
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    Very interesting object, Dragan! I observe Hubble's Variable Nebula often, but never tried sketching the changes within the nebula.

    There is an interesting website about HVN by Chris Brown
    http://www.umanitoba.ca/science/astr...roduction.html

    He has collected own and other material about HVN and there are besides animations also models about the main parabolic shell and other inner shell partly formed by the collimated wind from R Mon.

    There are not many YSOs for which the peculiar variability has been examined as well as for HVN and R Mon. For PV Cep and it associated Gyulbudaghian's Nebula, the variability of the nebula reflects the variability of the star itself. The brightness of the nebula correlates with the brightness of the star with a certain lag.
    http://adsabs.harvard.edu/abs/2012SASS...31...65B
    Reiner

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