Most red supergiants have metal contents similar to or greater than the Sun, although there are exceptions, but in any case, the metallicity of a star is a reflection of both its age and the environment in which it formed. Pop II red supergiants (both halo and old thick disk stars...very rare) will have lower than solar Fe/H ratios because they formed in metal poor nebulae, and also at a time when metal enrichment of the galaxy's gases wasn't as great as it became in later epochs. Most of these stars are of low mass and should really be classed more as AGB or Horizontal Branch stars, which are bloated red giants in a late stage of evolution. Much like the star Mira...technically not a supergiant (based on mass), but super sized nevertheless (450-500 solar radii).
Your more classical supergiants, young Pop I stars, will have Fe/H ratios similar to or greater than the Sun, because they formed in metal rich gases. There are exceptions to this rule, as there always is.
I can't remember the actual Fe/H ratio of Antares, off hand, but it would most likely be greater than the Sun's, considering the star is only about 8 million years old and part of the Centaurus-Scorpius OB1 Complex. Most of the stars there have metallicities x2 solar or greater.
Last edited by renormalised; 11-04-2010 at 12:26 PM.
Metallicity of red supergiants
