We investigate the launching of jets and outflows from magnetically diffusive accretion disks. Using the PLUTO code we solve the time-dependent resistive MHD equations taking into account the disk and jet evolution simultaneously. The main question we address is which kind of disks do launch jets and which kind of disks do not? In particular, we study how the magnitude and distribution of the (turbulent) magnetic diffusivity affect mass loading and jet acceleration. We have applied a turbulent magnetic diffusivity based on α-prescription, but have also investigate examples where the scale height of diffusivity is larger than that of the disk gas pressure. We further investigate how the ejection efficiency is governed by the magnetic field strength. Our simulations last for up to 5000 dynamical time scales corresponding to 900 orbital periods of the inner disk. As a general result we observe a continuous and robust outflow launched from the inner part of the disk, expanding into a collimated jet of super fast magneto-sonic speed. For long time scales the disk internal dynamics changes, as due to outflow ejection and disk accretion the disk mass decreases. For magneto-centrifugally driven jets we find that for i) less diffusive disks, ii) a stronger magnetic field, iii) a low poloidal diffusivity, or a iv) lower numerical diffusivity (resolution), the mass loading of the outflow is increased -resulting in more powerful jets with high mass flux. For weak magnetization the (weak) outflow is driven by the magnetic pressure gradient. We consider in detail the advection and diffusion of magnetic flux within the disk and we find that the disk and outflow magnetization may substantially change in time. This may have severe impact on the launching and formation process -an initially highly magnetized disk may evolve into a disk of weak magnetization which cannot drive strong outflows. We further investigate the jet asymptotic velocity and the jet rotational velocity in respect of the different launching scenarios. We find a lower degree of jet collimation than previous studies, most probably due to our revised outflow boundary condition.

Context. Transition disks typically appear in resolved millimeter observations as giant dust rings surrounding their young host stars. More accurate observations with ALMA have shown several of these rings to be in fact asymmetric: they have lopsided shapes. It has been speculated that these rings act as dust traps, which would make them important laboratories for studying planet formation. It has been shown that an elongated giant vortex produced in a disk with a strong viscosity jump strikingly resembles the observed asymmetric rings. Aims. We aim to study a similar behavior for a disk in which a giant planet is embedded. However, a giant planet can induce two kinds of asymmetries: (1) a giant vortex; and (2) an eccentric disk. We studied under which conditions each of these can appear, and how one can observationally distinguish between them. This is important because only a vortex can trap particles both radially and azimuthally, while the eccentric ring can only trap particles in radial direction. Methods. We used the FARGO code to conduct the hydro-simulations. We set up a disk with an embedded giant planet and took a radial grid spanning from 0.1 to 7 times the planet semi-major axis. We ran the simulations with various viscosity values and planet masses for 1000 planet orbits to allow a fully developed vortex or disk eccentricity. Afterwards, we compared the dust distribution in a vortex-holding disk with an eccentric disk using dust simulations. Results. We find that vorticity and eccentricity are distinguishable by looking at the azimuthal contrast of the dust density. While vortices, as particle traps, produce very pronounced azimuthal asymmetries, eccentric features are not able to accumulate millimeter dust particles in azimuthal direction, and therefore the asymmetries are expected to be modest.

The observation of the hot gas surrounding Sgr A* and a few other nearby galactic nuclei imply that electron and proton mean free paths are comparable to the gas capture radius. So, the hot accretion flows are likely to proceed under week‐collision conditions. Hence, thermal conduction has been suggested as a possible mechanism by which the sufficient extra heating is provided in hot advection‐dominated accretion flow (ADAF) accretion discs. We consider the effects of thermal conduction in the presence of a toroidal magnetic field in an ADAF around a compact object. For a steady‐state structure of such accretion flows, a set of self‐similar solutions are presented. We find two types of solutions which represent high and slow accretion rate. They have different behaviours with saturated thermal conduction parameter, φ.

We carry out self‐similar solutions of viscous–resistive accretion flows around a magnetized compact object. We consider an axisymmetric, rotating, isothermal steady accretion flow, which contains a poloidal magnetic field of the central star. The dominant mechanism of energy dissipation is assumed to be the turbulence viscosity and magnetic diffusivity due to the magnetic field of the central star. We explore the effect of viscosity on a rotating disc in the presence of constant magnetic diffusivity. We show that the dynamical quantities of advection‐dominated accretion flows (ADAFs) are sensitive to the advection and viscosity parameters. An increase of the α coefficient in the α‐prescription model decreases the radial velocity and increases the density of the flow. It also affects the poloidal magnetic field considerably.

We examine the effects of a hydrodynamical wind on advection dominated accretion flows with thermal conduction in the presence of a toroidal magnetic field under a self-similar treatment. The disk gas is assumed to be isothermal. For a steady state structure of such accretion flows a set of self similar solutions are presented. The mass-accretion rate $\dot{M}$ decreases with radius $r$ as $\dot{M}\propto r^{s+1/2}$, where $s$ is an arbitrary constant. We show that existence of wind will lead to enhance the accretion velocity. Cooling effects of outflows or winds are noticeable and should be taken into account for calculating luminosity and effective temperature of optically thin and thick ADAFs. Increasing the effect of wind, decreases the disk's temperature, because of energy flux which is taken away by winds. We will see that for a given set of input parameters, the solution reaches to a non-rotating limit at a specific value of $\phi_s$. The values of this limitation on $\phi_s$ will increase by adding $s$, wind parameter. In fact, the higher values of $s$ will allow the disk to have physical rotating solution for larger $\phi_s$.Comment: Accepted for publication, MNRA