3D NLTE modelling of Y and Eu
Nicholas Storm, P. S. Barklem, S. A. Yakovleva, A. K. Belyaev, P. Palmeri, P. Quinet, K. Lodders, M. Bergemann, Richard Hoppe
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.