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Centro de Astrofísica da Universidade do Porto

Searching for Li-rich giants in a sample of 12 open clusters
Li enhancement in two stars with substellar companions

E. Delgado Mena, M. Tsantaki, S. G. Sousa, M Kunitomo, V. Zh. Adibekyan, P. Zaworska, N. C. Santos, G. Israelian, C. Lovis

Abstract

Aims. The aim of this work is to search for Li-rich giants in a sample of clusters where planets have been searched, thus we can study the planet engulfment scenario to explain Li replenishment using a proper comparison sample of stars without detected giant planets.
Methods. We derived Li abundances for a sample of 67 red giant stars in 12 different open clusters using standard spectral synthesis techniques and high-resolution spectra (from HARPS and UVES). We also determined masses, ages, and radius from PARSEC stellar isochrones to constrain the evolutionary stage of these stars.
Results. We found three stars in different clusters with clearly enhanced Li abundances compared to other stars within the cluster. Interestingly, the only two stars with a detected substellar companion in our sample belong to that group. One of the planet hosts, NGC 2423 No. 3, might lie close to the luminosity bump on the HR diagram, a phase where Li production by the Cameron-Fowler process is supported by extra-mixing to bring fresh Li up to the surface. On the other hand, NGC 4349 No. 127 is a more massive and more evolved giant that does not seem to be in the evolutionary phase where other Li-rich stars are found. We discuss the possibility that the Li enhancement of this star is triggered by the engulfment of a planet, considering that close-in planets hardly survive the RGB tip and the early AGB phases.

Keywords
stars: abundances – planetary systems – stars: rotation – stars: evo lution – planets and sate llites: physical evolution

Astronomy and Astrophysics
Volume 587, Page A66
March 2016

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