Watch List notes:

Lydia, Philadelphia. Gaius Caligula. A.D. 37-41. AE 17 (17.2 mm, 3.66 g, 12 h). Gaios Ioulios Diodotos, magistrate. ΓΑΙΟΣ ΚΑΙ ΑΡ, bare head of Caligula right, star behind / ΦΙΛΑΔΕΛΦΕΩΝ ΓΑΙΟΣ ΙΟΥΛΙΟΣ ΔΙΟΔΟΤΟ , laureate busts of the Dioscuri, jugate, right. RPC I, 3020. Fine, rough surfaces and edges. Rare variety.

RPC lists ten specimens but only one with the star on the obverse, there are a few more to be found at ACSearch. This variety is certainly the rarer form of an already rare type.