How can I make only a part of this texture emissive in a circle shape?

[dabbbbbbbb5656]

I want to make only a part of this texture in a circle shape emissive with the color red; right now all of it is emissive:

I want to make it look like this:

but I don’t know much about which nodes are used for this. I tried the SphereMask node but couldn’t make it work.

[3dRaven]