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Astronomy and Space Physics

Arief Ahmad (Uppsala University): Pulsations of dying giants – Investigating the self-excited pulsations of cool, luminous, and evolved stars in 3D models (Licentiate)

Europe/Stockholm
80127 (Ångströmlaboratoriet)

80127

Ångströmlaboratoriet

Description

Title: Pulsations of dying giants – Investigating the self-excited pulsations of cool, luminous, and evolved stars in 3D models
Speaker: Arief Ahmad (Uppsala University)
Date: December 7 2022, 1315
Location: 80127Å
Opponent: Theo Khouri (Chalmers University of Technology)

Abstract:

The cycle of cosmic matter and life's very beginnings both greatly depend on evolved stars. Critical chemical elements, like carbon, are created inside dying stars reaching the climax of their stellar evolution on the asymptotic giant branch (AGB). Enriched material is carried to the surface by turbulent gas flows, and ejected into interstellar space by massive outflows of gas and dust. Stellar winds will ensue, which we are yet to fully understand with respect to how they affect stellar evolution and how they enrich the surroundings of evolved stars.

On the stellar surface and in the surrounding dust clouds, observations reveal dynamic intricate structures. Such complex structures show up in our 3D radiation-hydrodynamics simulations of evolved cool giants, performed using the CO5BOLD code. The dynamics are governed by small surface granules, global convection cells, stochastically excited waves, and pulsations in the radial fundamental mode. Pulsations play a crucial role in dust formation in the outer stellar atmosphere; the very dust which eventually drives stellar winds by radiation pressure. Thorough analyses of the self-excited pulsations are important in advancing our understanding of, and the stages that precede and succeed, stellar winds of AGB stars.

The work here aims to evaluate various properties of the pulsations in 3D models of AGB stars, as simulated with the CO5BOLD code. Convection and pulsations are emergent properties of the models. Extracting and analysing the pulsation properties thus required careful consideration of the dynamic motions involved. Correlations between the pulsation period, in the radial fundamental mode, and stellar parameters were investigated. The correlations were found to be in good agreements with available observations which, importantly, reaffirms that the 3D models represent realistic stars.