--- DOAJ_listed: '1' OA_place: publisher OA_type: gold PlanS_conform: '1' _id: '22262' abstract: - lang: eng text: 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. acknowledgement: 'We would like to thank the referee for their careful reading of the manuscript and their constructive comments that helped improve the paper. N.B.V. would like to thank K. Belkacem and J. Philidet for helpful discussions. N.B.V. is supported by STFC grant ST/Y002164/1. A.L.S. acknowledges support from the European Research Council (ERC) under the Horizon Europe program (Synergy grant agreement 101071505: 4D-STAR) from the CNES SOHO-GOLF and PLATO grants at CEA-DAp, and from ATPS (CNRS/INSU). Part of this work was supported by the ERC grant No. 787361-COBOM. R.H.D.T. acknowledges support from NASA grants 80NSSC24K0895 and 80NSSC23K1517, and NSF grant 2407636. A.L. is supported by ERC Starting Grant 101165631 (“Calcifer”). The authors would like to acknowledge the use of the University of Exeter High-Performance Computing (HPC) facility, ISCA, in carrying out this work. This work used the DiRAC Memory Intensive service (Cosma8) at Durham University, managed by the Institute for Computational Cosmology, and the DiRAC Data Intensive service (DIaL3) at the University of Leicester, managed by the University of Leicester Research Computing Service. These facilities are managed on behalf of the STFC DiRAC HPC (www.dirac.ac.uk). The DiRAC services at Durham and Leicester were funded by BEIS, UKRI, and STFC capital funding, and STFC operations grants. The service at Durham received funding from Durham University. DiRAC is part of the UKRI Digital Research Infrastructure.' article_number: '154' article_processing_charge: Yes article_type: original arxiv: 1 author: - first_name: Nils B. full_name: De Vries, Nils B. last_name: De Vries - first_name: Arthur full_name: Le Saux, Arthur last_name: Le Saux - first_name: Isabelle full_name: Baraffe, Isabelle last_name: Baraffe - first_name: Thomas full_name: Guillet, Thomas last_name: Guillet - first_name: Richard H.D. full_name: Townsend, Richard H.D. last_name: Townsend - first_name: Armand full_name: Leclerc, Armand id: 2a1fb1fc-f373-11ef-901a-87cee43a1217 last_name: Leclerc - first_name: Adrien full_name: Morison, Adrien last_name: Morison citation: ama: De Vries NB, Le Saux A, Baraffe I, et al. Revealing mixed modes in compressible hydrodynamical simulations of red giant stars. The Astrophysical Journal. 2026;1005(2). doi:10.3847/1538-4357/ae7a3c apa: De Vries, N. B., Le Saux, A., Baraffe, I., Guillet, T., Townsend, R. H. D., Leclerc, A., & Morison, A. (2026). Revealing mixed modes in compressible hydrodynamical simulations of red giant stars. The Astrophysical Journal. IOP Publishing. https://doi.org/10.3847/1538-4357/ae7a3c chicago: De Vries, Nils B., Arthur Le Saux, Isabelle Baraffe, Thomas Guillet, Richard H.D. Townsend, Armand Leclerc, and Adrien Morison. “Revealing Mixed Modes in Compressible Hydrodynamical Simulations of Red Giant Stars.” The Astrophysical Journal. IOP Publishing, 2026. https://doi.org/10.3847/1538-4357/ae7a3c. ieee: N. B. De Vries et al., “Revealing mixed modes in compressible hydrodynamical simulations of red giant stars,” The Astrophysical Journal, vol. 1005, no. 2. IOP Publishing, 2026. ista: De Vries NB, Le Saux A, Baraffe I, Guillet T, Townsend RHD, Leclerc A, Morison A. 2026. Revealing mixed modes in compressible hydrodynamical simulations of red giant stars. The Astrophysical Journal. 1005(2), 154. mla: De Vries, Nils B., et al. “Revealing Mixed Modes in Compressible Hydrodynamical Simulations of Red Giant Stars.” The Astrophysical Journal, vol. 1005, no. 2, 154, IOP Publishing, 2026, doi:10.3847/1538-4357/ae7a3c. short: N.B. De Vries, A. Le Saux, I. Baraffe, T. Guillet, R.H.D. Townsend, A. Leclerc, A. Morison, The Astrophysical Journal 1005 (2026). das_tickbox: '1' dataavailabilitystatement: The kinetic energies and surface velocities shown in Figure 4, as well as the underlying spectral data of this work, can be found in a Zenodo repository at doi:10.5281/zenodo.18661976. date_created: 2026-07-12T22:02:17Z date_published: 2026-07-10T00:00:00Z date_updated: 2026-07-13T08:16:25Z day: '10' ddc: - '520' department: - _id: LiBu doi: 10.3847/1538-4357/ae7a3c external_id: arxiv: - '2606.07125' file: - access_level: open_access checksum: d32061d2341bac3adeb404975c6bd59e content_type: application/pdf creator: dernst date_created: 2026-07-13T08:14:01Z date_updated: 2026-07-13T08:14:01Z file_id: '22275' file_name: 2026_AstrophysicalJour_deVries.pdf file_size: 14866194 relation: main_file success: 1 file_date_updated: 2026-07-13T08:14:01Z has_accepted_license: '1' intvolume: ' 1005' issue: '2' keyword: - Stellar physics - Stellar interiors - Asteroseismology - Stellar oscillations - Hydrodynamical simulations language: - iso: eng month: '07' oa: 1 oa_version: Published Version project: - _id: 914d8549-16d5-11f0-9cad-bbe6324c93a9 grant_number: '101165631' name: 'Unveiling the mysteries of stellar dynamics: a pioneering journey in magnetoasteroseismology' publication: The Astrophysical Journal publication_identifier: eissn: - 1538-4357 issn: - 0004-637X publication_status: published publisher: IOP Publishing quality_controlled: '1' researchdata_availability: yes scopus_import: '1' status: public supplementarymaterial: yes title: Revealing mixed modes in compressible hydrodynamical simulations of red giant stars tmp: image: /images/cc_by.png legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0) short: CC BY (4.0) type: journal_article user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87 volume: 1005 year: '2026' ... --- OA_place: publisher _id: '19853' abstract: - lang: eng text: "The internal dynamical properties of red giant stars have been explored extensively in recent\r\nyears as a result of the increase in high precision data availability from the space missions\r\nKepler and TESS (Transiting Exoplanet Survey Satellite), and in this exploration, it has been\r\ndiscovered that some of these stars are not behaving as expected. Red giants are stars that have\r\nevolved off of the main sequence after having completed fusing hydrogen into helium in their\r\ncore. Observational data shows that the cores are rotating significantly slower than models can\r\nrecreate consistently across evolutionary stages. This discrepancy has prompted investigation\r\ninto the efficiency of angular momentum transport mechanisms and mixing processes including\r\nmeridional circulation, shear instability, internal gravity waves, Tayler-Spruit dynamo, fossil\r\nmagnetic fields etc., to explain this behavior.\r\nAnalyzing seismic oscillations in stars, via asteroseismology, is a powerful tool as it is the only\r\nway in which the deep stellar interior can be probed and subsequently characterized; this is\r\npossible as global oscillations modulating the stellar surface are effected by internal processes.\r\nFor red giants, p-modes (pressure modes; resonating through the entire star) and g-modes\r\n(gravity-modes; resonating in the radiative interior) couple to create mixed modes. These\r\nmixed modes give access to the otherwise hidden stellar interior as g-modes couple to p-modes,\r\ndelivering information from the interior to the surface.\r\nInternal magnetic signatures have been observationally confirmed in red giant stars via\r\nasteroseismology and characterized in two ways. One being that dipole mixed modes with\r\nℓ = 1 will display a global asymmetric frequency shift of its azimuthal components; where\r\nthe m = 0 and m = ±1 components of the ℓ = 1 dipole mode will be shifted by two\r\ndifferent power laws, respectively. And the other being a reduced visibility of dipole mixed\r\nmode amplitudes in the power spectra, where stars presenting with this feature are denoted as\r\nsuppressed.\r\nSeveral studies of the suppressed dipole mixed mode amplitudes have been carried out, but thus\r\nfar, no dedicated studies of the asymmetric frequency shifts of suppressed red giants have been\r\nconducted; one reason being that the asymmetric frequency shifts cannot be characterized\r\nwhen the dipole mixed mode amplitudes are severely reduced in many of the suppressed stars.\r\nSincefullysuppressedstarsdonothavedetectablemixed-modestoevaluate, partiallysuppressed\r\nstars, that is, red giant stars presenting with suppressed dipole mixed modes in select parts of\r\ntheir power spectra rather than across the entire spectra, will be the subject of this study as\r\nthe respective mode amplitudes are still visible at high frequencies.\r\nAs such, this study will search for asymmetric frequency shifts on the dipole mixed\r\nmodes of partially suppressed red giant stars; the aim here is to investigate if both\r\nmode suppression and magnetic shifting of dipole mixed modes occur simultaneously.\r\nThisstudywillbeconductedbycreatingapipelinetoestimatepriorsofasteroseismicparameters,\r\nuse the priors to model the power spectra with the stellar modeling code sloscillations_ISTA,\r\nand perform a Bayesian fit of the parameters with the simulated data on the star KIC 6975038,\r\na target with partially suppressed dipolar mode amplitudes identified in the literature, to fit its\r\nmagnetic parameters. I present a novel method to model the stellar power spectra of\r\npartially suppressed red giants by application of a sigmoid profile to the ℓ= 1 dipolar\r\nmode component of the spectra. With the results of this study I aim at constraining\r\nthe cause of this partial dipole mode amplitude suppression, allowing for more detailed\r\nstudies regarding their astrophysical nature. Furthermore, the long term hope for the method\r\nused in this study will be to expand the sample of partially suppressed red giants and fit their\r\nasteroseismic parameters accordingly." acknowledgement: "I would like to give thanks to myself for my hard work on this document. This paper includes data collected by the Kepler mission and obtained from the MAST data\r\narchive at the Space Telescope Science Institute (STScI). Funding for the Kepler mission is\r\nprovided by the NASA Science Mission Directorate. STScI is operated by the Association of\r\nUniversities for Research in Astronomy, Inc., under NASA contract NAS 5–26555.\r\n" alternative_title: - ISTA Master's Thesis article_processing_charge: No author: - first_name: Kanah full_name: Smith, Kanah id: 7703505d-3211-11ee-a6a9-a2ab9d936c15 last_name: Smith citation: ama: Smith K. Exploring internal magnetism in partially suppressed red giant stars. 2025. doi:10.15479/AT-ISTA-19853 apa: Smith, K. (2025). Exploring internal magnetism in partially suppressed red giant stars. Institute of Science and Technology Austria. https://doi.org/10.15479/AT-ISTA-19853 chicago: Smith, Kanah. “Exploring Internal Magnetism in Partially Suppressed Red Giant Stars.” Institute of Science and Technology Austria, 2025. https://doi.org/10.15479/AT-ISTA-19853. ieee: K. Smith, “Exploring internal magnetism in partially suppressed red giant stars,” Institute of Science and Technology Austria, 2025. ista: Smith K. 2025. Exploring internal magnetism in partially suppressed red giant stars. Institute of Science and Technology Austria. mla: Smith, Kanah. Exploring Internal Magnetism in Partially Suppressed Red Giant Stars. Institute of Science and Technology Austria, 2025, doi:10.15479/AT-ISTA-19853. short: K. Smith, Exploring Internal Magnetism in Partially Suppressed Red Giant Stars, Institute of Science and Technology Austria, 2025. corr_author: '1' date_created: 2025-06-20T13:27:08Z date_published: 2025-10-08T00:00:00Z date_updated: 2026-04-07T12:01:37Z day: '08' ddc: - '520' degree_awarded: MS department: - _id: GradSch - _id: LiBu doi: 10.15479/AT-ISTA-19853 file: - access_level: closed checksum: 80d241d11b69af771c1fab0998be4f19 content_type: application/zip creator: ksmith date_created: 2025-10-08T08:01:42Z date_updated: 2025-10-08T09:45:33Z file_id: '20434' file_name: 2025_Smith_Kanah_Thesis.zip file_size: 8263624 relation: source_file - access_level: open_access checksum: 13cb48cc98e00fdfe32f3ff66f17aa26 content_type: application/pdf creator: ksmith date_created: 2025-10-09T14:38:57Z date_updated: 2025-10-09T14:38:57Z file_id: '20439' file_name: 2025_Smith_Kanah_Thesis.pdf file_size: 9748339 relation: main_file success: 1 file_date_updated: 2025-10-09T14:38:57Z has_accepted_license: '1' keyword: - asteroseismology - stellar physics - red giant - magnetism - suppressed language: - iso: eng month: '10' oa: 1 oa_version: Published Version page: '38' publication_identifier: issn: - 2791-4585 publication_status: published publisher: Institute of Science and Technology Austria status: public supervisor: - first_name: Lisa Annabelle full_name: Bugnet, Lisa Annabelle id: d9edb345-f866-11ec-9b37-d119b5234501 last_name: Bugnet orcid: 0000-0003-0142-4000 title: Exploring internal magnetism in partially suppressed red giant stars type: dissertation user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd year: '2025' ...