WR 22, also known as V429 Carinae or HR 4188, is an eclipsing binary star system in the constellation Carina. The system contains a Wolf-Rayet (WR) star that is one of the most massive and most luminous stars known, and is also a bright X-ray source due to colliding winds with a less massive O class companion. Its eclipsing nature and apparent magnitude make it very useful for constraining the properties of luminous hydrogen-rich WR stars. System The WR 22 system contains two massive stars which orbit every 80 days. The spectrum and luminosity are dominated by the primary, which has a spectral type of WN7h, indicating that it is a WR star on the nitrogen sequence, but also with hydrogen lines in its spectrum. The secondary is an O9 star which appears to have the spectral luminosity class of a giant star, but the brightness of a main sequence star. There is a shallow eclipse detectable when the primary passes in front of the secondary, which would be classed as the secondary eclipse. However, no primary eclipse is detected, which is believed to be due to the eccentricity of the system placing the stars further apart when the primary eclipse would occur. The separation of the stars varies from over to less than . This strongly constrains the possible inclinations of the system. Properties The masses of the two stars can be determined fairly accurately because WR 22 is an eclipsing binary. It is one of the most massive star systems measured in this way rather than by assumptions about stellar evolution. Despite this, the dynamical masses derived from orbital fitting vary from over to less than for the primary and about for the secondary. The spectroscopic mass of the primary has been calculated at or . The temperature of both stars is high, but somewhat poorly defined. The Wolf Rayet primary has a temperature of approximately 44,700 K derived from a model atmosphere fitting of the spectrum, and the secondary is assumed to have a temperature of 33,000 K which is typical for a star of its spectral type. The brightness of the two stars cannot be measured separately, but the luminosity ratio can be calculated. The total system absolute magnitude, for a distance of 2.7 kpc and extinction of 1.12 magnitudes, is −6.85. The luminosities calculated for a similar distance are and . Evolution High mass hydrogen-rich