arXiv subjects

U. Lebreuilly

Publications and source records attributed to U. Lebreuilly.

22 records · Page 2Linked to original sources

arXiv2023

Synthetic populations of protoplanetary disks. Impact of magnetic fields and radiative transfer

Protostellar disks are the product of angular momentum conservation during the protostellar collapse. Understanding their formation is crucial because they are the birthplace of planets and because their formation is tightly related to star formation. Unfortunately, the initial properties of Class 0 disks and their evolution are still poorly constrained observationally and theoretically. We aim to better understand the mechanisms that set the statistics of disk properties as well as to study their formation in massive protostellar clumps. We also want to provide the community with synthetic disk populations to better interpret young disk observations. We use the ramses code to model star and disk formation in massive protostellar clumps with MHD including the effect of ambipolar diffusion and RT including the stellar radiative feedback. Those simulations, resolved up to the astronomical unit scale, allow to investigate the formation of disk populations. Magnetic fields play a crucial role in disk formation. A weaker initial field leads to larger and massive disks and weakens the stellar radiative feedback by increasing fragmentation. We find that ambipolar diffusion impacts disk and star formation and leads to very different disk magnetic properties. The stellar radiative feedback also have a strong influence, increasing the temperature and reducing fragmentation. Comparing our disk populations with observations reveals that our models with a mass-to-flux ratio of 10 seems to better reproduce observed disk sizes. This also sheds light on a tension between models and observations for the disk masses. The clump properties and physical modeling impact disk populations significantly. The tension between observations and models for disk mass estimates is critical to solve with synthetic observations in future years, in particular for our comprehension of planet formation.

astro-ph.SR↗

arXiv2023

Dust dynamics in current sheets within protoplanetary disks. I. Isothermal models including ambipolar diffusion and Ohmic resistivity

Context: Chondrules originate from the reprocessing of dust grains. They are key building blocks of telluric planets, yet their formation, which must happen in strongly localized regions of high temperature, remains poorly understood. Aims: We examine the dust spatial distribution near regions of strong local heating produced by current sheets, as a step toward exploring a potential path for chondrule formation. We further aim to investigate current sheet formation under various conditions in protoplanetary disks in the presence of ambipolar diffusion and Ohmic resistivity and the effect of current sheet morphology on dust dynamics in their vicinity. Methods: We use the RAMSES code including modules for non-ideal magnetohydrodynamics and solution of the dynamics of multiple sizes of dust grains to compute unstratified shearing box simulations of current sheet formation. We investigate, through seven models the effect of the ambipolar diffusion and Ohmic resistivity strength, the initial density, and magnetic field, as well as the resolution and box size. Results: We find that current sheets form in all our models, with typical widths of 0.001-0.01 AU and that strong dust fraction variations occur for millimeter-sized grains. These variations are typically of an order of magnitude and up to two orders of magnitude for the most favorable cases. We also show that the box size and resolution has a strong impact on the current sheet distribution and intensity. Conclusions: The formation of current sheets that can intensely heat their surroundings near strong dynamical dust fraction variations could have important implications for chondrule formation, as it appears likely to happen in regions of large dust fraction.

astro-ph.EP↗

arXiv2023

On the propagation of Alfvén waves in the dusty interstellar medium. Can we neglect dust inertia in molecular clouds?

Alfvén waves are fundamental magnetized modes which play an important role in the dynamics of magnetized flows such as the interstellar medium (ISM). In weakly ionised medium, their propagation critically depends on the ionisation rate but also on the charge carriers which, depending on gas density can be ions, electrons or dust grains. The latter in particular are well known to have a drastic influence on the magnetic resistivities in the dense ISM such as collapsing dense cores. Yet, in most calculations, for numerical reasons, the grain inertia is usually neglected. We investigate analytically the propagation of Alfvén waves both in a single-size and multi-size grain medium such as the ISM and we obtain exact expressions giving wavenumbers as a function of wave frequencies. These expressions are then solved analytically or numerically taking into account or neglecting grain inertia. Whereas at large wavelengths, neglecting grain inertia is a very good approximation, the situation is rather different for wavelengths shorter than a critical value, which broadly scales as $1/n$, $n$ being the gas density. More precisely, when inertia is neglected the waves do not propagate at short wavelengths or, due to the Hall effect, develop for one circular polarisation only, a whistler mode such that ${\cal R} _e (ω) \propto k^2$, whereas the other polarisation presents a zero group velocity, i.e. ${\cal R} _e (ω) \propto k^0$. When grain inertia is accounted for, the propagation of the two polarisations tend to be more symmetrical and the whistler mode is only present at density higher than $\simeq 10^8$ cm$^{-3}$. At lower density it is replaced by a mode having ${\cal R} _e (ω) \propto k^{\simeq 1.2}$. Abridged

astro-ph.GA↗

arXiv2018

Case A and B evolution towards electron capture supernova

Most super AGB stars are expected to end their life as oxygen-neon white dwarfs rather than electron capture supernovae (ECSN). The reason is ascribed to the ability of the second dredge-up to significantly reduce the mass of the He core and of the efficient AGB winds[...]. In this study, we investigate the formation of ECSN through case A and case B mass transfer. In these scenarios, when Roche lobe overflow stops, the primary has become a helium star. With a small envelope left, the second dredge-up is prevented, potentially opening new paths to ECSN. We compute binary models using our stellar evolution code BINSTAR. We consider three different secondary masses of 8, 9, and 10 $M_\odot$ and explore the parameter space, varying the companion mass, orbital period, and input physics. Assuming conservative mass transfer, with our choice of secondary masses all case A systems enter contact either during the main sequence or as a consequence of reversed mass transfer when the secondary overtakes its companion during core helium burning. Case B systems are able to produce ECSN progenitors in a relatively small range of periods ($3\le P(d)\le 30$) and primary masses ($10.9\le M/M_\odot\le 11.5$). Changing the companion mass has little impact on the primary's fate as long as the mass ratio $M_1/M_2$ remains less than 1.4-1.5, above which evolution to contact becomes unavoidable. We also find that allowing for systemic mass loss substantially increases the period interval over which ECSN can occur. This change in the binary physics does not however affect the primary mass range. We finally stress that the formation of ECSN progenitors through case A and B mass transfer is very sensitive to adopted binary and stellar physics. Close binaries provide additional channels for ECSN but the parameter space is rather constrained likely making ECSN a rare event.

astro-ph.SR↗