  One of the predictions of high eccentricity planetary migration is that many
planets will end up plunging into their host stars. We investigate the
consequence of planetary mergers on their stellar hosts' spin-period. Energy
and angular momentum conservation yield that a planet consumption by a star
will spin-up the star. We find that our calculations align with the observed
bifurcation in the stellar spin-period in young clusters. For example, after a
Sun-like star has eaten a Jupiter-mass planet it will spin up by ~60% (i.e.,
spin-period is reduced by ~60%), causing an apparent gap in the stellar spin
period, between stars that consumed a planet and those that did not. The
spun-up star will later spin down due to magnetic braking, consistent with the
disappearance of this bifurcation in clusters (>300Myr). The agreement between
the calculations presented here, and the observed spin-period color diagram of
stars in young clusters provides circumstantial evidence that planetary
accretion onto their host stars is a generic feature of planetary-system
evolution.
