In a narrowband filter we still have light coming from light sources emitting a continuous spectrum. The main idea behind this picture is to isolate the pure H-alpha emission line by removing the continuum emission coming from the stars in the galaxy. This can be done by subtracting the red image from the H-alpha image. This way, we can unveil the hydrogen spiral structure right to the galaxy core.
This image is a collaboration with Alicia Lozano. It was acquired from the Observatorio Astronómico de Aras de los Olmos in Spain with a Canon EF 400mm f/2.8L IS II USM lens and a QHY600L CMOS camera. Exposure time was 51 hours in H-alpha and 14 hours in broadband red filter. The red image is used only to subtract the continuum emission from the H-alpha image.
The long red exposures were acquired with a Finger Lakes Microline ML16200 camera; a 2x1 mosaic was needed to cover the entire FOV of the QHY600 camera. All the other exposures we acquired with the QHY600 camera.
You can learn about this technique and the use of the improvements added to the preprocessing tools in PixInsight 1.8.9 by reading the
processing notes in the PixInsight website.
You can see a comparison of the galaxy before and after applying the continuum subtraction in the
PixInsight gallery.
And read some words about the galaxy in the
website of the Astronomical Observatory of the University of Valencia (in Spanish).
All the processing done with PixInsight 1.8.9.
© 2022 Vicent Peris (OAUV), Alicia Lozano, OAUV, OAO.
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