Continuum computational kinetic plasma models evolve the distribution function of a plasma species f_s on a phase-space grid over time. In many problems of interest the distribution function has limited extent in velocity space; hence, using a uniform, highly refined mesh would be costly and slow. Nonuniform velocity grids can reduce the computational cost by placing more degrees of freedom where f_s is appreciable and fewer where it is not. In this work we introduce a first-of-its kind discontinuous Galerkin approach to nonuniform velocity-space discretization using mapped velocity coordinates. This new method is presented in the context of a gyrokinetic model used to study magnetized plasmas. We create discretizations of collisionless and collisional terms using mappings in a way that exactly conserves particles and energy. Numerical tests of such properties are presented, and we show that this new discretization can reproduce earlier gyrokinetic simulations using grids with up to 6-60 times fewer cells and 22X-60X speed-ups depending on dimensionality, geometry and plasma parameters.

TYC 1083-12-1 (sp. type F8V) was identified as a potential exoplanetary candidate in the data from a photometric survey with a 30 -cm telescope. From the radial velocity observations of the star, we found that it is a double -lined binary with very similar components. We present the basic parameters of this system.

This work studies the interaction between colliding plasma jets to understand regimes in which jet merging results in shock formation versus regimes in which the shock formation is mitigated due to the collisionless interpenetration of the jets. A kinetic model is required for this study because fluid models will always produce a shock upon the collision of plasma jets. The continuum-kinetic, Vlasov-Maxwell-Dougherty model with one velocity dimension is used to accurately capture shock heating, along with a novel coupling with a moment equation to evolve perpendicular temperature for computational efficiency. As a result, this relatively inexpensive simulation can be used for detailed scans of the parameter space towards predictions of shocked versus shock-mitigated regimes, which is of interest for several fusion concepts such as plasma-jet-driven magneto-inertial fusion (PJMIF), high-energy-density plasmas, astrophysical phenomena, and other laboratory plasmas. The initial results obtained using this approach are in agreement with the preliminary outcomes of the Plasma Liner Experiment (PLX).

When a plasma sheath forms next to a dielectric wall, material properties determine electron absorption and reflection from the surface, impacting the sheath formation and structure. The low energy regime of this interaction is often not considered rigorously in emissive sheath simulations, but may be modeled from quantum mechanical first principles, and has important applications to plasma thrusters and fusion devices. In this work, low energy electron reflection from the wall is implemented as a boundary condition in a continuum kinetic framework and the sheath is simulated for dielectric material parameters in high and low emission cases. The results presented here demonstrate that the material parameters can have significant effect on the resulting sheath profile and particle distribution functions. Surfaces with high reflection rates see the formation of a space-charge limited sheath.

Rayleigh-Taylor (RT) instabilities are prevalent in many physical regimes ranging from astrophysical to laboratory plasmas and have primarily been studied using fluid models, the majority of which have been ideal fluid models. This work presents a five-dimensional (two spatial dimensions, three velocity space dimensions) simulation using the continuum-kinetic model to study the effect of the collisional mean free path and transport on the instability growth. The continuum-kinetic model provides noise-free access to the full particle distribution function permitting a detailed investigation of the role of kinetic physics in hydrodynamic phenomena such as the RT instability. For long mean free path, there is no RT instability growth, but as collisionality increases, particles relax towards the Maxwellian velocity distribution, and the kinetic simulations reproduce the fluid simulation results. An important and novel contribution of this work is in the intermediate collisional cases that are not accessible with traditional fluid models and require kinetic modeling. Simulations of intermediate collisional cases show that the RT instability evolution is significantly altered compared to the highly collisional fluidlike cases. Specifically, the growth rate of the intermediate collisionality RT instability is lower than the high collisionality case while also producing a significantly more diffused interface. The higher moments of the distribution function play a more significant role relative to inertial terms for intermediate collisionality during the evolution of the RT instability interface. Particle energy flux is calculated from moments of the distribution and shows that transport is significantly altered in the intermediate collisional case and deviates much more so from the high collisionality limit of the fluid regime.

Context. We present a new study of the eclipsing cataclysmic variable CzeV404 Her ( P orb = 0.098 d) that is located in the period gap. Aims. This report determines the origin of the object and the system parameters and probes the accretion flow structure of the system. Methods. We conducted simultaneous time-resolved photometric and spectroscopic observations of CzeV404 Her. We applied our light-curve modelling techniques and the Doppler tomography method to determine the system parameters and analyse the structure of the accretion disk. Results. We found that the system has a massive white dwarf M WD = 1.00(2) M ⊙ , a mass ratio of q = 0.16, and a relatively hot secondary with an effective temperature T 2 = 4100(50) K. The system inclination is i = 78.8°. The accretion disk spreads out to the tidal limitation radius and has an extended hot spot or line region. The hot spot or line is hotter than the remaining outer part of the disk in quiescence or in intermediate state, but does not stand out completely from the disk flux in (super)outbursts. Conclusions. We claim that this object represents a link between two distinct classes of SU UMa-type and SW Sex-type cataclysmic variables. The accretion flow structure in the disk corresponds to the SW Sex systems, but the physical conditions inside the disk fit the behaviour of SU UMa-type objects.

Multifluid simulations of plasma sheaths are increasingly used to model a wide variety of problems in plasma physics ranging from global magnetospheric flows around celestial bodies to plasma-wall interactions in thrusters and fusion devices. For multifluid problems, accurate boundary conditions to model an absorbing wall that resolves a classical sheath remains an open research area. This work justifies the use of vacuum boundary conditions for absorbing walls to show comparable accuracy between a multifluid sheath and lower moments of a continuum-kinetic sheath.

Continuum kinetic simulations of plasmas, where particle distribution functions are directly discretized in phase-space, permit fully kinetic simulations without the statistical noise of particle-in-cell methods. Recent advances in numerical algorithms have made continuum kinetic simulations computationally competitive. This work presents a continuum kinetic description of high-fidelity wall boundary conditions that utilize the readily available particle distribution function without coupling to additional physical models. The boundary condition is realized through a reflection function that can capture a wide range of cases from simple specular reflection to more involved first principles models. While the framework is usable for various numerical methods and boundary conditions, this work focuses on the discontinuous Galerkin implementation of electron emission using a first-principles quantum-mechanical model. Presented results demonstrate effects of electron emission from a dielectric material on formation of a classical plasma sheath.

The available minima timings of 14 selected eclipsing binaries (V1297 Cas, HD 24105, KU Aur, GU CMa, GH Mon, AZ Vel, DI Lyn, DK Her, GQ Dra, V624 Her, V1134 Her, KIC 6187893, V1928 Aql, V2486 Cyg) were collected and analyzed. Using the automatic telescopes, surveys, and satellite data, we derived more than 2500 times of eclipses, accompanied with our own ground-based observations. These data were used to detect the period variations in these multiple systems. The eclipse timing variations were described using the third-body hypothesis and the light-time effect. Their respective periods were derived as 2.5, 16.2, 27, 20, 64, 5.6, 22, 115, 27, 42, 6.9, 11.2, 4.1, and 8.4 years for these systems, respectively. The predicted minimal mass of the third body was calculated for each of the systems, and we discuss here their prospective detectability. The light curves of HD 24105, GH Mon, DK Her, V1134 Her, KIC 6187893, V1928 Aql, and V2486 Cyg were analyzed using the PHOEBE program, resulting in physical parameters of the components. Significant fractions of the third light were detected during the light-curve analysis, supporting our hypothesis of the triple-star nature of all these systems. The majority of these systems (nine out of 14) were already known as visual doubles. Our study shifts them to possible quadruples, what makes them even more interesting.

Aims: Our goal was to increase number of known doubly eclipsing systems such that the resulting dataset would allow to study them via statistical means, as well as prove that they constitute gravitationally bound 2+2 quadruple system. Methods: We analysed photometric data for eclipsing binaries provided by the OGLE survey in the LMC fields. We found a large number of new doubly eclipsing systems (our discoveries are 3x more numerous than previous studies). With a typical orbital period of days for the binaries, we sought eclipse time variations (ETVs) on the timescale of years. In the cases where we were able to detect the ETV period, the difference between the inner and outer periods in the quadruple system is large enough. This allows us to interpret ETVs primarily as the light-time effect, thus providing an interesting constraint on masses of the binaries. Results: In addition to significantly enlarging the database of known doubly eclipsing systems, we performed a thorough analysis of 72 cases. ETVs for 28 of them (39% of the studied cases) showed evidence of relative motion. We note OGLE BLG-ECL-145467 as the most interesting case; it is bright (I=12.6 mag), consists of two detached binaries with periods of about 3.3 d and 4.9 d (making it a candidate for a 3:2 resonant system), mutual period about 1538 d. Distribution of the orbital period ratio P_A/P_B of binaries in 2+2 quadruples shows statistically significant excess at 1 and 1.5. The former is likely a natural statistical preference in weakly interacting systems with periods within the same range. The latter is thought to be evidence of a capture in the 3:2 mean motion resonance of the two binaries. This sets important constraints on evolutionary channels in these systems. The total number of doubly eclipsing systems increased to 146, more than 90% of which are at low declinations on the southern sky.

Continuum kinetic simulations of plasmas, where the distribution function of the species is directly discretized in phase-space, permits fully kinetic simulations without the statistical noise of particle-in-cell methods. Recent advances in numerical algorithms have made continuum kinetic simulations computationally competitive. This work presents the first continuum kinetic description of high-fidelity wall boundary conditions that utilize the readily available particle distribution function. The boundary condition is realized through a reflection function that can capture a wide range of cases from simple specular reflection to more involved first principles models. Examples with detailed discontinuous Galerkin implementation are provided for secondary electron emission using phenomenological and first-principles quantum-mechanical models. Results presented in this work demonstrate the effect of secondary electron emission on a classical plasma sheath.

This paper presents a brief survey of a variety of plasma modeling techniques applied to several space- and fusion-relevant plasma instabilities that are presently of significant interest. These include simulations of the Weibel instability that occurs in astrophysical and laser plasmas, two-fluid plasma instabilities in fusion concepts such as Z-pinches that occur beyond the well-known magnetohydrodynamic instabilities, the magneto-Rayleigh-Taylor instability that occurs in a range of plasmas from the laboratory to space, the Richtmeyer-Meshkov instability which is an important instability in astrophysical and fusion plasmas, and the gradient-drift instability which is known to occur in ionospheric and magnetospheric plasmas. Recent advances in kinetic and fluid modeling provide the ability to study a wide variety of problems using the model that is best suited for the parameter regimes of interest. Some of the key findings are summarized here.