Coronal Mass Ejection Effect on Envelopes of Hot Jupiters

Abstract—Currently, hot Jupiters have extended gaseous (ionospheric) envelopes extending far beyond the Roche lobe. The envelopes are loosely bound to the planet and are subject to a strong influence by stellar wind fluctuations. Since hot Jupiters are close to the parent star, the magnetic field of the stellar wind is an important factor which defines the structure of their magnetospheres. For a typical hot Jupiter, the velocity of stellar wind plasma flowing around the atmosphere is close to the Alfvén velocity. Thus, fluctuations of the stellar wind parameters (density, velocity, magnetic field) can affect conditions for the formation of the bow shock around a hot Jupiter, such as transforming the flow from sub-Alfvén to super-Alfvén regime and back. The study results of three-dimensional numerical MHD simulations confirm that, in a hot Jupiter’s envelope located near the Alfvén point of the stellar wind, both the disappearance and appearance of a detached shock can occur under the influence of a coronal mass ejection. The study also shows that this process can affect the observational manifestations of a hot Jupiter, including the radiation flux in the spectrum’s hard region.     

The possible escape of electron cyclotron maser radiation from hot stellar coronas through a window of transparency

The main argument against the idea that the intense radio emission observed from active regions on the Sun and flare stars is electron-cyclotron maser (ECM) radiation is that such radiation should be strongly absorbed in higher-lying layers where the condition for the cyclotron resonance at harmonics of the electron gyrofrequency is fulfilled. Cyclotron absorption lowers the efficiency of ECM radiation virtually to zero for a broad range of angles between the direction of propagation of the radiation and the magnetic field. Less severe absorption is possible only in narrow angular “windows” along (for ordinary and extraordinary waves) and perpendicular to (for ordinary waves) the magnetic field. However, the ECM radiation that is generated does not fall into these windows of transparency due to the kinematic conditions corresponding to coronal magnetic traps. We investigate the efficiency of induced scattering of ECM radiation on ions in the equilibrium plasma in the source. Under certain conditions, induced scattering leads to the formation of a condensate of ECM radiation with the direction of its wave vectors approximately along the magnetic field, enabling the escape of the radiation through windows of transparency. The most favorable conditions for this phenomenon are realized for ordinary waves. We estimate the optical depths of the sources of the ECM radiation to the scattering and the angular width of the condensate for ordinary and extraordinary waves for the cases of the flare radio emission of the star AD Leo and the sources of type I noise storms in the solar corona. In both cases, the polarization of the emergent radiation should correspond to the ordinary wave.     

Solution of the transfer equation in a moving medium

The integral transfer equation for resonance radiation in a semi-infinite medium expanding with a constant velocity gradient is considered. A method for the numerical-analytical solution of this problem is presented, together with an estimation of the associated errors. This method is based on a discretization in optical depth and the application of non-linear equation factorization equations.     

The formation of polarized lines: Allowance for the Hanle effect

The paper formulates the standard theory for the transport of polarized radiation in the presence of resonance scattering in an atmosphere with a weak magnetic field, so that the Zeeman splitting is small compared to the Doppler line width. For an atmosphere with conservative scattering, this reduces to the Milne problem, which consists of computing a polarized radiation field in a medium with sources lying in infinitely deep layers. In the approximation of complete frequency redistribution, the problem reduces to solving a Wiener-Hopf integral equation for a (6×6)-matrix source function. Asymptotic and numerical solutions for the standard problem are obtained, including solutions for the Milne problem, for the case of a Doppler absorption profile. The line polarization profiles for the emergent flux at various angular distances from the disk center are derived, and the dependence of the limiting degree of polarization (at the line center at the disk edge) on the direction of the magnetic field is computed. For nearly conservative scattering with photon destruction probability ε?1, the limiting degree of polarization varies with ε in accordance with a simple empirical law similar to that found earlier for a medium with zero magnetic field.     

Broadening of electron cyclotron maser emission lines in a nonuniform magnetic field

The formation of cyclotron maser emission lines in a non-uniform (regular or random) magnetic field is studied. In the presence of sufficiently small inhomogeneity, the line shape can be described by a broadened Gaussian profile. In the case of stronger inhomogeneity, the initial Gaussian profile splits into two Gaussian components, which could be observationally perceived as “harmonics.” A relation between the distribution of local magnetic trap sizes and the distribution of the spectral widths of solar radio spikes is derived. Possible applications of the results to the interpretation of solar radio spikes and related problems are discussed.     

Adaptive analysis of infinite beams dynamics problems using the periodic configuration update method in the time domain

This paper proposes a new approach for the assessment of the dynamic response of continuously supported infinite beams under high‐speed moving loads. A change in the representation of equations of motion in the dynamics of discrete structures is proposed to obtain an improved accuracy of the numerical integration in the time domain. The proposed numerical method called the “periodic configuration update” or “PCU method” is applied to solve the problem of a vertical moving harmonic load on an infinite classical Euler‐Bernoulli beam resting on a continuous viscoelastic foundation. This study shows the superiority of the proposed method in comparison with other methods presented in the literature that suffer from the material time derivative, i.e., convective terms, that arises from the Galilean transformation. To confront this numerical problem, the PCU method retains the principle of the spatial follow of loads while zeroing the relative velocity with the traversed beam via a step‐by‐step adaptive integration of the equation of structural dynamics. The dynamic load is modeled with high theoretical velocities that can reach the critical velocity of the studied beam with different angular frequencies belonging to moderate frequency range. A parametric study is carried out to analyze the influence of key parameters on the convergence. The obtained results show a high efficiency of the PCU method for solving these types of problems relative to the dynamics of high speed trains/tracks.     

Solar millisecond spikes manifest large-and small-scale inhomogeneities of the coronal plasma

A model for the generation of solar millisecond radio spikes via a maser cyclotron resonance is proposed. The model takes into account the large-scale inhomogeneity of the magnetic field and small-scale inhomogeneities of the coronal plasma. The efficiency of the energy transformation from a electron beam into maser radiation is estimated. Appropriate parameters of the magnetic field inhomogeneity and the plasma turbulence are found.     

Intercombinational line profiles in the UV spectra of T Tauri stars and analysis of the accretion zone

We have analyzed for the first time profiles of the SiIII 1892 Å and CIII 1909 Å intercombinational lines in HST spectra of the stars RY Tau and RU Lup. The widths of these optically thin lines exceeded 400 km/s, ruling out formation in the stellar chromosphere. Since the intensity of the Si line exceeds that of the C line, it is unlikely that a large fraction of the observed line flux is formed in a stellar wind. The observed profiles can be reproduced in the framework of an accretion shock model if the velocity field in the accretion zone is appreciably nonaxisymmetric. In this case, the line profiles should display periodic variations, which can be used to determine the accretion zone geometry and the topology of the magnetic field near the stellar surface; corresponding formulas are presented. In addition, periodic variations of the 0.3–0.7 keV X-ray flux should be observed.     

Early-type disk galaxies: Structure and kinematics

Spectroscopic observations of three lenticular (S0) galaxies (NGC 1167, NGC 4150, and NGC 6340) and one SBa galaxy (NGC 2273) have been taken with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences aimed to study the structure and kinematic properties of early-type disk galaxies. The radial profiles of the stellar radial velocities and the velocity dispersion are measured. N-body simulations are used to construct dynamical models of galaxies containing a stellar disk, bulge, and halo. The masses of individual components are estimated formaximum-mass disk models. A comparison of models with estimated rotational velocities and the stellar velocity dispersion suggests that the stellar disks in lenticular galaxies are “overheated”; i.e., there is a significant excess velocity dispersion over the minimum level required to maintain the stability of the disk. This supports the hypothesis that the stellar disks of S0 galaxies were subject to strong gravitational perturbations. The relative thickness of the stellar disks in the S0 galaxies considered substantially exceed the typical disk thickness of spiral galaxies.     

Propagation and localization of wave in multi‐span Timoshenko beams on elastic foundations under moving harmonic loads

Wave propagation and localization in ordered and disordered multi‐span beams on elastic foundations due to moving harmonic loads are investigated by using the transfer matrix methodology. The transfer matrix, as a function of the frequency and velocity of the moving harmonic load, of the periodic beam is formulated in a coordinate system moving with the load. The expressions of critical velocities, cut‐off frequency of an associated uniform beam without discrete spaced supports, are determined through the analysis of the wavenumbers, and the dynamic responses of the beam are also examined. For the ordered and disordered case, the propagation constants and localization factors are respectively employed to identify the velocity and frequency pass bands and stop bands in order to examine whether the perturbation can propagate along the structure or not. The effects of the periodicity, disorder level, excitation frequency, and moving velocity are studied in detail. The validity of the obtained results is confirmed by evaluating the transverse deformation of the beams through the finite element simulations. Copyright © 2017 John Wiley & Sons, Ltd.     

On the weak turbulent motions of an isothermal dry granular dense flow with incompressible grains: part II. Complete closure models and numerical simulations

The complete thermodynamically consistent turbulent closure models of isochoric and isothermal dry granular dense flows with incompressible grains and weak turbulent intensity are established on the basis of a linearized theory with respect to the granular coldness for the dynamic responses of the closure conditions. The models are applied to study a gravity-driven stationary turbulent flow down an inclined moving plane, and the numerical simulations are compared with the experimental outcomes. It shows that while the mean velocity decreases monotonically from its boundary value on the moving plane toward the free surface, the mean porosity and granular coldness display more “exponential-like” increasing/decreasing tendencies. Of particular interest is that the granular coldness evolves from its maximum value on the moving plane toward its minimum value on the free surface, leading to the turbulent dissipation evolving in a similar manner, while the turbulent kinetic energy demonstrate a reverse tendency. The obtained results show good agreements to the experimental outcomes and are similar to the characteristics of conventional Newtonian fluids in turbulent shear flows.     

Comparison of Dimensionless Parameters in Astrophysical MHD Systems and in Laboratory Experiments

Estimates of typical parameters of accretion flows in the representative intermediate polar EX Hydrae, the polar AM Herculis, and the “hot Jupiter” WASP-12b are presented. Dimensionless parameters of astrophysical systems are compared with those of laboratory experiments on laser ablation in magnetic fields. It is shown that laboratory simulations of astrophysical flows is possible in principle, provided that some adjustment to the magnetic field, plasma density, and plasma velocity are made.     

On Possible Types of Magnetospheres of Hot Jupiters

As a rule, the orbits of “hot Jupiter” exoplanets are located close to the Alfven point of the stellar wind of the host star. Many hot Jupiters could be in the sub-Alfven zone, where the magnetic pressure of the stellar wind exceeds the dynamical pressure. Therefore, the magnetic field in the wind should play an extremely important role in the process of stellar wind flowing around the atmosphere of a hot Jupiter. This must be taken into account when constructing theoretical models and interpreting observational data. Analyses show that many typical hot Jupiters should have shockless induced magnetospheres, which have no analogs in the solar system. Such magnetospheres are characterized first and foremost by the fact that there is no bow shock, and the magnetic barrier (ionopause) is formed by induced currents in upper layers of the ionosphere. This conclusion is confirmed here using three-dimensional numerical simulations of the flow of the stellar wind from the host star around the hot Jupiter HD 209458b, taking into account both the intrinsic magnetic field of the planet and the magnetic field in the wind.

     

The cyclotron spectrum of anisotropic ultrarelativistic electrons: Interpretation of X-ray pulsar spectra

The spectrum of cyclotron radiation produced by electrons with a strongly anisotropic velocity distribution is calculated taking into account higher harmonics. The motion of the electrons is assumed to be ultrarelativistic along the magnetic field and nonrelativistic across the field. One characteristic feature of the resulting spectrum is that harmonics of various orders are not equally spaced. The physical properties and observed spectra of four X-ray pulsars displaying higher cyclotron harmonics are analyzed. It was shown that at least in one of them, the cyclotron feature can apparently be only an emission line. Moreover, the observed harmonics are not equidistant, and display certain other properties characteristic of emission by strongly anisotropic ultrarelativistic electrons. In addition, there are indirect theoretical arguments that the electrons giving rise to cyclotron features in the spectra of X-ray pulsars are ultrarelativistic and characterized by strongly anisotropic distributions. As a result, estimates of the magnetic fields of X-ray pulsars (which are usually derived from the energies of cyclotron lines) and certain other physical parameters require substantial revision.     

Initial formation of an “impulsive” coronal mass ejection

An “impulsive” coronal mass ejection (CME) observed on August 24, 2014 is analyzed using ultraviolet images obtained in the SDO/AIA 193, 304, 1600, and 1700 Å channels and Hα (6562.8 Å) data obtained with the EI Teide and Big Bear telescopes. The formation of this impulsive CME was related to a magnetic tube (rope) moving with a velocity of ≈35 km/s and containing plasma that was cooler than the photospheric material. Moving in the corona, the magnetic tube collides with a quasi-stationary coronal magnetic rope, with its two bases rooted in the photosphere. This interaction results in the formation of the CME, with the surface of the coronal magnetic rope becoming the CME frontal structure. According to SDO/HMI data, no enhancements or changes in magnetic flux were detected in the vicinity of the CME bases during its formation. This may support the hypothesis that the magnetic tube starts its motion from layers in the vicinity of the temperature minimum.     

Formation of close binary black holes merging due to gravitational-wave radiation

The conditions for the formation of close-binary black-hole systems merging over the Hubble time due to gravitational-wave radiation are considered in the framework of current ideas about the evolution of massive close-binary systems. The original systems whose mergers were detected by LIGO consisted of main-sequence stars with masses of 30–100M _⊙. The preservation of the compactness of a binary black hole during the evolution of its components requires either the formation of a common envelope, probably also with a low initial abundance of metals, or the presence of a “kick”—a velocity obtained during a supernova explosion accompanied by the formation of a black hole. In principle, such a kick can explain the relatively low frequency of mergers of the components of close-binary stellar black holes, if the characteristic speed of the kick exceeds the orbital velocities of the system components during the supernova explosion. Another opportunity for the components of close-binary systems to approach each other is related to their possible motion in a dense molecular cloud.     

Discontinuous plasma flows near reconnecting current layers in solar flares

A model for magnetic reconnection in high-conductivity plasma in the solar corona is analyzed in a strong-magnetic-field approximation. The model includes a Syrovatskii current layer and magnetohydrodynamic (MHD) discontinuities attached to the ends of the layer. A two-dimensional analytical solution for the magnetic field is used to compute the distributions of the plasma flow velocity and plasma density in the vicinity of the corresponding current configuration. The properties of jumps in the density and velocity along the attached discontinuities are studied. Based on the character of the variations of the magnetic field and plasma flows at the MHD discontinuities, it is shown that, with the parameter values considered, an MHDdiscontinuity can include regions of trans-Alfvénic, fast, and slowshocks. The results obtained could be useful to explain the presence of “super-hot” (with effective electron temperatures exceeding 10 keV) plasma in solar flares. Other possible applications of the theory of discontinuous flows near regions of magnetic reconnection to analogous non-stationary phenomena in astrophysical plasmas are noted.     

Radio synchrotron emission by protons and electrons in pulsars and the nuclei of quasars

Relations enabling estimation of the limiting brightness temperature of synchrotron radiation subject to self-absorption and inverse Compton scattering are presented for the case of relativistic electrons (positrons) and protons. Analogous expressions are presented for relativistic particles moving along curved magnetic lines of force (curvature radiation) and coherent radiation by relativistic particles. These relations can be used to determine the brightness temperatures expected for the central regions of active galactic nuclei, neutron stars, and other objects that produce relativistic particles. Radiation by relativistic protons yields higher intensities, and could be a source of the highest-energy cosmic rays.     

理论模型分析卡尔曼滤波在航空全张量磁力梯度测量中的应用效果

航空全张量磁力梯度测量数据中包含非常复杂的运动噪声,在频谱图中从低频至高频均有分布,并以白噪声为主,如何有效压制运动噪声是一个较大的挑战。传统的数字滤波只能滤除指定频段的噪声,对于混叠在全张量磁力梯度有用信号中的噪声不能有效分离。鉴于卡尔曼滤波是一种快速、高效和实时的最优估计方法,笔者将其应用到航空全张量磁力梯度数据处理中,搭建合理的状态方程和观测方程,通过模型实验验证了方法的有效性,结果显示全区噪声衰减因子优于0.92,即能够去除92%以上噪声成分,全区均方误差优于10 pT/m,可应用于航空全张量磁力梯度数据实时处理。     

A point source of radiation in the early Universe: Solution in a one-dimensional approximation

The radiation field of a point source with a specified power in the early Universe acting for a specified time in the radiation-dominated epoch after the annihilation of electron-positron pairs is considered. A three-component model for this period is adopted. The equations of radiative transfer for the source are formulated, taking into account polarization arising during scattering of the radiation by free electrons. Analytical, numerical, and asymptotic solutions of the transfer equation are obtained for a flat model in a one-dimensional approximation, which describe the evolution of the intensity and flux of scattered radiation of the source in periods close to the onset of its action. Intervals of redshift corresponding to these periods are estimated. The behavior of the linear polarization near the source is traced. It is shown that the source radiation can be comparable to the thermal background only if the source energy is very high or we consider regions in its immediate vicinity. More optimistic estimates will require that we take into account the decrease in the degree of ionization of matter in the epoch of recombination.