Probing the formation of the first low-mass stars with stellar archaeology

We investigate the conditions under which the first low- mass stars formed in the Universe by confronting theoretical predictions governing the transition from massive Population III to lowmass Population II stars with recent observational C and/ or O abundance data of metal- poor Galactic stars. We introduce a new ` observer- friendly' function, the transition discriminant D-trans, which provides empirical constraints as well as a powerful comparison between the currently available data of metal- poor halo stars and theoretical predictions of the formation of the first low- mass stars ( less than or similar to 1M circle dot). Specifically, we compare the empirical stellar results with the theory that fine- structure lines of C and O dominate the transition from Population III to Population II in the early Universe. We find the currently available data for halo stars as well as for dwarf spheroidal ( dSph) galaxies and globular clusters to be consistent with this theory. An explanation for the observed lack of metal- poor stars in dSph galaxies and globular clusters is also suggested. Finally, we predict that any star to be found with [ Fe/ H] less than or similar to - 4 should have enhanced C and/ or O abundances. The high C and O abundances of the two most iron- poor stars are in line with our prediction.