Need a couple dumbbells StrongmanMike?
Hi All,
Back to business after the recent CWAS posts. In an attempt to cater for different tastes, my latest efforts have leaded me down two paths of which I’m pleased to present:
M27 – Dumbbell nebula in true colour for the traditionalists.
True colour image is a Ha [Ha+R]GB composite totalling 4.7 hours (Ha:120mins;R:55mins;G:55mins;B55mi ns).
and...
M27 – Dumbbell nebula in mapped colour for the NB aficionado (Fred, Ric and others).
NB image is a SII:Ha:OIII (Hubble Palette) composite totalling 4.3 hours (SII:70mins;Ha:120mins;OIII:70mins)
About the target;
The Dumbbell nebula (M27) is a gaseous emission nebula residing in the constellation Vulpecula. Its name was derived from early astronomers who sighted it has having two distinctly shaped sides looking like a Dumbbell weight. The shape of the nebula is due to the central star expelling its layers as its core nuclear fuel supply diminishes. M27 resides 1,200 light years away.
Some words on the image (Usual bantering for those interested):
All NB data was acquired using
Lightbuckets 24” RCOS (4876mm @ F/8) under the pristine dark skies of New Mexico. Attached to the business end of the scope is the Apogee Alta U42 CCD camera which is a great match for this instrument (NABG, back illuminated, high QE, good sampling, 100k well depth – enough said). The camera is deceptive – I would have thought it would bloom on the Ha filter on 600sec subs, but it didn’t. It may with a different field i.e. a bright star present but around the dumbbell this wasn’t an issue. Rather impressive to capture the outer shell in only 120mins of Ha data. I guess that's what sensitivity coupled with 600mm aperture will provide. This optical system will devour any galaxy in its sight. Big drool factor.
OK, with that rant out the way on to the more interesting side of imaging, the processing. Ha data was acquired on the Dumbbell as it crossed the meridian so was of great quality. No meridian flips - it’s an eq. fork. For the purpose of this exercise, I’m only going to explain the narrowband processing. If you want info on how I conducted the processing on the true colour data, pls PM me – it was similar to the M83 image where I used RGB data from a different focal length system to colour the high resolution luminance – a bit of star colour matching required – not fun.. Anyway, subs calibrated in MaximDL, registered in Registar and then combined using Sigma Reject back in MaximDL. Ha, SII and OIII combined files passed through 2 iterations of LR deconvolution. Proceeded to perform an initial stretch in DDP. The stretch wasn’t aggressive i.e. to fill the full bit space, but mild. This is to make the clipping masks a little easier to deal with in the next phase. I thought I’d try the Hubble palette on this target even though I knew I wouldn’t shine towards green Ha nebulosity. I’ve seen a few other renditions such as CFHT (Canada-France-Hawaii Telescope) aka HOS and also simple Ha and OIII (bi-colour mapping). So SII:Ha:OIII were mapped to R:G:B respectively. I introduced each layer into PS and began creating clipping masks. I used the same process in which Dr. Travis Rector utilises to map some of the Hubble images. I’m not going to cover the specific clipping mask process here. You’ll find a white paper by Dr. Rector under the resources section of my site titled “Creation of Presentation-Quality Astronomical images”. A worthy read if you’re looking to step up your imaging output. Further stretch images using curves (as clipping masks). Image was then flattened after clipping masks looked close to bring out each emission line. The dumbbell does not contain much SII data. Looking at the subs, the signal is rather weak. Ha and OIII (particularly OIII –
raw data sample of OIII) are very strong. The SII data is shown as a yellow hue as it mixes with the green Ha data. No mixing of Ha into the other channels to provide resolution – nothing but clean emission lines here. The background noise in the NB image is due to stretching the SII rather hard – classic example of a weak signal (I should have masked it). May look at doing a Ha:OIII rendition in the future. Strangely, I’m starting to warm to the SHO palette despite the green Ha data!
Quick note on the RGB version, the RGB was acquired sometime ago (actually last year) using a TOA-150/ST10XME. I did have intentions to use the 24” RC to collect the RGB data, but with full moon around at the moment, I thought I’d try my hand a mixing different focal length data (yet again). I think some luminance data on this target would bring back the stars in a more pleasing manner. The Ha data stars were very tight and round which didn’t match well with the lower res RGB data. (Check out the star trio at top left – prime resolution as you would expect from this aperture).
Before I close, I’d like to say a few words about the Lightbuckets operation. Steve and Alvin have been exceptional to deal with during the data acquisition process. They are imagers at heart and take great pride in delivering the best possible data to you. While they are just warming up, they’ve completed an amazing array of features to make it easier to image remotely. From configuring a “set and forget” fully automated acquisition session through to intricate details of a flats library for any potential imaging angle you choose, thus providing flat field accuracy. Incredible work and dedication. Again, like GRAS, I’m not associated with their operations (this is based on personal experience), I’m simply a user of their services.
Anyway, hope you enjoy them.
Hmmm (5m F/L)…Nothing like a bit of deep space in your face! YEAH!
Cheers