145 G. Canis Majoris (HD 56577) is a single K giant or supergiant star in the southern constellation of Canis Major. This star is Gould's 145th of Canis Major in his Uranometria Argentina. [1] Kostjuk erroneously lists it as simply "145 CMa". SIMBAD follows this error in its object query result as "* 145 CMa – Star".[2]
The properties and evolutionary state of 145 G. CMa are disputed, it being classed either as a young massive supergiant or a somewhat older and less massive giant. It has been given two MK spectral classifications: K3Ib (corresponding to a supergiant) and K4III (corresponding to a giant). Tezzlaff et al. gives a large mass of and a young age of 35million years, while Earle Luck gives a smaller mass of and a higher age of 1.05billion years. The effective temperature of the star is of 3,980K, which gives it a orange hue typical of K-type stars.[3]
Based on the assumption that it is a supergiant, 145 CMa has been given a large radius of and a luminosity of . Assuming it is a giant, Earle Luck give a much lower luminosity of with a corresponding radius of . By the distance implied by its Gaia DR2 parallax, it would have a luminosity of, rather high for a giant. An older measurement based on the Hipparcos distance of 435pc give a lower luminosity of .
The star is one component of a close double, the other being HD 56578 which on its own would be a faint naked-eye star. The two are separated by . The two stars appear to be unrelated and the close alignment accidental, with HD 56578 being a much closer and less luminous Am star.