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Stellar Wind and Magnetic Fields

​Astrophysicists from IRFU have studied the evolution over time of the "wind" in stars similar to the Sun. They were able to perform 3D computer simulations of these stellar winds based, in particular, on spectropolarimetric measurements of the surface magnetic field of the stars. 

Published on 8 February 2017

Stars similar in composition to the Sun eject matter in the form of plasma (electrons and protons) into their corona (or high "atmosphere") and beyond. This "wind" of particles is coupled to the magnetic field located in the outer layer of the star, where convective movements occur. This flow of particles, which picks up speed to the point of becoming supersonic, is difficult to observe and must therefore be reconstructed through computer simulations.

A team of researchers gathered all available information relating to the corona—including spectropolarimetric measurements—of six young stars aged 25 million to 4.5 billion years (the same age as the Sun), with masses comparable to that of the Sun. Such data allowed the scientists to determine the polarization of light emitted in a spectral line of hydrogen, which is found to be sensitive to the magnetic field. The scientists used the entire set of data to constrain the 3D magneto-hydrodynamic simulations of the complex coronal structure, as well as the "wind".

They were able to clarify the nature of the interstellar medium of the young solar system. They also highlighted the unexpected properties of the winds of some young stars, whose speed distribution includes three modes.

The effect of the magnetic field of the star on the structuring of its environment must now be taken into account when studying the past of the planets of the solar system, as well as the environment of exoplanets gravitating around young stars.

This research was based on data collected by the spectropolarimeters from the Pic-du-Midi Observatory, France, and from the Canada-France-Hawaii telescope, Hawaii, in particular. The simulations were carried out on the GENCI supercomputer (Large National Equipment for Supercomputing) at the CEA Center in Bruyères-le-Châtel. 

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