HII and IFN confusion! How much have I detected of SH2-73?

[pipnina]

With the big moon and uncertain weather last night, I decided to try and find a narrowband target to make use of the relatively clear weather. At this time of year of course that is no easy task!

I eventually found in Stellarium two objects, in the LDB and SH2 catalogs, which seemed promising, in a good sky position and would fit in my scope's FOV! Perfect.

One night's imaging later (and half my subs thrown away due to a frosting sensor window! not doing -15c again!) I have my subs and put the scope to bed before heading to work.

At work I look up these objects to see what I might expect from my images. To my horror they look like IFN objects, which I was shooting with a 3nm Ha filter!

Fully expecting a blank void, I download the subs to my PC when I get home, calibrate and stack them. The SNR is poor... but is this an object I detect anyway?

It looks like *something*, but even binned 4x4 the image has such a low SNR it's hard to make out. I will need more assistance!

So I use RawTherapee's denoise features and turn them up to 11, and in a separate attempt I use Pixinsight's annotation feature. The grainy blob in the middle of my image DOES line up with where pix expects SH2-73 to be!

My image is not pretty, but given I only ended up with 2h40m of subs to include, and possibly of the wrong wavelength bandpass, I think I am pleased!

I'll include the downsampled, unedited tiff if anyone else wants their own look.

Now I wonder if Stellarium is lying about the objects being HII regions, or if my idea of what a HII region is, is wrong! In my mind HII regions are clouds of hydrogen that glow in mostly H-alpha!

master.tif

Edited May 3, 2023 by pipnina
Wrong sharpless catalogue item number

[symmetal]

You confused me as the title says Sh2-76 while the image is Sh2-73. 

Sh2-73 is in fact a reflection nebula and classed as IFN. It was included in the Sharpless catalogue by mistake. You managed to get something though which is quite a feat. 😊

Alan

[pipnina]

7 hours ago, symmetal said:

You confused me as the title says Sh2-76 while the image is Sh2-73. 

Sh2-73 is in fact a reflection nebula and classed as IFN. It was included in the Sharpless catalogue by mistake. You managed to get something though which is quite a feat. 😊

Alan

Whoops! Thankfully I can correct the title haha.

Given how hard it has been for me to pick out IFN in the past, I am very surprised to have caught some while using a Ha filter!

It must be a very bright piece of ifn!

[Fegato]

Ha ha!  Yes it is quite a bright - I had a go at it last month. I had some advantage though - dark skies, no moon, a very fast scope, and more to the point, no 3nm filter!

https://astrob.in/6n78xm/0/

[ollypenrice]

This is indeed surprising. Apparently it was included in the Sharpless catalogue 'erroneously' classified as an emission nebula, whereas it is now regarded as IFN.  I wonder if there might not have been some truth in the original classification since you've captured Ha in a filter which would not, I don't think,  pick up faint reflection nebulosity.  Perhaps the object contains both ionized hydrogen and the stuff of molecular clouds?

As a control, you could take a test run on some bright (or less faint!) IFN in the same filter.

Olly

[pipnina]

1 hour ago, Fegato said:

Ha ha!  Yes it is quite a bright - I had a go at it last month. I had some advantage though - dark skies, no moon, a very fast scope, and more to the point, no 3nm filter!

https://astrob.in/6n78xm/0/

Cracking shot Robin! Definitely looks like IFN to me, I think I might have to suggest something on the Stellarium GitHub or something because it's currently down as a HII region...

 

1 hour ago, ollypenrice said:

This is indeed surprising. Apparently it was included in the Sharpless catalogue 'erroneously' classified as an emission nebula, whereas it is now regarded as IFN.  I wonder if there might not have been some truth in the original classification since you've captured Ha in a filter which would not, I don't think,  pick up faint reflection nebulosity.  Perhaps the object contains both ionized hydrogen and the stuff of molecular clouds?

As a control, you could take a test run on some bright (or less faint!) IFN in the same filter.

Olly

I could possibly give it a try, what regions could you recommend I point at? I chose this area because it is one of few non-galaxy objects I can point at at the moment haha.

I know there is IFN around Polaris and near m81/82, but is it bright(er) than this object I wonder?

[ollypenrice]

18 minutes ago, pipnina said:

 

 

I could possibly give it a try, what regions could you recommend I point at? I chose this area because it is one of few non-galaxy objects I can point at at the moment haha.

I know there is IFN around Polaris and near m81/82, but is it bright(er) than this object I wonder?

M81/82 might do it and the data would be useful in their own right.

Olly

[gorann]

Here is my recent image of it with RASA8 and no filter. Looks like IFN with a bit of reddish tone than may indicate some Ha that you managed to pick up. Actually a lot of IFN all around:

https://www.astrobin.com/uahkpy/

[pipnina]

13 minutes ago, gorann said:

Here is my recent image of it with RASA8 and no filter. Looks like IFN with a bit of reddish tone than may indicate some Ha that you managed to pick up. Actually a lot of IFN all around:

https://www.astrobin.com/uahkpy/

Also a cracking image!

I notice a good trend of RASA owners and this object emerging. Starting to think I should have picked one up and put up with manual filter swapping back in september when I went with my APO instead! Certainly it's very hard to pass up the speed of f2 imaging given the UK's weather!

How have you balanced the colour in this image? I notice the other two examples in this thread have a very neutral grey colour in the IFN while you have an almost golden colour in yours. I can only assume at least some of this comes down to artistic interpretation in the various images. I can only guess that the most accurate interpretation we could make would be using PixInsight's SPCC tool after background extraction? I can see some reddish hints in areas of your image though which as you say, could be little bits of hydrogen?

[gorann]

3 hours ago, pipnina said:

Also a cracking image!

I notice a good trend of RASA owners and this object emerging. Starting to think I should have picked one up and put up with manual filter swapping back in september when I went with my APO instead! Certainly it's very hard to pass up the speed of f2 imaging given the UK's weather!

How have you balanced the colour in this image? I notice the other two examples in this thread have a very neutral grey colour in the IFN while you have an almost golden colour in yours. I can only assume at least some of this comes down to artistic interpretation in the various images. I can only guess that the most accurate interpretation we could make would be using PixInsight's SPCC tool after background extraction? I can see some reddish hints in areas of your image though which as you say, could be little bits of hydrogen?

I have just balanced the colours with levels in PS for the darkest parts of the image, so no SPCC (never used it as I am mainly a PS person). The red signal was there and I liked it but I could of course desaturate it. However, what you picked up with the Ha filter may suggest that I am not all wrong with that reddish tone.

[ollypenrice]

It might be ERE - extended red emission. That's what we see around the Pleiades, for example. It's quite a strong brownish red in deep images.

Olly