Overview: Continuum Subtraction

Sungryong Hong's Page : https://sites.google.com/site/shongscience/

<Overview of Continuum Subtraction Technique and its IDL program >

* Please play this in 720p (or 1080p) resolution.

We presented an objective method to remove the stellar continuum emission from narrow–band images to derive emission–line images. (Hong et al. 2013; http://arxiv.org/abs/1311.3665).

The method is based on the skewness of the pixel histogram of the residual images. Specifically, we exploit a transition in the skewness of the signal in the continuum–subtracted image, which appears when the image changes from being under–subtracted to over–subtracted.

Denoting residual images by

(residual image) = (narrow-band image) - μ (continuum image), where μ is a parameter controlling the amount of subtractions,

the skewness value for the μ residual image can be written, called skewness function s(μ), as

s(μ) = skewness of (residual image for μ).

We can find a "transitional feature" in the landscape of s(μ).

The below shows how skewness functions look like in real applications.

The key point is to find a "symmetric transition", at which the optimal subtraction is located.

In this figure, "E" shows the best (locally symmetric) transition at 0.165.

The subtracted images are optimal at 0.165.

**If you have any question, please contact me to shongScience(at)gmail(dot)com.

**More mathematically, the term "symmetric" should be "anti-symmetric".