User evaluation by budgetary games

Parker, Chelsea

doi:10.1108/eb050677

Cited by 4 publications

(4 citation statements)

References 2 publications

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“…A 10 6 G magnetic field will traverse a stellar radius R ∼ 10 10 cm in approximately 10 5.5 s, or about 10 days, assuming a constant density of 10 2 g cm −3 . This rise time will be increased by non-adiabatic heating effects, but remains small compared to evolutionary timescales (Parker 1974). Figure 10 indicates that a radiative shell develops deep within the star in the presence of a super-MG magnetic field.…”

Section: Assessment Of Magneto-convectionmentioning

confidence: 98%

Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars

Feiden

Chaboyer

2014

ApJ

112

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We examine the hypothesis that magnetic fields are inflating the radii of fully convective main sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main sequence stars in DEBs.

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Section: Assessment Of Magneto-convectionmentioning

confidence: 98%

Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars

Feiden

Chaboyer

2014

ApJ

112

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“…In a barotropic fluid, with a unique pressure-density relation ρ(P ), these two relations cannot be satisfied simultaneously. If the first is satisfied, then P in < P out and therefore ρ in < ρ out , so the flux tube will buoyantly rise (Parker 1974). However, in neutron star matter, since the composition (here represented by the proton fraction Y ) is inhomogeneous, the equation of state has the form ρ(P, Y ).…”

Section: Single Flux Tube As a Toy Modelmentioning

confidence: 99%

Magnetic field evolution in neutron stars

Reisenegger

2007

Astron Nachr

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Neutron stars contain persistent, ordered magnetic fields that are the strongest known in the Universe. However, their magnetic fluxes are similar to those in magnetic A and B stars and white dwarfs, suggesting that flux conservation during gravitational collapse may play an important role in establishing the field, although it might also be modified substantially by early convection, differential rotation, and magnetic instabilities. The equilibrium field configuration, established within hours (at most) of the formation of the star, is likely to be roughly axisymmetric, involving both poloidal and toroidal components. The stable stratification of the neutron star matter (due to its radial composition gradient) probably plays a crucial role in holding this magnetic structure inside the star. The field can evolve on long time scales by processes that overcome the stable stratification, such as weak interactions changing the relative abundances and ambipolar diffusion of charged particles with respect to neutrons. These processes become more effective for stronger magnetic fields, thus naturally explaining the magnetic energy dissipation expected in magnetars, at the same time as the longer-lived, weaker fields in classical and millisecond pulsars.Comment: To appear in Astronomische Nachrichten (Astronomical Notes) as part of the Proceedings of the 5th Potsdam Thinkshop, "Meridional Circulation, Differential Rotation, Solar and Stellar Activity", held 2007 June 24-29. 5 pages, no figure

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“…Ramirez-Ruiz & suggest that the heating of materials through magnetic reconnection may also lead to the enhancement of neutrino luminosity. We would like to stress that the magnetoconvection and magnetic Rayleigh-Taylor instability of magnetic flux tube would assist the mixing of materials in the layers where is heretofore thought to be convectively stable (Parker 1974(Parker , 1975(Parker , 1979.…”

Section: Nonlinear Growth Of the Nmrimentioning

confidence: 99%

Nonaxisymmetric Magnetorotational Instability in Proto–Neutron Stars

Masada

Sano

Takabe

2006

ApJ

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We investigate the stability of differentially rotating proto-neutron stars (PNSs) with a toroidal magnetic field. Stability criteria for nonaxisymmetric MHD instabilities are derived using a local linear analysis. PNSs are expected to have much stronger radial shear in the rotation velocity compared to normal stars. We find that nonaxisymmetric magnetorotational instability (NMRI) with a large azimuthal wavenumber m is dominant over the kink mode (m = 1) in differentially rotating PNSs. The growth rate of the NMRI is of the order of the angular velocity Ω which is faster than that of the kink-type instability by several orders of magnitude. The stability criteria are analogous to those of the axisymmetric magnetorotational instability with a poloidal field, although the effects of leptonic gradients are considered in our analysis. The NMRI can grow even in convectively stable layers if the wavevectors of unstable modes are parallel to the restoring force by the Brunt-Väisälä oscillation. The nonlinear evolution of NMRI could amplify the magnetic fields and drive MHD turbulence in PNSs, which may lead to enhancement of the neutrino luminosity.

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User evaluation by budgetary games

Cited by 4 publications

References 2 publications

Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars

Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars

Magnetic field evolution in neutron stars

Nonaxisymmetric Magnetorotational Instability in Proto–Neutron Stars

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