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

TL;DR

This study investigates lithium enrichment in red giant stars within open clusters, finding two stars with substellar companions that exhibit enhanced lithium possibly due to planet engulfment or stellar processes.

Contribution

It provides the first comparative analysis of Li-rich giants in clusters with and without detected planets, linking Li enhancement to planetary interactions.

Findings

Two Li-rich giants with substellar companions identified.

Li enhancement possibly caused by planet engulfment or stellar mixing.

One Li-rich star near the luminosity bump phase.

Abstract

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. 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. We find 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, NGC2423No3, 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, NGC4349No127 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.