alan4908 Posted March 8, 2021 Share Posted March 8, 2021 Discovered by William Herschel in 1790, NGC 1491 is a bright emission nebula in Perseus about 12,000 light years distant and about 21 light years wide. Despite its large size, its distance from Earth means that it appears visually small. The HII region displays a great deal of structure. The 11th magnitude white/blue type O5 star BD+50 866, located near to the centre of the image below, illuminates the nearby hydrogen gas with high intensity ultra violet radiation, ionising the gas. Material ejected by the star has also created curtain fold and half bubble effects in the surrounding HII region. The bubble, which is closer to the star, is probably the result of high speed, gas outflows that push nearby gas and dust outward, creating a shock front and forming a layer around the star with variable density. A similar effect also seen in the bubble nebula, NGC 7635. Further from the star, the ionised ejected gas gradually slows down as it expands into non-ionised hydrogen. The boundary between the ionised non-ionised hydrogen is called an ionisation front which may have created the curtain fold. I decided to try to extract as much detail as possible by acquiring a significant amount of Ha data which was then blended into the Lum and Red channels. The structure within the brightest regions was better revealed after application of PI’s HDRMT. The image below represents 21 hours integration time and was taken with my Esprit 150. Alan LIGHTS: L:19, R:20;G:20:B:23 x 600s; Ha:21 x 1800s; BIAS:100; DARKS:30; FLATS:40 all at -20C. 18 Link to comment Share on other sites More sharing options...
simmo39 Posted March 8, 2021 Share Posted March 8, 2021 Nice! Link to comment Share on other sites More sharing options...
alan4908 Posted March 9, 2021 Author Share Posted March 9, 2021 16 hours ago, simmo39 said: Nice! Thanks for the comment ! Alan Link to comment Share on other sites More sharing options...
MartinB Posted March 10, 2021 Share Posted March 10, 2021 Oooh! This is a new one on me. Nice to have a new target to think about! This is a very well executed image, nice star colour and a great job integrating the Ha with the RGB. Link to comment Share on other sites More sharing options...
Allinthehead Posted March 10, 2021 Share Posted March 10, 2021 Very nice Alan, a new one for me too. Link to comment Share on other sites More sharing options...
alan4908 Posted March 11, 2021 Author Share Posted March 11, 2021 (edited) 17 hours ago, MartinB said: Oooh! This is a new one on me. Nice to have a new target to think about! This is a very well executed image, nice star colour and a great job integrating the Ha with the RGB. Thanks Martin. Yes, this is not often imaged, probably because of its small apparent size - I was at 0.7 arc seconds/pixel but still cropped the image in order for the detail to stand out a little more. On the Ha blend with the RGB I'm now use Adam Block's technique, which I find more effect than my previous method. Basically, you create a starless Ha and blend only the brightest parts via a Screen script into the Red channel. A video tutorial on this can be found at https://www.adamblockstudios.com/ - I would definitely recommend the videos. 16 hours ago, Allinthehead said: Very nice Alan, a new one for me too. Thanks for the comment ! Alan Edited March 11, 2021 by alan4908 Link to comment Share on other sites More sharing options...
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