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1.
A Monte Carlo simulation is used in order to study the effects of wave-particle interactions (WPI) on H+ distributions in the polar wind outflow. The simulation also considers effects of the gravity, the polarization electric field, the divergence of geomagnetic field lines and H+−O+ Coulomb collisions. The proton velocity distribution function (VDF) and the profiles of its moments (density, bulk velocity, parallel and perpendicular temperatures, heat flux…) are found for different levels of WPI, i.e., for different values of the normalized diffusion rate in the velocity space (D ⊥). We find that the wave-particle interactions accelerate the polar wind and can have important effects on the double-hump H+ distribution obtained in the transition region between the collision-dominated low altitudes and the collisionless high altitude regions.  相似文献   

2.
The inertial range of incompressible MHD turbulence is most conveniently described in terms of counter propagating waves. Shear Alfvén waves control the cascade dynamics. Slow waves play a passive role and adopt the spectrum set by the shear Alfvén waves. Cascades composed entirely of shear Alfvén waves do not generate a significant measure of slow waves. MHD turbulence is anisotropic with energy cascading more rapidly along k ⊥ than along k ∥. Anisotropy increases with k ⊥ such that the excited modes are confined inside a cone bounded by k ∥∝ k perp 2/3. The opening angle of the cone, θ(k ⊥)∝ k ⊥ -1/3, defines the scale dependent anisotropy. MHD turbulence is generically strong in the sense that the waves which comprise it are critically damped. Nevertheless, deep inside the inertial range, turbulent fluctuations are small. Their energy density is less than that of the background field by a factor θ2(k ⊥)≪. MHD cascades are best understood geometrically. Wave packets suffer distortions as they move along magnetic field lines perturbed by counter propagating wave packets. Field lines perturbed by unidirectional waves map planes perpendicular to the local field into each other. Shear Alfvén waves are responsible for the mapping's shear and slow waves for its dilatation. The former exceeds the latter by θ-1(k ⊥)≫ 1 which accounts for dominance of the shear Alfvén waves in controlling the cascade dynamics. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
Li  Xing  Habbal  Shadia R. 《Solar physics》1999,190(1-2):485-497
The effect of alpha particles on the dispersion relation of ion cyclotron waves and its influence on the heating of the solar wind plasma are investigated. The presence of alpha particles can dramatically change the dispersion relation of ion cyclotron waves, and significantly influence the way that ion cyclotron waves heat the solar wind plasma. We find that a spectrum of ion cyclotron waves affects the thermal anisotropy of the solar wind protons and other ions differently in interplanetary space: When alpha particles have a speed u α>0.5v A, and both protons and alpha particles have a thermal anisotropy T ⊥/T ∥>1, ion cyclotron waves heat protons in the direction perpendicular to the magnetic field, cool them in the parallel direction, and exert the opposite effect on alpha particles.  相似文献   

4.
Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference  相似文献   

5.
M. Lazar  S. Poedts 《Solar physics》2009,258(1):119-128
Electromagnetic instabilities in high-β plasmas, where β is the ratio of the kinetic plasma energy to the magnetic energy, have a broad range of astrophysical applications. The presence of temperature anisotropies T ∥ /T ⊥ >1 (where ∥ and ⊥ denote directions relative to the background magnetic field) in solar flares and the solar wind is sustained by the observations and robust acceleration mechanisms that heat plasma particles in the parallel direction. The surplus of parallel kinetic energy can excite either the Weibel-like instability (WI) of the ordinary mode perpendicular to the magnetic field or the firehose instability (FHI) of the circularly polarized waves at parallel propagation. The interplay of these two instabilities is examined. The growth rates and the thresholds provided by the kinetic Vlasov – Maxwell theory are compared. The WI is the fastest growing one with a growth rate that is several orders of magnitude larger than that of the FHI. These instabilities are however inhibited by the ambient magnetic field by introducing a temperature anisotropy threshold. The WI admits a larger anisotropy threshold, so that, under this threshold, the FHI remains the principal mechanism of relaxation. The criteria provided here by describing the interplay of the WI and FHI are relevant for the existence of these two instabilities in any space plasma system characterized by an excess of parallel kinetic energy.  相似文献   

6.
Kinetic Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of the kinetic Alfven wave in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species was modeled by drifting ring distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution was simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures. We find that for frequencies w* < wcH +\omega^{*} < \omega_{c\mathrm{H}^{ +}} (ω ∗ and wcH +\omega_{c\mathrm{H}^{ +}} being respectively the Doppler shifted and hydrogen ion gyro-frequencies), the growth rate increases with increasing negatively charged oxygen ion densities while decreasing with increasing propagation angles, negative ion temperatures and negative ion mass.  相似文献   

7.
In previous studies, transport of solar energetic particles in the inner heliosphere was regarded as one-dimensional along the Archimedean field spiral; i.e., any perpendicular transport is neglected. We extend Roelof’s equation of focused transport for solar energetic particles to accommodate perpendicular transport in the plane of the ecliptic. Numerically, this additional term is solved with an implicit Laasonen scheme. In this first approximation, it is solved for azimuthal instead of perpendicular transport – these are similar in the inner heliosphere where the Archimedean field is almost radial. The intent of the study is to estimate the possible influence of perpendicular transport, but not to fit energetic particle events; thus, the particle source stays fixed on the Sun. For typical ratios κ ⊥ /κ ‖ between 0.02 and 0.1 at 1 AU scaled with r 2 as suggested in nonlinear guiding-center theory, we find that i) an azimuthal spread over some 10° occurs within a few hours, ii) the variation of maximum intensities with longitude is comparable to the ones inferred from multispacecraft observations, and iii) on a given field line, intensity and anisotropy-time profiles are modified such that fits with the two-dimensional transport model give different combinations of injection profiles and mean free paths. Implications for the interpretation of intensity and anisotropy-time profiles observed in interplanetary space and consequences for our understanding of particle propagation and acceleration in space are discussed.  相似文献   

8.
We present narrow-band emission line (Hα + [N II]λλ 6548, 6583, [O III] λλ 4959, 5007)as well as green or red continuum images of selected Seyfert galaxies. The sample includes NGC 7214, IC 4218, Akn 479, Mrk 915, IC 1515 and F 348. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
Optical spectroscopic data are presented on nova LW Serpentis 1978, obtained during its decline fromV 9.0 to ≃10.2 (compared to a value of ∼ 8.0 at recorded maximum). The spectrum and its evolution compare well with a typical nova, though the principal absorption (∼ −750 km s−l) was very weak in comparison with the diffuse-enhanced absorption (∼ −1300 km s−1). The principal absorption could be identified only in the lines of O I λλ7774, 8446, and in moderate-resolution observations of Hα. The salient features of spectral evolution follow: The near-infrared triplet of Ca n continuously weakened. O I λ8446 was always brighter than O I λ 7774, indicating continued importance of Lyman Β fluorescence. The lines due to [O I], [N II] and N n brightened considerably near the end of our observations (37 days from maximum). The Hα emission line was asymmetric all through with more emission towards the red. Its emission profile showed considerable structure. Based on the individual peaks in the Hα line profile, a kinematical model is proposed for the shell of LW Ser. The model consists of an equatorial ring, and a polar cone on the side away from the earth. The nearer polar cone did not show significant emission of Hα during our observations. The polar axis of the shell is inclined at a small angle (∼ 15‡) to the line of sight.  相似文献   

10.
Stochastic temperatures and turbulence are characterized by average velocities u th and < u turb  > ≡ u 0 and fluctuations u￠th {u'_{th}} and u′ (<u′ > = 0). Thus, the Doppler width of a line also has a fluctuating component Dl￠D \Delta {\lambda '_D} . Observed spectra correspond to the radiative flux averaged over time and over a star’s surface, <Hλ>. Usually, only the average velocities u th and u 0 are taken into account in photospheric models and these yield the Doppler width DlD(0) \Delta \lambda_D^{(0)} of a line in the customary way. The fluctuations Dl￠D \Delta {\lambda '_D} mean that near a line center the average absorption coefficient < αλ > is larger than the usual αλ, which depends only on the average velocities u th and u 0. This enhances the absorption line near the center and is not explained by the photospheric models. This new statistical effect depends on the wavelength of the line. A comparison of observed lines with model profiles yields an estimate for the average level of fluctuations in the Doppler width, h = á | Dl￠D | ñ
/ DlD(0) \eta = {{{\left\langle {\left| {\Delta {{\lambda '}_D}} \right|} \right\rangle }} \left/ {{\Delta \lambda_D^{(0)}}} \right.} , which characterizes the average stochasticity of a photosphere and is important for understanding the physics of photospheres. The depths of lines in synthetic spectra of stars are often greater than the observed values. The observed disagreement between the theoretical and actually observed depths of lines can be corrected by introducing an additional parameter, the fluctuation level η. Then it is possible to obtain estimates of η for a number of stars.  相似文献   

11.
We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates were selected from the Massey et al. catalog based on the following criteria: emission in H α , V<18./m 5 and 0.m 35 < (B - V) < 1.m 2. The spectra of both stars reveal a broad and strong H α emission with extended wings (770 and 1000 kms−1). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L⊙) = 6.0–6.2 with the value of interstellar extinction A V = 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero Age Main Sequence is M∼ 60–80 M⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L⊙) = 6.3 − 6.6, the value of interstellar extinction is A V = 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two thermal components with the temperatures Twarm ∼ 1000K and Tcold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and broad H α emissions allow classifying the studied objects as LBV candidates.  相似文献   

12.
Based on our spectroscopic observations of the variable planetary nebula IC 4997 in 2003–2009, we have obtained the relative fluxes in optical emission lines. The interstellar extinction c = 0.35 has been found from the Balmer decrement by taking into account the effect of self-absorption in hydrogen lines in dense nebular regions. The variations in the Balmer decrement point to variability of the self-absorption and circumstellar extinction. We have investigated the variations in the relative intensities of some spectral lines and their ratios with time. The drop in the ratios F(λ4363)/F(Hγ) and F(λ363)/F(λ4959) that began back in 1990–1995 has continued, suggesting a decrease in the electron density and temperature in the central nebular region. The ratio F(λ6731)/F(λ6717) has remained constant. It gives an estimate for the electron density in the outer regions of IC 4997, N e ∼ 104 cm−3.  相似文献   

13.
It is argued that ozone measurements made by Weeks et al. (1972) can be interpreted in terms of the enhanced ionization present. The conversion of O2+ ions to oxonium, H3O+ · (H2O)n, ions plus the dissociative recombination of these ions provides for an increased OH and/or H formation rate. The resulting enhanced OH and HO2 concentrations reduce the ambient atomic oxygen and hence ozone populations. The net excess H + OH formation rate is found to lie between one and two times the ionization production rate at altitudes where oxonium ions are the dominant positive ion species.  相似文献   

14.
The study of nonequilibrium, self-gravitating, compressible, homogeneous and uniformly rotating gaseous ellipsoidal models is extended from parallel to nonparallel angular velocity and vorticity. The differential equations of motion governing these models are numerically integrated over ranges of initial values of angular velocity and vorticity. The dynamical behaviour of the ellipsoid is found to be almost unchanged when the initial values of Ω3/Ω3,e and λ3/λ3,e are interchanged, where λ is a function of the vorticity, Ω3 is the angular velocity along the x3 axis, and Ω3,e and λ3,e are equilibrium values. Models with the same initial value of | Ω3/Ω3,e - λ3/λ3,e | have similar dynamical behaviour. When this value becomes larger, the oscillations of the semi-axes are larger and are more nonperiodic. For all models, the ellipsoidal configuration is maintained at all times. The magnitude of Ωl depends on the difference between the values of the semi-axes am and an, where l, m, and n are cyclic. The smaller this difference is, the larger the angular velocity along the third axis. Thus whenever the model approaches a spheroidal configuration, there may be a large and rapid increase in the angular velocity along the axis of ‘symmetry’. The last two properties, namely the maintenance of the ellipsoidal configuration and the large increase in angular velocity of the model, configuration also hold in the model (T.T.Chia and S.Y.Pung, 1995, Astrophys.\ Space Sci., 229, 215.) with parallel angular velocity and vorticity. However, unlike the earlier model, Ω2 and Ω3 are observed to reverse their directions at certain instants during the oscillations; this may have interesting astrophysical implications. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

15.
The present work is about the interpretation of the linear polarization of the O VI D2 (λ1032) coronal line observed by SUMER/SoHO. We take into account the effect of the Doppler redistribution due to the scattering ions motion. We consider the cases of isotropic and anisotropic velocity field distributions. The latter can be interpreted by the ioncyclotron effect that affects heavy ions in the solar corona. The comparison of the numerical results with the observations yields constraints on the solar wind outflow speed and on the velocity field distribution of the O5+ ions at low coronal altitudes in the polar holes.  相似文献   

16.
If cooled-down neutron stars have a thin atomic crystalline–iron crust, they must diffract X-rays of appropriate wavelength. If the diffracted beam is to be visible from Earth (an extremely rare but possible situation), the illuminating source must be very intense and near the reflecting star. An example is a binary system composed of two neutron stars in close orbit, one of them inert, the other an X-ray pulsar. (Perhaps an “anomalous” X-ray pulsar or magnetar, not powered by gas absorption from the companion or surrounding space, would be the cleanest example.) The observable to be searched for is a secondary peak added (quasi-) periodically to the main X-ray pulse. The distinguishing feature of this secondary peak is that it appears at wavelengths related by simple integer numbers, λ,λ/2,λ/3,…,λ/n because of Bragg’s diffraction law.  相似文献   

17.
The results of morphological and spectral study of the galaxies Kaz 5, Kaz 92, and Kaz 390 are presented. The observations were made on the 2.6-m telescope at the Byurakan Observatory with the VAGR microlenses spectrograph. Isophotes of the images of the galaxies are constructed in the Hα, [NII] λλ6584 , 6548, and [SII] λλ6731, 6717 emission lines and in the continuum. The masses of Kaz 5 and Kaz 92 are determined to be 8.6 × 108 M⊙ and 6.1 × 109 M⊙ , respectively. The mass of the gaseous component in the centers of regions I and IV of Kaz 390, which encompass a 1 pixel area, are also determined. The morphological structure of the central region of Kaz 5 in the observed spectral range, λλ6400–6800?, differs completely from the structure of the same part of the galaxy observed with the 6-m and 2.5-m telescopes. It is shown that these differences in the structure in images of Kaz 5 are mostly explained by the comparatively low resolution of the telescope in combination with the VAGR spectrograph. Absorbing matter also contributes to this effect. It is also shown that a “deficit” of nitrogen has been observed in the region of Kaz 390 studied here (a circle of diameter 40″). Translated from Astrofizika, Vol. 52, No. 1, pp. 63–74 (February 2009).  相似文献   

18.
We calculated the variations of Rayleigh optical depth with changes of pressure and temperature for three observation sites: Simferopol (φ = 44°57′N, λ = 34°8′E, h = 265 m above sea level), Nauchny (φ = 44°43′N, λ = 34°3′E, h = 583 m), and Ai-Petry meteorological station (φ = 44°24′N, λ = 34°6′E, h = 1180 m).  相似文献   

19.
The nonlinear ion-acoustic double layers (IADLs) in a warm magnetoplasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive a modified Zakharov–Kuznetsov (MZK) equation, in the small amplitude regime. It is found that compressive and rarefactive IADLs strongly depend on the mass and density ratios of the negative-to-positive ions as well as the nonthermal electron parameter. Also, it is shown that there are one critical value for the density ratio of the negative-to-positive ions (ν), the ratio between unperturbed electron-to-positive ion density (μ), and the nonthermal electron parameter (β), which decide the existence of positive and negative IADLs. The present study is applied to examine the small amplitude nonlinear IADL excitations for the (H+, O2-)(\mathrm{H}^{+}, \mathrm{O}_{2}^{-}) and (H+,H−) plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the nonlinear IADLs in either space or laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.  相似文献   

20.
We present new ultraviolet spectra of the hottest known, peculiar white dwarf H1504+65, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. H1504+65 is the hottest known white dwarf (T eff=200 000 K) and has an atmosphere mainly composed by carbon and oxygen, augmented with high amounts of neon and magnesium. This object is unique and the origin of its surface chemistry is completely unclear. We probably see the naked core of either a C–O white dwarf or even a O–Ne–Mg white dwarf. In the latter case, this would be the first proof that such white dwarfs can be the outcome of single-star evolution. The new observations were performed to shed light on the origin of this mysterious object.  相似文献   

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