3D NLTE modelling of Y and Eu

Centre-to-limb variation and solar abundances

¹ Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: storm@mpia-hd.mpg.de
² Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
³ Institute of Physics, Herzen University, 191186 St. Petersburg, Russia
⁴ Physique Atomique et Astrophysique, Université de Mons – UMONS, 7000 Mons, Belgium
⁵ IPNAS, Université de Liège, 4000 Liège, Belgium
⁶ Planetary Chemistry Laboratory, Dept of Earth & Planetary Sciences and McDonnell Center for Space Sciences, Washington Univ, St Louis MO, USA

Received: 15 December 2023
Accepted: 20 January 2024

Abstract

Context. Abundances of s- and r-process elements in Sun-like stars constrain nucleosynthesis in extreme astrophysical events, such as compact binary mergers and explosions of highly magnetised rapidly rotating massive stars.

Aims. We measure solar abundances of yttrium (Y) and europium (Eu) using 3D non-local thermal equilibrium (NLTE) models. We use the model to determine the abundance of Y, and also explore the model’s ability to reproduce the solar centre-to-limb variation of its lines. In addition, we determine the Eu abundance using solar disc-centre and integrated flux spectra.

Methods. We developed an NLTE model of Eu and updated our model of Y with collisional data from detailed quantum-mechanical calculations. We used the IAG spatially resolved high-resolution solar spectra to derive the solar abundances of Y across the solar disc and of Eu for integrated flux and at disc centre using a set of carefully selected lines and a 3D radiation-hydrodynamics model of the solar atmosphere.

Results. We find 3D NLTE solar abundances of A(Y)_{3D NLTE} = 2.30 ± 0.03_stat ± 0.07_syst dex based on observations at all angles and A(Eu) = 0.57 ± 0.01_stat ± 0.06_syst dex based on the integrated flux and disc-centre intensity. 3D NLTE modelling offers the most consistent abundances across the solar disc, and resolves the problem of severe systematic bias in Y and Eu abundances inherent to 1D LTE, 1D NLTE, and 3D LTE modelling.