M51 Whirlpool Galaxy (broad- and narrowband merge)

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Menno555
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M51 Whirlpool Galaxy (broad- and narrowband merge)

#1

Post by Menno555 »

M51 the Whirlpool Galaxy

A merge of broadband and narrowband data (Ha + OIII), in total a bit more than 8 hours integration time.
Also first light for the Optolong L-eXtreme filter, a duo filter for 7nm Ha and OIII.
The color image is a blend of broad- and narrowband data. Also the capture of the only narrowband.

Bortle 7/8
Meade LX200 8" f/10 ACF OTA
Ioptron CEM25EC montering (no guiding)
Baader Neodymium Skyglow filter
Optolong L-Pro filter
Optolong L-eXtreme filter
Zwo ASI071MC Pro camera

Captured with SharpCap Pro @ -10 Celsius / White balance R50 B50
Baader Neodymium: 30 x 400 sec / Gain 0 / Offset 4
Optolong L-Pro: 11 x 600 sec / Gain 0 / Offset 4
Optolong L-eXtreme: 19 x 600 sec / Gain 100 / Offset 10

Stacked with DeepSkyStacker
Each set apart

Processed with Siril and Photoshop
Siril: Background Extraction and Histogram of each stack
Photoshop: layered the 3 stacks. Then Curves, Levels, Camera Raw Filter (blacks, color saturation, clarity, noise reduction)

M51 broad- and narrowband
M51 broad- and narrowband
M51_sm.jpg (492.91 KiB) Viewed 1854 times
M51 narrowband
M51 narrowband
M51-H-sm.jpg (457.57 KiB) Viewed 1854 times
timh
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#2

Post by timh »

Very nice resolution and colour Menno. M51 is a great object that I always come back to. A picture to mark the end of 'galaxy season'? I also did a fair amount of galaxy 'work' - if you can call it that - 'play' more like - these past months and will also post up a couple of the best so far.

Incidentally - and you may never have tried it? I do find that when I image with no filter in place at all (except for IR/UV cut off) then the HA red regions just appear white - or maybe a faint pinkish white. Dop you see the same? All of the filters (even my UHC filter) make quite a difference in terms of enhancing the red - but your 'extreme' narrow band is certainly living up to its name.

Tim
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Menno555
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#3

Post by Menno555 »

Thanks Tim.
And as coincidence will have it, I just ordered a 2" IR/UV cut filter with that in mind what you described :)
Till now I backed out of that cause of the Bortle 7/8 but I'm learning more and more with capturing but also with processing. Going to see if any light pollution haze can be "battled" :)

Menno
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Menno555
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#4

Post by Menno555 »

Like usual i like to do some extra things with captures.
I had so much data of M51 that I decided to focus on the core.
Stacked everything again in DeepSkyStacker but now with 3x drizzle. In Photoshop I cropped the core area and reduced the highlights. This brought forward a lot more of detail. Of course noisy and not "sharp" but I am not disappointed with the end result :)
For comparison also a Hubble capture of the core which I made to the same scale.

M51 core Hubble
M51 core Hubble
kern_m51.jpg (228.18 KiB) Viewed 1783 times
M51 core 3x drizzle
M51 core 3x drizzle
kern_m51_hubble.jpg (242.46 KiB) Viewed 1783 times
timh
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#5

Post by timh »

Very impressive Menno. You must have had sharp focus and and reasonable steady (even if bright at Bortle 7/8) skies because the detail at the core is really very good. I am surprised though that drizzle should have done much - and especially as high as 3X? I thought that it was mainly for use when undersampled and I would guess that you wouldn't be at F 10? Can't argue with the result though!

TimH
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Menno555
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#6

Post by Menno555 »

Thanks Tim!
I use a Bahtinov mask together with the Bahtinov Grabber software and check focus every hour or so.
And this is what I did read on the drizzle too, so I never tried it. But I tried it now and somehow it worked. I did try also with no-drizzle stack but then when enlarging in Photoshop, to much got lost.
My PC had to work hard though: it produces a 2 Gb FITS file after much crunching and then in SiriL it's also not that fast anymore. But I have enough power in my PC and am not in a hurry :p

Menno
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Menno555
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#7

Post by Menno555 »

Since the clouds completely took over here the last month (and coming weeks), I decided for some experimenting with my M51 data.
This is Photoshop processed Ha data captured through the Optolong L-eXtreme filter.
I also stacked all the broad- and narrowband data I have of M51 in 1 stack, made that grayscale and used that as Luminance over de Ha data.
And then some "playing" to get this result. I call it "Ha Plus". I'm 100% sure that it's already a known way of processing, but for me it's just experimenting :)
Because of this, one feature really popped: in the upper arm (upper left) there is a OIII source, really the only one I captured in M51. See also the cut-out in the upper left corner.
According to the NED Catalogue, there are 3 star clusters there, including a "Ultraviolet excess source".

Menno

M51_LHaSc.jpg
M51_LHaSc.jpg (906.92 KiB) Viewed 1589 times
timh
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#8

Post by timh »

Hi Menno,

The dual band filter colour camera combination must mean that your image reports on the ratio of deepred (~ 656nm) versus teal (~500 nm) coloured light coming from any given spot on the galaxy. But I don't think that you can describe any of the predominantly blue 500 nm spots as 'OIII sources' since that term implies something very specific about the way that the light was generated (i.e. as emission lines arising from doubly ionized oxygen) whereas it is much more likely that these spots represent regions of hot blue stars and associated reflection nebulae from which H (and therefore HA emission) has been depleted (i.e it has been blown away)? Because there is relatively just so much H the dual band filter is probably much better at pointing to HA regions ? I hope you don't mind but I thought it interesting to compare your 'luminosity added' dual band image with a pure broadband image (no filter) of M51 in order to better understand how the dual band filter shifts the detection of the different features of the galaxy. Quite a few - in fact most - of the bluish newly forming star regions are turned red by the filter (presumably by amplifying relative detection of the red light associated with their otherwise invisible HA regions). So the remaining blue/ teal spots likely reflect where the new stars are but HA isn't?

Tim
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Menno555
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#9

Post by Menno555 »

Hi Tim

I don't mind this at all :) For me all new and the more info, the more knowledge.
I deduced that the spot is OIII from the fact that the only color data here is with the L-eXtreme filter. All the Ha data is red and the OIII is blue/green.
If it were as you described, that blue spot should have been white.
That smal dot is home of 3 star clusters and a "Ultraviolet excess source". So maybe it's a nebulosity region with a lot of emission in that wavelength?
I mean, it really is the only spot in the narrowband that is clear green/blue (or teal, didn't know that word :).

As for Ha and star forming regions or regions with very recent stars: as I understand it, is goes hand in hand. What is (bright) blue in broadband is the visible blue light of that. When the blue is filtered out by the narrowband, the Ha is what remains and indicates the regions with ionized gasses where stars are formed.
In the case of this spot, it is blue in broadband and blue/green in narrowband. So no Ha and than OIII is what remains.
I didn't notice it before but it's also in the 2nd image above which is only the L-eXtreme data, so no luminance added. If it was anything else, it should have shown as white-ish but it's clear blue/green.

Menno
timh
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Re: M51 Whirlpool Galaxy (broad- and narrowband merge)

#10

Post by timh »

Hi Menno,

I really must stop throwing in words like 'teal' and stick to international English

I am by no means an expert on galactic spectroscopy and happy to be corrected but the main point that I was making is that I doubt that the L-extreme filter can really be used to pinpoint OIII light from a galaxy arm?

So I query the terminology - i.e. I don't think that the blue-green light that is detected by the filter can accurately or at all be described as ' OIII' since ionized oxygen would likely contribute only a tiny part of it? My assumption is that the blue green light just reflects the filter's particular window of selection upon the continuous temperature-dependent black body spectrum of starlight - with the window at 500 nm passing relatively more light from the hotter bluer stars than from cooler stars? It is a bit of a different situation with the deep red, 656 nm, pass band since while HA light would still be by no means the only contributor to the light passed by the filter (i.e. a lot would still be stellar) hydrogen is just so abundant that HA may likely predominate? - So HA terminology better justified.

I may of course be wrong and very happy to learn - but I was sort of uncomfortable with the idea of the detection of spots of OIII in a galaxy arm -- but happy with the idea that the filter helps pulls out spots where there are hot bluish stars but little surrounding HII?

Tim
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