Reflection halos

 

Because of internal reflections inside the camera (against the CCD or dewar), bright objects produce extended halos, which are particularly visible on deep images in the red filters (i in particular). The stellar halos might hide the outer structure of nearby galaxies. More subtly, the nucleus of each galaxy produces its own halo, which creates an artificial reddening in its outskirts. Ways to subtract these halos are under investigation.

Reflection halos in a nutshell


  1. • Shape: round for stars, round but more fuzzy for galaxies

  2. • Surface brightness: fainter than 27 mag.arcsec-2

  3. • Number: one

  4. • Color: red


Examples of extended, low-surface brightness, halos produced by bright stars (left) and galactic nucleus (bottom).