Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe..31f&link_type=abstract
"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199
Astronomy and Astrophysics
Astronomy
Scientific paper
The interaction of convective motion and magnetic fields suggests a number of interesting problems in astrophysical scenarios.The thermal stability of to confined plasma can be modified by the presence of an intense magnetic field. The approaches of Walen and Chandrasekhar establish the conditions under which the convection can be more or less efficient due to the hydromagnetic forces. Idealized studies with a large scale magnetic field threads a convectively unstable layer sandwiched between convectively stable region have been made using those approaches. But the formulation of Walen and Chandrasekhar are based on the law of Maxwell-Fourier (MF) for thermal energy transport equation, it is assumed that the energy flux is proportional to a temperature gradient and, it is well known, leads to a parabolic equation for the temperature according to wich pertubations propagate wich infinite speed. This is a valid approach for non degenerate matter, that is to say, when the time of relaxation is negletting. In the plasma and degenerate material the MF law not describes well the transport of heat. A heat flux equation leading to a hyperbolic equation (causal) is the Cattaneo law and their employment in the Mixing Length Theory (MLT) modified the local flux of convective energy. The Cattaneo law predicts that the convective fluxes and thermal stability condition are very different. This result insinuates new thermal stability condition for plasmas. Also, the MLT before relaxation based on the law of Cattaneo it predicts modifications in the frequency of Brunt-Vaisala. The new thermal stability condition for plasmas, using Cattaneo law, predict that the non radial oscillation modes are delimited inferiorly by the values of the magnetic field, result that it is not predicted by the Walen and Chandrasekhar approaches. One scenario where we could expect this instability to play an important role is in neutron stars (NS), magnetic field arises as a consequence of the thermomagnetic instability in their outer crust and liquid core superfluid ( Blandford et al 1983). Another scenario is the quasi periodic oscillation (QPO) in the emission in low mass x-ray binaries stars, some models suggest that magnetic fields and variation are generated locally due to turbulent dynamo-action in the NS envelope, where the convection and thermomagnetic instability are present.
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