Fireworks Galaxy: live luminance and H-alpha combination

[Martin Meredith]

One of the advantages of the multispectral function in StarlightLive is the ability to perform combination of filtered images. This is useful for live RGB imaging with a mono camera, and also for narrowband filtering, with arbitrary mappings from filters to RGB, allowing e.g. the use the Hubble palette in near-live viewing. Another possibility is to combine luminance with narrowband. In this example from last night I was exploring the effect of different kinds of filter combinations on the Fireworks Galaxy (NGC 6946) on the border of Cygnus. This is a very active galaxy with lots of star-forming regions, so I thought it would be interesting to look at the effect of H-alpha filtering. What I've done here is to generate a luminance base of 4x30s stacked subs from the Baader C (clear) filter, and then stacked increasing amounts of H-alpha on top of this base, mapping the H-alpha to the red channel only.

StarlightLive provides a checkbox to permit display of a single channel only or the combination of channels. By checking and unchecking this checkbox one can observe 'live' the effect of adding the H-alpha data. By saving the images with and without the checkbox checked, I've created an animated GIF to show the precise effect that I was able to observe live.

 

Note that is necessary to stack a lot of H-alpha to reach this saturation because the signal is a lot weaker than the luminance data. Also, it is necessary to set the colour saturation slider to max. But since one is observing the stack building up, the effect is to see the star-forming regions emerge gradually as pinkish zones. And having the luminance data as a base provides a decent resolution image of the galaxy and the starfield.

There is a huge amount of potential in multispectral combination. The trick is to get the balance of channels right (number of subs/saturation/additive stacks etc), and this needs more experimentation, but the results are I think worth it, particularly for outreach situations.

Thanks for looking

Martin

[Paul81]

Great showcase of what this capability was intended for Martin. Although its great for creating RGB observations, the real power is adding the effect of NB filters to reveal extra details in objects. The Ha layer here certainly reveals where the star forming regions are in the galaxy :-)

I've been toying with adding a luminance (i.e. LRGB) layer to the live stack and adding a blend function, but holding off to see how real usage pans out. If you or any of the other folks doing multispectral have any suggestions or improvements let me know - all ideas welcome (the cogs are already ticking on your scripting idea...).

[RobertI]

Lovely demonstration Martin, really looking forward to giving this a try myself.

[Ain Soph Aur]

Very interesting indeed. Mono stacks then adding Ha on red channel to bring out star forming regions. Wow.

Martin, thank you for being on the cutting edge of this EAA stuff and sharing your awesome experimentation and observations.

[Martin Meredith]

Thanks for the comments everyone.

Paul, in addition to this I tried out some LRGB with clusters (open and globs) with similar findings -- the need to increase saturation to get a reasonable colour balance. Here's the result for the Fireworks using 4x30s L (clear filter, actually) plus the same amount of each of RGB. Note that the star-forming parts are showing quite well even though this is only LRGB. I don't have a comparison without the luminance unfortunately but my impression is that for galaxies the colour noise is much worse without the luminance, so LRGB is definitely worth pursuing for galaxies. My next target with this approach will be a galaxy cluster which in the past I've only considered worthwhile observing in mono.

Martin

[Robrj]

On 10/28/2016 at 09:08, Paul81 said:

I've been toying with adding a luminance (i.e. LRGB) layer to the live stack and adding a blend function, but holding off to see how real usage pans out. If you or any of the other folks doing multispectral have any suggestions or improvements let me know - all ideas welcome (the cogs are already ticking on your scripting idea...).

I'd like to see the luminance and blend feature in a future release.