Magnetic Cores in Evolved Stars and the Galactic Context of Hidden Stellar Dynamos

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Description
Recent asteroseismic studies have revealed that a significant fraction of red giant stars show an unusual feature in their oscillation frequencies: dipole modes with reduced oscillation amplitudes compared to the amplitudes of their fundamental modes (Stello et al. Nature 529, 364–367, 2016). This dipole “suppression” is thought to be caused by strong magnetic fields hidden deep in their cores, remnants of powerful dynamos that once operated when these stars had convective cores (Fuller et al. Science, Vol. 350, Issue 6259, pp. 423-426, 2015). The occurrence of this magnetic signature depends strongly on stellar mass and may also depend on metallicity and Galactic environment, but this connection has not yet been mapped in detail across the Milky Way.

This project aims use machine learning to identify and characterise these magnetic red giants in both the Kepler and TESS samples, cross match them with spectroscopic surveys such as APOGEE, and map their distribution, chemistry and motion across the Galaxy. The student will explore the influence of metallicity, birth environment and stellar mass on the presence of strong internal magnetic fields. The outcome will be the first broad view of where magnetic cores appear in the Galaxy and how they relate to stellar evolution and Galactic structure.

What the student will do

The student will work with the power spectra of solar-like oscillators, will determine which red giants show suppressed modes, build algorithms to analyse their metallicities and kinematics, and build maps that reveal how magnetic cores are distributed throughout the Milky Way.

Why this project is important

This project provides a unique opportunity to study stellar dynamos through the fossil magnetic fields they leave behind in giant stars. Detailed characterisation of the stars that show suppressed modes will explain the persistence of these hidden fields, offering new insights into stellar physics and the characteristics of the populations shaped by these ancient dynamos.