Metal-poor stars in the Milky Way halo: relics from the very beginning of chemical evolution

The chemical element abundance pattern measured in a star's atmosphere is a record of the chemical enrichment history of the environment in which it formed.  This "fossil imprint" contains key information regarding star formation histories, nucleosynthesis events and galaxy formation processes.  In the context of this talk, the abundance patterns of extremely metal-poor stars in our Galaxy's halo provide constraints on the nature of the very first stars to form after the Big Bang and their supernova explosions.  I will describe the high-resolution spectroscopic analysis of extremely metal-poor stars newly discovered by the SkyMapper Survey, including the most chemically primitive star yet observed in which the presence of only four elements could be detected.

The abundance patterns of halo stars can also be used to constrain nucleosynthesis yields and models of chemical evolution.  The production and chemical evolution of phosphorus, a building block of life, has been very little studied until recently.  I will present the first measures of phosphorus abundances in metal-poor stars and show that the current theoretical yields of phosphorus production in massive stars must be increased by a factor of 2-3.  With these new phosphorus measures, the full chemical evolution of all the building blocks of life (C-N-O-P-S) can be modeled for the first time.

Speaker: Heather Jacobson, MIT