A short period O star binary in the Large Magellanic Cloud

The period of this binary, LH54-425, is 2.25 days. The stars have around 62 and 37 solar masses and the mean orbital velocity is 1.1 million mph, making it one of the most extreme main sequence binaries so far identified.

NGC 3603 A1 is a galactic example of a pair whose masses have been measured dynamically, as it is a double-lined eclipsing binary. The masses are 116 and 89 solar masses and the period 3.77 days. These are Wolf-Rayet stars, a classification which includes the most massive stars, and is defined by the exclusive presence of emission lines in their spectra. They originate as O stars on the zero age main sequence (ZAMS) but are evolving so quickly and undergoing such extreme mass loss that they cannot be thought of or classified even as O stars more massive than 03V. Near-infrared spectra of point 2MASS sources with IRAS counterparts but no optical detection can also show emission lines due to dense circumstellar material.

Update: A hierarchical triple consisting only of O stars is known, HD 150136, which has been studied interferometrically using the PIONIER combiner at VLT. The dynamical masses are 63, 40 and 33 solar masses.

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