Delayed growth of large-scale instabilities on the surface of double-layer (Cu + Ti) conductors in strong magnetic fields

AbstractA-type stars have both a near-surface layer of fast convection that can excite acoustic modes and a deep zone of core convection whose properties may be probed with asteroseismology. Many A-type stars also exhibit large magnetic spots that are often attributed to surviving primordial fields of global scale in the intervening radiative zone. We have explored the potential for core convection in rotating A-type stars to build strong magnetic fields through dynamo action. These 3-D simulations using the ASH code provide guidance on the nature of differential rotation and magnetic fields that may be present in the deep interiors of these stars, thus informing the asteroseismic deductions now becoming feasible. Our models encompass the inner 30% by radius of a two solar mass A-type star, rotating at four times the solar rate and capturing the convective core and a portion of the overlying radiative envelope. Convection in these stars drives a strong retrograde differential rotation and yields a core that is prolate in shape. When dynamo action is admitted, the convection generates strong magnetic fields largely in equipartition with the dynamics. Remarkably, introducing a modest but large-scale external field threading the radiative envelope (which may be of primordial origin) can substantially alter the turbulent dynamics of the convective interior. The resulting convection involves a complex assembly of helical rolls that link distant portions of the core and stretch and advect magnetic field, ultimately yielding magnetic fields of super-equipartition strength.

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New Insights into the Puzzling P-Cygni Profiles of Magnetic Massive Stars

Proceedings of the International Astronomical Union ◽

10.1017/s174392131700309x ◽

2016 ◽

Vol 12 (S329) ◽

pp. 246-249 ◽

Cited By ~ 1

Author(s):

Christiana Erba ◽

Alexandre David-Uraz ◽

Véronique Petit ◽

Stanley P. Owocki

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Massive Stars ◽

Uv Spectra ◽

Exact Integration ◽

Strong Magnetic Fields ◽

Profile Variation ◽

Material Forming ◽

Rotational Phase ◽

Line Profile Variation

AbstractMagnetic massive stars comprise approximately 10% of the total OB star population. Modern spectropolarimetry shows these stars host strong, stable, large-scale, often nearly dipolar surface magnetic fields of 1 kG or more. These global magnetic fields trap and deflect outflowing stellar wind material, forming an anisotropic magnetosphere that can be probed with wind-sensitive UV resonance lines. Recent HST UV spectra of NGC 1624-2, the most magnetic O star observed to date, show atypically unsaturated P-Cygni profiles in the Civ resonant doublet, as well as a distinct variation with rotational phase. We examine the effect of non-radial, magnetically-channeled wind outflow on P-Cygni line formation, using a Sobolev Exact Integration (SEI) approach for direct comparison with HST UV spectra of NGC 1624-2. We demonstrate that the addition of a magnetic field desaturates the absorption trough of the P-Cygni profiles, but further efforts are needed to fully account for the observed line profile variation. Our study thus provides a first step toward a broader understanding of how strong magnetic fields affect mass loss diagnostics from UV lines.

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Strong magnetic fields

Uspekhi Fizicheskih Nauk ◽

10.3367/ufnr.0070.196004e.0693 ◽

1960 ◽

Vol 70 (4) ◽

pp. 693-714 ◽

Cited By ~ 2

Author(s):

G.M. Strakhovskii ◽

N.V. Kravtsov

Keyword(s):

Magnetic Fields ◽

Strong Magnetic Fields

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Magnetic molecular nanoclusters in strong magnetic fields

Uspekhi Fizicheskih Nauk ◽

10.3367/ufnr.0172.200211h.1303 ◽

2002 ◽

Vol 172 (11) ◽

pp. 1303 ◽

Cited By ~ 2

Author(s):

Anatolii K. Zvezdin ◽

Viktor V. Kostyuchenko ◽

V.V. Platonov ◽

V.I. Plis ◽

A.I. Popov ◽

...

Keyword(s):

Magnetic Fields ◽

Strong Magnetic Fields

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Asymptotic analysis of 3D buoyant magnetohydrodynamic flows in strong magnetic fields

Magnetohydrodynamics ◽

10.22364/mhd.42.2-3.13 ◽

2006 ◽

Vol 42 (2-3) ◽

pp. 219-223

Keyword(s):

Magnetic Fields ◽

Asymptotic Analysis ◽

Strong Magnetic Fields ◽

Magnetohydrodynamic Flows

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An 84-μG Magnetic Field in a Galaxy at Z=0.692?

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027439 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 95-96

Author(s):

Arthur M. Wolfe ◽

Regina A. Jorgenson ◽

Timothy Robishaw ◽

Carl Heiles ◽

Jason X. Prochaska

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Faraday Rotation ◽

Large Scale ◽

Dynamo Model ◽

Magnetic Field Generation ◽

Interstellar Gas ◽

Splitting Technique ◽

Average Value ◽

The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

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