A self-consistent hybrid model of kinetic striations in low-current Argon discharges

A self-consistent hybrid model of standing and moving striations was developed for low-current DC discharges in noble gases. We introduced the concept of surface diffusion in phase space (r,u) (where u denotes the electron kinetic energy) described by a tensor diffusion in the nonlocal Fokker-Planck kinetic equation for electrons in the collisional plasma. Electrons diffuse along surfaces of constant total energy ε=u-eφ(r) between energy jumps in inelastic collisions with atoms. Numerical solutions of the 1d1u kinetic equation for electrons were obtained by two methods and coupled to ion transport and Poisson solver. We studied the dynamics of striation formation in Townsend and glow discharges in Argon gas at low discharge currents using a two-level excitation-ionization model and a “full-chemistry” model, which includes stepwise and Penning ionization. Standing striations appeared in Townsend and glow discharges at low currents, and moving striations were obtained for the discharge currents exceeding a critical value. These waves originate at the anode and propagate towards the cathode. We have seen two types of moving striations with the 2-level and full-chemistry models, which resemble the s and p striations previously observed in the experiments. Simulations indicate that processes in the anode region could control moving striations in the positive column plasma. The developed model helps clarify the nature of standing and moving striations in DC discharges of noble gases at low discharge currents and low gas pressures.

Characterizing Extreme Emission-line Galaxies. I. A Four-zone Ionization Model for Very High-ionization Emission*

Stellar population models produce radiation fields that ionize oxygen up to O+2, defining the limit of standard H ii region models (<54.9 eV). Yet, some extreme emission-line galaxies, or EELGs, have surprisingly strong emission originating from much higher ionization potentials. We present UV HST/COS and optical LBT/MODS spectra of two nearby EELGs that have very high-ionization emission lines (e.g., He ii λλ1640,4686 C iv λλ1548,1550, [Fe v]λ4227, [Ar iv]λλ4711,4740). We define a four-zone ionization model that is augmented by a very high-ionization zone, as characterized by He+2 (>54.4 eV). The four-zone model has little to no effect on the measured total nebular abundances, but does change the interpretation of other EELG properties: we measure steeper central ionization gradients; higher volume-averaged ionization parameters; and higher central T e , n e , and log U values. Traditional three-zone estimates of the ionization parameter can underestimate the average log U by up to 0.5 dex. Additionally, we find a model-independent dichotomy in the abundance patterns, where the α/H abundances are consistent but N/H, C/H, and Fe/H are relatively deficient, suggesting these EELGs are α/Fe-enriched by more than three times. However, there still is a high-energy ionizing photon production problem (HEIP3). Even for such α/Fe enrichment and very high log U s, photoionization models cannot reproduce the very high-ionization emission lines observed in EELGs.

Spatially resolved X-ray spectroscopy of the archetype type 2 active galactic nucleus NGC 1068 with Chandra

We investigate spatial distributions of iron Kα (Fe-Kα) lines in the cental 100 pc of the Seyfert 2 galaxy NGC 1068 observed with Chandra. The spatial distributions of Fe-Kα lines, neutral and highly ionized, around the center of the galactic nucleus are not isotropic, as consistently confirmed in both image and spectral analyses. The hydrogen number density of the gas clouds responsible for the neutral Fe-Kα line emission is estimated to be 102–103 cm−3 for the sampled regions near the galactic core. The photo-ionization model, where iron is assumed to be ionized by X-rays from the galactic nucleus, yields ionization parameters lower than 19 for these clouds. The range of this ionization parameter is two or three orders of magnitude lower than the theoretically expected value to produce the observed helium-like Fe-Kα line intensities. Therefore, the photo-ionization model is excluded from the explanation of the amount of highly ionized iron that is responsible for the observed Fe-Kα lines. Also, we find anti-correlation in the spatial distributions between the molecular cloud in the area observed with ALMA and that of the Fe-Kα lines, including that from neutral iron. We suggest that X-ray iron-line and radio molecular cloud observations are complementary to probe the distribution of matters in the central regions around the cores of active galactic nuclei.

Особенности описания импульсной электрической прочности полимерных диэлектриков

The scenario based on the macro molecules field ionization model is proposed to describe the polymer dielectrics pulse breakdown. The decisive role of the real dielectric space-field inhomogeneity on formation of the ionization “sources” and redistribution of charge carries is taken into account. The justification of the choice of the defining model parameters - energy gap width and frequency factor is carried out. The possibility of using these parameters to describe the pulse electric strength of polymers in both uniform and sharply non-uniform electric fields (on the example of polymethylmethaacrylate) is shown.

Heat Accumulation in Ultrafast Laser Scanning of Fused Silica

In this work, a numerical model to predict the heat accumulation of fused silica induced by ultrafast laser scanning is put forward, which is composed of an ionization model and a steady electromagnetic model. The ionization model is to obtain the energy deposition induced by single laser pulse. Subsequently, the temperature evolution during ultrafast laser scanning is estimated through the superposition of the heat impact by each laser pulse. The ablated profile from experiments is compared with the predicted profile of heat-affected zone (HAZ) to illustrate the nonthermal processing window, which is validated by Raman spectrum. The analysis of the parametric sensitivity on heat accumulation is carried out, and the laser pulse energy is the dominating factor.

On the origin of X-ray oxygen emission lines in obscured AGN

ABSTRACT We present the Catalogue of High Resolution Spectra of Obscured Sources (CHRESOS) from the XMM–Newton Science Archive. It comprises the emission-line luminosities of H- and He-like transitions from C to Si, and the Fe 3C and Fe 3G L-shell ones. Here, we concentrate on the soft X-ray O vii (f) and O viii Lyα emission lines to shed light on to the physical processes with which their formation can be related to active galactic nucleus (AGN) versus star-forming regions. We compare their luminosity with that of two other important oxygen key lines [O iii] λ5007 Å, in the optical, and [O iv] 25.89 μm, in the infrared (IR). We also test O vii (f) and O viii Lyα luminosities against that of continuum bands in the IR and hard X-rays, which point to different ionization processes. We probe into those processes by analysing photoionization and collisional ionization model predictions upon our lines. We show that both scenarios can explain the formation and observed intensities of O vii (f) and O viii Lyα. By analysing the relationships between O vii (f) and O viii Lyα, and all other observables: [O iii] λ5007 Å, [O iv] 25.89 μm emission lines, and mid-infrared (MIR) 12 μm, far-infrared (FIR) 60 and 100 μm, 2–10 and 14–195 keV continuum bands, we conclude that the AGN radiation field is mainly responsible of the soft X-ray oxygen excitation.

GIARPS High-resolution Observations of T Tauri stars (GHOsT)

Context. The mechanism for jet formation in the disks of T Tauri stars remains poorly understood. Observational benchmarks to launching models can be provided by tracing the physical properties of the kinematic components of the wind and jet in the inner 100 au of the disk surface. Aims. In the framework of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project, we aim to perform a multi-line analysis of the velocity components of the gas in the jet acceleration zone. Methods. We analyzed the GIARPS-TNG spectra of six objects in the Taurus-Auriga complex (RY Tau, DG Tau, DL Tau, HN Tau, DO Tau, RW Aur A). Thanks to the combined high-spectral resolution (ℜ = 5°0 000−115 000) and wide spectral coverage (~400−2400 nm) we observed several O 0, S +, N 0, N +, and Fe + forbidden lines spanning a large range of excitation and ionization conditions. In four objects (DG Tau, HN Tau, DO Tau, RW Aur A), temperature (Te), electron and total density (ne, nH), and fractional ionization (xe) were derived as a function of velocity through an excitation and ionization model. The abundance of gaseous iron, X(Fe), a probe of the dust content in the jet, was derived in selected velocity channels. Results. The physical parameters vary smoothly with velocity, suggesting a common origin for the different kinematic components. In DG Tau and HN Tau, Te, xe, and X(Fe) increase with velocity (roughly from 6000 K, 0.05, 10%X(Fe)⊙ to 15 000 K, 0.6, 90%X(Fe)⊙). This trend is in agreement with disk–wind models in which the jet is launched from regions of the disk at different radii. In DO Tau and RW Aur A, we infer xe < 0.1, nH ~ 106−7 cm−3, and X(Fe) ≲ X(Fe)⊙ at all velocities. These findings are tentatively explained by the formation of these jets from dense regions inside the inner, gaseous disk, or as a consequence of their high degree of collimation.