Claudia Aguilera-Gómez Libros

This thesis offers fresh insights into the widespread occurrence of lithium-rich red giant stars, which contradicts the stellar evolution theory that predicts negligible lithium levels on their surfaces. Defined as stars with more than three times the lithium content of the Sun, these Li-rich giants are found universally, challenging established astrophysical models. The author explores various explanations for this anomaly, including interactions with binary companions, internal lithium production and transport, and interactions with planets. Focusing on the latter, the author posits that lithium enrichment may result from the ingestion of planets or brown dwarfs as these stars expand into giants. This process accounts for a significant portion of giants exceeding the three times solar lithium threshold, although additional mechanisms are necessary for the remaining cases. A groundbreaking aspect of this thesis is its finding that the boundary between lithium-normal and lithium-rich stars is mass-dependent rather than a fixed ratio of the Sun’s lithium content. This insight corrects a fundamental misunderstanding of the phenomenon and establishes a new framework for addressing lithium enrichment in giants. The author also presents intriguing observational applications and samples to test this innovative approach.