Alpha Camelopardalis

Alpha Camelopardalis is actually the third-brightest star in Camelopardalis, the Giraffe, a faint constellation gracing far northern skies. The constellation's brightest stars are only fourth magnitude; they are β Cam (4.03), HR 1035 (4.21), α Cam (4.29), and γ Cam (4.63).

Properties and Evolution

α Cam is a rare class O9.5 Ia blue supergiant. It seems faint mostly because it is far away, but also because it is dimmed nearly a full magnitude by interstellar dust. The star is so far away that we have no actual distance measurement for it. For many years the star has been thought to be a "runaway" from the Camelopardalis OB1 association, a huge collection of dispersing young O and B stars that were all born together. α Cam has also been thought to be a runaway from the associated cluster NGC 1502, possibly expelled by interactions with other stars, or by the supernova explosion of a massive companion.

The estimated distance of Cam OB1 and of NGC 1502 is about 3200 light years. If we adopt this as the distance to α Cam, its luminosity would be a magnificent 530,000 times the Sun's (corrected for ultraviolet light emission and interstellar dust). This is almost exactly what we would expect from such a supergiant, implying that our adopted distance is pretty close to the mark. This magnificent star, which has a mass between 25 and 30 times the Sun's, will someday explode as a supernova. At the moment, it is losing matter through a powerful stellar wind, at a rate of six millionths of a solar mass per year, consistent with its great luminosity and coming fate.

Newer observations show that α Cam is not moving directly away from NGC 1502. Not only is its motion through space in the wrong direction, but a wake that the star is leaving as it passes through a local interstellar cloud points the wrong way. (The cloud might have its own confusing motion, however.) More recent observations suggest that the Cam OB1 association might not even be real. Clearly, more research needs to be done.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]