Insights into Core Magnetism and Rotation in Low-Luminosity Red Giants

Recent research has unveiled significant insights into the core magnetism and rotation of low-luminosity red giants, a type of star that has been less understood compared to their more luminous counterparts. The study, titled "Asteroseismic Signatures of Core Magnetism and Rotation in Hundreds of Low-Luminosity Red Giants," was conducted by Emily J. Hatt and a team of eight other researchers. It focuses on the asteroseismic properties of these stars, which are sensitive to both core rotation and magnetic fields.

The researchers analyzed data from 302 low-luminosity red giants, employing an automated method to fit power spectra directly. Their findings indicate a clear bimodality in core rotation rates, with primary and secondary peaks identified at 0.32 μHz and 0.47 μHz, respectively. Notably, the study also found that the percentage of stars rotating significantly faster than the average increases with their evolutionary state.

Additionally, the researchers measured magnetic splittings with a significance of 2σ in 23 stars. The most extreme magnetic splitting values were observed in stars with masses greater than 1.1 solar masses, suggesting these stars previously hosted a convective core. Interestingly, a small but statistically significant magnetic splitting was also detected in lower mass stars.

The study further revealed that 43% of the stars with significant magnetic perturbations did not exhibit strong asymmetry in their frequency distributions, a factor previously used to diagnose magnetic presence. Overall, the research contributes to a growing catalog of magnetic and rotational characteristics in red giants, enhancing our understanding of stellar evolution and the dynamics of these celestial bodies.

This research is set to be published in the Monthly Notices of the Royal Astronomical Society and can be cited as follows: Hatt, E. J., Ong, M. J., Chaplin, W. J., Davies, G. R., Deheuvels, S., Ballot, J., Li, G., Bugnet, L. (2024). Asteroseismic Signatures of Core Magnetism and Rotation in Hundreds of Low-Luminosity Red Giants. arXiv:2409.01157.