Dipole model of the Earth's magnetic field

About: Dipole model of the Earth's magnetic field is a research topic. Over the lifetime, 2756 publications have been published within this topic receiving 83021 citations.

Note on the geometry of the Earth magnetic field useful to Faraday effect experiments

Abstract: The geometric factor (M) involving the earth's magnetic field in the Faraday effect equation is studied. A total of 48 coefficients is used to compute this factor. Some representative curves are shown. It is found that in general this factor is not a constant for a given ray. However, when a ray passes near the saddle point of the ‘M-surface’ M can be assumed to be constant along the ray with reasonable accuracy. In other regions of the sky an empirical average value of M must be used for a given ray and its value depends on the direction of the ray and the a priori ionization density profile. The results are compared with values computed by using dipole earth field.

From solar to stellar corona: the role of wind, rotation and magnetism

Abstract: Observations of surface magnetic fields are now within reach for many stellar types thanks to the development of Zeeman-Doppler Imaging. These observations are extremely useful for constraining rotational evolution models of stars, as well as for characterizing the generation of magnetic field. We recently demonstrated that the impact of coronal magnetic field topology on the rotational braking of a star can be parametrized with a scalar parameter: the open magnetic flux. However, without running costly numerical simulations of the stellar wind, reconstructing the coronal structure of the large scale magnetic field is not trivial. An alternative -broadly used in solar physics- is to extrapolate the surface magnetic field assuming a potential field in the corona, to describe the opening of the field lines by the magnetized wind. This technique relies on the definition of a so-called source surface radius, which is often fixed to the canonical value of 2.5Rsun. However this value likely varies from star to star. To resolve this issue, we use our extended set of 2.5D wind simulations published in 2015, to provide a criteria for the opening of field lines as well as a simple tool to assess the source surface radius and the open magnetic flux. This allows us to derive the magnetic torque applied to the star by the wind from any spectropolarimetric observation. We conclude by discussing some estimations of spin-down time scales made using our technique, and compare them to observational requirements.