A star disk for a rotor of an externally excited synchronous machine, having a central disk body, from which multiple webs extend radially, at the ends of which an end plate is provided each time, so that between the disk body and the respective end plate there is formed a winding groove, being bounded by the web forming the groove bottom and laterally by the disk body and the end plate, forming groove flanks, and serving to contain a conductor winding led around the web and formed from a conductor wire which is wound in multiple layers, wherein the web is provided with flutes running in the winding direction and serving to contain a respective conductor wire segment, there being provided at least one additional flute on a groove flank at least on one side of the web.