The impact of asteroseismically calibrated internal mixing on nucleosynthetic wind yields of massive stars

¹ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
² Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, HUN-REN, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
³ CSFK, MTA Centre of Excellence, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
⁴ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone, Italy
⁵ Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

Received: 16 February 2024
Accepted: 19 June 2024

Abstract

Context. Asteroseismology gives us the opportunity to look inside stars and determine their internal properties, such as the radius and mass of the convective core. Based on these observations, estimations can be made for the amount of the convective boundary mixing and envelope mixing of such stars and for the shape of the mixing profile in the envelope. However, these results are not typically included in stellar evolution models.

Aims. We aim to investigate the impact of varying convective boundary mixing and envelope mixing in a range based on asteroseismic modelling in stellar models up to the core collapse, both for the stellar structure and for the nucleosynthetic yields. In this first study, we focus on the pre-explosive evolution and we evolved the models to the final phases of carbon burning. This set of models is the first to implement envelope mixing based on internal gravity waves for the entire evolution of the star.

Methods. We used the MESA stellar evolution code to simulate stellar models with an initial mass of 20 M_⊙ from zero-age main sequence up to a central core temperature of 10⁹ K, which corresponds to the final phases of carbon burning. We varied the convective boundary mixing, implemented as ‘step-overshoot’, with the overshoot parameter (α_ov) in the range 0.05−0.4. We varied the amount of envelope mixing (log(D_env/cm² s⁻¹)) in the range 0−6 with a mixing profile based on internal gravity waves. To study the nucleosynthesis taking place in these stars in great detail, we used a large nuclear network of 212 isotopes from ¹H to ⁶⁶Zn.

Results. Enhanced mixing according to the asteroseismology of main-sequence stars, both at the convective core boundary and in the envelope, has significant effects on the nucleosynthetic wind yields. This is especially the case for ³⁶Cl and ⁴¹Ca, whose wind yields increase by ten orders of magnitude compared to those of the models without enhance envelope mixing. Our evolutionary models beyond the main sequence diverge in yields from models based on rotational mixing, having longer helium-burning lifetimes and lighter helium-depleted cores.

Conclusions. We find that the asteroseismic ranges of internal mixing calibrated from core hydrogen-burning stars lead to similar wind yields as those resulting from the theory of rotational mixing. Adopting the seismic mixing levels beyond the main sequence, we find earlier transitions to radiative carbon burning compared to models based on rotational mixing because they have lower envelope mixing in that phase. This influences the compactness and the occurrence of shell mergers, which may affect the supernova properties and explosive nucleosynthesis.