Why would two close stars have similar metallicity, but different color?

[quarky2001]

This is the exact question:

Stars in a globular cluster are observed to be one magnitude redder (in terms of B-V color, so the color excess E_(B-V) = 1, and extinction in the V band is 3.1) than other nearby stars having similar metallicity. What causes this?


I'm aware of why two stars might have different metallicity - one being older than the other means it incorporated less iron from the ISM during formation. I don't understand why two stars with the same metallicity, and from the same part of a galaxy, would have significantly different color.

Does it just relate to their size and temperature? If so, I'm not sure why the question would bother to invoke the concept of metallicity, except to ask that we ignore it.

 

[zhermes]

Does it just relate to their size and temperature? If so, I'm not sure why the question would bother to invoke the concept of metallicity, except to ask that we ignore it.

Yes.

 

[quarky2001]

Thanks for the reply - I asked the professor today. He just worded the question funny. By "nearby", he meant that the globular cluster's stars were redder than other stars of similar metallicity "nearby" the solar system, not nearby other stars in the globular cluster!