  Rotation is thought to drive cyclic magnetic activity in the Sun and Sun-like
stars. Stellar dynamos, however, are poorly understood owing to the scarcity of
observations of rotation and magnetic fields in stars. Here, inferences are
drawn on the internal rotation of a distant Sun-like star by studying its
global modes of oscillation. We report asteroseismic constraints imposed on the
rotation rate and the inclination of the spin axis of the Sun-like star HD
52265, a principal target observed by the CoRoT satellite that is known to host
a planetary companion. These seismic inferences are remarkably consistent with
an independent spectroscopic observation (rotational line broadening) and with
the observed rotation period of star spots. Furthermore, asteroseismology
constrains the mass of exoplanet HD 52265b. Under the standard assumption that
the stellar spin axis and the axis of the planetary orbit coincide, the minimum
spectroscopic mass of the planet can be converted into a true mass of 1.85
(+0.52,-0.42) M_Jupiter, which implies that it is a planet, not a brown dwarf.

Solar and Stellar Astrophysics