Analysing the chemical fingerprints left by the first stars: chemical abundances in the oldest stars

• Applicant: Dr. Cristina Chiappini Moraes Leite
• Subject Area: Astrophysics and Astronomy
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283705981

Soon after the Big Bang, the appearance of the first stellar generations (first stars) drastically changed the course of the history of the Universe by enriching the primordial gas with elements heavier than helium through both stellar winds and supernova explosions. Today these stars are long dead and even though next generation facilities will push the observational frontier to extremely high redshifts, with the aim of discovering the first galaxies, the first stars will still lie beyond reach. Thus, the only way to constrain our theoretical understanding of the formation of the first stars is to search for their imprints left in the oldest, still surviving, stars in our own backyard: the Milky Way and its satellites. The strategy taken so far by the Galactic Archaeology community has been to look for the mostmetal-poor stars in resolved stellar populations, and directly compare their individual chemical abundances with the outputs of the different stellar models proposed for the first stars. The two underlying assumptions are a) that the most metal-poor stars are also the oldest ones, and b) that in their atmospheres these stars have preserved a record of the gas from which they were born, which was enriched by only one/ a few first supernovae. The time is ripe to replace thisvaluable but simplistic approach with a far more sophisticated one, which can potentially lead to a breakthrough in this field. We will compute Smoothed-Particle Hydrodynamics (SPH) simulations of the earliest phases of the galaxy assembly, in a cosmological framework, including detailed chemistry. The novelty of our approach is that the large parameter space given by alternative nucleosynthesis scenarios will be explored with an inhomogeneous chemical evolution model,and only the best nucleosynthesis will be implemented in the SPH simulation. Currently, there is no cosmological simulation with the level of chemical detail the present project will deliver.With this tool we will, for the first time, explore the unique information contained in the abundance scatter of key abundance ratios, in three different environments hosting old stars, which have undergone different starformation histories: the halo, the bulge, and the oldest (thick) disk stars. Our ultimate goal is to provide constraints for the nature of the first stars (their mass spectrum, their chemical and energetic outputs). Our theoretical predictions will bedirectly compared to the large amount of data now available for halo stars with iron abundance below 1/1000th solar. In addition, the thick disk and bulge have become the focus of the observational efforts only very recently, and these datasets are still an unexplored gold mine for finding the imprints of the first stars is the study of the of key abundance ratios of the oldest stars in our MW (Chiappini et al. 2011, Nature). This project is key in preparing future large campaigns such 4MOST.

• DFG Programme: Research Grants
• International Connection: Brazil, Switzerland, United Kingdom
• Cooperation Partners: Beatriz Barbuy, Ph.D.; Professor Dr. Norbert Christlieb; Professor Raphael Hirschi, Ph.D.; Professor Georges Meynet, Ph.D.; Cecilia Scannapieco, Ph.D.