Axisymmetric ideal MHD stellar wind flow

Heinemann, Michael; Olbert, S.

doi:10.1029/ja083ia06p02457

Cited by 101 publications

(71 citation statements)

References 10 publications

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“…It is expected, that matter in the boundary layer is hotter than in the disk, and is emitting radiation with a larger effective temperature. The equations of a heat balance in the boundary layer are different from the similar equations in the accretion disk (115), (116), (124). The component of the stress tensor should be written on the form (119) only, because in the boundary layer Ω deviates strongly from the keplerian value.…”

Section: Boundary Layers With Account Of Thermal Processes Heat Prodmentioning

confidence: 99%

Advective accretion disks and related problems including magnetic fields

Бисноватый-Коган

Lovelace

2001

New Astronomy Reviews

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Accretion disk theory was first developed as a theory with the local heat balance, where the whole energy produced by a viscous heating was emitted to the sides of the disk. One of the most important new invention of this theory was the phenomenological treatment of the turbulent viscosity, known the " alpha" prescription, where the (rφ) component of the stress tensor was approximated by (αp) with a unknown constant α. This prescription played the role in the accretion disk theory as well important as the mixing-length theory of convection for stellar evolution. Sources of turbulence in the accretion disk are discussed, including hydrodynamical turbulence, convection and magnetic field role. In parallel to the optically thick geometrically thin accretion disk models, a new branch of the optically thin accretion disk models was discovered, with a larger thickness for the same total luminosity. The choice between these solutions should be done of the base of a stability analysis. The ideas underlying the necessity to include advection into the accretion disk theory are presented and first models with advection are reviewed. The present status of the solution for a low-luminous optically thin accretion disk model with advection is discussed and the limits for an advection dominated accretion flows (ADAF) imposed by the presence of magnetic field are analysed. Related problems of mass ejection from accretion disks and jet formation are discussed.

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Section: Boundary Layers With Account Of Thermal Processes Heat Prodmentioning

confidence: 99%

Advective accretion disks and related problems including magnetic fields

Бисноватый-Коган

Lovelace

2001

New Astronomy Reviews

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“…However, here the source term is different and is directly related to the internal structure of the star through its density profile (ρ). The general form of the GradShafranov equation in an astrophysical context is discussed for example in Heinemann & Olbert (1978) and Ogilvie (1997). Moreover, since the field has to be non force-free in stellar interiors G 0 (see the previous discussion in Sect.…”

Section: The Barotropic Equilibrium State Familymentioning

confidence: 99%

Relaxed equilibrium configurations to model fossil fields

Duez

Mathis

2010

A&A

132

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Context. The understanding of fossil fields' origin, topology, and stability is one of the corner stones of the stellar magnetism theory. On one hand, since they survive on secular time scales, they may modify the structure and the evolution of their host stars. On the other hand, they must have a complex stable structure since it has been demonstrated that the simplest purely poloidal or toroidal fields are unstable on dynamical time scales. In this context, the only stable configuration found today is the one resulting from a numerical simulation by Braithwaite and collaborators who studied the evolution of an initial stochastic magnetic field, which is found to relax on a mixed stable configuration (poloidal and toroidal) that seems to be in equilibrium and then diffuses. Aims. We investigate an equilibrium field in a semi-analytical way. In this first article, we study the barotropic magnetohydrostatic equilibrium states. Methods. The problem reduces to a Grad-Shafranov-like equation with arbitrary functions. These functions are constrained by deriving the lowest-energy equilibrium states for given invariants of the considered axisymmetric problem, in particular for a given helicity known to be one of the causes of such problems. These theoretical results were applied to realistic stellar cases, the solar radiative core and the envelope of an Ap star, and discussed. In both cases we assumed that the field is initially confined in the stellar radiation zone.Results. The generalization of the force-free Taylor's relaxation states studied in laboratory experiments (in spheromaks) that become non force-free in the self-gravitating stellar case are obtained. The case of general baroclinic equilibrium states will be studied in Paper II.

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“…derivative of the stream function or mass flux per magnetic flux, Bernoulli or energy function, entropy, specific angular momentum on a given stream function, effective rotation rate of the field lines) that are constants of motion along each field line (e.g. Heinemann & Olbert 1978;Lovelace et al 1986;Ustyugova et al 1999;Keppens & Goedbloed 2000). In order to examine the accuracy of each of our numerical solutions, we check that each of the above quantities are conserved within some tolerance.…”

Section: B Accuracy Of the Numerical Solutionsmentioning

confidence: 99%

Magnetic Braking of Sun-like and Low-mass Stars: Dependence on Coronal Temperature

Pantolmos

2017

ApJ

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Sun-like and low-mass stars possess high temperature coronae and lose mass in the form of stellar winds, driven by thermal pressure and complex magnetohydrodynamic processes. These magnetized outflows probably do not significantly affect the star's structural evolution on the Main Sequence, but they brake the stellar rotation by removing angular momentum, a mechanism known as magnetic braking. Previous studies have shown how the braking torque depends on magnetic field strength and geometry, stellar mass and radius, mass-loss rate, and the rotation rate of the star, assuming a fixed coronal temperature. For this study we explore how different coronal temperatures can influence the stellar torque. We employ 2.5D, axisymmetric, magnetohydrodynamic simulations, computed with the PLUTO code, to obtain steady-state wind solutions from rotating stars with dipolar magnetic fields. Our parameter study includes 30 simulations with variations in coronal temperature and surfacemagnetic-field strength. We consider a Parker-like (i.e. thermal-pressure-driven) wind, and therefore coronal temperature is the key parameter determining the velocity and acceleration profile of the flow. Since the mass loss rates for these types of stars are not well constrained, we determine how torque scales for a vast range of stellar mass loss rates. Hotter winds lead to a faster acceleration, and we show that (for a given magnetic field strength and mass-loss rate) a hotter outflow leads to a weaker torque on the star. We derive new predictive torque formulae for each temperature, which quantifies this effect over a range of possible wind acceleration profiles.

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Axisymmetric ideal MHD stellar wind flow

Cited by 101 publications

References 10 publications

Advective accretion disks and related problems including magnetic fields

Advective accretion disks and related problems including magnetic fields

Relaxed equilibrium configurations to model fossil fields

Magnetic Braking of Sun-like and Low-mass Stars: Dependence on Coronal Temperature

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