Centigrade/Kelvin symbol in LaTeX

Does anyone here happen to know how to set a centigrade/kelvin symbol in LaTeX (raised small circle). I could hack about with math symbols to do it, but most fonts have proper glyphs for this and I'd prefer to use the real thing. Any clues? I've drawn a blank with my usual sources.

(crossposted to my own journal and other likely places on LJ)