Dynamical Mass Loss at the End of TP-AGB stars

TL;DR

This study uses hydrodynamic simulations to explore how envelope instabilities in TP-AGB stars can cause rapid mass loss at the end of their evolution, potentially explaining the final envelope ejection.

Contribution

It demonstrates that dynamical instabilities driven by envelope mass reduction can serve as a primary mass-loss mechanism in late TP-AGB stars, using detailed hydrodynamic modeling.

Findings

Envelope mass decrease leads to increased pulsation amplitude and period.

Violent pulsations occur when envelope mass drops below ~0.25 Msun.

Envelope ejection can happen within a few hundred years at the end of TP-AGB.

Abstract

The thermally pulsating asymptotic giant branch (TP-AGB) phase plays a key role in the evolution of low- to intermediate-mass stars, driving mass loss that influences their final stages and contributes to galactic chemical enrichment. However, the mechanisms behind mass loss, particularly at the end of AGB, are still not well understood. We aim to investigate the relationship between stellar parameters and envelope dynamics during the TP-AGB phase, evaluating whether dynamical instabilities in the envelope can act as a possible mass-loss mechanism. We use hydrodynamics method in MESA to simulate the dynamical pulsations and resulting mass loss during the TP-AGB phase of a star evolved from a 1.5 Msun zero-age main sequence. Our simulations reproduce the dynamical pulsation behavior of stars during the TP-AGB phase, demonstrating that the envelope mass is a key factor governing pulsational properties. As the envelope mass decreases, both the pulsation period and radial amplitude increase, consistent with observational trends. For 1.5 Msun model, once the envelope mass declines to approximately 0.25 Msun, the model enters a regime of violent pulsations, potentially ejecting the remaining envelope within a few hundred years. We suggest that the instability can act as the dominant mass-loss mechanism in the end of the TP-AGB phase, marking a rapid transitional stage toward the post-AGB phase.