Astronomy Reports最新文献

The article proposes a new method for estimating the number of particles in experiments on modeling the interaction of cosmic and lunar dust with the surface of spacecraft. The experiments are based on the creation of a dusty plasma cloud, when exposed to radiation from a powerful pulsed gyrotron on a substance simulating cosmic or lunar dust. This approach was tested using a lunar regolith simulator. The dynamics of particles in dust clouds obtained as a result of microwave discharge is analyzed using the ImageJ program.

In the paper, we demonstrate the application of X-ray spectroscopy with high spatial resolution to study magnetic reconnection in laboratory astrophysical experiments performed with nano- and pico-second duration laser facilities at a moderate laser density on the target of <10¹⁸ W/cm². A brief overview of the commonly used experimental schemes is given. Atomic kinetic calculations for the L-shell spectra of Ne- and F‑like Fe ions (iron, Z = 26) demonstrate the high sensitivity of the measurements to changes in plasma parameters. The scope of the different diagnostic approaches to measure electron temperature and laser plasma density is discussed. It is shown that transitions in Ne-like ions are a universal tool for measuring plasma parameters, both in the region of laser interaction with the target and in the reconnection zone.

A brief review of the results of experimental modeling of cosmic jets in superstrong magnetic fields of laser relativistic plasma is given. It is noted that the development of cyclotron instability with the generation of cyclotron radiation plays a key role in a number of processes in a plasma with a magnetic field: self-localization of plasma in the form of solitons, conversion of rotational motion of plasma into translational motion, cyclotron acceleration of charged particles, and separation (stratification) of a plasma jet into separate plasma formations.

This paper presents the results of MHD simulations of astrophysical and laboratory supersonic jets under a superposition of poloidal (({{B}_{r}}), ({{B}_{z}})) and toroidal (({{B}_{phi }})) magnetic fields. It is shown that the escaping matter is quickly collimated by the magnetic field. A shock wave of an elongated shape is formed, which moves from the target to the boundary of the chamber, leaving behind a stable flow. A periodic shock wave structure is observed inside the main conical expanding shock wave. It is shown that the toroidal component of the magnetic field remains in the region throughout the entire calculation and plays a role in the collimation of the flow. The poloidal magnetic field decreases in the region of the jet cone, but remains in the simulation region throughout the calculation and also participates in flow collimation. Thus, both components ({{B}_{z}}) and ({{B}_{phi }}) take part in the collimation of the flow by the magnetic field. The width of the jet and the opening angle of the cone (theta ) depend on the magnitude of the magnetic field induction. As the field increases, the jet becomes narrower and the cone angle decreases. Initially, we do not specify the rotation of the jet (Omega ). However, due to the presence of the ({{B}_{phi }}) field, the substance acquires angular velocity and twists along the (z) axis. The simulation results are in agreement with laboratory jets arising in the experiment at the Neodymium laser installation, and with the previously obtained results of MHD modeling of jet formation separately, in poloidal or toroidal magnetic field.

This paper describes the results of a laboratory experiment on the sub-Alfvén expansion of a quasi-spherical laser plasma cloud into a vacuum magnetic field in the regime of nonmagnetized ions. The role of Hall fields and currents in the anomalously fast dynamics of the magnetic field during the collapse phase of a diamagnetic cavity is considered. Detailed spatial measurements of the azimuthal Hall fields configuration are demonstrated and their relationship to diamagnetic cavity collapse is determined. As a result of the experiment, data were obtained confirming the hypothesis about the transfer of the main magnetic field by the movement of electrons associated with Hall currents.

The use of “plasma focus” type facilities, such as PF-3 (Kurchatov Institute), allows carrying out well-controlled and diagnosable laboratory experiments to study laboratory jets with scale parameters close to the jets of young stars. In this paper, we present the results of numerical modeling of plasma outburst propagation in PF-3. A self-consistent configuration was chosen as the initial conditions, which correctly describes the internal structure of the jet. This allowed us to obtain a detailed structure of the interaction between the magnetized emission and the ambient gas. Due to the scalability of such a structure, one should expect such a structure from the head shock waves of jets of young stars.

Using ground-space VLBI data from the RadioAstron project archive, the phase distortions of the cross-spectrum caused by the ionosphere have been calculated and their influence on the results of determination of the visibility function has been studied. The Arecibo Observatory’s 300-m antenna served as the ground station for the interferometer. The separation of ionospheric phase distortions from the influence of the interstellar and interplanetary medium and instrumental errors is based on different frequency dependencies of these effects. The amplitude of ionospheric phase variation caused by electron density fluctuations in the ionosphere above the Arecibo radio telescope is several radians per observation session of about one hour. The structure function of phase variations indicates a continuous spectrum of electron density fluctuations at typical times of ( gtrsim )2–5 min with no pronounced signs of quasi-periodic processes. Ionospheric phase f-luctuations during pulsar observations increase the width of the maximum of the amplitude of the visibility function as a function of the residual fringe rate by 5–10 mHz with a decrease in the value at the maximum of ( approx {kern 1pt} 10% ). When constructing images of radio galaxies and quasars from ground-based VLBI observations, these phase shifts can significantly distort the final results.

In April 2017, the Event Horizon telescope received an image of a supermassive black hole in the Sagittarius A* source. This image consists of a ring-like structure that contains three areas with increased brightness (spots). If we assume that these spots are associated with flares near the event horizon of a black hole, then we can estimate its spin. Our estimate gives a value of the order of (a approx 0.9).

The paper presents the principle of operation, the main components and the results of the work of the software created in the Sternberg Astronomical Institute of Moscow State University. The PC is designed for processing of large volumes of space geodetic data. The developed software was used to process inter-satellite measurements of a space-based constellation intended to measure the parameters of the Earth’s gravitational field (EGF). The experimental option of the software enables working with both simulated data and real data of GRACE and GRACE Follow-on missions. This experimental version was used to recover the EGF parameters on real GRACE and GRACE-FO mission data. Solutions were developed for every month within the measurement time intervals from 2010 to 2021, as well as for extended time intervals of 4.3 and 7.6 years. A comparison of the obtained solutions with the results of the EGF recovery obtained by other researchers is presented.

The estimation of the initial spin period of pulsars involves the important questions such as the late stage evolution of massive stars and the formation process of neutron stars. However, the estimated initial spin exists the bias based on the magnetic dipole radiation (MDR) model, since the braking index of a dozen of observed pulsars ranges in (1 < n < 3) that is deviated from the expected value of 3 by MDR. The magnetic dipole radiation plus wind (MDRW) model for a pulsar successfully explains the evolution of the braking index between 1 and 3, by which we calculate the initial spins of the pulsars with the measured braking index, and obtain their distribution between ( sim {kern 1pt} 18) and ( sim {kern 1pt} 50) ms. This result is consistent with the statistics of the observed young pulsars, less than the fastest spin period of 16 ms of the rotation-powered X-ray pulsar PSR J0537–6910.