Tidal friction is thought to be important in determining the long-term
spin-orbit evolution of short-period extrasolar planetary systems. Using a
simple model of the orbit-averaged effects of tidal friction, we study the
evolution of close-in planets on inclined orbits, due to tides. We analyse the
effects of the inclusion of stellar magnetic braking by performing a
phase-plane analysis of a simplified system of equations, including the braking
torque. The inclusion of magnetic braking is found to be important, and its
neglect can result in a very different system history. We then present the
results of numerical integrations of the tidal evolution equations, where we
find that it is essential to consider coupled evolution of the orbital and
rotational elements, including dissipation in both the star and planet, to
accurately model the evolution. The main result of our integrations is that for
typical Hot Jupiters, tidal friction aligns the stellar spin with the orbit on
a similar time as it causes the orbit to decay. This means that if a planet is
observed to be aligned, then it probably formed coplanar. This reinforces the
importance of Rossiter-McLaughlin effect observations in determining the degree
of spin-orbit alignment in transiting systems. We apply these results to the
XO-3 system, and constrain the tidal quality factors Q' in both the star and
planet in this system. Using a model in which inertial waves are excited by
tidal forcing in the outer convective envelope and dissipated by turbulent
viscosity, we calculate Q' for a range of F-star models, and find it to vary
considerably within this class of stars. This means that assuming a single Q'
applies to all stars is probably incorrect. We propose an explanation for the
survival of WASP-12 b & OGLE-TR-56 b, in terms of weak dissipation in the star.Comment: 19 pages, 8 figures, accepted in MNRA