The onset of the AGB wind tied to a transition between sequences in the period–luminosity diagram

McDonald, I. and Trabucchi, M. (2019). The onset of the AGB wind tied to a transition between sequences in the period–luminosity diagram. Monthly Notices of the Royal Astronomical Society, 484(4) pp. 4678–4682.

DOI: https://doi.org/10.1093/mnras/stz324

Abstract

We link the onset of pulsation-enhanced, dust-driven winds from asymptotic giant branch (AGB) stars in the Magellanic Clouds to the star’s transition between period–luminosity sequences (from B to C′). This transition occurs at ∼60 d for solar-mass stars, which represent the bulk of the AGB population: this is the same period at which copious dust production starts in solar-neighbourhood AGB stars. It is contemporaneous with the onset of long secondary period (LSP) variability on sequence D. The combined amplitude of the first-overtone (B + C′) and fundamental (C) modes and (perhaps) long-secondary period (D; LSP) variability appears to drive a sudden increase in mass-loss rate to a stable plateau, previously identified to be a few ×10−7 M⊙ yr−1. We cite this as evidence that pulsations are necessary to initiate mass-loss from AGB stars and that these pulsations are significant in controlling stars’ mass-loss rates. We also show evidence that LSPs may evolve from long to short periods as the star evolves, counter to the other period–luminosity sequences.

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