The Andromeda Galaxy in H-alpha Light

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Image Caption and Credits: Image of the Andromeda galaxy showing the pure H-alpha line emission acquired from the Observatorio Astronómico de Aras de los Olmos. Vicent Peris (PTeam / OAUV), Alicia Lozano, OAUV, OAO. Entirely processed with PixInsight 1.8.9. Click on the image to download a full-resolution version (image scale of 2 arcsec per pixel).

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The Andromeda Galaxy in H-alpha light

Not everything in a narrowband image comes from the emission line itself. In a narrowband filter we still have light coming from light sources emitting a continuous spectrum; mostly stars in this image. 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. In this way we can unveil the delicate geometry of hydrogen clouds forming a spiral structure right to the galaxy core. While the H-alpha image of the galaxy shows its classical appearance with a bright bulge at the center, below we can see the effect of subtracting the continuum light to isolate the pure H-alpha emission line:

Vicent Peris and Alicia Lozano describe this technique and the preprocessing improvements that have been implemented in PixInsight 1.8.9 in their Processing Notes in our Processing Examples section.

This image was acquired with a Canon EF 400mm f/2.8L IS II USM lens, a QHY600L CMOS camera, and a Finger Lakes Microline ML16200 CCD camera. Total exposure time was 51 hours in H-alpha and 14 hours in red. The long red exposures were acquired with the Finger Lakes Microline ML16200 camera; a 2×1 mosaic was needed to cover the entire FOV of the QHY600 camera. The rest of exposures were acquired with the QHY600 camera. The red image was used to subtract the continuum light from the H-alpha image.