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The orbital angular momentum of a close-orbiting giant planet can besufficiently large that, if transferred to the envelope of the host star duringthe red giant branch (RGB) evolution, it can spin-up the star's rotation tounusually large speeds. This spin-up mechanism is one possible explanation forthe rapid rotators detected among the population of generally slow-rotating redgiant stars. These rapid rotators thus comprise a unique stellar samplesuitable for searching for signatures of planet accretion in the form ofunusual stellar abundances due to the dissemination of the accreted planet inthe stellar envelope. In this study, we look for signatures of replenishment inthe Li abundances and (to a lesser extent) 12C/13C, which are both normallylowered during RGB evolution. Accurate abundances were measured from highsignal-to-noise echelle spectra for samples of both slow and rapid rotator redgiant stars. We find that the rapid rotators are on average enriched in lithiumcompared to the slow rotators, but both groups of stars have identicaldistributions of 12C/13C within our measurement precision. Both of theseabundance results are consistent with the accretion of planets of only a fewJupiter masses. We also explore alternative scenarios for understanding themost Li-rich stars in our sample---particularly Li regeneration during variousstages of stellar evolution. Finally, we find that our stellar samples shownon-standard abundances even at early RGB stages, suggesting that initialprotostellar Li abundances and 12C/13C may be more variable than originallythought.

Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment