Explaining the decrease in ISM lithium at super-solar metallicities in the solar vicinity

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: gguiglion@aip.de
² INAF, Astrophysics and Space Science Observatory, Via Gobetti 93/3, 40129 Bologna, Italy
³ Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy
⁴ INAF Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy
⁵ INFN Sezione di Trieste, Via Valerio 2, 34134 Trieste, Italy
⁶ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France

Received: 7 September 2018
Accepted: 7 February 2019

Abstract

We propose here that the lithium decrease at super-solar metallicities observed in high-resolution spectroscopic surveys can be explained by the interplay of mixed populations that originate in the inner regions of the Milky Way disk. The lower lithium content of these stars is a consequence of inside-out disk formation plus radial migration. In this framework, local stars with super-solar metallicities would have migrated to the solar vicinity and depleted their original lithium during their travel time. To obtain this result, we took advantage of the AMBRE catalog of lithium abundances combined with chemical evolution models that take into account the contribution to the lithium enrichment by different nucleosynthetic sources. A large proportion of migrated stars can explain the observed lower lithium abundance at super-solar metallicities. We stress that no stellar model is currently able to predict Li-depletion for these super-solar metallicity stars, and solar Li-depletion has to be assumed. In addition, no solid quantitative estimate of the proportion of migrated stars in the solar neighborhood and their travel time is currently available. Our results illustrate how important it is to properly include radial migration when chemical evolution models are compared to observations, and that in this case, the lithium decrease at larger metallicities does not necessarily imply that stellar yields have to be modified, contrary to previous claims in the literature.