Searching for Chemical Evidence of Planet Accretion in Red Giant Rapid Rotators

Details Searching for Chemical Evidence of Planet Accretion in Red Giant Rapid Rotators Searching for Chemical Evidence of Planet Accretion in Red Giant Rapid Rotators

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21730704c&link_type=abstract

American Astronomical Society, AAS Meeting #217, #307.04; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

Red giants stars are generally slow rotators, but a small fraction of them exhibit rapid rotation. The deposition of a planet's orbital angular momentum into the stellar envelope is one model that can account for this unusually rapid rotation. As the star evolves, it expands and fills the gap between itself and its planet. Eventually, the planet is near enough to cause stellar tides, and tidal torques can transfer the planet's orbital angular momentum to the stellar envelope.
If the planet is accreted, it can have a detectable effect on the chemical composition of the stellar envelope for elements that are either depleted during stellar evolution or that are preferentially enhanced in planets themselves. In the former case, the stellar convection envelope deepens into the hot stellar interior during first dredge-up, thereby depleting lithium by several orders of magnitude and decreasing the ratio of 12C to 13C by factors of 2 to 20. An accreted planet could replenish these depleted elements. An accreted planet could also preferentially enhance stellar abundances of refractory elements because planets are thought to form in environments where refractory elements are relatively enhanced compared to volatiles. At the very least, core accretion models predict the accumulation of rocky cores before the gaseous atmosphere of the planet forms.
Armed with these expectations, I undertook a search for planet accretion signatures in a sample of rapid rotators. The rapid rotators and control stars were found in a sample of candidate giants for the Space Interferometry Mission's Astrometric Grid. Follow-up spectra at high S/N and high resolution were obtained for measuring precise abundances. In this talk, I will summarize the outcome of my search for chemical signatures of planet accretion. I will give conclusions drawn from the total sample and discuss a few individual cases.

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