Internal structure of red-giant stars through the sound of dipole oscillation modes

What would a star look like below its opaque surface? What are the physical conditions in a star? What physical processes play an important role in stars? How do these physical conditions and processes interact? How do they change with time, when a star evolves? Answering these kinds of questions is of fundamental importance for astronomy and beyond.

Stars are a dominant source of light in the universe as well as main building blocks of planetary systems and galaxies. Thus, understanding of stars has a major impact in these fields.

Closer to home, understanding the past and future of the Sun has a potentially wide-ranging impact on other scientific fields. To pierce inside stars, we need observable features that are sensitive to the hidden layers in stars. Intrinsic global oscillations are observable, and are sensitive to the internal structures of stars.

The application of these global modes to study internal stellar structures is the field of asteroseismology. Particularly interesting and opportune stars to apply asteroseismology to are red-giant stars.

These evolved stars are abundant, relatively bright, exhibit different stellar structures, allow to trace back a long history, and possess probes that are sensitive to both their deep and their more shallow layers; the so-called mixed dipole oscillation modes.

The observed characteristics of mixed dipole modes differ significantly between different red-giant stars, leading to the following questions: • ‘What are the physical differences in the structures of / conditions in red-giant stars which lead to different mixed dipole mode oscillation spectra?’ • ‘What is the cause of the different structures / conditions in these stars?’ The aim of the DipolarSound proposal is to unravel the physical conditions and physical processes at play in red-giant stars using mixed dipole oscillation modes and to understand the underlying physical origin of the different oscillation spectra observed in red-giant stars.