Those are stars. Duotone is (obviously) a toning process, sorry, but I'm late for work maybe someone else could chime in here? Or google could probably tell you.
The duotone effect is very cool, the cool white stone sweeping into the dark night sky. I can't offer any higher critique, but, to amplify the comment, the angle of the photos is superb. Gives it sort of a leery/eerie feeling.