We present a numerical Magnetohydrodynamic ( MHD ) study of the dependence of stellar mass and angular momentum- loss rates on the orbital distance to close-in giant planets .
We find that the mass loss rate drops by a factor of \approx 1.5-2 , while the angular momentum loss rate drops by a factor of \approx 4 as the distance decreases past the Alfvén surface .
This reduction in angular momentum loss is due to the interaction between the stellar and planetary Alfvén surfaces , which modifies the global structure of the stellar corona and stellar wind on the hemisphere facing the planet , as well as the opposite hemisphere .
The simulation also shows that the magnitude of change in angular momentum loss rate depends mostly on the strength of the planetary magnetic field and not on its polarity .
The interaction however , begins at greater separation if the overall field topology of the star and the planet are of anti-aligned .
Our results are consistent with evidence for excess angular momentum in stars harboring close-in giant planets , and show that the reduction in wind-driven angular momentum loss can compete with , and perhaps dominate , spin-up due to tidal interaction .