View Full Version : Metallicity measures

Tom Mazanec
2018-Feb-01, 03:41 PM
I always seem to see metallicities measured as [Fe/H]. Can other elements be used? Would these measurements be close to that of iron?

2018-Feb-01, 04:59 PM
That convention grew up because iron is fairly easy to estimate in the spectra of stars not too different from the Sun, and such stars have similar patterns of elemental ratios. However, as we look at stars from different environments (including very old stars formed when the Galaxy's abundance pattern was different), different elements have quite different abundance patterns from what we became accustomed to locally. For example, some of the extremely metal-poor stars (with [Fe/H]<-5, which means less than 10-5 times the Sun's already modest iron abundance) are not nearly as poor in carbon or nitrogen. There are also changes in the fraction of elements produced through rapid or slow addition of neutrons to the nuclei (r- and s-process species), which must be telling us about the early star-formation and supernova history of the part the Galaxy these stars were formed in.

2018-Feb-02, 04:32 PM
This applet doesn't directly address your question re. specific metallicity ratios, but it will help you put the metals content of a given stellar object as it shows up in the H-R diagram: