The bi-modal ⁷Li distribution of the Milky Way’s thin-disk dwarf stars

The role of Galactic-scale events and stellar evolution

¹ Departamento de Física de la Tierra y Astrofísica and IPARCOS, Facultad de Ciencias Físicas, Plaza Ciencias, 1, Madrid 28040, Spain
e-mail: sroca01@ucm.es
² Ateneo de Almagro, Sección de Ciencia y Tecnología, 13270 Almagro, Spain
³ Departmento de Astrofísica, Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba, CONICET, Laprida 854, 5000 Córdoba, Argentina
⁵ Observatório Nacional, Rua General José Cristino 77, 28921-400 São Cristovão, Rio de Janeiro, RJ, Brasil

Received: 10 May 2021
Accepted: 7 September 2021

Abstract

Context. The lithium abundance, A(Li), in stellar atmospheres suffers from various enhancement and depletion processes during the star’s lifetime. While several studies have demonstrated that these processes are linked to the physics of stellar formation and evolution, the role that Galactic-scale events play in the galactic A(Li) evolution is not yet well understood.

Aims. We aim to demonstrate that the observed A(Li) bi-modal distribution, in particular in the FGK-dwarf population, is not a statistical artefact and that the two populations connect through a region with a low number of stars. We also want to investigate the role that Galactic-scale events play in shaping the A(Li) distribution of stars in the thin disk.

Methods. We use statistical techniques along with a Galactic chemical evolution model for A(Li) that includes most of the well-known ⁷Li production and depletion channels.

Results. We confirm that the FGK main-sequence stars belonging to the Milky Way’s thin disk present a bi-modal A(Li) distribution. We demonstrate that this bi-modality can be generated by a particular Milky Way star formation history profile combined with the stellar evolution’s ⁷Li depletion mechanisms. We show that A(Li) evolution can be used as an additional proxy for the star formation history of our Galaxy.