Mode mixing and rotational splittings. I. Near-degeneracy effects revisited

article Mode mixing and rotational splittings. I. Near-degeneracy effects revisited published yes J. M. Joel Ong author Lisa Annabelle Bugnet author d9edb345-f866-11ec-9b37-d119b52345010000-0003-0142-4000 Sarbani Basu author Rotation is typically assumed to induce strictly symmetric rotational splitting into the rotational multiplets of pure p- and g-modes. However, for evolved stars exhibiting mixed modes, avoided crossings between different multiplet components are known to yield asymmetric rotational splitting, in particular for near-degenerate mixed-mode pairs, where notional pure p-modes are fortuitously in resonance with pure g-modes. These near-degeneracy effects have been described in subgiants, but their consequences for the characterization of internal rotation in red giants have not previously been investigated in detail, in part owing to theoretical intractability. We employ new developments in the analytic theory of mixed-mode coupling to study these near-resonance phenomena. In the vicinity of the most p-dominated mixed modes, the near-degenerate intrinsic asymmetry from pure rotational splitting increases dramatically over the course of stellar evolution, and it depends strongly on the mode-mixing fraction ζ. We also find that a linear treatment of rotation remains viable for describing the underlying p- and g-modes, even when it does not for the resulting mixed modes undergoing these avoided crossings. We explore observational consequences for potential measurements of asymmetric mixed-mode splitting, which has been proposed as a magnetic-field diagnostic. Finally, we propose improved measurement techniques for rotational characterization, exploiting the linearity of rotational effects on the underlying p/g-modes, while still accounting for these mixed-mode coupling effects. American Astronomical Society2022 eng Space and Planetary ScienceAstronomy and Astrophysics The Astrophysical Journal 0004-637X 1538-4357 2210.0192810.3847/1538-4357/ac97e7 9401 yes Ong JMJ, Bugnet LA, Basu S. 2022. Mode mixing and rotational splittings. I. Near-degeneracy effects revisited. The Astrophysical Journal. 940(1), 18. Ong, J. M. Joel, Lisa Annabelle Bugnet, and Sarbani Basu. “Mode Mixing and Rotational Splittings. I. Near-Degeneracy Effects Revisited.” The Astrophysical Journal. American Astronomical Society, 2022. <a href="https://doi.org/10.3847/1538-4357/ac97e7">https://doi.org/10.3847/1538-4357/ac97e7</a>. Ong JMJ, Bugnet LA, Basu S. Mode mixing and rotational splittings. I. Near-degeneracy effects revisited. The Astrophysical Journal. 2022;940(1). doi:<a href="https://doi.org/10.3847/1538-4357/ac97e7">10.3847/1538-4357/ac97e7</a> Ong, J. M. Joel, et al. “Mode Mixing and Rotational Splittings. I. Near-Degeneracy Effects Revisited.” The Astrophysical Journal, vol. 940, no. 1, 18, American Astronomical Society, 2022, doi:<a href="https://doi.org/10.3847/1538-4357/ac97e7">10.3847/1538-4357/ac97e7</a>. J. M. J. Ong, L. A. Bugnet, and S. Basu, “Mode mixing and rotational splittings. I. Near-degeneracy effects revisited,” The Astrophysical Journal, vol. 940, no. 1. American Astronomical Society, 2022. Ong, J. M. J., Bugnet, L. A., & Basu, S. (2022). Mode mixing and rotational splittings. I. Near-degeneracy effects revisited. The Astrophysical Journal. American Astronomical Society. <a href="https://doi.org/10.3847/1538-4357/ac97e7">https://doi.org/10.3847/1538-4357/ac97e7</a> J.M.J. Ong, L.A. Bugnet, S. Basu, The Astrophysical Journal 940 (2022). 134452023-08-01T14:20:41Z2023-09-06T07:27:45Z