arXiv subjects

Giovanni Leidi

Publications and source records attributed to Giovanni Leidi.

3 recordsLinked to original sources

arXiv2026

Continuous mass ablation of planets engulfed in stellar envelopes

Most stars host short-period planets that are expected to be engulfed during post-main-sequence expansion. The dissolution of engulfed planets has been proposed as a possible mechanism for producing stars enriched in lithium and refractory elements. We perform three-dimensional hydrodynamical simulations of a Jupiter-like planet engulfed within a stellar envelope using the Seven-League Hydro code. Unlike previous studies that represent the planet as a point mass or rigid sphere, we adopt a wind-tunnel setup that resolves the planet's gaseous structure. We find that a continuous mass-ablation process operates during planetary engulfment, contrary to the common assumption that destruction occurs at a specific depth due to ram pressure, tidal forces, or thermal evaporation. The ablation rate scales nearly linearly with the wind momentum flux and is largely insensitive to the Mach number, consistent with an analytical model based on Kelvin-Helmholtz instability developing at the planetary surface. We define efficiency coefficients for drag and ablation, finding pressure-drag coefficients of 0.44-0.56 and smaller ablation efficiencies of 0.054-0.11. Applying these coefficients to a numerically integrated inspiral through a stellar profile, we find that continuous ablation could lead to complete dissolution of the planet within the convective envelope, producing observable lithium enrichment at the stellar surface. Our results provide prescriptions for drag and mass loss that enable large parameter-space studies of planetary engulfment and suggest that chemical enrichment may occur over a broader range of stellar parameters than previously thought.

astro-ph.SR↗

arXiv2026

Drawing the line between explosion and collapse in electron-capture supernovae -- I. Impact of conductive flame speeds and ignition conditions on the explosion mechanism

Electron-capture supernovae (ECSNe) are commonly thought to result in a collapse to a neutron star. Recent work has shown that a thermonuclear explosion is also a possible outcome. The division between the two regimes has not yet been mapped out. In this study, we investigate the conditions under which the transition from thermonuclear explosion to collapse occurs, and what physical mechanisms drive each outcome. We conducted a parameter study of 56 3D hydrodynamic simulations of ECSN in ONe white dwarfs using a level set based flame model implemented in the Leafs code. We varied both the ignition location and the central density at ignition to determine the conditions of the transition regime. Additionally, we explored two different laminar flame parameterizations and how they impact the simulation outcome. From our parameter study, we find a transition density in the range of $\logρ_c^{ini}=10.0$ and $10.15$ g cm$^{-3}$, depending on the ignition location and utilized laminar flame speed parameterization. Importantly, we find that for sufficiently high central densities, the burned ashes can sink into the core and trap large amounts of neutron-rich material in the bound remnant. In the transition regime between explosion and collapse, we find that the laminar flame speed plays a critical role by suppressing the formation of instabilities and thereby reducing the nuclear energy generation needed to overcome the collapse. We find that a thermonuclear explosion is possible for a wide range of parameters, whereby a more off-center ignition allows for higher central densities to still result in an explosion. Both the conditions at ignition and the flame physics are critical in determining the outcome. Detailed 3D hydrodynamic simulations of the preceding stellar evolution and the ignition process of the thermonuclear flame are necessary to accurately predict the outcome of ECSNe.

astro-ph.SR↗

arXiv2025

Magnetically driven outflows in 3D common-envelope evolution of massive stars

Recent three-dimensional magnetohydrodynamical simulations of the common-envelope interaction revealed the self-consistent formation of bipolar magnetically driven outflows launched from a toroidal structure resembling a circumbinary disk. So far, the dynamical impact of bipolar outflows on the common-envelope phase remains uncertain and we aim to quantify its importance. We illustrate the impact on common-envelope evolution by comparing two simulations -- one with magnetic fields and one without -- using the three-dimensional moving-mesh hydrodynamics code AREPO. We focus on the specific case of a $10 M_\odot$ red supergiant star with a $5 M_\odot$ black hole companion. By the end of the magnetohydrodynamic simulations (after $\sim 1220$ orbits of the core binary system), about $6.4 \%$ of the envelope mass is ejected via the bipolar outflow, contributing to angular momentum extraction from the disk structure and core binary. The resulting enhanced torques reduce the final orbital separation by about $24 \%$ compared to the hydrodynamical scenario, while the overall envelope ejection remains dominated by recombination-driven equatorial winds. We analyze field amplification and outflow launching mechanisms, confirming consistency with earlier studies: magnetic fields are amplified by shear flows, and outflows are launched by a magneto-centrifugal process, supported by local shocks and magnetic pressure gradients. These outflows originate from $\sim 1.1$ times the orbital separation. We conclude that the magnetically driven outflows and their role in the dynamical interaction are a universal aspect, and we further propose an adaptation of the $α_\mathrm{CE}$-formalism by adjusting the final orbital energy with a factor of $1+ M_\mathrm{out}/μ$, where $M_\mathrm{out}$ is the mass ejected through the outflows and $μ$ the reduced mass of the core binary. (abridged)

astro-ph.SR↗