Impacts of radiative accelerations on solar-like oscillating main-sequence stars

Abstract

Context. Chemical element transport processes are among the crucial physical processes needed for precise stellar modelling. Atomic diffusion by gravitational settling nowadays is usually taken into account, and is essential for helioseismic studies. On the other hand, radiative accelerations are rarely accounted for, act differently on the various chemical elements, and can strongly counteract gravity in some stellar mass domains. The resulting variations of the abundance profiles may significantly affect the structure of the star. Aims. In this study we aim at determining whether radiative accelerations impact the structure of solar-like oscillating main-sequence stars observed by asteroseismic space missions. Methods. We implemented the calculation of radiative accelerations operating on C, N, O, Ne, Na, Mg, Al, Si, S, Ca, and Fe in the CESTAM code using the Single-Valued Parameter method. We built and compared several grids of stellar models including gravitational settling, but some with and others without radiative accelerations. We considered masses in the range [0.9, 1.5] M and 3 values of the metallicity around the solar one. For each metallicity, we determined the range of mass where differences between models due to radiative accelerations exceed the uncertainties of global seismic parameters of the Kepler Legacy sample or expected for PLATO observations. Results. We found that radiative accelerations may not be neglected for stellar masses larger than 1.1 M at solar metallicity. The difference in age due to their inclusion in models can reach 9% for the more massive stars of our grids. We estimated that the percentage of the PLATO core program stars whose modelling would require radiative accelerations ranges between 33 and 58% depending on the precision of the seismic data. Conclusions. We conclude that, in the context of Kepler, TESS, and PLATO missions, which provide (or will provide) high quality seismic data, radiative accelerations can have a significant effect when inferring the properties of solar-like oscillators properly. This is particularly important for age inferences. However, the net effect for each individual star results from the competition between atomic diffusion including radiative accelerations and other internal transport processes. Rotationally induced transport processes for instance are believed to reduce the effects of atomic diffusion. This will be investigated in a forthcoming companion paper.A&A proofs: manuscript no. cestamI_v8 asteroseismology analysis(coupled with spectroscopic observations) which will provide precise masses, radii and more importantly ages of the host stars.

The Dependence of Convective Core Overshooting on Stellar Mass: Reality Check and Additional Evidence

“…If CB2018 did not include diffusion, then there would be a tendency for them to allow higher values of f ov in their fits, such as they report. Additionally, diffusion alters the surface abundances (i.e., the abundances accessible to observation) to a degree that depends on metallicity and evolutionary state (see, e.g., Dotter et al 2017;Deal et al 2018). Enforcing the measured (surface) abundances when fitting models while at the same time ignoring diffusion can therefore bias the results, including the inferred f ov and α MLT values.…”

Testing Stellar Evolution with Asteroseismic Inversions of a Main-sequence Star Harboring a Small Convective Core

“…Since gravitational settling in higher-mass models leads to the unobserved consequence of zero-metallicity atmospheres unless it is resisted by mass loss or radiative levitation (e.g., Deal et al 2018), the computation of which is computationally expensive, we tapered off diffusion for evolutionary tracks with M > 1.25 M according to the equation given by Viani & Basu (2017). Despite the unphysical nature of this prescription, the star under investigation here is of a low enough mass that the diffusion-tapered models are irrelevant.…”

Relevance of the small frequency separation for asteroseismic stellar age, mass, and radius

“…As a matter of fact the extension of the present investigation to an higher mass range will be affected not only by this supplementary degree of freedom, which would force the building of a huge dataset of stellar tracks, but also by the requirement of following the evolution of the convective core with a spatial resolution much higher than the one needed for the present investigation. Moreover, Deal et al (2018) point out that more massive stars may suffer from additional biases because of the effect of radiative accelerations.…”