New single-valued-parameters radiative accelerations of Sc and Ni for modelling stellar interiors

¹ LUX, Observatoire de Paris, CNRS, Sorbonne Université, PSL Université, 5 place Jules Janssen, F-92190 Meudon, France
² Département de physique et d’astronomie, Université de Moncton, Moncton, NB E1A 3E9, Canada
³ IRAP, Université de Toulouse, CNRS, CNES, Toulouse, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 15 January 2026
Accepted: 15 March 2026

Abstract

Context. The precise evaluation of the radiative accelerations of chemical elements in stars is critical since these accelerations are often the principal contributor to atomic diffusion. Atomic diffusion causes the migration of elements inside stars and therefore affects their structure and evolution. For stellar modelling, the maximum number of elements need to be included, especially for the most abundant species.

Aims. This study presents radiative accelerations of scandium and nickel in stellar interiors. The abundance of scandium is important for identifying AmFm stars, and nickel can contribute strongly to the total opacity at certain depths in stars. Our results for these two elements complement existing tables used to compute radiative accelerations with the single-valued-parameters method; such tables now include up to 12 elements.

Methods. We used the single-valued-parameters method to calculate radiative accelerations. This method simplifies the integration of radiative accelerations in astrophysical codes. It is also more numerically efficient than other calculation methods. The single-valued-parameters method is implemented in three widely used stellar evolution codes.

Results. We present radiative accelerations of scandium and nickel in various stellar models and for different abundances. The parameters needed to evaluate them are made available for main-sequence stars from 1 to 10 solar masses and have been added to our existing publicly available data.

Conclusions. Radiative accelerations calculated here for nickel are comparable to those obtained by the Opacity Project method. According to our results on the radiative accelerations of scandium, calculations that take atomic diffusion into account should explain its underabundances as measured from observations of stars with masses of less than 3 solar masses.