At magnitude 1.86, Avior (or ε Car) is the third brightest star in Carina, the keel of the ship Argo Navis. Not quite 60 degrees below the celestial equator, it is out of sight in most of the northern hemisphere where most traditional astronomy has been done. Too far south to have received a classical Greek or Arabic name, "Avior" was assigned by Her Majesty's Nautical Almanac Office in the late 1930s, during the creation of a navigational almanac for the Royal Air Force.
Avior is perhaps best known as the brightest member of the "False Cross" which includes ι Ca, δ Vel, and κ Vel; and is sometimes confused with Crux, the Southern Cross.
Components
Some 630 light years away, Avior is a double star, but has never been resolved into two visible components. Separated by only 0.02", we know of Avior's duplicity only because two stars are simultaneously visible in its spectrum. One star is a hot blue class B2 hydrogen-fusing main-sequence star, the other a dying class K3 orange giant. Together they shine with a luminosity 6000 times the Sun's.
It is hard to say which star produces most of the light, however. The blue B star should be brighter of the two, but the color of the star suggests the opposite. Theory shows that the B dwarf should have a mass of some 7 suns. Since high mass stars evolve faster as a result of much greater fuel consumption, the orange giant must once have been even more massive.
The stars may eclipse each other, producing a 30% dip in brightness every 2.2 years. If so, they would be only about 4 AU apart, less than the distance of Jupiter from the Sun. The components are too far apart for mass transfer to take place.
Planets could hardly orbit either star. If one were to orbit the pair, it would have to be twice as far as Pluto from the Sun to receive our level of daylight, and perhaps four times as far to keep from being fried by the infrared heat and ultraviolet from the stunning duo at the center of the orbit. No one, of course, yet knows if such planets exist. If nothing else, Avior presents a great opportunity for study.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]