Description
SNe, Hypernovae, GRB, kilonova, at high redshift, what they tell us about stellar evolution in metal-poor environments? : the C-rich Damped Lyman alpha systems, any relation or not with CEMP stars? CEMP stars in metal poor environments such as dwarf galaxies. Do we need first stars for reionization? Observation of infall, outflows in galaxies? Supermassive BH at high redshifts.
I will review the current standard model of how the first stars formed at the end of the cosmic dark ages, and how they impacted the subsequent history of the universe. The Population III formation process is intricately linked to the particle physics nature of dark matter, and can thus serve as an astrophysical laboratory to probe this elusive component of the cosmic matter-energy content. I...
The accretion disks around Population III (PopIII) stars are known to fragment under fast H$_2$ cooling.
Based on the vertical disk structure, we study the optical depth for H$_2$ line cooling under an accretion disk geometry. With the physically motivated optical depth, we find that cooling in the inner disk with $r < 10 {\rm\ AU}$ is attenuated significantly due to the large surface...
It is well known that the adiabatic index of H2 varies as its rovibrational modes are excited as a function of temperature. For the formation of the first stars at redshifts 20 and above, this variation can be significant because the primordial molecular clouds where the first stars form and the material present in accretion shocks near the first protostars can reach high temperatures where...
As of now, the initial mass function (IMF) of metal-free stars is one of the key unsolved problems in the early Universe. Of particular interest is whether there are low-mass population III (Pop III) stars that survive until today. To determine how many such stars we should find in the Milky Way, we model Pop III star formation and feedback in the progenitors of Milky Way-like haloes. Assuming...
Stellar nucleosynthesis defines a sequence of abundances: - pure products of H-burning; - pure products of He-burning; - products of He-burning mixed into the H-burning region (class 2); - products of class 2 mixed in He-burning (class 3); - products of class 3 again mixed in H-burning zone (class 4). CEMP-no stars with enough observed data are distributed in classes 2, 3 and 4. Spinstars...
The study of the long-dead early generations of massive stars is crucial in order to obtain a complete picture of the chemical evolution of the Universe. The nature of these stars can be inferred indirectly by investigating the origin of the low-mass extremely metal-poor stars observed in our neighborhood, some of which are almost as old as the Universe. The material forming these low-mass...
Mass loss is expected to be very low at very low metallicities, even more for the first generations of stars. A lower mass loss induces a lower angular momentum lost during the main sequence, resulting in faster rotators. As the surface velocity increases, due to internal angular momentum transport from the core to the surface, the first stars reach critical velocity at their surface way...
Understanding the nature of the first stars is essential to decipher the chemical abundance patterns in the most iron-poor CEMP stars. Due to their zero-metallicity nature, Pop III stars were structurally quite different than stars of higher metallicity. Namely, interactions between H- and He-burning layers have been recorded in the literature for both rotating and non-rotating stellar models....
Most C-enhanced metal poor stars show substantial enhancements of heavy n-capture elements, mostly of second-peak elements such as Ba, La and Eu. We report on a comprehensive simulation program involving 3D hydrodynamic simulations, 1D stellar evolution and nucleosynthesis simulations, galactic chemical evolution simulations as well as novel approaches to neutron-capture nucleosynthesis...
Understanding the nature of the first stars and their explosive deaths is key to understanding the early universe and the evolution of high-redshift galaxies. With new facilities such as JWST we may soon have the first observations of the earliest stellar populations, but to understand these observations we will require detailed theoretical models. Using the Geneva stellar evolution code, we...
Models of zero metallicity and extremely metal-poor stars show that they evolve differently to their more metal-rich counterparts. In particular they suffer violent proton-ingestion episodes (PIEs) that lead to extreme carbon enrichment at the surface. The fresh carbon has a fundamental effect on their further evolution, and can be transferred to binary companions, producing CEMP stars. As...
Theoretical investigations have long indicated that supernovae of the first stars would explode in an asymmetric fashion, mainly driven by their fast rotations. However, insufficient observational evidence has prevented in-depth studies. Ultra metal-poor stars ([Fe/H]<-5) encode information about their First progenitor star, such as the explosion mechanism, through the relative...
Large observation campaigns of metal-poor stars in Galactic halo and dwarf galaxies have revealed that there are stars with higher carbon abundance relative to the solar one ([C/Fe] > 0.7; carbon-enhanced metal-poor [CEMP] stars). It has been considered that long-lived or low-mass CEMP stars form through fragmentation of their parent clouds induced by gas cooling of carbon grains. Carbon...
JWST will uncover a vast population of low-luminosity galaxies at Cosmic Dawn that is responsible for most of reionization. We present predictions on this high-redshift population, focusing on their physical properties and role during reionization. We use two suites of high-resolution cosmological simulations -- the Renaissance Simulations and the Tempest Simulations -- that sample different...
The Local Group holds the living fossils of the first stars and galaxies. Still, these precious relics are extremely rare, and hence very difficult to catch. In this talk I will discuss the most recent observational findings and theoretical predictions for present-day metal-poor stars, underlying the links with the properties of the first stars. In particular, I will show that chemical...
We investigate the star formation histories and chemical evolution of isolated analogs of Local Group untra-faint dwarf galaxies (UFDs) and gas-rich, low-mass dwarfs. We perform a suite of cosmological hydrodynamic zoom-in simulations to follow their evolution from the era of the first generation of stars down to z = 0. We confirm that reionization, combined with supernova (SN) feedback, is...
Cosmic reionization corresponds to the period in the history of the Universe during which the predominantly neutral intergalactic medium was ionised by the emergence of the first luminous sources. I will first briefly describe what we know about cosmic reionisation from observations, and explain the actual limitations/challenges of state-of-the art simulations of this phenomenon.
In...
The carbon enhanced metal poor (CEMP) stars are of immense importance as they likely carry signatures of first few generations of stars in the Universe. At the observational front there has been a tremendous advance in our ours understanding of CEMP stars, and recently theoretical studies have provided new insights. Nevertheless, the origin of CEMP stars, and in particular that of their...
From low metallicity stars and the presence of radioactive isotopes in deep-sea sediments we know that the main r-process, producing the heaviest elements, is a rare event. The question remains whether neutron star mergers, via GW170817 the only proven r-process site, are the only contributors or also (a rare class of) supernovae, hypernovae/collapsars, as well as neutron star - black hole...
