arXiv subjects

N. Zimniak

Publications and source records attributed to N. Zimniak.

3 recordsLinked to original sources

arXiv2026

Comparison between axisymmetric numerical magnetohydrodynamical simulations and self-similar solutions of jet-emitting disks

Turbulent accretion disks threaded by a large-scale vertical field near equipartition can drive tenuous and fast self-confined jets. Self-similar solutions of these jet-emitting disks (JEDs) have been known for a long time and provide the distributions of all physical quantities, from the turbulent disk to the asymptotic regime of ideal magnetohydrodynamic (MHD) jets. However, a thorough comparison with time-dependent numerical simulations has never been achieved, mostly because mass-loss rates found in simulations were always larger than those found analytically. This tension may have cast doubt on the analytical approach, the numerical one, or both. Our goal is to bridge the gap between these two complementary approaches and settle this long-standing issue. We performed 2.5D (axisymmetric) simulations of resistive and viscous accretion disks described by the same parameter sets as analytical JED solutions. The results demonstrate an almost perfect agreement between the numerical and analytical solutions, thereby resolving the previously observed tension. The simulations also confirm that JEDs behave as dynamical attractors: starting from different initial conditions, the system consistently converges toward the expected steady-state solution. This work demonstrates that self-similar solutions provide valuable insights into accretion-ejection physics. However, as 2.5D numerical simulations which rely on alpha-prescriptions, they strongly depend on the assumptions made for turbulent terms. In contrast, 3D simulations capture the turbulence, but become prohibitively expensive when modeling large-scale astrophysical systems. We advocate for the use of global 3D simulations to investigate turbulence and to derive physically motivated prescriptions for use in 2.5D studies.

astro-ph.HE↗

arXiv2025

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) VII: the layered molecular outflow from HL Tau and its relationship with the ringed disk

The ringed disk around HL Tau stands out as the iconic signature of planet formation, but the origin of the substructures is still debated. The HL Tau system also drives a powerful bipolar wind, and we analyze its outermost component traced by CO emission, to determine the relationship of the flow with the disk and its substructures. We use ALMA observations of the ${}^{12}$CO (2-1) line at 1.3 mm, with 0.2 km/s and ~ 0.28" resolution, conducted within the ALMA-DOT project. The channel maps and position-velocity diagrams show a rich structure of concatenated bubble- and arc-shaped features, whose size and distance from the source increase with velocity. The superposition of the features generates the apparent conical shape. The tomographic reconstruction of the morphology and kinematics of the red-shifted lobe suggests the presence of distinct nested shells having higher velocity and steeper velocity gradient for shells closer to the axis, rotating in the same sense of the disk. Such configuration can be justified by different classes of models. In this paper we compare the derived wind parameters with the predictions of magnetohydrodynamic (MHD) disk winds. Under this hypothesis, the launch radii of the three outermost shells are found to be at about the position of three adjacent dust rings in the disk at 58, 72 and 86 au. The wind may be capable of removing angular momentum from the outer disk, and we derive a magnetic lever arm of $λ\sim 4 - 5$, higher than that commonly adopted for MHD winds from these regions. Interpretations are discussed. The arrangement of the wind in nested shells with brighter emission rooted at the location of ring substructures could support the results of non-ideal MHD simulations according to which magnetic instabilities can generate the disk ring-gap system with a connected layered wind, alternatively to the action of yet undetected protoplanets.

astro-ph.GA↗

arXiv2024

Influence of the turbulent magnetic pressure on isothermal jet emitting disks

The theory of jet emitting disks (JEDs) provides a mathematical framework for a self-consistent treatment of steady-state accretion and ejection. A large-scale vertical magnetic field threads the accretion disk where magnetic turbulence occurs in a strongly magnetized plasma. A fraction of mass leaves the disk and feeds the two laminar super-Alfénic jets. In previous treatments of JEDs, the disk turbulence has been considered to provide only anomalous transport coefficients, namely magnetic diffusivities and viscosity. However, 3D numerical experiments show that turbulent magnetic pressure also sets in. We included this additional pressure term using a prescription that is consistent with the latest 3D global (and local) simulations. We then solved the complete system of self-similar magnetohydrodynamic (MHD) equations, accounting for all dynamical terms. The disk becomes puffier and less electrically conductive, causing radial and toroidal electric currents to flow at the disk surface. Field lines within the disk become straighter, with their bending and shearing occurring mainly at the surface. Accretion remains supersonic, but becomes faster at the disk surface. Large values of both turbulent pressure and magnetic diffusivities allow powerful jets to be driven, and their combined effects have a constructive influence. Nevertheless, cold outflows do not seem to be able to reproduce mass-loss rates as large as those observed in numerical simulations. Our results are a major upgrade of the JED theory, allowing a direct comparison with full 3D global numerical simulations. We argue that JEDs provide a state-of-the-art mathematical description of the disk configurations observed in numerical simulations, commonly referred to as magnetically arrested disks (MADs). However, further efforts from both theoretical and numerical perspectives are needed to firmly establish this point.

astro-ph.HE↗