On the uncertain nature of the core of $\boldsymbol{\alpha}$ Cen A

TL;DR

This study uses advanced statistical modeling and observational data to analyze the internal structure of $oldsymbol{ extalpha}$ Cen A, revealing a significant probability of it having a convective core, influenced by nuclear reaction rates.

Contribution

It applies Bayesian statistical methods to stellar modeling, providing new insights into the likelihood of convective cores in $oldsymbol{ extalpha}$ Cen A.

Findings

Approximately 40% chance of a convective core in $oldsymbol{ extalpha}$ Cen A.

The probability drops to a few percent with reduced $^{14}$N(p,$ extgamma$)$^{15}$O reaction rates.

About 30% of models place $oldsymbol{ extalpha}$ Cen A in the subgiant phase.

Abstract

High-quality astrometric, spectroscopic, interferometric and, importantly, asteroseismic observations are available for $\alpha$ Cen A, which is the closest binary star system to earth. Taking all these constraints into account, we study the internal structure of the star by means of theoretical modelling. Using the Aarhus STellar Evolution Code (ASTEC) and the tools of Computational Bayesian Statistics, in particular a Markov chain Monte Carlo algorithm, we perform statistical inferences for the physical characteristics of the star. We find that $\alpha$ Cen A has a probability of approximately 40% of having a convective core. This probability drops to few percents if one considers reduced rates for the $^{14}$N(p,$\gamma$)$^{15}$O reaction. These convective cores have fractional radii less than 8% when overshoot is neglected. Including overshooting also leads to the possibility of a convective core mostly sustained by the ppII chain energy output. We finally show that roughly 30% of the stellar models describing $\alpha$ Cen A are in the subgiant regime.