27 Canis Majoris

27 Canis Majoris, also known by its variable star designation EW Canis Majoris, is a binary star system in the northern part of the constellation Canis Major. It lies roughly 1,700 light-years from the Sun and is visible to the naked eye as a blue-white star of the 4th magnitude. The system is moving away from Earth at a heliocentric radial velocity of 16 km/s.

The two stars were first distinguished as separate objects by W. S. Finsen in 1953, and the gap between them has been increasing ever since. They orbit each other with a period of about 119 years, an eccentricity of 0.7, and a semimajor axis of 0.178 arcseconds. The primary star, component A, has a magnitude of 4.92 and is classified as a Be star of type B3 IIIpe. It spins rapidly, with a projected rotational velocity of 290 km/s, compared to a critical velocity of 389 km/s.

This star is also a Beta Cephei variable, pulsating with a period of 0.0919 days and an amplitude of 0.0080 in magnitude. The secondary, component B, has a magnitude of 5.39 and is classified as a Gamma Cassiopeiae type variable star. Because of this variability, the overall brightness of the system fluctuates between magnitudes +4.42 and +4.82.