Plaskett's Star (V640 Mon)
Plaskett's Star (V640 Mon) is a spectroscopic binary,
of visual magnitude 6.05, lying about 5,000 light-years away in the constellation Monoceros. It is named after John Plaskett who, in 1922, discovered the system's great claim to fame: it was at the
time, and until recently, the most massive binary star system known. According
to a recent estimate, the two components, both blue
supergiants of type O8, are respectively
51 and 43 times more massive than the Sun. They orbit around their common
center of gravity with a period of just 14.4 days and are exchanging material.
Plaskett's Star is found just east of 13 Monocerotis and is very probably
a member of NGC 2244, which in turn is part of the Rosette Cluster.