Carina Dwarf Galaxy reprocessed.

sjastro · #1 31-07-2009, 02:24 PM

When I initially posted this image it was difficult to locate the object in the image. This is not surprising as the Carina Dwarf Galaxy is much fainter than the naturally occurring sky glow from the darkest sites. (The surface brightness of the galaxy is 16 Vmag/square metre, naturally occurring sky glow is 13 Vmag/square metre.)

The galaxy is therefore nothing more than a tiny blip in the sky glow.

Initially I attempted to measure the sky glow of each of the 120 images that went into the total exposure, and subtract 13/16 of this value from each image in the hope of extracting the galaxy from the background.
This wasn't very successful.

Much against my processing instincts I extracted the background information from the final stacked image and created a noise free and ultimately sky glow free background which was blended back into the image.

I was able to stretch the blended image and extract the galaxy from the background.

20 hr exposure total BRC-250, ST-10XME.

http://users.westconnect.com.au/~sjastro/carinadwf.html

The attachment shows a comparison before and after image.

Steven

renormalised (Carl) · #2 31-07-2009, 03:00 PM

Damn good job on that, Steven.

TheDecepticon · #3 31-07-2009, 05:13 PM

That's what I call a labour of love! Top stuff!

Alchemy (Clive) · #4 31-07-2009, 05:24 PM

hmmmm dont know , its tough call, i see what you have tried to do... but there is a faint loop on the left of the initial image thats quite obvious, but not so in the second. i actually prefer the first but i would like to see it in a wider FOV to judge the edges better , but it looks as though its an extremely hard one to image.... not one ive done.... but then most of the ones you do arent ones ive done.

as always, i enjoy looking at your work

cheers clive.

sjastro · #5 31-07-2009, 06:57 PM

Quote:

Originally Posted by Alchemy

hmmmm dont know , its tough call, i see what you have tried to do... but there is a faint loop on the left of the initial image thats quite obvious, but not so in the second. i actually prefer the first but i would like to see it in a wider FOV to judge the edges better , but it looks as though its an extremely hard one to image.... not one ive done.... but then most of the ones you do arent ones ive done.

as always, i enjoy looking at your work

cheers clive.

Hello Clive,

This is the sort of object that doesn't lead to natural processing. It's a case of digging it out of the background and hope for the best.

I think the second image shows the galaxy more clearly differentiated from the background compared to the first.

Incidentally the AAO image is so stretched the galaxy looks more like a globular cluster.

Quote:

Originally Posted by TheDecepticon

That's what I call a labour of love! Top stuff!

Thanks for that. Actually it's been one big headache.

Quote:

Originally Posted by renormalised

Damn good job on that, Steven.

Thanks for your comments Carl.

Regards

Steven

Robh (Rob) · #6 31-07-2009, 09:28 PM

Steven,

Nice work! The reprocessed image is much more defined.
Wish I could take out the skyglow when I'm observing!

Regards, Rob

Alchemy (Clive) · #7 31-07-2009, 10:21 PM

Quote:

Originally Posted by sjastro

Hello Clive,

Incidentally the AAO image is so stretched the galaxy looks more like a globular cluster.

do you have an NGC number for this item... did a little bit of looking but not much under carina dwarf galaxy in the pics dept

Robh (Rob) · #8 31-07-2009, 11:08 PM

Quote:

Originally Posted by Alchemy

do you have an NGC number for this item... did a little bit of looking but not much under carina dwarf galaxy in the pics dept

No NGC number. Only discovered in 1977.
Wikipedia has this info ...
http://en.wikipedia.org/wiki/Carina_Dwarf

Regards, Rob

renormalised (Carl) · #9 31-07-2009, 11:08 PM

Doesn't have an NGC number but its PGC number is 19441.

Here's some info from SEDS and SIMBAD

renormalised (Carl) · #10 31-07-2009, 11:18 PM

Quote:

Incidentally the AAO image is so stretched the galaxy looks more like a globular cluster.

More like they ripped a gash in spacetime to even get this one to make an appearance!!!!

sjastro · #11 01-08-2009, 07:42 AM

Quote:

Originally Posted by Robh

No NGC number. Only discovered in 1977.
Wikipedia has this info ...
http://en.wikipedia.org/wiki/Carina_Dwarf

Regards, Rob

The Wikipedia image illustrates how dim this object is!

Steven

Alchemy (Clive) · #12 01-08-2009, 07:50 AM

i looked at the wikipedia prior to my last post.... i wouldnt have guessed it was more than an open cluster,

looked at the seds one.... yours shows more.
looked at the simbad one ..... what galaxy ???? just a plain starfield.

i think its going to be difficult to find any reference material.

so i guess in hindsight maybee i should congratulate you on achieving what you have.

cheers clive.

Hagar (Doug) · #13 01-08-2009, 09:19 AM

Nice image Steven but I think I like the first image a little more. It seems to have structure missing in the filtered version.

sjastro · #14 01-08-2009, 10:29 AM

Quote:

Originally Posted by Hagar

Nice image Steven but I think I like the first image a little more. It seems to have structure missing in the filtered version.

It's difficult to ascertain whether the detail is a flat related issue or genuine.
I'm inclined to think it's not real.

This is only image where I have put more emphasis on processing the background and not the object itself.

After all it's an image of an irregularity in the sky background.

Regards

Steven

glenc (Glen) · #15 01-08-2009, 11:53 AM

Thanks Steven for another different object, I like the skyglow subtracted one.

seeker372011 (Narayan) · #16 01-08-2009, 12:30 PM

great stuff..nice to something really different

sjastro · #17 01-08-2009, 03:17 PM

Thanks Narayan and Glenn.

Here is the discovery image of the Carina Dwarf taken with the UK Schmidt scope in 1977. Taken with a photographic emulsion that required a keen eye for spotting detail.

Regards

Steven

seeker372011 (Narayan) · #18 01-08-2009, 03:18 PM

Quote:

Originally Posted by sjastro

required a keen eye for spotting detail.

lol!

renormalised (Carl) · #19 01-08-2009, 04:15 PM

It's there....just look for a slight overabundance of stars in one area cf the background. You do need a good eye, though.

sjastro · #20 01-08-2009, 06:55 PM

Quote:

Originally Posted by renormalised

It's there....just look for a slight overabundance of stars in one area cf the background. You do need a good eye, though.

They probably would have also confirmed its presence by density measurements of the developed emulsion.

The IIIaJ emulsion was blue sensitive making it ideal for galaxy searches although although the exposure times would have been limited due to the fogging of the emulsion due to sky glow.

Steven