@article{22262,
  abstract     = {Mixed modes are observed in many low-mass evolved stars. They provide information about core rotation rates of these stars, which are lower than predicted by stellar evolution models. The mixed modes themselves have been invoked as an angular momentum (AM) transport mechanism, but estimating their transport efficiency requires knowledge of their amplitudes. We constrain, for the first time, the mixed-mode amplitudes in 2D hydrodynamical simulations of a 1.3M⊙ red giant using the code MUSIC. We perform two simulations with outer radial truncations at fractional radii ro/r⋆ = 0.90 and 0.98. We compare the modes in the simulation with those found using both GYRE and a Dedalus eigenvalue solver. Excellent frequency agreement is found for all p-dominated modes, with minor discrepancies for g-dominated modes, especially in the frequency range [60, 240] μHz. We find excellent eigenfunction agreement for all modes except those in this frequency range. According to empirical predictions, the largest kinetic energies are located around Vmax= 312.μHz, but in both simulations, the modes with frequencies of ν < 50 μHz have the largest kinetic energies. In the simulation with r/r⋆ = 0.98, the simulated modes have extrapolated surface velocities comparable to the empirical predictions, with the highest surface velocities in a bell-shaped curve peaking around ν = 700 μHz. The extrapolated surface velocities of the low-frequency modes are small and thus hard to observe, but their large kinetic energies deeper in the interior could significantly impact AM transport, which has not yet been investigated.},
  author       = {De Vries, Nils B. and Le Saux, Arthur and Baraffe, Isabelle and Guillet, Thomas and Townsend, Richard H.D. and Leclerc, Armand and Morison, Adrien},
  issn         = {1538-4357},
  journal      = {The Astrophysical Journal},
  keywords     = {Stellar physics, Stellar interiors, Asteroseismology, Stellar oscillations, Hydrodynamical simulations},
  number       = {2},
  publisher    = {IOP Publishing},
  title        = {{Revealing mixed modes in compressible hydrodynamical simulations of red giant stars}},
  doi          = {10.3847/1538-4357/ae7a3c},
  volume       = {1005},
  year         = {2026},
}

@phdthesis{19853,
  abstract     = {The internal dynamical properties of red giant stars have been explored extensively in recent
years as a result of the increase in high precision data availability from the space missions
Kepler and TESS (Transiting Exoplanet Survey Satellite), and in this exploration, it has been
discovered that some of these stars are not behaving as expected. Red giants are stars that have
evolved off of the main sequence after having completed fusing hydrogen into helium in their
core. Observational data shows that the cores are rotating significantly slower than models can
recreate consistently across evolutionary stages. This discrepancy has prompted investigation
into the efficiency of angular momentum transport mechanisms and mixing processes including
meridional circulation, shear instability, internal gravity waves, Tayler-Spruit dynamo, fossil
magnetic fields etc., to explain this behavior.
Analyzing seismic oscillations in stars, via asteroseismology, is a powerful tool as it is the only
way in which the deep stellar interior can be probed and subsequently characterized; this is
possible as global oscillations modulating the stellar surface are effected by internal processes.
For red giants, p-modes (pressure modes; resonating through the entire star) and g-modes
(gravity-modes; resonating in the radiative interior) couple to create mixed modes. These
mixed modes give access to the otherwise hidden stellar interior as g-modes couple to p-modes,
delivering information from the interior to the surface.
Internal magnetic signatures have been observationally confirmed in red giant stars via
asteroseismology and characterized in two ways. One being that dipole mixed modes with
ℓ = 1 will display a global asymmetric frequency shift of its azimuthal components; where
the m = 0 and m = ±1 components of the ℓ = 1 dipole mode will be shifted by two
different power laws, respectively. And the other being a reduced visibility of dipole mixed
mode amplitudes in the power spectra, where stars presenting with this feature are denoted as
suppressed.
Several studies of the suppressed dipole mixed mode amplitudes have been carried out, but thus
far, no dedicated studies of the asymmetric frequency shifts of suppressed red giants have been
conducted; one reason being that the asymmetric frequency shifts cannot be characterized
when the dipole mixed mode amplitudes are severely reduced in many of the suppressed stars.
Sincefullysuppressedstarsdonothavedetectablemixed-modestoevaluate, partiallysuppressed
stars, that is, red giant stars presenting with suppressed dipole mixed modes in select parts of
their power spectra rather than across the entire spectra, will be the subject of this study as
the respective mode amplitudes are still visible at high frequencies.
As such, this study will search for asymmetric frequency shifts on the dipole mixed
modes of partially suppressed red giant stars; the aim here is to investigate if both
mode suppression and magnetic shifting of dipole mixed modes occur simultaneously.
Thisstudywillbeconductedbycreatingapipelinetoestimatepriorsofasteroseismicparameters,
use the priors to model the power spectra with the stellar modeling code sloscillations_ISTA,
and perform a Bayesian fit of the parameters with the simulated data on the star KIC 6975038,
a target with partially suppressed dipolar mode amplitudes identified in the literature, to fit its
magnetic parameters. I present a novel method to model the stellar power spectra of
partially suppressed red giants by application of a sigmoid profile to the ℓ= 1 dipolar
mode component of the spectra. With the results of this study I aim at constraining
the cause of this partial dipole mode amplitude suppression, allowing for more detailed
studies regarding their astrophysical nature. Furthermore, the long term hope for the method
used in this study will be to expand the sample of partially suppressed red giants and fit their
asteroseismic parameters accordingly.},
  author       = {Smith, Kanah},
  issn         = {2791-4585},
  keywords     = {asteroseismology, stellar physics, red giant, magnetism, suppressed},
  pages        = {38},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Exploring internal magnetism in partially suppressed red giant stars}},
  doi          = {10.15479/AT-ISTA-19853},
  year         = {2025},
}