Magnetic fields of 30 to 100 kG in the cores of red giant stars

Strong magnetic fields detected in the cores of 11 red giant stars using gravity-mode period spacings

“…where K(r) is a weight function that probes the g-mode cavity and sharply peaks in the vicinity of the H-burning shell (HBS), I is a factor that depends on the core structure (see Eq. 45 and 46 of Li et al 2022), and…”

“…The red dashed line indicates the critical field Bc and the grey long-dashed line shows the minimal field strength B th required to detect the distortions in the g-mode pattern. The blue star symbols show the stars from Li et al (2022).…”

“…Recently, their effects on mixed modes in red giants have been addressed in the special case of dipolar fields with specific radial profiles, which are either aligned with the rotation axis (Hasan et al 2005;Gomes & Lopes 2020;Mathis et al 2021;Bugnet et al 2021) or inclined (Loi 2021). Li et al (2022) extended these studies to an arbitrary magnetic field and obtained a general expression for the magnetic frequency shift that is valid provided that the azimuthal component is not much larger than the radial one (B φ /B r ω max /N, where ω max is the angular frequency at the maximum power of oscillations and N is the Brunt-Väisälä frequency 1 ). Accordingly, the multiplets of l = 1 pure g modes (that is, g modes that are not coupled to p modes) undergo an average shift ω B , given by…”

“…where K(r) is a weight function that probes the g-mode cavity and sharply peaks in the vicinity of the H-burning shell (HBS), I is a factor that depends on the core structure (see Eq. ( 45) and ( 46) of Li et al 2022), and B 2 r = (4π) −1 B 2 r sin θ dθ dφ. The angular frequency shifts of the components of g-mode dipole multiplets are then given by…”

“…Several studies have recently investigated the impact of internal fields on the frequencies of mixed modes in red giants (Gomes & Lopes 2020;Bugnet et al 2021;Loi 2021). Very recently, Li et al (2022) detected clear asymmetries in the rotational multiplets of dipole mixed modes in three Kepler red giants. They show that these features can only be accounted for by internal magnetic fields with intensities ranging from 30 to 130 kG in the vicinity of the hydrogen burning shell.…”