University of Wisconsin

Space Astronomy Laboratory



OBJECT: AO Cassiopeiae (AO-CAS)
Other names: HD 1337, Pearce's Star
ID # 3301

UW Astronomer: Geoff Fox

Cassiopeiae is a bright northern circumpolar constellation located high in the sky in the winter. AO-Cas, located about 7,000 light years away in the constellation of Cassiopeiae, the Queen, is a binary system consisting of young (O) stars. The system has a temperature of 28,000 oK. The stars' diameters are 23 times and 15 times the diameter of our Sun, with masses corresponding to 32 times and 30 times the mass of our Sun. AO-Cas is one of the most massive star systems known and is among the most luminous objects in our Galaxy, with the larger star radiating 300,000 times more our Sun! The stars are separated by 15 million miles, but their surfaces are almost touching. The time is takes for these stars to orbit around each other is about 3.5 days, and their orbits are nearly circular.