Severus Alexander AR Denarius. 

IMP SEV ALEXAND AVG, laureate, draped and cuirassed bust right.
PM TR P COS, Mars standing half left, holding branch and 
spear. 
Star in left field. 
RIC 262; RSC 201a; Sear 7890.

Courtesy of TimeLine Auctions (www.timelineauctions.com), Feb, 2013