Leto et al. have described ATCA measurements over the frequency range
2.1–21.2 GHz of the magnetic star ρ Oph A. The detection of two
highly polarized pulses at 2.1 GHz indicates that the coherent stellar
Auroral Radio Emission is being produced. Combining the radio light
curves with high-resolution optical spectra and new magnetic field
measurements enabled the stellar radio emission to be modelled. The
figure above is a sketch of the scenario proposed by Leto et al. to
explain the radio and the X-ray observations of ρ Oph A. In the inner
magnetospheric region (the light grey area) the magnetic energy is so
strong that the radiatively driven stellar wind cannot freely expand.
The stellar wind is channeled by the closed field lines of the
magnetic dipole producing shocks close to the magnetic equatorial
plane, giving rise to thermal X-ray emission. Far from the star, the
magnetic field strength decreases and the trapped plasma can open the
magnetic field lines to form current sheets. In these regions,
magnetic reconnection events can accelerate the local plasma up to
relativistic energy (illustrated by the the light-green areas). The
non-thermal electrons (represented by the small solid black arrows)
freely propagate within the middle-magnetosphere radiating at the
radio regime by the gyro-synchrotron emission mechanism. These
particles are directly towards to polar regions of the star, and the
energy released by the bombardment of the surface produces an unstable
energy distribution in the electrons moving outwards (white solid
small arrows), triggering the auroral coherent radio emission from
rings located above the polar regions. The Auroral Radio Emission
beams directed to the observer are highlighted by the two blue bright
spots.
More details are given in
the paper,
published in
Monthly Notices of the Royal Astronomical Society.
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