Context. Dust plays a key role during star, disk and planet formation. Yet, its dynamics during the protostellar collapse remains a poorly investigated field. Recent studies seem to indicate that dust may decouple efficiently from the gas during these early stages. Aims. We aim to understand how much and in which regions dust grains concentrate during the early phases of the protostellar collapse, and see how it depends on the properties of the initial cloud and of the solid particles. Methods. We use the multiple species dust dynamics solver multigrain of the grid-based code RAMSES to perform various simulations of dusty collapses. We perform hydrodynamical and magnetohydrodynamical simulations where we vary the maximum size of the dust distribution, the thermal-to-gravitational energy ratio and the magnetic properties of the cloud. We simulate the simultaneous evolution of ten neutral dust grains species with grain sizes varying from a few nanometers to a few hundredth of microns. Results. We obtain a significant decoupling between the gas and the dust for grains of typical sizes a few ∼ 10 µm. This decoupling strongly depends on the thermal-to-gravitational energy ratio, the grain sizes or the inclusion of a magnetic field. With a semi-analytic model calibrated on our results, we show that the dust ratio mostly varies exponentially with the initial Stokes number at a rate that depends on the local cloud properties. Conclusions. We find that larger grains tend to settle and drift efficiently in the first-core and in the newly formed disk. This can produce dust-togas ratios of several times the initial value. Dust concentrates in high density regions (cores, disk and pseudo-disk) and is depleted in low density regions (envelope and outflows). The size at which grains decouple from the gas depends on the initial properties of the clouds. Since dust can not necessarily be used as a proxy for gas during the collapse, we emphasize on the necessity of including the treatment of its dynamics in protostellar collapse simulations.
Protoplanetary disks form through angular momentum conservation in collapsing dense cores. In this work, we perform the first simulations with a maximal resolution down to the astronomical unit (au) of protoplanetary disk formation, through the collapse of 1000 M ⊙ clumps, treating self-consistently both non-ideal magnetohydrodynamics with ambipolar diffusion as well as radiative transfer in the flux-limited diffusion approximation including stellar feedback. Using the adaptive mesh-refinement code RAMSES, we investigate the influence of the magnetic field on the disks properties with three models. We show that, without magnetic fields, a population dominated by large disks is formed that is not consistent with Class 0 disk properties as estimated from observations. The inclusion of magnetic field leads, through magnetic braking, to a very different evolution. When it is included, small <50 au disks represent about half the population. In addition, about 70% of the stars have no disk in this case, which suggests that our resolution is still insufficient to preserve the smaller disks. With ambipolar diffusion, the proportion of small disks is also prominent and we report a flat mass distribution around 0.01–0.1M ⊙ and a typical disk-to-star mass ratios of ∼10−2–10−1. This work shows that the magnetic field and its evolution plays a prominent role in setting the initial properties of disk populations.
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