An analytical model of radial dust trapping in protoplanetary disks

We study dust concentration in axisymmetric gas rings in protoplanetary disks. Given the gas surface density, we derived an analytical total dust surface density by taking into account the differential concentration of all the grain sizes. This model allows us to predict the local dust-to-gas mass ratio and the slope of the particle size distribution, as a function of radius. We test this analytical model comparing it with a 3D magneto-hydrodynamical simulation of dust evolution in an accretion disk. The model is also applied to the disk around HD 169142. By fitting the disk continuum observations simultaneously at $\lambda = 0.87$, 1.3, 3.0 mm, we obtain a global dust-to-gas mass ratio $\epsilon_{\rm global} = 1.05 \times 10^{-2}$ and a viscosity coefficient $\alpha = 1.35 \times 10^{-2}$. This model can be easily implemented in numerical simulations of accretion disks

Understanding the Radio Emission from ϵ\epsilon Eridani

Some solar-type stars are known to present faint, time-variable radio continuum emission whose nature is not clearly established. We report on Jansky Very Large Array observations of the nearby star $\epsilon$ Eridani at 10.0 and 33.0 GHz. We find that this star has flux density variations on scales down to days, hours and minutes. On 2020 Apr 15 it exhibited a radio pulse at 10.0 GHz with a total duration of about 20 minutes and a peak four times larger than the plateau of 40 $\mu$Jy present in that epoch. We were able to model the time behavior of this radio pulse in terms of the radiation from shocks ramming into the stellar wind. Such shocks can be produced by the wind interaction of violently expanding gas heated suddenly by energetic electrons from a stellar flare, similar to the observed solar flares. Because of the large temperature needed in the working surface to produce the observed emission, this has to be non thermal. It could be gyrosynchrotron or synchrotron emission. Unfortunately, the spectral index or polarization measurements from the radio pulse do not have enough signal-to-noise ratio to determine its nature.Comment: 7 pages, 4 figures. To appear in Astronomy & Astrophysic

Kinematics of the Outflow From The Young Star DG Tau B: Rotation in the vicinities of an optical jet

We present $^{12}$CO(2-1) line and 1300 $\mu$m continuum observations made with the Submillimeter Array (SMA) of the young star DG Tau B. We find, in the continuum observations, emission arising from the circumstellar disk surrounding DG Tau B. The $^{12}$CO(2-1) line observations, on the other hand, revealed emission associated with the disk and the asymmetric outflow related with this source. Velocity asymmetries about the flow axis are found over the entire length of the flow. The amplitude of the velocity differences is of the order of 1 -- 2 km s$^{-1}$ over distances of about 300 -- 400 AU. We interpret them as a result of outflow rotation. The sense of the outflow and disk rotation is the same. Infalling gas from a rotating molecular core cannot explain the observed velocity gradient within the flow. Magneto-centrifugal disk winds or photoevaporated disk winds can produce the observed rotational speeds if they are ejected from a keplerian disk at radii of several tens of AU. Nevertheless, these slow winds ejected from large radii are not very massive, and cannot account for the observed linear momentum and angular momentum rates of the molecular flow. Thus, the observed flow is probably entrained material from the parent cloud. DG Tau B is a good laboratory to model in detail the entrainment process and see if it can account for the observed angular momentum.Comment: Accepted to Ap

Exploring the Formation of Resistive Pseudodisks with the GPU Code Astaroth

Pseudodisks are dense structures formed perpendicular to the direction of the magnetic field during the gravitational collapse of a molecular cloud core. Numerical simulations of the formation of pseudodisks are usually computationally expensive with conventional CPU codes. To demonstrate the proof-of-concept of a fast computing method for this numerically costly problem, we explore the GPU-powered MHD code Astaroth, a 6th-order finite difference method with low adjustable finite resistivity implemented with sink particles. The formation of pseudodisks is physically and numerically robust and can be achieved with a simple and clean setup for this newly adopted numerical approach for science verification. The method's potential is illustrated by evidencing the dependence on the initial magnetic field strength of specific physical features accompanying the formation of pseudodisks, e.g. the occurrence of infall shocks and the variable behavior of the mass and magnetic flux accreted on the central object. As a performance test, we measure both weak and strong scaling of our implementation to find most efficient way to use the code on a multi-GPU system. Once suitable physics and problem-specific implementations are realized, the GPU-accelerated code is an efficient option for 3-D magnetized collapse problems.Comment: 29 pages, 1 table, 15 figures, Accepted for publication in the Astrophysical Journa