scholarly journals Pulsar Polarization Limiting Radii and the Evolution of Pulsar Beams

1987 ◽  
Vol 125 ◽  
pp. 56-56
Author(s):  
John J. Barnard
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Radio Frequency ◽  
Magnetic Field Strength ◽  
Rotation Axis ◽  
Rotation Period ◽  
Position Angle ◽  
Polarization Angle ◽  
Beam Model ◽  
Plasma Parameters

We estimate the polarization limiting radius, rp1, as a function of rotation period P, magnetic field strength B, and radio frequency v, in radio pulsars assuming plasma parameters that are typical of polar-cap pair-creation models of pulsars. We find that rpl ⋍ 9 × 108(P/1s)0.4 cm, for a surface magnetic field strength of 1012 G, and radio frequency of 109 Hz. For short rotation periods, rpl approaches the light cylinder radius, rlc. Here the magnetic field becomes more azimuthal, and the excursion in position angle over a pulse is less, on average, than when rpl ≪ rlc. With the assumption of a vacuum magnetic field we calculate the polarization position angle as a function of pulse longitude, and the angles i (the angle between the magnetic moment and the rotation axis) and α (the angle between the line of sight and the rotation axis). We calculate the average change in polarization angle as a function of pulsar period, assuming a circular beam, and find consistency with the polarization data summarized by Narayan and Vivekand (1983). We conclude that the evidence is consistent with beams that are roughly constant in shape, providing an alternative to the evolving elliptical beam model of Narayan and Vivekand (1983). This interpretation is further supported by the frequency dependence of the polarization angle in the Crab Pulsar, the frequency of pulsars with double and multiple pulse components, the frequency of pulsars with interpulses, and the absence of pulsars in plerions. See Barnard (1986) for further details.

On the Configuration of the Magnetic Field of β CrB

1976 ◽  
Vol 32 ◽  
pp. 613-622
Author(s):  
I.A. Aslanov ◽  
Yu.S. Rustamov
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Radial Velocity ◽  
Magnetic Field Strength ◽  
Complex Shape ◽  
Rotation Period ◽  
Field Variation ◽  
Magnetic Field Variation ◽  
Secular Variations ◽  
The Magnetic Field

SummaryMeasurements of the radial velocities and magnetic field strength of β CrB were carried out. It is shown that there is a variability with the rotation period different for various elements. The curve of the magnetic field variation measured from lines of 5 different elements: FeI, CrI, CrII, TiII, ScII and CaI has a complex shape specific for each element. This may be due to the presence of magnetic spots on the stellar surface. A comparison with the radial velocity curves suggests the presence of a least 4 spots of Ti and Cr coinciding with magnetic spots. A change of the magnetic field with optical depth is shown. The curve of the Heffvariation with the rotation period is given. A possibility of secular variations of the magnetic field is shown.

scholarly journals roAp stars

1995 ◽  
Vol 10 ◽  
pp. 338-340
Author(s):  
D. Kurtz ◽  
P. Martinez
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Rotation Axis ◽  
Zeeman Effect ◽  
Spectral Lines ◽  
Effective Magnetic Field ◽  
Surface Magnetic Field ◽  
Ap Stars

Among the A stars there is a subclass of peculiar stars, the Ap stars, which show strongly enhanced spectral lines of the Fe peak, rare earth and lanthanide elements. These stars have global surface magnetic fields several orders of magnitude larger than that of the Sun, 0.3 to 30 kGauss is the measured range. For stars with the strongest magnetic fields, the spectral lines are split by the Zeeman Effect and the surface magnetic field strength can be measured. Generally, though, the magnetic fields are not strong enough for the magnetic splitting to exceed other sources of line broadening. In these cases residual polarization differences between the red and blue wings of the spectral lines give a measure of the effective magnetic field strength - the integral of the longitudinal component of the global magnetic field over the visible hemisphere, weighted by limb-darkening. In the Ap stars the effective magnetic field strengths vary with rotation. This is well understood in terms of the oblique rotator model in which the magnetic axis is oblique to the rotation axis, so that the magnetic field is seen from varying aspect with rotation.

scholarly journals Discovery of a young pre-intermediate polar

2021 ◽  
Author(s):  
David J Wilson ◽  
Odette Toloza ◽  
John D Landstreet ◽  
Boris T Gänsicke ◽  
Jeremy J Drake ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
White Dwarf ◽  
White Dwarfs ◽  
Hubble Space Telescope ◽  
Cataclysmic Variables ◽  
Rotation Period ◽  
Field Measurements ◽  
The Magnetic Field

Abstract We present the discovery of a magnetic field on the white dwarf component in the detached post common envelope binary (PCEB) CC Cet. Magnetic white dwarfs in detached PCEBs are extremely rare, in contrast to the high incidence of magnetism in single white dwarfs and cataclysmic variables. We find Zeeman-split absorption lines in both ultraviolet Hubble Space Telescope (HST) spectra and archival optical spectra of CC Cet. Model fits to the lines return a mean magnetic field strength of 〈|B|〉 ≈ 600–700 kG. Differences in the best-fit magnetic field strength between two separate HST observations and the high v sin  i of the lines indicate that the white dwarf is rotating with a period ∼0.5 hours, and that the magnetic field is not axisymmetric about the spin axis. The magnetic field strength and rotation period are consistent with those observed among the intermediate polar class of cataclysmic variable, and we compute stellar evolution models that predict CC Cet will evolve into an intermediate polar in 7–17 Gyr. Among the small number of known PCEBs containing a confirmed magnetic white dwarf, CC Cet is the hottest (and thus youngest), with the weakest field strength, and cannot have formed via the recently proposed crystallisation/spin-up scenario. In addition to the magnetic field measurements, we update the atmospheric parameters of the CC Cet white dwarf via model spectra fits to the HST data and provide a refined orbital period and ephemeris from TESS photometry.

Experimental study of fast hydromagnetic waves in an argon plasma

1964 ◽  
Vol 278 (1373) ◽  
pp. 243-255 ◽  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Argon Plasma ◽  
Wave Number ◽  
Axially Symmetric ◽  
Plasma Parameters ◽  
Quantitative Evidence ◽  
Hydromagnetic Waves

In these experiments fast hydromagnetic waves are excited by discharging a capacitor through a single turn coil surrounding a cylindrical column of magnetized argon plasma. The plasma column is 200 cm long and 22 cm in diameter, and the axial magnetic field strength is varied in the range from 1 to 6 kG. The wave amplitude is typically 10 G, and the frequency is varied between 1.2 and 6 times the ion cyclotron frequency. Measurement of the radial variation and the relative amplitudes of the three components of the wave magnetic field shows that the oscillation is the lowest axially-symmetric mode. As predicted by the theory, the wave is elliptically polarized in the rθ plane with the magnetic vector rotating in the same sense as the electron cyclotron rotation. The experimental results demonstrate the cut-off of this mode both as the frequency is decreased and as the axial magnetic field strength is increased. Measurements of the axial wave number and absorption coefficient are in good numerical agreement with theoretical dispersion curves computed from the measured plasma parameters. This work provides quantitative evidence to support the theories currently used in treating hydromagnetic oscillations, both stable and unstable, of magnetized plasmas.

scholarly journals Influence of magnetic field strength on nanoparticle growth in a capacitively-coupled radio-frequency Ar/C2H2 discharge

2019 ◽  
Vol 1 (1) ◽  
pp. 015012 ◽  
Author(s):  
L Couëdel ◽  
D Artis ◽  
M P Khanal ◽  
C Pardanaud ◽  
S Coussan ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Radio Frequency ◽  
Magnetic Field Strength ◽  
Capacitively Coupled ◽  
Nanoparticle Growth

On the mutual interaction between rotation and magnetic fields for axisymmetric bodies

1979 ◽  
Vol 368 (1732) ◽  
pp. 75-97 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Rotation Rate ◽  
Rotation Axis ◽  
Magnetic Torque ◽  
Rotation Rates ◽  
Driving Torque ◽  
Stable Rotation

As a simple example of the mutual interaction between magnetic fields and material motions, the rotation of an electrically conducting cylinder of solid material in a transverse magnetic field has been investigated. An applied driving torque produces the rotation, which is opposed by friction and the induced magnetic torque. It is well known that when the field is transverse to the rotation axis the magnetic torque rises from zero as the rotation rate Ω is increased, reaches a maximum and tends to zero as Ω → ∞, and the magnetic flux is expelled. We may consider B 0 (the applied magnetic field strength) and Ω 0 (the rotation rate at which the drive is just balanced by friction alone) as control parameters of the system. For sufficiently strong driving torques, the equilibrium surface Ω ( Ω 0 , B 0 ) develops a fold and consists of two branches - ‘ fast friction-dominated ’ and ‘ slow magnetically dominated ’ stable rotation rates. These solutions embrace an unstable intermediate equilibrium, and the system exhibits hysteresis depending on the manner in which the fold is approached. A ‘potential’ function can be introduced in terms of which the equilibria and stability can be analysed, and this potential function indicates that the equilibrium Ω -surfaces display the characteristics of the cusp catastrophe of Thom. One consequence of this folded structure is the existence of a forbidden band of rotation rates for a given driving torque irrespective of magnetic field strength. Similar properties can be shown for spheres, and we speculate that the general features - fold, upper and lower stable branches, forbidden band of stable rotation rates - are generic to all axisymmetric solid bodies and shells rotating about their axes of symmetry in the presence of a magnetic field with a transverse component. These features are absent if the magnetic field is aligned with the rotation axis. The hysteresis should be observable in the laboratory and experimentally verifiable.

2D analysis of magnetic field strength in GO SiFe steel sheets

1998 ◽  
Vol 08 (PR2) ◽  
pp. Pr2-579-Pr2-582 ◽  
Author(s):  
S. Tumanski ◽  
M. Stabrowski
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Steel Sheets

MAGNETIC FIELD, PRESSURE AND TEMPERATURE DEPENDENT OPTICAL PROPERTIES IN A GaAs 9.0 P 1.0 QUANTUM DOT

2014 ◽  
Vol 6 (2) ◽  
pp. 1178-1190
Author(s):  
A. JOHN PETER ◽  
Ada Vinolin
Keyword(s):  
Magnetic Field ◽  
Optical Properties ◽  
Quantum Dot ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Photon Energy ◽  
Nonlinear Optical ◽  
Binding Energies ◽  
Nonlinear Optical Properties ◽  
Optical Rectification

Simultaneous effects of magnetic field, pressure and temperature on the exciton binding energies are found in a 9.0 1.0 6.0 4.0 GaAs P / GaAs P quantum dot. Numerical calculations are carried out taking into consideration of spatial confinement effect. The cylindrical system is taken in the present problem with the strain effects. The electronic properties and the optical properties are found with the combined effects of magnetic field strength, hydrostatic pressure and temperature values. The exciton binding energies and the nonlinear optical properties are carried out taking into consideration of geometrical confinement and the external perturbations.Compact density approach is employed to obtain the nonlinear optical properties. The optical rectification coefficient is obtained with the photon energy in the presence of pressure, temperature and external magnetic field strength. Pressure and temperature dependence on nonlinear optical susceptibilities of generation of second and third order harmonics as a function of incident photon energy are brought out in the influence of magnetic field strength. The result shows that the electronic and nonlinear optical properties are significantly modified by the applications of external perturbations in a 9.0 1.0 6.0 4.0 GaAs P / GaAs P quantum dot.

Magnetic field strength dependence of chemical shift artifacts

1988 ◽  
Vol 12 (2) ◽  
pp. 89-96 ◽  
Author(s):  
R. Lufkin ◽  
M. Anselmo ◽  
J. Crues ◽  
W. Smoker ◽  
W. Hanafee
Keyword(s):  
Magnetic Field ◽  
Chemical Shift ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Strength Dependence
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