  Giant planets orbiting main-sequence stars closer than 0.1 AU are called hot
Jupiters. They interact with their stars affecting their angular momentum.
Recent observations provide suggestive evidence of excess angular momentum in
stars with hot Jupiters in comparison to stars with distant and less massive
planets. This has been attributed to tidal interaction, but needs to be
investigated in more detail considering also other possible explanations
because in several cases the tidal synchronization time scales are much longer
than the ages of the stars. We select stars harbouring transiting hot Jupiters
to study their rotation and find that those with an effective temperature
greater than 6000 K and a rotation period shorter than 10 days are synchronized
with the orbital motion of their planets or have a rotation period
approximately twice that of the planetary orbital period. Stars with an
effective temperature lower than 6000 K and a rotation period longer than 10
days show a general trend toward synchronization with increasing effective
temperature or decreasing orbital period. We propose a model for the angular
momentum evolution of stars with hot Jupiters to interpret these observations.
It is based on the hypothesis that a close-in giant planet affects the coronal
field of its host star leading to a topology with predominantly closed field
lines. Our model can be tested observationally and has relevant consequences
for the relationship between stellar rotation and close-in giant planets as
well as for the application of gyrochronology to estimate the age of
planet-hosting stars.
