Lithium evolution in the Galactic thin disc from main-sequence and early red-giant-branch stars

¹ University of Trieste, Piazzale Europa, 1, Trieste, Italy
² INAF Osservatorio Astronomico di Trieste, Via Giambattista Tiepolo, 11, Trieste, Italy
³ Institute for Fundamental Physics of the Universe, via Beirut, 2, 34151 Trieste, Italy
⁴ Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
⁵ INFN, Sezione di Trieste, via Valerio 2, 34134 Trieste, Italy
⁶ INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, 40129 Bologna, Italy
⁷ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁸ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁹ Division of Astronomy and Space Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹⁰ SISSA, Via Bonomea 265, 34136 Trieste, Italy
¹¹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova, Italy

^★ Corresponding author: chi.nguyen@inaf.it

Received: 23 July 2025
Accepted: 25 September 2025

Abstract

The role of novae as producers of galactic lithium-7 (Li) has been suggested since the 1970s, and it has been reconsidered recently with the detection of beryllium-7 in their outbursts. At the same time, stellar models are moving forward to help us understand the discrepancy between the primordial Li abundance predicted by the standard Big Bang nucleosynthesis theory and the measured value of old dwarf stars. For this work, we followed the evolution of Li in the Galactic thin disc starting from a primordial value of A(Li)= 2.69 dex and applying Li depletion corrections of the stellar model with overshoot to our chemical evolution models. We used the upper envelope of the observational data to constrain the models. In addition to the dwarf main-sequence (MS) stars, our analysis included, for the first time, the early red-giant-branch (RGB) stars. In addition to the renowned Spite plateau of the MS stars at low metallicities, we also confirm the existence of a second A(Li) plateau of the early RGB stars, which can be explained by our model with the corrections from stellar models. Our best-fit model was obtained with an effective averaged Li yield ^LY_Nova = 2.34 × 10^-5 M_⊙ during the whole lifetime of a nova. This reinforces the possibility that novae are the main galactic Li source, together with the stellar models’ ability to resolve the ‘cosmological Li problem’ in this context.