scholarly journals Pulsation of magnetic stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 197-204 ◽  
Author(s):  
Hideyuki Saio
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Amplitude Distribution ◽  
High Order ◽  
Frequency Separation ◽  
Strong Magnetic Fields ◽  
Magnetic Stars ◽  
Ap Stars ◽  
The Magnetic Field ◽  
Large Frequency

AbstractSome Ap stars with strong magnetic fields pulsate in high-order p modes; they are called roAp (rapidly oscillating Ap) stars. The p-mode frequencies are modified by the magnetic fields. Although the large frequency separation is hardly affected, small separations are modified considerably. The magnetic field also affects the latitudinal amplitude distribution on the surface. We discuss the properties of axisymmetric p-mode oscillations in roAp stars.

scholarly journals Pulsation of Rotating Magnetic Stars

1993 ◽  
Vol 139 ◽  
pp. 134-134
Author(s):  
H. Shibahashi ◽  
M. Takata
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Magnetic Fields ◽  
Rotation Axis ◽  
Dipole Field ◽  
Dipole Mode ◽  
Magnetic Stars ◽  
Ap Stars ◽  
The Magnetic Field ◽  
Split Frequency

Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of obliquely rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We suppose that the star is rigidly rotating and that the magnetic field is a dipole field and its axis is oblique to the rotation axis. We treat the effects of the rotation and of the magnetic field as perturbations. In doing so, we suppose that the rotation of the star is slow enough so that the effect of the rotation on oscillations is smaller than that of the magnetic field.

scholarly journals Magnetic fields of rapidly oscillating Ap stars

1993 ◽  
Vol 139 ◽  
pp. 132-132
Author(s):  
G. Mathys
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Rotation Frequency ◽  
Spectral Lines ◽  
Driving Mechanism ◽  
Line Splitting ◽  
Ap Stars ◽  
The Magnetic Field

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.

scholarly journals Oscillatory convection in strong magnetic fields and origin of active regions

1968 ◽  
Vol 35 ◽  
pp. 127-130 ◽  
Author(s):  
S. I. Syrovatsky ◽  
Y. D. Zhugzhda
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Oscillatory Convection ◽  
Strong Magnetic Fields ◽  
Various Boundary Conditions ◽  
Convective Cells ◽  
The Magnetic Field ◽  
Polytropic Atmosphere

The convection in a compressible inhomogeneous conducting fluid in the presence of a vertical uniform magnetic field has been studied. It is shown that a new mode of oscillatory convection occurs, which exists in arbitrarily strong magnetic fields. The convective cells are stretched along the magnetic field, their horizontal dimensions are determined by radiative cooling. Criteria for convective instability in a polytropic atmosphere are obtained for various boundary conditions in the case when the Alfvén velocity is higher compared with the velocity of sound.The role of oscillatory convection in the origin of sunspots and active regions is discussed.

scholarly journals Open charm and charmonium states in strong magnetic fields

2021 ◽  
pp. 2150064
Author(s):  
Amruta Mishra ◽  
S. P. Misra
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Constituent Quark ◽  
Open Charm ◽  
Charm Mesons ◽  
Strong Magnetic Fields ◽  
Decay Widths ◽  
State Formula ◽  
The Masses ◽  
The Magnetic Field

The mass modifications of the open charm ([Formula: see text] and [Formula: see text]) mesons, and their effects on the decay widths [Formula: see text] as well as of the charmonium state, [Formula: see text] to open charm mesons ([Formula: see text]), are investigated in the presence of strong magnetic fields. These are studied accounting for the mixing of the pseudoscalar ([Formula: see text]) and vector ([Formula: see text]) mesons ([Formula: see text], [Formula: see text] mixings), with the mixing parameter, [Formula: see text] of a phenomenological three-point ([Formula: see text]) vertex interaction determined from the observed radiative decay width of [Formula: see text]. For charged [Formula: see text] mixing, this parameter is dependent on the magnetic field, because of the Landau level contributions to the vacuum masses of these mesons. The masses of the charged [Formula: see text] and [Formula: see text] mesons modified due to [Formula: see text] mixing, in addition, have contributions from the lowest Landau levels in the presence of a strong magnetic field. The effects of the magnetic field on the decay widths are studied using a field theoretical model of composite hadrons with quark (and antiquark) constituents. The matrix elements for these decays are evaluated using the light quark–antiquark pair creation term of the free Dirac Hamiltonian for the constituent quark field, with explicit constructions for the charmonium state [Formula: see text], the open charm ([Formula: see text], [Formula: see text], [Formula: see text]) mesons and the pion states in terms of the constituent quark fields. The parameter for the charged [Formula: see text] mixing is observed to increase appreciably with increase in the magnetic field. This leads to dominant modifications to their masses, and hence the decay widths of charged [Formula: see text] as well as [Formula: see text] at large values of the magnetic field. The modifications of the masses and decay widths of the open and hidden charm mesons in the presence of strong magnetic fields should have observable consequences on the production of the open charm ([Formula: see text] and [Formula: see text]) mesons as well as of the charmonium states resulting from noncentral ultra-relativistic heavy ion collision experiments.

scholarly journals Theory of The Oblique Pulsator Model For The Rapidly Oscillating Ap Stars

1993 ◽  
Vol 137 ◽  
pp. 563-565 ◽  
Author(s):  
Hiromoto Shibahashi ◽  
Masao Takata
Keyword(s):  
Magnetic Fields ◽  
Rotation Axis ◽  
Dipole Mode ◽  
Oscillation Pattern ◽  
Frequency Pattern ◽  
Magnetic Stars ◽  
Dipole Oscillation ◽  
Ap Stars ◽  
The Magnetic Field ◽  
Split Frequency

AbstractRecently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We show that the magnetic field on axisymmetric dipole modes distorts the dipole oscillation pattern to have axisymmetric octapole components so that the frequency pattern becomes a septuplet rather than a triplet, and that the additional effect of the rotation leads the frequency pattern to be asymmetric. The formula allows us to get information about the magnetic fields, the rotation, and the geometrical configuration of the star from the oscillation data.

STABILITY OF DEUTERONS IN STRONG MAGNETIC FIELDS: AN EXACTLY SOLVED MODEL

1988 ◽  
Vol 03 (04) ◽  
pp. 345-351 ◽  
Author(s):  
M. MOSHINSKY ◽  
G. LOYOLA
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Triplet State ◽  
Strong Magnetic Field ◽  
Canonical Transformation ◽  
Singlet State ◽  
Oscillator Potential ◽  
Strong Magnetic Fields ◽  
Expectation Value ◽  
The Magnetic Field

We consider the nucleons in the triplet state of the deuteron bound by an oscillator potential and in a strong magnetic field. Using an appropriate linear canonical transformation, we solve the problem exactly. The expectation value of the distance between the nucleons in the plane perpendicular to the magnetic field diminishes slowly as we increase the latter, which suggests that the triplet state of the deuteron is stable. The conclusion is not altered when we consider possible transitions from the triplet to the singlet state due to the action of the magnetic field on the spins.

scholarly journals Modified Adiabatic Approximation for A Hydrogen Atom Moving in A Magnetic Field

1994 ◽  
Vol 147 ◽  
pp. 555-559
Author(s):  
V.G. Bezchastnov ◽  
A.Y. Potekhin
Keyword(s):  
Magnetic Field ◽  
Hydrogen Atom ◽  
Magnetic Fields ◽  
Density Distribution ◽  
Cross Sections ◽  
Electron Density Distribution ◽  
Adiabatic Approximation ◽  
Strong Magnetic Fields ◽  
Radiative Transitions ◽  
The Magnetic Field

AbstractMotion of a hydrogen atom across the magnetic field shifts center of electron density distribution. For strong magnetic fields, the radiative transitions can be considered in the modified adiabatic approximation in which the shifts are taken into account. The method is illustrated by calculating the photoionization cross sections.

Erklärung stellarer und planetarer Magnetfelder durch einen turbulenzbedingten Dynamomechanismus

1966 ◽  
Vol 21 (8) ◽  
pp. 1285-1296 ◽  
Author(s):  
M. Steenbeck ◽  
F. Krause
Keyword(s):  
Magnetic Field ◽  
Angular Velocity ◽  
Magnetic Fields ◽  
Cross Product ◽  
Skin Depth ◽  
Electrically Conducting ◽  
Magnetic Stars ◽  
The Magnetic Field ◽  
Component Parallel ◽  
Good Agreement

In a foregoing paper 1 the effects of a turbulent motion on magnetic fields were investigated. Especially turbulence was treated under the influence of CORIOLiS-forces and gradients of density and/or turbulence intensity. It was shown that on these conditions the average cross-product of velocity and magnetic field has a non-vanishing component parallel to the average magnetic field. Here we give the consequences of this effect for rotating, electrically conducting spheres.At first a sphere rotating with constant angular velocity is investigated. The quadratic effect provides for dynamo maintainance of the magnetic fields. A field of dipol-type has the weakest condition for maintainance. Applications to the magnetic field of the earth show a good agreement with the conceptions of the physical state of the earth’s core.For a second model differential rotation is included. We have also dynamo maintainance. Since we have to assume that generally the angular velocity is a function decreasing with the distance from the centre of the sphere, the calculations show that we have a preferred self-excited build-up of a quadrupol-type field. This model may be applicable to magnetic stars.Finally we look for dynamo maintainance of alternating fields. We consider the skin-depth to be small compared with the radius of the sphere, then we have plane geometry. The existence of periodical solutions is proved. Applications to the general magnetic field of the sun, which has a period of 22 years, are discussed.

NEUTRINOS IN EXTREMELY STRONG MAGNETIC FIELDS

2000 ◽  
Vol 15 (04) ◽  
pp. 523-534
Author(s):  
A. PÉREZ MARTÍNEZ ◽  
H. PÉREZ ROJAS ◽  
D. OLIVA AGÜERO ◽  
A. AMÉZAGA HECHAVARRÍA ◽  
S. RODRÍGUEZ ROMO
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Threshold Energy ◽  
Strong Magnetic Fields ◽  
Self Energy ◽  
Loop Approximation ◽  
The One ◽  
The Magnetic Field ◽  
Thermal Background

We compute the dispersion curves for neutrinos propagating in a very dense electroweak plasma, in magnetic fields of order [Formula: see text]. The neutrino self-energy is calculated in the one-loop approximation. The dispersion equation is solved for motion parallel and perpendicular to the external magnetic field. We obtain an effective neutrino mass which increases with the magnetic field, up to values B where threshold energy for creation of W± pairs (out from the thermal background) is reached.

scholarly journals Modeling surface magnetic fields in stars with radiative envelopes

2013 ◽  
Vol 9 (S302) ◽  
pp. 290-299
Author(s):  
Oleg Kochukhov
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Doppler Imaging ◽  
Magnetic Field Mapping ◽  
Ap Stars ◽  
Surface Fields ◽  
The Magnetic Field

AbstractStars with radiative envelopes, specifically the upper main sequence chemically peculiar (Ap) stars, were among the first objects outside our solar system for which surface magnetic fields have been detected. Currently magnetic Ap stars remains the only class of stars for which high-resolution measurements of both linear and circular polarization in individual spectral lines are feasible. Consequently, these stars provide unique opportunities to study the physics of polarized radiative transfer in stellar atmospheres, to analyze in detail stellar magnetic field topologies and their relation to starspots, and to test different methodologies of stellar magnetic field mapping. Here I present an overview of different approaches to modeling the surface fields in magnetic A- and B-type stars. In particular, I summarize the ongoing efforts to interpret high-resolution full Stokes vector spectra of these stars using magnetic Doppler imaging. These studies reveal an unexpected complexity of the magnetic field geometries in some Ap stars.

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