Celedons are golden automatons made by Hephaestus for Apollo. They are used as backup singers who play with Apollo. This is due to their natural musical abilities which are known to produce extreme reactions from mortals that hear them. For example, in Percy Jackson and the Singer of Apollo it is warned that they could cause mortals to riot depending on the lyrics in their song and one celedon was able to cause high temperatures when she sang of fire. In the same book, Percy uses wax to weaken their influence over him. At least one of them was capable of turning into a flying mechanical bird. They are also known to have strong ambitions for fame and unless tethered, will seek fame and glory for their talents which may cause havoc due to afore mentioned abilities.
Celedons are first mentioned by Apollo when he shows up asking Percy Jackson to find his fourth celedon for a concert that he is holding on Olympus. We are told that the golden lady went rogue on Apollo and has apparently wandered off into Times Square. There are very good at music and people love them. Apollo thinks they are sexy.