Galaxies with Lodestar(Live) Colour

[Dom543]

Galaxy season tilts the playing field in favor of the higher sensitivity and resolution of the mono sensors.

The only area left for owners of colour cameras is to try to catch the subtle blue of the star forming regions visible in some of the brighter galaxies. This is my first attempt to do that on a clear but windy night.

Three of the five live stacked frames were taken with a blue filter, the remaining two with no filter. More exactly with a clear focusing filter (with no IR-cut) to retain parfocality. Luminance had to be kept low not to overwhelm and wash out the subtle colours. So the cost of retaining colour was the low overall brightness and hence loss of most of the fainter spiral arms.

I would have also liked to try M101 but it was difficult to get even the one minute total needed for M51 between the gusts of the winds. M101 is much fainter and allows less focal reduction.

The crucial factor that makes these types of live images possible is the excellent stacking routine built into LodesterLive v.0.11.

Clear Skies!

--Dom

[Dom543]

This is the outcome of my second attempt from the leeward side of the house.

The cost of longer integrations, and hence of brighter image, is the larger blown out galaxy centers.

I cannot get the sharp contrasty separation of the areas of different colors with the non-linear DR mapping options.

I would be interested to hear any explanations of why the star forming regions in the smaller galaxy appear to be concentrated along the axis connecting the two galaxy centers. It's almost like an angular segment...

Clear Skies!

--Dom

[aparker]

Dom,

Check out this Hubble image:

http://en.m.wikipedia.org/wiki/NGC_5195#/media/File:Messier51_sRGB.jpg

It looks like there's not much star formation going on in NGC5195 at all - it appears to be a compact, hence bright, dwarf eliptical GX. The bright bar appearance is in part due to dust from the end of one of NGC5194's spiral arms obscuring one side of the smaller companion galaxy.

Nice images BTW!

[Dom543]

Thank you Alex. That's very interesting.

You are saying that the blue areas in the two galaxies have different physical origins. Taking a closer second look does, in fact, confirm that. The smooth blue shine in the smaller galaxy looks like a galactic equivalent of a reflection nebula. While the chunky-filamentary structure of the blue areas with distinct nodules seems to be consistent to what we would expect from star forming regions.

I don't often look at NASA images. They are from a different world and, I am afraid, they might just discourage me from even trying to capture anything with my childish amateur setup. To enhance their scientific usefulness, they also use a false-color coding that is not obvious to translate into our world of EAA, where we are limited to true colors.

Thank you for calling my attention to these facts. They helped to explain a mystery and added a dimension to the understanding of this beautiful object.

Clear Skies!

--Dom

P.s. I tried to look at M81 and M101 last night. They don't seem to have comparable color features. At least, not detectable with my modest setup and skills. So they are more suitable for mono cameras and the plural in the title of this thread may just remain referring to this single pair of galaxies.

--Dom

[arkosg]

Hi Dom,

I've had some (mixed) luck with pulling some colour out of some of the brighter galaxies, but it is difficult to do reliably - 

seems very much dependent on the seeing, Moon, etc.  Usually I can get the yellowy core and then a different (if not 

always very blue looking) disk/arms - they are just so much dimmer in general than the galaxy cores.  Not helping things

is that my usual viewing location is not particularly dark, so sky contrast is always an issue.  Here are some examples

where I've stretched the contrast as much as seemed reasonable and played with colour balance to try to emphasize

the colour variations.

Cheers,

- Greg A

[HiloDon]

Great results, Greg.

Don

[Dom543]

Nice smooth images Greg with good details!

Are you using the x^0.25 option?

Clear Skies!

--Dom

[arkosg]

Thanks Don!

Dom: these particular shots were before LL had those functions - I used

iPhoto to shift the gray point in the histogram.

I still find on the fly colour correction challenging - I can get close most

times, but often still need to tweak the colour balance afterwards to fine

tune things.

Cheers,

Greg A

[Dom543]

In a P.s. at the end of post #4 of this thread I said that I could not detect color features in M81 and M101 that would be comparable to those in M51.

To be more specific, I include two images of M101. One made with a simple luminance (UV/IR cut) filter and another with a blue filter.

The blue image is obviously fainter and looks noisier. This is logical, as the blue filter cuts out 2/3 of the photons. But apart from this, the blue image looks just like the full spectrum one. This is what I meant in Post #4, when I said that no color features were detectable.

White light is an equal proportion mixture of red, green and blue. If all three components look the same (I included only the blue one but believe me that the other two also look the same) as the full spectrum image, that means they are representing only their 1/3 contribution to an overall white image. I.e. no color features.

The situation is very similar for M81.

By the way, all the images in this post have been saved with the x^0.25 option of LL v.0.11. The camera was a Lodestar x2c.

Perhaps it's interesting to point out that the M101 images are sum-stacks, while the M81's are mean-stacks.

Clear Skies!

--Dom

[arkosg]

Hi Dom,

I haven't tried colour filters on my X2C with the galaxies.  But my understanding with the Lodestars' Sony chips is that they use 

a CMYG colour filter array, rather than an RGB array.  This accounts (at least somewhat) for better line filter response in the

Lodestars than in typical (DSLR?) RGB arrayed one-shot colour cams.  From looking at the spectral response curves for the ICX 829:

it appears that both green & red portions of the spectrum are well registered by *at least* 2/4 pixels in the array, while for blue 

the response is only moderate for *at best* 2/4.   So... given the spectral characteristics of the matrix, if you are seeing "equivalent"

luminosity in each of R, G, B, there should be proportionally more blue light coming from the galaxies to overcome the lower blue

response .... ?  That is, if you normalized the luminosities based on the response curve, your blue filtered results should look brighter 

than both green & red if they currently (unnormalized) look the same.

At any rate, I think I've convinced myself why it's difficult to get the blue details in galaxies to show up well!  

Cheers,

- Greg A