Dynamical mass loss at the end of thermally pulsating asymptotic giant branch stars

¹ Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
² Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, China
³ International Centre of Supernovae (ICESUN), Yunnan Key Laboratory of Supernova Research, Yunnan Observatories, Chinese Academy of Sciences (CAS), Kunming 650216, China
⁴ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China
⁵ New Cornerstone Science Laboratory, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
⁶ School of Physics, Henan Normal University, Xinxiang 453007, China
⁷ Center for Theoretical Physics, Henan Normal University, Xinxiang 453007, China

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 23 August 2025
Accepted: 22 January 2026

Abstract

Context. The thermally pulsating asymptotic giant branch (TP-AGB) phase plays a key role in the evolution of low- to intermediate-mass stars because it drives the mass loss that influences their final stages and contributes to galactic chemical enrichment. However, the mechanisms behind the mass loss, particularly at the end of the AGB phase, are still not well understood.

Aims. We investigated the relationship between the stellar parameters and envelope dynamics during the TP-AGB phase with the aim of evaluating whether dynamical instabilities in the envelope can act as a possible mass-loss mechanism.

Methods. We used the hydrodynamics method in MESA to simulate the dynamical pulsations and resulting mass loss during the TP-AGB phase of a star that evolved from a 1.5 M_⊙ zero-age main-sequence.

Results. Our simulations reproduced 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, as is consistent with observational trends. For the 1.5 M_⊙ model, once the envelope mass declines to approximately 0.25 M_⊙, the model enters a regime of violent pulsations, potentially ejecting the remaining envelope within a few hundred years.

Conclusions. We suggest that the instability can act as the dominant mass-loss mechanism at the end of the TP-AGB phase, marking a rapid transitional stage toward the post-AGB phase.