The chemical complexity that we observe on Earth and in the Solar System was built up through the nucleosynthesis products of many generations of stars starting from the primordial composition, that included only hydrogen and helium isotopes and traces of lithium. The very first generation of stars have been formed out of gas with this primordial composition. The massive stars of this generation exploded as supernovae polluted the gas with elements heavier than He. The difficulty of cooling a gas contracting cloud of primordial composition may result in the fact that low mass stars, the have a very long lifetime and would still be observable today, were not formed in the first generation of stars.
The theory is still unable to provide a clear-cut answer. The main questions we want to tackle in this study are :
- Were long-lived low mass stars formed in the first generation of stars ?
- If not what is the critical metal content above which low mass stars begin to form ?
- What was the mass distribution of the first generation of stars and their photon output ? Were they sufficient to reionise the Universe ?
The activity focuses on the search and chemical analysis of stars of extremely low metallicity. The chemical composition of such stars provides indirect information on the masses of the previous generations of stars. The most metal-poor object known in the Universe, star SDSS J102915.14+172927.9, with a metal content less than 1/10000 that of the Sun was discovered at Observatoire de Paris.
