The i-process yields of rapidly accreting white dwarfs from multicycle He-shell flash stellar evolution models with mixing parametrizations from 3D hydrodynamics simulations. Issue 3 (12th July 2019)

• Record Type: Journal Article
• Authors: Denissenkov, Pavel A; Herwig, Falk; Woodward, Paul; Andrassy, Robert; Pignatari, Marco; Jones, Samuel
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 488:Issue 3(2019)
• Page Start: 4258
• Page End: 4270
• Publication Date: 2019-07-12
• Subjects: Sun: abundances -- Galaxy: abundances -- binaries: close -- stars: interiors -- stars: white dwarfs -- nuclear reactions, nucleosynthesis, abundances; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz1921
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We have modelled the multicycle evolution of rapidly accreting CO white dwarfs (RAWDs) with stable H burning intermittent with strong He-shell flashes on their surfaces for 0.7 ≤ M RAWD /M⊙ ≤ 0.75 and [Fe/H] ranging from 0 to −2.6. We have also computed the i-process nucleosynthesis yields for these models. The i process occurs when convection driven by the He-shell flash ingests protons from the accreted H-rich surface layer, which results in maximum neutron densities N n, max ≈ 10 13 –10 15 cm −3 . The H-ingestion rate and the convective boundary mixing (CBM) parameter f top adopted in the one-dimensional nucleosynthesis and stellar evolution models are constrained through three-dimensional (3D) hydrodynamic simulations. The mass ingestion rate and, for the first time, the scaling laws for the CBM parameter f top have been determined from 3D hydrodynamic simulations. We confirm our previous result that the high-metallicity RAWDs have a low mass retention efficiency ($\eta \lesssim 10{{\ \rm per\ cent}}$ ). A new result is that RAWDs with [Fe/H] $\lesssim -2$ have $\eta \gtrsim 20{{\ \rm per\ cent}}$ ; therefore, their masses may reach the Chandrasekhar limit and they may eventually explode as SNeIa. This result and the good fits of the i-process yields from the metal-poor RAWDs to the observed chemical composition of the CEMP-r/s stars suggest that some of the present-day CEMP-r/s stars could be former distant members of triple systems, orbiting close binary systems with RAWDs that may have later exploded as SNeIa.