3D1D hydro-nucleosynthesis simulations of rapidly accreting white dwarfs and the anomalous abundances of very metal-poor stars

The most Fe-poor stars are C enhanced. C-enhanced metal-poor (CEMP) stars come in two flavours. CEMP-no stars are only enhanced in C and a few other light elements, while many CEMP stars are enhanced by neutron-capture elements. CEMP stars trace the formation of the first structure and the first stars. Here we present a new scenario to explain the observed abundances of CEMP stars that are enhanced in both Ba and Eu, commonly considered slow and rapid neutron-capture process elements respectively. In rapidly accreting white dwarfs at low Z He-shell flash convection with H ingestion give rise to a hydrodynamic nuclear production environment an intermediate time-scale neutron-capture process, or i process operates. It produces both Ba and Eu, but not some of the bonafide r-process elements such as Ir and Os. We model this process through 3D hydrodynamic convection simulations with 1D multi-zone post-processing. The abundance predictions reproduce the observed abundances of CEMP-r/s star CS31062-050 very well all the way from C to Pb. We thus reclassify this star as a CEMP-i star, which was likely polluted by a rapidly accreting WD. We plan to analyse all other known CEMP-r/s stars in terms of our 3D1D hydro-nucleosynthesis simulations. Presentation at AstroNWxSW meeting at UBC, Vancouver, BC, Canada, November 3rd, 2018.