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Cool stars

 

AB Dor   What determines the structure of stellar coronae?

A star's corona expands out until the magnetic field can no longer contain it. If the star is a rapid rotator, centrifugal forces will strip the outer parts of the corona leading to a reduction in X-ray emission and an enhancement of any rotation modulation in X-rays (Jardine, 2004).

We calculate the X-ray structure by taking a magnetic map of the surface (obtained using Zeeman-Doppler imaging), extrapolating the field into the corona and filling this structure with hot gas in hydrostatic balance. We test the code using solar magnetograms (Jardine et al 2002).

 
  Picture credit: Jardine, Wood, Donati & Collier Cameron