Magnetic signatures on mixed-mode frequencies. II. Period spacings as a probe of the internal magnetism of red giants

TL;DR

This paper explores how internal magnetic fields in red giants influence mixed-mode oscillation frequencies and proposes methods to detect and characterize these magnetic signatures through asteroseismology.

Contribution

It introduces a new corrected stretching function for power spectra to identify magnetic signatures and demonstrates how magnetic fields bias period spacing estimates in red giants.

Findings

Magnetic signatures cause biased lower estimates of period spacing.

A new method improves detection of internal magnetic fields in red giants.

Analysis across frequency ranges can reveal the presence of stellar magnetism.

Abstract

Theoretical works have looked into the various topologies and amplitudes, as well as the stability of the magnetic field that is expected to be present in the radiative interior of stars evolving after the main sequence. Such internal magnetic fields have never been observed in evolved stars. As a result, there is a major piece missing from our global picture of stars as dynamical bodies. Asteroseismology opened a window onto stellar internal dynamics, as oscillation frequencies, amplitudes, and lifetimes are affected by processes that are taking place inside the star. In this scope, magnetic signatures on mixed-mode frequencies have recently been characterized, but the task of detection remains challenging as the mixed-mode frequency pattern is highly complex and affected by rotational effects, while modes of different radial orders are often intertwined. In this work, we aim to build a bridge between theoretical prescriptions and complex asteroseismic data analysis to facilitate a future search and characterization of internal magnetism with asteroseismology. We investigate the effect of magnetic fields inside evolved stars with solar-like oscillations on the estimation of the period spacing of gravity-mode components of simulated mixed gravito-acoustic modes. We derived a new corrected stretching function of the power spectrum density to account for the presence of magnetic signatures on their frequencies. We demonstrate that the strong dependency of the amplitude of the magnetic signature with mixed-mode frequencies leads to biased estimates of period spacings towards lower values. We also show that a careful analysis of the oscillation frequency pattern through various period spacing estimates and across a broad frequency range might lead to the first detection of magnetic fields inside red giants and at the same time, we adjust the measured value of gravity-mode period spacing.