Blogtrek

K9 stars

I purchased a Sky and Telescope magazine today and read an article about the brightest red dwarf star in our sky, a rather obscure star named Lacaille 8760. It has a spectral type of M0. What does that mean? Astronomers long ago classified stars according to the spectrum that their light produce when passed through a prism. The classifications are now mostly by temperature, and some rearranging of the types were needed as more facts were discovered about stars. Today the sequence from hottest to coolest is O, B, A, F, G, K, M, with L and T added recently for brown dwarfs. A red dwarf star is of type M; it is cool as far as stars go but still a star. The types are subdivided into tenths; e.g., an F9 is hotter than a G2 is hotter than a G8 and so forth. Our sun is a G2 star.

The faintest red dwarf is interesting as there is a natural boundary at the faint end - between star and non-star. But there is no such boundary at the bright end. So saying the brightest red dwarf tends to make it a middle of the pack type of star. In fact, the next type up from M0 is K9. Now this reminds me of the Dog Star Sirius.

Sirius is the brightest star in the sky. It is bluish white and astronomers say that its spectral type is A1. But since it is the Dog Star I think the type should be K9 instead. Indeed, some legends of the past had Sirius as being a red star. I tried looking up K9 and Sirius in Google, and got an article about a K9 police dog named Sirius who died when the World Trade Center collapsed on 9/11. He was the K9 star of the day.

So what's the type of Sirius? Well, given that it's the Dog Star, I would say that its type is K9.