Astronomy Stuff:
According to Wikipedia
, NGC 7635, also known as the
Bubble Nebula,
Sharpless 162, or
Caldwell 11, is an
H II regionemission nebula in the constellation
Cassiopeia. The "bubble" is created by the
stellar wind from a massive hot, 8.7
magnitude young central
star, SAO 20575. The nebula is near a giant
molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in 1787 by
William Herschel.
Astrophotography Stuff:
The "shiny" intact spheroid shell of the nebula is the most distinctive feature of this target. Most of the images posted on Astrobin tend to be close ups of the "bubble" for that reason. However, I cropped to a wider frame as I thought the lower contrast of the surrounding nebulosity would emphasize the shine on bubble while also providing a relatively vivid background. The wider field includes part of the Cassiopeia Salt-and-Pepper Cluster near the top right corner of the image.
The stars in this image are somewhat elongated as I am challenged to get consistently sharp focus after filter changes with the fast f/4.8 Explore Scientific 152mm David H. Levy Comet Hunter Maksutov-Newtonian Telescope. Imaging was conducted over 6 sessions in early September 2021, but only selected frames with "passable" focus from 4 sessions ended up in the final image.
Processing the image in Pixinsight was relatively easy; I was able to remove a significant background gradient by following Adam Blocks tutorial on Dynamic Background Extraction (DBE). I was also challenged by cyan colored rings around the cores of larger stars. I was only able to reduce, not eliminate through the use of a Color Mask and by color desaturation. The cyan showed up at color combination and I am not sure yet how to prevent or minimize this artifact from the start.
Imaging Details:
Dates: Sept., 7, 8, 9, 10
Ha: 76 frames x 300 sec., 200 gain
Oiii: 69 frames x 300 sec., 200 gain
Darks: 30
Flats: 200 (2 x 100)
Dark Flats: 200 (2 x 100)
Bias: 200 (2 x 100)
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