  Hydrodynamical cosmological simulations predict that the metal-free
Population III (Pop III) stars were likely very massive and, therefore,
short-lived. However, they left their chemical imprint on their descendants,
which can also have masses $ < 0.8 \mathrm {M_{\odot}}$ and still be alive
today. The Milky Way stellar halo is one of the oldest and most metal-poor
component of the Local Group and a peculiar class of stars, the so-called
Carbon-Enhanced Metal-Poor (CEMP-no) stars, seem to be directly related to Pop
III stars. We aim at revealing if all metal-poor halo stars are true
second-generation stars or if they have also been enriched by the subsequent
generations of normal (Pop II) stars. For this purpose, we compare the measured
carbon and iron abundances of the metal-poor halo stars with the ones predicted
by our simple parametric model, varying the pollution level from Pop III and
normal stars. We find that only the most C-enhanced and Fe-poor stars enclose
in their photospheres the pure imprint of Pop III stars, while, as the [C/Fe]
decreases, the probability of being also polluted by normal Pop II stars
increases.
