共查询到20条相似文献，搜索用时 941 毫秒
1.
E. E. Benevolenskaya 《Solar physics》1995,161(1):1-8
The source of the poloidal magnetic field was fixed using a uniform series of surface low-resolution magnetic field observations begun at Wilcox Solar Observatory at Stanford. The results obtained confirm the idea that low-frequency dynamo waves with a period approximately equal to 22 years and a high-frequency wave of a quasi-two-year period can coexist. It seems that an interaction between these components in the convection zone takes place on the Sun. Surface large-scale solar magnetic fields are analyzed using a two-dimensional Fourier method technique to study the poloidal field distribution. The first harmonic approximately equals the period of the magnetic cycle, appears at all latitudes, and reaches its the maximum value in the polar regions. Moreover, spectral analyses of axisymmetric magnetic field derivative in time found that the second important harmonic of a period approximately equal to two years appears at all latitudes. This second high-frequency harmonic dominates the polar latitude regions at the same time as the low-frequency one. 相似文献
2.
P. P. Malovichko 《Kinematics and Physics of Celestial Bodies》2010,26(2):62-70
We consider the generation of low-frequency magnetic field disturbances in coronal loops when low density proton and electron
beams propagate in them. Two mechanisms of low-frequency magnetic field perturbation generation are analyzed. The first mechanism
is concerned with the longitudinal current generated by charged particles’ beams moving in the loop. It is shown that this
mechanism of the Alfvén waves’ generation can lead to development of low-frequency perturbations even if the currents are
very weak. It can facilitate the reconnection of magnetic fields and flare development. The second mechanism is not concerned
with currents propagating in the coronal loop. It is shown that, in this case, the proton beams can cause an instability with
significantly lower values of beam density. We found increments and criteria of the development of instabilities. Not only
Alfvén-type perturbations can be generated as a result of development of those instabilities but also kinetic Alfvén-type
perturbations can be generated. 相似文献
3.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2009,395(3):1723-1732
The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron–positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field and gives rise to the scattered component nearly antiparallel to the streaming velocity of the scattering particles. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside the MP can be explained in terms of our model. 相似文献
4.
E. E. Benevolenskaya 《Solar physics》1996,167(1-2):47-55
The polar magnetic field on the Sun changes its sign during the maximum of solar cycles. It is known that the phenomenon of three-fold reversal of the polar magnetic field occurred in solar cycle 20. Using the magnetograph data of the Mount Wilson Observatory from 1967 to 1993, we confirm a previously suggested topological model of the three-fold magnetic-field reversal (Benevolenskaya, 1991). From the data set we have found that cycles with three-fold polar magnetic field reversals are characterized by a pronounced high-frequency component of the magnetic field compared with cycles with single polar magnetic-field reversals. 相似文献
5.
A. Papageorgiou T. V. Cawthorne A. Stirling D. Gabuzda A. G. Polatidis 《Monthly notices of the Royal Astronomical Society》2006,373(2):449-456
A comparison between low-frequency space very long baseline interferometry (VLBI) and high-frequency ground-based VLBI images can, in principle, be used to detect small variations in rotation measure (RM) on fine angular scales inaccessible to ground arrays alone. This paper reports an attempt to perform such a comparison using the jet in the quasar 3C 380. Observations made with the VSOP antenna HALCA together with a ground array at wavelength 1.6 GHz provide total intensity and polarization images of comparable resolution to those from the ground array alone at 5 GHz. The results provide an image showing derotated magnetic vector position angle of somewhat higher resolution than that available earlier. The results show variations in an RM around component A of the order of 10 rad m−2 that could not have been detected with the ground array alone. It is concluded that satellite VLBI observations provide a promising means to study the distribution of matter and magnetic fields around parsec-scale jets.
The ground observations used here follow the steady outward drift of component A, which has approximately doubled its distance from the core since the first observations in 1982. They also reveal total intensity and polarization structure associated with a bright knot 0.7 arcsec from the core which is reminiscent of that expected for a conical shock wave. 相似文献
The ground observations used here follow the steady outward drift of component A, which has approximately doubled its distance from the core since the first observations in 1982. They also reveal total intensity and polarization structure associated with a bright knot 0.7 arcsec from the core which is reminiscent of that expected for a conical shock wave. 相似文献
6.
The phase relation of flare index in the northern and southern hemispheres in the time interval of January 1966 to December 2008 is investigated. It is found that, (1) the flare index in the northern hemisphere begin six months earlier than that in the southern one, which should lead to phase asynchrony between them but with a slight effect; (2) the main periods of the flare activity in the two hemispheres slightly differ from each other, which should also lead to phase asynchrony between them; (3) the low-frequency modes of the flare activity can be used to study the varying relationship of long-term solar activities and the high-frequency modes can be considered as the stochastic component that is amplitude modulated. 相似文献
7.
We investigate the two-dimensional boundary value problem of the linear wave excitation in the solar corona by a pair of periodic perturbers localized at the photosphere. The physical properties of the corona allow us to consider a magnetic configuration such as a potential arcade which is in a magneto-hydrostatic equilibrium with the surrounding plasma. The model excludes the A1fvén mode and since the slow mode is absent in a potential arcade, the excited waves are then the fast magneto-acoustic modes. The characteristic magnetic field scale length is twice the scale height of the coronal plasma, assumed isothermal and the induced fluid motions are in the direction perpendicular to the magnetic field, in the cross-sectional plane of the arcade.A particular example of two localized perturbers in a photospheric active region is given, pointing out the effects produced in the perturbed fields by the variation of the different parameters involved. Such example shows that, while a modification of the linear size or the horizontal wave number of the perturbers does not affect significantly the propagating disturbances, the variation of the perturbers' frequency produces important effects. Such effects can be summarized by saying that low-frequency perturbers are able to disturb the whole coronal magnetic configuration above the active region while high-frequency perturbers only disturb the coronal region just above them, producing a channeling feature. Moreover, for high frequencies the perturbations grow withz all the way from the photosphere while for very low frequencies evanescent waves are dominant, although thanks to the influence of the medium their amplitude starts to grow from somez on. 相似文献
8.
This work discusses theoretical models of chromospheric heating for \(\epsilon\) Eridani by shock waves. Self-consistent, nonlinear and time-dependent ab-initio numerical computations for the excitation of the atmosphere (i.e., arrays of flux tubes) are pursued based on waves generated in stellar convective zones. Based on previous studies the magnetic filling factor is estimated according to the stellar rotational period, although general models are described as well. The Ca II H+K fluxes are computed assuming partial redistribution (PRD). Time-dependent ionization notably affects the resulting Ca II fluxes, as expected. The emergent Ca II H+K fluxes are based on two-component models, consisting of a dominant magnetic component (as given by longitudinal tube waves) and a subordinate acoustic component. The Ca II fluxes as obtained are smaller by about a factor of 2 than those given by observations. Possible reasons for this discrepancy include (1) inherent limitations of our theoretical approach as it is based on 1-D rather than 3-D modelling and/or (2) the existence of additional heating processes in \(\epsilon\) Eridani (a young star) not included here. 相似文献
9.
Recent studies of the heliospheric magnetic field (HMF) have detected interesting, systematic hemispherical and longitudinal
asymmetries which have a profound significance for the understanding of solar magnetic fields. The in situ HMF measurements since the 1960s show that the heliospheric current sheet (HCS) is systematically shifted (coned) southward
during solar minimum times, leading to the concept of a bashful ballerina. While temporary shifts can be considerably larger,
the average HCS shift (coning) angle is a few degrees, less than the 7.2∘ tilt of the solar rotation axis. Recent solar observations during the last two solar cycles verify these results and show
that the magnetic areas in the northern solar hemisphere are larger and their intensity weaker than in the south during long
intervals in the late declining to minimum phase. The multipole expansion reveals a strong quadrupole term which is oppositely
directed to the dipole term. These results imply that the Sun has a symmetric quadrupole S0 dynamo mode that oscillates in
phase with the dominant dipole A0 mode. Moreover, the heliospheric magnetic field has a strong tendency to produce solar tilts
that are roughly opposite in longitudinal phase. This implies is a systematic longitudinal asymmetry and leads to a “flip-flop”
type behaviour in the dominant HMF sector whose period is about 3.2 years. This agrees very well with the similar flip-flop
period found recently in sunspots, as well as with the observed ratio of three between the activity cycle period and the flip-flop
period of sun-like stars. Accordingly, these results require that the solar dynamo includes three modes, A0, S0 and a non-axisymmetric
mode. Obviously, these results have a great impact on solar modelling. 相似文献
10.
D. C. Gabuzda A. B. Pushkarev T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,319(4):1109-1124
The results of very long baseline interferometry (VLBI) total intensity ( I ) and linear polarization ( P ) observations at are presented for 10 radio bright BL Lacertae objects. These images complete first-epoch polarization observations for the 1-Jy sample of northern BL Lacertae objects defined by Kühr & Schmidt. Estimates of superluminal speeds are presented for several sources, bringing the total number of sources in the sample for which such estimates are available to 16. Second-epoch observations currently being reduced should yield speed estimates for VLBI features in essentially all the sources in the sample. The jet magnetic fields of these BL Lacertae objects are usually transverse to the local jet direction, but a sizeable minority (about 30 per cent) have VLBI jet components with longitudinal magnetic fields. This may suggest that the conditions in the VLBI jets of BL Lacertae objects are favourable for the formation of relativistic shocks; alternatively, it may be that the toroidal component of the intrinsic jet magnetic field is characteristically dominant in these sources. 相似文献
11.
I. I. Romanyuk E. A. Semenko I. A. Yakunin D. O. Kudryavtsev A. V. Moiseeva 《Astrophysical Bulletin》2016,71(4):436-446
We present the results of magnetic field measurements of four chemically peculiar (CP) stars, the members of the Orion stellar association OB1. Observations were carried out with the circular polarization analyzer at the Main Stellar Spectrograph of the 6-m telescope. All the studied stars refer to the subtype of Bp stars with weak helium lines. Canadian astronomer E. F. Borra detected a magnetic field in three of them (HD35456, HD36313, and HD36526) from the Balmer line magnetometer observations. HD35881 was observed for the first time for the purpose to search for a magnetic field. We obtained the following results: HD35456 is a magnetic star with longitudinal field variation range from +300 to +650 G and a period of 4.9506 days; HD35881 is possible a new magnetic star, the longitudinal component of which varies from?1 to +1 kGwith a period of 0.6998 days, however, a small number of lines broadened by rotation does not allow us to conduct measurements more accurately; HD36313 is a binary star with the components similar in brightness, the primary component is a magnetic star with broad lines, the magnetic field of the secondary component (the star with narrow lines) was not detected. Measurements in the Hβ hydrogen line showed the variations of the longitudinal component from ?1.5 to +2 kG with a period of 1.17862 days; a strong longitudinal field was detected in HD36526 (from 0 to +3000 G) varying with a rotation period of the star of 3.081 days. In all the cases, we observe considerable discrepancies with the data on magnetic fields of these objects obtained earlier. 相似文献
12.
Historical sunspot records were analyzed by means of nonlinear tools to find synchronization phenomena at different time scales
on the Sun. Using cross-recurrence plots it is shown that the north – south sunspot synchronization demonstrates a set of
distinct periodic oscillations – 43.29, 18.52, and 7.63 years. Also we have traced the sunspot synchronization on shorter
time scales. Very rare and episodic synchronization within half of the Carrington rotation rate was detected. By using the
empirical mode decomposition technique the north – south sunspot time series were decomposed into intrinsic oscillatory modes.
To determine which modes of the signal are responsible for synchronization we separated them into high- and low-frequency
parts. It is shown that phase synchronization is detected only in the low-frequency modes. The high-frequency component demonstrates
noisy behavior with amplitude synchronization and strong phase mixing. 相似文献
13.
The data of light variations of six blazars with low peak frequencies (i.e., BL Lacerta, 0235+164, OQ530, 0716+714, 3C 345, and 3C 273) at 4.8, 8, 14.5, 22 and 37 GHz in the recent thirty years have been collected from immense amount of literature. By using the method of discrete correlation function the correlations and delays of the light curves of these six sources at the 5 wavebands are analyzed. With the method of structural function, the periods and timescales of the light variations of these six sources are analyzed, and their amplitudes of light variations are compared and analyzed. As revealed by the result of analysis, among the six blazars the amplitudes of light variations of 0716+714 and 0235+164 are relatively large, and those of 3C 345 and OQ 530 are less. The amplitudes of light variations of 3C 273 and BL Lacertae are relatively smaller. As shown by the multi-waveband analysis of delays between two neighboring wavebands, 0235+164 exhibits the tendency of variation that the high-frequency wavebands precede the low-frequency wavebands. On the whole, 3C 345 exhibits the tendency that the high-frequency wavebands lag be-hind the low-frequency wavebands. The analyses of the other blazars show that in a part of radio wavebands there appears the tendency of variation that the high-frequency waveband leads the low-frequency waveband. Yet in the other radio wavebands there appears the tendency that the high-frequency waveband lags behind the low-frequency waveband. As revealed by the results of analyses with the method of structural function, the timescale, fitted slope, and period of light variations of 3C 345 are larger than those of the other five blazars with low peak frequencies. This demonstrates that the activity of 3C 345 is comparatively weaker than the other five sources, and implies that in the interior of 3C 345 there may exist some physical processes which are different from those of the other five blazars with low peak frequencies. 相似文献
14.
The formation of Zeeman lines in Gaussian microturbulent magnetic fields is considered assuming LTE. General formulae are derived for the local mean values of the transfer matrix elements. The cases of one-dimensional (longitudinal), isotropic, and two-dimensional (transversal) magnetic microturbulence are studied in some detail. Asymptotic formulae are given for small mean as well as for small microturbulent magnetic fields. Characteristic effects of magnetic microturbulence on the transfer coefficients are: (i) the broadening of the frequency contours, although only for the case of longitudinal Zeeman effect and longitudinal magnetic microturbulence this effect can be described analogous to Doppler broadening, (ii) the appearance of a pseudo-Zeeman structure for nonlongitudinal magnetic microturbulence, (iii) the reduction of maximal values of circular polarization, and (iv) the appearance of characteristic linear polarization effects due to the anisotropy of the magnetic microturbulence.Line contours and polarization of Zeeman triplets are computed for Milne-Edddington atmospheres. It is shown that magnetic intensification due to microturbulent magnetic fields may be much more efficient than that due to regular fields. The gravity center of a Zeeman line observed in circularly polarized light remains a reasonable measure of the line of sight component of the mean magnetic field for a line strength47-1. For saturated lines, the gravity center distance depends significantly on the magnetic microturbulence and its anisotropy. The influence of magnetic microturbulence on the ratio of longitudinal field magnetographic signals shows that unique conclusions about the magnetic microstructure can be drawn from the line ratio measurement only in combination with further spectroscopic data or physical reasoning. 相似文献
15.
M. E. Gedalin J. G. Lominadze L. Stenflo V. N. Tsytovich 《Astrophysics and Space Science》1985,108(2):393-400
Wave conversion mechanisms causing large-frequency shifts are considered for an electron-positron plasma in a strong magnetic field. In particular, we discuss the effects of the nonlinear erenkov as well as the cyclotron resonances in order to associate pulsar radio-emissions with our present model for nonlinear conversion of high-frequency radiation into the low-frequency region. 相似文献
16.
本文简要综述重力波和磁重力波在各种天体物理场合中的应用 ,我们描述在具有开放径向磁场的恒星大气各种磁流体波之间的相互转换过程 ,强调磁重力波被束缚在恒星冕内的可能性 ,并探讨恒星内部高频的声波模 (p -模 )被低频的重力波模 (g -模 )所调制的过程 ,一旦有了足够长时间未间断高质量的日震数据 ,太阳内部的重力波模对声波模的调制效应—即每一个分立声波模的频率精细结构—则可被用来寻找深陷于太阳内部的重力波模或进一步独立地约束重力波模的振幅上限 相似文献
17.
Helicity of solar magnetic fields plays an important role in dynamo theories of the solar cycle. The helicity has been known to vary with the main 11-year period (Hale's cycle). Recent observations have revealed significant helicity variations on a shorter time scale, with a characteristic period of approximately 2 years. We suggest an explanation for the observed variations of the magnetic helicity, based on our model of the double magnetic cycle of solar activity. The quasi-biennial variations of the helicity are the consequence of the influence of erupted magnetic fields of the main cycle on the helicity in the regions of generation of the high-frequency component of magnetic field. This model suggests that the low-frequency component is generated at the base of the convective zone due to large-scale radial shear /r of angular velocity . The high-frequency component may be generated in the subsurface region due to latitudinal shear / or due to the radial shear in this region. 相似文献
18.
Transverse and longitudinal magnetic field scans together with K232 spectroheliograms that cover the early phases of active region formation reveal the following:
- The new active region forms near the periphery of an old magnetic region. There is evidence that the new region forms an interrelated system with the old magnetic structures on the sun.
- Noticeable changes in the background magnetic field are seen nearly 3 days prior to the appearance of the sunspot. Magnetic hills of the longitudinal component appear along with bright localized K232 emission. Subsequently the K232 emission spreads along the boundary of one or two adjacent supergranules and at the time of sunspot formation occupies the whole supergranular cell.
- Transverse fields with strengths of 100–150 gauss form closed regions in the area of the longitudinal component hills, in the very early phases of the region. These fields stretch and link up the two areas later, at which time the peak transverse fields with values near 250 gauss coincide with the zero line of the longitudinal field. When subsequently the spots appear in the new region, the transverse fields are located about the hills of the longitudinal field. The total field vectors just prior to sunspot formation are pressed to the surface. These are inclined about 45° to the surface after the spot appears. The findings indicate that the magnetic field of a new region emerges from the sub-photospheric layers. It is highly likely that the dynamics of a supergranule influences only the emergence of the magnetic field into the upper layers of the solar atmosphere.
19.
Complex sunspots in four active regions of April and May 1980, all exhibiting regions of magnetic classification delta, were studied using data from the NASA Marshall Space Flight Center vector magnetograph. The vector magnetic field structure in the vicinity of each delta was determined, and the location of the deltas in each active region was correlated with the locations and types of flare activity for the regions. Two types of delta-configuration were found to exist, active and inactive, as defined by the relationships between magnetic field structure and activity. The active delta exhibited high flare activity, strong horizontal gradients of the longitudinal (line-of-sight) magnetic field component, a strong transverse (perpendicular to line-of-sight) component, and a highly non-potential orientation of the photospheric magnetic field, all indications of a highly sheared magnetic field. The inactive delta, on the other hand, exhibited little or no flare production, weaker horizontal gradients of the longitudinal component, weaker transverse components, and a nearly potential, non-sheared orientation of the magnetic field. We conclude that the presence of such sheared fields is the primary signature by which the active delta may be distinguished, and that it is this shear which produces the flare activity of the active delta.NASA Graduate Student Research Fellow. 相似文献
20.
本文研究了磁流体力学与高频等离子体波（ 包括纵横模式） 之间的精巧的相互作用。研究表明,这些等离激元会在电流片内诱发一种阻抗不稳定,并最终导至磁重联,出现爆发性不稳定。在高涨的离声湍动情况下,高温电流片模型必须采用反常电导率,而非库仑电导率。理论估算的结果与观测相一致。因此这种计及等离激元有质动力作用的新磁重联理论,基本上能解释耀斑现象。 相似文献