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Thread: Object of the Week March 9, 2014 Sharpless 261 (Lower's Nebula)

  1. #1
    Member reiner's Avatar
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    Object of the Week March 9, 2014 Sharpless 261 (Lower's Nebula)

    Sh2-261 (Lower's Nebula)

    Orion

    RA 06 08 56.6
    Dek +15 48 07

    type: Emission Nebula
    size: 45'

    Sharpless 261 aka Lower's Nebula at the Orion/Gemini border is an object for the evening, that has now already passed the meridian when it turns dark.

    DSS image of Sh2-261
    Sh261_DSS.jpg


    There are several good images of this HII region, which lends in particular for narrowband imaging as it has lots of structural details in the different emission lines. Below is an image by Dean Salman in SII HII OIII (http://www.sharplesscatalog.com/Shar...aspx?Sharp=261)

    Sh261_salman.jpg

    Despite that Sharpless 261 looks spectacular and bright on narrowband images, it is not an easy visual object and there are not that many observing reports of this large HII region.

    My first observation of Sh2-261 was in 2010 during a sub-par night with my 22" Dob and my Panoptic 24mm, yielding an ep of 5.3mm. With OIII filter I could see a very difficult glow around the central area of the object, and a vague glow with the H-beta filter, of which I was not fully sure.

    One year later, in 2011, I re-visited this object under excellent skies, again both with OIII and H-beta filtering. This time, the visibility of the nebula was much better. Still, it did not really jump at you. With the OIII filter, I was able to pick up the central region of the nebula, corresponding to the lower part of the OIII emitting region in Dean Salman's image above. Below is a DSS red print of the nebula with a central star pattern being marked, that helps identifying the field.

    Sh261_filter.jpg

    With the H-beta filter, this central part is lost and other regions of the nebula become faintly visible. This is in particular a region south of the central region, which appears as the brightest and most structured part in the DSS image. Another more extended region was barely detectable NE of the central part. Both regions are marked in the DSS image above.

    Despite appearing bright and distinct on narrowband images, this is a very faint nebula, that required good conditions and some patience to reveal its details. Hence, it is one of these "prototypical" Sharpless regions that I love so much :-)

    Give it a go and let us know!
    Good luck and great viewing!
    Last edited by reiner; March 9th, 2014 at 11:04 AM.
    Reiner

    22" and 14" Dobs on EQ platforms and Deep Sky Observing
    www.reinervogel.net

  2. #2
    Member Howard B's Avatar
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    Hi Reiner,

    I have one decent observation of Lower's Nebula from January 2007 with my 28 inch:

    "Lower's Nebula is a faint bugger! Large and diffuse, one area is subtly brighter and that's what I first saw. The OIII filter showed nothing, the UHC filter showed the brightest part and the h-beta filter showed a complete oval. Pretty cool really - not many objects show best with the h-beta filter. 92x, LM of 6.2, no SQM reading."

    Sh2_261LowersNebula_crop.jpg Sh2_261LowersNebula_cropinvert.jpg

    The conditions were below average for this observation so I'm sure more could be seen from a darker, more transparent sky.
    Howard
    28 inch f/4 alt-az Newtonian

  3. #3
    Member Steve Gottlieb's Avatar
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    I think it's also cool this was an amateur discovery -- Lower's nebula was discovered on photographs taken in 1939 by Harold Lower with his son Charles (amateur telescope makers from San Diego, California) using a homemade 8-inch f/1 Schmidt Camera (that's right, f/1).

    Glad to hear about the H-beta tip! I've only observed this object using an OIII filter. Here's what I logged --

    18" (2/3/05): Lower's nebula was not initially noticed in a rich star field using the 31 Nagler (63x) unfiltered. Adding an OIII filter, much of the field took on an irregular patchy appearance (partly due to the unresolved background Milky Way glow), but in addition a 10'x8' oval glow (only part of the entire complex) was locally brighter surrounding a group of stars south of the geometric center of the nebula. The highest surface brightness region (still faint) was an extended patch situated south of mag 8.4 HD 41997 by a few arc minutes.
    Steve
    24" f/3.7 Starstructure
    18" f/4.3 Starmaster
    Adventures in Deep Space
    Contributing Editor, Sky & Tel

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