  A low mass star usually experiences stratification and abundance anomalies
during its evolution. A 0.95 solar mass star with a metallicity Z = 0.004 is
followed from the main-sequence to the Horizontal Branch (HB). On the
main-sequence the larger effects of stratification may come from accretion as
was suggested in relation to metallicity and planet formation. As it evolves
through the giant branch, stratification appears around the hydrogen burning
shell. It may create hydrodynamic instabilities and be related to abundance
anomalies on the giant branch. After the He flash the star evolves to the HB.
If it loses enough mass, it ends up a hot HB star (or in the field an sdB star)
with effective temperatures larger than 11000 K. All sdB stars are observed to
have an approximately solar iron abundance whatever their original metallicity,
implying overabundances by factors of up to 100. So should the 0.95 solar mass
star. How its internal hydrodynamic properties on the main sequence may
influence its fate on the HB is currently uncertain.

Solar and Stellar Astrophysics