My problem with sky subtraction for high contrast objects

[oleg]

Hi all,
I have the problem with good sky subtraction for high contrast objects (for ex. bright nebula near dark cloud).
I can't get the nice results of sky subtraction for similar objects

My results look as on attached picture: sky background near bright object is more dark, then sky background around faint stars.

[oleg]

On the other hand, you can see this region (one exposition) without sky subtraction: monotonous sky background.

[mischa]

Hi Oleg,

there isn't anything in Theli that can deal with such areas perfectly.
You'd need a mathematical model of the reflection ghosts positions, sizes, and offsets from the stars as a function of position on the detector. I think something like that is in development for MegaPrime@CFHT and will possibly be included in their ELIXIR pre-processing pipeline (Theli accepts the output of Elixir as input data), but within Theli there isn't much you can do about. You may try subtracting a constant sky?

mischa