[6] The system is unusual in the low ratio between the main two components and shortness of the orbital period.

R Canis Majoris, in Annie Jump Cannon's Second catalogue of variable stars, published in 1907.

This has led to the suggestion that there exists a third non-eclipsing body in the system whose gravitational pull is responsible for these variations.

The secondary star, originally the more massive of the two, has evolved away from the main sequence, expanded, and exceeded its Roche lobe.

The secondary now has a very reduced mass relative to its temperature and luminosity, while the primary has gained helium-rich material and become hotter and more luminous.