The accretion of planets and brown dwarfs by giant stars -- II. solar mass stars on the red giant branch

Abstract

This paper extends our previous study of planet/brown dwarf accretion by giant stars to solar mass stars located on the red giant branch. The model assumes that the planet is dissipated at the bottom of the convective envelope of the giant star. The giant's evolution is then followed in detail. We analyze the effects of different accretion rates and different initial conditions. The computations indicate that the accretion process is accompanied by a substantial expansion of the star, and in the case of high accretion rates, hot bottom burning can be activated. The possible observational signatures that accompany the engulfing of a planet are also extensively investigated. They include : the ejection of a shell and a subsequent phase of IR emission, an increase in the 7Li surface abundance and a potential stellar metallicity enrichment, spin-up of the star due to the deposition of orbital angular momentum, the possible generation of magnetic fields and a related X-ray activity due to the development of shear at the base of the convective envelope, and the effects on the morphology of the horizontal branch in globular clusters. We propose that the IR excess and high Li abundance observed in 4-8% of the G and K giants originate from the accretion of a giant planet, a brown dwarf or a very low-mass star.