The effect of a magnetic field on the adiabatic oscillation of convective stellar models with radiation pressure

1982 ◽  
Vol 258 ◽  
pp. 354 ◽  
Author(s):  
M. K. Das ◽  
J. Kar ◽  
J. N. Tandon
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
Stellar Models ◽  
Adiabatic Oscillation

scholarly journals The Effect of a Magnetic Field on Stellar Pulsations as a Singular Perturbation Problem

1980 ◽  
Vol 58 ◽  
pp. 661-666
Author(s):  
M. Goossens ◽  
D. Biront
Keyword(s):  
Magnetic Field ◽  
Magnetic Pressure ◽  
Matched Asymptotic Expansion ◽  
Perturbation Scheme ◽  
Regular Perturbation ◽  
Perturbation Problem ◽  
Stellar Pulsations ◽  
Thermodynamic Pressure ◽  
The Magnetic Field ◽  
Adiabatic Oscillation

AbstractThe perturbation problem that describes the effect of a weak magnetic field on stellar adiabatic oscillation is considered. This perturbation problem is singular when the magnetic field does not vanish at the stellar surface, and a regular perturbation scheme fails where the magnetic pressure is comparable to the thermodynamic pressure. The application of the Method of Matched Asymptotic Expansion is used to obtain expressions for the eigenfunctions and the eigenfrequencies.

scholarly journals Radiation-Driven Acceleration in Photospheres of Nonaccreting Magnetic White Dwarfs

1994 ◽  
Vol 142 ◽  
pp. 783-787
Author(s):  
Vladimir V. Zheleznyakov ◽  
A. V. Serber
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
White Dwarfs ◽  
Force Balance ◽  
Pure Hydrogen ◽  
Uv Spectrum ◽  
Dipole Magnetic Field ◽  
Cyclotron Line ◽  
The Magnetic Field ◽  
Radiation Pressure Force

AbstractRadiation transfer in a pure hydrogen, fully ionized, isothermal photosphere of an isolated white dwarf with dipole magnetic field is considered, and the radiation pressure force, both in the continuum and in the cyclotron line, is determined with the line saturation effect taken into account. It is shown that the magnetic field can reduce the critical luminosity for white dwarfs. This leads to the possibility of photospheric plasma ejection driven by the radiation in the cyclotron line and the formation of radiation-driven winds from sufficiently hot isolated magnetic white dwarfs.It is shown that cyclotron radiation pressure plays a significant role in the force balance of the photospheres of the magnetic white dwarfs GD 229, GrW +70° 8247, and PG 1031+234. The strong unidentified depression in the UV spectrum of GD 229 is attributed to cyclotron scattering by the radiation-driven plasma envelope with density N ≳ 108 cm−3 .Subject headings: radiative transfer — stars: atmospheres — stars: magnetic fields — white dwarfs

scholarly journals On the influence of magnetic fields in neutral planetary wakes

2016 ◽  
Vol 12 (S328) ◽  
pp. 192-197
Author(s):  
C. Villarreal D’Angelo ◽  
M. Schneiter ◽  
A. Esquivel
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radiation Pressure ◽  
Stellar Wind ◽  
Magnetic Moments ◽  
Radiative Processes ◽  
Planetary Magnetic Fields ◽  
Stellar Magnetic Fields

AbstractWe present a 3D magnetohydrodynamic study of the effect that stellar and planetary magnetic fields have on the calculated Lyα absorption during the planetary transit, employing parameters that resemble the exoplanet HD209458b. We assume a dipolar magnetic field for both the star and the planet, and use the Parker solution to initialize the stellar wind. We also consider the radiative processes and the radiation pressure.We use the numerical MHD code Guacho to run several models varying the values of the planetary and stellar magnetic moments within the range reported in the literature.We found that the presence of magnetic fields influences the escaping neutral planetary material spreading the absorption Lyα line for large stellar magnetic fields.

scholarly journals Dust trajectory simulations around the Sun, Vega, and Fomalhaut

2019 ◽  
Vol 626 ◽  
pp. A107 ◽  
Author(s):  
Johann Stamm ◽  
Andrzej Czechowski ◽  
Ingrid Mann ◽  
Carsten Baumann ◽  
Margaretha Myrvang
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
Gravitational Force ◽  
Charged Particles ◽  
Charged Dust ◽  
The Sun ◽  
Pressure Force ◽  
Electromagnetic Forces ◽  
Model Calculations ◽  
Radiation Pressure Force

Context. Vega and Fomalhaut display a thermal emission brightness that could possibly arise from hot dust near the stars, an inner extension of their planetary debris disks. An idea has been suggested that nanometer-sized dust particles are kept in the vicinity of the stars by electromagnetic forces. This resembles the trapping that model calculations show in the corotating magnetic field in the inner heliosphere within approximately 0.2 AU from the Sun. Aims. The aim of this work is to study whether the trapping of dust due to electromagnetic forces acting on charged dust near the Sun can occur around Vega and Fomalhaut and what are the conditions for trapping. Methods. We studied the dust trajectories with numerical calculations of the full equation of motion, as well as by using the guiding center approximation. We assumed a constant dust charge and a Parker-type magnetic field, which we estimated for the two stars. Results. We find no bound trajectories of charged particles around Vega or Fomalhaut as long as the radiation pressure force exceeds the gravitational force, that is, for particles smaller than 1 μm. A trapping zone could exist inside of 0.02 AU for Vega and 0.025 AU for Fomalhaut, but only for those particles with radiation pressure force smaller than gravitational force. In comparison to the Sun, the trapping conditions would occur closer to the stars because their faster rotation leads to a more closely wound-up magnetic field spiral. We also show that plasma corotation can be consistent with trapping. Our model calculations show that the charged particles are accelerated to stellar wind velocity very quickly, pass 1 AU after approximately three days, and are further ejected outward where they pass the debris disks at high velocity. We find this for particles with a surface charge-to-mass ratio larger than 10−6 elementary charges per proton mass for both negatively and positively charged dust and independent of the strength of the radiation pressure force. Based on charging assumptions, this would correspond to dust of sizes 100 nm and smaller.

scholarly journals MHD Models of Planetary Nebulae: Review

2003 ◽  
Vol 209 ◽  
pp. 457-464 ◽  
Author(s):  
Guillermo García-Segura
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Ab Initio ◽  
Radiation Pressure ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Basic Question ◽  
Red Giants ◽  
Outer Envelope ◽  
Parent Star

When we discuss about MHD effects in planetary nebulae (PNe), there naturally arises a basic question: which magnetic field do we study? One possibility is the ISM magnetic field (e.g. Heiligman 1980), even more if we are concerned with moving PNe (e.g. Soker & Dgani 1997). The next possibility is the internal or stellar magnetic field (Gurzadian 1962). It is important to start this review by quoting Aller (1958): “It has been pointed out by Minkowski and others that the structural appearance of many planetary nebulae strongly suggest the presence of magnetic fields. It seems unlikely that such magnetic fields are produced ab initio in the nebular shell. Rather, they must have existed in the outer envelope of the parent star. Certain red giants stars with magnetic fields may evolve in such a way that the expansion of the shell is largely governed by the presence of such a field. Magnetic effects may actually be more important than gas pressure differentials and radiation pressure in controlling the evolution of a planetary nebula”.

Challenges in Stellar Models from Helioseismology to Asteroseismology

2005 ◽  
Vol 13 ◽  
pp. 403-406
Author(s):  
Sylvaine Turck-Chièze ◽  
Phu Anh Phi Nghiem ◽  
Laurent Piau
Keyword(s):  
Magnetic Field ◽  
Internal Magnetic Field ◽  
Identification Problems ◽  
Mode Identification ◽  
Stellar Models

AbstractExperience in helioseismology provides guidance for modeling challenges in asteroseismology. It guides choices of targets and conditions of observation. The main objectives are the interplay between rotation and convection and the knowledge of the internal magnetic field. Progress on the structure of the outer layers is crucial to avoid mode identification problems.

scholarly journals Improvement of ion acceleration in radiation pressure acceleration regime by using an external strong magnetic field

2019 ◽  
Vol 37 (2) ◽  
pp. 217-222 ◽  
Author(s):  
H. Cheng ◽  
L. H. Cao ◽  
J. X. Gong ◽  
R. Xie ◽  
C. Y. Zheng ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Laser Pulse ◽  
Radiation Pressure ◽  
Longitudinal Magnetic Field ◽  
Ponderomotive Force ◽  
Two Dimensional ◽  
Particle In Cell ◽  
Combined Action ◽  
The Magnetic Field

AbstractTwo-dimensional particle-in-cell (PIC) simulations have been used to investigate the interaction between a laser pulse and a foil exposed to an external strong longitudinal magnetic field. Compared with that in the absence of the external magnetic field, the divergence of proton with the magnetic field in radiation pressure acceleration (RPA) regimes has improved remarkably due to the restriction of the electron transverse expansion. During the RPA process, the foil develops into a typical bubble-like shape resulting from the combined action of transversal ponderomotive force and instabilities. However, the foil prefers to be in a cone-like shape by using the magnetic field. The dependence of proton divergence on the strength of magnetic field has been studied, and an optimal magnetic field of nearly 60 kT is achieved in these simulations.

scholarly journals Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT

2019 ◽  
Author(s):  
L Ji ◽  
V Doroshenko ◽  
A Santangelo ◽  
C Güngör ◽  
S Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radiation Pressure ◽  
Timing Analysis ◽  
Theoretical Models ◽  
Accretion Disc ◽  
High Energies ◽  
Timing Properties ◽  
The Magnetic Field

Abstract We present a study of timing properties of the accreting pulsar 2S 1417-624 observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT and NICER observations. We report a dramatic change of the pulse profiles with luminosity. The morphology of the profile in the range 0.2-10.0 keV switches from double to triple peaks at ∼2.5 $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$ and from triple to quadruple peaks at ∼7 $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$. The profile at high energies (25-100 keV) shows significant evolutions as well. We explain this phenomenon according to existing theoretical models. We argue that the first change is related to the transition from the sub to the super-critical accretion regime, while the second to the transition of the accretion disc from the gas-dominated to the radiation pressure-dominated state. Considering the spin-up as well due to the accretion torque, this interpretation allows to estimate the magnetic field self-consistently at ∼7 × 1012 G.

Sign in / Sign up

Export Citation Format

Share Document