The path to metallicity: synthesis of CNO elements in standard BBN

Synthesis of CNO elements in standard BBN

Did the Universe start at Zero Metallicity?

Standard Big Bang nucleosynthesis predicts an essentially zero primordial metallicity. I speculate on possible metal (i.e. nucleon number A ≥ 12) production in scenarios of inhomogeneous Big Bang nucleosynthesis. It is conceivable, though not necessarily probable, that some primordial metallicity is synthesized if a small fraction of all cosmic baryons reside in very high-density regions. Such ...

Mass loss and very low-metallicity stars

Mass loss plays a dominant role in the evolution of massive stars at solar metallicity. After discussing different mass loss mechanisms and their metallicity dependence, we present the possibility of strong mass loss at very low metallicity. Our models at Z = 10−8 show that stars more massive than about 60 M⊙ may lose a significant fraction of their initial mass in the red supergiant phase. Thi...

On Using the Cmd Morphology of M67 to Test Solar Abundances

The open cluster M67 has solar metallicity and an age of about 4 Gyr. The turn-off mass is close to the minimum mass for which solar metallicity stars develop a convective core during main sequence evolution as a result of the development of hydrogen burning through the CNO-cycle. The morphology of the color-magnitude-diagram (CMD) of M67 around the turn-off shows a clear hook-like feature, dir...

Very low metallicity massive star models: Pre–SN evolution and primary nitrogen production

Context. Precise measurements of surface abundances of extremely low metallicity stars have recently been obtained and provide new constraints for the stellar evolution models. Aims. Compute stellar evolution models in order to explain the surface abundances observed, in particular of nitrogen. Methods. Two series of models were computed. The first series consists of 20 M⊙ models with varying i...