Scattering of magnetosonic waves in a relativistic and anisotropic magnetized plasma     

Joachim Moortgat †  Jan Kuijpers 《Monthly notices of the Royal Astronomical Society》2006,368(3):1110-1122

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Rotationally modulated X-ray emission from T Tauri stars   总被引：1，自引：0，他引：1  

S. G. Gregory  M. Jardine  A. Collier Cameron  J.-F. Donati 《Monthly notices of the Royal Astronomical Society》2006,373(2):827-835

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Atmosphere models of magnetized neutron stars: QED effects, radiation spectra and polarization signals     

M. van Adelsberg  D. Lai 《Monthly notices of the Royal Astronomical Society》2006,373(4):1495-1522

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The magnetic field draping direction at Mars from April 1999 through August 2004     

David A. Brain  David L. Mitchell  Jasper S. Halekas 《Icarus》2006,182(2):464-473

Using more than five years of data from the magnetometer and electron reflectometer (MAG/ER) on Mars Global Surveyor (MGS), we derive the draping direction of the magnetic field above a given latitude band in the northern hemisphere. The draping direction varies on timescales associated with the orbital period of Mars and with the solar rotation period. We find that there is a strongly preferred draping direction when Mars is in one solar wind sector, but the opposite direction is not preferred as strongly for the other solar wind sector. This asymmetry occurs at or below the magnetic pileup boundary (MPB), is observed preferentially on field lines that connect to the collisional ionosphere, and is independent of planetary longitude. The observations could be explained by a hemispherical asymmetry in the access of field lines to the low-altitude ionosphere, or possibly from global modification of the low-altitude solar wind interaction by crustal magnetic fields. We show that the draping direction affects both the penetration of sheath plasma to 400 km altitudes on the martian dayside and the radial component of the magnetic field on the planetary night side.  相似文献   

Wave processes in nonlinear beams during propagation of waves in pulsar plasmas with different magnetic field orientations     

A. G. Bagdoev  D. M. Sedrakian 《Astrophysics》2006,49(3):350-357

The propagation of nonlinear three-dimensional waves in the form of gaussian beams in pulsars is examined. The defining equations for the wave motion of a plasma with high particle velocities, high electrical conductivity, high wave frequency, and high magnetic fields are the standard equations of magnetogas dynamics. Nonlinear, time-dependent equations are derived for relatively small perturbations of the medium and the orders of magnitude of the parameters of motion such that all the terms in the time-dependent equation are of the same order are written down. Various directions of the unperturbed magnetic field and of the wave propagation which may arise during plasma motion in quasars are considered. In a number of cases a closed analytic solution can be constructed for the propagation of axially symmetric gaussian beams. __________ Translated from Astrofizika, Vol. 49, No. 3, pp. 409–417 (August 2006).  相似文献   

Design and status of Solar Vector Magnetograph (SVM-I) at Udaipur solar observatory     

Sanjay Gosain  P. Venkatakrishnan  K. Venugopalan 《Journal of Astrophysics and Astronomy》2006,27(2-3):285-292

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The impact of meridional circulation on stellar butterfly diagrams and polar caps     

V. Holzwarth  D. H. Mackay  M. Jardine 《Monthly notices of the Royal Astronomical Society》2006,369(4):1703-1718

Observations of rapidly rotating solar-like stars show a significant mixture of opposite-polarity magnetic fields within their polar regions. To explain these observations, models describing the surface transport of magnetic flux demand the presence of fast meridional flows. Here, we link subsurface and surface magnetic flux transport simulations to investigate (i) the impact of meridional circulations with peak velocities of  ≤125 m s⁻¹  on the latitudinal eruption pattern of magnetic flux tubes and (ii) the influence of the resulting butterfly diagrams on polar magnetic field properties. Prior to their eruption, magnetic flux tubes with low field strengths and initial cross-sections below  ∼300 km  experience an enhanced poleward deflection through meridional flows (assumed to be polewards at the top of the convection zone and equatorwards at the bottom). In particular, flux tubes which originate between low and intermediate latitudes within the convective overshoot region are strongly affected. This latitude-dependent poleward deflection of erupting magnetic flux renders the wings of stellar butterfly diagrams distinctively convex. The subsequent evolution of the surface magnetic field shows that the increased number of newly emerging bipoles at higher latitudes promotes the intermingling of opposite polarities of polar magnetic fields. The associated magnetic flux densities are about 20 per cent higher than in the case disregarding the pre-eruptive deflection, which eases the necessity for fast meridional flows predicted by previous investigations. In order to reproduce the observed polar field properties, the rate of the meridional circulation has to be of the order of 100 m s⁻¹, and the latitudinal range from which magnetic flux tubes originate at the base of the convective zone (≲50°) must be larger than in the solar case (≲35°).  相似文献   

SCUBA polarization observations of the magnetic fields in the pre-stellar cores L1498 and L1517B     

J. M. Kirk  D. Ward-Thompson  R. M. Crutcher 《Monthly notices of the Royal Astronomical Society》2006,369(3):1445-1450

We have mapped linearly polarized dust emission from the pre-stellar cores L1498 and L1517B with the James Clerk Maxwell Telescope (JCMT) using the Submillimetre Common User Bolometer Array (SCUBA) and its polarimeter (SCUBAPOL) at a wavelength of 850 μm. We use these measurements to determine the plane-of-sky magnetic field orientation in the cores. In L1498, we see a magnetic field across the peak of the core that lies at an offset of ∼19°± 12° to the short axis of the core. This is similar to the offsets seen in previous observations of pre-stellar cores. To the south-east of the peak, in the filamentary tail of the core, we see that the magnetic field has rotated to lie almost parallel to the long axis of the filament. We hypothesize that the field in the core may have decoupled from the field in the filament that connects the core to the rest of the cloud. We use the Chandrasekhar–Fermi (CF) method to measure the plane-of-sky field strength in the core of L1498 to be ∼10 ± 7 μG.
In L1517B, we see a more gradual turn in the field direction from the northern part of the core to the south. This appears to follow a twist in the filament in which the core is buried, with the field staying at a roughly constant ∼25°± 6° offset to the short axis of the filament, consistent with previous observations of pre-stellar cores. Hence these two clouds in an apparently similar evolutionary state, that exhibit similar masses, morphologies and densities, have very different magnetic field configurations. We again use the CF method and calculate the magnetic field strength in L1517B to be ∼30 ± 10 μG. Both cores appear to be roughly virialized. Comparison with our previous work on somewhat denser cores shows that, for the denser cores, thermal and non-thermal (including magnetic) support are approximately equal, while for the lower density cores studied here, thermal support dominates.  相似文献   

Time-dependent interaction of granules with magnetic flux tubes     

P. Venkatakrishnan  S. S. Hasan 《Journal of Astrophysics and Astronomy》1981,2(2):133-139

The time-dependent interaction of the granulation velocity field with a magnetic flux tube is investigated here. It is seen that when a magnetic field line is displaced normal to itself so as to simulate thebuffeting action of granules, a flow of gas is initiated along the field. By choosing a lateral velocity field which is consistent with observations of granules, it is found that the resulting gas motion is a downward flow with a velocity compatible with the observed downflow in isolated photospheric flux tubes. It is therefore proposed that the observed photospheric downflow is a manifestation of the interaction of granules with flux tubes.  相似文献   

Photospheric magnetic field and surface differential rotation of the FK Com star HD 199178     

P. Petit  J.-F. Donati  J. M. Oliveira  M. Aurière  S. Bagnulo  J. D. Landstreet  F. Lignières  T. Lüftinger  S. Marsden  D. Mouillet  F. Paletou  S. Strasser  N. Toqué  G. A. Wade 《Monthly notices of the Royal Astronomical Society》2004,351(3):826-844

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