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The Fighting Dragons of Ara ( NGC 6188 )


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The Fighting Dragons of Ara ( NGC 6188 )

Bright Nebula NGC 6188 and open cluster NGC 6193 are embedded 4,300 light years away in the Sagittarius arm of our Milky Way galaxy and can be seen with the naked eye south of Scorpius in the constellation of Ara.

With powerful stellar winds and energetic ultra-violet radiation, massive stars sculpt the interstellar gas and dust of the nebula into wonderful shapes and cause the interstellar gas to brightly fluoresce.  

Closer to the hot young stars of the cluster, bright blue “sunlight” reflects off the clouds of gas and dust to produce the blue reflection nebulae seenin the image.

Magnitude +5.19, RA 16h 41m 42s, Dec -48deg 48' 46".
Approx. 3800 light years away.

Image details:

This is an HDR image constructed from exposures ranging from 2 seconds to 240 seconds in length.  The aim was to capture the faint stars and details in the nebula whilst at the same time maintaining colour in the bright stars without clipping the highlights.

Plate Solution:
Resolution ........ 1.336 arcsec/px
Rotation .......... 90.002 deg ( North is to the right )
Focal ............. 1475.57 mm
Pixel size ........ 9.56 um
Field of view ..... 58' 28.5" x 39' 0.8"
Image center ...... RA: 16 40 09.903  Dec: -48 41 27.00

Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ).
Corrector: ASA 2" Coma Corrector Quattro 1.175x.
Effective Focal Length / Aperture : 1410mm f4.7.

Mount: Skywatcher AZ Eq6 GT.
Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2 .

Nikon D5300 (unmodified) (sensor 23.5 x 15.6mm, 6016x4016 3.9um pixels).

Blue Mountains, Australia 
Moderate light pollution ( pale green zone on darksitefinder.com map ).

Capture ( 24 June 2017 ).
8 sets of sub-images with exposure duration for each set doubling ( 2s to 240s ) all at ISO800.
34 x 240s + 10 each @ 2s to 120s.

Processing ( Pixinsight - 19 Aug 2017, 13 Jan 2018  ).
Calibration: master bias, master flat and no darks.
Integration in 8 sets.  HDR combination.


This is a reprocessed version using the data I captured earlier in the year...


Edited by MikeODay
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A timeline of my progress on capturing and processing “The Fighting Dragons of Ara”...

July 2015:    5523A45F-D61B-48A9-BE91-B9FCFE002C90.jpeg.cdb5795f0578a2e35ec4e8c894292258.jpeg

June 2017:  7F3232DB-EF21-4D57-AFE0-D0E3E33A1976.jpeg.b0071f46697b0fc139da113885f71386.jpeg

Jan 2018:    A71CA557-5D50-4661-9FB2-94692C001712.jpeg.8268f8ce7617eb00c9f4babd20c8d6db.jpeg

I believe the latest is the closest to the “true colours” of the stars and I assume the nebula ( with an un-modified camera ).  Note that I did not adjust the saturation or vibrance in the latest image; the bright colours were produced ( retained ? ) by using the new arcsinh tool in Pixinsight to stretch the image.

The colour processing consisted of:
- no adjustment until after HDR combination of the integrated images
- DynamicBackgroundExtraction tool used to remove / reduce the light pollution / sky glow in the HDR image
- determine the “daylight” colour balance factors, adjusted for the average altitude extinction for the main subs, and apply these to the unstretched HDR image
- final minor tweak to the stretched HDR image in Photoshop to reduce the green a little ( I guess from residual light pollution / sky glow ? )
- As I mentioned, no adjustment to saturation or vibrance

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A close up of NGC 6193

With apparent magnitudes of 6.9 and 5.6 respectively, the closely spaced O-type giants HD 150135 and HD 150136 dominate the open cluster NGC 6193 and provide much of the visible light that gives this part of nebula its blue glow.  These stars are also very luminous X-ray sources, with HD 150136 in particular thought to be one of the most luminous sources so far observed in the galaxy. 

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