September 2015 - Picture of the Month
M27 - The Dumbbell Nebula
I took my first images of M27, the Dumbbell Nebula in Vulpecula three years ago with a DSLR camera and this year thought to return to it to see what my QSI camera would reveal. I have read that in 1991, it was discovered that there exists a very faint outer halo around the main nebula that extends out to at least twice the 8 x 6 arc minute extent of the 'normal' nebula but is around 1000 times fainter. I wondered, therefore, if I had any chance of revealing this outer halo.
I gathered nine hours of H-alpha, Oxygen III and Sulphur II narrow band data and 3.5 hours of LRGB data during the three weeks 22 July to 10 August and have generated the two attached images.
The first image is a narrow band HST palette rendering with an LRGB image of the stars blended with it. In this image S II data are assigned to red, H-alpha to green and O III to blue.
The second image is also narrow band but with with H-alpha and S II data are added together and assigned to red (their normal colour), O III is assigned to blue and a synthetic green has been generated as a combination of O III (80%) and H-alpha (20%). This image has also been blended with the LRGB image and has the more normal looking colours.
I have read that the outer halo is cooler than the hotter central nebula and we can see the chaotic boundary between the two as the hotter core pushes outwards. We can see the cool outer halo of gas from the original supergiant star penetrated by columns of glowing hydrogen-alpha originating from the central star in the regions from the top to the left side: 1 o' clock round to 9 o'clock.I'm wondering if what we are seeing is evidence of the central star precessing and periodically having outbursts of radiation. At the 4 o'clock location there is a powerful jet which seems to extend as an extremely faint extension beyond the outer halo itself.
23' 35" X 16' 51" at 0.97 arc sec / pixel Exposure times: three hours, each of narrow band data in 20 minute frames; two hours of luminance and 30 minutes each of RGB in five minute frames
254 mm Newtonian at F/4 plus TV Paracorr giving F/4.5 QSI 583 plus Astrodon LRGB and 3 nm narrow band filters
David Davies (21 August 2015).
All images are courtesy of David Davies, Cambridge, UK. Please click on the images for the high resolution versions. For more images from David please visit his Flickr Photostream.