Stellar models of Betelgeuse constrained using observed surface conditions

Abstract

We study stellar models for Betelgeuse using the HR diagram and surface abundances as observational constraints. Previous studies on Betelgeuse have not systematically investigated the surface abundances, but we believe they can be impacted by, and thus be used as an observational constraint for various parameters such as initial mass, rotation, and overshoot scheme. We investigate stellar models with varying initial mass as they evolve past the main sequence, and we examine the red supergiant (RSG) properties in detail. For each mass, we vary the initial rotation up to $\sim$ 300 $km{s}^{-1}$, and test two different overshoot parameters. Overall, the acceptable initial mass range is 12 to 25 $M_{\odot }$, but for non-rotating models only, the range is decreased to 15 to 24 $M_{\odot }$. Also for rotating models, we find that $v/v_{\mathrm{K}}=0.3$ is the upper limit for initial rotation, as more rapidly rotating models are unable to fit to Betelgeuse's surface abundances as an RSG. In addition, we report two possibilities for the current stage of evolution, core helium burning or core carbon burning and beyond. We find that certain 17 $M_{\odot }$ models could fit to both stages. Finally, we discuss the implications of our results in the context of merger scenarios which have been suggested as a mechanism to attain the observed surface velocity of Betelgeuse.

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