Impact of near-degeneracy effects on linear rotational inversions for red-giant stars
arXiv:2509.26319 · doi:10.1051/0004-6361/202555537
Abstract
Accurate estimates of internal red-giant rotation rates are a crucial ingredient for constraining and improving current models of stellar rotation. Asteroseismic rotational inversions are a method to estimate these internal rotation rates. In this work, we focus on the observed differences in the rotationally-induced frequency shifts between prograde and retrograde modes, which were ignored in previous works when estimating internal rotation rates of red giants using inversions. We systematically study the limits of applicability of linear rotational inversions as a function of the evolution on the red-giant branch and the underlying rotation rates. We solve for the oscillation mode frequencies in the presence of rotation in the lowest-order perturbative approach. This enables a description of the differences between prograde and retrograde modes through the coupling of multiple mixed modes. We compute synthetic rotational splittings taking these near-degeneracy effects into account. We use red-giant models with one solar mass, a large frequency separation between 16 and 9 microhertz and core rotation rates between 500 and 1500 nHz covering the regime of observed parameters of Kepler red-giant stars. Finally, we use these synthetic data to quantify the systematic errors of internal rotation rates estimated by means of rotational inversions in the presence of near-degeneracy effects. We show that the systematic errors in the estimated rotation rates introduced by near-degeneracy effects surpass observational uncertainties for more evolved and faster rotating stars. The estimated rotation rates of some of the previously analysed red giants suffer from significant systematic errors that have not been taken into account yet. Notwithstanding, reliable analyses with existing inversion methods are feasible for a number of red giants within the parameter ranges determined here.
Accepted for publication in Astronomy and Astrophysics, 11 pages, 4 figures
References in corpus (26)
- Array Programming with NumPy
- Modules for Experiments in Stellar Astrophysics (MESA)
- Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
- Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
- Slowing the Spins of Stellar Cores
- Angular momentum transport by heat-driven g-modes in slowly pulsating B stars
- Angular Momentum Transport via Internal Gravity Waves in Evolving Stars
- Constraining the efficiency of angular momentum transport with asteroseismology of red giants: the effect of stellar mass
- 30 to 100-kG magnetic fields in the cores of red giant stars
- Angular momentum redistribution by mixed modes in evolved low-mass stars. II. Spin-down of the core of red giants induced by mixed modes
- Asteroseismology of evolved stars to constrain the internal transport of angular momentum II. Test of a revised prescription for transport by the Tayler instability
- Can plume-induced internal gravity waves regulate the core rotation of subgiant stars?
- Modeling of Magneto-Rotational Stellar Evolution I. Method and first applications
- Magnetic signatures on mixed-mode frequencies. I. An axisymmetric fossil field inside the core of red giants
- Angular momentum redistribution by mixed modes in evolved low-mass stars. I. Theoretical formalism
- Near-degeneracy effects on the frequencies of rotationally-split mixed modes in red giants
- Semi-analytic Expressions for the Isolation and Coupling of Mixed Modes
- Asteroseismic measurement of core and envelope rotation rates for 2006 red giant branch stars
- A Diagnostic for Localizing Red Giant Differential Rotation
- Topology and obliquity of core magnetic fields in shaping seismic properties of slowly rotating evolved stars
- Asteroseismology of evolved stars to constrain the internal transport of angular momentum. IV. Internal rotation of Kepler 56 from an MCMC analysis of the rotational splittings
- Mixed Modes and Asteroseismic Surface Effects: I. Analytic Treatment
- Mode Mixing and Rotational Splittings: I. Near-Degeneracy Effects Revisited
- Improved asteroseismic inversions for red-giant surface rotation rates
- The robustness of inferred envelope and core rotation rates of red-giant stars from asteroseismology
- The efficiency of mixed modes for angular momentum transport