The s process in rotating low-mass AGB stars. Nucleosynthesis calculations in models matching asteroseismic constraints

TL;DR

This study models the s-process nucleosynthesis in rotating low-mass AGB stars, constrained by asteroseismic data, and finds that realistic core rotation rates do not significantly affect s-process yields.

Contribution

It introduces stellar models with rotation rates matching asteroseismic constraints and assesses their impact on s-process nucleosynthesis, showing minimal effect.

Findings

Rotationally induced mixing has negligible impact on s-process yields.

Matching core rotation rates to observations reduces the influence of rotation on nucleosynthesis.

Uncertainties in rotation treatment remain and need further investigation.

Abstract

Aims. We investigate the s-process during the AGB phase of stellar models whose cores are enforced to rotate at rates consistent with asteroseismology observations of their progenitors and successors. Methods. We calculated new 2M$_{\odot}$, Z=0.01 models, rotating at 0, 125, and 250 km/s at the start of main sequence. An artificial, additional viscosity was added to enhance the transport of angular momentum in order to reduce the core rotation rates to be in agreement with asteroseismology observations. We compared rotation rates of our models with observed rotation rates during the MS up to the end of core He burning, and the white dwarf phase. Results. We present nucleosynthesis calculations for these rotating AGB models that were enforced to match the asteroseismic constraints on rotation rates of MS, RGB, He-burning, and WD stars. In particular, we calculated one model that matches the upper limit of observed rotation rates of core He-burning stars and we also included a model that rotates one order of magnitude faster than the upper limit of the observations. The s-process production in both of these models is comparable to that of non-rotating models. Conclusions. Slowing down the core rotation rate in stars to match the above mentioned asteroseismic constraints reduces the rotationally induced mixing processes to the point that they have no effect on the s-process nucleosynthesis. This result is independent of the initial rotation rate of the stellar evolution model. However, there are uncertainties remaining in the treatment of rotation in stellar evolution, which need to be reduced in order to confirm our conclusions, including the physical nature of our approach to reduce the core rotation rates of our models, and magnetic processes.