Program: GS-2006B-Q-47

We request Gemini-S/bHROS time to observe a sample of stars with planets to test whether there has been accretion of material as a result of planet formation. The rare lithium isotope, Li-6, is completely destroyed during the formation and pre-main sequence evolution of solar type stars having metallicities greater than about 1/30th solar. It is fully preserved, however, in low-mass brown-dwarfs and planets. Lithium's more robust isotope Li-7, is preserved to some degree in most solar-type stars. As almost all of the currently known stars with planets are solar types (i.e., spectral types F,G, or K) with near solar metallicities, no Li-6 should be present in any of those stars. Contrary to this picture, Li-6 has been detected in a planet-hosting F-dwarf by Israelian et al. (2003). This detection indicates that solid material from a protoplanetary disk was accreted into the thin surface convection zone of the planet hosting star and preserved after this star had settled onto the main sequence. Lithium-6 is thus a strategic probe of the dynamic interactions between stars and their surrounding protoplanetary disks or retinue of planetesimals or planets. We propose to bring the combination of light-gathering power and spectral resolution of Gemini-S plus bHROS to conduct the most sensitive search yet for Li-6 in a sample of stars with planets.