NGC 1499 Ha

[Knight of Clear Skies]

Here's my latest effort, NGC 1499 in Ha. The mysterious arc feature is showing at lower-right, my goal was to capture it.

Field of view is 7.84 x 5.93 deg, North is to the right. I like it in this orientation as it gives it a squid-like appearance.

Although it was only shot at 135mm focal length I think it's showing enough detail for the Deep Sky Imaging forum, due to the small pixels of the 1600MM cool. This is 48 minutes of data at f2, fully calibrated. My Ha filter is designed to work at f2 but I don't know how wide it is as that information isn't published. Some people have suggested it's at least 12nm.

Here's a quick go at a colour version, blending the Ha into a image taken with a 200mm lens and modded 100D.

 

Had a go at a starless version using StarNet (it's free and very easy to use, just a case of putting the image in the right folder and then dragging it onto either the mono or colour executable file).

An inverted version shows a little more detail.

And finally, here's an inverted version with a very heavy stretch of the background. There is a curious angled feature at lower-left (possibly two unrelated fronts or filaments).

Here's the deepest image I can find of the region, from the MDW survey. I still don't know what to make of that arc but even in a very deep image it doesn't show up as a circle. One theory is that it's a foreground faint planetary nebula in front of NGC 1499, but perhaps that's not the case.

Hope you like it, would welcome any feedback. I have a colour image on disc somewhere shot with a DSLR and 200mm lens so I'll have a go at blending in the Ha using Registar.

Edited May 9, 2020 by Knight of Clear Skies

[ollypenrice]

Lovely and the arc is a strange affair.

Mr and Mrs Gnomus and I gathered a lot of data on this target - 35 hours - but even so, and when using the equalize filter to exaggerate local contrasts, we could find no sign of a fuller circle. I was fairly convinced it would extend further but if it does we didn't find it. 

That's a great link to the MDW survey. I checked a couple of my more extreme Ha efforts against it, including the Ha background to the Double Cluster. I had to process that so brutally that I've always been fearful of having created some of it myself 🤣 but, to my great relief, the images concur very closely.  Phew. It's a super resource. Thanks for that.

Olly

Edited May 9, 2020 by ollypenrice
typo

[Knight of Clear Skies]

6 hours ago, ollypenrice said:

That's a great link to the MDW survey. I checked a couple of my more extreme Ha efforts against it, including the Ha background to the Double Cluster. I had to process that so brutally that I've always been fearful of having created some of it myself 🤣 but, to my great relief, the images concur very closely.  Phew. It's a super resource. Thanks for that.

Good to hear you'll find it useful. Yes, there are times I wonder if I've nixed or manufactured data while processing out gradients or vignetting (especially when I've had problems with flats and had to stack without them).

6 hours ago, ollypenrice said:

Lovely and the arc is a strange affair.

Mr and Mrs Gnomus and I gathered a lot of data on this target - 35 hours - but even so, and when using the equalize filter to exaggerate local contrasts, we could find no sign of a fuller circle. I was fairly convinced it would extend further but if it does we didn't find it. 

Looking on MDW there are a number of arcs in the area. My new theory: A concentrated region of molecular cloud is stretched out by tidal forces, and radiation pressure and stellar winds from a bright star 'bend' it. (The denser and more shaded area in the middle isn't moved as far). Plausible? I think so. Accurate? Goodness knows.

[Knight of Clear Skies]

Had a quick go at a colour version, was some way into the processing before I realised I wasn't using the full resolution version but never mind.