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1.
Faster than light or superluminal motion was originally predicted as a relativistic illusion of ballistic moving ejecta, and confirmed in a few tens of sources observationally. However, the recent results of the long-term multi-epoch observations of quasars, active galaxies, tracing the structure further along the jets and following the motion of individual features for longer time, raise questions that are difficult to understand by the standard ballistic model. That is, the ejecta are aligned with the local jet direction, instead of the core; and within individual jets apparently inward-moving features are observed. Here, we show that these unexpected phenomena, although only a small fraction among large samples, indicate the existence of non-ballistic jet motion, in which a continuous jet produces a discrete hot spot. And the precession of such a hot spot in the plane of the sky appears superluminal. Therefore, a unified and simple interpretation to the new results is obtained, which can be further tested through its predictions on the evolution of ejecta. The study is of importance in the understanding of the nature of superluminal motion, the interaction of jets and surrounding materials, as well as the common physics underlying quasars and microquasars.  相似文献   

2.
The importance of energetic particles in the generation of solar flares and related phenomena has been underestimated if not completely neglected. A reexamination of their role in the light of recent observations carried out during the last solar maximum by a number of experiments on SMM and Hinotori satellites points out the continuous and violent evolution of the solar atmosphere. Most observed features can be better explained by the old idea that particles are trapped in magnetic loops above active regions where they are first heated and then accelerated by absorbing part of the wave energy flowing upwards continuously from the convection zone. Their catastrophic release into the chromosphere as a consequence of an instability in the region such as chromospheric heating or due to the emergence of new magnetic flux is considered as being the flare proper. Since the trapping of the particles involves the generation of resonant waves, a reassessment of the isotopic overabundance problem as well as a search for these waves in interplanetary space are proposed.  相似文献   

3.
The continuous reflection of Alfven waves in the coronae of the Sun and stars is considered. Based on the WKB approximation, the solution to the linear wave equation in the case of a stratified isothermal atmosphere has been obtained. A critical analysis of results obtained by Ferraro and Plumpton (1958) and Hollweg (1972), as well as the relations in the Elsasser variables has been carried out. It has been shown that Alfven disturbances do not undergo a continuous reflection within the accepted model and are transformed into intermediate-type modes that possess the properties of vibrations and travelling waves. The problem of the turbulization of corona plasma is discussed. The origin of the Alfven waves that propagate toward the Sun is related to the development of parametric instability.  相似文献   

4.
This paper considers the hemispheric pattern of solar filaments using newly developed simulations of the real photospheric and 3D coronal magnetic fields over a six-month period, on a global scale. The magnetic field direction in the simulation is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or helicity of the opposite sign, then this percentage is much reduced. In addition, the simulation produces a higher proportion of filaments with the correct chirality after longer times. This indicates that a key element in the evolution of the coronal field is its long-term memory, and the build-up and transport of helicity from low to high latitudes over many months. It highlights the importance of continuous evolution of the coronal field, rather than independent extrapolations at different times. This has significant consequences for future modelling such as that related to the origin and development of coronal mass ejections.  相似文献   

5.
By reformulating the basic equations governing the steady, compressible dusty fluid in magneto-fluid flows, certain geometric results of physical importance are obtained. The congruence of the stream lines and magnetic field lines have been taken as the orthogonal coordinate curves on the Maxwellian surfaces.  相似文献   

6.
We undertake calculations of the time-dependent structure of shock waves propagating in dark and diffuse interstellar clouds. The results of the time-dependent model are compared with those obtained by means of an independent steady-state code and found to agree well at sufficiently late times. Discontinuities in the flow of the neutral fluid are handled by introducing a pseudo-viscosity. Special procedures are adopted to correct for the associated widening of the discontinuity, in order not to distort the role of inelastic collision processes. We find that, in dark clouds, C shocks will tend to predominate, but are unlikely to have attained steady state in the cloud lifetime. On the other hand, in diffuse clouds, steady state may be reached but the discontinuity in the flow of the neutral fluid remains. We find no evidence for the existence of C* shocks, in which the neutral fluid undergoes a continuous transition from supersonic to subsonic flow (in the reference frame of the shock wave). Attention is drawn to the possible importance of these results for the interpretation of H2 rovibrational line intensities.  相似文献   

7.
In this paper, an analysis of the aluminum reflector mesh panels for the Five-hundred meter Aperture Spherical Telescope (FAST) is described. The study concentrates on one element of the reflector surface with the shape of a triangle. For the analysis, the panel is modelled as a mesh of cables so that it can be treated as continuous. It is demonstrated that the results so obtained are reasonable. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
The process of disc accretion onto rotating nonmagnetized stars is considered. Closed system of equations is written for the boundary layer which exists between Keplerian outer part of the disc and more slowly rotating star surface. Under certain simplifying assumptions the system is solved numerically for main physical variables. Energy conservation equation is used for finding the boundary layer radiation intensity. The results are discussed with a special emphasize on their importance as well as on possible shortcomings.  相似文献   

9.
Results of calculations of the cross-sections of the basic processes forming continuous absorption in the photospheres of solar-type stars in the visible and infrared spectral ranges are reported. (These processes are photoionization of H– ions and excited hydrogen atoms, as well as absorption of photons by “free” electrons being in the partially ionized plasma of the photosphere.) The effective cross-section of hydrogen satisfying the observational data or the results of laboratory experiments was introduced, and its nonmonotonic behavior caused by photoionization of excited hydrogen atoms was ascertained in the spectral range of λ from 650 to 820 nm. For a plane-parallel model of the Sun, the continuous absorption coefficient κ c (λ|z) was calculated as a function of the wavelength and coordinate. Its spectral features caused by the effective cross-section structure in the above-mentioned spectral range were for the first time analyzed. The spectral dependence of the radiation intensity in the solar disk center in the continuous spectral range of λ from 600 to 900 nm was studied. The calculation results were compared to the currently available data of observations. It has been shown that the deviation of the observed radiation intensity from the Planck distribution (i.e., the depression) is caused by the processes of photoionization of the excited hydrogen atoms in the states with a principal quantum number n = 3. In the range of λ from 650 to 820 nm, the mean relative deviation is approximately 4%. It has been established that the magnitude of the depression effect significantly depends on the effective temperature of the photosphere of a solar-type star.  相似文献   

10.
We present the results of a year-long monitoring campaign on J1819+3845.We interpret the results of this WSRT campaign to infer critical source parameters such as source lifetime and structure on tens of microarcseconds. The long lifetime of the source at such high brightness temperatures requires continuous energy injection or exotic emission processes. We have previously interpreted the extreme scintillation ofJ1819+3845 as due to a relatively nearby (∼ 20 pc) scattering screen. We show this screen has a velocity w.r.t. the LSR of ∼ 25 kms-1, as measured by the changing scintillation properties throughout the year: the `velocity parallax'. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
The authors investigate the solution of a nonlinear reaction-diffusion equation connected with nonlinear waves. The equation discussed is more general than the one discussed recently by Manne et al. (2000). The results are presented in a compact and elegant form in terms of Mittag-Leffler functions and generalized Mittag-Leffler functions, which are suitable for numerical computation. The importance of the derived results lies in the fact that numerous results on fractional reaction, fractional diffusion, anomalous diffusion problems, and fractional telegraph equations scattered in the literature can be derived, as special cases, of the results investigated in this article.  相似文献   

12.
We discuss the effects of a Comptonizing corona on the appearance of the reflection components, and in particular of the reflection hump, in the X-ray spectra of accreting black holes. Indeed, in the framework of a thermal corona model, we expect that some (or even all, depending on the coronal covering factor) of the reflection features should cross the hot plasma, and thus suffer Compton scattering, before being observed. We have studied in detail the dependence of these effects on the physical (i.e. temperature and optical depth) and geometrical (i.e. inclination angle) parameters of the corona, concentrating on the slab geometry. Owing to the smoothing and shifting towards high energies of the Comptonized reflection hump, the main effects on the emerging spectra appear above 100 keV. We have also investigated the importance of such effects on the interpretation of the results obtained with the standard fitting procedures. We found that fitting Comptonization models, taking into account Comptonized reflection, by the usual cut-off power law + unComptonized reflection model may lead to an underestimation of the reflection normalization and an overestimation of the high-energy cut-off. We discuss and illustrate the importance of these effects by analysing recent observational results, such as those of the galaxy NGC 4258. We also find that the Comptonizing corona can produce and/or emphasize correlations between the reflection feature characteristics (like the iron line equivalent width or the covering fraction) and the X-ray spectral index, similar to those recently reported in the literature. We also underline the importance of these effects when dealing with accurate spectral fitting of the X-ray background.  相似文献   

13.
The question of whether or not the Earth's climate is influenced by solar activity has received considerable attention since the mid-nineteenth century. Most investigations have adopted the sunspot number as the parameter of solar activity. Recently, however, it has been shown by Friis-Christensen and Lassen (1991) that the mean northern hemisphere temperature, from 1861–1990, follows a strikingly similar trend to thelength of the sunspot cycle, suggesting that the recent global warming could, at least in part, arise from changes in solar activity. In view of the importance of this result, we have examined a set of continuous meteorological records, maintained at Armagh Observatory since 1844, to assess, first, whether data from a single site can give meaningful information on global trends, and second, whether the data from this particular site for the period 1844–1866 can be used to extend the baseline of the comparison with solar activity. We find that both are indeed the case and that there is a strong correlation between the solar cycle length and the mean temperature at Armagh over the past 149 years.  相似文献   

14.
A generalized form of the Bennett pinch is studied in both cylindrical geometry and plane-parallel geometry. In this kind of pinch electromagnetic forces, kinetic pressure gradient forces, centrifugal forces, and gravitational forces may act. For each of the two geometries considered a generalized Bennett relation is derived. By means of these relations it is possible to describe among other things the pure Bennett pinch, Jean's criterion in one and two dimensions, force-free magnetic fields, gravitationally balanced magnetic pressures, and continuous transitions between these states. The theory is applied to electric currents in the magnetosphere, in the solar atmosphere, and in the interstellar medium. It is pointed out that the currents in the solar atmosphere and in the interstellar medium may lead to pinches that are of vital importance to the phenomena of solar flares and star formation, respectively.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.  相似文献   

15.
We review large scale modelling of the ISM with emphasis on the importance to include the disk-halo-disk duty cycle and to use a dynamical refinement of the grid (in regions where steep variations of density and pressure occur) for a realistic modelling of the ISM. We also discuss the necessity of convergence of the simulation results by comparing 0.625, 1.25 and 2.5 pc resolution simulations and show that a minimum grid resolution of 1.25 pc is required for quantitatively reliable results, as there is a rapid convergence for Δ × ≤ 1.1 pc.  相似文献   

16.
In a correlated study using coronagraph and interplanetary data from 1978 to 1983, a set of 56 coronal mass ejections (CMEs) was confidently associated with interplanetary shocks by Sheeleyet al. (1985). In this paper we analyze the characteristics of these particular CMEs in contrast to the whole population of them during the period. We find that the associated CMEs are not a representative sample of all the variety of CMEs and that they share specific characteristics. Contrary to common beliefs, these characteristics are not a high velocity or a large extension, but have more to do with the importance and shape of the CME. Practically all the CMEs associated with shocks were of importance Y (bright and/or large) and had a curved-type front structural class (a continuous curved front with either straight edges or curved legs). Another common characteristic of these particular CMEs is that they show a considerable increase in their angular span as they go out from the Sun, moving the peak of the distribution from 30° to 70°.  相似文献   

17.
Inversion techniques of the radiative transfer equation for polarized light are presented as one of the best current procedures to infer the vector magnetic field, as well as other quantities governing the physical state of the atmospheric layers that photons are coming from. Several characteristics of the various available inversion procedures are pointed out. They are mostly based on the diagnostic contents of the spectral lines as well as on the main hypotheses assumed in these procedures. In particular, the role of gradients in the atmospheric quantities is emphasized as of paramount importance in any diagnostic analysis and, hence, in any interpretation of inversion results.  相似文献   

18.
We report results from 6 days' continuous recording of pulsation activity on a chain of magnetometers aligned East-West at 56.5°N geomagnetic latitude. We find phase differences between stations are relatively small. Signal propagation sense and horizontal polarisation correlate as low frequency inhomogeneous plasma theory predicts. There is no evidence of the Kelvin-Helmholtz instability being the major source. The most highly coherent signals often occur near midnight. We suggest the nightside may be the source region for a significant amount of dayside pulsation activity.  相似文献   

19.
We present a mathematically rigorous proof that the r-mode spectrum of relativistic stars to the rotational lowest order has a continuous part. A rigorous definition of this spectrum is given in terms of the spectrum of a continuous linear operator. This study verifies earlier results by Kojima concerning the nature of the r-mode spectrum.  相似文献   

20.
We succeeded in several attempts at measuring the solar limb-darkening in the continuous spectrum between 1800 Å and 2900 Å. Good spectroheliograms were obtained during a rocket flight in November 1964 and during a balloon flight in October 1966 at 2190 Å, 2665 Å, 2885 Å, and 1980 Å, 2235 Å respectively. A rocket flown at the beginning of 1967 provided excellent spectra allowing the measurement of center-to-limb variation in the continuum and lines from 1800 Å to 2800 Å.The first series of pictures yielded absolute values of the central intensity leading to a minimum temperature close to 4700 °K. The continuous opacity of the photosphere layers has been deduced from the two first experiments. It seems that a non-metallic source of continuous absorption must be taken into account between 2500 Å and 3000 Å. Moreover, as the source functions for the shortest wavelengths show a very flat variation near the minimum temperature, it seems that the transition zone between the photosphere and the chromosphere must be very gradual.These results are discussed in the light of the latest results deduced from the new spectra obtained.  相似文献   

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