NGC7635 – The Bubble Nebula

NGC7635 – Bubble Nebula
LRGB (1h each), H-Alpha (13.6h)

NGC7635, the Bubble Nebula. This strange object is the result of stellar winds produced by the star visible on the lower left, causing a shock wave on the clouds nearby. The propagation is not symmetric due to the differing density of those clouds.

This picture took nearly 14 hours of 300-second H-Alpha exposures, combined with one hour of each Red, Green, Blue and Light-Pollution filtered exposures. The length of the narrowband exposures is generally problematic with my mount as guiding deviations would often cancel capture, but the location of this particular object in the sky made that impact minimal. After those sessions, I started getting haze on the guiding sensor itself from lack of proper heating, causing even more disturbance to guiding. This made me close the project.

The LRGB integrated frames were first assembled and background-corrected, stretched and had stars removed. The Ha integrated frame was then denoised, stretched, had stars removed and was enhanced with masked curve transformation and HDR multiscale processing. The stars extracted from the photometrically corrected LRGB frame and saturated to emphasise their color. In order to avoid a tint to appear when adding the stars back on the final red-tinted frame and keep their photometry correct, their blue component was saturated slightly more and their magenta component corrected.

I thank user vnc1218 on CloudyNights for his very detailed processing of the Cygnus area, which inspired me on this activity.

All exposures taken with KStars/Ekos (v3.5.0 pre-release) and INDI, using the excellent Atik Horizon 2, Skywatcher HEQ5-PRO, Orion ED80T, with Atik 314E and Orion 50mm GuiderScope for guiding. Processed with PixInsight 1.8.8 and RawTherapee 5.8.

Plate-solving the Markarian Chain.

Widefield Markarian Chain in Leo - 2016
Widefield Markarian Chain in Leo – 2016

In astrophotography, plate-solving is the process of correlating stars in the field of view of a telescope with stars in a reference catalog. The name refers to the photographic glass plates that were in use for survey catalogs during 19th and 20th centuries.

By matching the relative position of light sources in an input capture with known star positions from its catalog, the plate-solver returns the sky coordinates of the field of view. Automated observatories use those results to align their target iteratively, but also to refine their mount model and optimize their slewing time. Information such as optical reversal, size of the field of view and pixel scale are very important to reduce the complexity of the task.

Human observers generally target a well-known star then hop from star to star until they are close enough to the target object. Conversely, plate-solvers match triangle proportions against a huge number of reference combinations, taking the astronomer’s old joke “can you see those three stars shaping a triangle?” to the letter.

(pic: widefield Markarian Chain in Leo, 2016, solved by

Bahtinov masks.

Bathinov Masks - 2018
Bathinov Masks – 2018

Bahtinov masks are easy to 3dprint, and are a very precise focus tool when preparing an astrophotography session. Grid holes in the mask cause diffraction spikes to appear when looking at the point light from stars. Achieving optimal focus consists in centering the middle spike between the side spikes, so that the figure is symmetric.