Studying the evolution of AGB stars in the Gaia epoch

TL;DR

This paper models the evolution of AGB stars at solar metallicity to interpret Gaia observations, revealing a critical mass threshold for hot bottom burning and its effects on stellar properties and nucleosynthesis.

Contribution

It provides new AGB star models at solar metallicity that identify a key mass threshold for hot bottom burning and compare model predictions with recent Gaia data.

Findings

Stars below 3.5 M_sun become C-stars and enrich the ISM with C, N, and O-17.

Massive AGB stars reach high luminosities between 30,000 and 100,000 L_sun.

Massive AGB stars show signatures of proton-capture nucleosynthesis, producing N and Na.

Abstract

We present asymptotic giant branch (AGB) models of solar metallicity, to allow the interpretation of observations of Galactic AGB stars, whose distances should be soon available after the first release of the Gaia catalogue. We find an abrupt change in the AGB physical and chemical properties, occurring at the threshold mass to ignite hot bottom burning,i.e. $3.5M_{\odot}$. Stars with mass below $3.5 M_{\odot}$ reach the C-star stage and eject into the interstellar medium gas enriched in carbon , nitrogen and $^{17}O$. The higher mass counterparts evolve at large luminosities, between $3\times 10^4 L_{\odot}$ and $10^5 L_{\odot}$. The mass expelled from the massive AGB stars shows the imprinting of proton-capture nucleosynthesis, with considerable production of nitrogen and sodium and destruction of $^{12}C$ and $^{18}O$. The comparison with the most recent results from other research groups are discussed, to evaluate the robustness of the present findings. Finally, we compare the models with recent observations of galactic AGB stars, outlining the possibility offered by Gaia to shed new light on the evolution properties of this class of objects.