NGC 253 Sculptor Galaxy under Bortle 8 Skies

[Startrek]

A couple of clear moonless nights presented themselves last week , so took the opportunity to do some galaxy imaging. Chose NGC 253 as its well placed later into the evening when that retched City Skyglow reduced a bit. Unfortunately one of the nights had fine smoke haze drifting across Sydney but struggled on regardless ( my 2600MC camera had small specs of ash on the red housing )

Same deal
Bortle 8
Sky conditions, poor to average
No moon
8” f5 Klaus Helmerich Carbon fibre Newt
EQ6-R pro mount
ZWO2600MC cooled to -10C , Gain 100
No filters ( just internal UV/ IR cut protective window)
210 x 60 sec subs ( dithered every 3rd )
40 x Flats
60 x Bias
EQMOD and Stellarium
APT
PHD2 Multistar guiding ( 0.50 to 0.60 arc sec total ) guiding was superb on this lowish end mount , guiding dropped down to 0.40 to 0.45 for a while. I’ve had a couple of these EQ6-R mounts now and they just do the job. Best performing value mount in their category ( 20kg )
Stacked in DSS
Processed in Startools v1.8

Heavy light pollution really plays havoc with your Star Color especially when imaging dim objects like galaxies.With imaging broadband on Reflection / Emission Nebula like M20 Trifid I seem to get good Star Color straight off the bat , as the Star field is immense with young and old stars ( blue , red , yellow and orange ) but with dim galaxies stars are quite sparse in comparison and don’t seem to exhibit strong Star Color being saturated with heavy LP.

Link to Astrobin below for more details and improved resolution

https://www.astrobin.com/dbf8vk/


Synthetic Luminance version
Colour version

Thanks
Comments welcome

Martin

[Mike in Rancho]

Hi Martin,

Just a great galaxy, wow. Have to say that.

This one only gets to about 30 degrees high for me. I'd probably have to move my mount to a more favorable position - like where I tried to grab those Milky Way DSLR shots from a few weeks ago. I don't have the length you do, but it might be cool to try anyway.

The stars I find interesting. I don't think it's LP. I'm in B8 and I can pull out plenty of star color. In fact, I think I managed decent(-ish) color in little stars when I horizon-skimmed for Cent A and Om Cent. Those were with a DSLR and refractor, and the individual subs looked like chocolate milk. So once gradients and casts are handled, color should be possible.

Plus, look at the color in your galaxy!

Now, I do notice that the stars are fairly tight, and the diffraction balls are rather faint and weak. Query if this is something similar to a recent discussion with Stefan on an a-bin image he linked. It could be that these are just all fairly high mag stars (8 and 9 for the big ones here), and per Stellarium none of them would be what I would call strong to either red or blue.

They do look like they could use a little attention though, as each sort of has a target/bullseye appearance. Maybe some different settings during processing could ameliorate this, or maybe just some cosmetic touch-up (if one was so inclined and considered them to be artifacted).

One other thing I notice is some pretty strong hot pixeling. You might be able to change some stacking settings to help with that. Or, take a set of darks for this target and re-stack. That should clean those up. With my 2600 I started out using just bias for both the lights and flats, but finally made a darks library after I got tired of hot pixels. They don't always get rejected or dithered out.

[Stefan B]

Hi Martin,

the Sculptor galaxy is looking great. I always admire that you are able to get such results from Bortle 8...

With regard to star color just two short questions: Are you using Autodev or Filmdev? And in the Color module, are you using Scientific color constancy or Artistic? If you are using Filmdev and/or Artistic, this could desaturate the stars.

But that would only make sense if you would have used different settings for your broadband nebulae since they obviously appear fine...

Regards
Stefan

[Startrek]

Hi Martin,

Just a great galaxy, wow. Have to say that.

This one only gets to about 30 degrees high for me. I'd probably have to move my mount to a more favorable position - like where I tried to grab those Milky Way DSLR shots from a few weeks ago. I don't have the length you do, but it might be cool to try anyway.

The stars I find interesting. I don't think it's LP. I'm in B8 and I can pull out plenty of star color. In fact, I think I managed decent(-ish) color in little stars when I horizon-skimmed for Cent A and Om Cent. Those were with a DSLR and refractor, and the individual subs looked like chocolate milk. So once gradients and casts are handled, color should be possible.

Plus, look at the color in your galaxy!

Now, I do notice that the stars are fairly tight, and the diffraction balls are rather faint and weak. Query if this is something similar to a recent discussion with Stefan on an a-bin image he linked. It could be that these are just all fairly high mag stars (8 and 9 for the big ones here), and per Stellarium none of them would be what I would call strong to either red or blue.

They do look like they could use a little attention though, as each sort of has a target/bullseye appearance. Maybe some different settings during processing could ameliorate this, or maybe just some cosmetic touch-up (if one was so inclined and considered them to be artifacted).

One other thing I notice is some pretty strong hot pixeling. You might be able to change some stacking settings to help with that. Or, take a set of darks for this target and re-stack. That should clean those up. With my 2600 I started out using just bias for both the lights and flats, but finally made a darks library after I got tired of hot pixels. They don't always get rejected or dithered out.

Thanks Mike ,
I looked back on previous images of this Galaxy and also had trouble with Star Color . All other Galaxy Ive imaged in past years had good Star Color , very strange

Bulls eye look of larger stars is caused by being to heavy handed with SV Decon

Hot pixels are a result of accidentally installing the camera on the second night at a different orientation ( 90deg to right ) During the day I’ve been fiddling around with my new 2600MM and filter wheel in the scope and have to orientate the camera so the filter wheel is directly below the OTA. Unfortunately I installed the 2600MC the same way the second night and this caused the stacked image to have misalignment of sensor FOV at 90 degrees
A big crop had to be done
DSS did a good job of stacking but couldn’t remove this anomalies ( I’m quite surprised DSS stacked both nights at different sensor orientation )
My Astrobin link explained the above !

Still very pleased with the result with only 3.5 hrs under B8
Hopefully in a few weeks when the moon disappears again I can capture more data on this gem.

Martin

[Startrek]

Hi Martin,

the Sculptor galaxy is looking great. I always admire that you are able to get such results from Bortle 8...

With regard to star color just two short questions: Are you using Autodev or Filmdev? And in the Color module, are you using Scientific color constancy or Artistic? If you are using Filmdev and/or Artistic, this could desaturate the stars.

But that would only make sense if you would have used different settings for your broadband nebulae since they obviously appear fine...

Regards
Stefan

Thanks Stefan,
Much appreciated
I only use AutoDev
I mostly use Scientific in Color , it does wonders with your stars ( with exception of OSC NB Bi Color , stars usually have a small halo ring of your background bi Color. Highlight repair usually helps a lot to morph the halo ring to the background color )
It’s strange though , other galaxies I image tend to have more prominent Star Color ( blues , oranges , reds and yellows etc… ) This galaxy doesn’t have prominent Star Color ?
Still very please with the result with only 3.5hrs under B8 skies

Clear Skies
Martin

[Mike in Rancho]

Yeah Martin, maybe the stars here are just mostly whitish. The B-V values aren't anything I would call exciting.

If you feel like linking a stack we could all see what color we might be able to tease out of them though.

With sufficient matching stars, a stacker shouldn't have much trouble with a 90° rotation. And in fact, that shift should really be helping rather than hurting when it comes to hot pixels. Just think of it as a super dither. And I would think things should average out with 210 subs. Your dither is every 3 minutes - I typically dither every 5 minutes, but again I do always use my darks libarary now.

I would think these hot pixels would be outside of almost any sigma you might set, so I'm a bit perplexed. Too bad DSS doesn't save out a reject map.

Perfectly matched darks for calibration really is one of the advantages of having a cooled camera in the first place.