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NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon

NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars

Revision title: cropped

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NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon

NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars

Revision title: cropped

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NGC 6888 - with and without stars (all constructive comments are welcome!)

Hello all,

The summer has been very wet in my province, tons of rain - most of the dark cycle in May and June were berefit of clear night (I know, this is a well worn compaint) .  The recent past two weeks have reversed this a little,  and so it has trended to less poor astro weather and so I decided to take a day off last week and maximize my time in the field.  I decided also to try a new dark site, which is only about 45 min travel time from my door.  

The target: NGC 6888 is a 20' x 10' NE-SW halo, and is unevenly illuminated and its brightest along the north side.  It lies in a star saturated field. Wolf-Rayet star:  NGC 6888 is formed by stellar wind from the Wolf-Rayet HD 192163. The star is shedding its outer envelope, ejecting our Sun's mass every 10,000 years. That stellar wind is energizing slower-moving stuff ejected by that star when it became a red giant around 400,000 years ago. The result of the collision is a shell about 25 light-years across. The central star will probably undergo a supernova explosion sometime in the next million years.

What is a Wolf-Rayet star?  I will quote Daniel Erickson (from this site):  "WR stars are ultra massive, highly evolved stars that show strong emission spectra of Nitrogen, Carbon or Helium, having depleted most of their surface Hydrogen. The first three WR stars were discovered in 1867 by French astronomers Mssrs. Wolf and Rayet. All three of these stars are in Cygnus."  Daniel's exceptional description of WR stars and why we should care about them can be seen here:  

https://astrob.in/8ckyee/0/

Back down to earth:
Corbett Road is what the map lists it as but the locals refer to it as "Wendigo Road".  We like it (quick poll in the early morning) because i)  its sort of close to the city  ii)  its named after a local monster (Note: the real name is Corbett, but no one calls it that), and iii) its quite dark. 

Now that I've set the tone for this report, down to the nitty gritty:

Filter:  Tonight's object was a nebula with a significant oxygen shell.  So I decided to use the L enhance filter, fresh from the sock drawer.
Scope:  5' apo.
Guiding:  I wanted to correct my (what was to me) a new issue.  The 9-12 step rule was in place for calibration steps east/west and north/south with my 420mm fl scope.  The problem was that for the backlash recovery steps the computer tried to do it all in one or two steps resulting in a massive jump, and loss of the guide star.  My buddy Ryan suggested making the max DEC and RA steps the same as the calibration step (relatively short).  Et voila, success.  We now refer to this as the Ryanization correction.  
Mount: AP 900 driven by the ASIair pro.
Vehicle: Ruby the overloaded 2003 Rubicon. 
Friends: Kev W and Ryan W.

Integration: 3 hours @ 180s lights (hey the nights are actually getting longer again!)
Clouds: Just a few.
Aurora:  Minimal, but the predictor was calling for a storm.
Calibration:  60 bias, 30 dark, 30 flats.

Thanks for looking.

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Revisions

  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
    Original
  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
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  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
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  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
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  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
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  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
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  • NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
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  • Final
    NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon
    H

B

Description: Shot of southern MW and sky.

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C

Description: Ian's rig, Kevin W beaming with joy ;0) , and Ryan's rig. The aurora kept themselves busy by occupying only 15-20 degrees of sky in the north, most of our evening's target were down low in the south or near zenith. :)

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D

Title: The same image of NGC 6888 but, with stars.

Description: This is the same image but with much less aggressive star reduction. Please let me know what you think. :)

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E

Title: Stars included, with a slightly more aggressive stretch.

Description: NGC 6888 with stars and some extra stretch to bring out the surrounding nebula.

Uploaded: ...

F

Title: Stars added back

Description: In this version I have manually increased the stretch to bring out the wispy nebulosity and have added back some stars.

If you like, please compare it to the first version and let me know your preference. Any CC is welcome.

Uploaded: ...

G

Title: Cropped

Description: Cropped slightly.

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H

Title: cropped

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NGC 6888 - The crescent nebula - my initiation to rare massive Wolf-Rayet stars, Ian Dixon