共查询到20条相似文献，搜索用时 359 毫秒
1.
A separation mechanism is proposed which is effective in collisions between ionized but unmagnetized clouds of matter and anti-matter. This involves an electromagnetic instability which grows at the encounter layer, producing magnetic fields strong enough to separate the clouds after a very small interpenetration. 相似文献
2.
J. Jimenez-Vicente E. Battaner C. Porcel M. Rozas H. Castañeda 《Astrophysics and Space Science》2001,276(2-4):445-449
We have studied the kinematics of the ionized gas in the nearly face-on galaxy NGC 3938 by means of observations made with
theFabry–Perot interferometer TAURUS II at the William Herschel Telescope, using the Hα line. We have been able to produce high-resolution velocity and velocity-dispersion maps which allow us to make a detailed
study of the kinematics of the ionized gas. In particular we have found that the vertical velocity dispersion is constant
with galactocentric radius, as has already been found for the atomic and molecular gas in this galaxy. This suggests the existence
of several heating mechanisms in the disc acting simultaneously to produce the observed behaviour.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
S. Hayakawa 《Astrophysics and Space Science》1974,31(2):L13-L14
Suprathermal dust grains as suggested by Wickramasinghe produce electrons of energies not higher than 20 eV by Coulomb collisions with free electrons in an interstellar medium. These electrons are responsible for the production of singly ionized ions but not effective for that of highly ionized ones. This explains a general feature of the composition of atoms and ions as observed from the Copernicus satellite. 相似文献
4.
Magnetic fields play an important role in astrophysics and they often dominate the behavior of magnetized media. We simulate
the mechanism (Tagger et al., 1995) by which turbulence in a weakly ionized plasma, as it cascades to the ambipolar scale
(where the neutrals are imperfectly coupled to the ions) leads to a filamentation of the magnetic flux tubes: the turbulent
velocity of the neutrals is higher in the more ionized regions, because they are better coupled to the ions. This results
in a non-linear ponderomotive (<v.∇ v>) force driving them out of the ionized regions, so that the initial ionization inhomogeneities
are strongly amplified. This effect causes the ions and magnetic field to condense and separate from the neutrals, resulting
in a filamentary structure. We present the first results of a 2-D, 2-fluid (ions and neutrals) simulation, where a magnetized,
weakly ionized plasma is submitted to turbulence in the ambipolar frequency range. We discuss the efficiency of this mechanism,
the filamentary structure it should produce, and its relevance to the astrophysical context.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Many observations indicate the occurrence of ionized gas in the distant haloes of galaxies (including our own). Since photoionization by stars (mainly O stars, young stars or evolved low-mass stars depending on the kind of galaxy) does not seem to be exclusively responsible for the ionization of the hydrogen filaments that should otherwise cool fast and recombine quickly, the question arises which extra energy source can produce the quasi-stationary ionization. We show that stationary localized magnetic reconnection in current filaments may contribute to the ionization of the extraplanar halo gas. In these filaments magnetic energy is dissipated. Consequently, the ionized as well as the neutral component is heated and re-ionized on a time-scale significantly shorter than the recombination time-scale. The amount of energy required for efficient re-ionization can in principle easily be provided by the free magnetic energy. We present quasi-static models that are characterized by plasma temperatures and densities that agree well with the observed values for the diffuse ionized gas component of the interstellar medium. Plasma–neutral gas fluid simulations are made to show that the recombination-induced dynamical reconnection process indeed works in a self-regulatory way. 相似文献
6.
S. Hayakawa 《Astrophysics and Space Science》1975,34(1):73-79
Dust grains expelled by radiation pressure of stars are charged to potentials in the range 30–40 V in Hi clouds. These grains may be responsible for the following phenomena which are otherwise hardly explicable. (1) A considerable fraction of electrons knocked-out by charged grains of high speeds have energies around 15 eV and produce singly ionized ions but not doubly ionized ones in accord with an ultraviolet observation of interstellar atoms and ions. (2) Transverse momentum transferred to grains by Coulomb scattering of ambient electrons and protons is greater than that by multiple scattering of cosmic ray protons, thus the former being more effective for the grain alignment than the latter. (3) At a shock front charge separation due to a large inertial mass of grains produces an electric field, thus accelerating charged particles and causing a drift of interstellar matter. 相似文献
7.
S. C. O. Glover 《Monthly notices of the Royal Astronomical Society》2007,379(4):1352-1358
H2 formation in metal-free gas occurs via the intermediate H− or H+ 2 ions. Destruction of these ions by photodissociation therefore serves to suppress H2 formation. In this paper, I highlight the fact that several processes that occur in ionized primordial gas produce photons energetic enough to photodissociate H− or H+ 2 and outline how to compute the photodissociation rates produced by a particular distribution of ionized gas. I also show that there are circumstances of interest, such as during the growth of H ii regions around the first stars, in which this previously overlooked form of radiative feedback is of considerable importance. 相似文献
8.
Douglas E. Gonzales 《Solar physics》1969,9(1):205-209
The solar wind-induced drag on magnetically large comets is estimated as follows. As the comet approaches the sun, solar radiation striking the comet surface generates a surrounding neutral atmosphere which is subsequently ionized. The resulting plasma cloud interacts with the solar wind to produce a comet magnetosphere and associated collision-free shock wave. An approximation to the accompanying drag is obtained using the similarity between the comet magnetosphere and that of the earth, and is shown to be much less than the mechanical mass loss force. 相似文献
9.
Rajat M. Thomas Saleem Zaroubi Benedetta Ciardi reas H. Pawlik Panagiotis Labropoulos Vibor Jeli&#; Gianni Bernardi Michiel A. Brentjens A. G. de Bruyn Geraint J. A. Harker Leon V. E. Koopmans Garrelt Mellema V. N. Pandey Joop Schaye Sarod Yatawatta 《Monthly notices of the Royal Astronomical Society》2009,393(1):32-48
10.
Andrea Ferrara Rosalba Perna † 《Monthly notices of the Royal Astronomical Society》2001,325(4):1643-1648
Most of the baryons in the low-redshift Universe reside in a warm/hot component which is difficult to detect with standard absorption/emission-line techniques. We propose to use quasar refractive scintillation as a useful, complementary probe for such ionized, intergalactic gas. In particular, an application to the case of the intracluster medium is presented. We show that clusters located at z ≈0.02 should produce a source rms intensity fluctuation at 50–100 GHz of several tens of per cent and on time-scales ranging from days to months, depending on the projected location of the source on the foreground cluster. However, in order to produce such a signal, the source needs to be very compact. This effect, if observed, can be used as an independent test of the baryonic mass fraction in clusters. 相似文献
11.
Broadening of lines of Be ii, Sr ii and Ba ii by collisions with hydrogen atoms and the solar abundance of strontium 总被引：1，自引：0，他引：1
In a previous paper by the present authors the theory of Anstee and O'Mara for the broadening of spectral lines of neutral atoms by collisions with hydrogen atoms was extended to singly ionized atoms. In this paper we apply the method to the resonance and triplet lines of ionized strontium, the infrared triplet of ionized barium, and the resonance lines of ionized beryllium. Analysis of five lines of ionized strontium, previously regarded as too strong for an abundance analysis, and two lines of neutral strontium results in a solar abundance of strontium of log( N Sr N H )+12=2.92±0.05, which is entirely consistent with the meteoritic value. 相似文献
12.
We present the 2-D, two fluid (ions + neutrals) numerical simulations that we are carrying out in order to study the ambipolar filamentation process, in which a magnetized, partially ionized plasma is stirred by turbulence in the ambipolar frequency range. The higher turbulent velocity of the neutrals in the most ionized regions gives rise to a non-linear force driving them out of these regions, and causes the ions and the magnetic flux to condense in the most ionized regions, resulting in a filamentary structure where initial ionization inhomogeneities are amplified. This mechanism might help to explain some features observed in magnetized and partially ionized astrophysical plasmas as the interstellar medium. 相似文献
13.
K. P. Chopra 《Planetary and Space Science》1961,5(4):288-291
A body moving in an ionized atmosphere acquires an electric charge through the processes of accretion of charged particles and emission of electrons by high energy photons. The moving charged body may then interact with the charged particles of the atmosphere and any pervading magnetic field to excite plasma waves. Of particular interest is the situation in which the body collects an ionized cloud in front of it. The motion of this ionized cloud in the atmosphere induces an electrostatic instability and causes a column of ionized gas to move ahead of the body. The electrostatic instability is conducive to the excitation of electrostatic oscillations which if already present are further enhanced. A magnetic field along the direction of motion assists in the formation of the ionized cloud. If the pervading magnetic field is of suitable weak strength, it may excite extraordinary electromagnetic waves. A pervading transverse magnetic field of suitable strength may cause the excitation of magnetohydrodynamic waves. 相似文献
14.
Mariner 9 ultraviolet spectrometer experiment: Mars airglow spectroscopy and variations in Lyman alpha 总被引：1，自引：0，他引：1
Mariner 9 ultraviolet spectrometer observations show the Mars airglow consists principally of emissions that arise from the interaction of solar ultraviolet radiation with carbon dioxide, the principal constituent of the Mars atmosphere. Two minor constituents, atomic hydrogen and atomic oxygen, also produce airglow emissions. The airglow measurements show that ionized carbon dioxide is only a minor constituent of the ionosphere. Using the airglow measurements of atomic oxygen, it is possible to infer that the major ion is ionized molecular oxygen. The escape rate of atomic hydrogen measured by Mariner 9 is approximately the same as that measured two years earlier by Mariner 6 and 7. If the current escape rate has been operating for 4.5 billion years and if water vapor is the ultimate source, an amount of oxygen has been generated that is far in excess of that observed at present. Mariner 9 observations of Mars Lyman alpha emission over a period of 120 days show variations of 20%. 相似文献
15.
Michael Dahlem 《Astrophysics and Space Science》2004,289(3-4):405-414
Starbursts are the most efficient producers of metals in the Universe at low redshifts. They produce enough energy to driveoutflows of material from their disks.This makes them important objects to study in order to understand the chemical evolution not only of the interstellar medium (ISM) in the starburst galaxies themselves, but also of the intergalactic medium (IGM) in their vicinity. However, several key quantities of starbursts that are neededas input to models of their ISM are still ill-constrained. Some of these critical parameters are e.g. the metalabundances of hot ionized gas, the ionization state ofwarm ionized gas, the amount of energy deposited intothe ambient by a starburst, the efficiency of itsconversion into mechanical energy and thus the totalkinetic energy of the star formation-driven outflowsand their kinematics. The latter are important when considering under whichcircumstances matter energized by a starburst will reach the so-called ‘blowout’ condition, i.e. supersede the threshold energy starting at which local energy injection into the ISM can drive an outflow first into the halo (where metal re-distribution might be very efficient) and eventually out into intergalactic space. I will discuss here a few of these quantities, how we canmeasure them better than in the past, and in which way some of our observing techniques need to be improved in order toobtain better constraints from the data. 相似文献
16.
The thermosolutal instability of a partially-ionized plasma in the presence of a horizontal magnetic field is considered to include the frictional effect of collisions of ionized with neutrals. The sufficient conditions for non-existence of overstability are derived. The solute gradient and magnetic field introduce oscillatory modes in thermosolutal convection which were non-existent in their absence. The magnetic field and stable solute gradient are found to have stabilizing effects whereas collisional effect of ionized with neutrals is found to have destabilizing effect on thermosolutal instability of a partially ionized plasma. 相似文献
17.
Solar observations show that magnetic reconnection can occur in the Sun's weakly ionized lower atmosphere (magnetic cancellation, Ellerman bombs and type II white-light flares). Unlike what the usual reconnection models have predicted, such a reconnection is accompanied by temperature enhancements which are less than 10%. To overcome this difficulty, we have reexamined the reconnection in a two-fluid model using a 2D numerical simulation. The numerical solutions demonstrate the following results: (1) Under the influence of Lorentz force, ionized gas carries the magnetic field into a diffusion region where part of the field is annihilated, and the current-sheet scaling laws for the weakly ionized plasma are basically the same as in the fully ionized case. (2) Though the neutral gas is not directly affected by the magnetic field due to frictional forces, its motion is almost the same as the ionized gas except in the region near stagnation point where the streamlines of both species differ appreciably. (3) The pressure of neutrals which governs the distribution of total pressure and temperature varies slightly. So the temperature of the whole domain is nearly uniform in space and constant in time. These results support the idea that magnetic cancellation, Ellerman bombs, and type II white-light flares are due to magnetic reconnection in the Sun's lower atmosphere. 相似文献
18.
V. A. Urpin 《Astrophysics and Space Science》1981,79(1):11-24
Hydrodynamical equations for a fully ionized hydrogen-helium plasma are derived by the Chapman-Enskog method. The electron and ion transport coefficients are found as the functions of electron and ion temperatures and number densities as well as of the magnetic field strength. The presented equations are needed for describing transport phenomena in laboratory and cosmic plasmas. It is shown that transport phenomena can produce abundance anomalies; e. g., a sound wave propagating through a homogeneous plasma may be accompanied by the oscillations of chemical composition. Various astrophysical consequences of the theory are discussed. 相似文献
19.
B. Lehnert 《Astrophysics and Space Science》1976,40(1):225-229
A one-dimensional model is being considered where a fully ionized plasma is separated from a neutral gas by a homogeneous magnetic field directed along the plasma boundary. The plasma and the neutral gas consist of two different types of ions and neutral particles. In a stationary state the outflux of plasma by diffusion across the magnetic field is compensated by an influx of neutrals which are ionized in a partially ionized boundary region. It is found that the ratio between the ion densities in the fully ionized region will in general differ from the density ratio of the two types of neutrals being present in the gas region. This provides a separation mechanism with applications both to cosmical and laboratory plasmas, such as in the following cases:
- The abundance anomalies in magnetic variable stars and in the solar wind.
- Separation processes of non-identical ions and neutral atoms in gas blanket systems.
20.
It is shown that nonlinear propagation of sound waves in partially ionized collisional plasmas is governed by a modified Korteweg-de Vries (mKdV) equation when the electron distribution function deviates from the Boltzmann distribution. The mKdV equation admits a sharply localized solitary sound pulse, the profile and width of which are different from that which involves the Boltzmann electron number density response. Since the electron-vortex distribution induced solitary sound pulses are more pronounced, it can easily be identified in partially ionized plasmas. 相似文献